Sedgwick Reserve

20 Jun, 03 AM - 22 Jun, 10 AM

Many exotic species rise to dominance following human manipulations of the landscape that either increase resources, like fertilization, or disturb the current patterns of resource use. Once these invaders are present in an ecosystem, however, natural sources of altered resource patterns may allow exotic species to persist despite competition from natives. Savanna trees, such as the oaks in California grasslands, form "islands of fertility" within the local matrix that may play a large role in structuring the patterns of native and exotic grasses. Identifying the extent to which oak trees are associated with exotic species and the mechanisms maintaining these patterns is critical for both land management and restoration goals. The objective of this study is to compare the understory vegetation of Sedgwick's three different oak species with and without grazing and to identify the extent to which past and present oak canopies of all species serve as preferential habitat for aggressive grassland invaders. This project will answer the following questions: (1) What are the effects on the three oak species on vegetation composition and soil properties beneath their canopies? (2) Do these properties differ between grazed and ungrazed areas? (3) How long after oak death do these changes persist? (4) What are the mechanisms responsible for reduced Nassella and Poa abundance beneath oak tree? To answer the final question, I will be initiating the transplant study described in brief in the original project description. The growth and phenology of Nassella pulchra and Poa secunda will be examined in a set of factorial treatments in order to determine the mechanisms contributing to their absence nearby or under oak trees. The treatments will cover 2 habitat types (under oaks and open grassland), 3 densities of Bromus diandrus (none, low and high) and two soil types (under oaks and open). I will be transplanting grasses in 5 paired sites on both the Mesa and in Figueroa, one site beneath a Quercus lobata and one outside the canopy relatively near. The transplants will be done in 2.5 x 2.5 m blocks, one in each habitat. Before digging holes, I will clear the block of thatch and litter then use a gas-powered auger to drill 36 holes 10 cm in diameter and 30 cm deep. The soil will be harvested, stored and used later to plant the seedlings. All the seedlings will be grown in a campus greenhouse from seed harvested from the Mesa and Figueroa, and the soil used will also only be soil form the reserve. The Bromus diandrus seed used to create the competitive treatments has also been collected from the reserve. I intend to have the plants in the ground several weeks after the first rain of the year. Before my first day of excavation I will provide (by e-mail or hard-copy in the office) a map of the locations. Throughout the next year and a half seedlings will be surveyed approximately once a month for survival and their height and bunch width measured. Any reproductive organs will be noted and all seeds will be harvested and weighed (if any). The final analysis should be able to relative the fitness and growth of two important natives to variation in abiotic environment, soil and competition, and hopefully be able to distinguish one as a mechanism limiting the growth of natives under oak trees.

Visit #25465 @Sedgwick Reserve

Approved

Under Project # 9731 | Research

Natural heterogeneity and the structure of invaded communities: the role of oaks in California grasslands

faculty - University of California, Santa Barbara

Reservation Members(s)

Karen Stahlheber Jun 20 - 22, 2011 (3 days)
Karen Stahlheber Jun 20 - 22, 2011 (3 days)

Reserve Resources(s) | Create Invoice

Ranch House Not Available 2 Jun 20 - 22, 2011