Angelo Coast Range Reserve

14 Feb, 03 AM - 15 Feb, 11 AM

The observation that some plant communities contain more non-native species than others has important implications for community ecological theory and for management decision-making. The degree to which a site is invaded is determined by two factors: the rate of exotic species arrival (propagule supply) and the biotic and abiotic site characteristics that determine invader success (ecological resistance). Although a number of studies have experimentally manipulated elements of resistance and documented their effects on the success of invading species, relatively few have manipulated propagule supply or tested for interactions between the two. We evaluated the importance of propagule supply and 'resistance' in determining invasion success of the exotic perennial grass Holcus lanatus in California coastal prairie. For two years we decreased competition from resident plants by clipping background vegetation and increased water availability while adding Holcus seeds at four densities. Reduced competition positively affected Holcus seedling establishment in 2002 but not in 2001 while watering caused an increase in total Holcus seedling numbers in both years. Nonetheless, even in watered plots most seedlings died before the end of the summer drought typical of this region, apparently of water stress. The relationship between propagule supply rate and seedling numbers was positive, with decreasing slope at higher values, suggesting a threshold value of seed rain above which seedling numbers saturate. There was no significant interaction between propagule supply rate and manipulation of competition or abiotic stress (watering). It seems likely, however, that the abiotic resistance of low water availability in this site is too strong to be overcome by any level of propagule supply. In other systems, propagule supply and resistance may be more likely to interact. We continue to monitor these plots for further Holcus recruitment from added seed. Furthermore, we have been monitoring the responses of the natural plant community to these watering treatments, with quarterly sampling of plant production and composition. We are also taking soil samples to evaluate standing pools of N at these timepoints. I assist Blake Suttle with some of this sampling. Finally, I am investigating how predicted increases in mean annual rainfall in northern CA may affect soil carbon pools in northern CA coastal prairie grasslands. To do so, I am making measurements every month and a half of soil carbon dioxide efflux using a Licor 6400.

Visit #5176 @Angelo Coast Range Reserve

Approved

Under Project # 4062 | Research

South Meadow vegetation responses to rainfall manipulation

graduate_student - University of California, Berkeley

Reservation Members(s)

Group of 3 Other Feb 14 - 15, 2004 (2 days)

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Wilderness Lodge 3 Feb 14 - 15, 2004