| Trees in pastures are 'recruitment foci' because they may attract seed dispersers and may provide deposited seeds with better growth conditions than those found in the open. Because trees vary in size, kinds of fruits produced, structure, etc., some trees may be better recruitment foci than others. In a Neotropical pasture, I studied seed arrival and species composition of woody plants under four tree taxa: Ficus species, Cecropia species, Cordia alliodora, and Pentaclethra macroloba. All trees received more seeds than open pasture, and Ficus trees received more seeds than Cordia trees, even while they were not fruiting. In active pasture (pasture grazed by cattle and managed by ranchers), more woody plants grew under trees than in the open. These recruits tended to be unpalatable, to 'hide' in unpalatable vegetation, to resprout after being cut by machete, or to reproduce clonally. They strongly influenced species composition of woody recruits after pasture abandonment, such that in both pasture phases four distinct patterns occurred: (1) Ficus plots were dense and species diverse, (2) Cecropia and Cordia plots were moderately dense and diverse, (3) Pentaclethra plots were dominated by Pentaclethra seedlings, and (4) open pasture plots had few recruits.;Abandoned pasture did, however, differ from active pasture. Because of the lack of cattle and management, abandoned pasture had approximately 1.5 times as many recruits and species as active pasture. Also, early-secondary forest species in some abandoned pasture plots grew rapidly, shading out grasses and producing fleshy fruits, thus effectively becoming additional recruitment foci. Because growth in plots of Cecropia, Cordia, and open pasture was more rapid than in plots of Pentaclethra and Ficus, the arrival, establishment, and growth of woody recruits in these plots was no longer influenced only by the studied trees, but also by vegetation growing around them. Because growth under Ficus was slow, Ficus trees are probably more important as keystone resources than as recruitment foci. Pentaclethra recruits, however, vigorously established and grew around parent trees, and thus will probably create patches of Pentaclethra trees in emerging forest. |
