Long-term dynamics of biotic and abiotic resistance to exotic species invasion in restored vernal pool plant communities

Published source details Collinge S.K., Ray C. & Gerhardt F. (2011) Long-term dynamics of biotic and abiotic resistance to exotic species invasion in restored vernal pool plant communities. Ecological Applications, 21, 2105-2118.
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This study is summarised as evidence for the following.

	Action	Category
	Excavate freshwater pools Action Link
	Introduce seeds of non-woody plants: freshwater wetlands Action Link

Excavate freshwater pools

A replicated study in 1999–2008 of 64 excavated ephemeral pools on an air force base in California, USA (Collinge et al. 2011) reported that they were colonized by vegetation, but became dominated by non-native species after eight years. After 3–6 years, the excavated pools contained a mixture of native Californian pool-characteristic plants, and non-native plants. The abundance of each group was similar (native pool-characteristic abundance 1.1–1.5 times greater than non-natives). However after 8–9 years, and following a period of flooding then drought, the pools were dominated by non-native plants (non-native abundance 5–10 times greater than native pool-characteristic plants). Absolute abundance was reported as the sum of frequencies of species in each group (see original paper for data). Methods: In December 1999, sixty-four ephemeral pools were excavated in recently farmed grassland. The pools were 25–100 m² and <150 m from natural pools. These pools were not sown with any seeds, but the surface was lightly raked. Each spring between 2002 and 2008, the frequency of every plant species was recorded in each pool, using a grid of one hundred 2.5-cm² cells. Frequencies were added together to give the overall abundance for native, pool-characteristic plants and non-native plants (data for native, generalist plants were not reported). This study was based on the same pools as (4).

(Summarised by: Nigel Taylor)
Introduce seeds of non-woody plants: freshwater wetlands

A replicated, controlled study in 1999–2008 in 256 excavated ephemeral pools on one air force base in California, USA (Collinge et al. 2011) found that plots sown with seeds of pool-characteristic herbs typically contained a greater abundance of native pool-characteristic plants than unsown plots (if a dense seed mix was used), but that sowing did not significantly affect the abundance of non-native plants. All data were reported as frequencies, added together for all species in each group. Over seven years of monitoring, plots densely sown with a mix of herb species typically supported a greater abundance of native, pool-characteristic plants than unsown plots (9 of 14 comparisons; other comparisons no significant difference). However, densely sown plots typically supported a similar abundance of non-native plants to unsown plots (9 of 14 comparisons; other comparisons lower abundance in sown plots). The study does not report data for native, generalist plants. In contrast, plots sparsely sown with single species typically supported a similar abundance – to unsown plots – of both native pool-characteristic plants (13 of 14 comparisons) and non-native plants (14 of 14 comparisons). Methods: Between 1999 and 2001, seeds of native, pool-characteristic herbs were sown onto 192 plots (each 0.25 m² and in a separate excavated pool). Of these, 128 were densely sown (600 seeds/plot; mix of five species) and 64 were sparsely sown (100–300 seeds/plot; one species). Sixty-four additional plots (pools) were not sown. Each spring between 2002 and 2008, the frequency of every plant species was recorded in each plot, using a grid of one hundred 2.5-cm² cells. This study was based on the same pools as (8).

(Summarised by: Nigel Taylor)