COMPARISON OF ENVIRONMENTAL RICHNESS IN NATURAL FOREST AND HOMEGARDENS A CASE STUDY FROM NACHCHADUWA CATCHMENT

Abstract

An attempt was made to develop an assessment indicator combining the most importantparameters which decide the environmental richness of a plant community. Stratalcoverage, species richness and plant density were included in the following formula todescribe the environmental richness as:

ER = S. / (KL NL + KM NM + Ks Ns), Where ER is environmental richness, K is acoefficient to represent stratal coverage and N is the number of plants per 100 sq.m forlarge (L), medium (M) and small (S) canopy types and S is the number of species per 100sq. m.

A plant composition survey was carried out in a selected forest block of 25 m x 25 m atPaindikulama in the Nachchaduwa watershed in 1997 to assess the environmental richnessin natural forest. A comparison was then made with results obtained from a previoushomegarden survey conducted in the same watershed.

During the survey 31 plant species were identified and the total number of plants surveyedwas 1360. The average plant density was 218 per 100 m2. Environmental richness of thisforest block was found as high as 108 whereas the value for homegardens has ranged from0.7 to 34.7. Results also revealed that the contribution made to environmental richnesswas higher (75%) by small canopy plants compared to large (3%) and medium (22%)categories. This may be due to the selective felling of large trees and subsequentemergence of small plants in the exposed patches. Results conclude that man madehomegardens could only achieve about one third of the environmental richness of naturalforest.