Embedding trait-based ecology within indigenous knowledge to advance sustainable management of Tibetan rangeland

On the eastern Tibetan Plateau, at three alpine meadow sites (A, B, and C) lightly grazed by livestock, we sampled and measured soil fertility [soil pH, soil organic matter (Soil_OM, g.kg-1), soil available nitrogen (Soil_AN, mg.kg-1) and phosphorus concentration (Soil_AP, mg.kg-1)], active burrow density of plateau pika (Pleteau_pika, N. 300m-2), ramet number (i.e. abundance, 0.25 cm2) of each functional groups (i.e. Forb_, Grass_, Sedge_, Legum_) and five key functional traits [mature height, specific leaf area (SLA, mm2·mg-1), leaf Nf dry matter content (LDMC, %), leaf nitrogen concentration (leaf N, mg·g-1) and phosphorus concentration (leaf P, mg·g-1)] for every plant community (CWM) within each of nine plots to detect trait-mediated, soil-plant-pika interactions.

We found that spatial variation in pika burrow density can be predicted by changes in soil fertility associated with shifts in plant functional groups and in community traits relevant to pika abundance. Specifically, in response to low available phosphorus on acidic soils, the density of pika burrows increased in plant communities characterized by shorter, slower-growing plants with higher foliar phosphorus content and with associated increases in forb and sedge abundance but decreases in grass abundance. Change in plant community traits were attributable not only to species turnover across study sites but also to within-species trait variation.

Pika outbreaks can be triggered by impoverishment of soil available phosphorus, which increases the quantity and quality of forage for pika while decreasing predation risk via changes in the functional structure of the plant community that are mediated by eco-evolutionary dynamics within sites. These results, which are in accord with indigenous knowledge, call into question government-led campaigns of pika extermination that are widely applied throughout the Tibetan Plateau, and suggest that maintaining levels of bio-available phosphorus coupled with a well-calibrated grazing rotation can provide bottom-up control of pika outbreaks in the Tibetan rangelands.