PLANT FUNCTIONAL TYPES AND ECOLOGICAL STRATEGIES IN PATAGONIAN FORBS

We identified four major functional types of forbs in the Patagonian steppe, taking into account phenological and morphological traits: (1) shallow-rooted mesophytic species (annuals), (2) shallow-rooted non-mesophytic species, (3) deep-rooted evergreen species, and (4) deep-rooted deciduous species. The major attributes differentiating these groups were the date at which seasonal growth ended, rooting depth, sprouting depth, distance between shoots of the same plant, and degree of 'mesophytism'. We used Cluster and Principal Components Analyses to identify the groups, and the attributes determining them. Late-growth-cycle types had deep roots and/or high 'xerophytism'. Late-cycle-xerophytic types had a great sprouting depth, and late-cycle-deep-rooted types had a great distance between shoots of the same plant. On the basis of current knowledge of the structure and functioning of the Patagonian steppe, we suggested three explanations to account for these correlations. 1. Late-cycle forbs survive summer water deficit if they have xerophytic characteristics that reduce transpiration water losses, and/or they have deep roots that increase water uptake. 2. Sprouting depth results from the shift of active buds to dormant buds at the end of the cycle. Summer forbs have a great sprouting depth because only buds which are located deep in the soil survive hot and dry summers. 3. Distant shoots of summer forbs allow them simultaneously to use the high protection against desiccating winds provided by shrubs, and the ample water availability of bare soil patches. All the functional types of forbs depend on winter water recharge to begin their cycles, but each one completes its cycle by using a different portion of the water resources available in spring and summer.