Report to Lake Shastina Property Owners Association on Dead and Dying Trees Around Zen Mountain

Transcription

1 Report to Lake Shastina Property Owners Association on Dead and Dying Trees Around Zen Mountain by John Kessler, CA Registered Professional Forester #2494

2 Issue of Concern Residents of Lake Shastina have been contacting the Lake Shastina Property Owners Association (LSPOA) about the number of trees dying on the sides of Zen Mountain, in the southern portion of the community. LSPOA General Manager John McCarthy contacted foresters John Kessler (John Kessler Forestry) and Jon Miller (Cal Fire) regarding the problem and took both foresters on a site visit. Following these visits, Cal Fire Pest Specialist Don Owen was contacted and asked to visit the area with John Kessler. During that visit, several forest pests were identified as present in the area and contributing to the tree mortality. Treatment options were discussed and recommendations proposed to treat the existing causes of tree mortality and to reduce the potential for these pest to move into the more dense stands of ponderosa pine in the nearby area. This report is intended to provide information to the community about current causes of tree mortality and provide some recommended actions that community members can take to reduce the risk to their trees. As most would guess, the underlying issue contributing to the dead and dying trees at Lake Shastina, as well as other areas in the state, is the on-going drought. The lack of precipitation this past year has increased the stress on the forest stands and made them more susceptible to attacks from insects and disease. When one drives around the Lake Shastina community, there are numerous areas with one or two dead trees or a small group of dying trees. This is normal and is part of the forested environment. As forest density increases and is influenced by climatic/ecological factors, pathogens that are always present attack weakened trees. The problem is that when a climate cycle hits an extreme point, whether it s drought, cold, heat, or excess precipitation, it can lead to an increased impact on ecological systems. In the case of Zen Mountain, the lack of precipitation over the past few years has increased stress on the pines in Lake Shastina. Junipers have also been impacted to a lesser extent, but the combination of cold and drought has led to some additional mortality among those trees. However, these conditions have been very detrimental to the trees on Zen Mountain and it s showing in the increased number of dead and dying trees there. Causes of tree mortality The drought induced stress has attracted several types of insects to these trees and some of the attacks are proving fatal. Chief among these, in impact to the forest, is the western pine beetle (Dendroctonus brevicomis). It is a black, cylindrical beetle about the size of a grain of rice (about 4mm long). The egg galleries (under the bark) are winding with the larval galleries leading away for a short distance before turning toward the outer bark (Fig. 1). Small, reddish pitch tubes are a sign of successful attack (Fig. 2). Attacked trees often exhibit woodpecker feeding with only portions of the outer bark removed. Successful attacks result in the death of the host tree and groups of trees are sometimes killed, especially when growing in crowded conditions.

3 Fig. 1 Western pine beetle galleries. Fig. 2 Western pine beetle pitch tubes. Photo by Kenneth E. Gibson This beetle prefers larger trees and can dramatically change the character of a forest that is attacked. In the southern part of its range and in lower elevations, this species can have three or four generations in a year. Attacks may be as early as March and as late as November. Females will attack a suitable tree by burrowing

4 though the bark into the cambium. They release a pheromone that attracts other beetles and leads to mass attacks of the host tree and sometimes several trees in a clump. The western pine beetle usually breeds in trees with reduced vigor. During periods of drought, the western pine beetle will be particularly prominent and can overcome apparently healthy trees. The effects of the western pine beetle can best be minimized by providing vigorous growing conditions for the host trees. This can be done by thinning dense stands of trees and removing less vigorous or healthy trees and giving the remaining trees sufficient room to receive nutrients, light, and water. The next insect found in the pine stands is the mountain pine beetle (Dendroctonus ponderosae). The adult of this species is a little larger than the western pine beetle (about 5 7.5mm long) and is black and cylindrical. The egg gallery inside the inner bark is long and straight, oriented vertically, and has a slight J-shaped curve at the bottom. Larval galleries extend perpendicular from both sides of the egg gallery. The sapwood (outer, light colored wood) often contains blue stain fungus. Pitch tubes are usually visible on the bole of the tree. On successfully attacked trees the pitch tubes are small, red, and numerous (Fig. 3). However, during drought years infested trees may not produce pitch, and boring dust will be the only external evidence of attack. Fig. 3 Mountain pine beetle pitch tubes Photo by William M. Ciesla The mountain pine beetle kills susceptible trees. Attacks may occur on either individuals or groups of trees. Normally, the mountain pine beetle attacks trees that are under stress due to competition with other trees, infected by dwarf mistletoe or root disease, or weakened by other pathogens or insects. During drought periods, all of these factors become more important, and mountain pine beetle activity is at its greatest. Younger stands of ponderosa pine are likely to be infested when their growth rate slows to less than ¾ in diameter in a decade.

5 In California, the mountain pine beetle typically has one generation per year, although during years with warmer and longer growing seasons there can be two generations. Adult flight occurs between June and October. Females initiate the attacks and release pheromones to attract males. The winter is spent in the late larval stage and pupation occurs in the spring or early summer. Adults may occasionally over-winter under the bark. The effects of the mountain pine beetle can best be minimized by providing vigorous growing conditions for the host trees. This can be done by thinning dense stands of trees and removing less vigorous or healthy trees and giving the remaining trees sufficient room to receive nutrients, light, and water. The impacts of small, localized populations may be reduced through the removal of green infested trees. The third significant insect pathogen is the California 5-spined Ips (Ips paraconfusus). The adult is black and cylindrical, about 4 mm in length, and has a concave depression at the rear of its wing covers with small spines along the outer edge of the depression (Fig. 4). Fig. 4 Ips beetle Photo by J.R. Baker and S. B. Bambara The egg galleries for this species (as with all Ips species) extend from a central nuptial chamber. The males are polygamous and there can be 2 5 female galleries associated with each attacking male. These insects may have 3 4 generations in a year. In standing trees, fading tops of large trees or whole crowns in small trees can be indicators of Ips infestation (Fig. 5). Other evidence of attack consists of accumulations of boring dust in bark crevices and at the base of the tree. Ips beetles are usually associated with stressed or wounded trees, logging slash and windthrown material such as broken limbs or tree tops, especially smaller diameters. Any activity or event that generates abundant amounts of slash or that stresses trees is likely to lead to elevated populations of Ips beetles, especially if the material is piled and not allowed to dry before beetle flights occur. These effects are most dramatic on the driest sites and during abnormally dry years.

6 Fig. 5 Tree mortality in smaller trees from Ips beetles. Photo by Don Owen Management activities designed to minimize Ips populations are generally only necessary on extremely dry sites and during drier than normal years. Under these conditions it is critical to cut slash (limbs, branches, and boles) into smaller pieces to promote rapid drying of the brood material. This means cutting pieces to three feet in length or shorter and being careful to allow firewood to dry before stacking for seasonal storage. One more bark beetle is found in the affected area of Zen Mountain, the red turpentine beetle (Dendroctonus valens). This is the largest of the Dendroctonus species averaging 8 mm in length with some adults reaching 12 mm. Adults are reddish-brown in color. Attacks are usually confined to the lower tree bole and stump, and are easily identified by their large pitch tubes, often near ground level (Fig. 6). The pitch tubes are typically at least one inch in diameter and often reddish brown. Eggs are laid along the edges of short, irregular galleries, although adults sometimes construct long galleries starting at the base of the tree and extending down into the roots. Fig. 6 Red turpentine beetle pitch tubes. Photo by Sheri Smith

7 Attacks by red turpentine beetles (RTB) are rarely lethal, although they may predispose the trees to attack by more aggressive beetles. The presence of RTB is often a sign that the tree has other problems. These insects usually play a secondary role to other pathogens affecting pines. They readily colonize freshly cut stumps and, during drought, populations that have developed in stumps may cause mortality in nearby medium-sized ponderosa pine (12 20 diameter). RTB have one generation per year with adults flying between May and September. RTB often attack trees that are infected by root disease, weakened by drought, attacked by other bark beetles, or wounded (especially if the wound results in sap flow). They are also commonly found on tree boles scorched by fire, on stumps of recently cut trees, and on the boles near the root masses on windthrown trees. To reduce the effects of this species during drought, avoid thinning pole-sized trees (8 12 diameter) during the spring and early summer. Two other insects are present in the area of Zen Mountain that are large enough to get residents attention, but do not cause mortality in trees. These are termites and flat headed borers. Most people recognize termites so this report will not give any additional information about them. Flat headed borers or Buprestids are a common insect that mostly attack weakened, fire-injured, dead, and recently felled trees. Some are attracted to smoke from forest fires. Larvae are large and many are shaped like horseshoe nails. The larval galleries are usually wide, meandering, and tightly packed with fine boring dust. Emerging adults make exit holes that are flattened or oval in cross section. Adults average over ¾ in length and some species can be up to about 1 3 / 5 (Fig. 7). Fig. 7 Adult flatheaded wood borer. Photo by Johnny Dell Ecologically, Buprestids facilitate nutrient cycling by accelerating the decomposition of dead trees, mainly by providing access for fungi and by reducing the wood they feed on to smaller particles that are more readily decomposed. Because of their habit of feeding largely on dead wood, these insects are not generally considered a threat to forest health.

8 Symptoms There are a number of visual indicators that let a property owner know that their trees are under stress or dying from an insect attack (see above under insect descriptions). These include pitch tubes on the bole of the tree, boring dust (or frass) at the base of the tree or in bark crevices, foliage turning light green to yellow before turning reddish brown after the tree dies. In dry years, needles on stressed or dying trees may also appear to be wilting. Another crown indicator is thinning or shortening of the foliage and a poodle or lion tail appearance of the branches indicating reduced vigor. A caution to foliage appearance: ponderosa pine needles live about 3 years and then naturally die toward the fall resulting in the appearance of a large quantity of dead needles and concern that a healthy tree is dying. In looking at dead pine needles consider the location on the branch: green needles at the end of the branch with dead needles closer to the bole means that the tree is exhibiting normal needle loss (Fig. 8). If the dead needles are toward or at the branch end, that branch has died, and the greater the number of dead branches the greater the likelihood that the tree is stressed or under attack (Fig. 9 and 10). Fig. 8 Normal needle cast.

9 Fig. 9 Needle and branch death related to a forest pathogen. Fig. 10 Needle and branch death related to a forest pathogen.

10 Affected Areas Fig. 11 Approximate areas of Zen Mountain showing significant tree mortality. The map above (Fig. 11) shows the estimated areas of significant mortality within the Lake Shastina community. There are additional areas of significant mortality outside of but near the community, as well as individual trees and small groups of trees scattered through the community that are being impacted by drought and insect activity. Landowners who are not part of the Lake Shastina community may be contacted to be included in any sanitation project where the scale of mortality on their property may affect property owners in the Lake Shastina community. The map below (Fig. 12) shows the approximate location of the parcel boundaries for impacted properties. The lot corners were not relocated for this report, so the areas shown as having significant mortality and affected lots are only an estimate of the areas in need of treatment.

11 Fig. 12 Approximate areas of significant tree mortality with approximate parcel boundaries. Recommended Actions There are actions that property owners can take to reduce the impacts from drought and insect attack. The primary step to take is to thin stands of trees so that the remaining trees have sufficient moisture, nutrients, and light to maximize tree vigor. This is done by first recognizing the healthiest trees on the property. These trees will generally have darker green needles and a dense crown of foliage. Then look at trees that are growing under larger trees and have smaller crowns these should, in general, be removed. Next, look for trees with yellowing foliage, which is usually a sign that the tree is stressed or dying, and remove them. Also look for trees with symptoms of insect attack as described above in the discussions about each insect and remove them. If the landowner has questions about their trees, they can contact a forester for assistance. After trees have been cut down, the property owner should either remove the trees from their property or treat the logs and slash as soon as is feasible so that insects such as Ips are not attracted to the fresh slash. If the property owner uses firewood, they can cut the larger parts of the tree into firewood length pieces. Pieces greater than 6 in diameter should be treated in this manner. Limbs and pieces less than 6 in diameter should

12 be cut into approximately 3 foot lengths to maximize drying speed, which will prevent the slash from becoming brood material for a new generation of insects. Wood that is kept for firewood should be allowed to dry before it is stacked to minimize insect activity. Conversely, piles of firewood can be covered with plastic in a sunny spot so that any insects in the wood will be killed. Watering trees is problematic in drought years. Watering should be limited and, if used, needs to be deep using a device that gets the water underground to the tree s roots. Surface watering, such as for a lawn, will not generally reduce drought stress on trees. Below are photos of dead and dying trees, and examples of thinning. Fig. 13 Dead and dying trees on the southeast side of Zen Mountain. Note the pine tree just right of center that has yellow-green, wilted needles. This tree is freshly dead.

13 Fig. 14 Example of larger pine showing evidence of stress and possible attack by pathogen. Note the tree in the center with the thinning crown and a lion tail appearance to the branches, especially when compared to the tree to its left. Fig. 15 Example of foliage color change related to pathogen attack. Note the tree on the left with healthy foliage and the tree on the right with yellowing foliage.

14 Fig. 16 Example of pines showing stress and mortality. Note trees in the back in various stages of health from stressed to dying to dead. There is healthy foliage on the trees in the foreground.

15 Examples of thinning on a lot next to Zen Mountain. Fig. 17 Before Thinning Fig. 18 After Thinning

16 Fig. 19 Before Thinning Fig. 20 After Thinning

17 References Much of the information on insects came from the following sources, which are available on line. At this website you can either select the Insects & Diseases link on the left menu or the Bark & Engraver Beetles link down the page under Native Insect Pests. California Forest Insect and Disease Training Manual, USDA Forest Service Region 5, 2010, viii pages. This manual is available at the above website. Forestry Images: Photos of Pests and Pest Damage, at Insect Images (a subcategory of this site) was used for photos of insects and their damage. Note: photos without photographer credit were taken by John Kessler. Insect Images is a project of the Center for Invasive Species and Ecosystem Health, The University of Georgia Warnell School of Forestry and Natural Resources and College of Agricultural and Environmental Sciences Department of Entomology. Also available from the Forest Service website is the brochure Are Your Trees Susceptible?, which gives good basic information about the ways bark beetles attack and kill trees. There are several good links on this web page, but you may have to adjust your internet security settings to use them. Another source of information is Cal Fire s web page for the Pest Management Program This page gives contact information for Forest Pest Specialists and links to some useful information about forest pests.