Influence of two site preparation treatments on ecophysiology of planted Piceaengelmannii × glauca seedlings

Abstract

The effects of mounding and soil scarification on microclimate, water relations, photosynthesis, and growth of planted Picea engelmanni .times. glauca seedlings were evaluated over three growing seasons. Mounding increased soil temperatures by up to 40% at depths of 5 and 12 cm, but not at 30 cm, during periods of dry, clear whether. Scarification resulted in small increases in soil temperature only at the 5 cm depth. Soil water potential and soil water content were lower in mounds, but similar in scarified patches and controls from midsummer through fall. Transpiration, leaf conductance, and xylem pressure potentials were generally reduced by mounding and to a much lesser extent by scarification compared with controls. However, these responses were complicated by interactions with leaf to air vapor density differences and possibly by soil temperatures. Treatments had no significant effects on diurnal or light responses of photosynthesis. Mounding increased stem and needle weights during the first one-half of the growing season in the first 2 years after planting, but growth was reduced later in the season, probably as a result of increased water stress. Root growth in mounds was significantly greater than scarified patches and controls in all 3 years. Growth patterns of seedlings planted in scarified patches and control treatments were similar to each other. By the end of the third growing season after planting, seedlings in mound treatments had greater stem diameters and total seedling weight was more than double that of controls, but there was little difference in height. Seedlings in scarified patches were similar to controls in diameter and height, but had slightly greater total weights. Results suggest that the positive effects of improved soil temperatures and root growth in mound treatments were negated to a large extent by increased water stress in the first two seasons. By the third growing season, roots were beyond significant drying influence of the mound and their greater length and mass served to increase seedling biomass substantially.