Savanna-woodland fire regimes: ecology, management and conservation of African protected areas

Thesis (PhDConsEcol)--Stellenbosch University, 2021.

ENGLISH ABSTRACT: Fire is an important process that shapes the structure and functioning of African savanna ecosystems, and frequently occurs as either prescribed burns or unintentional wildfires in protected areas. Though the level of understanding of the ecological effects of fires has grown substantially over the past century, comprehensive information on the practical application of fire is still restricted, and management information is scattered. Similarly, an improved understanding of how fire affects African mammals is important for the management of both fire regimes and mammal populations. This is also the case in Majete Wildlife Reserve (MWR), Malawi, where a lack of understanding of the past occurrence, determinants, features and effects of prevailing fire regimes prevents the development of appropriate fire management policies. Two separate reviews were conducted to describe the approaches to, and goals of, fire management in African savanna protected areas, as well as the response of large (>5 kg) mammals to fire. For MWR, combinations of remote-sensing and on-the-ground surveys were used to develop a spatially-explicit dataset of the recent fire regime (2001-2019), and to classify, describe and map the woody plant communities present. Additionally, the effect of long-term fire frequencies on vegetation composition, woody plant structure, and large mammal assemblages were assessed, as well as the immediate post-fire habitat selection of large herbivores in a comparative burnt and unburnt landscape. For protected areas, fifteen distinct fire management practices, used to achieve 10 broad ecological (e.g. reversing woody encroachment) and non- ecological (e.g. protecting infrastructure) goals, were identified. Additionally, the responses of 51 mammal species to fire were identified, showing that body size was strongly correlated with fire response, with smaller grazers more likely to respond positively to fire than larger browsers. In MWR, it was found that frequent fires dominate the landscape, with ~57% of MWR burning at intervals of two years or less, and an additional ~30% burning at intervals of 3-5 years. A current mismatch between intended fire management goals and actual trends was also highlighted. Five distinct woody plant communities, two of which were subdivided into three sub-communities each, were recognised, along with 118 woody species identified. Fire frequency had little effect on woody plant community composition, but did affect grass species composition. Mammal species clearly selected for either frequently-burnt or infrequently-burnt areas. Clear selection for either burnt (e.g. impala and warthog) or unburnt (e.g. elephant and bushbuck) habitats, that were unrelated to the availability of above-ground herbaceous biomass, were also shown post-fire. This information is intended to provide a basis for improved fire management planning and policy development, as well as providing a baseline against which to monitor change. Managers should re-evaluate fire policies based on these findings, setting clearly defined targets for the different vegetation types, and introducing flexibility in fire regimes to accommodate natural variation. Establishing a mosaic of patches exposed to different fire frequencies, intensities, seasons and sizes will likely be needed to create a range of habitat types that would best allow for the persistence of all facets of biodiversity in MWR.

AFRIKAANSE OPSOMMING: Verbranding is ‘n belangrike proses wat die struktuur en werking van Afrika-savanna- ekosisteme vorm, en ontstaan gereeld as voorgeskrewe of onbeplande veldbrande in beskermde gebiede. Alhoewel die begrip van die ekologiese effek van veldbrande die afgelope eeu aansienlik verbeter het, is omvattende inligting aangaande die praktiese toepassing van veldbrande steeds beperk. Net so is ‘n verbeterde begrip oor die invloed van veldbrande op Afrika-soogdiere belangrik vir die bestuur van beide brandstelsels en soogdierpopulasies. Dit is ook die geval in Majete Wildreservaat (MWR), Malawi, waar ‘n gebrek aan begrip van die historiese voorkoms, determinante, kenmerke en effekte van die heersende brandstelsels die ontwikkeling van toepaslike brandbestuurbeleide verhoed. Twee afsonderlike literatuurstudies was gedoen om die benaderings tot, en die doelstellings van brandbestuur, in Afrika- beskermde savanna-gebiede te beskryf, asook die reaksie van groot (> 5 kg) soogdiere tot veldbrande. Kombinasies van satelliet-afstandwaarneming en veldopnames was gebruik om ‘n ruimtelik-eksplisiete datastel van die onlangse brandregime (2001 – 2019) van MWR te ontwikkel, en om huidige houtagtige plantgemeenskappe te klassifiseer, te beskryf, en te karteer. Daarnewens is die effek van brand-intervalle op die plantegroedsamestelling, houtagtige plantstruktuur, en groot soogdierpopulasiesamestellings ondersoek, sowel as die onmiddelike seleksie van groot herbivore in ‘n vergelykende verbrande en onverbrande landskap. Aangaande beskermde gebiede was vyftien verskillende brandbestuurpraktyke geïdentifiseer wat gebruik was om 10 breë ekologiese (bv. die omkering van houtagtige indringing) en nie-ekologiese (bv. die beskerming van infrastruktuur) doelwitte te bereik. Daarnewens was die reaksies van 51 soogdierspesies op veldbrande geïdentifiseer, wat getoon het dat liggaamsgrootte sterk gekorreleer is met vuurrespons, sodat kleiner grasvreters meer geneig was om positief op vuur te reageer as groter blaarvreters. In MWR is gevind dat gereelde veldbrande die landskap oorheers, met ~57% van MWR wat met tussenposes van twee jaar of minder brand, en ‘n bykomende ~30% wat brand met tussenposes van 3 – 5 jaar. ‘n Wanverhouding tussen beoogde brandbestrydingsdoelwitte en werklike tendense is ook beklemtoon. Vyf verskillende houtagtige plantgemeenskappe, waarvan twee in drie verdere sub-gemeenskappe elk onderverdeel was, is geïdentifiseer, tesame met 118 houtagtige spesies. Brandintervalle het swak invloed gehad op die samestelling van houtagtige gemeenskappe, maar het wel die samestelling van grassoorte beïnvloed. Soogdiere het duidelik geselekteer vir gebiede wat óf gereeld verbrand word óf selde verbrand word. Duidelike seleksie vir die verbrande (bv. rooibokke en vlakvarke) of onverbrande (bv. olifante en bosbokke) habitatte, wat nie verband gehou het met die beskikbaarheid van bogrondse kruidagtige biomassa nie, is ook onmiddelik na die brand getoon. Hierdie inligting kan as ‘n basis dien vir beter brandbestuurbeplanning en beleidsontwikkeling, en kan ‘n basislyn bied waarteen toekomstige verandering gemonitor kan word. Bestuurders behoort brandbeleide op grond van hierdie bevindings te herevalueer, duidelik-gedefinieerde teikens vir die verskillende soorte plantegroei opstel, en buigsaamheid in brandstelsels implementeer om natuurlike variasie te akkommodeer. Die vestiging van ‘n mosaïek van areas wat aan verskillende brandintervalle, brandintensiteite, brandseisoene en brandgroottes blootgestel word sal waarskynlik nodig wees om ‘n verskeidenheid habitattipes te skep wat die kontinuïteit van alle fasette van biodiversiteit in MWR moontlik maak.

Doctoral