U52A-01 10:20h
Fire Regimes and Forest Structure in the Mountains of Northwestern Mexico and Southern California
In contrast to a few isolated forests in northern Mexico, most forests in the western Untied States have been significantly modified by fire suppression, harvesting, and livestock grazing. The culmination of these past management activities has produced over 20 million ha of US forests with high fire hazards and many of these areas are in need of restoration. Understanding reference conditions is challenging because we have few intact forests functioning under the continuing influence of climate variation, insects, diseases, and frequent fires. This presentation summarizes information from reference sites in northwestern Mexico and contrasts it to current forest structure and fire regimes in southern California forests. Heterogeneity is common in the intact forests of northwestern Mexico. Restoration targets across similar forests in the United States and elsewhere should incorporate variation and not manage for average characteristics at the stand level, replicated for all stands across very large spatial scales. Conservation of the forests in the northwester Mexico is critical because it is the last landscape-scale, old-growth mixed conifer forest in western North America with a relatively intact frequent fire regime.
U52A-02 10:35h
Sensitivity of Southwestern US Mountain Ecosystems to Climate Variability: Interactions Among Forest Dieback, Fire, and Erosion
Millions of hectares in the upland landscapes of the Southwestern United States have been affected by forest dieback and severe fire activity since the late 1990s, a period of ongoing severe drought and unusual warmth. Climate regulates physiological plant stress that can directly cause vegetation mortality, and also influences associated insect outbreak dynamics. Climate also interacts with fuel conditions to drive regional fire activity. Current and historic patterns of forest dieback, fire activity, and erosion are described across landscape gradients in Southwestern mountains, particularly the Jemez Mountains of New Mexico. Methods used include inventory and dating of live and dead woody plants to assess demographic changes through time, long-term (since 1991) measurements of ponderosa pine tree-growth at three sites with dendrometer bands, monitoring of herbaceous vegetation along 3 km of permanent transects since 1991, aerial photograph analyses of insect outbreaks and forest dieback and fire activity, and hydrological measurements of runoff and erosion. Similarities and differences in vegetation dieback and regional fire activity patterns between the current drought and the 1950s (when regional drought last affected the Southwest) are explained by changes in climatic and vegetation conditions. The current climate-induced vegetation dieback and pulse of regional fire activity have strong feedbacks with various key ecosystem processes, including water budgets and soil erosion. For example, severe drought and fire both markedly reduce the surface cover of live plants and dead plant materials ("litter"), triggering nonlinear increases in erosion rates once the connectivity of bare soil patches exceeds critical threshold values, particularly during high-intensity summer rainfall events that characterize the Southwestern summer "monsoon". These observations highlight the magnitude, rapidity, and complexity of climate-induced disturbance processes, and provide an analog for potential nonlinear impacts of climate change to mountain ecosystems.
U52A-03 10:50h
Climate Change Altered Disturbance Regimes in High Elevation Pine Ecosystems
Insects in aggregate are the greatest cause of forest disturbance. Outbreaks of both native and exotic insects can be spectacular events in both their intensity and spatial extent. In the case of native species, forest ecosystems have co-evolved (or at least co-adapted) in ways that incorporate these disturbances into the normal cycle of forest maturation and renewal. The time frame of response to changing climate, however, is much shorter for insects (typically one year) than for their host forests (decades or longer). As a result, outbreaks of forest insects, particularly bark beetles, are occurring at unprecedented levels throughout western North America, resulting in the loss of biodiversity and potentially entire ecosystems. In this talk, I will describe one such ecosystem, the whitebark pine association at high elevations in the north-central Rocky Mountains of the United States. White bark pines are keystone species, which in consort with Clark's nutcracker, build entire ecosystems at high elevations. These ecosystems provide valuable ecological services, including the distribution and abundance of water resources. I will briefly describe the keystone nature of whitebark pine and the historic role of mountain pine beetle disturbance in these ecosystems. The mountain pine beetle is the most important outbreak insect in forests of the western United States. Although capable of spectacular outbreak events, in historic climate regimes, outbreak populations were largely restricted to lower elevation pines; for example, lodgepole and ponderosa pines. The recent series of unusually warm years, however, has allowed this insect to expand its range into high elevation, whitebark pine ecosystems with devastating consequences. The aspects of mountain pine beetle thermal ecology that has allowed it to capitalize so effectively on a warming climate will be discussed. A model that incorporates critical thermal attributes of the mountain pine beetle's life cycle was constructed and used to predict the consequences of a changing climate under the 1990 IPCC "business as usual" scenario. Based on results from these simulations, sophisticated, high-resolution weather monitoring stations were established at a high elevation site in the summer of 1995 (Railroad Ridge, White Cloud Mountains, Central Idaho at an elevation of 10,000 ft.). Recently (summer 2003), the first trees were attacked on Rail Road Ridge. The outbreak has progressed at a truly astounding rate. The reasons for the unusually rapid progression of this outbreak event will be considered, as will the potential consequences of mortality that is occurring across the entire U.S. range of whitebark pine. Finally, I will discuss both the challenges to, and the potential for, formulating effective management responses.
<a href='http://www.usu.edu/beetle' >http://www.usu.edu/beetle
U52A-04 11:05h
Climatological, hydrological and vegetation change for the past 15,000 years based upon a new network of high resolution lake sites in the Sierra Nevada and Unita Mountains
Instrumented lake and watershed climatic data along with lake sediment surface samples and cores are being used to develop and apply paleolimnological transfer functions to reconstruct climate change and ecosystem response in the eastern Sierra Nevada Mountains of California and the Unita Mountains of Utah. The selection of the two ranges provides a circum Great Basin perspective on natural climate variability in the western mountains. The California study sites are located in the eastern Sierra Nevada. Surface sediment samples and water samples have been analyzed from 57 lakes extending across an altitudinal gradient of 1360 m. Transfer functions that estimate water temperature, salinity and depth on the basis of lake diatom flora or chironomid fauna have been developed and published. Long cores have been obtained from 8 lakes that provide a transect from treeline down to the sagebrush dominated Great Basin. The lake records extend back between 9000 and 15,000 Cal yr BP. Pronounced warming of ~ 4.5 degrees C and development of modern conifer forest started by ~13,800 Cal yr BP. At ~11,000 Cal yr BP temperatures were as warm or warmer than today. High resolution analysis shows that the general glacial to interglacial warming was interrupted by a climatic reversal at approximately 13,000 Cal yr BP during which time summer temperatures at mid-elevation lakes cooled by 4 to 6 degrees C. There was a pronounced three part hydrological shift during this temperature reversal. The temperature reversal corresponds in timing with Younger Dryas Stadial typical of circum North Atlantic records. There was only a muted response to this episode at higher elevations and in the terrestrial vegetation. The cooling is synchronous with the Younger Dryas Stadial. Between ~8000 and 4000 Cal yr BP there was pronounced drying and lake drawdown at lower elevations. The period from 4000 Cal yr BP to the present has been typified by shifts between relatively moist conditions, like the present, and drier multi-decadal intervals. Dry intervals observed in low elevation records correspond in time to the Stine events which have been deduced from radiocarbon dated stumps in lakes and river valleys in the eastern Sierra Nevada. At present, 35 lakes in the Uintas have been sampled for surface sediments and two long cores have been obtained. One of the cores is laminated throughout and offers the potential for sub-decadal to annual resolution of past climatic variability. The records obtained show that the ecosystems of the western mountains have experienced pronounced millennial to centennial/decadal scale climatic and hydrologic variability as a natural component in their development and persistence. It is possible that centennial/decadal scale shifts similar to those evident over the past 4000 years would occur in the future.
U52A-05 11:20h
Mountain Systems, Persistent Drought and the Vulnerability of Ecosystem Services: A Case Study from Glacier National Park, USA
The recent, persistent drought in the Western United States has invigorated interest in the findings of paleoclimatologists indicating that precipitation anomalies of a decade or more in duration are a substantial component of natural climatic variability over the past millennium. Further, we have accumulating evidence that large-scale, persistent climate features, such as the North Atlantic Oscillation and the Pacific Decadal Oscillation, can entrain ecosystem processes at regional scales. Demographic processes in fish, forests, and ungulates stand out as particularly compelling examples. These oft-cited examples are also interesting because they demonstrate that the sustainable provision of "ecosystem services" (i.e., the benefits people obtain from ecosystems) is subject to decadal-scale climatic variability. In this paper, we present a regional example of how precipitation varies at decade and longer time scales at Glacier National Park, Montana, USA. We examine how the climate variability expressed in Glacier National Park is coherent with larger regional patterns in Western North America and is associated with indices of large-scale atmospheric circulation features. We then explore how such variability might affect the ecosystem services offered by Glacier National Park. Our goal is to broaden the discussion of the impacts of climatic variability on protected areas by defining linkages between drought, climate regimes and the sustainable provision of ecosystem services. Decade and longer climate anomalies, and the attendant regime shift behavior, poses challenges for the management of ecosystem services in three ways. First, long-term climate reconstructions challenge the conventional strategy of defining mean, or average, conditions as a management tool. Second, step-like changes from one climate regime to another are often dramatic and may provide evidence of change that, in turn, may (or may not) represent human-induced changes. Third, decade-length persistence of either deficits or abundances of climate-related services solidify institutional arrangements that, in the long run, may not be robust under global climate change scenarios. After exploring this question in the data-rich context of Glacier National Park, we will suggest the broader implications of decade and longer scale variability for the services that we have come to expect from our parks and wildlands.
U52A-06 11:35h
Advance of Trees and Krummholz Into Alpine Tundra
Invasion of alpine tundra by trees is an expected outcome of climatic change, but observed responses are equivocal. To examine the invasibility of tundra we consider what might limit or facilitate seedling establishment and subsequent development into krummholz or trees. At the seed stage barriers to success include landing on an impenetrable surface. Many tundra sites are underlain by active or relict solifluction, however, and data show that these sites present opportunities for the exposure of fine soil through turf exfoliation on tread-riser boundaries. At the seedling stage negative and positive feedbacks are both present. A simulation with negative feedback in dense trees and positive feedback with fewer trees produces an advance of trees into tundra in which the rates vary in correlation with a fractal spatial pattern, not climatic change. Because the spatiotemporal patterns of tree advance into tundra will be related to climatic change nonlinearly and will, to some degree, be controlled by geomorphic conditions, places may respond individualistically.
U52A-07 11:50h
Increasing Temperatures in Mountainous Regions of the Western United States and Effects on Insect Outbreaks
Global temperatures have increased over the last 100 years and are projected to continue to rise as a result of greater atmospheric carbon dioxide concentrations. However, temperatures at high elevations are not uniformly increasing. Instead, trends vary regionally and depend on the time period of interest. Climate, specifically temperature, plays a major role in regulating outbreaks of bark beetles by synchronizing attacks on host trees during favorable temperature conditions. In this study, we characterize patterns of temperature change over the last 100 years for mountainous regions in the western United States, utilizing the VEMAP gridded database but also considering additional sources (e.g., SNOTEL, HCN). Although temperatures at higher elevations have changed little over the long term, recent decades have experienced warming. Projected temperatures in this region continue to warm through 2100. We explored the effects of changing temperatures on the spatial patterns of mountain pine beetle outbreak using a phenology model that predicts potential infestation. We show that temperature conditions suitable for outbreak existed in the past 100 years for most locations occupied by a favored host, lodgepole pine. At lower elevations, projected warming resulted in reductions in potential outbreak area. At higher elevations, potential outbreak area increased as temperatures became more favorable, then decreased as conditions became too warm to support synchrony of beetle attack. The shifts in climatically suitable conditions for mountain pine beetle outbreak have significant implications for lodgepole pine, a species dependent on disturbance, as well as other high-elevation pine ecosystems that are susceptible to infestation.
U52A-08 12:05h
Emergent Urban-Landscape Interactions in Mountain Catchments
The margins of mountain catchments can offer attractive residential attributes, but development is subject to an array of significant hazards. The question of how urban expansion and natural processes interact as a system to produce long-term, emergent patterns of coupled human-landscape dynamics is addressed in a model that treats natural processes on intermediate time scales on a cellular grid and urban processes using agent-based models of markets and local/regional government. In the model, shrubland vegetation grows between fires, wildfires consume vegetation and residences and promote erosion, and landslides, floods and sediment-laden debris flows damage or destroy residences. Developer agents build developments whose size and location are based on projected profits; homeowning agents buy houses based on projected appreciation and attributes such as view and commute distance. Based on their predicted effect on tax revenues, government agents approve developments; mitigate fires with prescribed burns; mitigate landslides, floods and debris flows with slope stabilization, debris basins, reservoirs and channel stabilization and entrenchment; and suppress fires. Initial investigation of the model has focused on long-time-scale behavior of the urban-wildland boundary. Mitigation measures filter out short, small-amplitude fluctuations in this boundary. As the relative time scales and interaction magnitudes characterizing natural processes, development and government action are varied, a nominally stable boundary becomes unstable to irregular, long period fluctuations that can be spatially complex. The role that market externalities play in producing nonoptimal states will be discussed. Supported by the Andrew W. Mellon Foundation.