Diversity-Productivity Relationship in the Northeastern Tamaulipan Thornscrub Forest of Mexico

This research examines the diversity-productivity relationship in a semiarid scrubland, initially under late successional conditions and subsequently under early successional conditions created by experimental clearing, to explore the roles that productivity and stochastic mortality play in species exclusion in this environment. A total of fifteen plots were studied by measuring environmental conditions and biomass components of shrubs and seedlings. These stands were distributed along a productivity gradient across five different landforms. A hypothesis about the stochastic self-thinning mortality model along the gradient was evaluated with the diversity-productivity-environment data. The diversity-productivity relationship was linear and reversed between the early and late succession stages. The hypothesis of stochastic mortality of species exclusion was rejected in the early stages of succession and partially accepted in the mature stage of succession. Species exclusion was negatively related to productivity gradients, suggesting that strong interspecific competition occurs in high productivity plots and that a larger number of species can survive in higher abiotic stress landscapes. Further research is needed to understand the temporal and spatial variations of the ecological interactions that shape this plant community. 1. Introduction Environmental gradients offer ideal conditions for exploring the interactions between evolutionary adaptations and ecological processes over short spatial distances. Productivity [1], temperature [2], evapotranspiration [3], and the energy and water balance [2] are potential drivers of species diversity that can vary significantly over short distances, within the dispersal range of a species pool. However, local regional peculiarities such as fires, land use, or drought may obscure interpretation of the response of species diversity to environmental gradients. Productivity is probably the single most important and most studied driver of species diversity because it is a function of several other critical factors such as the energy and water balance, evapotranspiration, and temperature [1–3]. Productivity is defined as the amount of plant mass produced over a certain time in a given area. Productivity is influenced by genetic adaptations and site environmental factors. Plant productivity is technically defined as net primary productivity or NPP, which is the difference between photosynthesis (gross primary productivity) and the total respiration of plants in an ecosystem. Both components are difficult to measure in