Forest Health in a Regional Context

How Are Our Forests Doing?

Understanding the condition of park natural resources is essential to making informed management decisions. However, when looking at raw data or statistics, it is hard to evaluate what those numbers tell us about park resources. For example, “Is 9,000 tree seedlings per hectare enough for the park’s forests to regenerate?” or “How bad is the exotic invasive species problem in this park?”

Banner showing a slice of forest midstory, with tree trunks and branches of many species

NPS

Putting raw data into context provides insight on how park resources are doing. Analyzing and comparing data from numerous parks lets managers assess how the forest condition at their parks compares to other parks in the region.

What We Are Doing

Eight Inventory and Monitoring (I&M) networks have been collaborating on forest health monitoring since 2005. Participants include 61 national parks (23% of all parks in the I&M Program) in the eastern United States (Figure 1). As a result of this collaboration, vegetation data are collected in similar ways, which allows us to compare various parks across the region.

Map of the midwest and northeastern United States, with several Inventory & Monitoring networks highlighted
Figure 1. Inventory and Monitoring networks and parks participating in the regional collcaboration.

NPS / K. Miller

Two examples of regional analyses that resulted from this collaboration are discussed below.

What We Are Finding

Exotic Invasive Plants

Exotic invasive plants pose a serious threat to many parks’ forests because they can outcompete native plants, suppress forest regeneration, degrade wildlife habitat, and affect soil fertility.

The diversity and distribution of exotic invasive plants varies among Eastern Rivers and Mountains Network (ERMN) parks and other parks in the region (Figures 2 and 3). Some important comparisons include:

  • Delaware Water Gap National Recreation Area (DEWA) forests contain more species of exotic invasive plants than most other parks in the region.
  • Relatively few species of exotic invasive plants have been detected in forests at Johnstown Flood National Memorial (JOFL).
Bar graph of the number of exotic invasive plant species in 40 national parks
Figure 2. Number of exotic invasive plant species detected in forest monitoring plots between 2007 - 2010 in 40 national parks with comparable invasive species sampling methods.

NPS / J.P. Schmit

  • Nearly all forest monitoring plots in Friendship Hill National Historical Site (FRHI) contain at least one exotic invasive plant species.
  • Gauley River National Recreation Area (GARI) contains a lower percentage of plots with exotic invasive species than most other parks in the region.
Bar graph showing the percentage of forest monitoring plots that contained at least one exotic invasive plant between 2007 - 2010 in 40 national parks
Figure 3. Percentage of forest monitoring plots that contained at least one exotic invasive plant between 2007 - 2010 in 40 national parks with comparable invasives sampling methods.

NPS / J.P. Schmit

One person collecting data from a plot on the forest floor, and another recording it.
Collecting forest monitoring data in New River Gorge National River.

NPS / S. Murphy

Forest Regeneration

The number of tree seedlings present on the forest floor is an important indicator of whether the forest can renew itself as older trees die. Seedling density in forest monitoring plots varies greatly among parks (Figure 4). In general, ERMN parks contain moderate densities of tree seedlings compared to other parks in the region. Friendship Hill National Historic Site, however, ranks in the lower 20th percentile of regional parks. None of the ERMN parks contain 14,000 seedlings / hectare, a target seedling density suggested by the U.S. Forest Service for forests with low deer browse pressure.

In ERMN parks, tree regeneration is strongly influenced by elevation, fern cover, grass cover, and number of stems of indicator plants sensitive to deer browse. In general, forests at higher elevation contain more regeneration. At sites with greater than 20% fern cover, tree regeneration decreases with greater fern cover. Similarly, as the cover of grasses increases, the amount of tree regeneration decreases. Sites with greater numbers of stems of herbaceous plants sensitive to deer browse contain more tree regeneration.

Bar graph of average tree seedling density measured between 2006 - 2009 in 39 national parks
Figure 4. Average tree seedling density measured between 2006 - 2009 in 39 national parks with comparable regeneration sampling methods. The solid pink line shows the suggested target of 14,000 seedlings per hectare for forests with low deer browse pressure.

NPS / S. Perles

For More Information

Stephanie Perles
Ecologist, Project Lead
Forest Vegetation & Soils Monitoring
814-441-9643
stephanie_perles@nps.gov

Eastern Rivers & Mountains Network
420 Forest Resources Building
University Park, PA 16802



Summary by the Eastern Rivers & Mountains Network, April 2011.

Last updated: November 8, 2018