Issues are stand dynamics, regeneration, and sustainability. Study stand dynamics, including regeneration, of aspen, spruce-fir, and ponderosa pine forests. Research vegetation manipulation and primarily silviculture. To help managers balance production of multi-resource production and the sustainability of forested ecosystems. Manitou Experimental Forest Black Hills Ponderosa Pine

Patterns of Recruitment and Mortality in Rocky Mountain Forests

Ponderosa Pine Forests along the Front Range of Colorado

A long-term seedfall collection study at the Manitou Experiment Forest (MEF) was initiated in 1981, using two overstory treatments (seedtree and shelterwood), two regeneration methods (planted versus natural seedlings), and two seedbed preparations (scarified and non-scarified). The results suggest that seedfall is dependent upon the density of overstory trees and varies considerably from year to year. Seedfall years producing less than 200,000 seed per hectare had few viable seed. Otherwise about 40% of the total seedfall is viable. On average, about 48% of the seedfall was consumed by animals regardless of the total seed production. Survival and growth of planted seedlings is much greater than that of natural seedlings. Most natural seedlings mortality occurs during the first years following germination and fewer seedlings die on scarified seedbeds. In June 2002, the Hayman Fire burned onto this area of the Manitou Experimental Forest. An evaluation was completed in August of the mortality, fire scorching, within the study areas. The early assessment indicates that many of the seedlings initiated in this study were lost in this fire. Opportunities for new research are being explored.

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Engelmann Spruce Forests in Colorado

Annual Engelmann spruce seed production and periodic (10 year) stocking and growth data has been monitored on the Fraser Experimental Forest since 1970. After the first five years, there was considerable variability in seed production, however good to heavy crops of seed were produced in 4 of those 5 years. Results after 15 years indicated good to bumper seed crops in 7 of the 15 years with considerable variability across locations.

Modeling Regeneration and Early Stand Dynamics

Above and Below Ground Effects of Aspen Clonal Regeneration and Succession to Conifers

Aspen in the western United States regenerates via root suckering after mature stems die either from fire, disease, or from other perturbances. In some instances mature aspen clones appear to be in decline and have not successfully suckered, either due to repeated animal herbivory, or competition from invading conifers. This apparent decline raises the question of how the clonal root system and residual aspen stems are effected by clonal decline or conifer invasion. In a recently published field study by Shepperd and others, above and below ground characteristics were measured and compared for six sets of paired aspen (Populus tremuloides Michx.) clones on the Fishlake National Forest in central Utah. Three self-regenerating clones were compared to three non-regenerating clones. Three pure aspen stands were compared to three mixed aspen/conifer stands. Regenerating clones had dense understories of younger aspen stems, which were not present in non-regenerating clones. Regenerating clones also had greater numbers of roots and greater total root surface area than non-regenerating clones. Aboveground biomass and growth of the aspen in mixed stands was less than that of pure stands. A corresponding difference in aspen root mass was not apparent, indicating that the decline of aspen in mixed stands had not yet affected the root system. Conifer height and basal area growth rates were clearly greater than those of aspen, suggesting that aspen will eventually disappear from these forests in the absence of stand-reinitiating disturbances. Based on these results, management intervention need are greater for non-regenerating clones, where root systems are in decline.

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Citation: Shepperd, W.D.; Bartos, D.L.; Mata, S A. 2001. Above- and below-ground effects of aspen clonal regeneration and succession to conifers. Canadian Journal of Forest Research. 31: 739-745.

New Silvicultural Techniques in the central Rockies and Southwest

Many western forests are at risk to forest health problems and catastrophic fire. Forest areas at high risk to catastrophic fire, commonly referred to as Red Zones, contain 2.4 million acres in the Colorado Front Range and 6.3 million acres statewide. The increasing frequency, size and intensity of recent forest fires have prompted large appropriations of federal funds to reduce fire risk, improve fire protection, explore appropriate vegetation management treatments in the urban-wildland interface, and to enhance the harvest and production of bio-based products. RM4451 has contributed to this area of research in several ways.
High fuel levels from fire suppression in the Central Rockies has resulted in altered spatial and temporal patterns of mortality and recruitment. A demonstration project of management techniques applicable in Front Range Urban-Interface Ponderosa Pine forests has been initiated at the Manitou Experimental Forest to test the applicability of several vegetation manipulation techniques that could be used to maintain the health and vigor of forested ecosystems within the urban-wildland interface. The 25 ha forested site near the MEF headquarters is readily accessible for public tours. A no treatment control will be compared with a prescribed fire treatment, an uneven-aged silvicultural treatment, and a combination of silvicultural treatments followed by fire. The silvicultural treatments were imposed in 2000 and a prescribed fire treatment is being scheduled.

Identifying Long-term Climatic Patterns and Disturbance Events in Rocky Mountains Forests with Dendrochronology

Fire Frequency Decreases with Latitude

Chronologies of fire histories in ponderosa pine in Colorado and Wyoming, reconstructed from trees scarred by fire over more than four centuries, showed several correlations with latitude. Fire-free intervals tended to be shorter in the southern stands than in the north. Fires in the south also tended to be early in the season, with late-season fires in the north. Super-imposing calculated drought severity indexes on plots of fire years showed, not surprisingly, that fire years were dry, but in the south were preceded by wet years. This supports the idea that fuels may have been limiting southern forests where fire intervals were shorter, and that longer intervals in the north permitted greater fuel buildup between fires. Knowing these patterns could be of great help to those planning suppression of catastrophic fires, except for one thing: the coming of Euro-American settlers effectively put a damper on forest fires for nearly a century, so that the forests – and the fire patterns within them – are now much different. With changes in our philosophy on the costs and benefits of fire, it will likely take a long time to reach – or understand – an equilibrium with fire in forests.

Brown, P.M.; Shepperd, W.D. 2001. Fire history and fire climatology along a 5° gradient in latitude in Colorado and Wyoming. Palaeobotanist. 50: 133-140.

Decay rates for large dead and down woody material in subalpine forests in the Rocky Mountains

Dead tree stems often constitute a large fraction of aboveground coarse woody debris in old-growth forests. They provide habitat and nutrition for many species of animals and plants, and influence the hydrologic and geomorphic processes in streams and rivers. The long-term dynamics of large dead wood biomass in most Rocky Mountain forest ecosystems, especially the residence time (it's age), are not well known. This information is needed to assess turnover rates of carbon and other nutrients, evaluate forest productivity, and help manage certain wildlife populations. Shepperd and others completed studies in the central Rocky Mountains that used cross-dating of tree rings to determine death dates of wind thrown, downed logs in a subalpine forest. Results show that sound lodgepole pine and Engelmann spruce logs lying on the ground persisted for many decades with a majority of their volume intact. No significant differences between species or exposure were found. In addition, there was little decrease in the specific gravity of wood remaining in logs with time, although there was a corresponding greater loss of wood volume. Knowing that both lodgepole pine and Engelmann spruce decay at relatively the same rate is critical information for resource specialists because it helps them better determine which logs provide the best habitat for wildlife and plants.

Citation: Brown, P.M.; Shepperd, W.D.; Mata, S.A.; McClain, D.L. 1998. Longevity of windthrown logs in a subalpine forest of central Colorado. Canadian Journal of Forest Research. 28: 1-5.

Long-term Landscape Patterns in Montane Ponderosa Pine Forest around Cheesman Lake

Brown and others in documenting the fire history of a montane ponderosa pine—Douglas-fir forest landscape around Cheesman Lake in Colorado have determined that this fire history exhibits a greater range in fire behavior in ponderosa pine forests than generally have been found in previous studies. Spatial extent of burned areas during fire years varied from the scale of single trees or small clusters of trees to fires that burned across the entire landscape. Intervals between fire years varied from 1 to 29 years across the entire landscape to 3 to 58 years in one stand to over 100 years in other individual stands. Fire severity varied from low-intensity surface fires to large-scale stand-destroying fires. These results suggest that the historical range of variability in fire regimes for at least this area of ponderosa pine ecosystems must be expanded to include greater complexity in fire behavior than has been previously recognized in ponderosa pine forests. However, how far beyond the montane forest landscape of the Cheesman Lake these results should be extrapolated will require more quantative data on fire history and stand structure in ponderosa pine forests from this and other regions.

Citation: Brown, P.M.; Kaufmann, M.R.; Shepperd, W.D. 1999. Long-term landscape patterns of past fire events in a montane ponderosa pine forest of central Colorado. Landscape Ecology. 14: 513-532.

Fire History in Interior Ponderosa Pine Stands in the Black Hills

Relatively little is known about presettlement fire regimes in ponderosa pine forests of the Black Hills of western South Dakota and eastern Wyoming. Photo points and analyses of current basal areas document the increases in ponderosa pine densities and invasion into meadows in the Hills over the past 100 years. Prior to Brown and Sieg's work, only one dendrochronology had been done for the fire histories of the Hills. Brown and Sieg, in cooperation with RMRS-4451, reconstructed chronologies of fire events from crossdated fire-scarred ponderosa pine trees for four sites in the south-central Black Hills. Compared to other ponderosa pine forests in the Southwest US or southern Rocky Mountains, these communities burned less frequently. For all sites combined, and using all fires detected, the mean fire interval or number of years between fire years was 16 years for the period 1388 to 1900. When a yearly minimum percentage of trees recording scars of greater than or equal to 25% is imposed, the mean fire interval was 20 years. The length of the most recent fire-free period exceeds the longest intervals in the pre-settlement era and is likely the result of human-induced land use changes. Based on fire scar position within annual rings, most past fires occurred late in the growing season or after growth had ceased for the year. These findings have important implications for management of ponderosa pine forests in the Black Hills and for understanding the role of fire in pre-settlement ecosystem function.

Citation: Brown, P.M.; Sieg, C.H. 1996. Fire history in interior ponderosa pine communities of the Black Hills, South Dakota, USA. International Journal of Wildland Fire. 6(3): 97-105.

Climate and Engelmann Spruce Growth at Treeline

Tree-ring width chronologies from Engelmann spruce at two treeline sites at the Fraser Experimental Forest in the central Rocky Mountains contain similar high and low frequency patterns in ring width, indicative of regional climate control on tree growth. Comparisons of annual ring widths with instrumental climate data show relationships with late spring temperature fluctuations on annual to century time scales. Ring width patterns in the earliest dated trees at one of the sites also infers upward migration in treeline at the site around A.D. 1250. No unusual growth increases were seen in recent years, suggesting that these trees have not recorded warmer conditions possibly associated with global climate change.

Citation: Brown, P.M.; Shepperd, W.D. 1995. Engelmann spruce tree-ring chronologies from Fraser Experimental Forest, Colorado: potential for a long-term temperature reconstruction in the Central Rocky Mountains. In: Tinus, Richard W., tech. ed. Interior West global change workshop. 1995 April 25-27. Gen Tech. Rep. RM-GTR-262. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 23-26.