SULPHUR TIMBER STAND IMPROVEMENT PROJECT

Transcription

1 SULPHUR TIMBER STAND IMPROVEMENT PROJECT PURPOSE AND NEED The overarching purpose of the Sulphur Timber Stand Improvement Project is to improve the overall health and vigor of immature lodgepole pine stands, while maintaining and improving vegetation conditions that will lengthen the period in which Canada lynx habitat is available within those regenerating stands. Improve the overall health and vigor of immature, developing lodgepole pine stands Over the past decade, north-central Colorado experienced a severe mountain pine beetle epidemic that killed a majority of mature lodgepole pine trees, resulting in an estimated 154,000 acres dominated by dead lodgepole pine forest on the Sulphur Ranger District. Since the start of the insect outbreak, the Sulphur Ranger District has been working to mitigate the impacts of the mountain pine beetle through a variety of projects, including: large scale timber sales, hazardous fuels treatments adjacent to National Forest boundaries, and hazard tree removal in developed recreation areas and along roads and trails. The landscape scale effects of the pine beetle epidemic dictated a forest management program largely dominated by salvage and hazardous fuels reduction projects. This situation created a backlog of forest management activities that were not directly related to responding to the effects of the pine beetle epidemic. Most notably, timber stand improvement needs in young, developing lodgepole pine stands have not been actively managed in any significant manner for many years. In the decades preceding the landscape disturbance, the Sulphur Ranger District was actively implementing a timber sale program focused, in part, on stand regeneration harvests in live lodgepole pine forest types. Many of the stands that were initiated as a result of these treatments exhibited overabundant reproduction, which will preclude good future stand growth and development in their current condition. Unlike many other tree species, lodgepole pine does not thin well naturally, which leads to stagnation and impeded diameter and height growth. Thinning is needed under such conditions because lodgepole pine will show good response at an early age if thinned before stagnation occurs. Maintain and improve vegetation conditions that will lengthen the period in which Canada lynx habitat is available within regenerating lodgepole pine stands The structural characteristics and developmental stage that make most immature lodgepole pine stands good candidates for pre-commercial thinning also make them suitable habitat for Canada lynx and their primary prey, snowshoe hare. The ranges of snowshoe hare and lynx are nearly coincident across North America (Bittner and Rongstad 1982, McCord and Cardoza 1982 in Ruediger et al. 2000). Lynx density, home range size, dispersal patterns, reproductive parameters and survival rates are strongly correlated to snowshoe hare abundance (Nellis et al. 1972, Brand and Keith 1979, Ward and Krebs 1985, Breitenmoser and Slough 1993, and Poole 1994 in Ruediger et al. 2000). Winter forage is most commonly the limiting factor to both lynx and

2 snowshoe hare survival. During winter, when snow covers low growing plants, conditions become critical for hares and they must feed on shrubs and seedlings exposed above the snow surface. Small diameter twigs and new growth are preferred browse during winter. Besides browse, hares need habitat that offers protection from predators and extreme cold. In fact, hares may select habitat where security and thermal cover is abundant even if browse is limited (Monthey 1986). There are conflicting suggestions about what cover type and structural stage are most beneficial to snowshoe hare, which influence the winter foraging habits of Canada lynx. Some research suggests that lynx require a mosaic of forest conditions: early successional forests for hunting and mature forests for denning (Koehler and Brittel 1990). Koehler s work in Washington (1990) found that among lodgepole pine and Engelmann spruce-subalpine fir cover types, snowshoe hares were most abundant in 20 year old lodgepole pine stands. Dolbeer and Clark (1975) found that areas most heavily utilized by hares in spruce-fir-lodgepole forests in Colorado contained dense undercover utilized by hares all year. Density estimates show that hares use certain seral stages more than others, and this pattern appears to be most correlated with horizontal understory cover from approximately 3-9 feet. Regardless of whether or not snowshoe hare prefer early successional or late successional forest structures, research shows common attributes between both that serve as factors for habitat selection. Snowshoe hare require forest structures that are dense enough to provide security and thermal cover, while also providing trees of a certain height that allow adequate amounts of browse at or within close proximity to average snow depths. It can be concluded that a range of forest structures can accommodate these requirements. How these requirements can be achieved over spatial and temporal scales should be the focus. Since home ranges of snowshoe hares are acres (Dolbeer and Clark 1975), units designated to provide habitat should be that size or larger. At the level of multiple stands, however, hares may be able to switch back and forth between different types of stands (Conroy et al. 1979). Habitat interspersion may be valuable to hares by providing them access to habitats with different protective abilities and food availabilities. The size of each stand and the degree of interspersion are likely to affect hare dynamics. A quilt of small stands benefits hare more than an array of large stands because the movement of hares between stands is easier when each stand is smaller (Ruggerio et al. 1999). In the aftermath of the epidemic, forest management can influence the diversity within stands and across landscapes, to reduce the probability of repeating the cycle. In the case of this project it can also be used as a tool to maintain and improve wildlife habitat conditions. Mature forest conditions, specifically in the lodgepole pine cover type experienced a profound change over the span of a seven year period from In 2008, lynx habitat suitability was remapped in an attempt to account for widespread forest mortality. All lodgepole pine classified as Habitat Structural Stage 4 or greater (>8.9 DBH) was projected to have been killed by the mountain pine beetle. The resulting output showed a drastic change in the percentage of habitat suitability (Table 1). While this exercise was most likely an over-simplification of actual habitat conditions across the forest, it is probably the best estimate of what effects the pine beetle epidemic had on

3 lynx habitat. The following is a comparison of pre and post epidemic habitat suitability by Lynx Analysis Unit (LAU). Table 1. Comparison of acres and percent total LAU area by suitable and currently unsuitable lynx habitat, 2001 assessment and 2008 post mountain pine beetle epidemic. LAU CLEAR CREEK HABITAT ORIGINAL REVISED ACRES % ACRES % LYNX HABITAT 41, % 41, % SUITABLE 39,696 95% 25,465 61% CURRENTLY UNSUITABLE 2,052 5% 16,283 39% FORAGE (w/o denning) 26,223 63% 14,136 34% DENNING (also forage) 10,008 24% 8,746 21% OTHER HABITAT 3,465 8% 2,583 6% FRASER UPPER COLORADO WILLIAMS FORK LYNX HABITAT 78, % 78, % SUITABLE 75,191 96% 43,796 56% CURRENTLY UNSUITABLE 3,068 4% 34,468 44% FORAGE (w/o denning) 26,522 34% 7,260 9% DENNING (also forage) 45,697 58% 34,527 44% OTHER HABITAT 2,972 4% 2,009 3% LYNX HABITAT 154, % 154, % SUITABLE 148,235 96% 66,236 43% CURRENTLY UNSUITABLE 5,903 4% 87,910 57% FORAGE (w/o denning) 67,152 43% 10,250 7% DENNING (also forage) 72,341 47% 48,850 32% OTHER HABITAT 8,742 6% 7,137 4% LYNX HABITAT 89, % 90, % SUITABLE 84,849 94% 40,030 44% CURRENTLY UNSUITABLE 5,110 6% 49,977 56% FORAGE (w/o denning) 37,962 42% 12,634 14% DENNING (also forage) 39,084 43% 23,391 26% OTHER HABITAT 7,803 9% 4,005 4% Purpose and Need in context of the Southern Rockies Lynx Amendment (SRLA) On October 29, 2008 the USDA Forest Service in the Rocky Mountain Region signed a Record of Decision which amended the eight Forest Land and Resource Management Plans in the Region to add consistent management direction that will conserve the Canada lynx. This Southern Rockies Lynx Amendment (SRLA) provides specific guidance and direction in the form of standards, guidelines, and objectives for vegetation management activities in lynx habitat on the Southern Rockies National Forests. The Forest Service considered the changed conditions

4 created by the mountain pine beetle epidemic and acknowledged that an estimated 1.5 million acres of forest mortality would likely impact lynx habitat. Maintaining some degree of management flexibility so that managers are able to influence the development of future forest conditions was an important consideration when the Forest Service made this decision. Management direction was designed to strike a reasonable balance in providing for the conservation and recovery of lynx, and reducing or eliminating potential adverse effects from land management activities and practices on national forests in the Southern Rockies, while preserving the overall multiple-use direction in existing Plans. Vegetation Standards most applicable to this proposed action include: Standard VEG S1 If more than 30 percent of the lynx habitat in an LAU is currently in a stand initiation structural stage that does not yet provide winter snowshoe hare habitat, no additional habitat may be regenerated by vegetation management projects. Standard VEG S5 Precommercial thinning practices and similar activities intended to reduce seedling/sapling density are subject to limitations from the stand initiation structural stage until the stands no longer provide winter snowshoe hare habitat. The intent of S1 is to provide a distribution of stand age classes that would maintain lynx habitat over time. The intent of S5 is to provide snowshoe hare habitat while permitting some thinning, to explore methods to sustain snowshoe hare habitat over time, reduce hazardous fuels, improve forest health and increase timber production. Project design must ensure any precommercial thinning provides an appropriate amount and distribution of snowshoe hare habitat with each LAU over time, and maintains lynx habitat connectivity within and between LAU s. Project design should focus on creating irregular shapes for the thinning units, creating mosaics of thinned and unthinned areas, and using variable density thinning (USDAFS 2008). Since pine beetle related mortality caused habitat unsuitability to exceed 30 percent in each LAU on the Sulphur Ranger District (Table 1), currently suitable habitat such as those stands proposed for treatment in this project are that much more important to maintain. There is a need to implement precommercial thinning, using an adaptive management approach, where it could be done to promote or prolong winter snowshoe hare habitat, while also improving stand composition and growth. This need can be met within the confines of vegetation standards S1 and S5 by designing thinning prescriptions that reduce stand density to promote stand growth while retaining at least 35 percent dense horizontal cover, which is identified in the SRLA as the lower hinge point for lynx use during the winter.

5 PROPOSED ACTION The Forest Service is proposing to address the purpose and need for action by implementing a variety of thinning and variable density prescriptions designed to reduce stand density, improve stand growth and composition, and promote or prolong vegetation conditions suitable for lynx habitat. Approximately 4,325 acres of immature lodgepole pine stands are proposed for treatment. Proposed thinning treatments range from fixed width crown spacing, which promote individual tree growth and delay crown recession to variable density spacing, which promote individual tree growth, release of later successional tree species already established in the understory, and delay crown recession. Recommended prescriptions are described in detail in Table 2. Proposed treatments apply to a range of stand conditions. All stands are dominated by lodgepole pine with varying degrees of density ranging from 300-5,700 trees per acre. Besides average tree density, stands are further categorized by composition of tree species established in their understories. Proposed treatment intensities are a function of the relationship between current stand density and the target percentage of residual dense horizontal cover of percent. Variable density treatments are related to understory species composition, with larger openings and a more clumpy distribution of residual stand density proposed in stands with late successional species regenerating in the understory. Fixed width spacing is proposed for stands with either lodgepole pine or no regenerating understory. There are many potential prescriptions which could be developed in an attempt to meet tree growth and wildlife objectives. An iterative approach will be used for this project. Treatment prescription efficacy will be verified through monitoring and additional prescriptions may be developed, if necessary, to better meet objectives. Thinning would be implemented with work crews using chainsaws. Activity slash may be treated by lop and scatter or a combination of pull back, lop and scatter. Pull back slash treatments would be focused in stands where there are Engelmann spruce and subalpine fir successfully regenerating in the understory to encourage the release of those species. Vegetation treatments could include the use of force account crews or service and stewardship contracts.

6 Table 2. Summary of proposed treatments, Sulphur Timber Stand Improvement Project SILVICULTURAL PRESCRIPTION Precommercial Thinning with Reserves (PCT-R) STAND CLASS 1A,1B, 1C, 1D DESCRIPTION ACRES NO. UNITS Thin 80% of the total stand area: Thin 80% of the total stand area to uniform spacing in the range of 6x6 to 10x10 foot spacing. Residual density in the uniformly spaced portions of the stand would be in the range of 400 1,200 trees per acre. Leave tree preference should favor retention of co-dominant and dominant trees with the highest crown ratios. Co-dominant and dominant trees shall have retention preference up to a crown ratio threshold of 75%, after which trees in intermediate, subordinate classes with higher crown ratios should be given preference. Trees with large crowns are not necessarily desirable because they do not utilize growing space efficiently. While crown width provides some valuable contribution to dense horizontal cover, the most productive thinned stands are not necessarily characterized by a certain amount of foliage, but by an efficient vertical distribution of foliage in the canopy. Therefore, distinction between crown ratio and crown width 2, is important when selecting desirable leave trees. Reserve 20% of the total stand area: Reserve 20% of the total stand area in un-cut patches, approximately ½ acre in size (150 x150 diameter). Patches should retain a spatially well-distributed selection of the very densest patches of saplings. Slash Treatment Slash shall be bucked into lengths no greater than 6 feet and scattered to a depth, not to exceed 18 inches. When necessary, slash should be pulled into retention zones or areas with less residual slash to meet depth requirements.

7 Crop Tree Cut 60% of the total stand area: Cut approximately 60% of the total stand area in 1/100 acre groups (16 foot diameter). Retain one tree per group. Residual density in crop tree cut portions of the stand would be approximately 100 trees per acre, spaced 21 feet apart. Leave tree preference should favor retention of co-dominant and dominant trees with the highest crown ratios. Placement of groups should be focused in areas of the stand where Engelmann spruce and subalpine fir are successfully regenerating in the understory (> 300 tpa). Preference for group placement in stands with non-uniform, clumpy distribution of sprucefir understories should be given, however some group selection opportunities may have to be foregone in order to adhere to group spacing requirements. Crop Tree Thinning with Reserves (CTT-R) 2A,2B, 2C,2D Reserve 40% of the total stand area: Reserve 40% of the total stand area in un-cut matrix, between selected crop tree thinning areas. Thinning within the matrix may be required to meet residual, relative density targets. 2, Slash Treatment (Group Areas): Slash shall be bucked into lengths no greater than 6 feet and scattered to a depth, not to exceed 8 inches within group areas. Low slash loading in crop tree group areas is needed to ensure the release of spruce-fir seedlings. When necessary, slash should be pulled into retention zones (matrix) or areas with less residual slash to meet depth requirements. Slash Treatment (Matrix): Slash shall be bucked into lengths no greater than 6 feet and scattered to a depth, not to exceed 18 inches, within the matrix. When necessary for meeting depth requirements, slash should be pulled back throughout the matrix only.

8 LITERATURE CITED Dolbeer, R.A. and Clark, W.R Population ecology of snowshoe hares in the central Rocky Mountains. Journal of Wildlife Management 39: Koehler, G.M Demographic and habitat characteristics of lynx and snowdhoe hares in north-central Washington. Canadian Journal of Zoology. 68: Koehler, G.M. and Britell, J.D Managing for Spruce-fir Habitat for Lynx and Snowshoe Hares, Journal of Forestry, p Monthey, R.W Responses of snowshoe hares, Lepus americanus, to timber harvesting in northern Maine. Can. Field-Nat. 100: Ruediger, B Canada lynx conservation assessment and strategy. U.S. Department of Agriculture, Forest Service; U.S. Department of the Interior, Fish and Wildlife Service; USDI, Bureau of Land Management, and USDI, National Park Service. Forest Service Publication #RR Missoula, MT. Ruggerio, L.F., Aubry, K.B., Buskirk, S.W., Koehler, G.M., Krebs, C.J., McKelvey, K.S., and Squires, J.R Ecology and Conservation of Lynx in the United States. Boulder: University Press of Colorado. USDAFS Implementation Guide for the Southern Rockies Lynx Amendment.