LEAF LEVEL RESPONSE OF PLANTED EASTERN WHITE-PINE (PINUS-STROBUS L.) 7 YEARS AFTER INTENSIVE SILVICULTURAL TREATMENTS

The present study examines the impact of intensive silvicultural treat ments on environmental conditions, leaf level morphology and physiolog y, and growth of planted eastern white pine (Pinus strobus L.) sapling s and evaluates how silvicultural treatments and the presence of compe ting vegetation influence the relationships between leaf nitrogen, lea f morphology, and leaf level photosynthetic capacity of saplings. The six silvicultural treatments evaluated consisted of combinations of sc arification (removal of entire humus layer), vegetation control (herbi cide), and fertilization (slow release fertilizer). Competing vegetati on (mainly Populus tremuloides Mickx.) had negative impacts on shoot w ater potential (Psi(x)), leaf nitrogen, leaf mass per unit leaf area ( LMA), height, and basal area of 7-year-old saplings. Net CO2 assimilat ion rate at light saturation (A; both on a mass and area basis) and st omatal conductance for water vapor (g(wv)) were not significantly infl uenced by the presence of competing vegetation. The only significant i mpact of competition on gas exchange variables was to decrease water-u se efficiency (both instantaneous and long-term WUE as expressed by ca rbon isotope discrimination or Delta). Scarification significantly inc reased predawn Psi(x), height, and basal area of suppressed saplings, and A(area), g(wv), and LMA of saplings subject to herbicide applicati on. These positive impacts of scarification were attributed to enhance d root growth due to higher soil temperatures. No positive impact of f ertilization was observed in either suppressed or open conditions. Lea f nitrogen and LMA were both driving variables for photosynthetic capa city of saplings across all conditions created by silvicultural treatm ents, but also within both suppressed and open conditions. This sugges ts that the dependency of the photosynthetic apparatus on leaf nitroge n and LMA occurs whether there is competing vegetation (and/or shade) or not. However, the gradient of light availability under suppressed c onditions was accompanied by a gradient of soil temperature due to sca rification. It would be pertinent to investigate more fully the intera ctions between light availability and soil temperature, both influenci ng root growth and leaf level morphology and physiology of young easte rn white pine. (C) 1998 Elsevier Science B.V.