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Climate anomalies provide opportunities for large-scale mapping of non-native plant abundance in desert grasslands

Huang, Cho-ying, Geiger, Erika L.
Diversity & distributions 2008 v.14 no.5 pp. 875-884
Eragrostis lehmanniana, arid zones, biomass, dormancy, grasslands, indigenous species, introduced plants, linear models, moderate resolution imaging spectroradiometer, phenology, plant communities, regression analysis, remote sensing, seeds, tissues, vegetation index, Arizona
Native plant communities are susceptible to climate anomalies, which would favour the invasion of non-native species. However, climate anomalies may also provide opportunities for detecting non-native plants at a regional scale using remote sensing. Based on this mechanism, we propose a direct and effective remote sensing approach to map the abundance of South African Eragrostis lehmanniana Nees (Lehmann lovegrass), a highly invasive, non-native plant in the desert grasslands of southwestern North America. The desert grassland of Fort Huachuca Military Reservation (31°34'N, 110°26'W) in southern Arizona, USA. Simple linear regression models were used to examine the relationships between additional (comparing to the normal level) remotely sensed greenness (delta Enhanced Vegetation Index (ΔEVI) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS)), and field actual (g m⁻²) and percentage (%) biomass of E. lehmanniana in an abnormal wet, cool period in October 2000. There was a strong and positive agreement (P < 0.005) between ΔEVI and field observations (R² = 0.72 and 0.64 for actual and percentage biomass of E. lehmanniana, respectively). These relationships allowed us to estimate the abundance of E. lehmanniana in the desert grassland. Phenology of native grass communities is quite similar to systems dominated by E. lehmanniana but responses differ when there are substantial amounts of precipitation in cool seasons. Eragrostis lehmanniana can produce significant amount of new tissues and seeds with sufficient cool season moisture, while native grasses are still in senescence or dormancy. Therefore, amplitude of ΔEVI during wet, cool seasons would indicate the abundance of E. lehmanniana. Long-term climate records denote an amplification of cool season precipitation in the southwestern USA. This regional climatic trend should allow us to monitor E. lehmanniana and possibly other non-native species frequently in this vast arid region.