Effect of shadecards, shelterwoods, and clearcuts on temperature and moisture environments

Abstract

This paper presents a comparison of two common techniques used to improve seedling survival on hot, dry reforestation. Adjacent shelterwood and clearcut sites were located and instrumented to compare temperature and moisture environments. In addition, cardboard shadecards were placed beside half of the seedlings studied so that effects of this treatment could be assessed. Seasonal measurements or observations of soil moisture, soil temperature, solar radiation, air temperature, stomatal diffusion resistance, seedling phenology and survival provided the basis for comparisons. Shelterwoods and shadecards improved seedling survival in relation to the clearcut. Both treatments affected soil temperature but the nature of the effects was different. The shelterwood canopy decreased solar radiation incident at the soil surface and caused cooler soil temperatures throughout the soil profile. Shadecards reduced soil temperatures only to a depth of 20 mm. Both treatments reduced the duration of periods of high soil temperature. The shelterwood treatment delayed seasonal water loss and decreased seedling water stress as measured by stomatal resistance. Shadecards did not significantly affect seedling stomatal resistance. The differences in seedling survival caused by shadecards and shelterwoods are apparently due to different influences on the seedling microclimate. The shelterwood causes a large reduction in soil temperature as well as decreased seedling water stress. Shadecards modify the soil temperature environment less extensively and so have less effect on seedling survival.