C-S-R triangle theory: community-level predictions, tests, evaluation of criticisms, and relation to other theories

Grime's C-S-R triangle theory has been discussed in plant ecology For two d ecades, but it has rarely been tested, and not often dispassionately evalua ted. We consider the theory From a community viewpoint, and attempt to deve lop and rest predictions for plant communities. C-S-R assumes that in high- disturbance (ruderal, R) patches or habitats, competition will be absent, o r low in intensity. Testing this is problematic because of the difficulty o f defining the intensity of competition, and we could find no rigorous evid ence to support or refute the prediction. The theory also implies that in h igh-disturbance habitats there will be no difference in species composition between 'competition' and 'stress sites, but from available evidence this does not seem to be true. C-S-R assumes that in stressful (S) habitats, com petition will be low. This assumption is difficult to define or test, becau se of the overall difference in plant growth rate between habitats. A predi ction From the theory is that in stressful habitats autosuccession should o ccur, i.e. that the climax species should regenerate directly. with no spec ialist secondary pioneer (R) species. There is some evidence that autosucce ssion occurs under the most extreme stresses of various types. Previous cri ticisms of C-S-R are evaluated. Only a few are considered valid, mainly tho se that emphasise that C-S-R theory is a considerable simplification of rea lity. Previous tests of C-S-R theory appear to be inconclusive. C-S-R theor y is basically a combination of r/K theory and Leaf Amortisation theory, We conclude that there is limited support for the C-S-R theory. Whether the g ain in generality that the theory offers justifies the loss via simplificat ion that it involves is still an open question. As formulated, it has limit ed utility as a predictive model in community ecology. Yet, it is currently the most comprehensive and coherent theory for community ecology.