Effects of early season defoliation on above-ground growth of Anthyulis cytisoides, a Mediterranean browse species

Anthyllis cytisoides L. is a traditional forage species, well adapted to grazing pressure, and so might be expected to respond positively to moderate grazing. We performed a hierarchical design analysis of variance with three levels of plant defoliation (10, 50 and 90%) and three of stem defoliation (10, 50 and 90% of shoots removed), in three age classes based on trunk base perimeter (less than or equal to 11 cm, 11-20 cm and > 20 cm). Response to herbivory was measured as total vegetative length, inflorescence length, leaf number, flower number, and the ratio of the number of floral axes to the total number of axes. We found that A. cytisoides compensated for herbivory. That is, aboveground growth of A. cytisoides increased with the percentage of plant defoliation, with respect to elongation of the stem and increase in the total flower and leaf number. In contrast, growth following stem defoliation declined in the target stem as stem defoliation increases. Stem defoliation effect was more evident in young plants than in older ones. The increase in plant growth with plant defoliation was seen both in the average growth per floral axes and the number of floral axes per stem. However, only the number of floral axis per stem was responsible for the reduction in stem productivity with experimental defoliation. Stem overcompensation (greater elongation in defoliated stems than control) occurred only in stems suffering 10% defoliation when plants were under medium and high experimental herbivore pressure, indicating the ability of A. cytisoides to produce a compensatory response to herbivory. The growth consequences of early season defoliation persist after two growing periods, increasing above-ground growth differences among treatment groups. (C) 1997 Academic Press Limited.