Plant functional traits of 337 native Texas grasses

Premise: Understanding relationships among grass traits, fire, and
herbivores may help improve conservation strategies for savannas that are
threatened by novel disturbance regimes. Emerging theory, developed in
Africa, emphasizes that functional traits of savanna grasses reflect the
distinct ways that fire and grazers consume biomass. Specifically,
functional trade-offs related to flammability and palatability predict
that highly flammable grass species will be unpalatable, while highly
palatable species will impede fire. Methods: We quantified six culm and
leaf traits of 337 native grasses of Texas—a historical savanna region
that has been transformed by fire exclusion, megafaunal extinctions, and
domestic livestock. Results: Multivariate analyses of traits revealed
three functional strategies. ‘Grazer grasses’ (n=50) had culms that were
short, narrow, and horizontal, and leaves with high width:length and low
C:N—trait values that attract grazers and avoid fire. ‘Fire grasses’
(n=104) had culms that were tall, thick, and upright, and leaves that were
thick, with low width:length, and high C:N—trait values that promote fire
and discourage grazers. ‘Generalist tolerators and generalist avoiders’
(n=183) had trait values that were intermediate to the other groups.
Conclusions: Our findings confirm that the flammability-palatability
trade-offs that operate in Africa also explain correlated suites of traits
in Texas grasses. This highlights that the grass flora of Texas bears the
signature of Pleistocene megafauna and the influence of fires that predate
human arrival. We suggest that grass functional classifications based on
fire and grazer traits can improve prescribed fire and livestock
management of savannas of Texas and globally.