The emerald ash borer (EAB) has killed almost 20 million ash trees in Michigan with the majority of the mortality occurring in southeastern Michigan, and is considered to be a serious threat to the forests of southern Michigan and the eastern United States. Such significant effects of exotic insects on forest structure may in turn have detrimental effects on sensitive animal communities, but such effects are currently poorly understood. For example, many amphibian species have low survivorship and growth rates in closed-canopy areas that provide mainly detrital food resources unsuitable for young life stages, while others thrive in closed-canopy or open-canopy areas that support a significantly larger amount of epiphytic algal growth which often make up a large portion of tadpole food. Young life stages of certain species often prefer shallow, warm water, however, which results in increased growth rate. We examined amphibian populations in twelve natural areas within the core outbreak area of the emerald ash borer in southeastern Michigan during spring and summer of 2008. We hypothesized that ash mortality would increase the amount of standing water (ephemeral ponds) during the amphibian breeding period and thereby alter amphibian population and community dynamics. Study sites were selected based on their location relative to the estimated annual front of the outbreak beginning in the year 2000 so as to capture the effect of time since ash mortality on amphibian communities. At each park, areas with ephemeral ponds with and without ash mortality were located, and 25 meter quadrats were used to conduct systematic amphibian surveys. Changes in amphibian fitness with ash mortality were estimated using amphibian length and weight, and basic water chemistry was described for each site.
Results/Conclusions
Our preliminary data provides a snapshot of what effects ash mortality due to EAB may have on amphibian populations. We expected that increased sunlight and subsequent warmer temperatures of ephemeral ponds beneath killed ash would alter the abundance and diversity of amphibian populations. Surprisingly, we detected little direct effect of ash mortality on amphibian populations regardless of time since EAB attack. This lack of an effect may be the result of the patchy nature of ash presence and mortality, and thus the presence of nearby, well-shaded ephemeral ponds that may act as refugia during harsh environmental periods and a source from which ponds beneath killed ash may be re-colonized during favorable periods.
