Kunhamu, T KSuresh Ramanan, S2020-01-212020-01-212017http://krishikosh.egranth.ac.in/handle/1/5810141457PGThe focus of forest management in India has moved from timber production to conservation and eco-restoration. Hence, plantations are the viable scope for meeting our ever increasing wood demand. Effective stand management practices are indispensable for deriving optimal productivity from these plantations. Thinning is generally recognised as an important silvicultural tool for creating qualitative and quantitative improvement in plantation productivity. However, its temporal effect varies with species and thinning regime. In this context, the present study was undertaken by destructive sampling of trees and assessing the aboveground and belowground biomass, soil parameters, understorey PAR and wood physical properties in a 20-year-old Acacia mangium stand that was subjected to stand thinning 13 years ago. The results indicated that the impact of stand thinning on radial growth, mean tree basal area and mean tree volume was still persisting even 13 years after thinning. The highest response was from two-third thinning intensity (533 trees ha-1) followed by half thinned stand (800 trees ha-1). The tree level biomass followed the same pattern with the maximum aboveground (663.67 ±121.03 kg tree-1) and belowground (225.20 ±20.62 kg tree-1) biomass production recorded from the two-third thinning intensity. However on stand basis, the effect of thinning on volume and biomass did not show significant variation across treatments, probably due to the confounding effect of the higher number of trees in the low density stands. This trend was visible in stand carbon sequestration potential also. Even though two-third thinning intensity had maximum carbon sequestration at tree level (405.62 kg C tree-1), the stand level carbon sequestration did not vary with thinning treatments. Long-term effects of thinning had no influence on soil bulk density, pH, and available phosphorus and exchangeable potassium. However, all the thinning regimes registered significantly higher soil carbon stock compared to contiguous treeless control plot. Total nitrogen content also followed the same trend. Understorey Photosynthetically Active Radiation (PAR) availability observed in this study revealed reduced availability across all thinning regime except for the heavily thinned stand suggesting the possibility for intercropping. Thinning also had an impact on the root spread on a long term basis. The maximum spread of 2.84 m was recorded in the two-third thinning treatment which was significantly higher compared to other thinning intensities. Characterization of spatial root distribution pattern using logarithmic spiral trenching method suggested restricted root spread for the unthinned stand, while better root spread was observed with increased intensity of thinning. The results indicate that influence on thinning on wood physical properties are not significant across treatments. The wood density of 20-year-old A. mangium was 570.50 (kg m-3) albeit, was higher compared to mangium wood of relatively younger ages. Mean moisture content (37.51±3.1 %) and shrinkage values were relatively very low compared to the values reported from previous studies. Furthermore, the incidence of the soft core which was relatively less indicates better seasoning of the harvested wood. Understanding the long-term effects of stand management activities on productivity will help in taking better management decisions. On the whole, the study revealed that, since long term effects of thinning were significant for most of the productivity traits, thinning intensity regimes have a strong influence/bearing on stand management objectives.ennullThesis