Unionville Serpentine Barrens Restoration and Management Plan.

by Roger E. Latham and Mike McGeehin.

Continental Conservation, Rose Valley, Pennsylvania and Natural Lands Trust, Media, Pennsylvania. 157 pp. + 10 maps, 2012.

Summary

In value for biodiversity conservation, the Unionville Barrens rank among the highest priority sites in southeastern Pennsylvania. A globally rare ecosystem and a cluster of rare species give the site national or even global significance. The ecosystem—temperate eastern North American serpentine barrens—consists of a species rich set of ecological communities associated with soils weathered from serpentinite bedrock, a rare geological formation. The Unionville Barrens feature traces of prehistoric and historical human land uses that also contributed in crucial ways to the site’s unique natural qualities. The flora and fauna include an exceptionally large number of rare, threatened and endangered species. However, the barrens vegetation has been losing ground for the past several decades, shrinking in area and declining in native species diversity with the waning of the disturbance regime that formerly sustained it, in all likelihood for a timespan of several thousand years. This plan offers an outline of how the decline of this treasured piece of our natural heritage can be reversed and key processes restored to insure the long term sustainability of the serpentine barrens ecosystem and its component species.

Grasslands make up a small fraction of the total serpentine barrens area but they harbor nearly all of the rare species. Other serpentine barrens communities intermixed with and surrounding the patches of grassland include unusual woodland and wetland communities. The total serpentine grassland area at the Unionville Barrens has declined drastically from more than 63 acres in 1937, the earliest credible size estimate, to 7 acres in 2010. It is crucial to the conservation of the entire set of serpentine barrens communities to restore as much as is feasible of the area of grassland recently lost to forest succession.

The plan’s underpinnings include two studies undertaken as part of the planning effort: (1) creation and analysis of a chronosequence of vegetation maps showing changes between 1937, 1958, 1971, 1990 and 2010 using air and satellite imagery and digital mapping (GIS) tools; (2) systematic sampling and mapping of soil physical characteristics. The GIS analysis documents the history of grassland loss to forest succession, providing signposts to the most suitable areas for grassland restoration. The soil study was based on research at another serpentine barren showing soil depth to be a key factor in grassland persistence and rate of loss due to forest succession. That finding was applied at the Unionville Barrens to explore the usefulness of simple, inexpensive soil measurements as a basis for evaluating areas where restoration and maintenance are likely to be cost effective versus those where they may be prohibitively costly.

Specific, measurable objectives for desired conditions were developed based on what is known about the ecology and history of the Unionville Barrens and other native grasslands and serpentine barrens in the region. In the plan, desired conditions are itemized and compared with existing conditions to serve as the basis for strategies to narrow the gap between the two. Methods to achieve the desired conditions are outlined. Specific areas of land are prioritized for such tasks as invasive species eradication, selective tree removal, creation of standing dead snags, soil organic matter removal, seedbank augmentation, propagation and planting of selected species, restoration burning and maintenance burning.

The plan takes an adaptive management approach, which, in brief, consists of carrying out a set of actions, periodically monitoring the results, reconsidering the 2 methods in light of those results, and adjusting the next round of implementation accordingly. This approach is a way of reducing uncertainty without high cost research. Trials of promising alternative methods for achieving objectives are carried out and results compared quantitatively as a part of routine management. Monitoring is an indispensible part of adaptive management, generating practical new knowledge that is promptly put to use. Monitoring is in essence an audit—a systematic, disciplined approach to evaluate and improve the effectiveness of management. The plan outlines a strategy for monitoring a set of indicators to track changes in conditions resulting from both management actions and external causes and to improve consistency, rigor and efficiency in measuring progress toward achieving and sustaining the desired conditions.

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