Silviculture, as a discipline, is being challenged by changing global economies, broader land ownership objectives and emerging environmental constraints (Aplet et al.1993, Kohm and Franklin 1997, Franklin and Johnson 2004). This is particularly pertinent to the southeastern US, where industrial fiber production capacity is increasingly being shifted from the region to more profitable operations in the southern hemisphere. Coincident with declining economic incentives for production of wood fiber, management objectives of many land owners have expanded to include conservation values, recreational amenities, aesthetics, and overall asset appreciation while concomitantly extracting timber products. The potential climate changes and threats from invasive species further challenge the discipline to find ways to manage the forest for today’s objectives, while leaving options open for the future. Consequently, an interest is developing in ecologically based silvicultural systems geared for wildlife and diversity concerns along with production of older and higher quality timber (Mitchell et al. 2002, 2006). To retain long-term viability, these systems should maintain future options in a landscape that is likely to experience changes in both the physical environment and the socio-economic climate in which it develops.
Longleaf pine systems are particularly appropriate models for development of ecologically based silvicultural systems due to their diversity, their conservation imperative, and their strong dependence on disturbance, including fire, that sustains their diversity. Additionally, these forests occur in a region dominated by private ownership with critical public land that provides reservoirs of biodiversity. Often these public lands have sustaining timber and wildlife production and biodiversity as multiple goals. The challenge today is to develop practical, economically and ecologically sound approaches to forest management.
Recently, Franklin et al. (2007) suggested a conceptual framework in which ecological approaches could be better incorporated into forest management systems. They proposed that characteristics of natural disturbances could be integrated into silvicultural practice through: 1) incorporating into silvicultural prescriptions the legacies, including the types, amounts and patterns (both spatial and temporal), found in natural disturbances, 2) including treatments that manage intermediate stand development of forest structure and 3) allowing for recovery periods following harvesting disturbance that are sufficient to sustain native biodiversity prior to subsequent harvest. However, in the Southeast, the salient legacies that characterize natural disturbance patterns of the longleaf pine ecosystem and how these legacies can be incorporated into silvicultural prescriptions are poorly understood (see Palik et al. 2002). Little is known about how natural disturbance recovery processes differ from those of timber harvests in ecologically-based silvicultural systems, and in particular, the connection between silviculture and prescribed burning through impacts on patterns of vegetation and fuels have largely been overlooked (Mitchell et al. 2006).
In its application to longleaf pine forests of the southeastern United States, Franklin’s conceptual model takes on additional complexity. Silvicultural prescriptions in longleaf pine ecosystems must account for a wide range of legacies that influence ecological response to harvest. Legacies of past longleaf pine management include overstory stocking, canopies of other pine species, abundance of hardwoods, alterations to groundcover diversity, presence/absence of advance regeneration, and alterations in fuel characteristics from historic fire regimes (Mitchell et al. 2006). Furthermore, because longleaf pine forests occupy a wide range of edaphic conditions (Wells and Shunk 1931, Kirkman et al. 2001) site productivity must be considered along with legacies in developing silvicultural prescriptions. Together, site productivity and legacies of past disturbance affect three key processes: fire return interval, understory disturbance and response, and intermediate stand development of overstory structure. These processes will dictate a necessary recovery period toward a desired future condition prior to subsequent forest harvest. Generally, the desired future conditions are defined as multi-aged longleaf pine forests that possess a diverse flora and fauna representative of site type that sustains timber yield and maintains continuous and frequent fire. From evaluations of this recovery stage and evaluation, future management prescriptions are developed. A conceptual framework for how these factors interact is shown in figure 1.
Our understanding of the relationships shown in figure 1, however, is not complete. Evaluation of the time required for recovery following disturbance is fairly straightforward, as is the progress toward achieving desired future conditions once they are suitably defined/delineated. After these assessments are made one can develop silvicultural prescriptions to direct changes toward the desired future conditions given our best knowledge of how the system will react to manipulations. On the other hand, our knowledge of how the factors listed above and shown in the center of figure 1, and especially their interactions, is imperfect and largely has been treated as a “black box.” It is these interactions that this research proposal will examine to gain better understanding of how the longleaf pine ecosystem responds to silvicultural manipulations designed to direct the longleaf forest toward a diverse and sustainable condition.
We propose a long-term study to provide the scientific rationale for development of silivcultural prescriptions for the longleaf pine ecosystem that incorporate critical ecosystem processes, such as fire, which are necessary to perpetuate native biodiversity and maintain a multi-aged forest. Conceptually, the project encompasses three general themes: a) integration of legacies into silvicultural prescriptions, b) connecting silviculture to fuels and prescribed fire, and c) understanding recovery periods from both anthropogenic and natural disturbance regimes. This study incorporates replicated, experimental silvicultural manipulations (including no harvest controls) in 80-90 year old longleaf/mixed pine stands to examine long term impacts on fuels, fire behavior, and stand development. The study also includes monitoring within benchmark forest stands, which represent the desired future conditions for the harvested stands. This will enable us to contrast natural disturbances with silvicultural disturbances and to examine wildlife response to both. Finally, the study evaluates restoration methods for converting slash pine plantations to multi-aged longleaf pine grasslands over time (Kirkman et al. 2007).
Experimental treatments will initially be implemented at Ichauway, but the study design will be exportable to other sites within the region. The broader regional component of the project is critical to develop a general understanding of how ecological processes vary with initial stand condition and across a range of sites. Furthermore, given the recent change in forest management objectives, there is a clear need for methods to manage for multi-age pine stands and at the regional scale, to convert existing even-aged pine plantations to multi-aged, older stands.
Education and outreach efforts are a critical component in achieving broader application of ecologically-based silvicultural systems for the management and conservation of the longleaf pine ecosystem. The Center has an existing suite of ongoing efforts in this arena that will incorporate new information as it is generated. New efforts are also proposed that seek to broaden opportunities and avenues for information transfer. In particular, it is hoped that a regional research network and stakeholders group will enfranchise a broader group of partners in the application and adaptation of ecologically-based silvicultural systems across the range of longleaf pine.
The draft proposal for this project is in the final stages of development and approval. Further details regarding the study will be posted when the proposal is finalized.