Do plants explore habitats before exploiting them? An explicit test using two stoloniferous herbs

We tested whether the processes of exploration and exploitation can be explicitly distinguished as plants grow and develop within a habitat using two stoloniferous clonal herbs, Hydrocotyle sibthorpioides (Umbelliferae) and Potentilla anserina (Rosaceae). Ramets were planted in four circular trays differing in diameter. One replicate from each diameter-group was sampled at intervals corresponding to plant coverage of the trays, and plant biomass allocation to leaves, stolons, and roots and internode length were quantified. For both species, at early sampling times (when the smallest trays were full), total plant biomass and ramet number were larger in the smaller trays than in the larger trays. However, this trend was reversed for plants collected at later times. For H. sibthorpioides, leaf mass ratios (leaf mass to total plant mass) were significantly greater, but stolon mass ratios (stolon mass to total plant mass) were less in the small trays than in the larger ones, particularly during the early stages of the experiment. Similarly, for P. anserina, leaf mass ratios decreased in the smaller trays but increased in the larger ones as the experiment progressed. Root mass ratios showed contrasting pattern to leaf mass ratios for both species; stolon mass ratios were significantly smaller in the smaller trays than in the larger ones, although there were no obvious patterns during the course of the experiment. In addition, for both species, internode length was shorter but the number of ramets was greater in the smaller trays at early sampling times. We conclude that plants invest greater biomass in resource-exploring organs (stolons) than in resource-exploiting organs (leaves or roots) as they initially establish in a habitat. The relatively lower plant productivity in the largest trays at early sampling times presumably reflects the cost of exploration prior to resource exploitation and utilization.