Detection of Early Season Invasives (DESI) shows that climate and landscape sensitivity controls annual grass density in Utah’s national parks and monuments

Background/Question/Methods

Determining the environmental influences over invasion by non-native annual grasses is critical if we are to reduce the impacts of invasive grass-fire cycles in deserts. This is particularly important in the US National Parks and Monuments where post-fire landscapes reduce the services desired from these ecosystems. To conduct a landscape-scale analysis of annual grass invasion requires remotely sensing the presence and abundance of early season invasives and observing how their abundance changes from year to year and within a landscape. We investigated the interactions between climate and year-to-year changes in invasion of cheatgrass in southern Utah deserts using the USGS developed Detection of Early Season Invasives (DESI) software. DESI depends on the phenological differences between early season invaders such as Bromusspp. and native vegetation to estimate invader biomass. Coupling these remotely sensed estimates of invasive grasses with PRISM climate data layers for 2000-2010, we developed a statistical model of climate interactions with the expansion of invasives within six National Parks and Monuments in Utah. Maps of cover were compared to permanent plots within the Parks and Monuments.

Results/Conclusions

We observed substantial year-to-year variation in the cover of invasives. This interannual variation over the period of record produced core areas that were occupied by invasives every year with edge areas where the presence or absence of invasives was controlled by climate variables. Our statistical models suggest that the abundance of core area invasives is controlled by a suite of climate and landscape drivers that are different from those in the edge areas. The principle control over invasive cover is fall precipitation amount. Changes in cover can also be seen with changes in temperatures seasonally. There are some site differences among the selected study areas, which show that they potentially have other interactive effects determining the growth or decline of non-native annuals.