Deutschman Lab - San Diego State University

The grasslands of today's California valleys and coasts stand in stark contrast to the verdant and diverse paradise described by the early missionaries who were some of the first to leave written comments on the high quality, astounding diversity and riotous wildflower displays of the native grasslands. Piecing together reports from 18th century missionaries, soldiers, and early ranchers, vast areas of early California rangeland were teeming with nutritious and diverse native plants that made cattle the most lucrative resource in the state until the discovery of gold. The composition of these early grasslands has been a matter of considerable debate, but was most likely a mix of perennial native grasses such as Stipa pulchra, Leymus triticoides, and Carex spp. as well as a wide range of native annual herbaceous and bulb species, many of which are now considered sensitive or rare and draw visitors from far afield in good wildflower years. In contrast, a survey from today's botanists and ranchers would be hard-pressed to find more than remnant populations of similarly diverse native rangelands, although restoration efforts are increasing their numbers. In fact, California's native grasslands are one of most threatened ecosystems and one that urgently needs restoration and further study.

The purpose of this research is to test the effectiveness of treatments that have been used in mainland California to restore burned San Clemente Island grasslands. Specifically, the project will attempt to determine the extent to which techniques such as seeding, irrigation, and weed control increase native cover and/or decrease non-native cover on burned grasslands. These data will be used to inform future restoration efforts in San Clemente Island grasslands to improve habitat for listed and rare taxa and return some of California's valuable grasslands to a more healthy and diverse state. In order to address each of the three primary challenges to grassland restoration (seed limitation, competition between native and invasive species, and the effects of climate), a combination of treatments will be applied.

Research Hypotheses

1. If the island's native species are seed limited, then seed addition should result in an increase in native species richness and percent cover, which may or may not be accompanied by a commensurate decrease in non-native abundances.

2. If competitive dominance of the invasive grasses is the driving force behind their prevalence, aggressive weed control should result in a decrease of non-native abundance accompanied by an increase in native abundance.

3. Supplemental irrigation in this project will interact with the seeding and weed control treatments in different ways. Adding supplemental water to the system eliminates moisture as a limiting resource by ensuring that the treatments receive sufficient irrigation to maximize germination rates and aspects of growth that tend to be water-limited. In the seeding treatment, newly germinated native seedlings will have an increased chance of establishing and contributing to the native seed bank, leading to an increase of natives over time. The increased water is anticipated to flush larger quantities of seeds out of the non-native seed bank, which may result in a stronger effect of competition, but in plots with weed control, this effect will decrease over time as the seed bank fails to replenish.

Lead Biologist: Emily Howe