Growth responses of an African savanna tree, <Emphasis Type="Italic">Bauhinia thonningii</Emphasis> Schumacher,to defoliation,fire and climate |
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Authors: | Emmanuel Ngulube Chidumayo |
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Institution: | (1) Department of Biological Sciences, University of Zambia, P. O. Box 32379, Lusaka, Zambia |
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Abstract: | This study investigated the growth responses to defoliation, fire-exposure and climate factors of a widespread Africana savanna
tree, Bauhinia thonningii Schumacher, at a site in central Zambia. Experimental trees (n = 47) were either exposed to fire (n = 12) in the first half of the dry season or protected from fire (n = 35). Some of the fire-protected trees (n = 12) were subjected to artificial defoliation in two consecutive years. Phenological responses (bud break, leaf flush and
leaf production) to fire-exposure and defoliation were monitored on permanently marked sample shoots over a 2-year period.
Radial tree growth (diameter at 1.3 m above ground) was measured annually over a 7-year period from 1998 to 2005. During the
first two years, defoliation and fire-exposure advanced the onset of bud break and leaf flush but fire-exposed trees produced
significantly less leaves than did trees protected from fire, probably because scorching caused more severe shoot die-back
than is normal. Leaf production was also significantly affected by experimental treatments and their interaction with year.
Although treatments had significant short-term effects on radial growth, previous-year growth significantly influenced current-year
growth, thereby confirming the existence of autocorrelation in the time-series growth data of B. thonningii. The interaction between previous-year growth and climate factors explained a significant proportion (25–40%, P < 0.001) of the variance in annual tree growth. Variogram models predicted that a 2-year manual defoliation treatment would
shorten the longer-term growth cycle while continuous fire-exposure extended the cycle by one year. The results are useful
for the management of savanna trees. |
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Keywords: | Autocorrelation Bauhinia thonningii Phenology Tree radial growth Zambia |
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