The effect of dominance by an alien grass species, Lehmann lovegrass, Eragrostis lehmanniana, on faunalpedoturbation patterns in North American Desert grasslands

Hupy, Christina M.

doi:10.1016/s0140-1963(03)00149-6

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“…In the semidesert grasslands of the Sonoran and Chihuahuan deserts, the introduction and spread of Lehmann lovegrass ( Eragrostis lehmanniana ) often results in a near replacement of diverse native bunchgrass communities [ Anable et al , 1992]. Lovegrass dominance strongly reduces desert grassland plant and animal diversity [ Bock et al , 1986], though this may vary regionally [ Hupy et al , 2004]. Lehmann lovegrass may better tolerate grazing and fire than most native species, and this may facilitate long‐term persistence and conversion of the ecosystem to a new steady state [ Anable et al , 1992; McClaran and Anable , 1992].…”

Section: Introductionmentioning

confidence: 99%

Carbon dioxide exchange in a semidesert grassland through drought‐induced vegetation change

et al. 2010

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Global warming may intensify the hydrological cycle and lead to increased drought severity and duration, which could alter plant community structure and subsequent ecosystem water and carbon dioxide cycling. We report on the net ecosystem exchange of carbon dioxide (NEE) of a semidesert grassland through a severe drought which drove succession from native bunchgrasses to forbs and to eventual dominance by an exotic bunchgrass. We monitored NEE and energy fluxes using eddy covariance coupled with meteorological and soil moisture variables for 6 years at a grassland site in southeastern Arizona, USA. Seasonal NEE typically showed a springtime carbon uptake after winter‐spring periods of average rainfall followed by much stronger sink activity during the summer rainy season. The two severe drought years (2004 and 2005) resulted in a net release of carbon dioxide (25 g C m−2) and widespread mortality of native perennial bunchgrasses. Above average summer rains in 2006 alleviated drought conditions, resulting in a large flush of broad‐leaved forbs and negative total NEE (−55 g C m−2 year−1). Starting in 2007 and continuing through 2009, the ecosystem became increasingly dominated by the exotic grass, Eragrostis lehmanniana, and was a net carbon sink (−47 to −98 g C m−2 year−1) but with distinct annual patterns in NEE. Rainfall mediated by soils was the key driver to water and carbon fluxes. Seasonal respiration and photosynthesis were strongly dependent on precipitation, but photosynthesis was more sensitive to rainfall variation. Respiration normalized by evapotranspiration showed no interannual variation, while normalized gross ecosystem production (i.e., water use efficiency) was low during drought years and then increased as the rains returned and the E. lehmanniana invasion progressed. Thus, when dry summer conditions returned in 2009, the potential for ecosystem carbon accumulation was increased and the ecosystem remained a net sink unlike similar dry years when native grasses dominated ecosystem structure.

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