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Ecological filters to seedling establish Ecological filters to seedling establish... - Complex Object ()
Ecological filters to seedling establishment for restoration in a Mediterranean climate / Lauren M. Hallett
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.
Root length increased with seed mass consistently across five harvests over 60 days. The benefits of large seed mass for establishment under environmental hazards are often considered temporary, but my findings suggest that seed mass can mediate other traits, including root length, which can influence longer-term survival through the summer drought that is characteristic of Mediterranean-climate ecosystems. Understanding the filters that govern seedling survival in a restoration context allows managers to target interventions to improve seedling survival, either by altering the constraining filters or selecting species with the traits to pass through them.
Thesis (M.Sc.(Nat.Res.))--University of Western Australia, 2010
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