Ecological filters are abiotic factors, such as limited rainfall, and biotic factors, such as competition, that over time reduce the number of species that can survive at a given site. The filters acting on a restoration site generally differ from those acting on a naturally regenerating community. Summer drought is a primary filter to plant establishment in Mediterranean-climate ecosystems. These two themes were central to my thesis. In the first half of my thesis I explored how local abiotic factors (soil type and nutrient composition) and biotic factors (weed cover) across a restoration site interact with summer drought to influence seedling establishment over time. I found that the effect of soil type differed temporally: spring recruitment was higher in sandy soils, but summer survival was higher in clayey soils. There was no clear relationship between soil type and end-of-summer establishment. Attempts to analyze restoration outcomes that do not consider interactions between local heterogeneity and temporal filters may therefore mask the mechanisms that drive plant establishment. In contrast, documenting these interactions provides a framework for targeted manipulative study and informed restoration decisions. Sandy soils had low water-holding capacities, which likely contributed to the low summer survival in these soils. In the second half of my thesis I explored how a specific plant trait, seed mass, influences a seedling’s ability to survive the summer in sandy soils. I tracked summer survival among four woody genera at a restoration site. Summer survival increased with seed mass within all genera. I hypothesized that the nutrient reserves in large seeds facilitated summer drought avoidance through greater root investment. I investigated this relationship in a glasshouse experiment assessing the growth of Acacia and Eucalyptus species, with a range of seed masses, under mild and severe drought compared with a well-watered control.
|Publication status||Unpublished - 2010|