|Issues are stand dynamics, regeneration,
|Study stand dynamics, including regeneration,
of aspen, spruce-fir, and ponderosa pine forests.
|Research vegetation manipulation and primarily
|To help managers balance production of multi-resource
production and the sustainability of forested ecosystems.
|Manitou Experimental Forest
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.
See Manitou Experimental Forest for more results
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
See Aspen Restoration for more info.
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.
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
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
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.