Influence of gap size microsite conditions regeneration structure and species diversity of woody vegetation in South western Mau forest Kenya

Abstract

Tropical forests are facing amalgam of disturbances cropping from human and natural stresses. South-Westem (SW) Mau Forest reserve is experiencing poor natural regeneration and loss of species diversity due to these disturbances. The objective of this study was to determine the influence of canopy gap sizes on microsite conditions, regeneration, stnlcture and diversity of woody vegetation species in SW Mau Forest reserve. The study involved field experiment employing Nested Research Sampling Design (NRSD) in disturbed and undisturbed sites. In disturbed sites, a plot of 500 by 500 m was nested and gaps randomly sampled in Itare, Maramara and Ndoinet blocks. A Handheld GPS device (Garmin e-Trex 10) was used to obtain gap coordinates. Microsite conditions (soil moisture, soil temperature and light intensity), regeneration, species diversity and tree phytosociological parameters (height, diameter at breast height) were measured in these micro-plots (gap sizes). Light intensity was measured using Luxmeter (model HTC LX-104) while soil moisture and soil temperature were measured using Kensizer soil tester (3-in-1 soil moisture/light/pH. . .). Regeneration was determined using two quadrats; 5 by 5 m and 1 by l m thrown four times and eight times for saplings and seedlings respectively. Tree height and dbh were measured using Suunto clinometer and diameter calliper/tape respectively while Shannon-Weiner Diversity Index was used for species diversity. In undisturbed sites, another plot of 500 by 500 m was laid in every block and sub-plots of 20 by 30 m thrown randomly and parameter determination repeated. Data was analysed using RStudio and Microsoft excel. A total of 41 canopy gaps and 19 sub-plots of 20 by 30 rn were randomly selected as the sample units. The study revealed a significant difference in soil temperature (Kruskal-Wallis chi-squared=19.00, df=3, P=0.00*) among the gap sizes with large gap sizes recording the highest mean (l8.600C). Additionally, there was a significant difference in light intensity between disturbed and undisturbed sites (W=555.00, P=0.0l) with disturbed sites recording the highest mean light intensity (804.00 Cd). Forest structure also differed significantly between disturbed and undisturbed sites (P=0.0l). Disturbed sites showed a more complex forest structure; Holdridge’s Complexity Index (HCI) 332.70 compared with the undisturbed sites (204.60). Non-significant results were attributed to Piper capensis invasion in SW Mau Forest reserve. It Was concluded that canopy cover influenced gap micro-environment by creating shade and utilizing soil moisture which in tum influenced woody vegetation population parameters. Therefore, there is need for enrichment planting using highly valued indigenous species in most disturbed sites for faster regeneration and forest continuity.