Interactions between indigenous southern Afrotemperate forest trees and arthropod diversity

verskeie spesies wat woud-ekosisteme bewoon, is insekte ‘n groot deel van die totale biodiversiteit, en die meeste hiervan kan in boomtoppe gevind word. Voor hierdie studie, is baie min fokus geplaas op insekte in suidelike Afro-gematigde woude in die algemeen, en geen studie het gepoog om die diversiteit en verspreiding van boomtop-insekte te beskryf nie. Die doel van hierdie navorsing, dus, is om te bepaal tot watter mate verskeie faktore die interaksies tussen inheemse boomspesies en geassosieërde arthropoda diversiteit affekteer in Suid-Afrikaanse Afro-gematigde woude. Eerstens het ek bepaal of die konteks en kontras waarin ‘n individuele boom groei, die fisiologie en geassosieërde arthropoda sal beïnvloed. Ek het bevind dat die kontras van die omringende plantegroei rondom ‘n boom die blaarmorfologie en gevolglik die arthropoda beïnvloed, met bome in laer kontraste (omring deur digter vegetasie) wat groter blare en verhoogde diversiteit getoon het. Plant fisiologie het gefluktueer op grond van die konteks waarin ‘n boom groei (natuurlik, semi-natuurlik, geplant), wat geassosieërde boomtop arthropoda geaffekteer het. Om plaaslike arthropoda optimaal te bewaar deur inheemse bome te plant, is dit daarom van kardinale belang om ‘n boom se natuurlike konteks en variasie in kontras in ag te neem. Woud arthropoda onderhou gesonde ekosisteme deur ekosisteem prosesse soos blaar dekomposisie te dryf. Ek het ‘n eksperiment ontwerp om die blaar dekomposisie wat uitgevoer word deur arthropoda teenoor fungi te vergelyk, en om te bepaal watter plaaslike faktore die variasies in dekomposisie tempo sal affekteer. Verder, het ek die tuisveld-voordeel (TVV) hipotese getoets, wat stel dat blare vinniger afbreek onder plante vanwaar die blare afkomstig is (tuis), teenoor ander plant spesies (weg). Hier demonstreer ek dat arthropoda die meeste dekomposisie funksie uitvoer, en dat hul vermoë om dit te doen beduidend varieër tussen verskillende boomspesies, alhoewel die rol van bakterieë substansieël Stellenbosch University https://scholar.sun.ac.za 6 mag wees. Anders as verwag, en ten spyte van selektiewe arthropoda reaksies tot verskillende boom- spesie blare, blyk TVV nie van belang te wees in hierdie gemengde woudsisteem nie. Gegewe die reaksies van woudvloer arthropoda tot boom identiteit, boom konteks- and kontras, en gepaardgaande veranderinge in plant fisiologie, is dit redelik om te verwag dat hierdie faktore die boomtop arthropoda in suidelike Afro-gematigde woude kan beïnvloed. Daarom het ek die relatiewe effekte van boomspesie-identiteit, plot eienskappe en plant fisiologie op die diversitiet en verspreiding van boomtop arthropoda bepaal. Boomspesie-identiteit en verskille in plant fisiologie het verskille in arthropoda diversiteit tussen individuele bome bepaal. Individuele bome omring deur digter plantegroei het minder diverse arthopoda samestellings gehad in vergelyking met meer oop areas. Ek argumenteer dat, in diverse, gemengde woude, heterogene boomtop lae van beduidende belang is om arthropoda diversiteit te bewaar, gedryf nie net deur variasie in argitektuur nie, maar ook deur fluktuasies in lig blootstelling. Verskille in plant fisiologie by die boomspesie-vlak het gepaardgegaan met ‘n diverse verskeidenheid effekte op boomtop arthropoda, wat algemene afleidings van hul reaksies tot mensgedrewe veranderinge bemoeilik. Aangesien hierdie studie ‘n eerste poging is om die diversiteit van arthropoda in boomtoppe van suidelike Afro-gematigde woude te beskryf, sluit ek dit af deur ‘n volledige sintese te verskaf van hierdie diversiteit, en om dit in ‘n globale konteks te plaas. Ek verskaf bewyse dat arthropoda diversiteit in hierdie woude meer soortgelyk is aan ander gematigde woude s’n, meer so as in vergelyking met tropiese woude. Tog het boomtoppe in hierdie area ‘n tien-maal hoër spesies rykheid as woudvloere in dieselfde area. Indien dit gekombineer word met die hoë aantal spesies wat versamel is, meeste waarskynlik onbeskryf, regverdig dit spesiale bewaringspogings om suidelike Afro-gematige woude se boomtoppe oor ‘n wye biogeografiese gradiënt te beskerm. Stellenbosch University https://scholar.sun.ac.za 7 Acknowledgements  Firstly, I want to sincerely thank both Francois Roets and Michael Samways for their advice and inputs throughout the study. Thank you also to James Pryke for your very valuable inputs. You make a great team, and I consider myself lucky to have been a part of the way you think about science and the field of ecology over the past few years.  Thank you also to everyone in the Conservation Ecology and Entomology department for administrative and technical support.  This research was financially supported by the National Research Foundation of South Africa (grant number SFH150723130214), while SANParks and CapeNature provided me with free accommodation and access to their reserves. Thank you very much.  I also want to thank Andries Cilliers for all of his help during the fieldwork phase of this study, and Joey Hulbert.  I also want to thank Dennis Bird from DynaFog Africa for his assistance and excellent service.  To all the people involved in helping me conduct this study, I am very grateful. This includes Marietjie Willemse from Oubos, Solms Beyers, Ian Allen and Llewellyn Michaels from CapeNature, Grootvadersbosch, Callie Schutte from Mossel Bay Municipality, Melanie de Mornay, Nerina Kruger, Graham Durrheim, Wessel Vermeulen, George Sass, Denzil de Vos, Wilfred Oraai and Klaas Havenga from SANParks, Garden Route National Park.  Thank you to everyone helping with species identifications, including Ansie Dippenaar- Schoeman, Charles Haddad and Melanie de Mornay.  A big thanks to my family and friends, especially my parents Crispin and Mariana Swart, my wife Corlé (& Bonnie), my brother Kirk, as well as my in-laws, Jaco and Surika, for their continued support. Stellenbosch University https://scholar.sun.ac.za 8 My biggest thank you goes out to the spectacular forests of Knysna and the southern Cape, which continues to be my sole inspiration behind this study. This has to be one of the most beautiful forests on earth, and I am privileged beyond words to have had the opportunity to walk through the ferns, Kamassi’s, Bladdernut’s, Silky bark’s, and so many more species, exploring the canopy, and having but a glimpse of the secrets still remaining in this Living Entity. Stellenbosch University https://scholar.sun.ac.za 9 Contents Chapter 1: General Introduction and Research Aim ............................................................................. 12 Forests of the world .......................................................................................................................... 12 Temperate rainforests ...................................................................................................................... 13 Southern Afrotemperate forest complex ......................................................................................... 14 Origin of southern Afrotemperate forests ........................................................................................ 14 Exploring the forest canopy .............................................................................................................. 17 Insects in trees – regional differences .............................................................................................. 18 Roles of insects in forests.................................................................................................................. 20 Global forest change and insect responses ...................................................................................... 22 Research aim and objectives ............................................................................................................ 25 Chapter 2*..................................................................................................................................... 26 Chapter 3*..................................................................................................................................... 27 Chapter 4....................................................................................................................................... 28 Chapter 5....................................................................................................................................... 28 Chapter 6....................................................................................................................................... 31 References ........................................................................................................................................ 31 Chapter 2............................................................................................................................................... 49 Individual tree context and contrast dictate tree physiological features and arthropod biodiversity patterns across multiple trophic levels ................................................................................................. 49 Abstract ............................................................................................................................................. 49 Introduction ...................................................................................................................................... 49 Materials and Methods..................................................................................................................... 52 Study area, host tree and sampling design ................................................................................... 52 Plant characteristics ...................................................................................................................... 55 Arthropod collection ..................................................................................................................... 56 Statistical analyses ........................................................................................................................ 58 Results ............................................................................................................................................... 59 Arthropod diversity ....................................................................................................................... 59 Effects of contrast and context on arthropod diversity ................................................................ 60 Effects of contrast and context on plant characteristics .............................................................. 62 Effects of plant characteristics on arthropod diversity ................................................................. 62 Discussion.......................................................................................................................................... 66 Acknowledgements........................................................................................................................... 69 References ........................................................................................................................................ 69 Supplementary material ................................................................................................................... 79 Stellenbosch University https://scholar.sun.ac.za 10 Chapter 3............................................................................................................................................... 99 No home-field advantage in leaf litter decomposition in an ancient temperate rainforest system despite selective detritivore responses toward different tree species ................................................ 99 Abstract ............................................................................................................................................. 99 Introduction .................................................................................................................................... 100 Materials and Methods................................................................................................................... 104 Study site..................................................................................................................................... 104 Litterbag preparation .................................................................................................................. 104 Sampling design .......................................................................................................................... 106 Data collection ............................................................................................................................ 108 Statistical analyses ...................................................................................................................... 109 Decomposition ............................................................................................................................ 109 Arthropods .................................................................................................................................. 110 Results ............................................................................................................................................. 111 Decomposition ............................................................................................................................ 111 Arthropods .................................................................................................................................. 114 Discussion........................................................................................................................................ 121 Acknowledgements......................................................................................................................... 124 References ...................................................................................................................................... 125 Supplementary material ................................................................................................................. 135 Chapter 4............................................................................................................................................. 144 Arthropods in Afrotemperate forest canopies reveal the unpredictability of biodiversity responses to environmental stressors ..................................................................................................................... 144 Abstract ........................................................................................................................................... 144 Introduction .................................................................................................................................... 145 Materials & Methods ...................................................................................................................... 148 Study area ................................................................................................................................... 148 Tree selection and arthropod collection..................................................................................... 149 Arthropods .................................................................................................................................. 151 Plant characteristics .................................................................................................................... 151 Statistical analyses ...................................................................................................................... 152 Effect of tree identity and plot characteristics on canopy arthropod diversity (H1) .................. 152 Effect of tree identity and plot characteristics on tree physiological features (H2) ................... 153 Effect of within-host physiological features on arthropod diversity (H3) .................................. 153 Results ............................................................................................................................................. 154 Effect of tree identity and plot characteristics on canopy arthropod diversity (H1) .................. 155 Stellenbosch University https://scholar.sun.ac.za 11 Effect of tree identity and plot characteristics on tree physiological features (H2) ................... 163 Effect of within-host physiological features on arthropod diversity (H3) .................................. 164 Discussion........................................................................................................................................ 171 Effect of tree identity on canopy arthropod diversity and tree physiological features ............. 171 Effect of plot characteristics on arthropod diversity and tree physiological features ............... 173 Effect of within-host physiological variation on arthropod diversity – implications for human induced environmental change .................................................................................................. 175 Acknowledgements......................................................................................................................... 178 References ...................................................................................................................................... 179 Supplementary material ................................................................................................................. 195 Chapter 5............................................................................................................................................. 201 Arthropods sampled from southern Afrotemperate forest canopies in a global perspective ........... 201 Abstract ........................................................................................................................................... 201 Introduction .................................................................................................................................... 202 Materials and Methods................................................................................................................... 205 Arthropod sampling .................................................................................................................... 207 Statistical analyses ...................................................................................................................... 207 Global comparisons..................................................................................................................... 208 Results and discussion .................................................................................................................... 209 Overall diversity patterns............................................................................................................ 209 Beetles......................................................................................................................................... 211 Hymenopterans .......................................................................................................................... 227 Flies ............................................................................................................................................. 228 Spiders......................................................................................................................................... 229 Bugs ............................................................................................................................................. 233 Ants ............................................................................................................................................. 234 Conclusion ................................................................................................................................... 238 References ...................................................................................................................................... 239 Supplementary material ................................................................................................................. 253 Chapter 6 – General discussion and conclusions ................................................................................ 269 References ...................................................................................................................................... 276 Stellenbosch University https://scholar.sun.ac.za 12 Chapter 1: General Introduction and Research Aim Forests of the world Forests form part of living nature’s largest manifestations. In forest ecosystems, trees are dominant features, creating many micro-climates and modifying life conditions below elevated greenery. Apart from emergent trees, natural forests are also home to shrubs, small trees, graminoids, herbaceous plants, ferns, vines, climbers and epiphytes. This complex and structurally diverse floral environment allows for a great variety of fauna to develop, leading to massive numbers of interactions between numerous species. Indeed, our most diverse ecosystems are natural forests, specifically those occurring in the tropics. Globally, Asia has by far the largest percentage (31%) of forest cover of all continents, including the Boreal forests of Russia and the subtropical to tropical, very threatened forests of Southeast Asia. This is followed by South America (21%), Africa (17%), North and Central America (17%), Europe (9%) and Oceania (5%) (FAO 2010). Today, 30% of the earth’s surface is covered by forests, 5% thereof being plantations (FAO 2010; Pan et al. 2013). Despite covering less than a third of the earth’s surface, forests contain 80% of the world’s total plant biomass (Kindermann et al. 2008). Three of the world’s five high biodiversity wilderness areas are forests: The Amazon, the Congo and the forests of New Guinea. Together, these three bio-diverse regions holds more than 65 000 vascular plant species, 1000 mammalian species and more than 2500 bird species, still counting (Mittermeier et al. 2003). Its insect fauna, as recently argued, goes well into the millions (Stork 2018), creating the most biodiverse regions on the planet. Apart from the hyper-diverse tropical forests around the equator, moving north we find the vast Boreal forests, hosting more than 2000 vascular plant species, 200 mammalian species and 650 or so species of bird. These forests, having gone through long periods of glaciation, especially during the Quaternary period (Davis 1983), are no less splendorous due to its sheer size (approximately 16 000 000 km²) and remoteness (80% intact) (FAO 2010). Evidently, without forests, the diversity of life on earth would be a fraction of what we see today. Stellenbosch University https://scholar.sun.ac.za 13 Temperate rainforests Further south of the equator occurs the scarce southern temperate rainforests of the world. These are areas receiving high rainfall occurring in the southern hemispheric, temperate zones of the earth. These forests include, among others, the Valdivian and Magellanic forest complexes of southern South America, the temperate rainforests of Australia and Tasmania and the New Zealand temperate rainforests. Temperate rainforests, even though not as species rich as their tropical counterparts, or as extensive as the Boreal forests, are among the densest and tallest forests (Pan et al. 2013). They occupy a small percentage of temperate regions, and usually grow near oceans and coastal mountains. Besides receiving high precipitation (more than 800-1000 mm p.a., Lee et al. 2016) and occuring in temperate zones across the globe, they do not necessarily share a common origin. However, in many forests in the southern hemisphere, including the forests of southern South America, New Caledonia, New Zealand, Australia, Tasmania, and to a lesser extent southern South Africa, a strong Austral floristic component occurs, hinting at a once shared geographical location now divided (McGlone et al. 2016). The similarities in physiognomy and shared key taxa between these forests have been noted from as early as the 1850’s (Hooker 1853; Darwin 1859). These similarities indicate a once connected forest ecosystem stretching across the southern continent of Gondwana, with some work suggesting that Antarctica was, during the Cretaceous, a region of origin and dispersal for many elements of today’s southern hemispheric forests (Dettmann 1989). New Zealand and southern South America, together with Australia and Tasmania, have received much attention because of similarities between lineages (Kooyman et al. 2014), such the close relation between Podocarpus nubigenus of Valdivian temperate rainforests and P. totara endemic to New-Zealand (Simpson 2017), separated by >8000 km of open ocean. Today, the Gondwanan forest lineages, having speciated in situ in their respective novel habitats over millennia, make up significant components of the present southern temperate rainforests and usually co-occur with other, widely-separated lineages to form unique forest communities (Kooyman et al. 2014). A good example is the remaining forests of South Africa, which today have taxa of Gondwanan origin persisting in forests which have strong subtropical and tropical affinity. Stellenbosch University https://scholar.sun.ac.za 14 Southern Afrotemperate forest complex Most of South Africa is extremely dry and unable to support forest establishment and growth. However, from the Cape Peninsula in the extreme southwest and following the major mountain ranges towards the Eastern Cape, and then extending north-eastwards through KwaZulu-Natal, the Eastern Free State and Mpumalanga, and even farther north towards the Soutpansberg Mountain range in the Limpopo province, there is a great variety of forest communities. In total, it is estimated that about 20 000 forest patches occur in South Africa, comprising a suggested eight forest groups, subdivided into 32 forest types (Berliner 2009). Perhaps the smallest, but nevertheless interesting examples of temperate rainforests on the globe, are the forests forming part of the Knysna-Amatole coastal complex at the southern tip of South Africa. Although small compared to other temperate rainforests in the southern Hemisphere, the southern Cape forest complex is the largest in South Africa and, although having a temperate location, has a conspicuous tropical affinity. However, before tropical elements became major contributors to these forests, ancient Gondwanan lineages were present in the present-day south- western Cape, and many lineages still thrive despite numerous historic climatic regime shifts and isolation from other southern land masses. Origin of southern Afrotemperate forests During the Palaeocene (55-65 my BP), the southern tip of Africa is speculated to have been covered by mostly temperate forests, mostly of Gondwanan origin (Axelrod & Raven 1978; Deacon 1983). By this time, Gondwana had already broken up (Burke & Gunnel 2008). Temperate lineages that were represented in this era, and are still present today, include among others the genera Widdringtonia, Podocarpus, Cunonia and Platylophus (Von Breitenbach 1974). Subtropical and tropical forests, during favourable climatic conditions in the Oligocene-Miocene, became dominant features of the south- western Cape by moving southward from continental Africa along river valleys and coastal plains, penetrating the original southern flora (Von Breitenbach 1974; Axelrod & Raven 1978; Deacon 1983). Whereas Podocarpus latifolius (Real Yellowwood) and the closely related Afrocarpus falcatus Stellenbosch University https://scholar.sun.ac.za 15 (Outeniqua Yellowwood), of temperate origin, became dominant features of these novel forests, lineages such as Widdringtonia in the south Western Cape for example, did not adapt to these mostly tropical forest communities and became restricted to mountainous shrublands and the outskirts of forests (Von Breitenbach 1974). Also, genera such as Podocarpus had relative success in these novel habitats, expanding northward and reaching Kenya around 25 my BP (Vincens et al. 2006; Galley et al. 2006). Cunonia capensis, the only species of the genus Cunonia occurring outside of New Caledonia, where 25 endemics occur (Pillon et al. 2008), again survived these floral shifts through adaptation, and today occur mostly close to water or forest edges in the southern Afrotemperate forests, while becoming dominant elements of many smaller natural Western Cape Afrotemperate forest patches (Von Breitenbach 1974). Despite the presence of temperate elements, lowland and montane subtropical rainforest, with palms being prominent, characterised the Oligocene-Miocene era (Coetzee 1978; 1983). At present, this vegetation type is absent, although the southern Cape Afrotemperate forest complex is considered as impoverished remnants (Coetzee 1978; 1983). Tropical lineages today are featured in both the southern Cape forests, and tropical Africa (Von Breitenbach 1974). Southern Cape forests also contain genera endemic to the Afromontane Archipelago, such as Olinia, regarded as a western Gondwanan clade, and Trichocladus, a genus native to South Africa and Zimbabwe (Endress 1989; Sebola & Balkwill 2013). Overall, there is a distinct decline in forest floral diversity moving east to west in South Africa, as many species migrating south either never reached the extreme south-western parts of the Cape, or have since retracted their distribution in accordance with climatic changes (Von Breitenbach 1974). Indeed, this pattern is seen for many woody species even in the small strip of land between Table Mountain and Tsitsikamma. Brachylaena glabra, commonly referred to as the Malabar tree, does not occur further west than the forests of Storms River in the Eastern Cape. Canthium pauciflorum does not occur across the Keurbooms River near Plettenberg Bay, Western Cape. Ochna natalitia distribution ends west of the Knysna forests, whereas common species such as Ficus capensis, Maytenus peduncularis, Ochna arborea, Trimeria grandifolia and Dovyalis rhamnoides only occur east of George (Von Breitenbach Stellenbosch University https://scholar.sun.ac.za 16 1974). In summary, many genera of tropical origin today are prominent components of southern Afrotemperate forests, and together with southern lineages, make up the bulk of southern Afrotemperate forests. Indeed, there are similarities in genera between the Cape and areas as far north as Ethiopia following the major mountain massifs, and has been of interest for botanists for more than 150 years (Grimshaw 2001). Also, the similarities between southern hemisphere temperate rainforests in general, including the southern Cape forests, are equally striking. Fynbos and arid shrublands today are the dominant vegetation in the south-western Cape, and are believed to have become dominant during the late Pleistocene (125 000 – 10 000 y BP) after having diversified rapidly during the late Miocene (Geldenhuys 1997; Mucina & Geldenhuys 2006). This is a result of the cold Benguela current, which at about 23-16 My BP gradually strengthened due to, predictably, the opening up of the Drake Passage (± 49-17 my BP; Scher & Martin 2006) between South America and Antarctica (Neumann & Bamford 2015). Since the beginning of the Miocene, the south- western Cape vegetation experienced the effect of the cool Benguela current which led to winter rainfall and semi-arid conditions (Deacon 1983). Predictably, inland forest patches of the south-western Cape became increasingly isolated as a result of this aridity (Geldenhuys 1997). During the late Miocene and Pliocene, fire-prone vegetation experienced ‘fast diversification and a maximum radiation of its clades’; suggesting that forest expansion would have, during this era, been controlled by fire along with drier limiting conditions (Mucina & Geldenhuys 2006; Neumann & Bamford 2015). Today these forests occupy a fraction of the natural landscape. Forests form the smallest biome in the country, with only about 0.56% of land surface area covered by indigenous, evergreen forests (Low & Rebelo 1996). The discontinuity of the forest biome we witness today is therefore a result of historic climatic fluctuations and natural disturbance regimes, especially during the last 180 000 years (Partridge et al. 1999; Eeley et al. 1999; Lawes et al. 2000). Indeed, forest patches are rarely larger than 1 km² and are essentially islands each of distinct floristic composition amidst differing, lower growing vegetation communities surrounding them (Eeley et al. 1999, 2001). However, even with its small size and fragmented nature, these forests contain much biodiversity worthy of conserving (Geldenhuys 1989). Stellenbosch University https://scholar.sun.ac.za 17 In summary, the tropical origin of the southern Afrotemperate forests explains their current composition. However, due to relict southern floral elements, these communities are not wholly tropical (Von Breitenbach 1974). Today they comprise a combination of floral elements from subtropical, tropical, and temperate origins, reflecting the major floristic and climatic shifts that have occurred at the southern tip of South Africa, the continent, and the southern hemisphere as a whole. Tree individuals are mostly part of a community, and associated with them is much other biodiversity that is fully or at least partly dependent on their presence, health, and continuance. Exploring the forest canopy Of the numerous species occurring within forest ecosystems, insects comprise a large part of the total biodiversity. Erwin (1982) first suggested that there had previously been a major underestimation of global biodiversity after his novel work on canopy arthropod diversity in the tropical forests of Panama. From his conservative estimates on insect diversity, he concluded that there could be 41 389 species per hectare of scrubby seasonal forest in Panama. He went even further to suggest that there might be up to 30 million species of tropical arthropods! Although these figures are only estimates and have since been challenged (e.g. Stork 2018), they do suggest that prior to 1982, we greatly underestimated the richness of global biodiversity. Since there has been much more work on forest canopies (e.g. Moran & Southwood 1982; Stork 1987; Reynolds & Crossley 1997). We now know that major consumers in forests are herbivorous insects (Novotny & Basset 2005). Moreover, it is estimated that about 40% of extant terrestrial species occur within the forest canopy (Price 2002; Novotny & Basset 2005), contributing greatly towards local and large-scale ecosystem functioning. Herbivorous insects, as a group, contribute greatly towards the high level of biodiversity found in forest canopies (Price 2002) and, as a result, we consider the interactions between herbivorous insects and their tree hosts as vitally important, and our understanding of them even more so. From the highly diverse, sunlit forest canopy down towards the damp, shaded forest floor, insects have colonised almost every available micro-habitat. Their role in maintaining forest Stellenbosch University https://scholar.sun.ac.za 18 ecosystems is unmatched compared to other animals, whether through herbivory, saproxyly, or pollination, and interactions ranging from antagonistic to mutualistic. Insects in trees – regional differences In terms of plant diversity, plant species richness reaches its peak near the equator (Novotny et al. 2006) with plant species richness being up to six times higher per hectare in the tropics compared to temperate forests (Novotny et al. 2006). Whether or not insects follow similar patterns remains poorly understood, but canopy sampling is helping improve knowledge. Novotny et al. (2006) concluded after comparing temperate and tropical tree host specificity for herbivorous insects, that no differences exist in herbivore-tree host specificity between the tropics and temperate zones, and that differences in insect species richness between these regions are driven more by plant species richness patterns. However, they did acknowledge that differences in specialization exists for different insect groups between the two regions, with for example, the Papilionidae being more specialized in the tropics compared to Lycaenidae: Polyommatini, which are more specialized in temperate regions (Scriber 1988). Other groups for which known differences occur are the bark beetles (Curculionidae: Scolytinae), and also treehoppers (Hemiptera: Membracidae), which are seemingly more specialized in temperate areas (Beaver 1979; Wood 1984). Ants are a particularly interesting canopy group, with great differences between tropical and temperate trees. Temperate trees have between 0.2 – 3 % ant abundance as a total of canopy catches (Moran & Southwood 1982), compared to 18 - 53 % for tropical trees (Moran & Southwood 1982; Erwin 1983; Adis et al. 1984; Stork 1987). From tropical Borneo, Stork (1988) found ants to dominate sampled abundance (± 18 %). However, ant species were represented by only 99 out of a total of 2 800 species (< 5 %). About 5 000 km southeast, canopy fogging of the Australian subtropical tree Argyrodendron actinophyllum, revealed only 2 % ant abundance placing it closer to temperate trees (Basset 1991). One hypothesis is that arboreal ants in temperate areas may be limited by seasonal variation in productivity (Majer 1990), a hypothesis supported by the findings of Basset (1991). The high abundance and biomass Stellenbosch University https://scholar.sun.ac.za 19 of spiders could indicate that spiders have taken over predatory roles from ants in temperate areas (Basset 1991), as this group is more resilient to seasonal limitations (Reichert & Harp 1987). Another interesting group is the rest of the Hymenoptera (i.e. non-Formicidae). In a Bornean canopy study, non-Formicidae Hymenoptera were the most species-rich group, followed by Coleoptera and Diptera (Stork 1988). About 1455 chalcidoid wasps (6 % of total abundance) were sampled, comprising a massive 739 species (> 26 % of total species richness). Of this hyper-diverse group, 437 species were sampled as singletons (Stork 1988). The abundance of non-Formicidae Hymenoptera is in line with other studies from the tropics, for example from Central Amazonia (6 % of total numbers; Adis et al. 1998) and the Pantanal (4 % of total numbers; Marques et al. 2006). The Coleoptera is arguably the best studied arthropod group in tree canopies, and also one of the most diverse. Between tropical and temperate sites, and between sites within these regions, there are great differences in the diversity of beetles. For instance, Alison et al. (1997) found a total of 418 beetle species from eight trees of a single species, Castanopsis acuminatissima, from tropical New Guinea (mean = 144 beetle spp. per tree). Here, the most abundant beetle families were (from highest to lowest): Chrysomelidae, Staphylinidae and Curculionidae. Erwin (1983) concluded from Manaus, Central Amazonia, that the top five species-rich families of beetle were Curculionidae, Chrysomelidae, Tenebrionidae, Coccinellidae and Cerambycidae in descending order. In Panama, Erwin & Scott (1980) found the most species rich beetle families from a single tree species, Leuhea seemmani, to be Chrysomelidae, Staphylinidae, Cerambycidae, Mordelidae and Carabidae, compared to Brunei, where from five tree species, the most species rich beetle families were Curculionidae, Staphylinidae, Chrysomelidae, Aderidae and Anthribidae (Stork 1991). From the subtropics, in a forest near Brisbane, fogging of the tree species A. actinophyllum showed the most dominant coleopteran families to be, from highest to lowest: Chrysomelidae, Scolytidae, Corylophidae, Staphylinidae and Curculionidae (Basset 1991). Another study, from the temperate rainforests in Chile which focused on Gondwanan lineages only, found nearly 500 beetle species, the most abundant and species rich family being Curculionidae (Arias et al. 2008). Regardless of much divergence between taxa found, the most represented beetle Stellenbosch University https://scholar.sun.ac.za 20 families largely seem to include Chrysomelidae, Staphylinidae and Curculionidae. Also, it is clear that there are large differences between tropical and temperate trees. Roles of insects in forests Insects exhibit not only great variety in their taxonomy, but also in the way they feed. Whereas there are large variations in classifying insect herbivores according to their guilds (Cornell & Kahn 1989), a comprehensive guild classification was described by Novotny et al. (2010). Initially suggesting 72 possible guilds for herbivorous insects, eventually this number was lowered to 24. Insect herbivores are placed into guilds based on an array of characteristics, e.g. leaf sucking, leaf chewing, leaf mining, phloem sucking, xylem chewing etc. Insect herbivory is, evidently, not restricted to leaves of green plants only, but encompass a wide range of niches within their respective habitats. Although the interactions between herbivorous insects and plant hosts account for much of terrestrial biodiversity, many species at higher trophic levels also depend on insect herbivores as food sources (Price et al. 1980). This highlights the central role of insect herbivores in maintaining complex ecosystems like forests. Recent work has shown that herbivorous insects could even significantly limit the capacity of forests to act as carbon sinks (Couture et al. 2016). Their functional importance therefore stretches far wider than only at the local- or regional scale, highlighting the significant ecological role of such a species-rich group. While insect herbivores are abundant in forest canopies and contribute significantly towards ecological functioning and diversity within the forest canopy, they also play important roles in the lower layers of the forest. Hunter et al. (2003), for example, suggested that canopy herbivores influence forest soil processes, but with strong spatial and temporal components. Hunter (2001) lists seven ways in which this is possible. Firstly, herbivores alter soil nutrients through deposition of herbivore faeces into the soil. Secondly, they do so through inputs into the soil by insect cadavers. The third way is by changing the chemistry of precipitation, or through fall via defoliator-mediated means. Fourthly, herbivorous insects alter the quality and quantity of litter inputs from the forest canopy. Fifthly, they change the Stellenbosch University https://scholar.sun.ac.za 21 nutrient uptake by plant communities. Sixthly, they could impact root/mutualists interactions, and lastly, they exhibit effects upon the physical structure of plant canopies and indirectly facilitate subsequent changes in the soil microclimate (from Hunter, 2001). The impact of such a functionally diverse and species-rich group as forest canopy herbivores consequently stretches across the different forest strata. Recent work further suggests that herbivory at the above-ground level, i.e. the forest canopy could markedly influence not only soil properties, but even the eventual leaf litter decomposition process (Grime et al. 1996; Wardle et al. 2004; van Dam & Heil 2011; Couture et al. 2016). The decomposition of leaf litter in forests returns nutrients from organic material back into the soil, with plant productivity strongly depending on this process (Gartner & Cardon 2004). This is one of the most important processes affecting nutrient cycling and forest productivity (Cuevas & Medina 1988; Didham 1998). Soil and leaf litter arthropods, together with microbes, play significant roles in leaf litter decomposition (Seastedt 1984; Seastedt & Crossley 1984, 1988), and are known to be greatly affected, as most arthropods are, by the micro-climate of a given location (Bokhorst & Wardle 2013; Cuke & Srivastava 2016). Further factors known to affect leaf litter decomposition include climate itself (Shanks & Olsen 1961; Aerts 1997), micro-environment surrounding the litter (Hornsby et al. 1995), chemical composition of the litter (Pereira et al. 1998; Lill & Marquis 2001) and the structure of the decomposer community (Seastedt & Crossley 1984; Zak et al. 1990). Another factor is the species composition of litter, with research suggesting the species to have a significant effect on the rate of leaf litter breakdown (Shanks & Olsen 1961). Other work even suggests that the species of tree has a greater effect on leaf litter breakdown than rainfall (Wieder et al. 2009; Dale et al. 2015). Soil communities tend to specialize on the plant species above it (Ayres et al. 2009; Strickland et al. 2009). These observations support previous work, suggesting that home-field advantage (HFA) greatly contributes to the eventual leaf litter breakdown process (Bocock et al. 1960; Hunt et al. 1988; Vivanco & Austin 2008). HFA states that leaf litter decomposes more rapidly underneath species from which it originates than from other species (Gholz et al. 2000). One reason put forward to explain this phenomenon is the local adaptation of the soil community, which through specializing locally, gains faster access to energy and nutrients contained within the leaf litter (Ayres et al. 2009). It is quite Stellenbosch University https://scholar.sun.ac.za 22 possible that resource use by macro- and micro-invertebrate decomposers could be species specific, and that such species are wholly dependent on a single species of host tree and, in the light of HFA, even dependent on a certain location within a larger community (i.e. underneath its host tree). However, HFA is still poorly understood at the level of individual trees. HFA in essence supports (for detritivores) the resource concentration hypothesis, stating that herbivorous insects are ‘less likely to find and remain in patches in which their host plant is less likely to be encountered’ (Castagneyrol et al. 2014). Viewing trees as creators of micro-habitats and, for the very small, even a ‘patch’ in its own right, we can expect to find at least some levels of specificity between a host tree’s leaf litter and micro- and even macro- arthropod decomposers. Global forest change and insect responses Across the globe, forests are experiencing change (Hansen et al. 2013). Globally, mean annual temperatures have been increasing since the 1970’s (Allen et al. 2010), with some work even suggesting an expansion of the earth’s tropical belt (Seidel et al. 2008; Lu et al. 2009). Since 1900, the global average temperature has increased by 0.8 °C (Hansen et al. 2006), and since 1880 the 12 warmest years were all recorded between 1990 and 2005 (Lindner et al. 2010). Even conservative estimates of global climate change suggest increases in mean annual temperatures, significant drying in certain regions, and increases in the intensity and incidence of droughts (Christensen et al. 2007; Seager et al. 2007). The effect/s of such changes on forest functioning is not yet resolved. Possibly, certain forests might experience positive feedbacks, such as increased forest vigour and growth, higher water use efficiency, and extended growing seasons, whereas other forests might show negative responses (for example reduced growth, increases in stress, higher tree mortality rates, or disruption of plant-insect dynamics) (Ayres & Lombardero 2000; Bachelet et al. 2003; Lucht et al. 2006; Scholze et al. 2006; Lloyd & Bunn 2007; Allen et al. 2010). Due to the longevity of trees, forests are especially vulnerable to rapid changes in climate (Lindner et al. 2010). Stellenbosch University https://scholar.sun.ac.za 23 Faunal biota associated with forest ecosystems are equally susceptible, with climate change already influencing species distributions and occurrence in forests. In the highland forests at Monte Verde in Costa Rica, for example, the golden toad (Bufo periglenes) has vanished, along with significant decreases in 42 of 113 species of the toad genus Atelopus. These observations are linked to warmer sea surface and air temperatures (Pounds & Crump1994; Pounds et al. 1997; Pounds et al. 1999; La Marca et al. 2005; Pounds et al. 2006). Apart from amphibians, evidence of insects (which are known to be sensitive to abiotic conditions (Gerlach et al. 2013)) responding to long-term changes in climate is steadily accumulating (Bale et al. 2002). Natural ecological disturbance is on the increase, with for example, the incidence of fire in the forests of Canada, Russia and Alaska increasing (Gillet et al. 2004; Soja et al. 2007). Stemming from subsequent warmer climatic conditions, insect outbreaks become affected (Berg et al. 2006). The spruce beetle (Dendroctonus rufipennis), for example (its numbers usually kept intact by cold and wet conditions), has caused large scale tree mortality, totalling approximately 1 million hectares of forest in Alaska following years of record warm temperatures (National Assessment Synthesis Team 2001). Forest insect range expansions are also occurring. The winter pine processionary moth (Thaumetopoea pityocampa) has shifted its elevation range following a record warm summer in southern Europe (Battisti et al. 2006). Its expanse in range to higher elevations were, during one summer, nearly a third of its total expansion during the previous three decades. This phenomenon is possibly linked to increased flight activity of newly emerged females with increases in temperature (Battisti et al. 2006). Expansions such as these could occur sporadically, with subsequent colder years causing range retractions not leading to long-term population settlement (Whittaker & Tribe 1998). Since the 1960’s, gradual north-eastern shifts in occurrence of Operophtera brumata (a temperature limited cyclic geometric moth) from the forests of Fennoscandia, Scandinavia, are linked to gradual increases in temperature, and not to spontaneous outbreaks outside its normal range (Jepsen et al. 2008). Evidently, range expansions of insects do not only occur relative to elevation, but also in latitude, and occur gradually over time. Forests in climates historically viewed as harsh for several insect herbivores might become increasingly exposed to establishment of new populations. The Boreal zone is a good example, lying beyond various insect’s distribution range (Lindner et al. 2010). However, increasing temperatures are expected to facilitate the northward expansion of two moth species, Stellenbosch University https://scholar.sun.ac.za 24 Lymantria dispar and L. monacha (Vanhanen et al. 2007), as well as that of Neodiprion sertifer (Virtanen et al. 1996; Veteli et al. 2005), a sawfly species, the larvae of which feeds on pine needles (Larsson & Tenow 1984). Evidently, insects associated with forests are greatly affected by changes in climate which severely affect their distributions and persistence in particular areas. As insects play disproportionately large roles in normal forest functioning, it means that understanding changes in insect distribution and behaviour is of critical importance for ecologists. Climate change will not only affect insect populations directly, but also indirectly, by impacting on tree physiology. Nitrogen (N) supplies to plants can affect the productivity of herbivores by affecting both the quantity and nutritional quality of plants (Augustine et al. 2003; Craine et al. 2010). Foliar nitrogen, for example, increases during times of plant stress (Huberty & Denno 2004). Earlier work suggests that plant stress facilitates insect herbivore outbreak (White 1969; Mattson & Haack 1987). The plant-stress hypothesis (PSH) developed by White (1969) ascribes such outbreaks to changes in plant physiology during stressful times, specifically higher available levels of nitrogen. Generally, nitrogen is limiting for herbivorous insects (McNeill & Southwood 1978; Mattson 1980), with increases in available plant nitrogen attributed to outbreaks of herbivorous insects during stressful times (White 1969; 1974; 1984; 1993). However, there is still large discrepancy regarding the PSH with some authors, suggesting a decrease in insect herbivore performance during plant stress (Wearing & van Emden 1967; Wagner & Frantz 1990), with some work rejecting the PSH (for a review see Huberty & Denno 2004). Furthermore, reductions in turgor and water content during prolonged times of plant stress might adversely affect herbivore performance (Inbar et al. 2001; Huberty & Denno 2004). Importantly, several studies point out a correlation between 15N amount (rare stable isotope of nitrogen in plant tissues and soil) and precipitation, whether it be along an environmental gradient or defined geographical areas (Shearer et al. 1978; Heaton 1987; Fry 1991; Fogel & Johnson 1996; Austin & Vitousek 1998). Heaton (1987), for example, found a correlation between aridity and the ratio of 15N/14N, with plants in wet sites (Knysna) having a lower foliar 15N component than drier sites (Namib Desert). Handley et al. (1999) found a large effect of rainfall on foliar 15N, ascribing it to the interaction Stellenbosch University https://scholar.sun.ac.za 25 of growth stimulating effects associated with increased rainfall. They further argue that any factor decreasing the proportional flux of ecosystem nitrogen (N) into organic matter storage pools conversely pushes ecosystem N toward 15N-enrichment (Handley et al. 1999). These factors can refer to anything from aridity, salinity, extreme pH, fire or grazing. Another study further confirms this pattern, with an increase in foliar 15N at drier sites compared to wetter sites in Hawaiian forests (Austin & Vitousek 1998). Temperature, too, has been found to influence the ratio of nitrogen stable isotopes, with higher mean annual temperatures resulting in a higher foliar 15N/14N ratio (Amundson et al. 2003). From the global patterns in linkages between N availability and 15N, we can interpret the relationship between climate and foliar 15N as drier, warmer ecosystems having higher N availability (Craine et al. 2009; Craine et al. 2015). Whereas N availability generally increases in drier conditions, predictably affecting insect herbivores, carbon isotope discrimination also provides insight into environmental impacts on plant functioning (Diefendorf et al. 2010). For example, numerous studies have shown a decrease in 13C (rare stable isotope of carbon) with increases in precipitation (Kohn 2010) and an increase in 13C with increasing temperature (Wang et al. 2013). Warren et al. (2001) tested the hypothesis that levels of 13C is a useful indication of water availability, and concluded it to be a useful indicator of drought stress / water availability. They found plant water potential to be highest during spring (after winter rains) and the lowest during late summer / autumn (before arrival of rain). Evidently, plants experiencing stress significantly affect insect herbivore phenology. With antagonistic (re: plant-herbivorous insect) interactions often highly specialized (Thebault & Fontaine 2010), long periods of stress could markedly impact such interactions. Research aim and objectives The Western Cape is predicted to be affected by global climate change in several ways, some of which include more hot days, higher average annual temperatures, and reduced average rainfall, especially in the western parts (Midgley et al. 2005). On a global scale, declines in forests are predicted to increase due to water limitation (Williams et al. 2013), with tree growth strongly dependent on water as well as Stellenbosch University https://scholar.sun.ac.za 26 nitrogen availability (Ibrahim et al. 1997). The largest forest complex in South Africa is situated in the southern Cape and, especially so for arthropod diversity, is still largely understudied. Botanically, the southern Cape forest complex has been extensively researched, with the focus mainly on tree production (e.g. Geldenhuys 1993a; Geldenhuys 1993b; Geldenhuys 1996; Vermeulen et al. 2012) and forest distribution (e.g. Geldenhuys 1991; Geldenhuys 1994). Some other research in South Africa’s largest forest complex includes work on birds (Koen 1988) and limited work on invertebrates (Koen & Crowe 1987). Recent work investigated both edge and road effects on local forest arthropod diversity (Swart et al. 2018; Swart et al. 2019). However, holistic research on arthropods in the southern Cape forest complex and forests to the west of the southern Cape complex is absent, with arthropod research being done mostly in the fynbos (e.g. Wright 1993; Wright & Samways 1998; Giliomee 2003; Augustyn et al. 2013; Vrdoljak & Samways 2014; Lee & Barnard 2015) and succulent Karoo biomes (e.g. Wright & Samways 1996; Braschler et al. 2012). Importantly, no study to date has aimed to assess the interaction between indigenous forest trees in this region with associated arthropods, nor has any study predicted how future environmental change might alter such interactions. The main aim of this thesis is to discern the relative effects of various aspects regarding landscape level effects, plot level effects, species level effects, and physiological level effects of forest trees on the arthropod diversity associated with trees. This is divided into four objectives, collectively comprising the four data chapters of this study. Chapter 2* *This chapter has been accepted for publication in Ecological Entomology, and is included here in its published form: Swart, R. C., Samways, M. J., Pryke, J. S., & Roets, F. (2019). Individual tree context and contrast dictate tree physiological features and arthropod biodiversity patterns across multiple trophic levels. Ecological Entomology (in press). Stellenbosch University https://scholar.sun.ac.za 27 The first objective is to evaluate how tree-level context and contrast might dictate canopy arthropods associated with a tree. The respective effects of context and contrast has been discussed at the landscape- level (Wiens et al. 1993; Tscharntke et al. 2002). However, due to the relatively high diversity of fauna contained in tree canopies, these same factors might be equally applicable at a much finer scale, the individual tree. For this objective, I selected a single indigenous tree species, Podocarpus elongatus, occurring both as a forest tree in sheltered mountain kloof forests, and as a very large shrub on rock screes, in its natural environment. This species is also widely planted in suburban and urban environments in towns surrounding its natural habitat, the south Western Cape. I selected trees based on predetermined criteria, regarding its context (natural, semi-natural, planted) and its contrast to surrounding vegetation (high, low). Canopies of focal trees were fogged with chemical pyrethroids, in order to sample arthropods from the foliage and branches. The diversity patterns of arthropods collected were then compared between the various tree categories to determine the effects of where a tree is growing in the landscape on its ability to host canopy arthropods. Resultantly, I answer the first objective of whether the immediate surroundings of an individual tree might affect its associated biota, and to what extent. Chapter 3* *This chapter has been submitted for publication in a scientific journal (Applied Soil Ecology), and is included here in its submitted form. The second objective is to determine the role of various tree species on detritivorous arthropod diversity patterns and leaf litter decomposition, and asking whether or not home-field advantage exists within single forests between different forest tree species. This was done in an indigenous southern Afrotemperate forest at the western extremity of these forests’ range, Oubos (descriptions of study forests at the end of this chapter). I selected three dominant forest tree species, Olea capensis macrocarpa, Podocarpus latifolius and Rapanea melanophloeos, and firstly wanted to determine whether the detritivorous arthropods in forest leaf litter respond towards identity of a source tree’s leaves. Secondly, I determine whether trees in diverse, mixed forests, create heterogeneous patches of Stellenbosch University https://scholar.sun.ac.za 28 arthropod diversity on the forest floor due to leaf-fall and build-up beneath source trees, and how this might impact leaf litter decomposition. Effectively, I answer the question of whether or not home-field advantage might occur at the tree-level in an indigenous forest. Also, I ascertain whether species of tree affect not only the arthropod diversity in canopies, as has been shown in numerous global studies, but also the arthropods associated with the breakdown of its leaves on forest floors. Chapter 4 Here, I aim to answer unresolved questions with regards to forest functioning in a changing environment by focussing on five southern Afrotemperate forests along a large biogeographical gradient (>390 km) in the Western and Eastern Cape of South Africa (details of each of the five forests are given at the end of this chapter). Specifically, the third objective is to evaluate, for the first time, the canopy arthropod diversity of southern Afrotemperate forests, and how it responds to not only tree species identity and plot characteristics, but also to tree physiological features. This I then linked with predictions of future global change, focussing on rising levels of CO2, increases in ambient temperatures, higher occurrences and incidences of drought, and increases in pollution. For this objective, I sampled canopy arthropods from 120 individual trees from 8 tree species, in the largest forest complex in South Africa, by means of chemical fogging. Chapter 5 The fourth objective is to describe, and place in a global context, the canopy arthropod diversity associated with indigenous southern Afrotemperate forest trees. Africa represents one of the largest geographical gaps in canopy science, and especially the forests forming part of the Afromontane archipelago, has received close to zero attention with regards to not only its canopy arthropod diversity, but its entire forest arthropod diversity. I review the global literature, and discuss the patterns in diversity, of the major arthropod taxonomic groups sampled. Stellenbosch University https://scholar.sun.ac.za 29 A short description of each forest included in this study (with the exception of the first data chapter) is detailed below. Oubos. Oubos forest lies near the town of Riviersonderend, at the foothills of the Riviersonderend Mountains. The forest comprises of a large main patch with many smaller strips of forest linked to the larger patch, totalling around 381 ha in size. It is the most westerly forest and also the most species poor in terms of floral diversity. Although it is situated in a strictly winter rainfall area, the forest itself receives rainfall throughout the year due to orographic precipitation (± 1000 mm annually), creating a rain shadow effect on the northern side of the mountain (Le Maitre 2009). Dominant emergent species include Olea capensis subs. macrocarpa, Rapanea melanophloeos, Olinia ventosa, Platylophus trifoliatus and Curtisia dentata. The understorey is generally sparse and dominated by Canthium inerme, Maytenus acuminata, Diospyros whyteana, Halleria lucida and Cassinopsis ilicifolia. The closest large forest patch to Oubos is the Koloniesbos-Duiwelsbos complex near Swellendam, is 56.96 km away to the east. Between Oubos and the next study forest, Grootvadersbosch, lies 92.71 km. These two forests are further separated by the wide Breede River Valley which splits the Riviersonderend Mountains to the west from the Langeberg Mountains to the east. Grootvadersbosch. Grootvadersbosch lies northwest of the town of Heidelberg at the foothills of the Langeberg Mountain Range. It is close in size to Oubos, at about 357 ha. Although situated in a winter rainfall area, this forest receives rain throughout the year similarly to Oubos. To the north east of Grootvadersbosch lies another relatively large indigenous forest, Boosmansbos, approximately 8.90 km away. Emergent tree species that occur here and not in Oubos include Afrocarpus falcatus, Elaeodendron croceum and Ekebergia capensis. The dominant overstorey species are similar to those found in Oubos, but with Podocarpus latifolius, Ocotea bullata, Scolopia zeyheri and Cassine peragua being more common. The understorey species are mostly similar to those found in Oubos, with Burchelia bubalina being the exception by being absent in Oubos. Along the same mountain range lies the next forest site, Kleinbos, 122.22 km to the east. With the exception of very few and very small forest patches, the area between Grootvadersbosch and Kleinbos is mostly dominated by mountain fynbos and farmland. Stellenbosch University https://scholar.sun.ac.za 30 Kleinbos. This forest is the smallest of the five patches at only 200 ha. However, due to its more easterly location it contains species not found in Grootvadersbosch, including Gonioma kamassi and Trichocladus crinitus, both species that make up the majority of the understorey biomass. Pterocelastrus tricuspidatus becomes especially more abundant in Kleinbos (and the forests to the east) compared to the more westerly forests. Kleinbos receives rainfall throughout the year due to orographic precipitation and lies in the transition zone between winter- and all year rainfall. The overstorey species are similar to those found in Grootvadersbosch, but with the species Nuxia floribunda being a common overstorey component not found in Grootvadersbosch. The closest large forest patch to Kleinbos is in the mountains north of George, southern Cape, approximately 30.75 km to the east. From here, the largest continuous forest in South Africa starts its distribution, moving east to Humansdorp. Woodville. Woodville forest forms part of the large, continuous southern Cape forest complex. On its own, it is about 504 ha, and lies 44.44 km east of Kleinbos. It lies in an all year rainfall region. It shares almost all its woody species with Kleinbos, but with some species only occurring in Woodville and further eastwards, including Maytenus peduncularis, Ochna arborea, Trimeria grandifolia and Dovyalis rhamnoides. In terms of understorey, there is little difference between Kleinbos and Woodville, with the dominant understorey trees being Trichocladus crinitus, Gonioma kamassi and various tree saplings. To the west of Woodville lies the relatively large Saasveld indigenous forest (± 450 m away) and to the east, across the Woodville River, lies the Bergplaas forest (± 200 m away), creating a large, continuous forest. Whereas Woodville is in close proximity to the nearby intact forests, Oubos, Grootvadersbosch and Kleinbos are relatively isolated in the landscape. Witelsbos. Between Woodville and Witelsbos, the next study forest, lies 137.4 km of interspersed forests, fynbos, farms and settlements. This stretch occupies the largest forest complex in South Africa. Witelsbos is 379 ha, occurring east of the Storms River in the Eastern Cape Province. It forms part of a network of large indigenous patches that are isolated by farmlands or plantations, with the nearest large forest to Witelsbos being only 1.49 km to the southwest. Forming part of a single complex, species found in Witelsbos are nearly identical to those found in Woodville, and to a lesser extent in Kleinbos. However, Brachylaena glabra only starts its easterly distribution in Witelsbos and forms, together with Stellenbosch University https://scholar.sun.ac.za 31 Trichocladus crinitus the bulk of the understorey plant biomass. The overstorey species are mostly identical to those found in Woodville. Chapter 6 The final chapter is a general discussion and conclusion of this thesis. References Adis, J., Lubin, Y. D., & Montgomery, G. G. (1984). Arthropods from the canopy of inundated and terra firme forests near Manaus, Brazil, with critical considerations on the pyrethrum‐fogging technique. Studies on Neotropical Fauna and Environment, 19, 223-236. Adis, J., Harada, A. 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