Management Approaches to Facilitating Desirable Tree Regeneration in Pitch Pine Barrens across the Northeast

In the Northeast, the range of the southern pine beetle (SPB) has expanded northward over the past decade due to warming winters associated with climate change. The result has been disastrous for pitch pine barrens, a rare fire-dependent ecosystem found primarily from New Jersey to Maine. These communities provide important habitat for many species, including rare, threatened, and endangered moths and butterflies, such as the Karner blue butterfly. Long periods of fire suppression have altered these communities, with many seeing the reintroduction of active management only in the past two decades. Without disturbance, especially fire, pine barrens will convert from open woodlands to dense forests, and trees will transition from pines and oaks to maples and other fire-sensitive species. 

This transformation not only threatens important habitat, but it also makes these pitch pine barrens more vulnerable to SPB, which thrives in denser, forested conditions. Pitch pine has been the primary host species for SPB in its expansion north, and an outbreak of the insect can cause the death of more than 90% of pines in a canopy in as little as one year. This rapid loss of the pine overstory further accelerates transition in these communities, increasing vulnerability, and demonstrating the need for desirable (e.g., pitch pine) seedlings and saplings to be established in barrens, supporting continuity through novel disturbances, including those caused by climate change.

To understand the impacts of management activities in pitch pine barrens on tree seedlings and saplings, a NE CASC team including Kathleen Stutzman, Anthony D’Amato, and Kevin Dodds collected and analyzed information on the effects of four common management approaches–prescribed fire applied in the spring, prescribed fire applied in the fall, mowing followed by prescribed fire, and harvesting–along with untreated control sites, across four Northeastern states (Maine, Massachusetts, New Hampshire, and New York). Their study was recently published in Forest Ecology and Management.

The authors found that all active management approaches were much more likely to have pitch pine seedlings present than the untreated control sites. Other factors, including the depth of leaf litter on the soil surface, the understory cover by other plant species, and the amount of shrub oak (scrub oak and dwarf chinkapin) seedlings was also influential to pitch pine seedling abundance. These factors can be manipulated by management activities, including burning, mowing, and bulldozing, which indicates that several approaches available to managers have the potential to create favorable conditions. Previous research has shown reductions in canopy density to reduce the vulnerability of pitch pine barrens to SPB outbreaks. This study indicates that there is potential for these treatments to also benefit desired seedlings and saplings when coupled with disturbance to the forest floor (e.g., removing leaf litter, knocking back competing understory plants), providing practical information useful to managers in their restoration and management efforts.

Management Implications

• Important factors to focus on when managing for pitch pine regeneration include reducing the depth of leaf litter on the soil surface and the amount of competing understory species, especially shrub oaks.
• Repeated and/or more severe disturbance is more likely to create the above desired conditions.
• Pitch pine regeneration success is also influenced by the presence and density of pitch pines in a canopy.
• All management approaches yielded significantly more desirable seedlings than the untreated control site, though no treatment approach clearly worked better than any others. This indicates that several management approaches can be effective, especially if they pay heed to the above factors.