Forested watershed

An increase in low-intensity fire will help restore xeric species, but if fires are too frequent, it can result in seedling and sapling mortality, and reduced soil nutrients. Severe fire could result in adult mortality and loss of the soil organic layer.

Suitable habitat was projected to increase for the southern oaks and hickories, whereas other common species are projected to persist over a smaller extent. Models project habitat suitability, basal area, trees per acre, and potential growth for pignut hickory and white oak to remain stable or increase slightly under both scenarios. Results for northern red oak suggest positive effects on regeneration where suitable habitat remains.

Increased drought conditions, especially during the growing season, may increase susceptibility to red oak borer, gypsy moth, Armillaria root rot, and other insect pests and diseases. Southern pine beetle outbreaks have been observed in New Jersey and Pennsylvania systems recently, and may increase due to warmer temperatures. Tree-of–heaven, Japanese stiltgrass, multiflora rose, bush honeysuckles, autumn olive and Japanese barberry often out compete native herbs and shrubs in this ecosystem, and are also likely to benefit from warmer temperatures and increased disturbance.

Models project that suitable habitat, potential growth, and trees per acre for chestnut oak and scarlet oak were projected to remain stable under low climate scenarios and decrease under high climate scenarios. Black oak was projected to remain stable under low climate scenarios, but under high climate scenarios suitable habitat is expected to increase while growth potential and trees per acre decrease. Models project increases in suitable habitat and potential growth for only one species, loblolly pine, which is expected to benefit from increased temperatures under both scenarios.

Increases in canopy-disturbing events are likely to provide regeneration opportunities.

Under moist soil conditions, lush herbaceous and shrub vegetation creates conditions unsuitable to low-intensity fires in this ecosystem. Drier soil conditions in summer and fall, especially on south facing slopes, may desiccate the lush vegetation that normally discourages conditions for wildfire and ultimately provide wildlfire fuel.

The dry oak and pine/oak forest and woodland ecosystem is the most resilient to heat and drought, with many of the species currently doing well, and projected to do well under future climate. Increased drought and fire are likely to benefit this ecosystem, discourage invasive species, and maintain an open structure that benefits oak and pine regeneration. Many pine and oak species are fire-adapted and drought tolerant, some requiring high intensity fire to regenerate. A history of fire suppression and succession has contributed to a reduced pine component in favor of oak species.

The co-occurrence of the dominant species is tightly linked to the unique soils derived from limestone, and movement on the landscape is limited to landscape positions where those soils form.

Invasive species are also common in this forest ecosystem, and climate change is expected to promote establishment and growth of invasives, resulting in increased competition with the high number of rare native plants in this ecosystem. Increases in invasive species such as cheat grass, stilt grass, and bush honeysuckles could increase fire fuels in this type, leading to potentially more intense fire when it does occur.

Many species in this forest ecosystem tolerate temperature and moisture extremes, especially on exposed landscape features, allowing them to out-compete other species. However, increased drought duration and extent may increase susceptibility to oak decline, or combine with insect and disease factors to increase stress or mortality.