Aaron Weiskittel – Research

My research focuses on three key areas in forest biometrics and modeling: (1) empirical and process-based growth models; (2) regional variation in forest productivity and (3) crown structure and dynamics. I currently have research projects sponsored by the Cooperative Forestry Research Unit, National Science Foundation Center for Advanced Forest Systems, Northeastern States Research Cooperative, and the US Forest Service. A brief description of some of the projects I am currently involved with are given below:

Development of an Acadian Variant of the Forest Vegetation Simulator

Individual tree growth models are needed to update forest inventories, compare silvicultural regimes, and quantify stand dynamics. The Forest Vegetation System Northeast variation (FVS-NE) has been the most widely used individual tree growth model in the region, but recent simulations have shown it to be highly biased. Although calibration factors have been provided to correct these biases, their robustness and difficulty to implement call for a more elegant solution. Substantial amounts of growth and yield data are currently managed by the CFRU and could be used to improve regional growth equations. This project proposes a 3-year plan to: (1) create a growth and yield database for the region; (2) refit diameter and height growth equations for the primary species; and (3) estimate growth modifiers for thinning treatments. The equations would be integrated into the current FVS-NE growth model and tested. The primary deliverable from this project would be a computer simulation tool in the form of a refined regional growth and yield model.

Do Silvicultural Outcomes Vary in Response to Climatic Gradient in the Northern Forest?

Long-term silvicultural studies on US Forest Service Experimental Forests of the Northern Research Station across the Northern Forest cover a climatic gradient from oceanic to continental, including the influence of the Great Lakes. This gradient represents a range of variables including temperature, precipitation, relative humidity, and growing season length. This climatic variability may affect the type or magnitude of stand response to silvicultural treatments. Responses of interest include gross and net tree growth, tree recruitment and mortality, dead wood recruitment, tree species composition including successional status and shade tolerance, and stand structural diversity. Other variables of interest for which existing datasets are not complete include carbon storage, wildlife habitat and response, understory and ground cover vegetation, and browse. An initial analysis of this data was completed by Sarah Johnson in 2011 (Link to thesis; Link to thesis presentation).

Using Pioneering Growth and Yield Studies to Inform Management and Modeling

Despite more than a century of research in the Northern Forest, many questions about growth and yield remain unanswered. The most important include long-term growth response to silviculture, regional drivers of forest productivity, and the variability of yield. Recently discovered archives from U.S. Forest Service studies established between the 1920s and 1960s in the northern conifer (previously called eastern-spruce fir) forest type present an unprecedented opportunity for addressing these research questions. We propose to re-open and, where possible, remeasure experimental plots from these historic studies, including some initiated by Marinus Westveld, the Father of Spruce-Fir Silviculture. Studies of interest include the now-closed Finch-Pruyn and Paul Smith’s Experimental Forests in New York, the Gale River Experimental Forest in New Hampshire, and a Soil-Site-Growth Study on industrial forestlands in Maine. Archived, unpublished, and remeasurement data will be used to generate new findings about growth and yield in the northern conifer forest type; these findings will inform contemporary forest management and strengthen regional modeling efforts.

Development of a regional taper and volume equations for the primary species in the Acadian Region

Prediction of individual stem total and merchantable stem volume is necessary to evaluate financial return of forestry investments. Equations developed by Honer (1967) are widely used in the Acadian region of Maine and maritime Canada. Recent evidence suggests that the Honer (1967) equations can be significantly biased by 5-15% for red spruce and balsam fir, particularly in precommercially thinned stands. This bias can partly be attributed to the Honer (1967) equations being parameterized with data only from unmanaged natural stands and are a function of just tree diameter and height. The use of taper equations has become the standard in several regions for a variety of reasons such as ability to reconstruct stem shape, estimate merchantable volume to a specified size, and provide unbiased volume estimates.

Influence of Partial Harvest Intensity and Technology on Northern Forest Sustainability and Productivity

Partial cutting and the use of mechanized logging equipment are now ubiquitous in the northern forest and have created unprecedented patterns of disturbance and residual structure. Specifically, whole-tree and cut-to-length operations using forwarders to transport wood within harvested stands generate more regularly spaced and parallel skid trails than historic manual felling/cable skidding operations. The resulting stand structures are characterized by a “raked” appearance that suggests an uneven distribution of growing space and spatially variable regeneration, recruitment, and residual tree growth response. However, the residual stand characteristics of forests harvested in this manner have yet to be quantified. In addition, the sustainability and productivity of these new structures is unknown; existing growth and yield models are of limited utility because the data used in their development came from stands with markedly different management histories and thus structures. To fill this need, we propose to quantify regeneration, recruitment, and residual tree growth response in current and past partial harvests at a range of removal intensities implemented with whole-tree and cut-to-length systems. Study areas will include a range of species mixtures, with the objectives of quantifying and analyzing spatial distribution and growth response of new and residual trees in mixed species stands. Our goals are to advance our understanding of forest response to mechanized harvesting patterns and alternative partial harvesting intensities, utilize that knowledge to update existing and in-development growth and yield models, and ultimately assess the sustainability and productivity of managed northern forest ecosystems.