The effect of rainfall and competition intensity on forest response to drought: lessons learned from a dry extreme

Abstract

We investigated forest responses to global warming by observing: (1) planted Pinus halepensis forests, (2) an aridity gradient-with annual precipitation (P) ranging from ~300 to ~700 mm, and (3) periods of wet and dry climate that included the driest period during at least the last 110 years. We examined: (1) how the length of climatic integration periods to which trees are most responsive varies in space and time, (2) the extent to which competition modulates growth decline during drought (2011) and subsequent recovery (2012) years. The temporal scale of rainfall that was most influential on growth shortened in progressing southward, and in the drier than in the wetter period. Long-term underground water storage, as reflected in the relationship of growth to multiple-year rainfall, remained significant up to the point where P ≈ 500 mm. Under drier conditions (P < 500 mm) in both space and time, influential rainfall scales shortened, probably reflecting a diminishing role of water storage. These drier locations are the first from which the species would be likely to retreat if global warming intensified. Competition appeared to set an upper limit to growth, while growth variation among individual trees increased as competition-intensity decreased. That upper limit increased in 2012 compared with 2011. The observed insensitivity of slow-growing trees to competition implies that mortality risk may be density independent, when even any potential for higher soil moisture availability in open stands is lost to evapotranspiration before it can benefit tree growth.

Cumulative Drought Stress Leads to a Loss of Growth Resilience and Explains Higher Mortality in Planted than in Naturally Regenerated Pinus pinaster Stands

“…These results are supported by the sensitive response of the naturally regenerated stands to precipitation, probably because they are located in the soils of better quality [41]-as the environmental analyses showed ( Figure 5). By contrast, the low sensitivity to climate of the planted stands indicates that their growth is conditioned more by non-climatic factors, such as the alteration of soil conditions as a result of soil preparation during plantation whose legacy effects last for several decades [61]-or intense tree-to-tree competition, leading to suppressed growth [9].…”

Responses of Natural Vegetation to Different Stages of Extreme Drought during 2009–2010 in Southwestern China

“…Extreme drought is a major environmental stress that affects the growth and development of vegetation, subsequently affects the energy balance on the earth's surface and provides invaluable ecosystem services [6]. It is quite important to monitor and assess the potential impacts of droughts on vegetation response [7,8].…”

Continuous planting under a high density enhances the competition for nutrients among young Cunninghamia lanceolata saplings

“…Conversely, a decrease in the Rubisco content or activity for other reasons would very likely be reflected in leaf N contents or the N/P ratio. In addition to nutrients in the soils and leaves, light and water also strongly affect photosynthesis (Anten and Hirose 2001;Dorman et al 2015). However, little is currently known about the process leading to a density-dependent decrease of photosynthesis in Chinese fir in soils from continuous plantations.…”