Kurt F. Kipfmueller

Recent unprecedented tree-ring growth in bristlecone pine at the highest elevations and possible causes

Great Basin bristlecone pine (Pinus longaeva) at 3 sites in western North America near the upper elevation limit of tree growth showed ring growth in the second half of the 20th century that was greater than during any other 50-year period in the last 3,700 years. The accelerated growth is suggestive of an environmental change unprecedented in millennia. The high growth is not overestimated because of standardization techniques, and it is unlikely that it is a result of a change in tree growth form or that it is predominantly caused by CO2 fertilization. The growth surge has occurred only in a limited elevational band within ≈150 m of upper treeline, regardless of treeline elevation. Both an independent proxy record of temperature and high-elevation meteorological temperature data are positively and significantly correlated with upper-treeline ring width both before and during the high-growth interval. Increasing temperature at high elevations is likely a prominent factor in the modern unprecedented level of growth for Pinus longaeva at these sites.

Watershed analysis of forest fragmentation by clearcuts and roads in a Wyoming forest

Remotely sensed data and a Geographic Information System were used to compare the effects of clearcutting and road-building on the landscape pattern of the Bighorn National Forest, in north-central Wyoming. Landscape patterns were quantified for each of 12 watersheds on a series of four maps that differed only in the degree of clearcutting and road density. We analyzed several landscape pattern metrics for the landscape as a whole and for the lodgepole pine and spruce/fir cover classes across these maps, and determined the relative effects of clearcutting and road building on the pattern of each watershed. At both the landscape- and cover class-scales, clearcutting and road building resulted in increased fragmentation as represented by a distinct suite of landscape structural changes. Patch core area and mean patch size decreased, and edge density and patch density increased as a result of clearcuts and roads. Clearcuts and roads simplified patch shapes at the landscape scale, but increased the complexity of lodgepole pine patches. Roads appeared to be a more significant agent of change than clearcuts, and roads which were more evenly distributed across a watershed had a greater effect on landscape pattern than did those which were densely clustered. Examining individual watersheds allows for the comparison of fragmentation among watersheds, as well as across the landscape as a whole. Similar studies of landscape structure in other National Forests and on other public lands may help to identify and prevent further fragmentation of these areas.

Fires and dwarf mistletoe in a Rocky Mountain lodgepole pine ecosystem

Abstract Forests in the western U.S. are subject to a variety of pathogens, whose role in forest health is being questioned. The relationship of dwarf mistletoe (Arceuthobium americanum Nutt. ex Engelm.) and time since stand-replacing fire was determined for part of the Medicine Bow National Forest in southeastern Wyoming. Mean dwarf mistletoe rating (0–6 scale) was found to be 0.85 in the study area as a whole and ranged from 0–5.82. Of 43 stands examined, 51% contained mistletoe to some degree. Dwarf mistletoe infection was light in the majority of the sampled stands in the study area. Dwarf mistletoe infection characteristics generally increased with increasing time since stand-replacing fire but were highly variable. Mean dwarf mistletoe infection characteristics generally increased with tree size, but were also highly variable. Chi-square analysis indicates that trees surviving the most recent stand-replacing fire increased dwarf mistletoe infection rates in the post-fire stands. Dwarf mistletoe infection at the landscape scale is characterized by infection centers, as some stands have heavy mistletoe infection while stands of similar age have no mistletoe infection present. If prescribed fires are used to restore the health of lodgepole pine forests, these fires will need to be intense, stand-replacing burns. But, healthy lodgepole pine forests may always contain a mosaic of mistletoe infection centers and uninfected stands that require a spatial approach to health assessment.

Multi-scale Influences of Slope Aspect and Spatial Pattern on Ecotonal Dynamics at Upper Treeline in the Southern Rocky Mountains, U.S.A

Abstract We focused on the mediating role of slope aspect and spatial pattern on upper treeline ecotonal dynamics at multiple spatial scales in the Southern Rocky Mountains to infer process interactions and gauge the importance of feedbacks in determining the potential response of upper treeline to climate change on contrasting south- and north-facing slopes. Dendroecological techniques were used to reconstruct tree establishment within the upper treeline ecotone and Ripleys K was used for spatial pattern analysis. Tree age was determined by using age to coring-height corrections, and the influence of slope aspect was quantitatively assessed at multiple spatial scales using Mann-Whitney U-Tests. Widespread tree establishment occurred within the treeline ecotone on both south- and north-facing slopes during the 20th century, but tree ages above timberline are significantly younger on north-facing slopes at all spatial scales (local, landscape, and regional). The spatial pattern of tree establishment above timberline was predominantly random, except for significant clustering on south-facing slopes in the Sangre de Cristo Mountains. The aspect mediation of tree age and spatial pattern suggest that the importance of feedbacks may vary according to slope aspect and that both of these environmental factors should be considered when assessing possible treeline response to climate change.

Tree rings detect earthworm invasions and their effects in northern hardwood forests

Invasions of European earthworms into the forests of northern North America are causing dramatic changes in forest floor structure, vegetation communities, biogeochemical cycling, and site hydrology. However, long-term studies on the effects of invasive earthworms are limited because little data exist on the timing and rate of earthworm invasion at specific sites. We successfully used tree rings to identify the timing of earthworm invasions and the effects of earthworm activity on the Acer saccharum overstory of two recently invaded sites in northern Minnesota, thereby establishing a method to date earthworm invasions at other sites. In addition to identifying a tree-ring signature related to earthworm invasion, we found trees growing in invaded conditions were more sensitive to drought than trees growing in earthworm-free conditions. Increased drought sensitivity by A. saccharum has important implications for possible range shifts under climate change scenarios that include increasing drought frequency and severity.

Complexity of Successional Pathways in Subalpine Forests of the Selway-Bitterroot Wilderness Area

Abstract We examined forest structure and composition in four watersheds in the Selway-Bitterroot Wilderness Area, Idaho and Montana, to better understand the complexity of successional processes following stand-replacing fires in subalpine forest ecosystems. Dendrochronological analyses of more than 1,100 trees were used to identify the timing of establishment of major forest species at sites that had experienced different intervals since the last fire. This was coupled with analyses of forest structure and composition using nonmetric multidimensional scaling. A conceptual model of stand development is presented to highlight our findings. Lodgepole pine (Pinus contorta var. latifolia Dougl.) dominated most overstories for the first 100–200 years but persisted as a canopy dominant for more than 250 years in some stands. As forests increased in age, Engelmann spruce (Picea engelmanii Parry) and subalpine fir (Abies lasiocarpa [Hook.] Nutt.) became more prominent in the overstory. Whitebark pine was present in some young stands and older stands but was most often represented as dead standing trees killed during twentieth-century mountain pine beetle outbreaks. Understory composition was a function of time-since-fire but showed considerable variation that is likely tied to seed arrival, environmental conditions, and establishment. Our results suggest that short fire intervals may limit the development of lodgepole pines capable of producing serotinous cones, leading to young forests dominated by spruce or fir. However, intervals longer than the lifespan of lodgepole pine (as long as 350 years) could also lead to early dominance by spruce or fir following fire. These results refine our understanding of the temporal development of subalpine communities following stand-replacing fires and have implications for the implementation of long-range management goals in these habitats.

Multiscale Influences of Climate on Upper Treeline Dynamics in the Southern Rocky Mountains, USA: Evidence of Intraregional Variability and Bioclimatic Thresholds in Response to Twentieth-Century Warming

We examined the influence of twentieth-century climate on upper treeline dynamics in the southern Rocky Mountains to better understand the role of temperature and precipitation on tree establishment and to determine whether bioclimatic thresholds have been exceeded as a result of warming during the twentieth century. By using dendrochronological techniques, we reconstructed tree establishment at upper treeline on six mountain peaks within the Front Range and Sangre de Cristo Mountains. We compared age–structure data with climate using Spearmans rank correlation coefficients between annual and seasonal climate indexes and tree establishment dates at both regional (southern Rockies) and landscape scales (mountain range). Regime-shift analysis detected thresholds in temperature, precipitation, and tree establishment data. Tree establishment has increased substantially at upper treeline throughout the southern Rockies, leading to varying degrees of treeline advance upslope. Tree establishment in the Front Range significantly correlates with temperature, but no significant correlations with temperature variables exist in the Sangre de Cristos. Significant inverse correlations exist with precipitation but remain confined to north-facing slopes in both mountain ranges. Synchronous regime shifts (within five years) occurred in the Front Range between temperature and tree establishment during the early 1950s (1950–1954), suggesting that increasing temperatures provided a possible mechanism for abrupt increases in establishment. This research highlights the intraregional variability in treeline sensitivity to climate in the southern Rocky Mountains and the usefulness of using a multiscale approach coupled with regime-shift analysis to examine the influence of twentieth-century climate on treeline.

Linear trend and climate response of five-needle pines in the western United States related to treeline proximity

Five-needle pines provide some of the world’s longest chronologies of paleoclimate interest. We examined 66 five-needle pine growth chronologies from 1896 to their end years using linear trend, correlation, and cluster analyses. Chronologies were categorized based on the sites’ proximity to upper treeline. A significant positive trend in ring width over the post-1896 interval was most common in upper treeline chronologies, but positive linear trend was found in all elevational proximity classes and all species. Cluster analysis of climate response patterns identified four groups exhibiting strong associations with (i) positive response to previous autumn, winter, and spring precipitation, (ii) positive response to spring and (or) summer precipitation coupled with an inverse relationship with summer temperature, (iii) positive response to winter and (or) spring precipitation coupled with an inverse relationship with spring temperature, and (iv) positive associations with temperature in all seasons except s...

Spatial Ecology of Pre –Euro‐American Fires in a Southern Rocky Mountain Subalpine Forest Landscape

Natural disturbances such as fires have been widely studied, but less is known about their spatial ecology than about other aspects of them. We reconstructed and mapped pre–Euro-American fire history in a subalpine forest landscape in southeastern Wyoming, and analyzed the fires using GIS. Mean fire interval varies little with topography (elevation, aspect, slope) and is spatially autocorrelated at distances of at least 2 km. Fires often spread downslope, and spread more than expected from the north and south and less than expected from the west, under the influence of particular synoptic climatic conditions. The landscape of 1868 a.d., at the time of Euro-American settlement, was strongly influenced by fires. However, it contained large patches of connected forest and few high-contrast edges, unlike the modern landscape, which is fragmented by industrial forestry and roads. The spatial ecology of the natural fire regime may be a useful guide for management.

An Assessment Of The Dendroclimatic Potential Of Three Conifer Species In Northern Minnesota

Abstract Ring-width chronologies from Pinus resinosa Ait., Pinus strobus L., and Thuja occidentalis L. were developed in two areas of the Boundary Waters Canoe Area Wilderness to assess their growth-climate response and their potential for developing reconstructions of climate. New red pine chronologies were combined with existing chronologies to extend the ring-width record both into the past and into the present. Ring-width response to climate, assessed using correlation analysis and response functions, was broadly similar among all three species with relatively significant positive relationships with June–July precipitation and significant negative (but less consistent) associations with June–July temperatures (p < 0.05). White-cedar appeared to have a broader phenological window of response with a stronger spring influence when compared to other species included in this study. Comparisons with other nearby proxies showed relatively strong coherence overall but with some important regional differences. Overall, these species may be useful for placing current climatic patterns in the Boundary Waters within a longer term perspective but care should be taken with respect to identifying appropriate climatic records for calibration.