Growth responses of an African savanna tree, Bauhinia thonningii Schumacher, to defoliation, fire and climate

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 exCommunicated by M. Zwieniecki E. N. Chidumayo ( ) tended the cycle by one year. The results are useful for the management of savanna trees.

Effect of Seed Size and Pretreatment Methods on Germination of Albizia lebbeck

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“…extensive crown vine coverage remains extensive from year to year); (ii) such variables influence the development and growth of the tree, limiting its future growth; and (iii) inherent genetic and site differences such as soil fertility and water availability among trees are immutable or strongly persistent. While the phenomenon of growth autocorrelation has been widely reported (Swaine et al 1987a;Kohyama & Hara 1989;Kammesheidt et al 2003;Chidumayo 2007;Drobyshev et al 2007), its strength, persistence, and importance relative to other explanatory variables is just beginning to be investigated. Growth autocorrelation's dramatic impact on population models (e.g.…”