Forest Diversity and Structure Surrounding Vernal Pools in Pictured Rocks National Lakeshore, Michigan, USA

Abstract

Vernal pools have been identified as unique contributors to forest biodiversity, with habitat management guidelines commonly recommending concentric zones of varying conservation intensity. However, little is known about the associated edaphic and forest structure characteristics associated with vernal pools. At Pictured Rocks National Lakeshore (Michigan, USA), we measured a stratified-random sample of 18 of 51 vernal pools to investigate soil pH, down dead wood, tree stocking, species richness, species evenness, species diversity, and species importance values within and across these zones. Within the pool zone, live tree basal area and live tree density was significantly lower and down dead wood volume was significantly higher than either the buffer or matrix zones. Nested-ANOVA and NMDS ordination indicated that importance values of under-represented species increased closer to the vernal pool. Tree diversity and richness were positively correlated with vernal pool area. These findings suggest the buffer zone serves as a transition zone between vernal pools and the surrounding forest, complementing the proposed guideline goals of reducing impacts of forest management. Vernal pools are unique forested wetlands and may provide an opportunity to maintain and enhance ecosystem complexity and resiliency.

Legacy and Opportunity in Northern Hardwood Forests

“…By walking the perimeter of the vernal pool, we also confirmed there were no visible inflow or outflow channels that potentially could connect to a wetland, river, or stream. Basin area, perimeter shape, maximum water depth (< 0.3 m, 0.3 -1.0 m, and >1.0 m), surrounding upland slope, and aspect were collected for each pool Previant and Nagel 2014;. Following Coburn (2004), each vernal pool was assigned an initial hydrological class based on when the basin was filled (spring or fall) and length of flooding duration (semi-permanent, short-or long-cycle).…”

“…This modified geomorphic system proved useful for two concurrent studies at Pictured Rocks. The classes provided the initial framework to help minimize the variability in the physical characteristics of vernal pools, and proved useful in characterizing differences in surrounding forest habitat (Previant and Nagel 2014), along with hydroperiod, vegetation community type, and amphibian species richness Shrank et al 2015).…”

“…given this pattern, the vast majority of vernal pool habitat descriptions quantify only what occurs within the vernal pool perimeter and not the surrounding forest , although and Previant and Nagel (2014)…”

“…Vernal pools are ephemeral or seasonal wetlands that occur in shallow depressions within the glaciated forests of northeastern North America Tiner 2003;. These wetland habitats have been identified as being important for the life-cycles of amphibians and invertebrates Calhoun and deMaynadier 2001;; locations for numerous at-risk plant species (Comer et al 2005); foraging areas for black bears (Ursus americanus L.) and bats (DeBrun 1997;; and transitions zones associated with shifts in forest structure and species importance values (Previant and Nagel 2014). Vernal pools have been described as an essential component within forests, and recent research in these discrete wetlands has highlighted risks to the frequency, density, and overall quality of these small-scale ecosystems (cf.…”