Resource use in indigenous forests of the Eastern Cape, South Africa and its effects on bird communities

Leaver, Jessica (2020-03)

Thesis (PhD)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: Indigenous forest represents South Africa’s most limited and fragmented biome, but supports disproportionality high levels of biodiversity. Furthermore, forests provide a range of resources for people, particularly the rural poor, and are thus of high socio-economic value. This is particularly true in the Eastern Cape, which harbours 46% of South Africa’s remaining indigenous forest cover, and some of the country’s most economically impoverished populace. Forest management in this region is thus required to balance the needs of resource users with the conservation of forest biodiversity through sustainable use. However, de facto open-access systems of resource use prevail, and there is concern that unregulated harvesting of forest products is driving forest degradation. Supporting this, a recent study found forest bird ranges to have declined in the region over the past 20 years, despite no loss of forest cover over the same time period. However, little research has investigated the link between resource use, habitat modification and forest avifauna in the Eastern Cape. Consequently, this study aimed to investigate patterns of resource use in state forests across the Eastern Cape; and the impact of different harvest regimes on forest habitat structure, and avifaunal communities. Specifically, three key resource use types were investigated: understory trees harvested for poles; canopy trees harvested for crafts and timber; and bark harvested for medicinal use. Regionally, harvest rates were low to moderate, however, the nature and extent of harvesting was site- and species-specific. Of particular concern was the high rate of ring-barking of focal canopy tree species of medicinal value, resulting in the mortality of 29% of harvested trees. Harvest activities modified habitat structure at the ground, understory and canopy layers, with the severity of impact dependent on the nature and extent of harvesting. Overall, harvest activities increased the frequency of canopy disturbances, with concomitant thickening of ground- and understory-layer foliage. At the regional-scale, avifaunal communities were shaped by variation in forest structure and harvest regimes, mediated by species’ feeding traits. Furthermore, harvest activities negatively affected functional organization of bird communities, dependent on the nature and extent of harvesting, but did not reduce species richness or the diversity of functional traits. At the forest-scale, the bird community in a montane forest was structured by harvest-mediated habitat modification, as well as elevation. Specifically, forest-specialist species richness was negatively affected by habitat modification, while forest-generalist species richness was positively affected. Similarly, avifaunal community composition was affected by habitat modification caused by timber harvesting in a scarp forest. Based on avifaunal reponses to harvesting, findings of this study indicate that resource use may be sustainable, but that better management is required to mitigate negative ecological impacts associated with high levels of extraction. By providing insight into the ecological implications of harvesting, this study contributes to the development of ecologically-informed resource use management strategies. While this represents an important contribution, the sustainable use of forests cannot be achieved without increased capacity of the state to implement management actions which integrate the ecological and social issues of forest management.

AFRIKAANSE OPSOMMING: Inheemse woude verteenwoordig Suid-Afrika se mees beperkte en gefragmenteerde bioom, maar ondersteun buitegewone hoë vlakke van biodiversiteit. Verder, verskaf woude ‘n verskeie natuurlike bronne aan mense, veral arm mense, woonagtig in landelike woudgebiede, en bied dus ‘n hoë sosio-ekonomiese waarde. Dit is veral so in die Oos-Kaap, waar 46% van Suid Afrika se oorblywende inheemse woude, maar ook van ons armste mense voorkom. Woudbestuur om die balans tussen bron-verbruikers en bewaring van woudsbiodiversitiet op ‘n volhoubare wyse te balanseer, word dus in hierdie streek dringend benodig. Maar, feit is, onbeperkte toegang tot die verbruik van natuurlike bronne is aan die orde van die dag, en daarom heers daar kommer dat diesulke onbeheerde oes van produkte die degradering van woude dryf. Ondersteuning vir hierdie toedrag van sake word deur ‘n onlangse studie, wat bevind het dat voëlgemeenskappe in hierdie woude die afgelope 20 jaar gedaal het, gemaak. Dit, alhoewel woudbedekking oor die selfde tydperk uitgebrei het. Maar min wetenskaplike navorsing het tot op hede die verwantskap tussen bron-verbruik, habitat- versteuring en woud-voëlgemeenskappe in die Oos-Kaap deeglik ondersoek. Gevolglik was die doel van hierdie studie gemik om die patrone van bron-verbruik in staatsbestuurde woude van die Oos-Kaap te ondersoek; asook die impak wat verskillende oespatrone op habitatstruktuur en voël-gemeenskappe mag hê. In hierdie studie word drie bronverbruikers-tipes spesifiek ondersoek: die oes van onderbome vir pale; oes van oorhoofse bome vir handgemaakte en konstruksie houtprodute; asook die insameling van bas vir medisinale gebruike. In streeksverband was gevind dat alhoewel die koers van oesting laag tot matig plaasvind, die aard en intensiteit van oesting, terrein- en spesies-spesifiek was. ‘n Spesifieke bekommernis was die hoë insidensie van ringbas-verwydering van belangrike oorhoofse bome met medisinale waarde. So is ‘n mortaliteit van tot 29% gevind by bome waarvan daar geoes was. Oestingsbedrywighede het die habitatstruktuur op grondvlak-, en plantegroei onderdak - asook en kapkroon-boom gebiede beduidend versteur, met die graad van impak wat gekoppel was aan die mate en uitgebreide aard van oesting. Oorsigtlik gesien, het die oestingsbedrywighede die frekwensie van kroon-versteuring, met gevolglike verdigting van grond en onderboom plantegroei veroorsaak. Op ‘n streeksvlak, is voëlgemeenskappe, deur veranderde spesies-voedingswyses, deur die gepaardgaande variasie in woudstruktuur en deur oes-benaderings stelsels, bepaal. Verder het oestingsbedrywighede, afhangend van die aard en intensiteit van oesting, die funksionele organisasie van voëlgemeenskappe negatief beinvloed, maar tog is spesiesrykdom of die funksionele diversiteit nie verlaag nie. Deur vergelykend na variasie tussen woude te kyk, is gevind dat die voëlgemeenskappe van bergagtige woude deur oestingsbemiddelde habitatsversteuring, asook hoogte bo seespieel, bepaal word. Resultate dui daarop dat spesifiek, spesialis-woudspesies-rykdomnegatief deur habitat habitatversteuring beinvloed is, terwyl algemene-woudspesies-rykdom positief beinvloed verhoog is. Op die selfde manier is die samesteling van voëlgemeenskappe deur habitatversteuring van hout-oesting in ‘n skarpwoud beinvloed. Gebaseer op die reaksies van voëlgemeenskappe op oesting in woude, dui die bevindinge van hierdie studie aan dat bron-verbruik volhoubaar mag wees, maar dat beter bestuur nodig is om die negatiewe ekologiese impakke verwant aan hoë verbruik teen te werk. Deur insig te kry rakende die ekologiese implikasies van oesting, maak hierdie studie ‘n belangrike bydrae tot die ontwikkeling van ekologies-gebaseerde bronverbruik-bestuurstrategië. Alhoewel hierdie bevinding ‘n beduidend is, kan die volhoubare verbruik in woude nie geskied sonder ‘n toenemende inisiatief van die Staat om toepaslike bestuursaksies, wat ekologiese en sosiale aangeleenthede rakende woud-bestuur integreer, in te stel en te handhaaf nie. Dit verteenwoordig ‘n belangrike bydrae, maar die houbare gebruik van woude sal net behaal word as die staat sy hoedanigheid om bestuursaksies uit te voer wat ekologiese asook sosiale sake van woudbestuur integreer.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/108125
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