Sedgwick Reserve

31 Mar, 05 PM - 29 Jun, 05 PM

Habitat heterogeneity is a major driver of animal species diversity. This relationship is directly related to the structural complexity of the vegetation which provides shelter and nesting sites, as well as the provisioning of diverse resources. This concept can also be applied to habitat heterogeneity and plant species diversity, however this relationship is more commonly linked through large-scale abiotic measures of heterogeneity such as topography or climate and rarely analyzed at the micro-scale in terms of the structure provided by a single dominant species. For instance, the life form and architecture provided by a dominant plant species may have substantial effects on the heterogeneity of resources, such as light, nutrients, and water, within that community. Partitioning of resources is likely to have a direct benefit on a greater number of plant species who have distinctive resource requirements and an indirect advantage for organisms, such as arthropods, that are closely tied to the plant community. With the wide-scale replacement of native dominant species via non-native invasions, it is critical that we address how the replacement of one life form for another affects resource heterogeneity and finally plant and animal diversity. California grasslands afford a unique opportunity to assess the ways in which life form alters resource heterogeneity and ultimately species diversity. Historically the grasslands of California are purported to have been dominated by perennial bunchgrasses, such as Nassella pulchra, which have distinctive clumping patterns across the landscape. Today most of California?s grasslands are dominated by annual non-native grass species from the Mediterranean basin such as Bromus madritensis, B. diandrus, B. hordeaceus and Avena sp. Grasslands invaded by non-native annual grasses have significantly lower species diversity at multiple scales when compared to grasslands dominated by perennial bunchgrasses. This trend may be driven by the unique clumping pattern created by the bunchgrasses and the ability for plants to colonize the interstitial spaces between bunchgrass individuals. Unlike perennial bunchgrasses, non-native annual grasses are characterized by a uniform above and belowground architecture which is likely to homogenize resources (Figure 2). Non-native annual grasses have roughly 90% of their roots distributed continuously in the top 5 to 30 cm of soil, whereas the roots of perennial bunchgrasses are more thoroughly spread throughout the vertical soil profile. The aboveground canopy structure of non-native dominated grasslands is characterized by dense continuous vertical growth with significantly reduced horizontal complexity. Holmes and Rice (1996) found that the non-native grass, B. diandrus, puts on two times as much yearly biomass as the native bunchgrass, N. pulchra. Light availability at the soil surface may further be reduced in non-native sites by the accumulation of thatch (Fig. 4). The difference in belowground and aboveground architecture in native and non-native dominated sites is likely to be linked with the heterogeneity of critical resources and processes such as water, nitrogen, and light. The factors driving differences in plant species diversity has yet to be explored within an architecture-heterogeneity framework. Here I propose to investigate the role of life form, resource heterogeneity and species diversity between native bunchgrass and non-native annual dominated grasslands. Specifically there are three research objectives I plan to address: 1. How do dominant species and their unique life forms affect light, water TEMP? and soil nitrogen? 2. Does resource heterogeneity influence plant diversity? 3. Will resource heterogeneity AND species diversity increase if the architecture of non-native annual grasses is modified to reflect that of a bunchgrass?

Visit #24737 @Sedgwick Reserve

Approved

Under Project # 20805 | Research

The effect of resource heterogeneity on native forb success

graduate_student - University of California, Santa Barbara

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Nicole Molinari Mar 31 - Jun 29, 2011 (91 days)

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Day Use Only 1 Mar 31 - Jun 29, 2011