Investigating the impact of fire on the natural regeneration of woody species in dry and wet Miombo woodland

Mwansa, Paul (2018-03)

Thesis (MScFor)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: The miombo woodland is an extensive tropical seasonal woodland and dry forest formation in extent of 2.7 million km². The woodland contributes highly to maintenance and improvement of people’s livelihood security and stable growth of national economies. The woodland faces a wide range of disturbances including fire that affect vegetation structure. An investigation into the impact of fire on the natural regeneration of six tree species was conducted along a rainfall gradient. Baikiaea plurijuga, Burkea africana, Guibourtia coleosperma, Pterocarpus angolensis, Schinziophyton rautanenii and Terminalia sericea were selected on basis of being an important timber and/or utilitarian species, and the assumed abundance. The objectives of the study were to examine floristic composition, density and composition of natural regeneration; stand structure and vegetation cover within recently burnt (RB) and recently unburnt (RU) sections of the forest. The study was conducted at Kanovlei, Caprivi, Sesheke and Kabompo State Forests, along a rainfall gradient from Namibia to Zambia. A systematic random sampling, using a 3-plot cluster, was replicated nine times. A 2 x 4 factorial treatment structure was used (two fire treatment and four rainfall classes) on the research design. Sixty-eight vascular plant species were encountered in 25 families and 54 genera, dominated by Caesalpinioideae (15.7 %), Papilionoideae (12.9 %) and Combretaceae (11.4 %). Species richness was high and increased with MAP along the rainfall gradient. High species richness translated into high species diversity among the fire treatments and ranged from 1.5 to 2.8 Shannon diversity index units. The selected tree species contributed to stand parameters as important timber species with importance value indices from 4.5 % to 44.8 % across the study sites. Woody species showed high regeneration density across fire treatments and ranged between 3 039 and 18 274 individuals per hectare with tree species contributing up to 55 %. Fire treatment (p<0.0001) and fire frequency (p=0.027) had a statistically significant relationship with regeneration density. All selected tree species were recruiting, evidenced by the > 1 recruitment ratios and negative regression slopes for size class distributions, however the latter also revealed that the populations of some of species are unstable and declining. Basal area was small and not significantly different among fire treatments at all sites except at Sesheke were recently burnt sites had significantly higher basal area. Furthermore, the basal area of the Sesheke (8.2 ± 0.2 m² haˉ¹) which was significantly greater than Kanovlei (1.2 ± 0.2 m² haˉ¹), Caprivi (1.7 ± 0.2 m² haˉ¹) and Kabompo (3.2 ± 0.2 m² haˉ¹) suggested that anthropogenic influences (forest harvesting and disturbance) are having an effect on the stand structure. Canopy cover varied from 20 % to 75 % in the forests showing an increase in forest cover from drier to wetter sites. The study proved fire treatment did not significantly affect or alter floristic composition of woody vegetation in the short-term. It also showed good recruitment for the selected tree species (as coppice or seedling) but lacking rejuvenation of the population structure. Fire treatment on vegetation cover is potentially useful and could be advantageous to regeneration of tree species for a few years. Hence, the study calls for a long-term investigation of natural regeneration of tree species taking into account the factors that could not be considered in this study.

AFRIKAANSE OPSOMMING: Die Miombo is ’n seisonaal-droë tropiese bosformasie wat strek oor ’n uitgebreide gebied van ongeveer 2.7 miljoen km2 in Afrika. Hierdie bosland dra by tot die lewensonderhoud van mense asook die stabiele groei van nasionale ekonomieë. Die bos word bedreig deur ʼn reeks van versteurings (o.a. vuur) wat die plantegroei struktuur negatief kan beïnvloed. ʼn Ondersoek na die effek van vuur op die natuurlike verjonging van ses boomspesies is gedoen op ʼn gradiënt van droë na vogtiger groeiplekke. Baikiaea plurijuga, Burkea africana, Guibourtia coleosperma, Pterocarpus angolensis, Schinziophyton rautanenii and Terminalia sericea is gekies op grond van hulle geskatte verspreidingsdigtheid asook hul belang vir hout en menslike benutting. Die doel van die studie was om die effek van vuur te ondersoek (in onlangs gebrande en onlangs ongebrande gebiede) op die samestelling, vegetasiebedekking, digtheid en struktuur van opstande, asook die digtheid die samestelling van natuurlike regenerasie. Die studie is onderneem op ʼn reënval gradiënt wat strek oor Kanovlei, Caprivi, Sesheke and Kabompo staatsbosse van Namibië en Zambië. Sistematiese bemonstering is gedoen m.b.v. gepaarde, ewekansig gekose persele in 9 herhalings. Die oorhoofse behandelingstruktuur is ’n 2 x 4 faktoriaal (2 vuur behandelings en 4 reënval klasse). Ses en tagtig vaatplante, versprei oor 25 families en 54 genera is waargeneem, met Caesalpinioideae (15.7 %), Papilionoideae (12.9 %) en Combretaceae (11.4 %) die dominante groepe. Daar was ʼn ryke spesieverskeidenheid, en dit het toegeneem met toenemende reënval. Die gevolg was hoë diversiteit tussen vuurbehandelings (vanaf 1.5 tot 2.8 eenhede op die Shannon-diversiteitsindeks). Die gekose spesies se bydrae tot die indeks van belangrikheid strek van 4.5 tot 44.8% oor studiepersele heen. Houtagtige spesies toon ʼn hoë digtheid van regenerasie (saailinge + stomplote), met tussen 3 039 en 18 274 individue per hektaar waarvan boomspesies 55% bydra. Die onlangse teenwoordigheid (p<0.0001) en frekwensie (p=0.027) van vuur het ʼn beduidende effek op digtheid van regenerasie. Al die gekose spesies toon tekens van effektiewe hervestiging soos bevestig deur hervestigingsverhoudings >1 en negatiewe regressie gradiënte, alhoewel grootteklas verspreidings onthul dat die populasie van sommige spesies klaarblyklik onstabiel is of taan. Die basale oppervlakte het nie beduidend verskil tussen vuurbehandelings nie, behalwe by die Sesheke groeiplek waar onlangs ongebrande groeiplekke ʼn beduidend groter basale oppervlak gehad het. Verder, die basale oppervlak van die Sesheke groeiplek (8.2 ± 0.2 m² ha-1) was beduidend groter as Kanovlei (1.2 ± 0.2 m² ha-1), Caprivi (1.7 ± 0.2 m² ha-1) of Kabompo (3.2 ± 0.2 m² ha-1), wat aandui dat mensgemaakte invloede (bos ontginning en versteuring) ’n invloed het op laasgenoemde drie. Die kroondak bedekking varieer van 20 tot 75% met ʼn toename van droër na vogtiger groeiplekke. Die studie het bewys dat vuur nie beduidende korttermyn veranderinge in die floristiese samestelling van die houtagtige plantegroei teweeg gebring het nie. Daar is voldoende aanvanklike regenerasie van die gekose spesies (as saailinge en stomplote), maar daar is nie altyd suksesvolle verjonging (van die populasiestruktuur) nie. Die gebruik van vuur kan bruikbaar wees om plantegroei te bestuur en kan voordelig wees vir regenerasie van sommige spesies vir ʼn beperkte aantal jare. Dit is egter noodsaaklik om langtermyn studies op die regenerasie van die spesies te doen ten einde faktore in ag te neem wat nie in hierdie studie gedek kon word nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103778
This item appears in the following collections: