Species diversity measurement for logged-over dipterocarp forest in the Philippines under different cutting regimes

Jackknifing [algorithm] resulted in the substantial reduction of bias, which may exceed 50 percent for greater than or equal to 20, with the relative bias 0.10. On the other hand, jackknifing has led to an increase in variance of the estimates. This, however, did not diminish the advantage of the jackknifing procedure over the usual sample-based procedure, since the mean square error of the sample-based estimates were considerably reduced when jackknifed. Tree species diversity measurement was also studied using the concept of intrinsic diversity ordering to compare the plant communities in forest stands that were logged under different harvesting regimes, namely: selective logging, clear cutting and seed tree method. Data on the frequency of the different tree species found in twelve 10 m x 50 m sample plots located in the dipterocarp forest along the coast of Surigao del Sur in the Philippines, were used to calculate the relative abundance vector of the tree species. The sample-based and jackknifed diversity profiles were also calculated from evenly spaced values of Beta in the range of -1.00 less than or equal to Beta less than or equal to 1.00. The intrinsic diversity profiles were computed as the right tail-sum of the relative abundance ranked from greatest to the least. Results reveal that the jackknifing procedure provided a useful method for reducing considerably the bias of the estimates when relative abundance date are based on samples rather than complete enumeration. The estimates of the usual sample-based estimators of the four diversity indices were found to be relatively smaller than the jackknifed estimates. The patterns exhibited by the diversity profiles of the three forest stand communities are consistent with biological trends and clearly indicate the dynamic nature of plant diversity of the dipterocarp forest under different cutting regimes. One year after logging (1985), selectively logged forest stands were more diverse than forest stand under the clean cut and seed three method. Over a period of six years (1991), however, the forest stands under the seed tree system were relatively more diverse in terms of the number of species than the clear cut and selectively logged forest stands