Tree species richness enhances stand productivity while stand structure can have opposite effects, based on forest inventory data from Germany and the United States of America

Forest Ecosystems, Feb 2018

Laura Zeller, Jingjing Liang, Hans Pretzsch

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Tree species richness enhances stand productivity while stand structure can have opposite effects, based on forest inventory data from Germany and the United States of America

Zeller et al. Forest Ecosystems Tree species richness enhances stand productivity while stand structure can have opposite effects, based on forest inventory data from Germany and the United States of America Laura Zeller 0 Jingjing Liang 1 Hans Pretzsch 0 0 Center of Life and Food Sciences Weihenstephan, Technical University of Munich , Hans-Carl-von-Carlowitz-Platz 2, 85354 Freising , Germany 1 Division of Forestry and Natural Resources, Davis College of Agriculture, Natural Resources & Design, West Virginia University , 340 Percival Hall, Morgantown, WV 26506-6108 , USA Background: In recent studies, mixed forests were found to be more productive than monocultures with everything else remaining the same. Methods: To find out if this productivity is caused by tree species richness, by a more heterogeneous stand structure or both, we analyzed the effects of forest structure and tree species richness on stand productivity, based on inventory data of temperate forests in the United States of America and Germany. Results: Having accounted for effects such as tree size and stand density, we found that: (I) tree species richness increased stand productivity in both countries while the effect of tree size heterogeneity on productivity was negative in Germany but positive in the USA; (II) productivity was highest at sites with an intermediate amount of precipitation; and (III) growth limitations due water scarcity or low temperature may enhance structural heterogeneity. Conclusions: In the context of forest ecosystem goods and services, as well as future sustainable forest resource management, the associated implications would be: Tree species richness is vital for maintaining forest productivity. As an optimum amount of precipitation is accompanied by the highest productivity, changes in climatic conditions should be considered when planning. Resource limitations enhance structural heterogeneity, which in turn can have positive or negative effects on stand productivity. Big data; Overyielding; Tree size heterogeneity; Tree species mixing; Climate; Biodiversity-productivity relationship Background Economic and political relationships, environmental issues, and the network of supply and demand for wood products and ecosystem services have become more global. Meanwhile, the pressure on forest ecosystems is increasing due to climate change ( Schröter et al. 2005 ; Wohlgemuth 2015 ) and a growing world population. Therefore, the need for globalizing and connecting forest research from different parts of the world to use synergy effects and combine knowledge is therefore becoming more and more important. Many countries are already advanced in forest research and are conducting national forest inventories to monitor the status, as well as to predict the future development, of forests. The Global Forest Biodiversity Initiative (GFBI) aims to connect the knowledge and data worldwide on forest biodiversity while spreading and using the available data more effectively for sustainable forest ecosystem management (Global Forest Biodiversity Initiative 2016) . The joint analysis of forest structure, tree species richness and stand productivity is becoming more relevant as recent studies have shown the different relationships among these attributes (Bohn and Huth 2017) , which can now be analyzed on a global scale thanks to the socalled “big data era” (Lokers et al. 2016) . There are many current silvicultural programs that are restoring, stabilizing, and diversifying forests in terms of tree species and stand structure to render forests more productive, resilient, and sustainable in the long run (Ammer 2008; Knoke et al. 2008) . In particular, a broader supply of forest ecosystem goods and services will be provided by more natural forest ecosystems. Not only would the provision of wood products be ensured, but the stabilizing function of water and nutrient cycles, the maintenance of different habitats, possibilities for hunting, the lowering of the risks of fire, wind throw, and land degradation, as well as the recreational and educational functions of forest areas, would also be secured (UN General Assembly 1987; MCPFE 1993; The Montréal Process 2015) . Forest management has been criticized for demolishing forest structure, diversity of habitats, and tree size heterogeneity by focusing only on timber production (Dieler et al. 2017) . As counteracting strategy, mixing and structuring forests has become a common measure in the transition of mainly timber-oriented forestry toward more sustainable management. The goal is a multifunctional forestry that ideally covers all ecosystem goods and services while striving to reduce risk (Puettmann et al. 2009; Paquette and Messier 2011; Puettmann et al. 2015; Lindenmayer et al. 2016) . Those tendencies, however, raise the question whether the achievement of a wider scope of functions and services would result in a reduction of forest productivity. Not only is (...truncated)


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Laura Zeller, Jingjing Liang, Hans Pretzsch. Tree species richness enhances stand productivity while stand structure can have opposite effects, based on forest inventory data from Germany and the United States of America, Forest Ecosystems, 2018, pp. 4, Volume 5, Issue 1, DOI: 10.1186/s40663-017-0127-6