Are productivity and richness related consistently after different crops in the Neotropics?

Abstract

To better understand the relationship between productivity and species richness after disturbance in the Neotropics, I tested two hypotheses using tree stem data collected in permanent plots set up after abandonment from agriculture. I found that (i) species richness had a significant positive relationship with productivity, where the slopes of the regression lines decreased over time for all fields taken together suggested the early upswing, leveling off, and later downswing of a unimodal curve; and (ii) this unimodal pattern held true both in the recovering sugarcane ( Saccharum officinarum  L.) and in the recovering banana ( Musa sp.) plantations. There was a delay, however, in the development of the unimodal pattern in the seeded pasture, perhaps due to root competition between the residual tussock grass ( Setaria sphacelata (Schumacher) Moss) and Neotropical tree seedlings. Taken together, the results imply that a unimodal model between productivity and species richness after agriculture may be independent of specific field conditions such as past crop and, therefore, represent a more universal ecological concept.