Functional structure of an arid steppe plant community

Abstract Questions (1) How do community‐weighted mean (CWM) trait
values of 23 functional traits measured on 34 plant species vary along
a gradient of aridity under grazed and ungrazed conditions in an arid
steppe? (2) How does variation in our CWM trait values differ from
those of more mesic grasslands? Location Eastern Morocco. Methods We measured relative abundance and functional traits along a
short aridity gradient over two consecutive years at five heavily
grazed sites, each with an exclosure preventing grazing. We analysed
the relationship between aridity, grazing, and the expression of CWM
trait values using ordination methods and a fourth‐corner analysis. Results Unconstrained and constrained ordinations identified three
distinct suites of temporally consistent functional traits that
co‐varied with aridity and grazing, and the fourth‐corner analysis
identified a number of significant but weak trait–environment
associations. Grazing selected for short, fast‐growing annual species
with high SLA, high pastoral value and low seed mass, while aridity
selected for species possessing succulent leaves with high δ13C leaf
content, spines, low LDMC and short stature, although the relative
importance of precipitation and grazing changed between years. Conclusions Although distinct from more mesic grasslands, our study
sites exhibited patterns of trait correlations that were similar to
the worldwide leaf economics spectrum. These correlation patterns
represented three groups that were reminiscent of Grime’s C‐S‐R model.
Direct ordinations supported this interpretation. Temporal variation
in our results was due in part to precipitation fluctuations. Our
results also indicated selection for a grazing avoidance strategy
under heavy grazing. Integrating plant functional traits in
conservation and management of arid ecosystems represents a novel and
challenging task to ensure more sustainable use of these lands.