Spatial and climatic patterns of the relative abundance of poisonous vs. non-poisonous plants across the Northern Tibetan Plateau.

It is the most serious challenge to promote degraded grassland recovery currently facing the developing Tibetan Autonomous Region. We conducted field surveys of 75 grazing sites between 2009 and 2012 across the Northern Tibetan Plateau and described the spatial and climatic patterns of the occurrence of poisonous plants. Our results showed lower ratios of species richness (SprRatio), coverage (CovRatio), and biomass (BioRatio) of non-poisonous vs. poisonous plants in the semi-arid alpine steppe zone, where the growing season precipitation (GSP) is between 250 and 350 mm; however, this result is in contrast to the relatively wetter meadow (GSP >350 mm) and much drier desert-steppe (GSP <250 mm) communities. Results from generalized additive models (GAMs) further confirmed that precipitation is primarily responsible for the initially decreasing and then increasing tendency of compositional ratios of non-poisonous to poisonous species. The wide confidence bands at GSP <250 mm indicated that precipitation is not an effective indicator for predicting compositional changes in desert-steppe communities. When mean annual livestock grazing pressure was incorporated into the optimal GAMs, the model performance improved: the Akaike information criterion (AIC) decreased by 1.20 for SprRatio and 3.09 for BioRatio, and the deviance explained (R (2)) increased by 6.0% for SprRatio and 3.6% for BioRatio. Therefore, more detailed information on grazing disturbance (timing, frequency, and density) should be collected to disentangle the relative contribution of climate change and grazing activities to changes in community assembly and ecological functions of alpine grasslands on the Northern Tibetan Plateau.