Influence of Gap Size on Regeneration, Structure and Species Diversity of Woody Vegetation in a Secondary Montane Forest Reserve, Kenya

Abstract

South-Western (SW) Mau forest reserve has been experiencing anthropogenic and natural disturbances creating canopy openings in the forest. The objective of this study was to determine how these canopy openings influence regeneration, forest structure and species diversity. The study employed nested sampling design in disturbed sites of the forest reserve. Plots of 500 by 500 m were laid once at 100 m inwards from the forest edge in the three blocks of SW Mau; Ndoinet, Maramara and Itare. Gaps were randomly identified in the plots and gap area calculated using Ellipse Method (EM). Gap sizes were categorized based on area (m2). Woody species surrounding the gaps were identified and names inventoried. To determine regeneration, two quadrats of 5 by 5 m and 1 by 1 m were randomly delineated in every gap size four times and eight times for saplings (1-3 m high) and seedlings (<1 m high), respectively. Tree heights surrounding the gaps were measured using suunto clinometer. Diameter at breast height (dbh) was measured using diameter caliper (65 cm for small trees) and diameter tape for large trees (dbh> 65 cm). A total of 41 gaps were identified with small gap sizes dominating (23). Kruskal-Wallis rank sum test indicated non-significant differences in regeneration, forest structure and species diversity in the three gap sizes. This was attributed to Piper capensis which invaded medium and large gap sizes creating a closed canopy. It was, therefore, concluded that canopy cover from the invasive species influenced woody vegetation parameters in the gap sizes. It is, therefore, recommended to clear the dense ground cover to allow better natural regeneration and also enrichment planting in the gaps.