Soil Compaction and Forest Floor Removal Affect Early Growth and Physiology of Lodgepole Pine and Douglas-Fir in British Columbia

Abstract

Abstract We investigated the effects of soil compaction and forest floor removal on growth and physiology of lodgepole pine (Pinus contorta ex Loud. var. latifolia Engelm.) and Douglas-fir (Pseudotsuga menziesii var. glauca [Baissn.] Franco) seedlings on a calcareous long-term soil productivity (LTSP) study site near Invermere, British Columbia. Treatments consisted of factorial combinations of soil compaction (noncompacted versus compacted) and forest floor removal (forest floor intact versus forest floor removed) as well as a remedial (rehabilitation) treatment of deep ripping following soil compaction. The experiment was not replicated at the treatment plot level, therefore no statistically based mean comparisons were made. After two growing seasons, we found that the two tree species responded differently to those treatments. Lodgepole pine height and diameter growth and unit needle-weight (dry mass per unit needle) averaged 25, 51, and 30% greater, respectively, in the rehabilitation than in the other treatments, whereas Douglas-fir responded to the rehabilitation treatment by increasing stem diameter growth by 27%, but not height growth (a change of 9%). Forest floor removal decreased height growth in lodgepole pine by 11%, but increased diameter growth in Douglas-fir by 15%. The decreases in growth for lodgepole pine in the forest floor removal treatments were accompanied by lower foliar N concentrations. Foliar N concentrations were positively correlated with rates of net photosynthesis (r = 0.69, P = 0.004) and height growth (r = 0.76, P = 0.004) in lodgepole pine, but not in Douglas-fir. Low N supply (as observed for lodgepole pine) and depletion of soil moisture as a result of forest floor removal likely played a role in shaping the growth and physiological responses of the trees in this study. FOR. SCI. 51(6):513–521.