Aspen Cover Type Research Articles

Selection of landscapes by male ruffed grouse during peak abundance

We studied the habitat relationships of male ruffed grouse (Bonasa umbellus) at the landscape scale when grouse were at the peak of their population cycle. We located 290 and 230 male grouse during 2009 and 2010, respectively, on 30 landscapes encompassing 5,349 ha. We used an information-theoretic model selection approach to examine 2 sets of a priori models. We designed our first model set to evaluate the relationships between Shannon's evenness index of cover types and grouse density and our second set to evaluate other relationships between grouse density and landscape configuration. The top model in the first set was a null model (intercepts only), but a competing model indicated that Shannon's evenness index was positively correlated with male grouse density (r = 0.43). Shannon's evenness index was confounded with cover type dominance in landscapes because it was positively correlated (r = 0.55) with the proportion of the aspen cover type and negatively correlated (r = −0.79) with the proportion of the conifer cover type. The top-ranked model from our second model set included only year and road density. Road density was negatively related to grouse density (r = −0.34), which could mean either hunting pressure along roads affected density or cover types were different in landscapes with greater road densities. The year-only model indicated that male grouse density was less in 2010 than in 2009 (βyear = −0.014, 95% CI = −0.024 to −0.005). We predict that forest management practices that result in an even distribution of cover types within landscapes should result in greater densities of grouse. © 2013 The Wildlife Society.

Effects and etiology of sudden aspen decline in southwestern Colorado, USA

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 of a subset of plots after 1–2 yrs showed significant increases in severity. Contrary to expectations, overstory age and diameter were not related to SAD severity as measured by recent crown loss or mortality. Severity of SAD was inversely, but weakly, related to basal area, stem slenderness, and site index, and positively related to upper slope positions. This is consistent with moisture stress as an underlying factor. To test the role of climate as an inciting factor for SAD, a landscape-scale climate model was used to compare moisture status of declining and healthy aspen at the height of the warm drought in water year 2002. Polygons identified as damaged aspen in the 2008 aerial survey had greater moisture deficits than healthy aspen in the 2002 water year. SAD has led to loss of aspen cover in some stands, and is occurring in areas where early loss of aspen due to climate change has been predicted. Further warm, dry growing seasons will likely lead to recurrence of SAD.

Rapid mortality of Populus tremuloides in southwestern Colorado, USA

Concentrated patches of recent trembling aspen ( Populus tremuloides) mortality covered 56,091 ha of Colorado forests in 2006. Mortality has progressed rapidly. Area affected increased 58% between 2005 and 2006 on the Mancos-Dolores Ranger District, San Juan National Forest, where it equaled nearly 10% of the aspen cover type. In four stands that were measured twice, incidence of mortality increased from 7–9% in 2002/2003 to 31–60% in 2006. Mortality generally decreased with increasing elevation over the primary elevation range of aspen and occurred on less steep slopes than healthy aspen. Slope-weighted mean aspects of aspen cover type were northern at low elevations and generally southern at high elevations. Relative frequency of mortality was generally highest on southern to western aspects. In 31 stands measured in detail, mortality ranged from 0 to 100% (mean 32%) and was negatively correlated with stand density ( P = 0.033). Size of trees affected was strongly correlated with amount of current mortality ( P < 0.001), and current mortality was skewed toward larger diameter classes. Density of regeneration was in a low range typical of undisturbed stands and did not increase with overstory mortality. Agents that typically kill mature trees in aspen stands were unimportant in this mortality. Instead, a group of interchangeable, usually secondary agents was most commonly associated with mortality, including Cytospora canker (usually caused by Valsa sordida), aspen bark beetles ( Trypophloeus populi and Procryphalus mucronatus), poplar borer ( Saperda calcarata), and bronze poplar borer ( Agrilus liragus). The rapidity of mortality, mortality agents involved, and probably other causal factors distinguish this phenomenon from the long-term loss of aspen cover usually attributed to successional processes operating in an altered disturbance regime (and often exacerbated by ungulate browsing). Our data are consistent with a hypothesis that (a) predisposing factors include stand maturation, low density, southern aspects and low elevations; (b) a major inciting factor was the recent, acute drought accompanied by high temperatures, and; (c) contributing factors and proximate agents of mortality are the common biotic agents observed. On sites with poor regeneration and weak root systems, clones may die, resulting in the long-term loss of aspen forest cover.

Observing succession on aspen-dominated landscapes using a remote sensing-ecosystem approach

In the North American upper Great Lakes region, forests dominated by the aspens (Populus grandidentata Michx. – bigtooth aspen, and P. tremuloides Michx. – trembling aspen), which established after late 19th and early 20th century logging, are maturing and succession will create a new forest composition at landscape to regional scales. This study analyzed the capabilities of Landsat ETM+ remote sensing data combined with existing ecological land unit classifications to discriminate and quantify patterns of succession at the landscape scale over the 4200 ha University of Michigan Biological Station (UMBS) in northern Lower Michigan. In a hierarchical approach first multi-temporal Landsat ETM+ was used with a landscape ecosystem classification to map upland forest cover types (overall accuracy 91.7%). Next the aspen cover type was subset and successional pathways were mapped within that type (overall accuracy 89.8%). Results demonstrated that Landsat ETM+ may be useful for these purposes; stratification of upland from wetland types using an ecological land unit classification eliminated confounding issues; multi-temporal methods discriminated evergreen conifer versus deciduous understories. The Landsat ETM+ classifications were then used to quantify succession and its relationship to landform-level ecological land units. Forests on moraine and ice contact landforms are succeeding distinctly to northern hardwoods (95% and 88% respectively); those on outwash and other landforms show greater diversity of successional pathways.

Early Growth Responses of Naturally Regenerated Eastern White Pine (Pinus strobus L.) to Partial Release from Juvenile Aspen and Pathological Pruning

Abstract Height, breast height diameter, and basal diameter growth responses of 7- to 12-year-old naturally regenerated eastern white pine (Pinus strobus L.) to partial release from juvenile (15-year-old) trembling and bigtooth aspen (Populus tremuloides Michx. and Populus grandidentata Michx.) and pathological pruning were monitored over four growing seasons. Pathological pruning is the removal of disease-infected branches before the disease can reach the stem or the removal of lower branches that are most susceptible to infection. Results indicated that seedling growth responses to release and pruning depended strongly on the height stratum to which a seedling belonged. Whereas growth rates of small white pine up to 190 cm tall were significantly reduced by increasing aspen densities and by pruning, growth rates of white pine taller than 190 cm were not significantly affected by either aspen density or pruning. Effects of pruning on small white pine were restricted to the first 2 years after release, after which growth rates were similar between pruned and unpruned individuals. This likely was due to natural crown recession of unpruned white pine, which brought crown lengths and crown ratios closer to those of pruned individuals. Besides affecting natural crown recession rates and growth of small unpruned white pines, release intensity also affected upper stratum aspen, which responded vigorously to release. Findings of this study suggest that early release from upper stratum juvenile aspen should enable the conversion of an aspen cover type to a mixture of aspen and white pine, but may have to be followed up by repeated interventions into the upper canopy stratum. It is, however, questionable if the expense of pruning to prevent blister-rust infections under a partial canopy is warranted. North. J. Appl. For. 22(1):27–34.

Harvesting impacts on soil and understory vegetation: the influence of season of harvest and within-site disturbance patterns on clear-cut aspen stands in Minnesota

We investigated impacts of harvesting on soil disturbance and vegetation in the aspen cover type of northern Minnesota, United States. The soil disturbance (resistance to penetration) and understory vegetation were characterized for 19 sites on five 60-m2 plots placed along a disturbance gradient: landings (high harvesting traffic), skid trails (intermediate harvesting traffic), and areas off skid trails (low to no harvesting traffic). Penetration levels were quite variable, but they still indicated that within-site responses to disturbance patterns created by clear-cut harvesting were not uniform. In general, soil disturbance and understory species composition within landings were similar to those with skid trails. The soil disturbance and vegetation composition of these two levels differed from those of the low-disturbance plots (off skid trails), indicating that removing trees alone did not affect vegetation composition as much as creating an established skid trail, regardless of harvest timing. However, sites with more variable species composition (winter-harvested sites) and lower disturbance levels were less altered than sites with likely lower initial diversity (summer-harvested sites). The results suggest that it is important for recovery of understory plant communities to not only limit the amount and level of disturbances but also consider the spatial layout of harvesting, thus maintaining a spatially connected network of remnant forest patches large enough to contain interior forest species.

STEMS Model Projection Capability with Incomplete Tree List Input Data

Abstract Projections were made using the STEMS individual tree based stand growth model for plots in red pine, maple-birch, and aspen cover types for periods up to 50 years. Effects of incomplete tree list input data on plots in the form of small tree censorship (omission of small trees) and tree list aggregation (by size class) were examined by comparing projections made for complete plot tree lists (controls) with projections made after these tree lists were censored and aggregated (treatments). Basal area and number of trees estimates proved highly sensitive to censorship, while volume estimates were much less sensitive. Augmentation of censored distributions by an “average” small tree distribution for the cover type resulted in significant improvement of these estimates. Projection model capability using input data aggregated by size class depended on the degree of aggregation. For some types of aggregation, for example by 2-in. dbh classes, the STEMS model retains much of its predictive utility. North. J. Appl. For. 5:190-194, Sept. 1988.

STEMS Model Projection Capability with Plot and Tree Data Aggregation

Abstract Projections of forest plot characteristics were made using the STEMS individual-tree based stand growth model for jack pine, red pine, maple-birch and aspen cover types from Michigan, Minnesota, and Wisconsin for periods of up to 50 years. Tree lists were constructed from forest survey records using various plot and tree aggregation methods, then projected and compared to projections of the same data without aggregation. The loss in projection precision due to aggregation was then weighed against savings in computer processing time as compared to the unaggregated projections. Differences between aggregated and unaggregated projections increased with greater aggregation and with longer projection periods, but in most cases were less than 10% at 50 years when the plot data were aggregated by stand density class. The largest differences were observed for pulpwood and sawtimber volumes. However, these differences were in part a function of merchantability limits based on tree size. Results indicate that dramatic cost savings can be realized with little loss in precision. North. J. Appl. For. 2:121-127, Dec. 1985.

Summer Forage Use by Tame Deer in Northern Michigan

The aspen (Populus tremuloides and P. grandidentata) cover type is one of the most important types for producing white-tailed deer (Odocoileus virginianus) in the northern Lake States, and maintaining it is the emphasis of deer habitat management there. The summer food habits, forage preferences, and habitat use of tame deer in a mature aspen stand and an adjacent aspen clear-cut were studied. Aspen, beaked hazel (Corylus cornuta), strawberry (Fragaria virginiana), willow (Salix spp.), and choke cherry (Prunus virginiana) leaves, and aster (Aster spp.) leaves and flowers averaged 66% of the monthly forage consumption in the mature stand and 80% of that in the clear-cut. Aspen leaves alone averaged nearly a quarter of the intake on both areas. Preferred foods included red maple (Acer rubrum), aspen, beaked hazel, choke cherry leaves, the ripe fruit of brambles (Rubus spp.), and aster leaves and flowers. Although the deer spent equal time foraging in the mature stand and the clear-cut during June, they used the mature stand more during July and August. The quantity of food eaten per unit of time, however, was greater in the clear-cut during July and August. The results suggest that clear-cutting aspen in small blocks on a 40year rotation would provide for an interspersion of age classes that may best meet the overall life requirement of deer on summer range. J. WILDL. MANAGE. 44(1):98-106 There is a close association of whitetailed deer with the aspen cover type in the northern Lake States. In Michigan, aspen is the most important deer-producing forest cover type, and maintaining this type is the major emphasis of the state's deer habitat management program (Byelich et al. 1972:124). In north-central Minnesota, deer use the aspen type intensively in the summer (Kohn and Mooty 1971:478), and it is the preferred summer habitat of Wisconsin deer (Habeck and Curtis 1959:50, McCaffery and Creed 1969:23). However, widespread conversion of aspen to later successional types places severe limitations on this habitat (McCaffery and Creed 1969:6; Byelich et al. 1972:121, 122). Because deer use of the aspen type appears forage related (Rutske 1969:35, McCaffery et al. 1974:218), we studied the summer food habits, forage preferences, and habitat use of tame animals in a mature stand and an adjacent clear-cut to understand better the association of deer with stands of different ages in the aspen type. Financial support for this study was provided by the McIntire-Stennis Program. The Michigan Department of Natural Resources provided 2 fawns and fencing materials. We acknowledge D. Wenzel and N. Karsten for their help in locating a study area. We thank also D. Schwandt for counsel in data analysis, D. Frederick for help in sampling design, and B. Dahl, F. Bryant, R. Dohrenwend, P. Herman, and N. Sloan for review of the manuscript.

Vegetation, site, and fire relationships within the area of the Little Sioux fire, northeastern Minnesota

The relationships among various landscape features were examined in an area in northeastern Minnesota that burned in a forest fire in May 1971. Maps based on fire intensity, cover types in 1948 and 1970, soils, and topography were randomly sampled. A total of 34 comparisons were made between pairs of classifications based on the mapped characteristics. The closest relationship was between dominant vegetation in 1948 and that in 1970. Relationships between soil mapping units and slope position and between vegetation and soils were also relatively high. The vegetation–soil relationships were influenced by the close associations of lowland vegetation to lowland soils and of upland vegetation to upland soils. However, specific categories of upland vegetation were not well related to specific categories of upland soils. Fire intensity was most closely related to slope position. An 80% decrease in balsam-fir cover types occurred from 1948 to 1970. This decrease was accompanied by a nearly equal increase in aspen cover types. This balsam-fir to aspen cover type change is attributed to the spruce budworm epidemic, which occurred from the mid-1950's to the mid-1960's. Decreases in jack pine, red pine, and white pine cover types are attributed to commercial logging.