The influence of seasonal precipitation and grass competition on 20 years of forb dynamics in northern Chihuahuan Desert grassland

Abstract

Aims In arid grasslands forbs represent a large component of species diversity and provide a key resource for pollinators and consumers. However, low abundances and high temporal variability make it challenging to successfully predict forb presence and abundance from 1 yr to the next. In this study we: (1) characterize patterns of semi‐arid forb diversity and abundance over time; (2) determine the relative importance of direct vs indirect (via grass competition) effects of precipitation on forb richness and abundance; and (3) separate the effect of precipitation timing on forb community composition from the effects of precipitation amount and season. Location Semi‐arid grassland, Sevilleta National Wildlife Refuge, Socorro County, central New Mexico, USA. Methods We analysed forb dynamics along two 400‐m long line‐intercept transects in response to inter‐annual and seasonal precipitation variability and abundance of perennial grasses using a unique 20‐yr species composition data set from ungrazed native grassland in the northern Chihuahuan Desert. Results Forb richness and cover were significantly positively associated with precipitation across seasons. Total richness was high across the time series but substantially lower within any given year. A direct, positive effect of precipitation overrode any potential negative, indirect effect via grass competition. Although aggregate forb responses were strongly linked with precipitation, individual species responses were highly variable and generally not linked with either precipitation timing or season. Conclusions In the hotter, drier climate predicted by meteorological models for the US southwest, forbs may be negatively impacted if winter moisture decreases and monsoon precipitation becomes more variable. On the other hand, the flexibility exhibited by forbs in germination and establishment throughout the growing season may help buffer some common species to increased inter‐annual precipitation variability.

Press–pulse interactions: effects of warming, N deposition, altered winter precipitation, and fire on desert grassland community structure and dynamics

“…Following the fire, forb ANPP was highest on the warmed, fertilized plots that received additional winter rain. Forb richness and ANPP in this Chihuahuan Desert grassland are tightly correlated with soil moisture accumulated during winter and spring precipitation events (Xia et al ., ; Mulhouse et al ., ), but grass ANPP is driven primarily by soil moisture derived from monsoon precipitation (Muldavin et al ., ). Thus, winter moisture is more likely to affect forb rather than grass richness and ANPP.…”

Assessing community and ecosystem sensitivity to climate change – toward a more comparative approach

“…Mulhouse et al. () use long‐term monitoring of plant communities to assess community dynamics in response to precipitation patterns. Sternberg et al.…”

“…On the other hand, Mulhouse et al. () do not use the term at all, and Sternberg et al. () discuss sensitivity, but not with regard to their results.…”

“…the lack thereof), both Mulhouse et al. () and Sternberg et al. () focus on terms such as ‘resistant’ and ‘buffering’.…”

Precipitation reduction alters herbaceous community structure and composition in a savanna

“…For the growth forms, precipitation reduction significantly reduced average height, percentage cover, and the relative abundance of graminoids, and significantly elevated those of forbs and legumes. These findings suggest that forbs and legumes may be more resistant to drought due to different root traits (Chelli et al., ; Mulhouse, Hallett, & Collins, ; Tetetla‐Rangel, Dupuy, Hernández‐Stefanoni, & Hoekstra, ). The graminoids in this savanna ecosystem belong to the shallower‐ and fibrous‐rooted species, whereas the forbs and legumes belong to taproot species (Jin et al., ; Jin, Li, Liu, Liu, Zhang, Song, et al., ).…”