The diversity and distribution of topsoil and leaf litter arthropods in timber plantation landscape mosaics

Eckert, Michelle (2017-12)

Thesis (MScConsEcol)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: Landscape planning for conservation is of great importance in high-impact production systems, such as commercial timber plantations. Ecological networks (ENs) have been applied on a large scale in exotic timber plantations in South Africa to mitigate the impacts of forestry by connecting remnant natural areas of high conservation value across the landscape. Natural remnants, such as Afromontane forests and grasslands have received much conservation attention within these ENs, yet the value of conserving grassland on hydromorphic soils remains poorly understood. We also still have limited information on arthropods occurring in the topsoil and leaf litter layer, despite their great functional importance, especially in hydromorphic grasslands. The removal of pine trees from these hydromorphic grasslands is a conservation measure to restore hydrological function within plantation landscapes. However, the effectiveness of restoration for biodiversity has not yet been determined. The study was conducted in the KwaZulu-Natal Midlands. The diversity and distribution of topsoil and leaf litter arthropods within four dominant biotopes (Afromontane forests, pine plantations, dry grasslands and hydromorphic grasslands) was determined. The biodiversity of hydromorphic grasslands was compared to the other biotopes occurring within an EN-plantation landscape mosaic. In addition, to determining whether restoration leads to successful recovery of the arthropod fauna after the removal of pine trees from hydromorphic grasslands, I compared the diversity of topsoil and leaf litter arthropods between natural untransformed hydromorphic grasslands, restored hydromorphic grasslands and pine plantations. All the natural untransformed biotopes (i.e. natural forest, dry and hydromorphic grassland) had higher arthropod species diversity compared to the transformed biotope (i.e. pine plantation). Hydromorphic grasslands differed significantly from the other dominant biotopes regarding arthropod assemblage structure, but not in terms of species richness. Thus, hydromorphic grasslands are unique landscape elements that complement the other untransformed biotopes, and contribute to landscape heterogeneity and overall biodiversity within the production landscape. Although hydromorphic and dry grasslands are classified as one vegetation type, I found that here, they were two distinct biotopes, both of which should be conserved separately owing to their unique arthropod assemblages. After the removal of pine trees from hydromorphic grasslands, the diversity and assemblages of topsoil and leaf litter arthropods have the capacity to recover to levels similar to that of natural hydromorphic grassland. However, contrary to what was expected, the assemblage similarity between the restored and natural hydromorphic grasslands was significantly negatively correlated to time since pine removal. American bramble (Rubus cuneifolius), which was more prevalent in older post-restoration sites, had the most significant negative effect on the assemblage similarity between the restored and natural hydromorphic grasslands, causing some restored sites to deviate from the restoration trajectory. Therefore, successful restoration of these hydromorphic grasslands to near natural conditions requires supplementary management inputs through removal and management of R. cuneifolius as a key management priority.

AFRIKAANSE OPSOMMING: Landskapsbeplanning vir bewaring is van groot belang in hoë-impak produksiestelsels, soos houtproduksie. Ekologiese netwerke (ENe) is op groot skaal in eksotiese houtplantasies in Suid-Afrika toegepas om die impak van bosbou te verminder deur die oorblywende natuurgebiede van hoë bewaringswaarde oor die landskap te verbind. Natuurlike oorblyfsels, soos Afromontane woude en grasvelde, het al baie aandag gekry met betrekking tot hul bewaringswaarde binne hierdie ENe, maar ons het steeds min kennis oor die waarde van grasvelde op hidromorfiese grond. Ook, 'n groep organismes waaroor ons nog beperkte inligting op het, maar wat van groot funksionele belang is, die geleedpotiges wat voorkom in die bogrond en blaarvullislaag. Die verwydering van dennebome uit hierdie hidromorfiese grasvelde word geïmplementeer om die hidrologiese funksie binne plantasielandskappe te herstel, maar die effek van restorasie op biodiversiteit is nog nie gemeet nie. Die studie is in die KwaZulu-Natal, Midlands, uitgevoer. Die diversiteit en verspreiding van bogrondse geleedpotiges binne vier dominante biotope (Afromontane woude, dennewoude, droë grasvelde en hidromorfiese grasvelde) is geëvalueer om die biodiversiteitswaarde van hidromorfiese grasvelde te bepaal, relatief tot die ander biotope wat voorkom in 'n EN-plantasie landskap mosaïek. Daarby, was die sukses van die herstel van geleedpotige biodiversiteit na die verwydering van dennebome van hidromorfiese grasvelde ook bepaal deur die diversiteit van natuurlike, ongetransformeerde hidromorfiese grasvelde, herstelde hidromorfiese grasvelde en denneplantasies te vergelyk. Al die natuurlike ongetransformeerde biotope (d.w.s. natuurlike woud, droë en hidromorfiese grasvelde) het hoër geleedpotige spesiediversiteit gehad in vergelyking met die getransformeerde biotoop (d.w.s. denneplantasies). Hidromorfiese grasvelde verskil aansienlik van die ander dominante biotope rakende geleedpotige spesiesamestelling, maar nie in spesiesrykheid nie. Dus, hidromorfiese grasvelde is unieke landskapelemente wat die ander ongetransformeerde biotope aanvul, en bydra tot landskap heterogeneiteit en algehele biodiversiteit in die produksie landskap. Alhoewel hidromorfiese en droë grasvelde as een biotoop aanskou word, het ek bevind dat hulle twee afsonderlike biotope was, wat albei as afsonderlike biotope bewaar moet word as gevolg van hul unieke geleedpotige samestellings. Na die verwydering van dennebome uit hidromorfiese grasvelde, blyk dit dat die diversiteit en samestelling van bogrondse geleedpotiges herstel tot vlakke wat soortgelyk is aan dié van natuurlike hidromorfiese grasvelde. In teenstelling met wat verwag is, was die gelykvormigheid van die samestelling tussen die herstelde en natuurlike hidromorfiese grasvelde aansienlik negatief gekorreleer met die tyd sedert denneboom verwydering. Amerikaanse braambos (Rubus cuneifolius), wat meer voorkom in areas wat al vir langer tye gerestoreer is, het die grootste negatiewe uitwerking op die samestelling van die herstelde en natuurlike hidromorfiese grasvelde gehad, wat veroorsaak het dat sommige herstelde areas van die restorasiepad afwyk. Om hierdie hidromorfiese grasvelde suksesvol te herstel tot naby natuurlike toestande, word aanvullende bestuursinsette benodig, met die verwydering en bestuur van R. cuneifolius as 'n sleutelbestuursprioriteit.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/102932
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