Respuesta de la vegetación leñosa del bosque seco tropical ante cambios en la frecuencia de incendios en la cuenca alta del río Magdalena

Abstract

In Colombia, the last two decades, the dry forests of the upper Magdalena river basin have been influenced by fire through fires of variable frequency. However, the response of these forests to the current fire regime, and specifically the effect of fire frequency on vegetation, is unknown. The response in the biodiversity attributes (composition, structure and functional traits) of the woody vegetation of the bs-T of upper Magdalena to four different frequencies of fire was evaluated. According to the Díaz map (2019), four frequency categories were determined for the 2000-2018 period: a) Nil: 0 Fires, b) Low 1 Fire, c) Intermediate: 2 to 3 Fires and High: ≥ 4 Fires. Three 10x100 m (0.1ha) vegetation plots were established in forests, for each category of fire frequency, and species, diameter at breast height, and plant heights> 10 cm in diameter were recorded in them. The functional traits that were used to define the functional diversity measures were obtained through a bibliographic review and include: foliar phenology, ecological union, regrowth capacity, type of seed storage, type of seed dormancy, basic wood density and foliar area specific. Structural, rich-diversity and functional analyzes were carried out. Attributes between categories of fire frequency were contrasted by means of three procedures: analysis of variance, analysis of indicator species, and multivariate analysis (principal components and multidimensional non-metric scaling). The results indicated that the taxonomic composition changes in forests with different frequencies of fire, and the alpha diversity of species is greater in the low frequency category, in contrast to the null or high frequency. In structural and functional terms, more heterogeneous forests, larger plants, and greater variability of attributes and traits were found in forests with low fire frequency. On the other hand, the high category showed more structural heterogeneity and functional diversity than the null category, which could be related to the role of fire in the renovation of environments. Thus, the present investigation showed that the bs-T in Upper Magdalena subjected to a low frequency of fire present a better response in the attributes of biodiversity (composition, structure and function) and behave according to the hypothesis of intermediate disturbance. , since the diversity is lower in areas with absence and high number of fires (> 1 fire in 18 years). Although it cannot be said that dry forests are adapted to fire, historically the inter-Andean valleys have been influenced by it, and this relationship could be conferring a certain tolerance to low frequency fires as they can behave as a dynamic disturbance.