Aspen Bibliography

Changes in Avian and Plant Communities of Aspen Woodlands over 12 Years after Livestock Removal in the Northwestern Great Basin

Susan L. Earnst et al. — Thu, 18 Apr 2013 09:57:47 PDT

Riparian and quaking aspen (Populus tremuloides) woodlands are centers of avian abundance and diversity in the western United States, but they have been affected adversely by land use practices, particularly livestock grazing. In 1990, cattle were removed from a 112,500-ha national wildlife refuge in southeastern Oregon. Thereafter, we monitored changes in vegetation and bird abundance in years 1–3 (phase 1) and 10–12 (phase 2) in 17 riparian and 9 snow-pocket aspen plots. On each 1.5-ha plot, we sampled vegetation in 6 transects. Three times during each breeding season, observers recorded all birds 50 m to each side of the plot's 150-m centerline for 25 minutes. We analyzed data with multivariate analysis of variance and paired t tests with p values adjusted for multiple comparisons. In both periods, riparian and snow-pocket aspen produced extensive regeneration of new shoots ( stems/ha and 7079 stems/ha, respectively). By phase 2, a 64% increase in medium-diameter trees in riparian stands indicated successful recruitment into the overstory, but this pattern was not seen in snow-pocket stands, where the density of trees was over 2 times greater. By phase 2 in riparian and snow-pocket stands, native forb cover had increased by 68% and 57%, respectively, mesic shrub cover had increased by 29% and 58%, and sagebrush cover had decreased by 24% and 31%. Total avian abundance increased by 33% and 39% in riparian and snow-pocket aspen, respectively, ground or understory nesters increased by 133% and 67% and overstory nesters increased by 34% and 33%. Similarly, ground or understory foragers increased by 25% and 32%, aerial foragers by 55% and 57%, and overstory foragers by 66% and 43%. We interpreted the substantial regeneration of aspen shoots, increased densities of riparian forbs and shrubs, and increased avian abundances as a multitrophic-level response to the total removal of livestock and as substantial movement toward recovery of biological integrity.

Effects of ungulate herbivory on aspen, cottonwood, and willow development under forest fuels treatment regimes

Bryan A. Endress et al. — Thu, 18 Apr 2013 09:57:43 PDT

Herbivory by domestic and wild ungulates can dramatically affect vegetation structure, composition and dynamics in nearly every terrestrial ecosystem of the world. These effects are of particular concern in forests of western North America, where intensive herbivory by native and domestic ungulates has the potential to substantially reduce or eliminate deciduous, highly palatable species of aspen (Populus tremuloides), cottonwood (Populus trichocarpa), and willow (Salix spp.). In turn, differential herbivory pressure may favor greater establishment of unpalatable conifers that serve as ladder fuels for stand-replacing fires. The resulting high fuel loads often require silvicultural fuels reductions to mitigate fire risk, which in turn may facilitate additional recruitment of deciduous species but also additional herbivory pressure. Potential interactions of ungulate herbivory with episodic disturbances of silviculture, fire, and other land uses are not well documented, but are thought to operate synergistically to affect forest dynamics. We evaluated individual and joint effects of ungulate herbivory and fuels reduction treatments in grand fir (Abies grandis) and Douglas-fir (Psuedotsuga menziezii) forests that dominate large areas of interior western North America. We applied fuels reduction treatments of mechanical thinning and prescribed fire and then evaluated the responses of aspen, cottonwood, and willow species to these treatments (N = 3) versus areas of no treatment (N = 3), and to exclusion from ungulate herbivory versus areas subjected to extant herbivory by free-ranging cattle (Bos taurus), elk (Cervus elaphus), and mule deer (Odocoileus hemionus). Densities of deciduous species were >4 times higher in response to fuels reduction treatments (84.4 individuals/ha) compared to areas of no treatment (19.7 individuals/ha). Additionally, when ungulates were excluded from fuels treated sites, the density of cottonwood was >5 times higher (122.5 individuals/ha) than fuels treated sites subjected to extant herbivory (24.3 individuals/ha). Similarly, densities of Populus spp. and Salix spp. were >3 times higher (211.6 individuals/ha) on fuels treated sites excluded from ungulate herbivory versus fuels treated sites subjected to extant herbivory (66.1 stems/ha). Deciduous species subjected to extant ungulate herbivory also were significantly lower in height, canopy surface area, and canopy volume than the same species inside the ungulate exclosures. Recruitment and long-term survival of aspen, cottonwood, and willow species in coniferous forests of interior western North America require a combination of episodic disturbances such as silviculture and fire to facilitate deciduous plant recruitment, followed by reductions in grazing pressure by domestic and wild ungulates during the time intervals between episodic disturbances to facilitate plant establishment, growth and survival.

Impact of harvesting intensity on wood-inhabiting fungi in boreal aspen forests of Eastern Canada

Hedi Kebli et al. — Thu, 18 Apr 2013 09:57:38 PDT

Environmental change, including human disturbance, can have a striking impact on the biodiversity of ecosystems. We used a molecular fingerprinting technique to determine how communities of saproxylic fungi on trembling aspen deadwood change under the influence of silvicultural treatments designed to emulate natural stand dynamics. We describe changes in richness, diversity, and species composition of fungal communities of trembling aspen logs and snags caused by these silvicultural practices. Our study was conducted in the SAFE Project, a series of silvicultural experiments that tests an ecosystem management model based on natural dynamics. We found that large trembling aspen logs and in advanced decay stages had approximately 9% higher fungal species richness and 10% higher fungal diversity than small and large logs at medium decay stages. The effect of log diameter was in turn strongly dependent on the silvicultural treatment. In burned stands, larger logs supported higher fungal richness and diversity, therefore potentially acting as fungal refuge. A negative relationship between the fungal diversity of logs and snags and the volume of fine woody debris was also related to silvicultural treatments, as fine woody debris increased with silvicultural intensity. Our results underline the negative effects of intense silvicultural practice on fungal diversity and species richness by modifying community composition, but they also highlight the benefits of partial harvest, which retain coarse woody debris volume.

SNP discovery, gene diversity, and linkage disequilibrium in wild populations of Populus tremuloides

Colin T. Kelleher — Thu, 18 Apr 2013 09:57:33 PDT

The use of single-nucleotide polymorphisms (SNPs) as molecular markers in plant studies has become increasingly common. With the development of these markers, there is an interest in determining levels of variation in natural populations. Here, we identify and characterize levels of SNPs in wild populations of aspen (Populus tremuloides Michx.). Four populations were sampled from Alberta and British Columbia in Western Canada. A total of 35 gene regions were selected for analysis. The loci selected are mainly involved in wood formation and include regions from genes for lignin biosynthesis, cellulose biosynthesis, and other cell wall compounds and a number of transcription factors. Other genes included those coding for growth hormones, disease resistance, and light responses. Primers were developed from conserved regions in multi-species EST alignments. Regions were PCR amplified, and products (approximately 500 to 1,000 bp) were assessed for levels of SNPs using Ecotilling. From a total of approximately 25 kb 462 SNPs were identified, over 18 SNPs/kb. Thus, SNPs are an abundant and potentially useful molecular marker in aspen. Gene diversity (heterozygosity) varied in the gene regions, with an overall average of H T = 0.18. Although gene diversity was considerable, genetic differentiation was low with the overall F ST value being 0.004. A surrogate measure of linkage disequilibrium (LD) was calculated, and overall, the LD was shown to decay relatively rapidly with distance along the gene region. The results obtained from the wood formation genes in this study will enable further targeting of regions for association studies on lignin and cellulose variation in aspen and other Populus species.

Compounded disturbances in sub-alpine forests in western Colorado favour future dominance by quaking aspen (Populus tremuloides)

Dominik Kulakowski et al. — Thu, 18 Apr 2013 09:57:29 PDT

Arthropod Community Similarity in Clonal Stands of Aspen: A Test of the Genetic Similarity Rule

Nashelly Meneses — Thu, 18 Apr 2013 09:57:25 PDT

Understanding the factors that affect community composition is essential for community ecology. The genetic similarity rule (GSR) identifies 3 variables (host genetic composition, phytochemistry, and the environment) that could affect community composition. Few studies have determined the relative influence of these variables on community composition. Using path analysis, we found that arthropod community similarity was better explained by geographic (56%) and environmental (32%) distance than genetic distance in clonal aspen (Populus tremuloides). Comparing our data with data from similar studies of poplars (P. fremontii and P. fremontii × P. angustifolia hybrids), we found that hybrid poplar stands had higher levels of genetic and arthropod diversity than did clonal aspen stands. We found a significant relationship between genetic and arthropod diversity only in hybrid stands and across Populus systems. Our findings agree with the GSR expectations that the importance of the genetic composition of the host in structuring communities depends in part on the amount of genetic variation present in the study system. This is relevant for management and restoration strategies of geographically restricted species and of disjunct populations of otherwise widespread species, as these tend to have lower effective population sizes and reduced levels of genetic diversity.

Genotypic Differences and Prior Defoliation Affect Re-Growth and Phytochemistry after Coppicing in Populus tremuloides

Michael T. Stevens et al. — Thu, 18 Apr 2013 09:57:20 PDT

Although considerable research has explored how tree growth and defense can be influenced by genotype, the biotic environment, and their interaction, little is known about how genotypic differences, prior defoliation, and their interactive effects persist in trees that re-grow after damage that severs their primary stem. To address these issues, we established a common garden consisting of twelve genotypes of potted aspen (Populus tremuloides) trees, and subjected half of the trees to defoliation in two successive years. At the beginning of the third year, all trees were severed at the soil surface (coppiced) and allowed to regenerate for five months. Afterwards, we counted the number of root and stump sprouts produced and measured the basal diameter (d) and height (h) of the tallest ramet in each pot. We collected leaves one and two years after the second defoliation and assessed levels of phenolic glycosides, condensed tannins, and nitrogen. In terms of re-growth, we found that the total number of sprouts produced varied by 3.6-fold among genotypes, and that prior defoliation decreased total sprout production by 24%. The size (d2h) of ramets, however, did not differ significantly among genotypes or defoliation classes. In terms of phytochemistry, we observed genotypic differences in concentrations of all phytochemicals assessed both one and two years after the second defoliation. Two years after defoliation, we observed effects of prior defoliation in a genotype-by-defoliation interaction for condensed tannins. Results from this study demonstrate that genotypic differences and impacts of prior defoliation persist to influence growth and defense traits in trees even after complete removal of above-ground stems, and thus likely influence productivity and plant-herbivore interactions in forests affected by natural disturbances or actively managed through coppicing.

Elevated growth temperatures alter hydraulic characteristics in trembling aspen (Populus tremuloides) seedlings: implications for tree drought tolerance

Danielle A. Way et al. — Thu, 18 Apr 2013 09:57:16 PDT

Although climate change will alter both soil water availability and evaporative demand, our understanding of how future climate conditions will alter tree hydraulic architecture is limited. Here, we demonstrate that growth at elevated temperatures (ambient +5 °C) affects hydraulic traits in seedlings of the deciduous boreal tree species Populus tremuloides, with the strength of the effect varying with the plant organ studied. Temperature altered the partitioning of hydraulic resistance, with greater resistance attributed to stems and less to roots in warm-grown seedlings (P < 0.02), and a 46% (but marginally significant, P = 0.08) increase in whole plant conductance at elevated temperature. Vulnerability to cavitation was greater in leaves grown at high than at ambient temperatures, but vulnerability in stems was similar between treatments. A soil–plant–atmosphere (SPA) model suggests that these coordinated changes in hydraulic physiology would lead to more frequent drought stress and reduced water-use efficiency in aspen that develop at warmer temperatures. Tissue-specific trade-offs in hydraulic traits in response to high growth temperatures would be difficult to detect when relying solely on whole plant measurements, but may have large-scale ecological implications for plant water use, carbon cycling and, possibly, plant drought survival.

Aspen and Willow Restoration Using Beaver on the Northern Yellowstone Winter Range

Samuel D. McColley et al. — Thu, 21 Feb 2013 12:08:16 PST

Understanding Cumulative Effects of Aspen Harvest on Wildlife Habitat and Timber Resources in Northern Michigan

Alexandra Locher et al. — Thu, 21 Feb 2013 12:08:12 PST

Using Inventory Data to Determine the Impact of Drought on Tree Mortality

Greg C. Liknes et al. — Thu, 21 Feb 2013 12:08:09 PST

The Interplay of Plant and Animal Disease in a Changing Landscape: The Role of Sudden Aspen Decline in Moderating Sin Nombre Virus Prevalence in Natural Deer Mouse Populations

Erin M. Lehmer — Thu, 21 Feb 2013 12:08:06 PST

Distribution of White Spruce Lateral Fine Roots as Affected by the Presence of Trembling Aspen: Root Mapping Using Simple Sequence Repeat DNA Profiling

Derek J. Lawrence — Thu, 21 Feb 2013 12:08:03 PST

Herbivore-simulated Induction of Defenses in Clonal Networks of Trembling Aspen (Populus tremuloides)

Hana Jelinkova et al. — Thu, 21 Feb 2013 12:08:00 PST

Facilitation Drives Mortality Patterns Along Succession Gradients of Aspen-conifer Forests

W. John Calder et al. — Thu, 21 Feb 2013 12:07:56 PST

Climate Change Intensification of Herbivore Impacts on Tree Recruitment

Jedediah Brodie et al. — Thu, 21 Feb 2013 12:07:52 PST

Climate Change has Indirect Effects on Resource use and Overlap among Coexisting Bird Species with Negative Consequences for their Reproductive Success

Sonya K. Auer et al. — Thu, 21 Feb 2013 12:07:48 PST

Aspen Restoration in the Eastern Sierra Nevada: Effectiveness of Prescribed Fire and Conifer Removal

Kevin D. Krasnow et al. — Thu, 14 Feb 2013 09:06:28 PST

Aspen (Populus tremuloides Michx.) comprises only a small fraction (1 %) of the Sierra Nevada landscape, yet contributes significant biological diversity to this range. In an effort to rejuvenate declining aspen stands, the Bureau of Land Management conducted conifer removal in three sites (2004 to 2006) and prescribed fire in two sites (2007). The goal of this study was to evaluate the efficacy of these treatments. In each site, aspen densities in three regeneration size classes were measured in treated and untreated transects before and up to five years post-treatment. Five years after treatment, two of the three conifer removal sites showed significant improvement over controls in the density of total stems and two of three regeneration size classes. The third site did not show significant gains over controls in any size class and experienced significant aspen overstory mortality three years after treatment, which was attributed to sunscald and advanced age at the time of treatment. Three years after treatment, the two prescribed fire sites showed significant increases in total stem density and two regeneration size classes, but also exhibited significant stem mortality, which was likely due to a combination of herbivory and drought. Overall, both treatments can be effective, but future treatments should incorporate methods to reduce post-treatment mortality of residual aspen and new sprouts.

Using Fire Regimes to Delineate Zones in a High-resolution Lake Sediment Record From the Western United States

Jesse L. Morris et al. — Thu, 14 Feb 2013 08:51:40 PST

Paleoenvironmental reconstructions are important for understanding the influence of long-term climate variability on ecosystems and landscape disturbance dynamics. In this paper we explore the linkages among past climate, vegetation, and fire regimes using a high-resolution pollen and charcoal reconstruction from Morris Pond located on the Markagunt Plateau in southwestern Utah, USA. A regime shift detection algorithm was applied to background charcoal accumulation to define where statistically significant shifts in fire regimes occurred. The early Holocene was characterized by greater amounts of summer precipitation and less winter precipitation than modern. Ample forest fuel and warm summer temperatures allowed for large fires to occur. The middle Holocene was a transitional period between vegetation conditions and fire disturbance. The late Holocene climate is characterized as cool and wet reflecting an increase in snow cover, which reduced opportunities for fire despite increased availability of fuels. Similarities between modern forest fuel availability and those of the early Holocene suggest that warmer summers projected for the 21st century may yield substantial increases in the recurrence and ecological impacts of fire when compared to the fire regime of the last millennium.

Changing Perspectives on Regeneration Ecology and Genetic Diversity in Western Quaking Aspen: Implications for Silviculture

James N. Long et al. — Thu, 14 Feb 2013 08:51:36 PST

A conventional view of regeneration ecology of quaking aspen (Populus tremuloides Michx.) in western North American holds that reproduction is strictly vegetative and, except on some marginal sites, only successful following high-severity disturbance. This view has strongly influenced silvicultural treatment of western aspen and has led to low expectations concerning genetic diversity of stands and landscapes. However, recent discoveries are fundamentally altering our understanding of western aspen regeneration ecology and genetics. For example, there are clearly multiple pathways of aspen regeneration and stand development. Research on a variety of fronts indicates that seedling establishment is common enough to be ecologically important and that genetic diversity is substantially greater than previously thought. We review conventional understanding of western aspen and put this into the context of silvicultural practice. We then review recent developments in aspen research and assess the silvicultural implications of these insights.