EXECUTIVE SUMMARY Most of the Aspen Examined Are in Very Poor
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EXECUTIVE SUMMARY Most of the aspen examined are in very poor health. There is a variety of reasons for this, but it boils down to the fact that aspen growth and vigor is susceptible to drought conditions, and drought- stressed trees become predisposed to secondary agents such as insects and disease. This has been a very dry summer and spring, further stressing the aspen clones. Most of these areas could benefit from removal treatments. A high priority would be to remove dead and hazardous trees along the road and trails so as to protect the public recreating on Howelsen and Emerald Mountain Parks. Cankers can only be prevented not cured; therefore the removal and proper disposal of this dead and hazardous material would be necessary to avoid further spread onto the adjacent and regenerating areas. Monitoring and evaluation would be recommended after treating these areas. Assessment of health and vigor of the regeneration would help in establishment of a new clone. 1 Howelsen Hill Park – Aspen Assessment Introduction The City of Steamboat Springs requested CSFS for an assessment of the aspen (Populus tremuloides) stands along Blackmer Drive. The evaluation was conducted from the lower gate to the quarry along the road. Blackmer Drive is the main access to Howelsen Hill and Emerald Mountain Parks. It is heavily used for biking, hiking, skiing and other recreation by locals and tourists throughout the year. Colorado Aspens Forests and Sudden Aspen Decline (SAD) The normal development of forests includes changes that are a result of natural processes. Gradual changes, at times barely noticeable, are sometimes interrupted by sudden changes, when forests experience fire, insect outbreaks, or major droughts. In recent years, the aspen forests of Colorado have experienced rapid changes that include the death of many large old trees, and at times entire clones. Most of aspen forests in Colorado developed after stand-replacing disturbances such as fire. After a disturbance, the root systems of aspens send up thousands of new stems (suckers). Some of these will survive browsing and competition and grow to be large trees. Most will die as a result of competition for light, water, and nutrients. Although aspens usually have strong regeneration, the amount and success of this regeneration can be affected by the health of the overall clone. Aspen forests are affected by a wide variety of insects and diseases. Canker (fungal) diseases and stem borer insects are more common as trees become more stressed, and they are often present when trees die, even though the primary factor in mortality might have been drought. It is difficult to assign a single cause of mortality. It is usually a combination of factors killing the aspen. The severe droughts of recent years (2000-2003, 2012) have played a large role triggering the widespread mortality in aspen across the landscape. Soils The geology of Emerald Mountain consists mainly of Mancos shale (sedimentary rock) with outcrops of glacial rocks or moraines. The Mancos Shale or Mancos Group is an Upper Cretaceous geologic formation of the Western United States dominated by mudrock that accumulated in offshore and marine environments of the Cretaceous North American Inland Sea. The Mancos was deposited around 95 to 80 million years ago. The main soil types along Blackmer Drive are Lintim loam and Routt loam. Lintim loam is loess derived from mixed and/or slope alluvium derived from shale, with a heavy clay component. Routt loam is colluvium derived from sandstone and shale and/or slope alluvium derived from sandstone and shale, with a heavy clay component and slightly more organic matter than the Lintim loam. In general, these two soil types are poor in organic matter and shallow in depth. Some of the areas assessed, especially on the eastern slopes, were very rocky and very dry. 2 Howelsen Hill Park – Aspen Assessment Insect & Disease Discussion Areas Six areas were identified in this assessment, mostly along Blackmer Drive. These areas do not encompass all of the aspen stands in the vicinity, and the boundaries are approximate for management purposes. Please see the attached map for further reference. With the exception of the stands labeled 5 and 6, most of the aspen examined are in very poor health. There is a variety of reasons for this, but it boils down to that aspen growth and vigor is susceptible to drought conditions, and drought- stressed trees become predisposed to secondary agents such as insects and disease. Drought and competition within the stand may impact the vigor and resiliency of an aspen stand, but even healthy aspen are subject to host of factors that impact individual tree health Young trees are sometimes killed by bark-eating mammals, that girdle the stem at or near the ground level, such as meadow mice and snowshoe hares. Larger animals, such as deer, elk, and moose, frequently seriously damage reproduction by browsing. They also damage older trees by rubbing their antlers against the stems. Elk and moose can also damage pole- and saw log-size trees by "barking" them with their incisors. Such injuries often favor secondary attack by insects or pathogens. A high population of porcupines can greatly damage tree crowns both directly by feeding, and indirectly by increasing the trees' susceptibility to attack by insects and diseases. The red-breasted and yellow-bellied sapsuckers may seriously damage trees with drill holes. Minor damage is caused by such woodland birds as the sharp-tailed grouse, which feed on the buds of quaking aspen. All of these animals are residents of Howelsen Hill and Emerald Mountain Parks. Aspen is susceptible to a large number of diseases. Two or more species of Ciborinia cause a leaf spot on trees of all ages. When the disease is severe, small trees may be killed, but older trees rarely die. Marssonina populi causes a leaf spot and shoot blight that is especially prevalent and damaging in the western states. It is responsible for occasional severe defoliation. Severe, repeated infection can cause mortality, although susceptibility to this disease varies greatly among clones. Stem cankers are common diseases of aspen that have a great impact on the aspen resource. Depending on the causal fungus, cankers can kill a tree within a few years or persist for decades. Ceratocystis canker is a target-shaped canker caused by Ceratocystis fimbriata, C. moniliformis, C. piceae, C. pluriannulata, C. ambrosia, C. cana, C. serpens, C. crassivaginata, C. populina, C. tremuloaurea, and C. alba. This canker is found throughout the range of aspen, with C. fimbriata the most common causal pathogen. These cankers seldom kill aspens but can reduce usable volume of the butt log. Infection is primarily through trunk wounds and insects are the primary vectors. Sooty-bark canker of aspen is caused by Phibalis pruinosa and is common and a major cause of mortality in the West. The fungus infects trunk wounds and spreads rapidly, killing trees of all sizes. Cytospora canker is caused by Cytospora chrysosperma, a normal inhabitant of aspen bark. The fungus is not considered a primary pathogen and causes cankers, lesions, or bark necrosis only after the host tree has been stressed, such as by drought, fire, frost, suppression, or 3 Howelsen Hill Park – Aspen Assessment leaf diseases. The disease is most serious on young trees and is found throughout the range of aspen. Trees with large cankers have extensive trunk rot and are frequently broken by wind. Aspen is susceptible to three types of rough-bark which are caused by the fungi Diplodia tumefaciens, Rhytidiella baranyayi, and Cucurbitaria staphula. Rough, corky bark outgrowths persist for many years but do little harm. Defoliators of aspen belong primarily to the orders Lepidoptera and Coleoptera. The forest tent caterpillar (Malacasoma disstria) and the western tent caterpillar (M. californicum) have defoliated aspens over large areas. The large aspen tortrix (Choristoneura conflictana) is found throughout the range of aspen. It has defoliated trees over very large areas as well. Both of these defoliators were observed throughout these areas earlier in the season. Wood-boring insects that attack aspen are primarily beetles of the Cerambycidae (round-headed borers or long-horned beetles) and Buprestidae (flatheaded borers or metallic beetles). The poplar borer (Soperda calcarata) is the most damaging. The larvae tunnel in the bole, weakening and degrading the wood. Breakage by wind increases and the tunnels serve as infection courts for wood-rotting fungi. I & D Area 1 Description: Area 1 is approximately 2.5 acres and has a north – northwest aspect. It is open and exposed to wind. It looks like it is a transition zone stand, on the edge of the oak-sage areas. The aspen trees are smaller than in the upper areas. This is a marginal site for aspen. Even with the recommended treatment, growth is limited by the quality of the soils and the availability of water. At least half of the trees are dead and the live component has both Sooty-bark canker and Cytospora canker. There was no regeneration observed. Damage/Importance: - Canker describes an area of dead cambium (living cells just beneath the thin bark). It can kill individual twigs, branches, and portions of trunks when it succeeds in girdling those parts. - Infected trees often break at the canker site and can be hazardous. - Canker fungi travel from tree to tree by disseminating their spores with the wind, rain, insects, birds and humans. Prescription/Recommendation: • Prevention is much more profitable than attempts to control. • Avoid wounding the aspen trees. • Regular tree inspection can improve early canker detection. If a smaller canker is found on a branch, prune that branch off. Small trunk cankers can sometimes be cleaned up by removing affected tissue to down to sound unstained wood.