The effect of commercial forestry plantations and roads on southern Afrotemperate forest arthropod diversity

Thesis (MSc)--Stellenbosch University, 2016.ENGLISH ABSTRACT: With only about 12% of the Earth’s surface under some form of official protection and the human population on the rise exponentially, production landscapes can and should contribute significantly towards biodiversity conservation in the future. Globally, management practices that balance production and conservation are important for creating sustainable agriculture and timber production landscape. This study aims to determine how a heterogeneous, unfenced national park in South Africa, containing a mosaic of commercial plantations, natural forests and fynbos is affected by land transformation. This was achieved by focussing on artificially created and natural edges found in this landscape, through analysing and comparing the composition and species richness of arthropods across linear transects. Specifically I determined if natural edges next to southern Cape Afrotemperate forests are altered by anthropogenic influences such as forestry plantations, and their felling, as measured by epigaeic arthropod diversity. The effects of different road types, and directions that these roads dissect the forest, were also assessed. I found that pine plantations provide little suitable habitat for either forest or fynbos arthropods. The natural fynbos-forest ecotone harbours a unique composition of arthropod assemblages, with the smallest edge effect into the forest. Once this is replaced by commercial pine plantations, an edge effect up to 30 m into the forests from the plantation edge is detected. When plantations bordering natural forests are felled, the edge effect increases to 50 m into natural forests. Research on edge effects created by roads showed that both wider, arterial roads as well as secondary roads affected the diversity of forest arthropods up to 50 m into the natural forest. These effects are therefore similar to that observed after clear felling of plantations except that, in contrast to possible regeneration of natural edge habitat after clear felling, these edges are now permanent fragmentary features in the forest with little chance of recovery. Even hiking trails affected overall arthropod assemblages in the adjacent forests up to 10 m. Although this likely does not lead to forest fragmentation due to an in-tact forest canopy, these areas alter natural assemblages with unknown population dynamic consequences. I also show that east-west directed roads have stronger fragmentary effects as determined by arthropod diversity, along their southern edge than north-south directed roads, with east and west facing edges. Increased sunlight penetration, with its accompanying changes in microclimatic conditions is put forward to explain these differences. Habitat loss due to the establishment of commercial plantation forestry in the region not only leads to a decrease in suitable fynbos habitat, but also impacts adjacent natural forest arthropod diversity. The remaining southern Cape Afrotemperate forests are greatly fragmented by a network of roads. Due to the uniqueness of these forests, special management is needed to ensure that the biodiversity in the region is optimally conserved without adversely affecting production yields. Some possible mitigation actions are put forward. However, these should be assessed for their effectiveness in future research studies before they are implemented.AFRIKAANSE OPSOMMING: Met slegs sowat 12% van die Aardoppervlak tans amptelik beskerm en die aanhoudende, eksponensiële groeikoers van die mens, het die tyd ryp geword vir die mens om te besef dat landskappe wat nie amptelik beskerm word nie kan en sal moet bydra tot biodiversiteitsbewaring. Wêreldwyd is bestuurspraktyke rakende volhoubare landskappe, wat poog om ‘n balans te handhaaf tussen bewaring en produksie, bewys om suksesvol by te dra tot bewaring. Hierdie studie het beoog om te bepaal hoe ‘n heterogene, onomheinde nasionale park in Suid-Afrika, met kommersiële plantasies, natuurlike woude en fynbos wat groot areas binne die grense van die park bedek, geraak word deur die rande van hierdie aangrensende habitat-tipes te bestudeer. Dit was gedoen deur na beide die natuurlike en versteurde woudrand te kyk. Spesifiek het ek bepaal of natuurlike woudrande se grondlewende arthropoda beïnvloed word deur kommersiële denne-plantasies en hul verwydering. Die moontlike effekte van verskillende pad-tipes en padrigtings op woudfragmentasie is ook bepaal. Ek het bevind dat denne-plantasies min geskikte habitat vir beide woud- en fynbos-arthropoda bied. Ook, sodra plantasies aangrensend aan natuurlike woude kaalgekap word, vergroot die afstand wat effekte penetreer tot sowat 50 meter binne woude. Die resultate in verband met paaie wat deur die woud loop toon aan dat wyer, hoofpaaie sowel as sekondêre paaie arthropoda gemeenskappe tot 50 meter in die woud in affekteer. Hierdie rand-effek afstand is vergelykbaar met dié van kaalkap-plantasie areas, alhoewel dit verskil in die feit dat die paaie permanente fragmentasie veroorsaak en kaalkap areas moontlik gerehabiliteer kan word. ‘n Interessante bevinding was dat ook staproetes die diversiteit van arthropoda beïnvloed tot en met 10 meter langs die roetes. Alhoewel dit nie tot fragmentasie lei nie, aangesien die blaredak steeds onbeskadig is, verander die natuurlike gemeenskappe met onbekende gevolge rakende hul populasie dinamika. Resultate toon ook aan hoe paaie wat in ‘n oos-wes rigting loop meer invloed uitoefen op woude aan die suiderkant van hierdie paaie, teenoor noord-suid paaie wat minder invloed uitoefen. Verhoogde vlakke van sonlig-penetrasie, met gepaardgaande mikro-klimatiese veranderings, kan moontlik hierdie bevindings verduidelik. Die verlies van habitat vanweë die plant van grootskaalse plantasies lei nie net tot ‘n vermindering in geskikte fynbos habitat nie, maar dit affekteer ook die aangrensende woude se natuurlike arthropoda diversiteit. Ter opsomming is gevind dat paaie wel die oorblywende Suid-Kaapse woude fragmenteer. Vanweë die uniekheid van hierdie woude, word spesiale bestuur vereis om te verseker dat die groter area se biodiversiteit optimaal bewaar word sonder om opbrengste te danke aan produksie te beïnvloed. ‘n Aantal moontlike versagtings-aksies word ter tafel gesit. Dit word egter aangeraai om die sukses van hierdie metodes eers te bepaal voordat dit geïmplementeer word

Interactions between indigenous southern Afrotemperate forest trees and arthropod diversity

Thesis (PhDConsEcol)--Stellenbosch University, 2020.ENGLISH ABSTRACT: Although small compared to other temperate rainforests in the southern Hemisphere, the southern Cape Afrotemperate forest complex is the largest in South Africa. While it occurs at temperate latitudes, it has strong tropical elements resulting from its paleo-history. Of the numerous species occupying forest ecosystems, insects comprise a major part of the total biodiversity, most of which occur in tree canopies. Prior to this study, little work had been done on insects in southern Afrotemperate forests in general, and no work at all has been done on the diversity and distribution of their canopy-inhabiting arthropods. Therefore, the aim here is to determine the extent to which various environmental factors affect the interaction between indigenous tree species and associated arthropod diversity in South African Afrotemperate forests. I first determine whether the context and contrast in which an individual tree grows (i.e. where it grows and what surrounds it) will impact its physiology and associated canopy arthropod diversity. I found that the contrast of vegetation surrounding an individual tree can affect leaf morphology, and, in turn, its ability to host particular arthropods, with trees with low contrast (i.e. surrounded by denser vegetation) revealing larger leaves and increased arthropod diversity. Furthermore, plant physiological features fluctuated according to the context in which a tree grows (natural, semi-natural, or planted vegetation), which affected associated canopy arthropods. Therefore, to optimally conserve local arthropod diversity using indigenous tree plantings in transformed landscapes, it is imperative to mimic natural tree context and natural variations in contrast. Forest arthropods maintain ecosystem health by driving ecosystem processes such as litter decomposition. I designed an experiment to compare the litter decomposition performed by arthropods vs. fungi, and determined which local factors influence variations in decomposition rates. In addition, I tested the home-field advantage (HFA) hypothesis at the tree-level. The HFA states that leaf litter decomposes more rapidly beneath plant species from which the leaves originate (home environment), than under other plant species. I demonstrated that arthropods perform the bulk of the decomposition function in these forests, and that their ability to do so varies significantly between different tree species, although the role of bacteria may also be substantial. Contrary to expectations, and despite selective arthropod responses toward different source leaves, HFA is not prevalent in this mixed forest system. Given the responses of arthropods to tree identity, tree context- and-contrast, and accompanying changes in plant physiological features, it was reasonable to assume that these factors may influence arthropods associated with the canopies of southern Afrotemperate forests. I therefore established the relative effects of tree species identity, plot characteristics, and plant physiology on the diversity and distribution of canopy arthropods. Tree species identity and differences in plant physiological features explained differences in arthropod diversity between individual trees. Individual trees surrounded by denser vegetation also had less diverse arthropod assemblages compared to trees in more open areas. I argue that in diverse mixed forests, tree crown heterogeneity is of significant importance in conserving arthropod diversity, driven not only by architectural variation, but also by fluctuating levels of light exposure. Differences in plant physiological features at the tree species level was accompanied by many effects on canopy arthropods, which would make generalisations of forest arthropod responses to anthropogenic changes difficult. As this study represents a first attempt to describe the diversity of arthropods in the canopies of southern Afrotemperate forests, I conclude by providing a synthesis of this diversity, placing it in a global context. I provide evidence that arthropod diversity in these forests is more similar to those of temperate forests than to arthropods associated with tree canopies in tropical forests. However, these forest canopies are ten-fold richer in species than the forest floors in this region. Combined with the high numbers of species sampled, many of which are undescribed, special conservation efforts is justified to protect southern Afrotemperate forest canopies across a wide biogeographical gradient.AFRIKAANSE OPSOMMING: Ten spyte daarvan dat die suidelike Afro-gematigde woudkompleks klein is in vergelyking met ander gematigde woude in die suidelike halfrond, vorm dit die grootse woudkompleks in Suid-Afrika. Vanweë die unieke paleo-geskiedenis van die area, het die woude egter ‘n tropiese affiniteit. Van al die 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 mag wees. Anders as verwag, en ten spyte van selektiewe arthropoda reaksies tot verskillende boomspesie 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.Doctora