Scale‐dependent relationships between tree species richness and ecosystem function in forests

Abstract

Summary The relationship between species richness and ecosystem function, as measured by productivity or biomass, is of long‐standing theoretical and practical interest in ecology. This is especially true for forests, which represent a majority of global biomass, productivity and biodiversity. Here, we conduct an analysis of relationships between tree species richness, biomass and productivity in 25 forest plots of area 8–50 ha from across the world. The data were collected using standardized protocols, obviating the need to correct for methodological differences that plague many studies on this topic. We found that at very small spatial grains (0.04 ha) species richness was generally positively related to productivity and biomass within plots, with a doubling of species richness corresponding to an average 48% increase in productivity and 53% increase in biomass. At larger spatial grains (0.25 ha, 1 ha), results were mixed, with negative relationships becoming more common. The results were qualitatively similar but much weaker when we controlled for stem density: at the 0.04 ha spatial grain, a doubling of species richness corresponded to a 5% increase in productivity and 7% increase in biomass. Productivity and biomass were themselves almost always positively related at all spatial grains. Synthesis. This is the first cross‐site study of the effect of tree species richness on forest biomass and productivity that systematically varies spatial grain within a controlled methodology. The scale‐dependent results are consistent with theoretical models in which sampling effects and niche complementarity dominate at small scales, while environmental gradients drive patterns at large scales. Our study shows that the relationship of tree species richness with biomass and productivity changes qualitatively when moving from scales typical of forest surveys (0.04 ha) to slightly larger scales (0.25 and 1 ha). This needs to be recognized in forest conservation policy and management.

Functional composition drives ecosystem function through multiple mechanisms in a broadleaved subtropical forest

“…We found evidence that variation in stem density serves as a mechanism by which both NC and MR hypotheses can operate simultaneously and indirectly in a forest to influence EF. Forest communities with higher stem density are generally associated with higher diversity and greater biomass (Chisholm et al 2013). Supporting this idea, we found a strong positive relationship between stem density and both CWP and AGB in all our models.…”

“…H 2 In accordance with the massratio hypothesis (MR), EF is strongly related to the functional identity of the community as measured by CWM trait values and negatively related to FDis (Díaz et al 2007). H 3 The effects of NC and MR on EF are mediated by stem density (canopy packing), because greater stem density is associated with both more diversity and more biomass and productivity (Chisholm et al 2013).…”

“…Ruiz-Jaen and found that functional composition was a better predictor of carbon storage than was species richness, and the effects of species richness and functional diversity were negative. Chisholm et al (2013) analyzed local variation within 25 temperate and tropical forests and discovered that the relationship of tree species richness to forest biomass and productivity varied among sites and with spatial grain, with a preponderance of significant positive relationships at small grains (0.04 ha) becoming mixed in direction and mostly insignificant at larger grains (1 ha). These conflicting patterns may be a result of a shift in the relative importance of NC and MR among sites, or may indicate that NC and MR operate simultaneously (Grace et al 2016).…”

Relations entre la diversité et la biomasse aérienne des espèces arborescentes dans les agroforêts traditionnelles à base de cacaoyers: Cas de la localité de Lakota (Côte d’Ivoire)

“…La détection de cette relation permettrait d'avoir une idée du compromis entre la diversité biologique dans les agroforêts et leur capacité à séquestrer du carbone. En forêt tropicale par exemple, il est admis que la diversité des espèces végétales, augmente la biomasse des arbres sur pied (Naeem et al, 1996 ;Chapin et al, 2000, Pacala et Kinzig, 2002Diaz et al, 2009 ;Ruiz-Jean et Potvin, 2010 ;Chisholm et al, 2013). Dans les plantations en générale et les cacaoyères en particulier, de telles relations ont été rarement étudiées.…”

Uncertainty and the design of in-situ biodiversity-monitoring programs

“…It is possible to scale up from local data to larger areas, but only if data are collected in spatially standardized arrays, and this may create conflicts with organizations and volunteers who collect the data (Turnhout and Boonman-Berson 2011). Relationships depend heavily on the sampling scale , Rosenzweig et al 2011, Chisholm et al 2013. Evaluations of the effects of scale of sampling are generally difficult with idiosyncratic sampling, but can be achieved with a few sites with standardized infrastructure.…”