Regeneration of Monodominant Stands of Banj Oak (Quercus leucotrichophora A. Camus) on Abandoned Terraces in the Central Himalayas

Abstract

Banj oak (Quercus leucotrichophora A. Camus) is an important hardwood species of the Central Himalayas that is heavily used for fuelwood, fodder and as an agricultural mulch. Disturbed sites that create large canopy openings and exposed topsoil are widely reported to promote stands of chir pine (Pinus roxburghii Sarg.). However, under some circumstances, observations contradictory to these findings suggest that stands of banj oak can also originate after agricultural abandonment in this region. To investigate this, a chronosequence of agricultural terraces, that had been subjected to differing levels of post-abandonment disturbance (grazing, fuelwood, fodder and litter collection), were sampled to record changes in regeneration size and density of chir pine and banj oak. Regeneration and soils on the flat parts of the terraces were compared to that on the risers of the terraces. Banj oak density was found to be higher than chir pine on terraces under both high and low post-abandonment disturbance for the chronosequence. Banj oak was also found to predominate on the terrace risers. Oak diameter was negatively affected by increased disturbance, but height was not affected. Chir pine was found to grow equally well in terms of height, diameter and stem density on all parts of the terrace, with a preference for sites with high post-abandonment disturbance. The length of time since field abandonment had no effect on stem density for either species. No significant differences were detected in nitrogen and soil carbon status between the flats and the risers of the terraces. Soil moisture content was found to be higher on the risers of the terraces, with soils on the risers higher in clay content. Results from this study show that management practices used on fields while they are still under cultivation are the main agent responsible for the release of large numbers of banj oak seedlings and sprouts on the risers of the terraced fields. Terraced lands thus act as a nursery for the subsequent release and development of future stands dominated by banj oak. Widespread abandonment of property in the late 18th century due to war and epidemics may therefore have led to the formation of many of the old banj stands existing today.