Pond biodiversity in a sugarcane-forestry mosaic in KZN

Briggs, Andrew John (2016-03)

Thesis (MSc)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: The wetlands of South Africa are threatened by dam creation, agricultural practices and urbanisation. Farm ponds within these wetlands act as habitat islands and are known to support heterogeneous communities of aquatic organisms which often include rare or unique species not found in other water body types. The timber and sugarcane industries of KwaZulu-Natal (KZN) province, South Africa, are very important to the local economy and make up a large portion of the farmland in the province. Timber, and more recently, sugar farmers in KZN are farming their lands with environmental sustainability in mind. This shift towards more biodiversity friendly agriculture should have positive effects on biodiversity conservation. This study aims to assess the differences in species assemblages of three different taxonomic groups within ponds found in forestry and sugarcane agriculture, and to look at the quality of habitat within the two agricultural mosaics using bioindicators. Sites within protected areas were used as benchmark sites. In Chapter 2, I assessed the conservation value of farm ponds within timber and sugarcane plantations by gathering biodiversity data on plants, aquatic Coleoptera and Odonata. Plants were sampled using transects, aquatic Coleoptera were sampled by sweeping a net through the aquatic area along the banks of the ponds and Odonata were sampled through visual observations. No significant differences were found between the wetland groups regarding species richness of plants, aquatic Coleoptera and Odonata. Species richness of the Coleoptera was low at all sites whilst the species richness of Odonata was highest in sugarcane sites which had a large open water surface, compared to smaller sites within sugarcane and forestry agriculture. Sugarcane sites contained the most invasive alien plants based on high levels of agricultural disturbance whilst still maintaining high levels of Odonata diversity, therefore indicating the importance they possess as alternative habitat for various invertebrates. In Chapter 3, the focus was primarily on utilising the Dragonfly Biotic Index (DBI) and the presences of rare and threatened Odonata to assess the conservation significance of ponds and reservoirs in a sugarcane-forestry mosaic. In order to achieve this I used the Odonata population data that was gathered, and assigned the various species their scores which subsequently allowed me to make deductions about the habitats in which they were found. The results indicate that the protected areas in my overall study area had the highest quality habitat with more Odonata species which are sensitive to disturbance being found at these localities. Despite this finding, ponds within sugarcane agricultural mosaics were able to support many Odonata species, including some which were not found in the protected areas. However, these were predominately widespread generalists with low conservation value. In conclusion, I found that species richness was a poor indication of pond conservation value and subsequently recommend using DBI for future monitoring. Although the sugarcane farms were able to support high numbers of generalist species, these results indicate that farmers could be doing more to encourage environmentally sensitive species into their wetlands, such as restoration through alien clearing.

AFRIKAANSE OPSOMMING: Die vleilande van Suid-Afrika word bedreig deur damskepping, landboupraktyke en verstedeliking. Plaasdamme binne hierdie vleilande funksioneer soos habitat eilande en ondersteun dikwels heterogene gemeenskappe van akwatiese organismes wat gereeld seldsame of unieke spesies insluit wat nie in ander soorte watermassas voorkom nie. Die bosbou en suikerriet nywerhede van KwaZulu-Natal (KZN) is baie belangrik vir die plaaslike ekonomie en beslaan 'n groot gedeelte van die landbougrond in die provinsie. Bosbou, en meer onlangs, suikerboere in KZN boer hul lande met omgewingsvolhoubaarheid in gedagte. Hierdie verskuiwing na meer biodiversiteits-vriendelike landbou behoort 'n positiewe uitwerking op die bewaring van biodiversiteit te hê. Die doel van hierdie studie was om die verskille in spesiesversamelings van drie verskillende taksonomiese groepe binne damme in bosbou- en suikerrietlandbou te evalueer, en om te kyk na die gehalte van die habitatte in die twee landboumosaïeke met behulp van bioindikatore. Liggings binne beskermde gebiede is gebruik as maatstaf liggings. In Hoofstuk 2, beoordeel ek die bewaringswaarde van plaasdamme binne bosbou- en suikerrietplantasies deur die insameling van biodiversiteitdata op plante, akwatiese Coleoptera en Odonata. Plantopnames is gemaak met behulp van transekte, akwatiese Coleoptera is versamel deur 'n net te vee deur die water langs die oewer van die dam en Odonata opnames is gemaak deur visuele waarnemings. Geen beduidende verskille is gevind tussen die vleiland groepe ten opsigte van spesierykheid van plante, akwatiese Coleoptera en Odonata nie. Spesierykheid van die Coleoptera was laag by alle liggings, terwyl die spesierykheid van Odonata die hoogste was in suikerrietliggings wat 'n groot oop water oppervlak het, in vergelyking met kleiner liggings binne suikerriet- en bosboulandbou. Suikerrietliggings bevat die meeste indringerplante gebaseer op die hoë vlakke van landbouversteuring, terwyl dit nog steeds hoë vlakke van Odonata diversiteit handhaaf, wat dus hulle belangrikheid as alternatiewe habitat vir verskillende invertebrate aandui. In Hoofstuk 3, was die fokus hoofsaaklik op die gebruik van die naaldekoker biotiese indeks (DBI) en die voorkoms van skaars en bedreigde naaldekokers en waterjuffers om die bewaringswaarde van damme en reservoirs in 'n suikerriet-bosbou mosaïek te evalueer. Om dit te bereik het ek die Odonata bevolkingsdata wat versamel is gebruik, en DBI tellings toegeken aan die verskillende spesies, wat my toegelaat het om afleidings te maak oor die habitatte waarin hulle voorkom. Die resultate dui daarop dat die beskermde gebiede in my algehele studie area die hoogste gehalte habitat het met meer Odonata spesies wat sensitief is vir versteuring wat gevind word by hierdie plekke. Ten spyte van hierdie bevinding, was damme binne suikerrietlandbou mosaïeke in staat om baie naaldekoker spesies, insluitend 'n paar wat nie gevind word in die beskermde gebiede nie, te ondersteun. Dit was hoofsaaklik wydverspreide generaliste met 'n lae bewaringswaarde. Ten slotte, ek het gevind dat spesierykheid 'n swak aanduiding was van dam bewaringswaarde en dus beveel die gebruik van die DBI aan vir toekomstige monitering. Hoewel die suikerrietplase in staat was om groot getalle generiese spesies te ondersteun, dui hierdie resultate daarop dat boere meer kan doen om omgewingsensitiewe spesies aan te moedig in hul vleilande, soos restorasie deur middel van die verwydering van uitheemse plante.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98397
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