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About this Research:
Snag (Standing Dead Trees) Demography in Eastside Pine Forests
Research Project Summary
Our understanding of snag (standing dead trees) demographic patterns, spatial and temporal, as well as whether current snag guidelines are sustainable, is very limited. To gain a better understanding of snag demographic patterns in eastside pine forests in Northeastern California, a snag demographic study was initiated in 1988. The study was also intended to gain an understanding of bird relations to different snags densities in these pine forests. Twenty-four 5-ha (100 m x 500 m) plots were selected from approximately 1,000 eastside pine land management polygons with large trees and at least moderate canopy density on the Modoc and Lassen National Forests and from suitable areas in Lassen Volcanic National Park.
From 1989 through 1991 cavity nesting bird studies were carried out on these plots. In general, all of the cavity nesting bird species expected were found on at least one of the study plots, regardless of the snag density, even where snags were absent from the 5 ha study plot. Where snags were absent, cavity nesting birds were found nesting in snags off the study plots or nested in spike tops (generally large diameter trees with dead tops) or some other form of live tree with a sufficient amount of exposed "deadness" (e.g., bark split by lightning exposing the sapwood). However, counts of cavity nesting birds generally increased as snag numbers increased.
Snags were inventoried and mapped in 1989 on each of the 24 5-ha plots. Each plot was subsequently revisited in 1990 and 1991 when the condition and character of each standing snag was evaluated and all new snags were inventoried and mapped. Snag numbers generally increased on most of the plots during this period, probably in response to relatively low precipitation in the late 1980s and early 1990s in concert with insect activity in the drought stressed trees. These patterns were interesting enough to justify continuation of the yearly inspection of all snags into the future. Thus, through 2003, all existing snags have been evaluated and all new snags have been mapped and data recorded on most of the plots yearly since 1989. One plot on the Modoc National Forest was lost to a wildfire. A second plot in Lassen National Park was terminated because of difficulty of access. Several of the remaining 22 plots have seen prescribed fire and/or understory thinnings but all of those have been revisited yearly through 2003. Findings to date suggest that both snag creation and loss is extremely variable in space and time and dependent on the existing stocking and structure of the forests coupled with site specific characteristics including soils, topography, position in the landscape, and historical contingences. Broad management guidelines, without flexibility for site to site variability or variability in time, ought to be reframed to reflect differences in snag capability and sustainability at more local scales.
Cavity nesting birds used only a small number of the snags available to them for nesting and there was no obvious reason why some trees were chosen and many others were not utilized. To gain some understanding in tree choice, the principal investigator, with several entomological colleagues, initiated a study in 1993 to evaluate the responses of insects and cavity nesting birds to bark beetle killed and girdled trees. Ponderosa pines (Pinus ponderosa) were the subject trees. Western pine beetles (Dendroctonus brevicomis) were induced to attack trees by placing attractant pheremone on subject trees. The second treatment of pines were girdled with approximately a 10 cm wide section around the tree removed to the sapwood with a chainsaw. Tree's characteristics have been evaluated yearly since the experiment was initiated. The bark beetle pheremone treated trees were immediately attacked by western pine beetles and quickly died whereas the girdled trees were generally not attacked by Dendroctonus despite being highly stressed; some of the girdled trees retained green needles for several years after girdling suggesting that tree death may be a gradual process when affected by some agents of mortality. Insect activity, both in terms of diversity and numbers, was very high in the bark beetle killed trees and very low in the girdled trees. Birds started excavating nest sites much earlier in the bark beetle killed trees; however, in recent years, more nest holes are being excavated suggesting that girdled trees may lag some years behind bark beetle trees in becoming suitable for nesting.
Following a prescribed burn in one of the Lassen Volcanic National Park plots in 1990, all of the large diameter Jeffrey pines (Pinus jeffreyi) within the snag study plot died within several years of the burn. This plot had gone many decades without seeing a wildfire, or prescribed burn, and the accumulation duff 'n' stuff (partially decayed needles, bark scales and other organic material) around the bases of the large, older trees, many times exceeded 0.5 m in depth. This degree of mortality seemed to be excessive so the principal investigator worked with Lassen Volcanic National Park managers to design a study to evaluate the efficacy of removal of the duff for 1 m around a sample of large diameter trees prior to the next prescribed burns. Removal of the duff and other material to bare mineral soils was done in the fall of 1996 and the burns were conducted shortly thereafter. Removal of the duff seemed to result in reduced mortality in the plot on the eastside of the Park but mortality was low in both the treated and untreated large diameter trees on the westside plot suggesting that such removals may not be worth the investment there. Each of the sample trees, both living and dead, have been evaluated yearly since the burns to learn more about snag decay processes in trees killed largely by fire albeit a much less intense fire than many wildfires.
Prescribed burns on one of the Lassen Volcanic National Park plots in 1990 and 1995, also provided us with an experiment to examine the survivorship of snags to fire and to contrast the deterioration of trees dying with fire versus those that died apparently from bark beetle attack. Many of the existing snags survived the fire, some without even much scorching whereas others were heavily charred in places. Variable fire behavior and fuel continuity were likely the key variables in whether snags were burned or not, although the amount of bark remaining on the snags seems to have influenced snag loss to some degree. Those trees dying following fire lost large portions of their boles more quickly than those trees dying without fire in the same periods in an adjacent plot.
Gain a better understanding of the pattern - spatial and temporal - of snag creation and loss in eastside pine forests.
Evaluate cavity nesting bird responses to differing snag densities.
Experimentally evaluate the differences between the decay trajectories of bark beetle killed trees and girdled trees of different diameters that died at different times of year.
Experimentally evaluate the fire effects on trees with no duff 'n' stuff within 1 m of the base of the bole versus trees with up to 0.5 m of duff 'n' stuff adjacent to the bole.
Examine the "survival" rates of snags following a prescribed burn intended to remove large quantities of existing dead and down material.
Gain a better understanding of the "lifespans" of dead trees dying from different mortality agents.
Methods and Design
Snag demography plots were randomly selected, in 1988, from a pool of eastside pineforest polygons of at least moderate canopy closures and having large diameter trees summarized on the 1980s era Modoc and Lassen National Forests land management planning maps. Three plots in each of 8 snag density classes (from 0 to > 3 snags per acre) were desired (a total of 24 transects). One 100 m x 500 m strip transect was randomly placed in each of the selected polygons. For snag density classes exceeding 2 snags per acre, the above process did not capture any areas with sufficient snags across the 100 x 500 m transect. Therefore, as groups of snags were encountered in our explorations on both forests and in Lassen Volcanic National Park, 100 x 500 m transects were carefully set around these large groups of snags.
Each snag (greater than 15 inches in diameter at breast height and greater than 10 ft in height) was talleyed, mapped, and information taken about its diameter, height, deterioration condition, percentage of bark remaining, evidence of insect activity and/or woodpecker foraging activity, and number of cavity nests. Yearly (through 2003 on most plots), each snag was revisited and changes in status were recorded. Yearly, also, all newly dead snags were added to the maps and data base. Over 3,000 snags are now in the database.
Bird abundance was assessed, from 1989 through 1991, using Christman's plot mapping procedure (S.P. Christman. 1984. Plot mapping: estimating densities of breeding bird territories by combining spot mapping and transect techniques. Condor 86:237-241). In addition to mapping all birds encountered each transect was completed in 1 hour so hourly counts of birds detected was derived from the data. Each plot was visited 10 times each year (30 time total) and each of the 4 observers visited each plot at least twice and not more than three times to ensure that observer variability was more or less standardized across all 24 transects. Visits to each transect varied between dawn and noon to ensure that species active for only short periods of time in the morning had some chance of being detected.
For the bark beetle killed versus girdled studies, 24 large diameter (>30 inches in diameter at breast height) and 24 smaller diameter (15-25 inches diameter at breast height) ponderosa pines were selected. Four of each size class of tree were selected in groups and each group was located at least 0.5 miles away from another. Trees in each of the diameter classes were randomly chosen to be killed either by application of the western pine beetle (Dendroctonus brevicomis) pheromone triplet (exo-brevicomin / frontalin / myrcene) placed 8 feet above the ground or by girdling through 2 chain saw cuts, placed 2 inches apart and 1 inch into the sapwood placed 2 feet above the ground. Placement of the pheromone and the girdling were done in May and September 1996, with half of the trees assigned to each temporal treatment. Yearly, each tree was visited, photographed, and information taken on insect activity, bird foraging, and bird cavity excavation. Information collection continues.
For the duff 'n' stuff removal studies, we randomly selected a number of pine trees (ponderosa, Jeffrey, or sugar) in each of two proposed prescribed burns, one in an eastside pine forest and the other in a more westside pine to mixed conifer forest. Thirty trees were selected in the proposed eastside burn and twenty trees in the proposed westside burn. Half of the trees were small diameter (less than 24 inches diameter at breast heights and half were large diameter trees (greater than 25 inches at breast height). Half of each class of trees were raked to bare mineral soil for 1 m in diameter around the tree and the remainder were not raked. Duff pins were set in the duff and soils and pins were set in the unraked trees at the duff level to provide measuring points for the change in the depth of the duff following the fire. Raking was done in September 1997 and the burns were completed later that month. Trees were revisited yearly through 2003 and information on whether the trees were alive or dead, and deterioration characteristics if dead were collected as for the snag demography work mentioned above.
The snag survival and snag deterioration study was conducted on two of the aforementioned 100 x 500 m snag demography plots within Lassen Volcanic National Park where all snags had been mapped and recorded starting in 1998. Following the prescribed burn in September 1995, an attempt was made to relocate all snags using the mapped locations and information about each snag in the data base. Snags were classified as being mostly consumed (nothing but ash and some wood fragments remained), versus snags that survived but were heavily charred or only received light scorching. For the snag deterioration part of the study, snags dying subsequent to the June 1990 prescribed burn were followed and their deterioration was recorded from the time when trees were fully dead (no green needles remained). These were contrasted with the deterioration sequence of trees dying in the same years probably principally from bark beetle attack in a companion study plot nearly adjacent to the burned plot. Information on the percentage of bark remaining each year and changes in snag height were compared from the two groups of trees.
Application of Research Results
Managers at Lassen Volcanic National Park are very interested in our findings and areapplying the results to their management activities especially their prescribed fire practices. Our findings have been applied to fire salvage questions as well to the development of criteria for determining which trees to consider for salvage.
Our conclusions from the snag demographics study suggest that snag management guidelines ought to be based on the capability of the landscapes to support snags through time and space. From the cavity nesting bird perspective, a continual flow of dying and dead trees is necessary to provide a flow of food and potential nesting locations in a landscape. Birds can and do nest in live trees with dead portions but the vast majority of such trees are rather large in diameter (greater than 24 inches diameter at breast height) and have persisted for sufficient time to acquire dead areas from agents including top killing insects, mechanical damage or lightning. Conclusions from the bark beetle vs. girdling experiment suggest that because bark beetle killed trees are rich in insect life, food for many of the cavity nesting birds, and supply nest sites too, that using bark beetles to create snags is more ecologically sound than girdling which may produce nest sites but little food. Some prescribed burns result in excessive numbers of dead trees shortly after a burn thus reducing substantially the persisting number of live trees and incipient snags. One mechanism for reducing mortality is removal of the duff 'n' stuff to mineral soil around the base of the tree but this is expensive, does not save all of the trees, and other studies suggest may actually cause mortality under certain conditions.
Other important snag related questions being contemplated, that would dovetail into the work summarized here, include examining whether cavity nesting birds in ponderosa and Jeffrey pines in northeastern California are restricted to the sapwood as has been found in eastern Oregon in ponderosa pines and examining the effects of scale of wildfires and the different severity classes within burns and the ability of insects and birds to exploit these resources. Prescribed fires, and likely wildfires, do not consume all of the existing snags but the numbers consumed are variable and depend on the nature of the fire and the fuels in which the snags are embedded. Further, surviving snags are often scorched or heavily charred. It is not known what such carbonization means to the insects remaining or to the birds as they choose snags in which to excavate a nest location. So, while many snags remain after fire, and of course, new snags are created, it is not clear that snag remaining after fire that are scorched or charred have the same utility, for foraging or nesting, as snags not affected by fire.
Northeastern California, Modoc and Lassen National Forests and from suitable areas Lassen Volcanic National Park.
1) Laudenslayer, William F., Jr., 2) Arnold, Jonathan 3), Borys, Robert, 4) Farris, Kerry 5) Ferrell, George 6) Fettig, Christopher, 7) Flores, Mary 8) George, T. Luke, 9) Landram, F. Michael, 10) Rickman, Thomas, 11) Shea, Patrick J., 12) Steger, George N., 13) Zack, Steve
1) USDA Forest Service, PSW Research Station
Sierra Nevada Research Center
Forestry Sciences Laboratory
2081 E. Sierra Avenue
Fresno, CA 93710-4639
(530) 279-6116; Fax: (559) 297-3355
2) USDI National Park Service
Lassen Volcanic National Park
P.O. Box 100
Mineral, CA 96063
(530) 595-4444 ext 5171
3) Forest Service, PSW Research Station
Applied Ecology and Management of Forest Insects
Institute of Forest Genetics
2480 Carson Road
Placerville, CA 95667
4) Wildlife Conservation Society
5) Forest Service, PSW Research Station
6) Forest Service, PSW Research Station
Applied Ecology and Management of Forest Insects
1107 Kennedy Place, Suite 8
Davis, CA 95616
7) USDA Forest Service, Modoc National Forest
Warner Mountains Ranger District
P.O. Box 229
Cedarville, CA 96104
8) Department of Wildlife
Humboldt State University
Arcata, CA 95521
9) USDA Forest Service
Pacific Southwest Region
1323 Club Drive
Vallejo, CA 94592
10) USDA Forest Service, Lassen National Forest
Eagle Lake Ranger District
477-050 Eagle Lake Road
Susanville, CA 96130
11) Forest Service, PSW Research Station
Applied Ecology and Management of Forest Insects
12) USDA Forest Service, PSW Research Station
Sierra Nevada Research Center
Forestry Sciences Laboratory
13) Wildlife Conservation Society
219 SW Stark Street, Suite 200
Portland, OR 97204
Publications and Reports
George, T. Luke, William F. Laudenslayer, Jr., and Steve Zack. Submitted. The effect of large-diameter trees on bird community composition in two ponderosa pine forests. submitted for the Ponderosa Pine Workshop Proceedings to be published as a U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station General Technical Report, edited by Martin Ritchie and Douglas Maguire.
Harris, R., and B. Laudenslayer. 1998. Dead and dying trees: part of a healthy forest. Forest Land Steward published by University of California Extension and California Department of Forestry Winter 1998:1, 4
Landram, F. Michael, William F. Laudenslayer, Jr., and Thomas Atzet. 2002. Demography of snags in eastside pine forests of California. pp 605-620. In: William F. Laudenslayer, Jr., Patrick J. Shea, Brad Valentine, C. Phillip Weatherspoon, and Thomas E. Lisle (tech. coords). Proceedings of the Symposium on the Ecology and Management of Dead Wood in Western Forests. USDA Forest Service, Pacific Southwest Research Station Gen. Tech. Rep. PSW GTR-181.
Laudenslayer, W.F., Jr. 1997. Dead, dying, and diseased trees and their values to wildlife. pp 9-14 in D.H. Adams and J.E. Rios (eds.). Proceedings, 45th Annual Meeting of the California Forest Pest Council, November 13 and 14, 1996. California Department of Forestry and Fire, Sacramento, Calif.
Laudenslayer, William F., Jr. 2002. Effects of prescribed fire on live trees and snags in eastside pine forests in California. pp 256-262 in Neil G. Sugihara, Maria E. Morales, and Tony J. Morales (eds.). Proceedings of the Symposium: Fire in California Ecosystems: Integrating Ecology, Prevention and Management. Association for Fire Ecology, Davis, Calif. Misc. Publ. No. 1.
Laudenslayer, William F., Jr. 2002. Cavity-nesting bird use of snags in eastside pine forests of northeastern California. pp 223-236. In: William F. Laudenslayer, Jr., Patrick J. Shea, Brad Valentine, C. Phillip Weatherspoon, and Thomas E. Lisle (tech. coords). Proceedings of the Symposium on the Ecology and Management of Dead Wood in Western Forests. USDA Forest Service, Pacific Southwest Research Station Gen. Tech. Rep. PSW-GTR-181.
Laudenslayer, William F. Jr. Submitted. Effects of Site and Scale on the Demographics of Standing Dead Trees in Eastside Pine Forests. submitted for the Ponderosa Pine Workshop Proceedings to be published as a U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station General Technical Report, edited by Martin Ritchie and Douglas Maguire.
Laudenslayer, W.F., Jr., and H.H. Darr. 1990. Historical effects of logging on the pine forests of California. Trans. Western Section of The Wildlife Society 26:12-26. s
Laudenslayer, W.F. Jr., H.H. Darr, and S. Smith. 1989. Historical effects of forest management practices on eastside pine communities of northeastern California. pp 26-34 in A. Tecle, W.W. Covington, and R.H. Hamre (tech. coords.). Multiresource Management of Ponderosa Pine Forests. USDA Forest Service., Rocky Mtn. Forest and Range Experiment Station, Ft. Collins, Colo. Gen. Tech. Rep. RM-185. 282 pp
Laudenslayer, William F., Jr., Patrick J. Shea, Brad Valentine, C. Phillip Weatherspoon, and Thomas E. Lisle (tech. coords). Proceedings of the Symposium on the Ecology and Management of Dead Wood in Western Forests. USDA Forest Service, Pacific Southwest Research Station Gen. Tech. Rep. PSW GTR-181
Laudenslayer,, William F., Jr., George N. Steger, Jonathan Arnold. In Press. Survivorship of Raked and Unraked Trees to Prescribed Fires in Conifer Forests in Northeastern California. Proceedings of the 2002 Fire Symposium, San Diego, California. U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station General Technical Report, edited by Marcia Narog.
Shea, Patrick J., William F. Laudenslayer, Jr., George Ferrell, and Robert Borys. 2002. Girdled versus bark beetle-created ponderosa pine snags: utilization by cavity-dependent species and differences in decay rate and insect diversity. pp 145-153. In: William F. Laudenslayer, Jr., Patrick J. Shea, Brad Valentine, C. Phillip Weatherspoon, and Thomas E. Lisle (tech. coords). Proceedings of the Symposium on the Ecology and Management of Dead Wood in Western Forests. USDA Forest Service, Pacific Southwest Research Station Gen. Tech. Rep. PSW GTR-181.
Zack, S., W.F. Laudenslayer, T.L. George, C. Skinner, and W. Oliver. 1999. A Prospectus on Restoring Late Successional Forest Structure to Eastside Pine Ecosystems Through Large-scale, Interdisciplinary Research. Pp. 343-355 in J.E. Cook and B.P. Oswald (compilers), First Biennial North American Forest Ecology Workshop. Forest Ecology Working Group, Society of American Foresters, Bethesda, Md.
Zack, Steve, T. Luke George, and William F. Laudenslayer, Jr. 2002. Are there snags in the system? Comparing cavity use among nesting birds in "snag rich" and "snag-poor" eastside pine forests. pp 179-191. In: William F. Laudenslayer, Jr., Patrick J. Shea, Brad Valentine, C. Phillip Weatherspoon, and Thomas E. Lisle (tech. coords). Proceedings of the Symposium on the Ecology and Management of Dead Wood in Western Forests.USDA Forest Service, Pacific Southwest Research Station Gen. Tech. Rep. PSW-GTR-181.