Abstract
Climate forcing is the major abiotic driver for forest ecosystem functioning and thus significantly affects the role of forests within the global carbon cycle and related ecosystem services. Annual radial increments of trees are probably the most valuable source of information to link tree growth and climate at long-term time scales, and have been used in a wide variety of investigations worldwide. However, especially in mountainous areas, tree-ring studies have focused on extreme environments where the climate sensitivity is perhaps greatest but are necessarily a biased representation of the forests within a region. We used tree-ring analyses to study two of the most important tree species growing in the Alps: Norway spruce (Picea abies) and silver fir (Abies alba). We developed tree-ring chronologies from 13 mesic mid-elevation sites (203 trees) and then compared them to monthly temperature and precipitation data for the period 1846–1995. Correlation functions, principal component analysis and fuzzy C-means clustering were applied to 1) assess the climate/growth relationships and their stationarity and consistency over time, and 2) extract common modes of variability in the species responses to mean and extreme climate variability. Our results highlight a clear, time-stable, and species-specific response to mean climate conditions. However, during the previous-year's growing season, which shows the strongest correlations, the primary difference between species is in their response to extreme events, not mean conditions. Mesic sites at mid-altitude are commonly underrepresented in tree-ring research; we showed that strong climatic controls of growth may exist even in those areas. Extreme climatic events may play a key role in defining the species-specific responses on climatic sensitivity and, with a global change perspective, specific divergent responses are likely to occur even where current conditions are less limited.
Highlights
The growth and distribution of forests and the related roles of forests within the terrestrial carbon cycle are closely intertwined with climate forcing and variability at both short and long timescales [1]
This relationship between climate and forests is not homogeneous across geographical areas or among species. Significant differences, at both physical and biological levels, have been found across continents [2,3], regions [4,5], ecosystems, taxa and seasons [6]. This variability is clearly associated with spatial changes in environmental factors, and associated with the corresponding positive or negative plant-plant interactions that are able to significantly shape the composition and dynamics of forest communities [7,8]
A careful site and tree selection to enhance tree-growth responses to the environmental feature of interest and to maximize age or length of record is the typical mode of sampling in most traditional dendroecological investigations
Summary
The growth and distribution of forests and the related roles of forests within the terrestrial carbon cycle are closely intertwined with climate forcing and variability at both short and long timescales [1]. The altitudinal and latitudinal treeline is one key research area, where there is i) high sensitivity to environmental changes, ii) frequent presence of long-lived trees and iii) decreasing importance of competition - in terms of its effect on adult growth - with increasing limiting conditions [8,10]. This usually permits the effective isolation, at various time scales, of the role of the most stressful growth limiting factor (temperature) on plant growth processes [10,11]. For xeric habitats, water is the primary limiting factor, and tree growth is more sensitive to corresponding changes in hydrological cycle [12]
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