Abstract
Can CSR theory, in conjunction with a recently proposed globally calibrated CSR ordination (“StrateFy”), using only three easily measured leaf traits (leaf area, specific leaf area and leaf dry matter content) predict the functional signature of herbaceous vegetation along experimentally manipulated gradients of soil fertility and disturbance? To determine this, we grew 37 herbaceous species in mixture for five years in 24 experimental mesocosms differing in factorial levels of soil resources (stress) and density-independent mortality (disturbance). We measured 16 different functional traits and then ordinated the resulting vegetation within the CSR triangle using StrateFy. We then calculated community-weighted mean (CWM) values of the competitor (CCWM), stress-tolerator (SCWM) and ruderal (RCWM) scores for each mesocosm. We found a significant increase in SCWM from low to high stress mesocosms, and an increase in RCWM from lowly to highly disturbed mesocosms. However, CCWM did not decline significantly as intensity of stress or disturbance increased, as predicted by CSR theory. This last result likely arose because our herbaceous species were relatively poor competitors in global comparisons and thus no strong competitors in our species pool were selectively favoured in low stress and low disturbed mesocosms. Variation in the 13 other traits, not used by StrateFy, largely argeed with the predictions of CSR theory. StrateFy worked surprisingly well in our experimental study except for the C-dimension. Despite loss of some precision, it has great potential applicability in future studies due to its simplicity and generality.
Highlights
Grime’s CSR model of plant strategies [1,2,3] has been proposed as a framework for both functionally classifying plants and for predicting how plant community structure changes along environmental gradients
Most of these new species came from seeds already present in the clay soil and, since the same amount of this clay soil was added to each mesocosm, the same average number of seeds of each of these new species was added to each mesocosm at the start of the experiment
The high stress treatment produced only 20% of the biomass of the low stress treatment (p
Summary
Grime’s CSR model of plant strategies [1,2,3] has been proposed as a framework for both functionally classifying plants and for predicting how plant community structure changes along environmental gradients It is perhaps the most influential modern niche-based theory of plant community assembly, vegetation succession and ecosystem functioning and continues to heavily influence the field as shown by current citation rates. The three remaining combinations are associated with the evolution of different suites of correlated traits conforming to each of the three distinct habitat extremes. CSR theory claims that the dynamics and structure of vegetation is a consequence of specific adaptive trade-offs among multiple correlated functional traits (“plant strategies”) with respect to stress and disturbance, such that increased fitness in one circumstance inescapably involves a reduced fitness in another
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