Rainfed agriculture and firewood extraction modify differently the taxonomic and functional structure of biocrusts in a tropical semiarid region

Abstract

In temperate arid regions, livestock production and irrigation agriculture are known to alter the taxonomic and functional structure of biocrusts. However, the effect of land use on biocrusts has not been evaluated in tropical semiarid regions. This study evaluated the effect of rainfed agriculture and firewood extraction on the taxonomic and functional structure of biocrusts in a tropical semiarid region of Central Mexico. We collected biocrusts in sites of rainfed agriculture and firewood extraction to identify species by morphology and then, to count the number of species and to estimate the cover of total biocrust, taxonomic groups (cyanobacteria, lichens, and bryophytes), and functional groups (cyanobacteria with and without heterocysts, chlorolichens, cyanolichens, and bryophytes). In addition, we analyzed the relationship between the cover of total biocrust, taxonomic, and functional groups, and vegetation and soil traits of sites of rainfed agriculture and firewood extraction. In sites of rainfed agriculture, biocrusts had 14–18 species, with 50–70% cover, and were dominated by cyanobacteria with heterocysts. Biocrusts were associated with high bare soil cover and compact soil with a high pH. In sites of firewood extraction, biocrusts had 23–29 species, with 70–90% cover, and were dominated by cyanolichens and bryophytes. Biocrusts were associated with soils with high infiltration and nutrient content. These differences suggest that rainfed agriculture has negative effects on biocrusts, similar to the effects of livestock production and irrigation agriculture in temperate arid regions. In comparison to rainfed agriculture, firewood extraction had less detrimental effects on biocrusts.