Thesis (PhD(For))--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Widdringtonia whytei is a tropical endemic, fire-adapted pioneer coniferous tree species
within natural fire-fragmented Afromontane forest patches in a confined area on Mulanje
Mountain in Malawi. Natural and anthropogenic fires within the surrounding fire-prone
landscape, insect attacks, and uncontrolled harvesting of mature trees for timber
threaten the survival of W. whytei. This study investigated the effects of population
fragmentation on the reproductive biology of W. whytei, through four specific studies:
effects of population size, tree size and crown position on viable seed output; seed rain
variation among population sizes; effects of temperature and light on viability and
germination of W. whytei seeds; and the influence of population size on natural
regeneration patterns.
The study was conducted during 2008 and 2009 on three sites using three W. whytei
population sizes: small (≤10 reproductively mature cone-bearing W. whytei trees),
medium (11-20 cone-bearing trees) and large (>20 cone-bearing trees). Data were
collected using field and laboratory experiments and a review of secondary information.
The effect of fragment size and crown position on viable seed output and seed rain
pattern was tested with a nested linear mixed model. The influence of stem diameter
(dbh) on viable seed output was tested using a separate data set. The variation in seed
rain was explored with a generalised linear model (GLM) with a negative binomial link
function. Variations in seed germination was analysed with a Weibull regression model.
The influence of fragment size on seedling regeneration was tested with a GLM (binary
logistic regression).
Viable seed output from W. whytei cones was very low (23%) and was not affected by
population size, tree diameter or crown position. W. whytei population size influenced
seed rain with large fragments having higher seed rain densities. Number of dispersed
seeds was generally very low and poorly dispersed. W. whytei cones are semiserotinous
and depends on moderate to severe fires for heavy seedfall and wider
dispersal. Such fires did not occur during the study period. Temperature is a critical
factor for seed germination. Seeds germinate between 15 and 25°C with the optimum at
~ 20°C either under light or dark conditions. Regeneration density followed the seed
rain pattern indicating that seed availability is a critical factor for regeneration. Regular
cool fires outside the forest patches and along the edges during the hot dry season, and
the thick litter layer and shady conditions inside forest patches, caused most of the
seedling mortality.
This study highlighted the difficulties W. whytei experiences with low output of viable
seed, limited seed dispersal and low seedling regeneration in and around forest
patches, i.e. factors important for conservation management of this species. It is
recommended that gaps with diameter equal to canopy height and occasional spot fires
would promote seed dispersal onto exposed mineral soil for rapid seedling
establishment and subsequent population growth. Such natural fire disturbance events
may show the true seed rain and seedling establishment patterns in this species. / AFRIKAANSE OPSOMMING: Widdringtonia whytei is ‘n tropiese endemiese, vuuraangepaste pionier naaldhoutagtige
boomsoort binne die natuurlike vuurgefragmenteerde Afromontane woudkolle binne ‘n
beperkte area op Mulanje berg in Malawi. Natuurlike en menslike vure binne die
omringende vuurgeneigde landskap, insekaanvalle, en onbeheerde kap van volwasse
bome vir hout bedreig die voortbestaan van W. whytei. Hierdie studie het die effek van
populasiefragmentasie op die voortplantingsbiologie van W. whytei ondersoek, deur vier
spesifieke studies: die effek van populasiegrootte, boomgrootte en kroonposisie op
produksie van lewenskragtige saad; saadreënvariasie tussen populasiegroottes; die
effek van temperatuur en lig op lewenskragtigheid en ontkieming van W. whytei saad;
en die invloed van populasiegrootte op natuurlike verjongingspatrone.
Die studie is gedurende 2008 en 2009 uitgevoer op drie groeiplekke met drie W. whytei
populasiegroottes: klein (≤10 keëldraende (volwasse) W. whytei bome), medium (11-20
keëldraende bome) en groot (>20 keëldraende bome). Data is versamel in veld- en
laboratorium eksperimente asook 'n oorsig van sekondêre inligting. Die invloed van
populasie fragmentgrootte en kroonposisie van bome op saadproduksie en die
saadreënpatroon is getoets met ‘n geneste liniêre gemengde model. Die invloed van
boomstamdeursnee op die produksie van kiemkragtige saad is met ‘n aparte datastel
getoets. Die variasie in saadreënpatroon is met 'n algemene liniêre model (GLM) met 'n
negatiewe binomiese skakelfunksie getoets. Variasies in ontkiemingspersentasie van
sade is met 'n Weibull regressiemodel ontleed. Die invloed van fragmentgrootte op
saailingverjonging is met 'n algemene linêre model (binêre logistiese regressie) getoets.
Produksie van lewenskragtige saad in W. whytei keëls was baie lag (23%) en was nie
deur populasiegrootte, boomstamdeursnee of kroonposisie beïnvloed nie. W. whytei
populasiegrootte het saadreën beïnvloed en groot fragmente het groter
saadreëndigthede gehad. Die aantal verspreide sade was in die algemeen baie laag en
swak versprei. W. whytei keëls is semi-saadhoudend (serotinous) en is afhanklik van
matige tot intense vure vir massiewe saadvrystelling en wyer saadverspreiding. Sulke
vure het nie gedurende die studieperiode voorgekom nie. Temperatuur is ‘n kritiese
factor vir saadontkieming. Sade ontkiem goed tussen 15 en 25°C met die optimum
rondom ~ 20°C onder beide lig en donker toestande. Fragmentgrootte het nie die
saailingverjonging in W. whytei beïnvloed nie. Verjongingsdigtheid het die
saadreënpatroon gevolg, wat daarop dui dat saadbeskikbaarheid ‘n kritiese factor is vir
saailingverjonging. Gereelde koel vure buite die woudkolle en langs die woudrand
gedurende die droë warm seisoen, en die dik lae blaarval (litter) en skadutoestande
binne ‘n woud, het meeste van die saailingmortaliteit veroorsaak.
Hierdie studie het die probleme beklemtoon wat W. whytei ondervind met die lae
produksie van kiemkragtige saad, saadverspreiding en saailingverjonging binne en
rondom die woudkolle, m.a.w. faktore wat belangrik is vir bewaringsbestuur van hierdie
boomsoort. Die aanbeveling word gemaak dat kroonopeninge met ‘n deursnee gelyk aan minstens die kroonhoogte, en sporadiese kolbrande binne die woudkolle kan
saadverspreiding op blootgestelde minerale grond vir vinnige saailingvestiging en
gevolglike populasiegroei bevorder. Sodanige vuurversteuringsgeleenthede mag die
werklike patrone in saadreën en saailingvestiging in hierdie species toon.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/85589 |
| Date | 12 1900 |
| Creators | Chanyenga, Tembo Faera |
| Contributors | Geldenhuys, Coert Johannes, Sacande, Moctar, Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 193, [17] p. : ill., maps |
| Rights | Stellenbosch University |
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