Vernal pool soil properties and their role in restoration success

Background/Question/Methods

California’s vernal pools are ephemeral wetlands that host numerous endemic species, many of which are now rare and endangered because of extensive habitat loss from agriculture and development. This high incidence of habitat loss makes the construction of new pools and the restoration of existing pools critical to vernal pool recovery. One little-studied aspect of vernal pool ecology is the role of soil properties in hindering or facilitating restoration success. To gain a better understanding of these properties, we used a long-term vernal pool restoration experiment (Travis Air Force Base Solano Co.) with three functional pool types; 1) constructed for restoration, 2) naturally occurring pools dominated by native species and 3) naturally occurring pools dominated by invasive species.  We then collected soil samples in the field, when aboveground biomass was at its peak, from the three different pool types (N=24). To account for both abiotic and biotic soil conditions we measured soil microbial biomass, pH, moisture, and carbon:nitrogen (C:N) content for each soil sample. Microbial biomass is a strong indicator of decomposition potential in a system whereas our abiotic metrics provide a good representation of soil quality.

Results/Conclusions

Tukey’s HSD test results showed significantly lower microbial biomass in constructed pools than in invasive dominated pools and a marginally significant difference between constructed pools and native species dominated pools. Little variation occurred between the two naturally occurring pool types with only a slight microbial biomass increase in invasive dominated pools. Constructed pools displayed more homogenous pH and generally lower soil moistures than the highly variable naturally occurring pools. Constructed pools contained significantly less soil carbon and nitrogen and had significantly lower C:N ratios than in naturally occurring pools. With these strong trends toward lower microbial biomass, nutrient content and soil moisture in constructed pools the data suggest restoration success may be limited by microbial activity, nutrient availability and low soil moisture. Finding no significant differences in these parameters between the naturally occurring invaded and native pools suggests that plant invasions are most likely driven by other factors such as pool environment or seed bank characteristics.