Conifer Invasion Research Articles

Density‐dependent impacts of exotic conifer invasion on grassland invertebrate assemblages

Summary 1. Globally, temperate grasslands have been heavily modified by agricultural intensification. The ecological integrity of many remaining semi‐natural grasslands is further threatened by the encroachment of invasive alien woody plant species, such as conifers. 2. Although the ecological impact of conifers is often inferred to be directly related to increasing conifer density at invaded sites, interpretation of these density‐dependent effects on native biodiversity is almost always confounded by strong correlations between density and time since invasion. Here, we isolate the direct effects of exotic conifer density on native invertebrate assemblages from the confounding effects due to time since invasion, by establishing replicated experimental plantings of the invasive Pinus nigra (densities of 400, 800, 1600, 2500 and 3500 trees per ha, established in 1993) in New Zealand. 3. From the 29 549 invertebrates captured, the relative abundance of major classes and orders was largely unaffected by conifer invasion at densities below 800 trees per ha at age 14 years, but differed substantially in higher‐density conifer stands (canopy cover >50%). At the species level, beetle species composition was highly sensitive to conifer invasion at densities as low as 400 trees per ha at age 14 years. Changes in beetle species composition were correlated with reduced soil moisture, increases in canopy cover, and trap distance from the nearest semi‐natural grassland. 4. Synthesis and applications. The effects of exotic conifer invasion on grassland invertebrate assemblages were strongly dependent on conifer density. In our study, the negative effects of conifer invasion on biodiversity were comparatively low at densities below ≤800 trees per ha at 14 years after invasion. To conserve invertebrate diversity in semi‐natural grasslands we recommend a dual focus of conservation actions targeting: (i) immediate control, or thinning, of high density conifer infestations (>800 trees per ha) to restore habitat to a state suitable for grassland species, and (ii) longer‐term removal of sparse, pre‐coning infestations in order to prevent further spread. We propose the use of canopy cover as a proxy for the confounded relationship between conifer density and time since invasion.

Spread and impact of introduced conifers in South America: Lessons from other southern hemisphere regions

AbstractThe history of conifers introduced earlier elsewhere in the southern hemisphere suggests that recent invasions in Argentina, Brazil, Chile and Uruguay are likely to increase in number and size. In South Africa, New Zealand and Australia, early ornamental introductions and small forestry plantations did not lead to large‐scale invasions, while subsequent large plantations were followed with a lag of about 20–30 years by troublesome invasions. Large‐scale conifer plantation forestry in South America began about 50–80 years later than in South Africa, Australia and New Zealand, while reports of invasions in South America lagged behind those in the latter nations by a century. Impacts of invading non‐native conifers outside South America are varied and include replacement of grassland and shrubland by conifer forest, alteration of fire and hydrological regimes, modification of soil nutrients, and changes in aboveground and belowground biotic communities. Several of these effects have already been detected in various parts of South America undergoing conifer invasion. The sheer amount of area planted in conifers is already very large in Chile and growing rapidly in Argentina and Brazil. This mass of reproductive trees, in turn, produces an enormous propagule pressure that may accelerate ongoing invasions and spark new ones at an increasing rate. Regulations to control conifer invasions, including measures to mitigate spread, were belatedly implemented in New Zealand and South Africa, as well as in certain Australian states, inspired by observations on invasions in those nations. Regulations in South America are weaker and piecemeal, but the existing research base on conifer invasions elsewhere could be useful in fashioning effective regulations in South America. Pressure from foreign customers in South Africa has led most companies there to seek certification through the Forestry Stewardship Council; a similar programme operates in Australia. Such an approach may be promising in South America.

Pinus contorta invasion in the Chilean Patagonia: local patterns in a global context

Alien conifer invasions are affecting ecosystems across the globe, but until recently, reports of such invasions in South America were scarce. Pinus contorta was first established in Chilean Patagonia for erosion control caused by historical fires and cattle farming. Recently, the species has been planted over large areas for commercial purposes. It is well adapted to local conditions and is now spreading into natural areas. This study analyzes natural regeneration of Pinus contorta around Coyhaique city, Chile, to determine the spatial patterns of invasion. Five study sites were selected, four with grasslands dominated by exotic species and one site in the steppe. In each site, the plantation (seed source) was characterized using morphological attributes and density. Regeneration, density, height and age at different distances from the seed source were recorded, and ground cover was measured as an environmental factor influencing the invasion process. A comparative analysis was also conducted between the situation in Chile and other countries affected by P. contorta invasion. In Chile, P. contorta regeneration is significantly influenced by distance from the seed source. Higher densities are found close to the parent stand (up to 13,222 trees ha−1), decreasing as distance from the seed source increases. Age and height structure indicate that the invasion process is at an early stage, and this offers a unique opportunity to study the process of invasion and to monitor it over time. In order to preserve the distinctiveness of Patagonian ecosystem, decisive action is required to control invasive conifers, with P. contorta as the number one priority. Relative to control, there is much that can be learnt from the experiences of other countries, such as New Zealand.

Tree invasion of a montane meadow complex: temporal trends, spatial patterns, and biotic interactions

Questions: Do spatial and temporal patterns of encroachment of Pinus contorta and Abies grandis in a montane meadow suggest strong biotic controls on the invasion process? Location: Forest–meadow mosaic, 1350 m a.s.l., Cascade Range, Oregon, US. Methods: We combined spatial point pattern analysis, population age structures, and a time-series of stem maps to quantify spatial and temporal patterns of conifer invasion over a 200-yr period in three plots totaling 4 ha. Results: Trees established during two broad, but distinct periods (late 1800s, then at much greater density in the mid-1900s). Recent invasion was not correlated with climatic variation. Abies grandis dominated both periods; P. contorta established at lower density, peaking before A. grandis. Spatially, older (� 90 yr) P. contorta were randomly distributed, but older A. grandis were strongly clumped (0.2-20 m). Younger (o90 yr) stems were positively associated at small distances (both within and between species), but were spatially displaced from older A. grandis, suggesting a temporal shift from facilitation to competition. Establishment during the 1800s resulted in widely scattered P. contorta and clumps of A. grandis that placed most areas of meadow close to seed sources permitting more rapid invasion during the mid-1900s. Rapid conversion to forest occurred via colonization of larger meadow openings – first by shade-intolerant P. contorta, then by shade-tolerant A. grandis – and by direct infilling of smaller openings by A. grandis. Conclusions: In combination, spatial and temporal patterns of establishment suggest an invasion process shaped by biotic interactions, with facilitation promoting expansion of trees into meadows and competition influencing subsequent forest development. Once invasion is initiated, tree species with different life histories and functional traits can interact synergistically to promote rapid conversion of meadow to forest under a broad range of climatic conditions.

Little evidence of invasion by alien conifers in Europe

AbstractAim Conifers are invasive species in many parts of the world, especially in the Southern Hemisphere. There are many introduced conifers in Europe, but their status as alien species is poorly documented. We conducted a comprehensive literature review to ascertain the extent to which alien conifers can be considered invasive.Location Europe.Methods We reviewed the historical record of alien conifer invasion in Europe (i.e. species with a native range outside the continental boundaries of Europe) by screening the DAISIE database and the ISI Web of Science.Results According to DAISIE, there are 54 alien conifer species in Europe. Pseudotsuga menziesii is the species recorded as naturalized in the most countries (12) and the UK is the country with the most naturalized species (18). Thirty‐seven of these conifers have been studied, to some extent, in a total of 131 papers (212 records). Nevertheless, only a few papers have investigated aspects related to biological invasions. In fact, the species are not referred to as alien by the authors in more than half of the papers (66%). Twenty‐five per cent of the papers have investigated plant traits, 46% are about biotic and abiotic factors influencing tree performance and 29% deal with ecological and economic impacts. Most papers are related to entomology, dealing with natural enemies affecting the alien conifers.Main conclusions Scientists have not yet perceived alien conifers in Europe as problematic species. Moreover, the low introduction effort, long lag‐time since plantation and phylogenetic closeness between alien and native conifers are possible reasons for their low expansion in Europe to date. From a management point of view, careful observations of sites with alien conifers is necessary to watch for new invasions. From a scientific perspective, thorough analyses of the extent that introduction, rates of naturalization and biogeographical differences influence invasive spread between the two hemispheres will prove timely.

Seed predation as a barrier to alien conifer invasions

Interactions between exotic plants and animals can play a major role in determining success or failure of plant introductions. Seed predation has been seen as important in explaining biotic resistance to plant invasion, but this hypothesis has rarely been tested. We studied seed predation on exotic forest plants on an island in Patagonia, Argentina where 43 pine species, including 60% of the world’s known invasive Pinaceae, were introduced ca. 80 years ago, but where exotics attain relatively high densities only near the original plantings. To test if seed predation limits exotic conifer establishment in this area, we compared seed predation in areas close to plantations (colonized by exotics) and far from them (not invaded). Seeds of exotics were preferred over seeds of native species, possibly because exotic seeds are bigger. Predation was more intense in areas far from plantations than in areas close to them, substantially reducing the chances of exotic seed establishment. Using automatic cameras, we found that both rodents and birds preyed on exotic seeds. This study suggests that native seed predators can be an important component of biological resistance to plant invasion.

A typology of stand structure and dynamics of Quaking aspen in northwestern Colorado

The regeneration of Quaking aspen ( Populus tremuloides) in the western U.S. in some habitats occurs after severe fire which removes competing conifers and also triggers root suckering of aspen. Consequently, fire exclusion during the 20th century, sometimes in combination with elk browsing, has often been argued to have resulted in a decline in the extent of aspen relative to its pre-20th century extent. However, aspen regeneration is not always dependent on fire and many stands have structures indicative of aspen persistence even in the absence of fire. Thus, to investigate regeneration dynamics of both persistent and seral aspen stands, we reconstructed patterns of stand development in 26 aspen stands in northwestern Colorado. Seral and persistent aspen stands were initially selected based on geographic information system-based analysis of historic vegetation and fire occurrence. Stand-level age structures were determined from 1919 increment cores and size structures from counts and diameters of all juvenile, subcanopy and canopy trees in 40 m × 40 m plots. Stand structures were interpreted to determine modes of tree regeneration and patterns of stand development. As expected, in the eight seral stands aspen regeneration generally depended on coarse-scale, severe disturbance by fire. However, most aspen stands in this study showed signs of aspen self-replacement despite presence of conifers. In the 16 persistent aspen stands showing no conifer invasion, aspen are able to regenerate through a variety of regeneration modes that did not appear to require severe disturbance. Over 70% of the persistent aspen stands sampled did not require coarse-scale disturbance to regenerate. Two (11%) of the persistent stands regenerated continuously through time, and 11 (61%) had aspen cohorts that appeared to develop episodically without being triggered by severe fire or other severe disturbance. In the persistent stands sampled in our study, episodic regeneration not dependent on severe fire is the main mode of stand re-initiation. At many sites in northwestern Colorado aspen regeneration occurs episodically and fits a general stand development model of cohort senescence. According to this model, many of the currently “decadent” or deteriorating aspen stands in western Colorado may be replaced by regenerating stands as the senescent stages experience high levels of canopy tree mortality, thus assuring aspen persistence in the future.

Alien conifer invasions in South America: short fuse burning?

Alien conifers have been widely planted in the Southern Hemisphere. Australia, New Zealand and South Africa, all with long histories of alien conifer planting, have major problems with invasive conifers (“wildings”). Widespread planting of alien conifers has a much shorter history in South America, and invasions are a recent phenomenon. A workshop was convened in Argentina in May 2007 to discuss the rapid emergence of problems with invasive conifers in South America. Workshop delegates agreed that: the problem is likely to increase substantially and rapidly in many parts of the continent; the problem is not widely recognized; lessons from elsewhere can be transferred; and collaboration can bring benefits. The need was expressed: for an accurate assessment of the dimensions of the problem; to raise awareness of the problem; for a common research agenda; to initiate management interventions. This paper summarizes the key aims, deliberations, and planned outcomes of the workshop.

Vegetation responses to conifer encroachment in a western Cascade meadow: a chronosequence approach

Conifer invasion of mountain meadows is pervasive in western North America, but its consequences for plant composition and diversity have not been studied. We used a chronosequence approach to reconstruct temporal patterns of vegetation change in response to ~200 years of conifer encroachment of a dry, montane meadow in the western Cascade Range, Oregon. Tree age distributions, forest structure, light, and vegetation composition were determined for three hundred and fifty-six 10 m × 10 m samples representing a gradient from open meadow to old forest (>90 years). Nonmetric multidimensional scaling revealed strong turnover in species composition from open meadow to old forest. Ordination axes were highly correlated with light availability and density/basal area of encroaching grand fir, Abies grandis (Dougl. ex D. Don) Lindl., and lodgepole pine, Pinus contorta Dougl. ex Loud. Cover of meadow species declined steeply with establishment of A. grandis ; richness declined more gradually and extirpations of meadow species were rare. Forest herbs colonized within two decades of tree establishment and within 60–80 years dominated the understory flora. In contrast with meadow species, changes in richness and cover of forest herbs were weakly related to changes in forest structure. Rapid replacement of meadow by forest species and long-term effects of trees on soils may limit potential for restoration of these unique habitats.

ASPEN AND CONIFER HETEROGENEITY EFFECTS ON BIRD DIVERSITY IN THE NORTHERN YELLOWSTONE ECOSYSTEM

We addressed the following question: Do conifers within aspen stands (conifer invasion) increase bird species diversity in western landscapes? We tested the hypotheses that bird species diversity, measured as species richness or with the Shannon-Weiner diversity index, responds to aspen-conifer ratios (from 0% to 100% conifer) in a quadratic manner with a maximum occurring at an intermediate ratio of aspen and conifer. Extra sum-of-squares F tests comparing quadratic with linear models suggested that migratory bird diversity was inversely linearly related to the extent of conifer invasion. These linear responses were moderate (species richness: R2 ≥0.34, P < 0.01; Shannon-Weiner diversity index: R2 ≥0.34, P < 0.01). Resident species diversity appeared quadratically related to conifer invasion. However, variation was poorly described for species richness (R2 ≤0.13, P ≥0.09) and was marginal for the Shan-non-Weiner diversity index (R2 ≤0.27, P ≤0.01). We concluded that mixed aspen-conifer stands do not have higher bird species diversity than pure aspen stands and that management activities should focus on heavily conifer-invaded stands to increase bird diversity in western landscapes and help reverse the decline of aspen habitat due to conifer invasion.

The fate of alien conifers in long‐term plantings in the USA

ABSTRACTFor more than 100 years, non‐native conifers have been introduced into habitats in the USA that already support native conifers. These introductions have yielded few naturalizations and even less evidence of invasions. We investigated the specific fates of nine non‐native conifers in an array of introduction sites across the USA (Priest River, Idaho, Wind River, Washington, Cedar Creek, Minnesota, and Nantucket Is. and Martha's Vineyard, Massachusetts) through tree‐ring analyses, comparisons of growth with adjacent native conifer populations, and surveys for regeneration and spread. Most of the original non‐native tree plantings have died (e.g. Abies veitchii, Pinus densiflora, and Pinus halepensis at Wind River, WA); a few have survived but display low vigour and are not regenerating (e.g. Larix decidua, Pinus mugo, and Picea abies stands at Priest River, ID). Pinus sylvestris recruitment is apparent at all sites examined. Pinus thunbergii appears to be invasive on Nantucket Is., although the native Bursaphelenchus xylophilus (pinewood nematode) causes high mortality in mature trees. Non‐native Pinus spp. at the Eddy Arboretum, California and Pack Forest, Washington also experienced high mortality. Dendroclimatic analyses revealed no difference in the effect of climate on the annual growth of native and non‐native conifers. Plantations of introduced conifers in the south‐eastern USA have died en masse (e.g. Harrison Experimental Forest, Mississippi, Olustee Arboretum, Florida). Such widespread extirpations are in sharp contrast to the fate of native conifers in adjacent stands as well as the multiple cases of large‐scale conifer invasions in the Southern Hemisphere. Given the diversity of alien plant species that have invaded the USA, the circumstances surrounding the lack of persistence of introduced conifers becomes an important line of inquiry for understanding the factors and circumstances that facilitate or thwart biological invasions.

Slowing down a pine invasion despite uncertainty in demography and dispersal

Summary Management decisions regarding invasive plants often have to be made quickly and in the face of fragmentary knowledge of their population dynamics. However, recommendations are commonly made on the basis of only a restricted set of parameters. Without addressing uncertainty and variability in model parameters we risk ineffective management, resulting in wasted resources and an escalating problem if early chances to control spread are missed. Using available data for Pinus nigra in ungrazed and grazed grassland and shrubland in New Zealand, we parameterized a stage‐structured spread model to calculate invasion wave speed, population growth rate and their sensitivities and elasticities to population parameters. Uncertainty distributions of parameters were used with the model to generate confidence intervals (CI) about the model predictions. Ungrazed grassland environments were most vulnerable to invasion and the highest elasticities and sensitivities of invasion speed were to long‐distance dispersal parameters. However, there was overlap between the elasticity and sensitivity CI on juvenile survival, seedling establishment and long‐distance dispersal parameters, indicating overlap in their effects on invasion speed. While elasticity of invasion speed to long‐distance dispersal was highest in shrubland environments, there was overlap with the CI of elasticity to juvenile survival. In shrubland invasion speed was most sensitive to the probability of establishment, especially when establishment was low. In the grazed environment elasticity and sensitivity of invasion speed to the severity of grazing were consistently highest. Management recommendations based on elasticities and sensitivities depend on the vulnerability of the habitat. Synthesis and applications. Despite considerable uncertainty in demography and dispersal, robust management recommendations emerged from the model. Proportional or absolute reductions in long‐distance dispersal, juvenile survival and seedling establishment parameters have the potential to reduce wave speed substantially. Plantations of wind‐dispersed invasive conifers should not be sited on exposed sites vulnerable to long‐distance dispersal events, and trees in these sites should be removed. Invasion speed can also be reduced by removing seedlings, establishing competitive shrubs and grazing. Incorporating uncertainty into the modelling process increases our confidence in the wide applicability of the management strategies recommended here.

Twenty-year change in aspen dominance in pure aspen and mixed aspen/conifer stands on the Uncompahgre Plateau, Colorado, USA

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 on the Uncompahgre Plateau. Pure aspen stands were self-thinning, but stable over the twenty-year study period, with high amounts of regeneration and without conifer invasion. Mixed stands of aspen and conifer had undergone significant change. In aspen dominated mixed species stands, conifer basal area increased from 10 to 23 m 2 ha −1 in the last 20 years, while aspen basal area decreased. In conifer dominated mixed species stands, conifer basal area increased from 18 to 24 m 2 ha −1. Most overstory aspen in pure aspen stands were between 80 and 120 years old. Substantial aspen suckering was occurring, but all suckers were <20 years old, indicating lack of current growth into the overstory. Aspen suckering was occurring in mixed species stands, but again, most suckers were <20 years old, and few overstory trees were <100 years old. In contrast, understory and overstory conifers spanned ages from <20 to over 250 years old. Aspen dominance is decreasing in the forested communities of the study area. Pure stands are likely to persist without decline for a considerable time. Mixed stands are likely to continue to experience a decrease in overstory aspen canopy dominance. These changes are probably within the historic range of variability, but restoration of aspen canopy cover consistent with an early- to mid-seral landscape condition would require disturbances such as fire or cutting to create canopy gaps to permit growth of suckers into the overstory of mixed species stands.

Conifer invasion of forest meadows transforms soil characteristics in the Pacific Northwest

In many areas, chemical and biological characteristics of soils change when trees colonize meadows. To determine if the invasion of high meadows by forests in the central Cascade Mountains of Oregon altered soil properties, we measured soil properties along transects from mountain meadows through transition zones, where trees were becoming established, into mature forest. The differences observed in this study support the view that N is more available in meadow soils than in forest soils and that N pools and cycling change markedly when trees invade mountain meadows. β-Glucosidase activity in the transition zone soil was close to that in the forest soil and much lower than that in the meadow soil, suggesting qualitative changes in microbial populations as microorganisms adjusted to changes in litter quality. High correlations between litter depth and most variables in meadow soil, which were not observed in transition zone soil or mature forest soil, suggest that litter may control other aspects of biogeochemical cycling in meadows. With the exception of laboratory respiration, the values observed in the transition zone soil lay between those in meadow soil and those in forest soil; in most cases, they were closer to those in forest soil. This suggests that soil properties shift rapidly toward those found in forests as trees invade meadows. These rapid changes may alter soils so that they are more likely to support trees than grass.

Trophic Cascades and Historic Aspen Recruitment in the Gallatin Elk Winter Range of Southwest Montana

The extirpation of the gray wolf (Canis lupus) by 1930 in Yellowstone National Park (YNP) provided us with an opportunity to study historic aspen (Populus tremuloides ) recruitment with and without a top carnivore predator present. Herbivory, climate trends, fire records, and current conifer invasion were also examined within the context of aspen recruitment. We obtained tree cores and diameter at breast height measurements to create an aspen age-diameter relationship which we used to approximate aspen origination dates. One elk (Cervus elaphus) exclosure, erected in 1945 within the same elk winter range, was compared to the rest of the winter range. Consistent recruitment inside the exclosure began in the 1940s and has continued into the present. Outside of the exclosure, aspen recruitment began decreasing in the 1930s and ceased in the 1950s. Within the scope of the study, we found little correlative evidence between aspen decline and climate trends, conifer invasion, or fire suppression. The results are suggestive of a trophic cascade between aspen recruitment, and historical elk browsing activities as affected by the absence or presence of wolf predation.

Conifers as invasive aliens: a global survey and predictive framework

ABSTRACTWe summarize information on naturalized and invasive conifers (class Pinopsida) worldwide (data from 40 countries, some with remote states/territories), and contrast these findings with patterns for other gymnosperms (classes Cycadopsida, Gnetopsida and Ginkgoopsida) and for woody angiosperms. Eighty conifer taxa (79 species and one hybrid; 13% of species) are known to be naturalized, and 36 species (6%) are ‘invasive’. This categorization is based on objective and conservative criteria relating to consistency of reproduction, distance of spread from founders, and degree of reliance on propagules from the founder population for persistence in areas well outside the natural range of species. Twenty‐eight of the known invasive conifers belong to one family (Pinaceae) and 21 of these are in one genus (Pinus). The Cupressaceae (including Taxodiaceae) has six known invasive species (4%) in four genera, but the other four conifer families have none. There are also no known invasive species in classes Cycadopsida, Gnetopsida or Ginkgoopsida. No angiosperm family comprising predominantly trees and shrubs has proportionally as many invasive species as the Pinaceae.Besides the marked taxonomic bias in favour of Pinaceae, and Pinus in particular, invasiveness in conifers is associated with a syndrome of life‐history traits: small seed mass (&lt; 50 mg), short juvenile period (&lt; 10 year), and short intervals between large seed crops. Cryptomeria japonica, Larix decidua, Picea sitchensis, Pinus contorta, Pinus strobus, and Pseudotsuga menziesii exemplify this syndrome. Many rare and endangered conifer species exhibit opposite characters. These results are consistent with earlier predictions made using a discriminant function derived from attributes of invasive and noninvasive Pinus species. Informative exceptions are species with small seeds (&lt; 4 mg, e.g. Chamaecyparis spp., Pinus banksiana, Tsuga spp. — mostly limited to wet/mineral substrates) or otherwise ‘non‐invasive’ characters (e.g. large seeds, fleshy fruits, e.g. Araucaria araucana, Pinus pinea, Taxus baccata that are dependent on vertebrates for seed dispersal). Most conifers do not require coevolved mutualists for pollination and seed dispersal. Also, many species can persist in small populations but have the genetic and reproductive capacity to colonize and increase population size rapidly. The underlying mechanisms mediating conifer invasions are thus easier to discern than is the case for most angiosperms. Further information is needed to determine the extent to which propagule pressure (widespread dissemination, abundant plantings, long history of cultivation) can compensate for low ‘inherent invasiveness’.

Turf-banked terrace treads and risers, turf exfoliation and possible relationships with advancing treeline

Fine-scale geomorphic/pedogenic processes at alpine treeline may facilitate the initial stages of conifer invasion of alpine tundra. Turf-banked terraces and turf exfoliation associated with solifluction may provide both the topographic protection and the seedbed necessary for conifer establishment above treeline. The morphometry, stoniness and surface penetrability of turf-banked terraces were recorded. Whereas differences among sites exist due to topographic constraints, differences in soil penetrability depend on turf exfoliation. Exfoliated turf risers are significantly more penetrable than non-exfoliated solifluction risers and adjacent treads. These penetrable microsites provide favorable conditions for seed germination. The process of turf exfoliation may play a role in conifer advance into tundra during climatic change.

Ecology and management of sage-grouse and sage-grouse habitat

Sage-grouse (Centrocercus urophasianus and C. minimus) historically inhabited much of the sagebrush-dominated habitat of North America. Today, sage-grouse populations are declining throughout most of their range. Population dynamics of sage-grouse are marked by strong cyclic behavior. Adult survival is high, but is offset by low juvenile survival, resulting in low productivity. Habitat for sage-grouse varies strongly by life-history stage. Critical habitat components include adequate canopy cover of tall grasses (≥ 18 cm) and medium height shrubs (40-80 cm) for nesting, abundant forbs and insects for brood rearing, and availability of herbaceous riparian species for late-growing season foraging. Fire ecology of sage-grouse habitat changed dramatically with European settlement. In high elevation sagebrush habitat, fire return intervals have increased (from 12-24 to &gt; 50 years) resulting in invasion of conifers and a consequent loss of understory herbaceous and shrub canopy cover. In lower elevation sagebrush habitat, fire return intervals have decreased dramatically (from 50-100 to &lt; 10 years) due to invasion by annual grasses, causing loss of perennial bunchgrasses and shrubs. Livestock grazing can have negative or positive impacts on sage-grouse habitat depending on the timing and intensity of grazing, and which habitat element is being considered. Early season light to moderate grazing can promote forb abundance/availability in both upland and riparian habitats. Heavier levels of utilization decrease herbaceous cover, and may promote invasion by undesirable species. At rates intended to produce high sagebrush kill, herbicide-based control of big sagebrush may result in decreased habitat quality for sage-grouse. Light applications of tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea) can decrease canopy cover of sagebrush and increase grass and forb production which may be locally important to nesting and foraging activities. The ability of resource managers to address sage-grouse habitat concerns at large scales is aided greatly by geomatics technology and advances in landscape ecology. These tools allow unprecedented linkage of habitat and population dynamics data over space and time and can be used to retroactively assess such relationships using archived imagery. The present sage-grouse decline is a complex issue that is likely associated with multiple causative factors. Solving management issues associated with the decline will require unprecedented cooperation among wildlife biology, range science, and other professional disciplines.

Ecology and management of sage-grouse and sage-grouse habitat

Abstract Sage-grouse (Centrocercus urophasianus and C. minimus) historically inhabited much of the sagebrush-dominated habitat of North America. Today, sage-grouse populations are declining throughout most of their range. Population dynamics of sage-grouse are marked by strong cyclic behavior. Adult survival is high, but is offset by low juvenile survival, resulting in low productivity. Habitat for sage-grouse varies strongly by life-history stage. Critical habitat components include adequate canopy cover of tall grasses (≥ 18 cm) and medium height shrubs (40–80 cm) for nesting, abundant forbs and insects for brood rearing, and availability of herbaceous riparian species for late-growing season foraging. Fire ecology of sage-grouse habitat changed dramatically with European settlement. In high elevation sagebrush habitat, fire return intervals have increased (from 12–24 to > 50 years) resulting in invasion of conifers and a consequent loss of understory herbaceous and shrub canopy cover. In lower elevatio...

Aspen Recruitment and Stand Structure in the Gallatin Elk Winter Range of Southwest Montana

This study examines the relationship between wolf, elk, and aspen within the framework of trophic cascades inside and outside of the Gallatin elk winter range. The overall goal of this study is to determine if an association exists between aspen recruitment, and historic and current elk browsing activities as affected by the absence or presence of wolf predation. This study also examines if other factors (climate fluctuations, conifer invasion, ftre suppression) may have had a role in aspen decline. Through the examination of current and historic elk browsing levels, current and historic browsing effects on aspen recruitment are addressed. Potential historic browsing affects were assessed with tree rings, aspen age structures, historic documents, and an elk exclosure erected in 1945. Current browsing levels were assessed through plant architecture methods and elk pellet counts. Initial results indicate that a gap in aspen recruitment is present yet aspen have successfully recruited inside an elk exclosure located within the same elk winter range. The lack of recruitment outside the exclosure appears to be due to chronic elk herbivory, although other factors need further evaluation. Future results will elucidate if the recruitment gap occurred after wolf extirpation in the 1920's.