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.

Masters