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

In Nepal, the natural Shorea robusta (sal) dominated forests have been subject to selective felling, encroachment, uncontrolled grazing and annual forest fires for the past 30-50 yr, 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 , Syzygium cumini and Ficus sp. The experiment consisted of 3 regeneration felling methods using different numbers of remaining shelter trees/ha - 75, 25 and none. 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 <50 cm). The removal of Lantana camara and Eupatorium odoratum [Chromolaena odorata ] 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. 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 between treatments. The height development of the dominant 2000 seedlings/ha during the second growing season was fastest in the area without shelter trees (127 cm), and lowest in the control area (81 cm). The results from the area without shelterwood trees 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 shelter trees was almost 4 times the growth in the control area. Significant differences were detected between all treatments, except between the areas where 25 and 75 shelter trees were left. The dieback of Shorea robusta seedlings was not a problem in the treatment areas, where the removal of old crop and protection led to the fast growth of already recruited seedlings.