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Weekly Highlights for 8-11-2017


Physiological Mechanisms in Drought-induced Tree Mortality

Widespread tree mortality associated with drought has been observed on all forested continents, and global change is expected to exacerbate vegetation vulnerability. The proposed mechanisms of drought-induced mortality, including hydraulic failure and carbon starvation, are unresolved. A team of international authors reviewed the literature to show that multiple tree taxa had 60% or greater loss of xylem hydraulic conductivity upon drought-induced mortality. They found diverse responses in non-structural carbohydrate reserves at mortality, indicating that evidence supporting carbon starvation was not universal. Reduced non-structural carbohydrates were more common for gymnosperms than angiosperms, associated with xylem hydraulic vulnerability, and may have a role in reducing hydraulic function. Their findings indicate that substantial improvement in vegetation modeling can be achieved using thresholds in hydraulic function.

Adams, H.D., Zeppel, M.J., Anderegg, W.R., Hartmann, H., Landhäusser, S.M., Tissue, D.T., Huxman, T.E., Hudson, P.J., Franz, T.E., Allen, C.D., Anderegg, L.D., Barron-Gafford, G.A., Beerling, D.J., Breshears, D.D., Brodribb, T.J., Bugmann, H., Cobb, R.C., Collins, A.D., Turin Dickman, L., Duan, H., Ewers, B.E., Galiano, L., Galvez, D.A., Garcia-Forner, N., Gaylord, M.L., Germino, M.J., Gessler, A., Hacke, U.G., Hakamada, R., Hector, A., Jenkins, M.W., Kane, J.M., Kolb, T.E., Law, D.J., Lewis, J.D., Limousin, J., Love, D.M., Macalady, A.K., Martínez-Vilalta, J., Mencuccini, M., Mitchell, P.J., Muss, J.D., O'Brien, M.J., O'Grady, A.P., Pangle, R.E., Pinkard, E.A., Piper, F.I., Plaut, J.A., Pockman, W.T., Quirk, J., Reinhardt, K., Ripullone, F., Ryan, M.G., Sala, A., Sevanto, S., Sperry, J.S., Vargas, R., Vennetier, M., Way, D.A., Xu, C., Yepez, E.A., McDowell, N.G., 2017, A multi-species synthesis of physiological mechanisms in drought-induced tree mortality: Nature Ecology and Evolution, v. 1, p. 1285–1291,[Details]

Contact: Matthew Germino, FRESC, 208-426-3353, Profile

Differences in Seedling Attributes Affect Tree Range Shifts with Climate Warming

Low temperatures inhibit growth and thus presence of some trees at high elevations, implying that forest boundaries will move upslope with climate warming. However, temperature and moisture availability act in concert to affect seedling establishment. Researchers examined the growth and physiology of limber pine, lodgepole pine, and subalpine fir seeded below, at, and above treeline while manipulating precipitation and temperature at plots in the Rocky Mountains. Heat inhibited tree seedling establishment at the cold, high-elevation edge of forests when soil moisture was inadequate because newly germinated seedlings have poor moisture-stress tolerance. This places heavy reliance on seed carbon reserves, and species with larger seeds such as limber pine have an advantage over smaller seeded species. Scientists also found that that heating may reduce growth by limiting root development. With warming, initial establishment of tree seedlings in subalpine and alpine settings may occur only with relatively abundant moisture.

Lazarus, B.E., Castanha, C., Germino, M.J., Kueppers, L.M., Moyes, A.B., 2017, Growth strategies and threshold responses to water deficit modulate effects of warming on tree seedlings from forest to alpine: Journal of Ecology, v. 00, p. 1-15,[Details]

Contact: Matthew Germino, FRESC, 208-426-3353, Profile

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