Understanding Our Forest

A healthy forest is more than a stand of trees—it is a living, interconnected system of plants, animals, fungi, and soil processes. In Mount Gretna, our woodlands are the foundation of our community’s beauty, ecological function, and historic character. They filter rainwater before it enters the lake and creek, stabilize slopes against erosion, cool our neighborhoods in summer, store carbon, and sustain a rich web of life.

The Lebanon County Natural Areas Inventory (2003) identifies oak-dominated forests in and around Mount Gretna as ecologically significant natural communities. These forests are valued for their biodiversity, their role in wildlife corridors, and their importance for watershed resilience—but are also noted as vulnerable to invasive species, development, and environmental stress.

A 2020 LandStudies assessment of my half-acre property documented a diverse mix of native and non-native plants, noting that the overall species composition is typical of temperate deciduous forests in Pennsylvania’s Piedmont region. The Piedmont is the band of rolling hills between the Appalachians and the coastal plain, and here in Mount Gretna it supports oak- and maple-dominated forests that tie us into this larger landscape. A 2023 Brandywine Urban Forest inventory further described the site as a terrestrial Red Maple Forest, with dominant species such as red maple, chestnut oak, tulip tree, black cherry, and hickories. Because the lots here are small and the forest is continuous, this classification is considered typical of much of the surrounding woodland. This forest type supports a wide variety of wildlife and provides essential ecosystem services, but it is also sensitive to certain pests, diseases, and environmental stresses.

Because much of the forest in the Mount Gretna Borough is contiguous, we can look at a detailed analysis of one parcel as an illustration of the larger picture. A recent assessment of a half-acre property found the same dominant species seen throughout the community’s woodland, including red maple, black tupelo, and chestnut oak. Since many of our lots are small but connected, these snapshots illustrate patterns that affect the community as a whole.

Our Tree Composition

Tree diversity is a key indicator of forest resilience. The commonly referenced 10-20-30 guideline recommends:

• No more than 10% of any single species

• No more than 20% of any single genus

• No more than 30% of any single family

Our local forest, as illustrated by the Simpson Residence data (2023), exceeds these thresholds in several ways:

• • Red maple is the most common species, making up nearly 27% of all trees—almost three times the recommended limit.

  • Black tupelo accounts for about 19%, also well above the 10% threshold.

  • Chestnut oak comprises roughly 14%, and 

  • Black cherry is just under 10%.

  • These top four species alone represent approximately 74% of all trees recorded.

  • Several other native species, such as tulip tree, sassafras, and American beech, are present but in much lower numbers, leaving the forest less diverse and more vulnerable to species-specific pests and diseases.

This dominance by a few species means that a single pest, pathogen, or environmental stressor could have a disproportionate impact on canopy cover and overall forest health.

Current Threats in Mount Gretna’s Forest

 The challenges facing our woodlands are not abstract—they are already visible here in Mount Gretna. Among the most pressing are:

• • Red maple health risks – Susceptible to climate-related stress, especially prolonged droughts and extreme weather events.

  • Black tupelo stressors – Sensitive to root disturbance and soil compaction, which can occur near trails and developed areas.

  • Chestnut oak decline – Signs of dieback linked to oak wilt and environmental stress reduce canopy cover and wildlife food sources.

  • Eastern hemlock loss – Infestation by the hemlock woolly adelgid threatens remaining hemlocks, which provide critical shade along stream corridors.

  • American beech under threat – Beech leaf disease, caused by a microscopic nematode, is spreading across Pennsylvania and poses a serious risk to one of our iconic canopy trees.

  • Invasive plants – Japanese stiltgrass, multiflora rose, and other aggressive species crowd out native understory plants.

  • Pests and pathogens – Emerald ash borer, spotted lanternfly, and other invasive insects threaten hardwood regeneration.

  • Climate stress – Warmer winters, heavier rain events, and longer droughts strain tree health and alter species composition.

  • Human impacts – Soil compaction, unmanaged tree removals, and trail overuse degrade root systems and fragment habitat.

Why This Matters

Loss of canopy or decline in tree health has cascading effects:

• • Ecological – Reduced stormwater absorption, hotter microclimates, and loss of wildlife habitat.

  • Cultural – Loss of the historic woodland character that defines Mount Gretna, eroding the natural setting that gives the Pennsylvania Chautauqua’s cultural and educational mission its unique sense of place.

  • Economic – Decreased property values, higher costs for stormwater management, and increased cleanup after storms.

Once mature trees are lost, it can take decades to restore comparable ecological function. That’s why understanding what we have now—and what threatens it—is such an important first step in keeping our woodlands healthy for the generations to come.