7th Biennial Conference on Agroforestry in North America and .... In 1995, we established the Beaver Creek Riparian Buffer project to develop better information.
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Establishment of Riparian Forest Buffers on Agricultural Lands in the Oregon Coast Range: Beaver Creek Case Study
Badege Bishaw1, William Rogers2 and William Emmingham1
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Paper presented at, and submitted for publication in the proceedings of, 7th Biennial Conference on Agroforestry in North America and The 6th Annual Conference of Plains and Prairie Forestry Association August, 2001 Regina, Saskatchewan, Canada Establishment of Riparian Forest Buffers on Agricultural Lands in the Oregon Coast
2 Range: Beaver Creek Case Study Badege Bishaw, William Rogers and William Emmingham
Abstract Riparian areas in the Pacific Northwest have traditionally been a source of natural resources such as timber and grazing and for transportation corridors, and homesteads. A primary impact has been the removal of riparian trees, whose crowns and roots provide shade and stream bank protection. Increases in water temperature can be lethal to salmonid fish and decreasing salmon populations over the past few decades have resulted in an urgent need for improving the management of watersheds, fish habitat, and water quality. Leaving streamside buffers is now required by state forest practices regulations on forestlands, but no regulations are in place on agriculture lands where riparian trees have frequently been removed. In 1995, the Beaver Creek riparian buffer project was established to develop better information about how to establish riparian buffers on coastal pastureland near Newport, Oregon. No riparian trees were present. A replicated tree filter belt trial was established along the south bank of the creek to compare unplanted pasture (controls) with commercially valued red alder (Alnus rubra) planted at 6 ft spacing in: (1) one row, (2) three row, and (3) six tree row widths. We will report tree survival, height and diameter growth and compare the amount of shade produced by the four treatments. We used the Licor LAI-2000 plant Canopy Analyzer to quantify shade. We found that intensive site preparation, continued vegetation management and both fencing and tubing of tree seedlings were necessary to gain survival and protect seedlings from beaver, and cattle. Fencing out cattle provided stream bank protection within one year. Significant shading of the stream occurred 2-6 years after planting, as trees grew tall enough to intercept a significant amount of light. Single row plantings that take a minimal amount of pasture offer significant shading only after 5-7 years. A wider 6-row filter belt occupies a greater amount of pasture, but stream shading occurs sooner.
____________________________________________________________________________ 1. Badege Bishaw, Ph.D., Research Associate, and Emmingham, H. William, Ph.D., Professor and Silviculture Extension Specialist, College of Forestry, Oregon State University. 2. Rogers William, Professor and Agricultural Extension Specialist, Oregon State University
3 Establishment of Riparian Forest Buffers on Agricultural Lands in the Oregon Coast Range: Beaver Creek Case Study Badege Bishaw, William Rogers and William Emmingham
Introduction Riparian areas in the Pacific Northwest have traditionally been used as a source of natural resources, such as timber and grazing and for transportation corridors, and homesteads (Malanson, 1993; Gregory, 1997). Recently, management practices on riparian areas on forestlands have been modified to protect and restore stream conditions for anadromous fish (Newton, 1996, Nicolas 1997). Buffering of streams on forestland is required by law, however, buffering on farmland is unregulated (ODF, 1994). Because of frequent disturbances from flooding, landslides, and debris flows, riparian areas in most of the Pacific Northwest are inherently unstable. Human activities, such as logging, homesteading, grazing, and cultivation, have further modified the nature of riparian areas (Hardesty, 1993). A primary impact has been the removal of riparian tree roots and stems that provided shade and stream bank protection. Streams flowing through many agricultural areas have little or no natural tree protection. Loss of vegetation increases the velocity and erosive force of flowing water, compounding bank cutting and scouring that can eventually result in a lowering of the water table. In the Pacific Northwest, decreasing salmon populations over the past few decades have resulted in an urgent need for improving the management of watersheds, fish habitat, and water quality (Beschta, 1997; Nicolas, 1997; IMST, 1999). Riparian zones are particularly important for wildlife habitat during different seasons or stages of the life cycle. Anadromous fish spawn in streams tens to hundreds of miles inland from the ocean where they grow to maturity. Juvenile salmonids live in freshwater streams and rivers, and are critically dependent upon the water temperature and quality in-stream habitats. Thus, land uses anywhere in the watersheds can affect salmonid survival and reproductive success (Beschta, 1997; Hardesty, 1993). Riparian forest buffers in crop and grazing lands have gained increasing attention in the Northwest due to popular demand to protect salmon and steelhead and through the Governor’s Salmon and Watershed Restoration initiative (Nicolas 1997, IMST, 1999). This has generated interest in riparian forest buffers from landowners, watershed councils, and extension workers in the region. However, there is very little research base in riparian forest buffers on crop and grazing lands from which to develop and recommend suitable practices for the Pacific Northwest. Most research to support recommendations for riparian planting is from other regions (Adams, 1995; Lawrance, 1984; Vellidis, 1993; Welsch, 1991; Shultz, 1994 and 1996). The unique quality of Pacific Northwest climate, geology and stream ecology requires that caution be used in extrapolating results from other regions. In 1995, we established the Beaver Creek Riparian Buffer project to develop better information about how to establish riparian buffers on pasture land in western Oregon. Beaver Creek is a typical coastal stream with headwaters on the west flank of the Coast Range and its lower
4 reaches flowing through miles of pasture directly into the Pacific Ocean. Pastures along Beaver Creek now used for raising beef cattle were used earlier for dairy production. Pasture “improvement” and grazing have eliminated most trees and reduced vegetation to the waters edge. Our objective was to test options for re-establishment of tree cover along the stream while maintaining grazing opportunities in the pastures. We choose to plant red alder, a commercial hardwood species with a rapid juvenile growth rate. The Beaver Creek Riparian project was established by a multidisciplinary team with the cooperation of Oregon State University, Coastal Oregon Productivity Enhancement program; OSU Extension Service, Lincoln Soil and Water Conservation Program; USDA; Natural Resource Conservation Service and Forest Service, and Oregon Department of Fish and Wildlife. It was supported by the Oregon Governor’s Watershed Enhancement Program grant.
Objectives The primary goal of the Beaver Creek Riparian project was to develop information on how to establish riparian filter belts that lead to improved stream protection and fish habitat in the agricultural portions of coastal watersheds while removing as little pasture as possible from production. Specific objectives of the project were as follows: 1) control livestock access to the stream to prevent further deterioration of the stream bank, and allow natural plant regeneration to stabilize existing erosion problems; 2) establish tree filter belts to determine how effective varying widths of tree plantings will be in providing stream shading over a long period of time, and 3) test a variety of approaches to establish red alder including planting individual trees, groups of trees and rows of trees with and without protection and variations on vegetation management and weight the costs and benefits of different strategies. This paper will mainly focus on objectives one and two.
Methods Study Site The Beaver creek riparian project area lies on private property on the north fork of Beaver Creek about 8 miles south of Newport, Oregon. Beaver Creek is a meandering perennial stream that supports a productive Coho salmon run. The portion of the stream within the study area is classified as summer rearing habitat for Coho. Almost the entire length of the stream after it leaves the National Forest is used as pasture. Cattle graze to the edge of the stream in many places and there are very few streamside trees. See Fig. 1 (photo omitted). The stream channel is cut into deep alluvial soils, perhaps partially due to cattle grazing practices. The conditions are typical of many coastal streams. Installation During winter and spring of 1995 the riparian tree filter belt was established along the banks of Beaver Creek. Various trials were installed on the fenced south side and on the unfenced north
5 side of the stream. An 1100 ft stream reach along the south bank was fenced by barbed wire to keep cattle out and protect the young trees from animal browsing. Within the fenced area, a 10 ft grass strip along the bank of stream was left unplanted and untreated with herbicides to minimize soil erosion. One hundred foot long treatment areas were identified, marked, site prepared, and planted with red alder (Alnus rubra). The replicated trial involved planting red alder seedlings in 100 foot-long blocks of: one row, three rows, and six tree rows in width (See Fig. 2). The control was an unplanted, unsprayed 100 ft pasture strip. Each treatment was replicated three times. Spacing was 6 ft between trees and 6 ft between rows. Eleven hundred alder trees were planted. A U.S. Forest Service (USFS) Job Corps forestry crew did the planting in April 1995. Site preparation included herbicide treatment with a backpack sprayer. The first year with Accord (glyphosate), then Oust (sulfometuron), herbicides were used to eliminate existing pasture grasses in all areas to be planted. Control sections and stream banks were not sprayed. Follow-up treatments with Roundup Ultra (glyphosate) around individual seedlings occurred in years 2 and 3.
Tree Growth and Light Measurement We collected data on tree survival, height and diameter growth for five years. Survival and damage was determined by counting the dead and browsed trees. Height and diameter measurements were taken using measuring poles and diameter tapes, respectively, and data was recorded on a spreadsheet. Height and diameter measurements were taken at the end of each growing season, in September. To determine the amount of shade produced by tree filter belts, light measurement was recorded with a Licor LAI-2000 Plant Canopy Analyzer. This instrument records the incoming direct sunlight and diffused skylight. We used two instruments; one was set in an open field to measure the direct and diffused total light at the same time another instrument was used to measure the amount of light under the trees. Then, shade produced is estimated as the difference between light received in the open and light under the filter belt canopy. Light was recorded in August of each year, when trees were in full foliage. Shade estimates were made for points at the waters edge, near the first row of trees, and in between the rows of trees (middle and far) depending on the treatments. Light readings were taken at five sample points for each treatment. Data were analyzed and summarized with a Licor LAI-2000 Plant Canopy Analyzer computer program and Excel spreadsheet, respectively.
Results and Discussion Survival and Management of Trees Only about half of the trees planted in the Beaver Creek filter belt survived after six months (Table 1). Most of the mortality was due to early browsing and clipping by beaver and cattle.
6 There was no trend in tree survival among treatments. Table1. Percent-undamaged trees at Beaver Creek six and eight months after planting % Undamaged Trees Treatment Trees /plot (Average) Six month Eight month 6 rows of alder 102 53.9 39 3 rows of alder 51 26.1 12 1 row of alder 17 50.1 41 In July 1995, all surviving trees were Vexar-tubed and double staked by a USFS Job Corps forestry crew. Beaver damage continued through the fall of 1995 despite the fact that trees had been surrounded by Vexar tubes (see Fig. 3). By early November, the average number of undamaged trees per plot was 40 trees in the 6-row treatments (39%), 6 trees in the 3-row treatments (12%), and 7 trees in the1-row treatments (41%). In December 1995 and January 1996, 3- and 5-ft tall Protex growth tubes were placed on half of the surviving trees (See fig. 3). Most of the 5-ft tubes were later bent over or removed by severe winter winds and floods. Very few of the shorter tubes were lost. Between January and March 1996, about 125 additional alder were planted to replace all mortality. Hybrid poplar, western red cedar, western hemlock, and grand fir were also planted in small blocks, and protected with Protex growth tubes. All of the western hemlock died within 2 months during a period of heavy flooding in February 1996. Because we were able to apply better protection, browsing damage to trees was very low after the first year.
7 Fig. 3. Three types of protective devices used at Beaver Creek to protect seedlings from beaver. By August, 1996, 65 out of 80 alder trees (81%) protected only by Vexar tubes had been removed or heavily damaged by beaver. Beavers were able to climb these tubes. Only 10 out of 450 (2%) of the trees protected with Protex tubes had been damaged or removed. Beaver trails continued to be found up the riverbanks throughout the project, but the beavers were unable to climb these smooth sided tubes. With all trees protected by Protex, only occasional beaver damage was observed during the following years, but the Protex tubes required maintenance each year to make sure they were secure before beaver feeding began each spring. In April 1998, 3 years after the initial planting and 2 years after the follow-up planting, the overall survival rate was 73% (264 trees) for the 6-row treatments, 75% (135 trees) for the 3-row treatments, and 67% (40 trees) for the 1-row treatments, for a total of 439 healthy young red alder trees growing along the stream. Beavers continued to cut down trees protected only by Vexar tubes. Between September 1998 and May 1999, tree shelters were replaced throughout the project with 3-ft diameter chicken wire cages supported be 3 stakes (See Fig. 3); 143 trees at about 15-ft spacing were protected with cages. The main reason for this replacement was that the diameter of many of the trees exceeded the diameter of the Protex tubes. Many of the Protex tubes were removed from other trees in the hope that beaver would remove those trees to help thin the stands. By July 2000, however, beaver had only removed only 25 unprotected trees, accomplishing only a portion of the desired thinning. The remaining excess trees could be considered a food source for beavers that may provide desired wildlife diversity. In March 2001, many of the excess trees were cut to provide the needed thinning. Other unprotected and partially protected trees were left for beavers. Height and Diameter Growth Alder height and diameter growth was measured each year beginning in 1997. Trees grew about 1 meter during the first year. By the end of the third growing season, trees averaged 3 meters in height and had formed a closed canopy in the 3 and 6 row treatments. Throughout the measurement period, height growth was greater in the 6-row treatments (Fig. 4). Trees achieved an average height of 5.56 m, 6.12 m, and 7.43 m for the 1-, 3- and 6-row treatments in 5 years. The mean fifth year tree height for the 6-row treatment was significantly greater than that in the 3- and 1-row treatments at (P=0.05). The diameter of trees in the 6- row treatment was greater than that in the 1- and 3-row treatments, which had similar diameters in 1997 and 1998 (Fig. 5). After five growth years, trees achieved a mean DBH of 7.3 cm, 6.5 cm and 7.7 cm for the 1-, 3and 6-row treatments, respectively. Again, mean fifth year DBH for the 6-row treatment is significantly greater than the 1- and 3-row treatments. Although growth rates were not tested, the 1-row treatment had apparently grown better diameter growth than the 3-row treatment in 1999 (Fig. 5).
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Fig. 4. Mean HT (m) for Red Alder Trees at Beaver Creek Riparian Area 8.00 7.00 6.00 5.00
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Fig. 5: Mean DBH (mm) for Red Alder Trees at Beaver Creek Riparian Area 90.00 80.00 70.00 60.00
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Creation of Shade With Riparian Filter Belts An important function of a tree filter belts is provision of shade for streams and lowering stream temperature by intercepting both direct and diffuse solar radiation; preventing it from reaching the surface of the earth or a body of water. In general, shade is constrained by a number of factors. The angle and direction of solar radiation is controlled by latitude, time of the year, and time of day. The greatest solar angle during the summer in the northern hemisphere occurs at noon on June 21 and decreases on the succeeding days. Similarly, the greatest daily solar angle occurs at noon (standard time) and decreases in both the AM and PM (Larson and Larson, 1996; Beschta, 1997). At about 45 degrees north latitude, the sun is never directly overhead. Even at noon on June 21, the sun is still about 21 degrees from vertical. Tree height, direction, and distance away from the stream are all important components in determining the amount of shade a given tree or stand of trees cast on the stream. Placement of trees on the south side of an eastwest flowing stream is far more effective in providing shade than trees on the north side. The percent shade produced by each treatment at the Beaver Creek site during mid-day (10 AM2 PM) is shown in Fig. 6, 7, and 8. Shade at the waters edge was produced by reed canary grass, shrubs, and partly from trees. The amount of shade produced at the bank of the stream ranged from 22 to 34 percent at the end of the fifth growing season (Table 2), up only slightly from the 20 percent shade early in the experiment before the trees were established. As expected, the lowest percent shade was recorded for the 1-row treatment, while the highest reading was recorded for the 6-row treatment. Thus, the wider tree filter belts provided more shade than did single rows after 5 years. This can be attributed to the fact that the trees in the six-row treatment were a bit taller, and to the fact that less light could penetrate through the canopy of a stand of trees. The middle rows of trees in the 3- and 6-row treatments produced the most shade, 90 and 99%, respectively. Over all, when we compared the amount of shade produced between the treatments, the 6-row treatment produced the highest percentage of shade at all measurement points, i.e., at the bank (34%), near trees (86%), middle rows (99%), and in between far rows (96%), (Fig. 8). This was followed by the 3-row treatment, which produced 25% shade at the bank, 81% in the near rows, and 90% in the middle rows (Fig.7). The 1-row treatment produced the lowest amount of shade, i.e., 22% at the bank and 75% in the near row (Fig. 6).
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Fig. 6: Shade Produced by Red Alder Single Row Filter Belt
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Fig. 7: Shade Produced by Red Alder Three Rows Filter Belts 100 90 80 70 60 50 40 30 20 10 0 1994
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Fig. 8: Shade Produced by Red Alder Six Rows of Filter Belts 100 90 80 70 60 50 40 30 20 10 0 1994
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12 Both tree height and percent shade increased with an increase in the number of rows in the filter belts, i.e., from one row to six rows of trees (Table 2). There was a positive relationship between tree height and percent shade, i.e., as tree height increases, so did percent shade. Table 2: Fifth year tree height and percent shade produced for near row by all treatments. % Shade Treatment Average Tree Ht. Bank Near rows 1-row 5.7 m (18.7 ft) 22 75 3-row 6.1 m (20.0 ft) 25 82 6-row 7.4 m (24.3 ft) 34 87 Other factors that affect stream temperature are the stream channel morphology, flow rates and stream surface area. These are important because the capacity of a stream to buffer against temperature increase is directly influenced by water volume and the size of the surface area that is exposed to the energy source. Beaver Creek is characterized as a narrow, meandering stream with a width of 8-12 ft during the summer season. A study by Larson and Larson in July 1996, on riparian shade and stream temperature provides an illustration of the influence of solar angle on shading. In this illustration the trees were 20 and 50 feet in height and July shadows (450 North Latitude) were being cast at 12:00 noon and 2:00 pm, respectively. The trees are 10 feet from the edge of a 40-foot wide water channel that flows from east to west. Given these parameters the 20 foot trees cast 9 ft shade at 12 Noon and 14 ft shade at 2:00 pm, while the 50 foot tree cast 22 ft and 36 ft shade at 12:00 noon and 2:00 pm, respectively. In this particular case, the 20-foot tree did not cast shadow on the water at either time, while the 50-foot tree a shadow extending 12 feet into the channel at noon and 15 feet into the channel at 2:00 pm. The 50-foot trees reduce direct solar radiation on the water surface by 30-40 %. At five years after planting, the shade produced at the waters edge was increasing when measured during mid-day. During other times of the day when the sun is lower, trees 6 m tall will cast more shade. The much greater shade produced earlier at the edge of the stand illustrate in importance of getting the filter belt trees planted close to the stream. Considering the average tree height (6.0 m or 20 ft) and average stream width of 8-12 ft at Beaver Creek, we anticipate that all of the strategies will be more effective in casting shade on the stream with each passing growing season.
Conclusions Effective establishment of a red alder filter belt along a coastal stream required close attention to the details of site preparation, vegetation management and animal damage prevention. Site preparation with herbicides created essentially weed free conditions and trees with adequate protection from animal browsing survived and grew well. Additional herbicide treatments in the second and third growing season allowed trees planted at 6 by 6 ft spacing to form a closed
13 canopy in three years. After five growing seasons, all three options were producing increased shade at the edge of the stream. Although weeds may have an important function in filtering and nutrient cycling in riparian areas, weed control near planted trees is important to insure early survival and growth of red alder trees. Herbicides, as used in this study, were the most costeffective way to control weed growth. With good protection and weed control, trees grew to a height of 18-24 feet in five years, a height that was beginning to cast significant shade on the stream. Protection of tree seedlings from beaver, deer, and cattle was critical. Very early in this study, we learned that successful establishment of alder trees along riparian areas of agricultural lands required protection from both beaver and cattle. In this trial, a conventional barbed wire fence effectively excluded the cattle. Fencing out the cattle provided other benefits such as stream bank stabilization and reduced soil erosion. Beavers had to be restricted by use of plastic tree shelters at least 3 ft. high. Plastic mesh (Vexar) tubes were not effective in controlling beaver damage. Nutria, where present in the Willamette Valley or the coast, act in much the same fashion as beavers. The use of 3-ft high, smooth plastic tree shelters (Protex growth tubes) was important for promoting high tree survival and growth in this riparian area. Tree shelters provided good protection of trees from browsing by beaver. However, the Protex tubes also required maintenance at least once a year, and must be replaced by a larger effective protective mechanism when the trees outgrow the four-inch diameter tubes. We installed chicken wire cages, reinforced by wooden stakes. These appeared effective after two years, but will surely require annual maintenance to remain effective. Flooding could cause problems with any of the shelters early in the establishment process. Another effective, but very short-term technique for protecting seedlings from animal browsing, was to use Magic Circle repellent. In this study, animal browsing was not observed for a few weeks after applying Magic Circle on the trees. After more than a month, the repellent had no effect. Although, it was not quantified in this study, restoring riparian vegetation by planting trees and allowing natural regeneration on the bank of the stream will also benefit channel stabilization and reduce soil erosion. By fencing the riparian area to protect young seedlings from cattle and beaver, we have seen a natural spread of grasses, herbs, and shrubs along the stream bank. This will have direct impact in reducing soil erosion and sediment transport. In summary, the Beaver Creek Riparian project has provided valuable information on growing tree filter belts along riparian areas in the Pacific Northwest region. We were able to measure and quantify the amount of shade produced by filter belts, which is critical to improving stream temperatures. Overall, this work has helped us to generate important information that could be used to improve the water quality for fish habitat in Oregon.
References
14 Adams, B. and L. Fitch, 1995. Caring for Green Zone: Riparian Areas and Grazing Management. Environmental Canada – Eco-Action Program. Pub. No. I-581. ISBN:0-7732-1435-6. 37 pp. Beschta, R.L. 1997. Riparian Shade and Stream Temperature: An Alternative Perspective. Rangelands 19(2): 25-28. Gregory, S. V. 1997. Riparian Management in the 21st century. In: Creating a forestry for the 21st century: the science of ecosystem management. Kohn, K. A. and J.F. Franklin, (eds.). Island Press. Washington D.C. 475p. Hardesty, L.H, and Lyon, L.M. 1993. Agroforestry Opportunities in Northern California, Oregon and Washington. Dept. of Natural Resource Sciences. Washington State University, Pullman, Washington. IMST (Independent Multidisciplinary Science Team). 1999. Recovery of Wild Salmonids in Western Oregon Forests: Oregon forest Practices Act Rules and Measures in the Oregon Plan for Salmon and Watersheds. Technical Report 1991-1 to the Oregon Plan for Salmon and Watersheds, Governor’s Natural Resources Office, Salem. Larson, L.L., and S.L. Larson, 1996. Riparian shade and stream temperature: A perspective. Rangelands 18(4): 149-152 Lawrance, R., R. Todd, J. Fail, Jr., O. Hendrickson, R. Leonard, and L. Asmussen. 1984. Riparian Forests as Nutrient Filters in Agricultural Watersheds. BioScience, 34:374-377. Malanson, G.P. 1993. Riparian Landscapes. Cambridge University Press. Cambridge, Great Britain. 296 p. Newton, M., R. Wills, J. Walsh, E. Cole and S. Chan. 1996. Enhancing riparian habitat for fish, wildlife and timber. Weed Technology. Vol. 10: 429-438. Nicholas, W. Jay, 1997. The Oregon Plan: Coastal Salmon Restoration Initiative, Executive Summary & Overview. State of Oregon. 13pp. Oregon Department of Forestry. (ODF) 1994. Forest practice water protection rules, Division 24 and 57. Salem, Oregon. 59pp. Schultz, R.C., T.M. Isenhart and J.P. Colletti. 1994. Riparian Buffer systems in Crop and Rangelands. In Proceedings of Agroforestry and Sustainable Systems: Symposium Proceedings, August 7 -10, Fort Collins, Colorado. Schultz, R. 1996. Streamside buffer strips improve water quality and wildlife habitat. US Department of Energy Office of Fuels Development Energy Corps Forum. Spring 1996: 2-3.
15 Villidis, G. and R. Lowrance, 1993. Assessing the Water Quality Impact of Restored Riparian Wetland Forest. Proceeding of the Georgia Water Resource Conference, held April 20-23. Welsch, D.J. 1991. Riparian Forest Buffers: Function and Design for Protection and Enhancement of Water Resources. Forest Resource management, Northeastern Area, State and Private Forestry USDA Forest service, Radnor, Pennsylvania.
