Heat damage in tree seedlings and its prevention     

Ole T. Helgerson 《New Forests》1989,3(4):333-358

Tree seedlings start to suffer stem damage or tissue death when the temperature at the soil surface reaches approximately 52°C. Seedling mortality rate accelerates as temperatures increase. Resistance to heat damage increases with size as the ability of a seedling to shade its base increase. Small newly germinated seedlings are at risk in late spring and early summer, while larger nursery-grown seedlings are at risk in mid to late summer, especially on soils with low heat capacity or conductivity, or with surfaces that are dry, dark colored or covered with organic matter. Heat damage to natural and planted seedlings usually occurs on flat or south-facing sites in regions with hot dry summers and clear skies, but can also occur in wetter regions under dry clear conditions. Shading only the basal portion of the stem appears to be as effective in preventing heat damage as shadingthe entire stem and some foliage, which can also reduce transpiration. Overhead shade and shade from live plants can reduce growth and survival.  相似文献