Stabilizing effects of diversity on aboveground wood production in forest ecosystems: linking patterns and processes.

Both theory and evidence suggest that diversity stabilises productivity in herbaceous plant communities through a combination of overyielding, species asynchrony and favourable species interactions. However, whether these same processes also promote stability in forest ecosystems has never been tested. Using tree ring data from permanent forest plots across Europe, we show that aboveground wood production is inherently more stable through time in mixed-species forests. Faster rates of wood production (i.e. overyielding), decreased year-to-year variation in productivity through asynchronous responses of species to climate, and greater temporal stability in the growth rates of individual tree species all contributed strongly to stabilising productivity in mixed stands. Together, these findings reveal the central role of diversity in stabilising productivity in forests, and bring us closer to understanding the processes which enable diverse forests to remain productive under a wide range of environmental conditions.This is the author's accepted manuscript and will be under embargo until the 13th of October 2015. The final version will be published by Wiley in Ecology Letters. The 'Early View' article is available online here: http://onlinelibrary.wiley.com/doi/10.1111/ele.12382/abstract

Climate modulates the effects of tree diversity on forest productivity

1. Despite growing evidence that, on average, diverse forests tend to be more productive than species-poor ones, individual studies often report strongly contrasting relationships between tree species richness and above-ground wood production (AWP). In the attempt to reconcile these apparently inconsistent results, we explored whether the strength and shape of AWP–diversity relationships shifts along spatial and temporal environmental gradients in forests across Europe. 2. We used tree ring data from a network of permanent forest plots distributed at six sites across Europe to estimate annual AWP over a 15-year period (1997–2011). We then tested whether the relationship between tree species richness and AWP changes (i) across sites as a function of large-scale gradients in climatic productivity and tree packing density and (ii) among years within each sites as a result of fluctuating climatic conditions. 3. AWP–species richness relationships varied markedly among sites. As predicted by theory, the relationship shifted from strongly positive at sites where climate imposed a strong limitation on wood production and tree packing densities were low, to weakly negative at sites where climatic conditions for growth were most suitable. In contrast, we found no consistent effect of interannual fluctuations in climate on the strength of AWP–species richness relationships within sites. 4. Synthesis. Our results indicate that the shape and strength of the relationship between tree diversity and forest productivity depends critically on environmental context. Across Europe, tree diversity shows the greatest potential to positively influence forest productivity at either end of the latitudinal gradient, where adverse climatic conditions limit productivity and lead to the development of less densely packed stands.The research leading to these results received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 265171.This is the author accepted manuscript. The final version is available from Wiley via http://dx.doi.org/10.1111/1365-2745.1252

Untangling methodological and scale considerations in growth and productivity trend estimates of Canada’s forests

In view of the economic, social and ecological importance of Canada's forest ecosystems, there is a growing interest in studying the response of these ecosystems to climate change. Accurate knowledge regarding growth trajectories is needed for both policy makers and forest managers to ensure sustainability of the forest resource. However, results of previous analyses regarding the sign and magnitude of trends have often diverged. The main objective of this paper was to analyse the current state of scientific knowledge on growth and productivity trends in Canada's forests and provide some explanatory elements for contrasting observations. The three methods that are commonly used for assessments of tree growth and forest productivity (i.e. forest inventory data, tree-ring records, and satellite observations) have different underlying physiological assumptions and operate on different spatiotemporal scales, which complicates direct comparisons of trend values between studies. Within our systematic review of 44 peer-reviewed studies, half identified increasing trends for tree growth or forest productivity, while the other half showed negative trends. Biases and uncertainties associated with the three methods may explain some of the observed discrepancies. Given the complexity of interactions and feedbacks between ecosystem processes at different scales, researchers should consider the different approaches as complementary, rather than contradictory. Here, we propose the integration of these different approaches into a single framework that capitalizes on their respective advantages while limiting associated biases. Harmonization of sampling protocols and improvement of data processing and analyses would allow for more consistent trend estimations, thereby providing greater insight into climate-change related trends in forest growth and productivity. Similarly, a more open data-sharing culture should speed-up progress in this field of research

Twentieth Century Redistribution in Climatic Drivers of Global Tree Growth

Energy and water limitations of tree growth remain insufficiently understood at large spatiotemporal scales, hindering model representation of interannual or longer-term ecosystem processes. By assessing and statistically scaling the climatic drivers from 2710 tree-ring sites, we identified the boreal and temperate land areas where tree growth during 19301960 CE responded positively to temperature (20.8 3.7 Mio km2; 25.9 4.6%), precipitation (77.5 3.3 Mio km2; 96.4 4.1%), and other parameters. The spatial manifestation of this climate response is determined by latitudinal and altitudinal temperature gradients, indicating that warming leads to geographic shifts in growth limitations. We observed a significant (P < 0.001) decrease in temperature response at cold-dry sites between 19301960 and 19601990 CE, and the total temperature-limited area shrunk by 8.7 0.6 Mio km2. Simultaneously, trees became more limited by atmospheric water demand almost worldwide. These changes occurred under mild warming, and we expect that continued climate change will trigger a major redistribution in growth responses to climate

Good things take time – diversity effects on tree growth shift from negative to positive during stand development in boreal forests

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Assessing forest availability for wood supply in Europe

The quantification of forests available for wood supply (FAWS) is essential for decision-making with regard to the maintenance and enhancement of forest resources and their contribution to the global carbon cycle. The provision of harmonized forest statistics is necessary for the development of forest associated policies and to support decision-making. Based on the National Forest Inventory (NFI) data from 13 European countries, we quantify and compare the areas and aboveground dry biomass (AGB) of FAWS and forest not available for wood supply (FNAWS) according to national and reference definitions by determining the restrictions and associated thresholds considered at country level to classify forests as FAWS or FNAWS. FAWS represent between 75 and 95 % of forest area and AGB for most of the countries in this study. Economic restrictions are the main factor limiting the availability of forests for wood supply, accounting for 67 % of the total FNAWS area and 56 % of the total FNAWS AGB, followed by environmental restrictions. Profitability, slope and accessibility as economic restrictions, and protected areas as environmental restrictions are the factors most frequently considered to distinguish between FAWS and FNAWS. With respect to the area of FNAWS associated with each type of restriction, an overlap among the restrictions of 13.7 % was identified. For most countries, the differences in the FNAWS areas and AGB estimates between national and reference definitions ranged from 0 to 5 %. These results highlight the applicability and reliability of a FAWS reference definition for most of the European countries studied, thereby facilitating a consistent approach to assess forests available for supply for the purpose of international reportinginfo:eu-repo/semantics/publishedVersio

dendrometeR : analyzing the pulse of trees in R

Dendrometers are measurement devices proven to be useful to analyze tree water relations and growth responses in relation to environmental variability. To analyze dendrometer data, two analytical methods prevail: (1) daily approaches that calculate or extract single values per day, and (2) stem-cycle approaches that separate high-resolution dendrometer records into distinct phases of contraction, expansion and stem-radius increment. Especially the stem-cycle approach requires complex algorithms to disentangle cyclic phases. Here, we present an R package, named dendrometeR, that facilitates the analysis of dendrometer data using both analytical methods. By making the package freely available, we make a first step towards comparable and reproducible methods to analyze dendrometer data. The package contains customizable functions to prepare, verify, process and plot dendrometer series, as well as functions that facilitate the analysis of dendrometer data (i.e. daily statistics or extracted phases) in relation to environmental data. The functionality of dendrometeR is illustrated in this note