CHEYENNE CANYON TUSSOCK MOTH CONTROL PROJECT

Transcription

1 CHEYENNE CANYON TUSSOCK MOTH CONTROL PROJECT FOREST VEGETATION REPORT Pike National Forest, Pikes Peak Ranger District El Paso County, CO PURPOSE AND NEED The purpose of this project is to minimize the spread and intensity of the Douglas-fir Tussock Moth outbreak in the Colorado Springs area. The project is needed to complement state and local agency and landowner efforts to control the moth. The greater Colorado Springs area is mosaic of private, city, state, and federal lands. The juxtaposition of different landownership, as well as divergent management objectives among local, state, and federal agencies, requires a high level of collaboration and communication to control the current outbreak. The Tussock Moth causes defoliation and kills Douglasfir and other coniferous trees. These trees are a valued component of the scenic backdrop for the communities, enhance recreation values, and provide watershed protection and wildlife habitat. On National Forest lands, the Tussock Moth outbreak is immediately adjacent to private, municipal, and state lands; lies within the Wildland Urban Interface; and is occurring within a heavily-used recreation area. There are concerns that the outbreak may continue to spread on National Forest lands and onto adjacent private, city, and state lands. The project is intended to minimize additional Douglas-fir mortality on the Pike National Forest adjacent to current infestations. The Tussock Moth is a native defoliator with well documented outbreaks occurring in Colorado since at least the 1930 s. These outbreaks typically last for two to four years. On the Pike National Forest, the 1993 to 1996 outbreak resulted in 30 to 40 percent Douglas-fir mortality, affecting 18,000 acres. Other outbreaks have been smaller and more isolated. The current outbreak was first noticed in 2014 on Cheyenne Mountain State Park and Cheyenne Mountain Air Force Station land. The current Cheyenne Canyon Tussock Moth infestation covers approximately 1,000 acres across private, city, state, and federal land ownership. In the Cheyenne Canyon area, there are approximately 50 acres of infestation on National Forest lands. There are mixed stands of ponderosa pine, Douglas-fir, and white fir adjacent to existing infestations that could potentially be affected by spread of the Tussock Moth. Within the project area there are old growth Douglas-fir and Douglas-fir plantations that are now 80 to 110 years old. Treatments within the project area would maintain desired forest structure by protecting high-value trees, including old growth and large diameter Douglas-fir adjacent to current infestations, and complement moth control actions on nearby lands under state, local and private ownership. PROPOSED ACTION The Pike & San Isabel National Forests and Cimarron & Comanche National Grasslands propose to implement control measures to minimize the spread and intensity of the Douglas-fir Tussock Moth outbreak on National Forest System Lands within the Wildland Urban Interface near Colorado Springs. The Project Area encompasses 408 acres near Cheyenne Canyon in El Paso County, Colorado. The affected areas are in portions of T14S, R67W, Sections 28, 29, 32, and 33; and T15S, R67W, Sections 4, Page 1 of 8

2 5, 9, and 10. The attached map shows the current outbreak and the areas on National Forest System Land that are proposed for treatment. In separate actions, treatments are scheduled to occur on private, city, and state lands adjacent to the National Forest. Those treatments are separate from this proposal and are not part of the Forest Service proposed action. Control of the moth would be accomplished using Foray 48B Biological Insecticide. The insecticide would be applied from the air by helicopter. A single treatment would occur during the period when treatment would be most effective, which is most likely to happen during the month of June No application would occur in areas where surface water is present, including ponds, lakes, and wetlands and perennial, intermittent, and ephemeral streams. A 100 foot no spray buffer on either side of all perennial and ephemeral streams will be applied. Best management practices and all EPA label directions will be strictly followed. The treatment area would be closed to the public during the period of aerial application. EXTRAORDINARY CIRCUMSTANCES DISCUSSION Not applicable to this vegetation report. There are no resource conditions related to vegetation and forest health that could lead to an extraordinary circumstance. EFFECTS ANAYSIS Topography The project area is very steep with an average slope of approximately 50%. Aspect is varied with groups of stands proposed for treatment occurring on south, north, and east facing slopes. The terrain is too steep for mechanized work with conventional ground based logging equipment and only limited manual chainsaw work would be feasible for most silvicultural treatments. Forest Cover The forest cover in the area is outside of the natural range of variation. Under a mixed severity fire regime, forest cover would be more open with a higher percentage of ponderosa pine. Fire suppression and forest management practices such as tree planting have altered forest composition and structure over the past 110 years. These changes have resulted in conditions more conducive to outbreaks of both Douglas-fir tussock moth and Douglas-fir beetle at the lower elevations of eastern Colorado s forest (Schaupp et al.). Species Composition Forest cover is dominated by ponderosa pine (Pinus ponderosa)-douglas fir (Pseudotsuga menziesii) woodlands and dry mixed conifer stands. The ponderosa pine-douglas-fir woodland type occurs primarily on southern aspects. Douglas-fir is generally a minor component in these stands, typically comprising 20-30% of the overall stand stocking. Ponderosa pine forest types will transition into dry mixed conifer forest at the ridgetops. This forest type is prevalent on northern aspects. These stands are dominated by Douglas-fir. White fir (Abies concolor) is present in the understory. In natural stands, common associates are limber pine (Pinus flexilis), and Page 2 of 8

3 Acres blue spruce (Picea pungens). Since the project area is heavily planted, limber pine and blue spruce occur at very low densities if present at all. Dry mixed conifer forest types will transition into wet mixed conifer types on the northern aspects adjacent to riparian areas. Engelmann spruce (Picea engelmanii) may be present in moist mixed conifer types. Aspen (Populus tremuloides) may be present in all forest types. At the lower elevations in the project area gamble oak (Quercus gambelii) is an understory associate with ponderosa pine. Since majority of the project area was planted between 1905 and 1931 (Stahelin) with ponderosa pine and Douglas-fir, other common associates of the ponderosa pine, dry mixed conifer, and moist mixed conifer forest types in natural stands are either absent or occur at very low densities, often in groups where site conditions are most favorable. Shade intolerant species have become more common. This shift in species composition has increased the susceptibility of these sites to Douglas-fir tussock moth damage because there is a greater food supply (Schaupp et al.) Figure 1. Project area forest cover types. 250 Forest Cover Type LESS THAN 25% VEGETATION MX CONIFER - cool and/or moist MX CONIFER - warm and/or dry PONDEROSA PINE - DOUGLAS-FIR PONDEROSA PINE/GAMBLE OAK PONDEROSA PINE/GRASS UNCLASSIFIED Structure and Canopy Closure Majority of the area is classified as intermediate (Habitat Structural Stage - HSS 3B) and mature (HSS 4A) structure, open stands (less than 40% canopy closure). Habitat Structural Stage is forest vegetation classification method that allows managers to classify forest vegetation by species composition, size class, and density (see Figure 2 for definitions). It is a useful tool for describing existing conditions and potential environmental effects in vegetation management analysis areas. Closed stands (HSS 3C and HSS 4C) currently occupy one third of the project area per the forest vegetation layer. This is likely an underestimate as closed canopy conditions in these forest types tend to comprise 50% or more of the forested areas on the Pikes Peak Ranger District for comparable vegetation, including plantations. Majority of the closed stand conditions occur in the ponderosa pine-douglas-fir and dry mixed conifer forest types. Page 3 of 8

4 Figure 2. Habitat Structural Stage by Forest Cover Type. HSS 4A HSS 3A HSS 1M PONDEROSA PINE/GAMBLE OAK PONDEROSA PINE/GAMBLE OAK HSS 4A PONDEROSA PINE/GAMBLE OAK HSS 2S PONDEROSA PINE - DOUGLAS-FIR PONDEROSA PINE - DOUGLAS-FIR HSS 4A PONDEROSA PINE - DOUGLAS-FIR PONDEROSA PINE - DOUGLAS-FIR HSS 3A HSS 3B MX CONIFER - warm and/or dry MX CONIFER - warm and/or dry MX CONIFER - cool and/or moist MX CONIFER - cool and/or moist HSS 4A HSS 3B HSS 3A Habitat Structural Stage Definitions 2T = trees under 0.9 diameter breast height (dbh); 3A = trees dbh, cover percent <40; 3B = trees dbh, cover percent >= 40 and <=70; 3C = trees and cover percent >70; 4A = trees >8.9 dbh and cover percent <40; 4B = trees >8.9 dbh, cover percent >= 40 and <=70; and 4C = trees >8.9 and cover percent >70. Mortality and Defoliation Tree mortality in the area is currently limited to small pockets of tussock moth and spruce budworm activity. Majority of the tussock moth mortality in the area occurs on property owned by the city of Colorado Springs in the North Cheyenne Canyon Park area. Recent surveys by staff from the Forest Health Protection, Lakewood Service Center group found low densities of egg masses at sites in North Cheyenne Canyon on property owned by the City of Colorado Springs and within the project area on national forest lands (Stephens and Powell, 2016). These surveys indicate that no or light defoliation is expected to occur on these sites. Spruce budworm activity, although present, is more concentrated at higher elevations above the project area. Page 4 of 8

5 Plantations Plantation were established on the Pike National Forest and elsewhere in Colorado between 1905 and 1938 to restore forest cover where it had been destroyed by wildfires, for erosion control, stream regulation, and timber production (Stahelin). Approximately 75% of the Pikes Peak Reserve burned in a series of fires that occurred between 1846 and approximately 1880 with majority of the fires occurring between 1850 and 1853 (Gardner). Planted species in the North Cheyenne Canyon area were primary ponderosa pine and Douglas-fir. Although available records do not list white fir as a planted species in this area, it is possible that a minor amount of white fir was also planted and recorded as other conifers. Little effort was made during early planting operations to use seed of local origin (Stahelin). Early plantations were established when genetics as a science was in its infancy (Scott et al.). Consequently the genetics for some of these plantations are not adapted to local conditions. Monitoring of early plantations indicates early senescence and the near absence of natural regeneration (Scott et al.). Plantations established with off-site genetics tend to exhibit one or more of the following symptoms: 1. Poor survival. 2. Reduced growth and cold hardiness. 3. Increased incidence of insect and disease problems. 4. Sparse crowns. 5. Broken tops (low elevation or low latitude sources planted at higher elevation or higher latitudes). 6. Increased fuel loads. 7. Increased pollen production. 8. Production of stress cone or seed crops. These symptoms are characterized as a stress response (USDA Forest Service). Early plantations were also planted at higher densities than current reforestation practices (now seedlings/acre). Plantations containing 250 or more living trees per acre were considered satisfactory (Stahelin). In order to meet this stocking requirement it is estimated that seedlings were planted at a minimum spacing of 8 feet by 8 feet (681 trees/acre) when considering published survival rates on the Pikes Peak National Forest (approximately 40% five years following planting) (Stahelin). The combination of high densities and stress responses due to off-site genetics increase the susceptibility of Douglas-fir plantations to tussock moth defoliation and Douglas-fir bark beetle damage. Old Growth Scattered remnant, old trees (> 150 years of age) are present in the project area in the areas that escaped wildfires. Old growth stand are not. Old trees are present at very low densities, typically less than one tree per acre, and often in groups. Older trees will be a mix of ponderosa pine and Douglas-fir. These trees are often larger diameter, dominant and codominant trees however old, suppressed, small diameter trees may also be present in unburned areas that were not planted. Old growth ponderosa pine trees have likely exceeded the optimum age for cone production ( years). Old growth Douglas-fir trees are an important seed source for the regeneration of locally adapted trees in the project area. Optimal cone bearing age for Douglas-fir occurs between years of age (Hermann and Lavender). Climate Change Ponderosa pine is a very drought tolerant species and its range is expected to expand in the Pikes Peak area under dryer and warmer conditions. Douglas-fir covers a wide range of sites and can tolerate moderately dry conditions. In the long term Douglas-fir may still occur in association with ponderosa Page 5 of 8

6 pine but its distribution may be more restricted. Douglas-fir that is currently established on moister sites may persist. The range of Engelmann spruce will likely move up in elevation under dryer and warmer conditions. Some of these trees will be at risk of decline due to drought stress and infestation by other damage agents including spruce beetles. Blue spruce can tolerate dryer conditions than Engelmann spruce however some of these trees would also be at risk of decline if present in the project area. STATEMENT OF EFFECTS Only light defoliation can be expected in the project area based on the Lakewood Service Center survey results (Stephens and Powell) which indicate that tussock moth egg masses are present in low numbers. The timing of the outbreak, year three, also indicates that population may be declining in the project area (phase three): Douglas-fir tussock moth outbreaks can be divided into four phases, the release, characterized by rapid population growth to outbreak population size, the peak, during which insect density and current defoliation are maximum, the decline when survival and population numbers fall precipitously; and the post decline, when the population size returns to the endemic condition. Each phases typically lasts for one year. (Schaupp Jr. et al.) Treatment may reduce some of the defoliation in the project area on host trees. This effect would be minor and would generally occur in the smaller size classes. The risk of mortality of old, large diameter host trees is low. A few scattered individual trees or groups of these trees may be more resilient to both tussock moth and bark beetle damage following treatment. This effect would only apply to host trees with higher than expected levels of larval activity. Tree mortality as a direct result of Douglas-fir tussock moth defoliation is generally greater in the smaller diameter classes. Following defoliation, larger diameter trees tend to die more as a result of attack by opportunistic insects such as bark beetles. Some top kill can result from secondary insect attack following defoliation too. However, mortality of large diameter trees as a direct result of defoliation does occur. Studies indicate that trees that are defoliated at 90% or more in one year have a high probability of dying (Wickman 1978; Weatherby and others 1992). (Schaupp et al.) Should tussock moth related mortality occur consistent with historical levels in the project area, 30-40% (Schaupp Jr. et al.), then forest cover would be more open and species composition would shift to a higher percentage of ponderosa pine which would be more consistent with historical or future warmer, dryer conditions. It is unknown how the plantations will respond to climate change but it can be expected that the conditions within the project area will not be well suited for shade intolerant species or trees that are not genetically adapted to local conditions. Since the project area was most likely dominated by ponderosa pine prior to Euro-American settlement, only a minor amount of shade intolerant species such as Douglasfir were likely present prior to the 1850s. Some tussock moth related defoliation and bark beetle related mortality of Douglas-fir and white fir trees in the project would be consistent with either reference condition. In summary, the effect of the proposed action would likely be limited to a small amount of individual trees and groups of trees of all sizes unless tussock moth larval levels are higher than expected. A reduction in tussock moth defoliation and secondary attacks by Douglas-fir beetles on an incidental amount of old growth Douglas-fir may maintain a locally adapted seed source and some structural Page 6 of 8

7 diversity within treated stands where larvae are concentrated in high numbers. The proposed treatment is not expected to alter the overall structure, density, and species composition at the project scale. LITERATURE CITED Gardner Results of a Rocky Mountain Forest Fire Studied Fifty Years after Its Occurrence. Proceedings of the Society of American Foresters. Volume 1. No. 2, November Hermann, R.K. & D.P. Lavender Pseudotsuga menziesii (Mirb.) Franco Douglas-Fir. Pages IN: Silvics of North America Vol. 1: Conifers. R. M. Burns and B.H. Honkala (tech. coordinators). USDA, Forest Service Agriculture Handbook 654. Schaupp, W. C., Costello, S. L., and Ciesla, W. M The History of Douglas-fir Tussock Moth in Colorado and Wyoming. Technical Report R2-67. USDA Forest Service, Forest Health Management, Renewable Resources, Rocky Mountain Region, Lakewood, CO. Scott, G., Mahalovich, M. F., Rinehart, S., and Krueger, J Reforestation Revegetation Climate Change Primer for the Northern Region/ USDA Forest Service, Northern Region. Stahelin, R Thirty-five years of planting on the National Forests of Colorado. Rocky Mountain Forest & Range Experimental Station. Fort Collins, Colo. Stephens, S. and Powell, R Douglas-Fir Tussock Moth Egg Mass Survey at North Cheyenne Canyon Park, Colorado Springs, Colorado. USDA Forest Service, Forest Health Protection, Lakewood Service Center. USDA Forest Service. Forest Service Handbook (FSH) F Seed Handbook, Chapter 200 Seed Transfer Rules Part A. Amendment No.: R F-2009-x. Northern Region (R1). Missoula, MT. Jeffrey Underhill Regional Silviculturist USDA Forest Service Rocky Mountain Region May 13, 2016 Page 7 of 8

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