Natural regeneration potential and early development of Shorea robusta Gaertn.f. forest after regeneration felling in the Bhabar-Terai zone in Nepal

Abstract

In Nepal, the natural Shorea robusta (local name ‘sal’) dominated forests have been subject to selection felling, encroachment, uncontrolled grazing and annual forest fires for the past 30–50 years, and the forest cover has declined by about 1.3% per annum. The aim of this study was to obtain information on the natural regeneration potential of the Shorea robusta forests, when these forests are treated with different types of regeneration fellings, and when the areas are protected from grazing and forest fire. The study was conducted in a mature irregular ‘Moist Bhabar Sal’ forest. The main species were Shorea robusta, Terminalia tomentosa, Lagerstroemia parviflora, Sysigium cuminii and Ficus sp. The experiment consisted of three different regeneration felling methods: (1) regeneration felling with 75 sheltertrees ha −1; (2) regeneration felling with 25 sheltertrees ha −1; (3) regeneration fellings without sheltertrees. These areas were fenced and protected from fire and grazing. A control area was fenced and protected in the same forest. Bushes and advanced growth were cleaned from the harvested areas with only the smallest seedlings remaining (height less than 50 cm). The removal of Lantana camara and Eupatorium odoratum was done in the treated areas 14 months after the felling. Permanent plots were measured one growing season after the felling, and again 12 months later. The number of Shorea robusta seedlings was high after the felling, varying from 74500 to 91000 seedlings ha −1. During the dry period between the measurements, 4.2–10.2% of the seedlings died back, but an analysis of variance did not reveal any significant differences. The height development of the dominant 2000 seedlings ha −1 during the second growing season was the fastest in the area without sheltertrees (127 cm), and the lowest in the control area (81 cm). The results of the area without sheltertrees differed significantly from all the other treatments in Tukey's HSD test of means; other significant differences were not observed. Differences in diameter growth were more distinct than those for height; the growth in the area without sheltertrees was almost four times the growth in the control area. Significant differences were detected between all treatments, except between the areas where 25 and 75 sheltertrees were left. The die-back of Shorea robusta seedlings was not a problem in the treatment areas. Removal of old crop and protection led to the fast growth of already recruited seedlings.