Competition modulates the adaptation capacity of forests to climatic stress: insights from recent growth decline and death in relict stands of the Mediterranean fir Abies pinsapo

Abstract

Summary1. Long-term basal area increment (BAI) in Abies pinsapo was studied to investigate the way density-dependent factors modulate the responses of radial growth to climatic stresses in relict stands of a drought-sensitive Mediterranean fir. 2. First, we verified that spatially explicit competition predicts mean A. pinsapo BAI at our study site; i.e. it modulates the degree to which the average climate-driven potential for growth is expressed. Second, we verified that the long-term pattern of temperature predicts the long-term pattern of BAI, estimated as the main trend over a time period of c. 40 years. Finally, we assessed whether the intensity of tree-to-tree competition restrains the potential improvements achieved by our model of BAI when a short-term, high-frequency stressor such as drought (inter-annual precipitation variability) is introduced. 3. We applied Dynamic Factor Analysis (DFA) to characterize regional climatic trends and to test the hypothesis that trees subjected to contrasting competition intensity may differ in their growth pattern. Significant long-term climate trends obtained by DFA were used as predictors of long-term BAI. 4. The mean BAI was mainly determined by competition, whereas growth trends obtained by DFA did not differ among dominant, suppressed and dying trees. Common trends of growth decline were strongly related to long-term, late-winter to summer temperatures, while the residuals were related to total annual precipitation, although with decreasing significance as competition increased. Our results support the contention that the reported patterns of A. pinsapo growth decline and death occur as a result of the interacting effects of both competition and climate stressors acting at longand short-term time scales. 5. Synthesis. Long-term climatic drought stress was the main driving factor of growth decline in A. pinsapo. Moreover, trees already suffering from competition (a long-term stress) were predisposed to decline given an additional short-term stress, such as a severe drought.

Forests synchronize their growth in contrasting Eurasian regions in response to climate warming

“…29) may counteract the effect of CO 2 fertilization or rising N deposition, negatively impacting photosynthesis, especially in high latitudes (30). Fourth, changes in stand structure due to rural abandonment, limited forest management, and encroachment usually increase competition for resources and could reduce tree growth (31). A detailed examination of these drivers (SI Appendix, section 2B) led us to discard them as major causes of growth synchrony as opposed to climate.…”

The effects of thinning intensity and tree size on the growth response to annual climate in Cedrus atlantica: a linear mixed modeling approach

“…The interpretation of this higher sensitivity from the viewpoint of the ability of cedar to cope with drought effects is not straightforward, and we still lack a conceptual framework linking the growth signal features to life traits (Cuny et al 2012) and demography (Martínez-Vilalta et al 2012). Indeed, previous studies produced seemingly contradictory results, reporting higher mortality rates for trees showing highly variable growth (Suarez and Ghermandi 2004) or a weaker correlation between the growth of the dying trees and the climate variables (Linares et al 2010). As recent reports suggest a lower capacity of large trees to overcome severe drought (Bigler and Veblen 2009), the long-term effect on thinning on the ability of mature cedar stands to survive extreme water stress events need further investigations.…”

“…The buffer effect on environmental conditions provided by dominant tree canopy (Aussenac 2000) could be more important at water-limited sites, thereby explaining that the suppressed trees at our study site are less sensitive to the inter-annual water balance variability. In another view, the lower growth sensitivity of suppressed trees is due to a loss of plastic capacity in those trees strongly constrained by competition (Linares et al 2010). A third plausible explanation of the greater sensitivity of large trees to climatic stress is their higher water needs and the higher risk of cavitation that they face due to their longer xylem path (Bigler and Veblen 2009).…”

Age-Effect Radial Growth Responses of Picea schrenkiana to Climate Change in the Eastern Tianshan Mountains, Northwest China

“…Growth is also controlled by biological characteristics and genetic factors, including species, life, age, competition, and sensitivity [1,2]. Through the informed choice of sample trees, available settings and a thorough dendroclimatology research process, the effects of noise, such as forest disturbance and competition, on tree growth trends can usually be avoided.…”