Canopy Gap Regeneration and Dynamics In the Afromontane Forest of Bale Mountains
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Date
2006-06
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Addis Ababa University
Abstract
Change in forest communities and recruitment of new individuals into tree populations depend on the dynamics and
formation of canopy gaps. Gap dynamics and canopy gap regeneration were investigated in Harena Forest of Bale
Mountains, Southeastern Ethiopia at altitudes ranging from 3000 – 2000 m a.s.l. Wind was found to be the main
type of natural disturbance resulting in the overthrow and snapping of heavily crowned emergent canopy trees. The
most affected canopy species by this disturbance regime was Dombeya torrida. 14 species were found to be gap
makers. The mean DBH of the gap makers was 50.4cm. Mean gap size of the forest was (289.74+165.48 m2) and
almost all the gaps were found in sloppy areas. Twenty-four different woody species were encountered as gap–filler
species along different altitudes. Of these species, six were recruited only in gap sites while the gap environment
favored most of the rest. Seedling and sapling density of the gaps were higher than that of closed canopied sites
indicating the importance of gaps for maintaining woody species diversity in the forest. The strong negative
correlation between slope, altitude, and species and seedling densities indicates that both factors affect gap
regeneration. Otherwise, gap size differentiation in the forest and replacement probabilities in the Harena forest was
weak (less than 0.5) except for Diospyros abyssinica(0.86); most of the gap makers were replaced by other subcanopy
species of the forest. Thus, species recruitments in gaps of the forest are likely due to chance effects.
Germination trial of the soil seed banks of Harena forest collected from the sampled gaps and canopied sites has
revealed a high dominance of herbaceous species. Only five of the 24-gap filling species and three of the gap maker
species were recovered in the soil seed bank of the gap sites and even that was in smaller density. Thus, the chance
of getting an immediate replacement of the canopy trees, if removed naturally, was found to be minimal.
Key words: Canopy regeneration, Disturbance, Gap regeneration, Gap makers, Gap filler
species, Replacement probabilities, soil seed Bank.
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Keywords
Canopy regeneration, Disturbance, Gap regeneration, Gap makers, Gap filler species, Replacement probabilities, soil seed Bank