Plant co-occurrence and functional trait data from drylands, along with soil, grazing pressure, and climate data

Plant functional traits can influence interaction outcomes between nurse
and target plants through a “functional trait match”, which occurs when
the traits of nurse plants ameliorate their environment, and target plants
possess traits that allow them to benefit from this ameliorated
environment. We investigated how the traits of putative nurse species
affect interaction outcomes across global drylands and determined the
functional match that promotes facilitation. We also investigated how
grazing pressure and global climatic and edaphic gradients affected this
trait match. We used a collaborative survey conducted across 29 sites from
five continents, where we gathered in situ co-occurrences of dominant
species (‘nurses’) and other vascular plant species, as well as their
functional traits [plant height and leaf dry matter content (LDMC)].
Climate, edaphic variables, and grazing pressure were measured in situ or
extracted from databases. We used a model-building approach to determine
the effect of dominant plant traits on interaction outcomes, and how the
functional trait match between nurse and target species is affected by
environmental variables. Tall dominant plants with conservative leaves
generally had a greater positive effect on species richness and cover
beneath their canopies, but these effects were strongly modulated by
grazing pressure and soil pH. Target plants that were significantly
associated with dominant plants tended to be shorter and have more
acquisitive leaves than dominant plants, regardless of environmental
conditions. However, the difference in height and LDMC between dominant
plants and negatively associated target plants was strongly affected by
environmental conditions. Functional traits play a significant role in
determining interaction outcomes between dryland plants. Facilitation in
drylands is driven by a conservative-acquisitive trait match, a pattern
observed regardless of grazing pressure, climate, and soil conditions.