Heat damage in tree seedlings and its prevention

Abstract

Application. Heat damage to natural and planted seedlings can be prevented by recognizing adverse conditions, identifying susceptible seedlings, and taking preventive measures, such as shading, planting resistant seedlings, and modifying the soil environment. Shade from live vegetation can prevent heat damage, but the associated competition may kill seedlings.Abstract. 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 shading the entire stem and some foliage, which can also reduce transpiration. Overhead shade and shade from live plants can reduce growth and survival.

Influences of Mechanized Thinning and Prescribed Fire on Natural Regeneration in an Uneven-Aged Jeffrey Pine Stand

“…Influences of competing understory vegetation on seedling abundance here were confined to a positive correlation between white fir and mahala mat cover, a relationship that has been previously attributed to increased soil moisture availability beneath this prostrate shrub (Tappeiner & Helms, 1971). Previous reports of forest floor materials, characterized here as downed and dead fuels, impeding natural regeneration because they dry out readily and reach high temperatures (Fowells & Stark, 1965;Helgerson, 1990;Gray & Spies, 1997), were not substantiated here given the positive correlations between seedling counts irrespective of species and fine fuel loads as well as that between total count and total loading. A documented exception, however, is white fir (Gray et al, 2005).…”

Forest responses to climate change in the northwestern United States: Ecophysiological foundations for adaptive management

“…High temperatures may directly damage cell membranes and disrupt structure and function of proteins, leading to a number of harmful metabolic changes (Levitt, 1980;Nilsen and Orcutt, 1996). Exposure to high temperatures at the soil surface often results in cambial girdling in open-grown seedlings (Helgerson, 1990), but exposure to heat in excess of 40 • C may lead to other injuries and mortality (Seymour et al, 1983;Seidel, 1986). Abnormalities in bud development were observed when P. menziesii seedlings were exposed to temperatures exceeding 40 • C (Apple et al, 1998).…”

Gap Size, Within-Gap Position and Canopy Structure Effects on Conifer Seedling Establishment

“…The northern edges of ).4 gaps and the northern halves of 1.0 gaps were the )nly zones that received substantial amounts of direct ,olar radiation in this study (Gray 1995). Seedling nortality in exposed environments is commonly issociated with high surface temperatures that can cill the cambium at the soil line (Silen 1960;Helgerson 1990) or lead to high transpiration rates and desccation (Livingston & Black 1988). Differences in -stablishment among gaps were greater on natural ,ubstrates (Fig.…”