MSc

A field study was carried out to evaluate the biomass production, carbon
sequestration and nutrient dynamics in a 22-year-old Ailanthus triphysa stand managed at
variable densities viz., 2360 trees ha-1, 1560 trees ha-1, 900 trees ha-1 and 560 trees ha-1.
Total number of 80 trees (20 from each density regime) was destructively sampled for the
biomass and carbon stock assessment. Also nutrient stocks (N, P and K) in various tissue
types were assessed following standard procedures. The soil carbon and nutrient contents
were assessed for one meter soil depth at regular depth intervals.
The average stand height and bole height were 12.84 m and 8.19 m respectively
which varied significantly with stand density with maximum value recorded for 1560
trees ha-1. The average dbh, mean tree volume and bole volume put in by the 22- yearold
A. triphysa stand was 18.78 cm, 0.15 m3 and 0.16 m3 respectively which however
could not yield a predictable trend with stand density. Despite this, the stand volume
exhibited a proportional increase with stand density. The mean tree biomass production
by the stand was 129.81 kg tree-1 that varied with stand density. Biomass production at
stand level showed a consistent increase with increasing stand density with highest
produced corresponding to 2360 trees ha-1 stand (384.67 Mg ha-1) and lowest for 560
trees ha-1 stand (93.86 Mg ha-1). Component wise biomass allocation was highest for
stemwood (63 %) followed by roots (20 %) for all the density regimes while twig portion
registered the least (0.97 %).
The mean tree C stocks and corresponding MAI for A. triphysa at 22 years of
stand age were 74.54 kg tree-1 and 3.38 kg tree-1 yr-1 respectively which was comparable
with many fast growing MPT’s similar growth habit in humid tropics. Elemental carbon
storage at stand level showed proportionate increase with density (177.00 Mg ha-1, 2360
tree ha-1; 140.47 Mg ha-1, 1560 tree ha-1; 49.06 Mg ha-1, 900 trees ha-1 and 43.33 Mg ha-1,
560 trees ha-1). Allometric models were developed for total aboveground biomass, bole
biomass, aboveground carbon sequestration, total volume and bole volume using dbh and
height as predictor variables. Among various models tried single variable (dbh) quadratic
equations were best fitting with high R2 value. The nutrient concentration varied
substantially among various biomass components with foliage registering highest N,
P and K concentration (%). Tissue nutrient concentration followed the general order:
leaves> twig> branch> root> stemwood. Biomass nutrient stocks at stand level
varied considerably with stand density which was closely following biomass production
trends. Nutrient storage followed the order N > P > K with highest stocks corresponding
to stemwood followed by roots, branchwood, leaves and twigs. High nutrient
accumulation in the stemwood suggests possible higher levels of nutrient export from
the site through harvest. Transfer of nutrient rich leaf biomass into the soil at harvest
would be a viable strategy in this context that replenish the nutrient loss through
harvest. Carbon and nutrient contents in the soil were substantially higher in all sampled
depths implying the dominant role of trees in improving the soil productivity in wooded
systems. Study converges to the generalization that A. triphysa trees have a good
potential for volume and biomass production under proper silvicultural management
regimes.