3.3. Ecosystem N and P stocks
In the present study, tree, shrubs, and herbaceous and litter components N and P stock increased from 346.77 kg ha-1 in AER (youngest) stand to 4662.06 kg ha-1 in the AOOM stand (oldest) and 19.17 kg ha-1 in AER stand to 233.91 kg ha-1 in AOOM stand, respectively. Across the forest chronosequence, tree bole biomass N and P stock were significantly greater than any other vegetation biomass components. The N and P stocks in different vegetation biomass components follow similar patterns as reported in our previous study (Joshi and Garkoti 2021b) and follow the order: bole > branch > stump root > twig > lateral root > foliage > litter > fine root > shrub aboveground > herbs aboveground > shrubs belowground > herbs belowground and in all vegetation components both N and P stocks increased with forest chronosequence (Table 1). Average total soil N and P varied from 816.44 to 7334.24 kg ha-1 and 56.95 to 595.36 kg ha-1,, respectively, and increased along with the forest chronosequence (Figures 5 and 6). Across the forest chronosequence, the contribution ofA. nepalensis trees to the ecosystem nitrogen and phosphorus stock ranged from 9 % in ALR stand to 23.23 % in AMR stand and 3.31 % in AYM stand to 12.31 % in the AMR stand, respectively (Figure 6 & Figure 7). Of the total ecosystem N stock, the soil contributed from 48.82 % in the ALR stand to 70.18 % in the AER stand. Similarly, the contribution of soil to the total ecosystem P stock ranged from 63.49 % in the ALR stand to 74.8 % in the AER stand. The soil was the largest P reservoir among all the ecosystem compartments. The understory vegetation (shrubs, herbs) and litter layer added a small fraction to the total N and P stock of the ecosystem. Overall, across the stands, soil and trees were the two largest contributors to the total ecosystem nitrogen and phosphorus stock (Figure 6, and Figure 7).