Monika P. Calef

Plant community responses to experimental warming across the tundra biome

Recent observations of changes in some tundra ecosystems appear to be responses to a warming climate. Several experimental studies have shown that tundra plants and ecosystems can respond strongly to environmental change, including warming; however, most studies were limited to a single location and were of short duration and based on a variety of experimental designs. In addition, comparisons among studies are difficult because a variety of techniques have been used to achieve experimental warming and different measurements have been used to assess responses. We used metaanalysis on plant community measurements from standardized warming experiments at 11 locations across the tundra biome involved in the International Tundra Experiment. The passive warming treatment increased plant-level air temperature by 1-3°C, which is in the range of predicted and observed warming for tundra regions. Responses were rapid and detected in whole plant communities after only two growing seasons. Overall, warming increased height and cover of deciduous shrubs and graminoids, decreased cover of mosses and lichens, and decreased species diversity and evenness. These results predict that warming will cause a decline in biodiversity across a wide variety of tundra, at least in the short term. They also provide rigorous experimental evidence that recently observed increases in shrub cover in many tundra regions are in response to climate warming. These changes have important implications for processes and interactions within tundra ecosystems and between tundra and the atmosphere.

Increasing Wildfire in Alaska's Boreal Forest: Pathways to Potential Solutions of a Wicked Problem

ABSTRACT Recent global environmental and social changes have created a set of “wicked problems” for which there are no optimal solutions. In this article, we illustrate the wicked nature of such problems by describing the effects of global warming on the wildfire regime and indigenous communities in Alaska, and we suggest an approach for minimizing negative impacts and maximizing positive outcomes. Warming has led to an increase in the areal extent of wildfire in Alaska, which increases fire risk to rural indigenous communities and reduces short-term subsistence opportunities. Continuing the current fire suppression policy would minimize these negative impacts, but it would also create secondary problems near communities associated with fuel buildup and contribute to a continuing decline in subsistence opportunities. Collaborations between communities and agencies to harvest flammable fuels for heating and electrical power generation near communities, and to use wildland fire for habitat enhancement in surrounding forests, could reduce community vulnerability to both the direct and the indirect effects of global climate change.

Recent Climate-Driven Increases in Vegetation Productivity for the Western Arctic: Evidence of an Acceleration of the Northern Terrestrial Carbon Cycle

Abstract Northern ecosystems contain much of the global reservoir of terrestrial carbon that is potentially reactive in the context of near-term climate change. Annual variability and recent trends in vegetation productivity across Alaska and northwest Canada were assessed using a satellite remote sensing–based production efficiency model and prognostic simulations of the terrestrial carbon cycle from the Terrestrial Ecosystem Model (TEM) and BIOME–BGC (BioGeoChemical Cycles) model. Evidence of a small, but widespread, positive trend in vegetation gross and net primary production (GPP and NPP) is found for the region from 1982 to 2000, coinciding with summer warming of more than 1.8°C and subsequent relaxation of cold temperature constraints to plant growth. Prognostic model simulation results were generally consistent with the remote sensing record and also indicated that an increase in soil decomposition and plant-available nitrogen with regional warming was partially responsible for the positive produc...

Human Influences on Wildfire in Alaska from 1988 through 2005: An Analysis of the Spatial Patterns of Human Impacts

Abstract Boreal ecosystems in Alaska are responding to climate change in many ways, including changes in the fire regime. While large-scale wildfires are an essential part of the boreal forest ecosystem, humans are changing fire regimes through ignition and suppression. The authors analyzed the impact humans have on fire ignitions and relative area burned with distance into the forest from human access points such as settlements, highways, and major rivers in Alaska from 1988 to 2005. Additionally, a fire prediction model was created to identify drivers for lightning fires in the boreal forest. Human presence increases the number of ignitions near settlements, roads, and rivers and appears to reduce the area burned within 30–40 km of villages and rivers. In contrast to fires near roads and rivers, human presence may somewhat increase the area burned within 30–40 km of highways. The fire prediction model indicated that the probability of fire increases as distance from human settlements increases. In contr...

Vulnerability and adaptation to climate-related fire impacts in rural and urban interior Alaska

This paper explores whether fundamental differences exist between urban and rural vulnerability to climate-induced changes in the fire regime of interior Alaska. We further examine how communities and fire managers have responded to these changes and what additional adaptations could be put in place. We engage a variety of social science methods, including demographic analysis, semi-structured interviews, surveys, workshops and observations of public meetings. This work is part of an interdisciplinary study of feedback and interactions between climate, vegetation, fire and human components of the Boreal forest social–ecological system of interior Alaska. We have learned that although urban and rural communities in interior Alaska face similar increased exposure to wildfire as a result of climate change, important differences exist in their sensitivity to these biophysical, climate-induced changes. In particular, reliance on wild foods, delayed suppression response, financial resources and institutional connections vary between urban and rural communities. These differences depend largely on social, economic and institutional factors, and are not necessarily related to biophysical climate impacts per se. Fire management and suppression action motivated by political, economic or other pressures can serve as unintentional or indirect adaptation to climate change. However, this indirect response alone may not sufficiently reduce vulnerability to a changing fire regime. More deliberate and strategic responses may be required, given the magnitude of the expected climate change and the likelihood of an intensification of the fire regime in interior Alaska.

Spatial and Temporal Heterogeneity of Vegetation Properties among Four Tundra Plant Communities at Ivotuk, Alaska, U.S.A.

Abstract Intraseasonal patterns of normalized difference vegetation index (NDVI), leaf area index (LAI), and phytomass were compared for four tundra vegetation types at Ivotuk, Alaska, during summer 1999. The vegetation types included moist acidic tundra (MAT), moist nonacidic tundra (MNT), mossy tussock tundra, and shrub tundra. The seasonal curves of NDVI were similar among the vegetation types but with varying magnitudes of the peak values. Peak NDVI in the shrub tundra (0.83) was significantly greater than in MAT (0.76), which was significantly greater than in MNT (0.71) and mossy tussock tundra (0.70). LAI and phytomass exhibited high temporal variability with distinct seasonality only in shrub tundra. Seasonal LAI and NDVI patterns were therefore correlated only in shrub tundra, which was attributed to the high quantity of deciduous shrub foliage present in this community and absent in the other vegetation types. Shrub tundra peak live above-ground phytomass (1256 ± 123 g m−2) was significantly greater than peak live above-ground phytomass for MAT, MNT, and mossy tussock tundra (722 ± 71, 773 ± 53, 703 ± 39 g m−2 respectively, P < 0.05). Relative abundances of deciduous shrubs, mosses, and graminoids were revealed as key components controlling differences in NDVI, LAI, and phytomass among tundra vegetation types.

The Western Arctic Linkage Experiment (WALE): Overview and Synthesis

Abstract The primary goal of the Western Arctic Linkage Experiment (WALE) was to better understand uncertainties of simulated hydrologic and ecosystem dynamics of the western Arctic in the context of 1) uncertainties in the data available to drive the models and 2) different approaches to simulating regional hydrology and ecosystem dynamics. Analyses of datasets on climate available for driving hydrologic and ecosystem models within the western Arctic during the late twentieth century indicate that there are substantial differences among the mean states of datasets for temperature, precipitation, vapor pressure, and radiation variables. Among the studies that examined temporal trends among the alternative climate datasets, there is not much consensus on trends among the datasets. In contrast, monthly and interannual variations of some variables showed some correlation across the datasets. The application of hydrology models driven by alternative climate drivers revealed that the simulation of regional hyd...