Growth Behavior of Selected Agroforestry Tree Species under the Hilly Ecosystem of Northeast India—An Expanding Role for Agroforestry

Abstract

Tree species have varied canopy architecture, which influence light interception or quantum of light available to crops grown underneath their canopies. Therefore, it is necessary to understand the growth pattern of different agroforestry tree species so that potential light available to crops under a particular tree is known. The Khasi mandarin (Citrus reticulata) and alder (Alnus nepalensis) show conforming Roux's model of tree architecture. The architecture of pine is similar to Rauh's model. Leaf flushing in alder and Khasi pine (Pinus kesiya) occurs during the months of February and March, while in the case of Khasi mandarin it occurs twice (February and August) in a year. The active shoot growth was observed during February to April in the case of Khasi mandarin and Khasi pine, however, it continued for over four months (February to May) in the case of alder. Leaf fall started during the post-rainy period (October to February) and peaked during the dry winter (January) in Khasi mandarin and alder, but in Khasi pine, it occurred throughout the year with a peak in February. In terms of height growth, the species ranked as Alnus nepalensis> Pinus kesiya> Citrus reticulata, and in terms of growth in diameter (dbh) the order was Pinus kesiya> Alnus nepalensis> Citrus reticulata. The total aboveground biomass was highest in Khasi pine, followed by alder and Khasi mandarin. Bole contributed about 59% to 78% of total aboveground biomass while leaves contributed only about 8% in all the tree species. The fine root biomass in alder and Khasi pine decreased with increase in distance from the tree trunk, but in Khasi mandarin, it showed a reverse trend. The maximum total fine root mass (trees and herbaceous fine root) was recorded in the upper soil layer of Khasi pine-based agroforestry system