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Reports of decreasing quaking aspen (Populus tremuloides) cover in forests of the western USA have caused concern about the long-term persistence of aspen on landscape scales. We assessed changes in overstory aspen dominance on the Uncompahgre Plateau in western Colorado over a 20 year period. We measured stand density, species composition and regeneration in 53 undisturbed, mature pure aspen, pure conifer, and mixed aspen/conifer stands originally inventoried between 1979 and 1983. Ages of overstory and understory trees were used to evaluate long-term change in regeneration and overstory development. While pure aspen stands occupy 16% of the study area, mixed aspen and conifer stands cover 62% of the forested landscape...
We examined patterns of non-native plant diversity in protected and managed ponderosa pine/Douglas-fir forests of the Colorado Front Range. Cheesman Lake, a protected landscape, and Turkey Creek, a managed landscape, appear to have had similar natural disturbance histories prior to European settlement and fire protection during the last century. However, Turkey Creek has experienced logging, grazing, prescribed burning, and recreation since the late 1800s, while Cheesman Lake has not. Using the modified-Whittaker plot design to sample understory species richness and cover, we collected data for 30 0.1 ha plots in each landscape. Topographic position greatly influenced results, while management history did not. At...
Old-growth forests of Engelmann spruce (Picea engelmannii Parry ex. Engelm.) and subalpine fir (Abies lasiocarpa (Hook.) Nutt.) dominate much of the landscape of the Rocky Mountains. We characterized the structure, biomass and production of 18 old-growth (200?450-year-old) spruce/fir forests in Rocky Mountain National Park, Colorado, as well as the stand-level supply and use of light and nitrogen. Stands were chosen to span a broad range of elevation, aspect, and topography. Aboveground tree biomass in these old-growth forests averaged 253 Mg/ha (range 130?488 Mg/ha), with aboveground net primary production of 3700 kg ha?1 yr?1 (range from 2700 to 5200 kg ha?1 yr?1). Within stands, trees >35 cm in diameter accounted...
We examined changes in small mammal habitat and densities of four small mammal species, including deer mice (Peromyscus maniculatus), gray-collared chipmunks (Tamias cinereicollis), golden-mantled ground squirrels (Spermophilus lateralis), and Mexican woodrats (Neotoma mexicana), 2?3 years after thinning and prescribed fire treatments in ponderosa pine (Pinus ponderosa) forests of northern Arizona, US. These treatments were designed to simultaneously reduce high-severity fire risk while returning forests to conditions more representative of pre-European settlement structure and function. Treatments resulted in changes in important components of small mammal habitat, including increased herbaceous vegetation, decreased...
Repeat photography samples were used to analyze how the structure and site-specific distribution of forests may or may not have changed during the past century in the San Juan Mountains, Colorado. Systematic evaluation of 146 photosets was combined with field observations to identify trends in vegetation change. Both conifers and deciduous trees (e.g., aspen) have increased in extent. Forest recovery from large disturbances that occurred during Euro-American settlement contributed substantially to this increase. Trees also encroached into grass/shrublands, but less than half of photosets show tree invasion, and invasion is more common in small grass/shrubland openings interspersed with forest than in large openings....
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The fire history of Piñon–Juniper (Pinus edulis–Juniperus osteosperma) woodlands in much of the southwestern United States is poorly understood, and as a result, fire management decisions are being made without a rigorous ecological underpinning. We investigated the historic fire regimes in Piñon–Juniper woodlands on the Mesa Verde cuesta utilizing stand and age structures. All Piñon trees in eight stands were aged and stand age was extrapolated to the surrounding landscapes using digital imagery, creating a time-since-fire map of the 1995 landscape. Six sampled stands were over 400 years, while two were between 200 and 300 years. Stand-replacing fire with a rotation of 400 years or longer characterized this Piñon–Juniper...
Invasion of natural ecosystems by exotic plant species is a major threat to biodiversity. Disturbance to native plant communities, whether natural or management induced, is a primary factor contributing to successful invasion by exotic plant species. Herbivory by both wild and domestic ungulates exerts considerable impact on structure and composition of native plant communities. Intensive herbivory by ungulates can enhance exotic plant invasion, establishment, and spread for three reasons: (1) many exotic plants are adapted to ground disturbances such as those caused by ungulate feeding, trampling, and movements; (2) many exotic plants are adapted for easy transport from one area to another by ungulates via endozoochory...
We assessed species composition, richness and abundance of understory vegetation, as well as arbuscular mycorrhizal (AM) inoculum potential on the San Francisco Peaks, tallest mountains in Arizona, crossing a steep, south-facing elevational gradient. These mountains have a high conservation value due to their rare habitats but previous vegetation studies have been limited. Because mature trees in the Pinaceae do not form associations with AM fungi, there may be more variation in plant community and AM fungal associations in coniferous forest than in ecosystems where all species associate with AM fungi. Differences in species composition between forest types reflected differences in the historical disturbance regimes....
Pi�ons and junipers, that dominate many semi-arid landscapes in the western United States, have invaded some sagebrush and grassland areas and possibly increased in density since EuroAmerican settlement. Exclusion of fire by livestock grazing and intentional suppression is thought to have been a cause of these changes. National assessments suggest that many woodlands have missed one or more low-severity surface fires and are thus in poor condition, requiring restoration. We undertook a systematic review of seven questions about fire history, fire severity, and the role of fire in these woodlands to evaluate the scientific basis for the national assessment. First, unless pi�ons and junipers record fire by means of...
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In recent years, the demand has grown for information on how to conserve bat populations in forested ecosystems. Many researchers have responded with studies of bats in forests, but few have studied bat communities in arid-adapted forest types, such as pinyon-juniper woodlands, which are widespread and abundant throughout the west. In this study, I evaluated the relative use and importance of pinyon-juniper woodlands to bats in west-central New Mexico by comparing bats captured in pinyon-juniper woodlands with those captured in ponderosa pine forest. I compared species richness and relative abundance of bats captured in these vegetation types and evaluated the relative importance of each based on its use as reproductive...
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We examined age structure and spatial arrangement of piñon–juniper woodlands and savannas on six plots distributed across three different soil types in northern Arizona. These stands, as typical of many others in piñon–juniper ecosystems, have experienced increases in tree densities since the arrival of European settlers. The goal of this study was to reconstruct stand conditions in 1860, prior to livestock grazing, using stem-mapping to determine tree arrangement and tree-ring analysis to examine age structure and density. Ripley's K(t), Ripley's K12(t), and Moran's I were used to analyze nearest neighbor distances, spatial association, and spatial autocorrelation, respectively. All sites have long term presence...
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Armillaria root disease is common and widely distributed in campgrounds of southwestern Colorado. Armillaria ostoyae spreads clonally underground and kills and decays tree roots, causing mortality or predisposing the trees to windthrow. We intensively surveyed and mapped genets (clones) of the pathogen in two campgrounds on the San Juan National Forest and one on Grand Mesa National Forest (GMNF). Three additional campgrounds on the GMNF were also surveyed. Infection (based on mycelium under the bark on or near the root collar) of all sampled live trees was 10.5% (range 7.5–15.0) inside campgrounds and 12.7% (3.3–25.9) immediately outside campgrounds, suggesting that campground construction and management practices...
Juniper and pinon woodlands have been expanding throughout the Intermountain West, USA since the late 1800s. Although causal factors attributed to woodland expansion have been documented, data are lacking that describe the influence of topographic features on rates of development and structural attributes of expanding woodlands. Our primary objective was to determine the relationship between stand-level developmental and structural attributes of four expanding western juniper (Juniperus occidentalis) woodlands with two topographic features commonly important to forest vegetation patterns, site exposure (an index of insolation exposure based on slope and aspect) and elevation. To accomplish this we measured tree...
In western North America, quaking aspen (Populus tremuloides) is the most common hardwood in montane landscapes. Fire suppression, grazing and wildlife management practices, and climate patterns of the past century are all potential threats to aspen coverage in this region. If aspen-dependent species are losing habitat, this raises concerns about their long-term viability. Though lichens have a rich history as air pollution indicators, we believe that they may also be useful as a metric of community diversity associated with habitat change. We established 47 plots in the Bear River Range of northern Utah and southern Idaho to evaluate the effects of forest succession on epiphytic macrolichen communities. Plots were...
Phellinus tremulae is an important fungal decay agent common to aspen and a critical component to the cavity-nesting previous termbirdnext term complex found in western aspen stands. Little information exists on the conditions that facilitate infection and spread of P. tremulae in aspen forests. I used Forest Inventory and Analysis (FIA) data to explore the relationships of several tree and stand characteristics to the presence and frequency of P. tremulae in aspen measured across several western states of the United States. Results suggest a strong relationship between tree age, tree diameter, and compacted crown ratio with infection frequency in trees while stand purity, canopy cover and stand age had a positive...
Sudden aspen decline (SAD), affecting Populus tremuloides, was first observed in Colorado in 2004. By 2008 it affected at least 220,000 ha, an estimated 17% of the aspen cover type in the state. In southwestern Colorado, we examined site and stand features in paired healthy and damaged plots to assess the effects of SAD on aspen and to identify factors associated with decline. Root mortality increased significantly with recent crown loss. Consequently, density of regeneration did not increase as the overstory deteriorated, and regeneration that originated since 2002 decreased significantly in stands with moderate to severe SAD. However, mortality of regeneration did not increase with that of the overstory. Remeasurement...
Stands of quaking aspen (Populus tremuloides) rank among the most biologically diverse plant communities across the intermountain region of western North America. Marked declines of aspen have occurred in recent decades, likely due to a combination of effects from changes in fire regimes, herbivory, climate (e.g. drought), and interspecific competition with conifer species. However, it is poorly understood how the effects of these factors are manifested at a landscape scale over decadal time periods. Analysis of field data combined with topographic information collected across the 500,000 ha Owyhee Plateau in southwestern Idaho revealed that aspen in the area occur in three different biophysical settings; First,...
Numerous watershed practices currently being implemented for erosion control and water augmentation purposes have improved hydrologic conditions in southwestern streams and enhanced establishment of riparian vegetation. This paper summarizes some potential opportunities for better managing existing riparian ecosystems, or for creating hydrologic regimes favoring re-establishment of new riparian communities in the southwestern United States. Generally, management opportunities exist where either the amount of water or duration of streamflow can be increased, or both. Various-sized channel structures, ranging from small gully check dams to large flood-control structures, have been used successfully for both stabilizing...
During the 20th Century the flow of most rivers in the United States was regulated by diversions and dams, with major impacts on riparian forests. Few unregulated rivers remain to provide baseline information for assessing these impacts. We characterized patterns in riparian plant communities along chronosequences on the unregulated Yampa River and the regulated Green River in northwestern Colorado, examining patterns in plant species diversity in relation to the ages of floodplain terraces. On both rivers, mean plant species richness in cottonwood (Populus deltoides Marshall subsp. wislizenzii (Watson) Eckenwalder) dominated riparian forests declined by more than 50% from young sites (<20 years) to old upland terraces...
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Many of the streams and aquifers that sustain Interior riparian deciduous forests in the US Southwest are being dewatered, yet we know little about how the plant communities are being affected by these hydrologic changes. This study found that several measures of biotic integrity, including Platanus wrightii xylem water potential, P. wrightii radial growth rate, tree species diversity, and woody plant wetland indicator scores, varied significantly with ground water depth and fluctuation among nine sites in Arizona. P. wrightii trees had highest productivity, and the forests had greatest compositional diversity, where ground water averaged less than 2 m below the tree base during the growing season and less than...
map background search result map search result map Biotic integrity of Platanus wrightii riparian forests in Arizona: first approximation Twenty-year change in aspen dominance in pure aspen and mixed aspen/conifer stands on the Uncompahgre Plateau, Colorado, USA Historical and recent fire regimes in Piñon–Juniper woodlands on Mesa Verde, Colorado, USA Reconstruction of age structure and spatial arrangement of piñon–juniper woodlands and savannas of Anderson Mesa, northern Arizona Incidence, host relations and population structure of Armillaria ostoyae in Colorado campgrounds Use of pinyon-juniper woodlands by bats in New Mexico Historical and recent fire regimes in Piñon–Juniper woodlands on Mesa Verde, Colorado, USA Reconstruction of age structure and spatial arrangement of piñon–juniper woodlands and savannas of Anderson Mesa, northern Arizona Twenty-year change in aspen dominance in pure aspen and mixed aspen/conifer stands on the Uncompahgre Plateau, Colorado, USA Incidence, host relations and population structure of Armillaria ostoyae in Colorado campgrounds Biotic integrity of Platanus wrightii riparian forests in Arizona: first approximation Use of pinyon-juniper woodlands by bats in New Mexico