Dynamics of litter fall and nutrient return in paradoxically reestablishing white oak (Quercus leucotrichophora A. Camus) forests in the central Himalaya

Background/Question/Methods

White oak (Quercus leucotrichophora) is widely distributed between 1200 and 2000 m asl in central Himalaya. Increased demand for the resources like fodder and fuel wood by the local communities resulted into degradation of these ecologically and socially important forest ecosystems during recent decades and a large area under the oak has now been encroached by fire adapted chir pine (Pinus roxburghii). It has however, been observed that in certain microsites in oak- pine transition zones, fire damages to pine during certain particular years have paradoxically resulted vigorous regeneration of oak. This study described litter fall and nutrient return in two such reestablishing white oak forests (16 years old and 34 years old). The aim of the tudy was to study the changes that occur in litter production, nutrient return and litter quality as the forests regenerate on the habitats previously invaded by pine. Litter input was measured every month by using randomly located litter traps. Monthly litter samples of a given category of the litter were pooled seasonally, ground and analyzed for nutrients (N, P, K). Concentrations of N, P and K were multiplied with the respective litterfall dry mass samples to get N, P and K contents.

Results/Conclusions

Total annual litter fall was 258.5 g m^-2 and 561.7 g m^-2, respectively in the 16 and 34 year old oak stands. Litter fall increased with an increase in tree basal area.  The proportional contribution of the leaf litter fraction to the total litter fall decreased with stand age (77 % and 73% of the total litter fall, respectively, in the 16 and 34 years old oak forests). Litter nutrient concentration in the 34 year old oak stand was higher than in the 16 year old stand. In both forests, litter nutrient concentration was highest during the rainy season and lowest during summer. Relatively high litter nutrient concentration and low nutrient retranslocation from senescing tissues, low litter dry matter: litter N ratio in the 34 year old forest indicate improved available soil N pool in the 34 year old oak forest and may indicate improvement of soil fertility with forest age. Present values for litter dry matter production, litter nutrient concentrations, and nutrient retranslocation from the senescing leaves in 34 years old stand are comparable with the old growth oak forests indicating that the restoration of these forests may require over three decades.