Effect of induced warming on seedling emergence of Tamaulipan thornscrub at northeastern Mexico

Abstract

We carried out two experiments to test the effect of temperature increase and distance to the edge of remnant vegetation on seedling emergence, speed of seedling emergence, and seedling species diversity from Tamaulipan thornscrub. We carried out one experiment during the dry period, and a second one in the rainfall season. For both experiments, we collected 60 soil samples of 30 × 60 cm by 4 cm depth in a remnant Tamaulipan thornscrub fragment, from 5 m from the edge to the interior of remnant vegetation in a grid of six columns (15 m apart) per 10 rows (17 m apart). We divided each sample into two. One was set to grow in trays inside six acrylic open-top chambers (OTCs) to simulate global warming and the other in trays next to them, outside the OTCs. Mean temperature was 1 °C higher inside OTCs during the irrigation experiment and 2 °C higher during rainfall trial. We used generalized linear mixed models (GLMM) with Poisson link distribution to determine if there was an effect of the increase in temperature on the number of seedlings and species. Number of seedlings and species were similar inside and outside OTCs during irrigation trial, but there were more species and seedlings outside OTCs during the rainfall trial. For both experiments, speed of seedling emergence was similar inside and outside OTCs. Increased temperature affected number of seedlings and species, diversity, and abundance more than distance to the edge of the thornscrub fragment. Simulated warming under rainfall seems to decrease number of species, diversity, and abundance of seedlings; however, this difference could be due to other aspects not considered in this study. Further studies might consider seed dormancy and viability variations in the soil seed bank throughout the year.