Over large areas of California (southwest USA) grasslands dominated by non-native annual grasses have replaced native communities. Prescribed spring fires can temporarily reduce these annuals but does not usually result in re-establishment of native perennials. This study compared spring burning with solarization (i.e. plastic sheeting over an area of cultivated moist soil, trapping solar energy which eliminates most types of seed with moist heat) on establishment and growth of seeds and transplants of a native perennial grass (purple needlegrass Nassella pulchra) and California sagebrush Artemisia californica.
In March 2002, 192 (1 m2) plots were established in 10 areas dominated by ripgut brome Bromus diandrus (consistently 97% cover), five within and five outside (control) the region to be burned in April.
There were 48 fire plots (24 burn, 24 control) and 144 plots that received additional seeding treatments (no seed; Nassella pulchra seeded; and Artemisia californica seeded) and solarization treatment combinations (12 plots/treatment/seeding combination). Four 3 × 12 m plots were established for transplants.
Seed bank, seedling densities, percent cover and soil moisture (top 20 cm of soil) data were periodically collected to September 2003.
Burned areas had 96% fewer viable ripgut brome seeds, leading to replacement by forbs from the seed bank (almost entirely non-native annual black mustard Brassica nigra). In early spring, ripgut still dominant in unburned areas depleted soil moisture to a greater extent between rains than forbs in burned areas. However, ripgut died off early (April/May), leaving more moisture available in unburned areas after late-season rains.
N. pulchra and A. californica established far better on burn plots (60 and 40%), solarisation plots (80 and 15%) and burn + solarisation (75 and 40%) than on untreated plots (25 and <5%) respectively.
Burning and/or solarization produced conditions where some perennials (both native and non-native species) established. For native perennial, their relative contribution appears dependent on the species concerned. A drawback of solarization is that it is fairly costly.
If using or referring to this published study, please read and quote the original paper, this can be viewed at: http://onlinelibrary.wiley.com/doi/10.1111/j.1526-100X.2005.00084.x/full