Flowering under stress: Reproductive strategies of black grama and mesquite in a water-limited ecosystem

Authors: Browning, Dawn; Yeater, Kathleen; James, Darren; Baca, Ruben; Denham, Sander

Submitted to: American Geophysical Union Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 10/1/2025
Publication Date: 12/19/2025
Citation: Browning, D.M., Yeater, K.M., James, D.K., Baca, R.A., Denham, S.O. 2025. Flowering under stress: Reproductive strategies of black grama and mesquite in a water-limited ecosystem. American Geophysical Union Meeting Abstract. Abstract.

Interpretive Summary:

Technical Abstract: Background/Methods Niche partitioning is a key mechanism proposed to explain the coexistence of perennial grasses and deciduous shrubs in rangeland ecosystems. While spatial resource partitioning has been well-studied, temporal partitioning related to phenology remains less explored. Reproductive phenology, particularly flowering and fruiting, is a critical functional trait that affects species persistence and ecosystem function. This study evaluates temporal niche partitioning between black grama (Bouteloua eriopoda) and mesquite (Prosopis glandulosa) in a desert grassland in southern New Mexico. From 2013 to 2024, we made weekly field observations on five individuals per species using standardized protocols from the U.S. National Phenology Network. We quantified the timing, duration, and abundance of flowering for each species. Linear mixed models (SAS 9.4, PROC MIXED) assessed the effects of species, year, and their interaction on flowering duration (weeks) and number of flowers. Species and year were fixed effects, with year treated as a repeated effect and individual plants as subjects. Type III tests of fixed effects were used to determine statistical significance. Results/Discussion Mesquite produced more flowers on average and exhibited greater interannual variability in flower production compared to black grama (F = 21.38, p = 0.008). Significant species × year interactions were detected for both flowering duration and flower abundance. Mesquite flowered significantly longer (5.67 ± 0.31 weeks) than black grama (3.23 ± 0.31 weeks; F = 30.89, p < 0.001). Flowering times were distinct, with black grama flowering later (DOY 235–276) than mesquite (DOY 125–186), indicating strong temporal separation. Flower production for black grama was more sensitive to drought, producing no flowers in 2020 and 2024, whereas mesquite flowered every year despite high interannual variability in rainfall amount. A positive correlation (r = 0.60) was found between annual precipitation and black grama flower production, but no correlation was observed between precipitation and flowering duration for either species. These findings suggest that mesquite may be less reliant on current-year precipitation for reproduction, while black grama’s reproductive success is more drought-sensitive. Ongoing work will examine the roles of soil moisture, vapor pressure deficit, and rainfall patterns to better predict reproductive phenology in these species. Understanding these drivers is essential for forecasting forage availability and maintaining ecosystem stability in arid rangelands.