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Patch
Retention Project
Manomet Forest Conservation Program Project Manager: Andrew Whitman (awhitman@ime.net) The global demand for wood is expected to increase well into the next century (Aspey and Reed 1995). This demand has fueled significant changes in timber harvesting and utilization. Under the right conditions, a landowner can derive economic value out of trees with a top >4" in diameter. The demand for wood products has also made it financially more attractive for landowners to invest in intensive practices that increase tree growth. These two recent changes have altered forest practices in such a way that Maine's forest may be at risk to losing ecological features such as very large trees and snags. As a result the demand for wood is increasingly coming into conflict with other human values, such as the desire to maintain biodiversity that might depend on these ecological features. Variable retention is a popularly promoted tool for helping resolve the dilemma between demands for wood and desire to maintain biodiversity in managed forests. Either few trees or many trees can be retained under this system, and trees can be retained in clumps (patches) or left uniformly throughout a stand (hence the name 'variable'). It is a technique for retaining trees as key structural elements of a harvested stand for at least the next harvest rotation in an effort to maintain both species and forest processes. There are four key mechanisms through which variable retention is presumed to maintain biodiversity:
Timber harvesting affects forest species in different ways, depending on an array of life history traits. The ability of a species to disperse may be the most critical trait that determines a species' vulnerability in dynamic landscapes. Small organisms, such as herbaceous plants, lichens, mosses, invertebrates, and terrestrial amphibians may not fare as well in the face of intensive forestry. Harvesting can eliminate habitat and locally extirpate plants, lichens, mosses, invertebrates, and terrestrial amphibians (Ash 1997, Frisvoll and Presto 1997, Lesica et al. 1991, Petranka et al. 1993, Soderstrom 1988). Once extirpated, re-colonization by these species can be slow because their dispersal and recruitment rates are inherently low (Bailey 1976, Brunet and von Oheimb 1998, Duffy and Meier 1992, Essen et al 1996, Halme and Niemela 1993, Matlack 1994, Tapper 1976). Moreover, recruitment rates may be lower in young versus mature forest because young forests lack the habitat structure necessary for young herbs, mosses, lichens, and beetles (Cain and Damman 1997, Chandler 1987, Metzger and Schultz 1981, Rose 1992). In some cases it may take decades to fully restore important elements of forest structure and these species to managed stands (Ash 1997, Halme and Niemela 1993, Hansen et al. 1991, Meier et al. 1995, Petranka et al. 1993, Selva 1994). Thus, harvesting can affect poor dispersers, at the stand level: (1) by temporarily changing structure and eliminating critical habitat features, and (2) by creating large areas of unsuitable habitat for years or decades. The concept of variable retention originated from the observation that natural forest disturbances such as fire, blow down, and insect infestation typically leave patches of forest or isolated trees intact. Indirect evidence from studies of northern flying squirrels (Carey 1995), birds (Hansen et al. 1995), and lichens (Sillet 1995) suggests that such stand "legacies" can help maintain biodiversity. Nonetheless variable retention must be considered a hypothesis- the scientific basis is not yet established, especially in the northeast. Directly establishing the scientific underpinning of variable retention is complicated because of the many factors that affect outcomes, including dispersion of trees, dispersion of patches, tree species composition, site quality, stand age, stand history, and initial stand conditions (Aubry et al. 1999). We at Manomet are studying aggregated retention (patch retention) because there is evidence that it may benefit the most species and have the lowest cost for landowners. The Patch Retention Project is evaluating the usefulness of patch retention in three ways. We have initiated an experimental project which samples to be patches before and after timber harvesting in order to assess the short-term usefulness of individual patches on land provided by Plum Creek Timber Company. We have initiated three retrospective projects. One retrospective study will sample patch retention as it has been applied over the last three years by J.D. Irving, Ltd. in order to assess the real world usefulness of patch retention across entire clearcuts. A second retrospective study is sampling 8-10 year old upland clearcut buffers to assess the long term usefulness of patch retention. A third retrospective study is studying 80 year old fire remnants to asses the very long-term usefulness of patch retention. Finally economic feasibility will be measured through studies on timber loss due to wind throw and modeling of harvesting operations, tree growth, and wood yield that assess the operational costs and long-term opportunity costs of patch retention. In our biodiversity studies we are surveying vulnerable species, biodiversity features, and sensitive indicators. The vulnerable species that we have focused on are herbaceous plants, macro-lichens, mosses, and ground beetles. The biodiversity features include large trees and snags, large logs, sensitive microhabitats (e.g., seeps and springs), inclusions of tree species different from species composition of the overall stand, smooth barked beech, and trees with big tree epiphytic mosses and macro-lichens. Our indicators include air temperature, relative humidity, and red-backed salamanders. The patch experiment study is a before and after study of patch retention in partial harvested forest and in clearcut forest. Partial harvested sites were northern hardwood sites dominated by sugar maple and yellow birch. Clearcut sites were mixedwood sites dominated by red spruce, balsam fir, mountain paper birch, and yellow birch. Earlier work indicated that air temperatures 10-20 m (33-66 ft) from a clearcut edge were similar to air temperature found in interior forest. Hence we elected to study 30 m radius patches, expecting that the interior of the patches would have a microclimate similar to that of interior forest. We were unable to study variation in patch size because the addition of a factor would dramatically increase the need for replicates and substantially increase the cost of the experiment. In each harvest type, we sampled three types of forest before logging: forest to be logged, forest to be left intact, and forest to be patches (Figure 1) in order to address three questions:
All plots were surveyed in the summer of 2000. Logging is occurring January-March 2001. We will revisit plots in the summers of 2001 and of 2002 in order to answer our research questions. Plots were permanently marked so that the study could be extended decades into the future. Partial Harvested Treatments
Figure 1. Location of survey plots in intact forest, patches, and a harvest area for both a clearcut and partial harvested stand. The retrospective patch study is a study of mixedwood patches left in clearcuts 2 years ago. Mixedwood forest is dominated by red spruce, balsam fir, mountain paper birch, and yellow birch. This study will be conducted on J.D. Irving Company land in northern Maine. These patches are the result of Irving's strategy for sustainability managing its forests under the standards established by Forest Stewardship Council (FSC). This poses an opportunity to determine how well patch retention works in a real world setting. In this study we will sample patches, clearcuts, and uncut forest in order to address three questions:
We will begin sampling patches in the summer of 2001 and will finish sampling in summer 2002. Plots will be permanently marked so that the study could be extended decades into the future. The retrospective buffer study is a study of mixedwood buffer strips left between clearcuts 8-10 years ago. Mixedwood forest is dominated by red spruce, balsam fir, mountain paper birch, and yellow birch. In Maine's industrial forest, these buffers or forest remnants often are the result of laws governing the management of clearcuts. Maine regulations require forested separation zones between clearcuts that are >250' wide and equal in size to adjacent clearcuts in order to "address adverse impacts on wildlife habitat and provide for a healthy and sustainable forest" (State of Maine 2000). Where clearcutting is practiced, separation zones might play an important role in maintaining species in a well-distributed manner that might be sensitive to clearcutting. If so, patch retention might be a tool that further enhances retention of sensitive plant and animal species in a more well distributed pattern. In this study we have begun sampling buffers, clearcuts, and uncut forest (Figure 2) in order to address three questions:
We began sampling buffers in the summer of 2000 and will finish sampling in summer 2001. Plots were permanently marked so that the study could be extended decades into the future.
Figure 2. An example of the location of survey plots in intact forest, a buffer, and a clearcut. Retrospective Fire Remnant Study The retrospective fire remnant study is a study of unburnt forest remnants in a area of forest that burned 80 year ago (Figure 3). By studying these old remnants, it may be possible to determine how well patch retention may provide refugia over the long term and provide colonizers to the surrounding landscape. We began sampling fire remnants in the summer of 2000 and will finish sampling in summer 2001. We found that remnants contained big tree epiphytic mosses and lichens absent from much of the burn area. Some of the larger remnants (> 1 acre) harbored state listed herbaceous plant species. We are conducting this study in order to address three questions regarding the long-term usefulness of patch retention:
Figure 3. 1949 aerial photo of northeastern Skinner Township indicating extent of 1932 burn and location of fire remnants. The fire remnant noted in the middle of the photograph is about 200 m by 250 m (about 650 ft by 820 ft). Revised: April 26, 2005
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