Confounding Factors in the Observational Productivity-Diversity Relationship in Forests

摘要: Field experiments conducted in randomly assembled grassland communities have demonstrated that changes plant species diversity affect ecosystem productivity over a range of environmental conditions (Hector et al. 1999; Tilman 2001). However, there is still controversy as to whether this causal relationship also found natural systems (Loreau 2001; Schmid 2002), especially at regional scales (Bengtsson 2002). For example, Troumbis and Memtsas (2000) Greek shrub lands were more productive stands with high diversity. the positive correlations between may be confounded other less conspicuous or unknown factors such site quality fertility both variables underlie observed correlation (Huston 1997; Wardle Furthermore, observational studies not always productivity. The available evidence shows multiple patterns exist change spatial scale. Exhaustive reviews on vascular richness hump-shaped (unimodal) occurred often than monotonically increasing relationship, depending geographical scale ecological organization (e.g., within across community types; Waide Mittelbach This can partially reconciled by superposing experimental results (Fig. 4.1). That is, diversity–productivity relationships compare sites different productivities driven conditions. observations (data points) fill area below humpbacked line. Instead, experimentally established levels single maintaining all influencing constant