Influence of resource pulses and perennial neighbors on the establishment of an invasive annual grass in the Mojave Desert

Abstract

Invasion by exotic annual grasses is one of the most significant threats to arid ecosystems in the western USA. Current theories of invasibility predict plant communities become more susceptible to invasion whenever there is an increase in the amount of unused resources. The objective of this field study was to examine how resource pulses and temporal variation in resource demand by the native shrub vegetation influences establishment of the invasive annual grass Schismus arabicus. Water and nitrogen were applied as pulses in early spring, mid-spring, or continuously throughout the growing season to plots containing either Atriplex confertifolia or Atriplex parryi shrubs. The effect of resource pulses on Schismus density and biomass was highly dependent on the seasonal timing of the resource pulses and the identity of the neighbor shrub. When resource pulses coincided with high rates of resource capture and growth of the native vegetation, density and biomass of Schismus was reduced. Schismus establishment was greater under continuous resource supply compared to pulsed resource supply, likely because more soil resources were available at a shallow depth when resources were supplied at a continuous low rate. These results suggest that the establishment of invasive annual grasses in arid systems can be influenced by the magnitude and spatial distribution of resource pulses in addition to the seasonal timing of resource pulses. r

Responses of native and non-native Mojave Desert winter annuals to soil disturbance and water additions

“…However, these effects would need to be balanced with the potentially positive influences (e.g., shading) of the shrubs on Schismus, suggesting that competition studies would be necessary to achieve an accurate mechanistic understanding of species interactions and their roles in plant community invasibility. Although we did not experimentally manipulate N levels, soil N has been suggested to be a co-limiting factor for non-native plant establishment in the Mojave Desert (Brooks 2003;Rao and Allen 2010;James et al 2006). Nitrogen is typically more available following pulses of precipitation, which increase mineralization and nutrient supply to roots (Fisher et al 1987).…”

“…Species-specific patterns of germination for desert native and non-native winter annuals have been demonstrated in field conditions in response to water manipulations (Gutierrez and Whitford 1987;Pake and Venable 1995;James et al 2006), suggesting that changes in the amount and timing of precipitation pulses could have major effects on population dynamics and plant community composition. For example, Adondakis and Venable (2004) found heterogeneous germination responses to environmental conditions in a guild of Sonoran Desert winter annuals.…”

Weed Flora of Citrus Orchards and Factors Affecting its Distribution in Western Mediterranean Region of Turkey

“…A recent study also reported the dominance of annuals in citrus orchards surveyed in a neighboring province (Arikan et al, 2015). The variation in weed density and coverage areas can be explained by heterogeneity in soil properties and microclimatic conditions (Gaston et al, 2001;James et al, 2006). Spatial variation of soil properties is affected by inherent soil characteristics such as particle size distribution (sand, silt and clay content), ground water availability, topography and management practices (Alignier et al, 2012;Shehata et al, 2015).…”

Short-term soil inorganic N pulse after experimental fire alters invasive and native annual plant production in a Mojave Desert shrubland

“…Subsequently, early spring precipitation (February and March) was sufficient to stimulate germination and establishment very late in the growth season. The late season precipitation patterns can afford advantages to different functional groups depending on the timing and the amount of resources available during the pulse versus inter-pulse periods (James and Richards 2006;James et al 2009). Invasive Mojave Desert annuals have the potential to use water and N more rapidly than native annual species (DeFalco et al 2003); however, invasive annuals established in response to later season rainfall have less competitive potential (James and Richards 2006;DeFalco et al 2007).…”

“…Desert fires reduce the abundance of perennial vegetation (Brown and Minnich 1986), thus increasing soil resource availability for alien annual species. Alternatively, Schismus abundance can be affected by the timing and amount of moisture and N pulses, and on the phenological status of neighboring native shrubs (James et al 2009). Thus, pulse dynamics, timing of resource availability, and the condition of the plant community all play roles in the trajectory of vegetation communities.…”