BETWEEN PLOT AND POINT SAMPLING USING A COMPUTER BASED TREE POPULATION
OF Pinus caribaea SRI LANKA
W M Lalith Perera and S G Banyard
University of Sri Jayewardenepura, Nugegoda.
Research was conducted in the University Forest at Yagirala Forest Reserve,
Kalutara District, Sri Lanka, to compare the efficiency of point and plot
sampling in Pinus caribaea plantation using computer simulated sampling
on a population of trees using data collected in the field. In all, 3294
trees on 5.4 hectares constitute the population. The data base has been
filed with tree number, dbh, X and Y co-ordinates. Edge effect bias was
minimized using the reflection method.
Random sampling was used in all cases for sample sizes n = 10, 20, 30,
60 and 100. In order to make meaningful comparisons, the concept of equivalent
plot was used which aimed at obtaining equal tallies per sampling unit
for point and plot sampling. Basal area factors applied were 2, 4, 9 and
16. Efficiency for given point - plot equivalents were based on standard
error % and cost values (where cost was based on time). In 19 of the 20
point-plot combinations studied, point sampling was found to be the more
efficient. The most suitable BAF is BAF2 and it is recommended that point
sampling be applied in plantation forest inventories in Sri Lanka where
trained staff are available.
Department of Forestry and Environmental Science,
of Sri Jayewardenepura,Sri Lanka. 1999. All rights reserved.