Contrasting vulnerability and resilience to drought-induced decline of densely planted vs. natural rear-edge Pinus nigra forests

Sanchez-Salguero R., Camarero J.J., Dobbertin M., Fernandez-Cancio T., Vila-Cabrera A., Manzanedo R.D., Zavala M.A., Navarro-Cerrillo R.M. (2013) Contrasting vulnerability and resilience to drought-induced decline of densely planted vs. natural rear-edge Pinus nigra forests. Forest Ecology and Management. 310: 956-967.
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Doi: 10.1016/j.foreco.2013.09.050

Resum:

The southernmost European natural and planted pine forests are among the most vulnerable areas to warming-induced drought decline. Both drought stress and management factors (e.g., stand origin or reduced thinning) may induce decline by reducing the water available to trees but their relative importances have not been properly assessed. The role of stand origin - densely planted vs. naturally regenerated stands - as a decline driver can be assessed by comparing the growth and vigor responses to drought of similar natural vs. planted stands. Here, we compare these responses in natural and planted Black pine (Pinus nigra) stands located in southern Spain. We analyze how environmental factors - climatic (temperature and precipitation anomalies) and site conditions - and biotic factors - stand structure (age, tree size, density) and defoliation by the pine processionary moth - drive radial growth and crown condition at stand and tree levels. We also assess the climatic trends in the study area over the last 60. years. We use dendrochronology, linear mixed-effects models of basal area increment and structural equation models to determine how natural and planted stands respond to drought and current competition intensity. We observed that a temperature rise and a decrease in precipitation during the growing period led to increasing drought stress during the late 20th century. Trees from planted stands experienced stronger growth reductions and displayed more severe crown defoliation after severe droughts than those from natural stands. High stand density negatively drove growth and enhanced crown dieback, particularly in planted stands. Also pine processionary moth defoliation was more severe in the growth of natural than in planted stands but affected tree crown condition similarly in both stand types. In response to drought, sharp growth reduction and widespread defoliation of planted Mediterranean pine stands indicate that they are more vulnerable and less resilient to drought stress than natural stands. To mitigate forest decline of planted stands in xeric areas such as the Mediterranean Basin, less dense and more diverse stands should be created through selective thinning or by selecting species or provenances that are more drought tolerant. © 2013 Elsevier B.V.

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Patterns of Forest Decline and Regeneration Across Scots Pine Populations

Vilà-Cabrera A., Martínez-Vilalta J., Galiano L., Retana J. (2013) Patterns of Forest Decline and Regeneration Across Scots Pine Populations. Ecosystems. 16: 323-335.
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Doi: 10.1007/s10021-012-9615-2

Resum:

To predict future changes in forest ecosystems, it is crucial to understand the complex processes involved in decline of tree species populations and to evaluate the implications for potential vegetation shifts. Here, we study patterns of decline (canopy defoliation and mortality of adults) of four Scots pine populations at the southern edge of its distribution and characterized by different combinations of climate dryness and intensity of past management. General linear and structural equation modeling were used to assess how biotic, abiotic, and management components interacted to explain the spatial variability of Scots pine decline across and within populations. Regeneration patterns of Scots pine and co-occurring oak species were analyzed to assess potential vegetation shifts. Decline trends were related to climatic dryness at the regional scale, but, ultimately, within-population forest structure, local site conditions, and past human legacies could be the main underlying drivers of Scots pine decline. Overall, Scots pine regeneration was negatively related to decline both within and between populations, whereas oak species responded to decline idiosyncratically across populations. Taken together, our results suggest that (1) patterns of decline are the result of processes acting at the plot level that modulate forest responses to local environmental stress and (2) decline of adult Scots pine trees seems not to be compensated by self-recruitment so that the future dynamics of these forest ecosystems are uncertain. © 2012 Springer Science+Business Media New York.

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