2 research outputs found
Competition for light and water play contrasting roles in driving diversity-productivity relationships in Iberian forests
Mixedâspecies forests generally sequester and store more carbon in aboveâground woody biomass compared to speciesâpoor systems. However, the mechanisms driving the positive relationship between diversity and aboveâground wood production (AWP) remain unclear. We investigate the role of competition for light and water as possible sources of complementarity among Iberian pine and oak species. Using tree core data from permanent plots, we test the hypotheses that (i) contrasting abilities of pines and oaks to tolerate shade will promote AWP in mixtures, while (ii) drought stress results in less room for complementarity. We found that pine species receive more light, develop larger crowns and grow 138â155% faster when in mixture with oaks. However, this positive effect of species mixing on growth was severely reduced under drought conditions due to increased competition for water with neighbouring oaks. In contrast to pines, oak trees were less responsive to mixing, primarily as a result of their ability to tolerate shade and water shortage. Mixed pineâoak forests produce an average 48% more aboveâground woody biomass compared to monocultures each year. However, the magnitude of the diversity effect on AWP fluctuates with time, decreasing noticeably in strength during drought years. Synthesis. Complementary light use strategies among neighbouring trees are critical in explaining why aboveâground wood production (AWP) increases in mixedâspecies stands. In contrast, drought causes trees in mixture to compete more fiercely for belowâground resources, leaving less room for complementarity and causing positive diversity effects to lessen in strength. Together, these two mechanisms provide much needed context for AWPâdiversity relationships in Mediterranean forests. Whether or not managing for mixed pineâoak forests proves to be beneficial for AWP is likely to depend on how climate changes in the Iberian Peninsula.European Union Seventh Framework Programme. Grant Numbers: FP7/2007-2013, 265171This is the accepted manuscript version of the following article: Jucker, T., Bouriaud, O., Avacaritei, D., DÄnilÄ, I., Duduman, G., Valladares, F., Coomes, D. A. (2014), Competition for light and water play contrasting roles in driving diversityâproductivity relationships in Iberian forests. Journal of Ecology. doi: 10.1111/1365-2745.12276, which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1111/1365-2745.12276/abstract