Functional groups for response to disturbance in Mediterranean old fields

Experimental disturbance and fertilization in two Mediterranean old fields, three and nine years old, respectively, were used to identify functional g roups for response to disturbance. Five morphological traits (canopy struct ure, height, lateral spread, habit and plasticity) and five regeneration tr aits (life cycle, seed mass, fecundity, dispersal mode and germination seas onality) were used for species classification. Correlation patterns of spec ies composition and species attributes with disturbance treatments were ana lysed in order to characterize groups of response to disturbance. The class ification based on morphological traits was repeatable across fields and re flected natural correlation patterns among attributes. Erect rosettes with low morphological plasticity and moderate lateral spread, mostly grasses, w ere intolerant of disturbance. Partial rosettes with low morphological plas ticity and wide lateral spread, e.g. Asteraceae species, colonized disturbe d locations. Flat proto-rosettes with a plastic architecture were indiffere nt to disturbance in the young plot but required disturbance to establish i n the older plot. The classification based on regeneration traits repeatedl y identified germination period to be correlated with disturbance response. Species with early germination were intolerant of disturbance while late-g erminating species colonized disturbances. These groups were clearly distin ct from groups based on natural attribute correlation patterns which relate d primarily to seed mass, and secondarily to dispersal mode and fecundity. Effects of fertilization were detected only within disturbed quadrats of th e old plot. Fertilization favoured the colonization of disturbances by spec ies with a partial rosette and low plasticity and by species with late germ ination and high fecundity. These results, complemented by direct analyses on individual traits, are mo stly consistent with previous descriptions of the ruderal strategy. This st udy shows that additional understanding can be gained from a deductive appr oach that examines more specific traits such as derailed descriptors of pla nt architecture and seasonal germination dynamics. Our results are intended to contribute to the general discussion on the identification and use of f unctional classifications. In particular, it is argued that communities suc h as Mediterranean old fields, where the dynamics is already well understoo d, should serve as testing grounds for new methods and the development of t heories to be later applied to less well known vegetation types.