Plant functional traits of 337 native Texas grasses
Data files
Dec 24, 2024 version files 25.70 KB
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Dryad_dataset_Nerlekar_et_al._2025_AJB.csv
22.58 KB
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README.md
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Abstract
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.
README: Plant functional traits of 337 native Texas grasses
https://doi.org/10.5061/dryad.9s4mw6msf
Description of the data and file structure
Maximum culm height—(cm) is the maximum attainable height of the grass culm. Because maximum culm height for many species is not accurately reflected in herbarium specimens, we extracted data from Silveus (1933), Gould (1975), Shaw (2011) and Clayton et al. (2016).
Culm diameter—(mm) is the diameter of the internode of the culm at its widest point. At the S. M. Tracy herbarium, Texas, we measured one randomly selected culm per specimen using a digital micrometer (Mitutoyo 293-344-30 Digimatic Micrometer, 0.001 mm precision) positioned at the thickest part of the second long internode following standard protocols (Wigley et al., 2020). In cases where the culm was not round, we measured the shortest dimension.
Culm angle—(no units, categorical variable) is the angle between the grass culm and the soil surface. We extracted culm angle data from published literature [Silveus (1933), Gould (1975), Shaw (2011) and Clayton et al. (2016)]. From the species’ descriptions, we coded the culm angles following the classification of Hempson et al. (2022): ‘spreading’, ‘creeping’, ‘prostrate’ = 1; ‘spreading to ascending’, ‘spreading to geniculate’, ‘creeping to ascending’, ‘creeping to geniculate’ = 2; ‘geniculately ascending’, ‘decumbent’, ‘geniculately ascending and/or decumbent’, ‘erect or spreading’, ‘erect or prostrate’ = 3; ‘erect or geniculately ascending’, ‘erect or decumbent’ = 4; ‘erect’ = 5. Thus, culm angle values range from 1 to 5, representing prostrate horizontal angle (1) to an erect vertical angle (5).
Leaf W:L *(no units)—*is the ratio of the width measured at the widest portion of the leaf to the maximum length of the leaf. Because literature-derived measurements are a good proxy for (and ultimately derived from) herbarium specimens (as in Jardine et al., 2020), we extracted leaf dimensions from published literature [Silveus (1933), Gould (1975), Shaw (2011) and Clayton et al. (2016)].
Leaf thickness *(mm)— is the distance between adaxial and abaxial surfaces of the leaf measured just near (not at) the midrib. From each specimen we rehydrated leaf sections for 24 hours in distilled water (Jardine et al., 2020) and then measured the thickness with a digital micrometer (*Mitutoyo 293-344-30 Digimatic Micrometer, least count = 0.001 mm).
*Leaf C:N *(no units)—is the ratio of carbon to nitrogen in leaves. Due to the large number of samples (N= 996), we contracted four labs [Stable Isotopes for Biosphere Science Lab, Texas A&M University (427 samples); Cornell Isotope Lab, Cornell University (104 samples); Stable Isotope Ratio Facility for Environmental Research, The University of Utah (289 samples); Boston University Stable Isotope Laboratory, Boston University (176 samples)] to measured leaf C and N of leaf sections taken from herbarium specimens at the S. M. Tracy Herbarium.