Distribution, abundance, and conservation status of threatened plant species in agricultural landscapes

Abstract

The transformation of natural ecosystems resulting from agricultural expansion and intensification constitutes one of the main threats to plant diversity. However, productive landscapes may retain vegetation remnants, ecological corridors, hedgerows, and other elements capable of providing habitats for threatened plant species. The objective of this research was to analyse the distribution, abundance, and conservation status of threatened plant species occurring in agricultural landscapes with different levels of transformation. Twenty-four landscape units classified into three agricultural intensity categories—low, medium, and high—were evaluated. Floristic sampling was conducted using 120 plots proportionally distributed among the study units. For each threatened species, presence, abundance, frequency, density, population structure, and habitat characteristics were recorded. Spatial configuration was analysed using geographic information systems and metrics related to natural vegetation cover, fragment size, edge density, isolation, and connectivity. A total of 2,846 individuals belonging to 32 plant species included in different threat categories were recorded. Low-intensity agricultural landscapes presented an average richness of 18.6 threatened species per unit, compared with 13.2 in medium-intensity landscapes and 7.8 in highly transformed landscapes. Mean abundance decreased from 168.4 to 72.7 individuals per unit. Natural vegetation cover was positively correlated with species richness (r = 0.81; p < 0.001), whereas isolation showed a negative association (r = −0.76; p < 0.001). Statistical models demonstrated that natural vegetation cover, connectivity, and landscape heterogeneity explained 79.4% of the variability observed in threatened species richness. It is concluded that agricultural landscapes maintain plant populations relevant to conservation; however, increasing intensification, fragmentation, and isolation significantly reduce their richness, abundance, and regeneration capacity. The conservation of natural remnants, ecological corridors, and diversified productive matrices constitutes a fundamental strategy for protecting threatened plant species within agricultural territories.