Incorporating intertree competition into an ecosystem model
Current research suggests that projected climate change may influence the growth of individual tr... more Current research suggests that projected climate change may influence the growth of individual trees. Therefore, growth and yield models that can respond to potential changes in climate must be developed, TREE-BGC, a variant of the ecosystem process model FOREST-BGC, calculates the cycling of carbon, water, and nitrogen in and through forested ecosystems. TREE-BGC allocates stand-level estimates of photosynthesis to "each tree using a competition algorithm that incorporates tree height, relative radiation-use efficiency, and absorbed photosynthetically active radiation, TREE-BGC simulated the growth of trees grown in a dense and an open stand of interior Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) near Kamloops, B.C. The competition algorithm dynamically allocated stand estimates of photosynthesis to individual trees, and the trees were grown using an allometric relationship between biomass increment and height and diameter increment. Asymptotic height growth and the changes in the height–diameter relationship with competition were also incorporated in the model algorithms. Sapwood and phloem volume were used to calculate maintenance respiration. Predicted reductions in diameter growth with stand density were similar to those observed in the study stands. Although the carbon balance of individual trees was not tested, simulated tree diameter increments and height increments were correlated with the actual measurements of tree diameter increment (r2 = 0.89) and tree height increment (r2 = 0.78) for the 5-year period (n = 352). Although the model did not work well with trees that had diameters <5 cm, the model would be appropriate for a user who required an accuracy of ± 0.03 m3•ha−1 for volume, ± 0.02 m2•ha−1 for basal area, or ± 0.4 m for tree height over a 5-year period.
Assessing the impact of lawn management practices on the US carbon and water budgets
Agu Fall Meeting Abstracts, Dec 1, 2004
ABSTRACT Despite the ubiquity of turf grasses in the United States, the large-scale functioning o... more ABSTRACT Despite the ubiquity of turf grasses in the United States, the large-scale functioning of these ecosystems has been largely understudied. Although we know that turf grass systems are sequestering carbon at the expense of a large amount of freshwater resources, a continental carbon and water budget has yet to be attempted. The limited existing information on the total extent and spatial distribution of turf grasses and the variability in management practices are the major factors complicating this assessment. In this study, relating turf grass area to fractional impervious surface area, it was estimated that potentially 165,000 km2 (± 31,500 km2) of land are cultivated with turf grasses in the continental United States, an area three times larger than that of any irrigated crop. Using the Biome-BGC ecosystem process model, the growth of warm season and cool season turf grasses was modeled for 865 sites across the 48 conterminous states under different management scenarios, including either removal or recycling of the grass clippings, different nitrogen fertilization rates and two alternative water irrigation practices. The simulations portray potential carbon and water fluxes as if the entire turf surface was to be managed like a well-maintained lawn. The results indicate that well watered and fertilized turf grasses act as a carbon sink, even assuming removal and bagging of the grass clippings after mowing. The potential carbon sequestration that could derive from the total surface under turf (up to 17 Tg C/yr with the simulated scenarios) would require a 30% to 70% increase in current domestic and commercial water use, depending on the modeled water irrigation practices. Landscaping water conservation practices such as xeriscaping and irrigation with recycled waste-water may need to be extended as municipalities continue to face increasing pressures on freshwater resources due to continued population growth.
1. Climate change is increasing the vulnerability of many forests to ecosystem changes and tree m... more 1. Climate change is increasing the vulnerability of many forests to ecosystem changes and tree mortality through fire, insect infestations, drought, and disease outbreaks. 2. U.S. forests and associated wood products currently absorb and store the equivalent of about 16% of all carbon dioxide (CO 2) emitted by fossil fuel burning in the U.S. each year. Climate change, combined with current societal trends in land use and forest management, is projected to reduce this rate of forest CO 2 uptake. 3. Bioenergy could emerge as a new market for wood and could aid in the restoration of forests killed by drought, insects, and fire. 4. Forest management responses to climate change will be influenced by the changing nature of private forestland ownership, globalization of forestry markets, emerging markets for bioenergy, and U.S. climate change policy. FORESTS 7 Forests occur within urban areas, at the interface between urban and rural areas (wildland-urban interface), and in rural areas. Urban forests contribute to clean air, cooling buildings, aesthetics, and recreation in parks. Development in the wildland-urban interface is increasing because of the appeal of owning homes near or in the woods. In rural areas, market factors drive land uses among commercial forestry and land uses such as agriculture. Across this spectrum, forests provide recreational opportunities, cultural resources, and social values such as aesthetics. 3 Management choices for public, private, and tribal forests all involve similar issues. For example, increases in wildfire, disease, drought, and extreme events are projected for some regions (see also Ch. 16: Northeast; Ch. 20: Southwest; Ch. 21: Northwest, Key Message 3; and Ch. 22: Alaska). At the same time, there is growing awareness that forests may play an expanded role in carbon management. Urban expansion fragments forests and may limit forest management options. Addressing climate change effects on forestlands requires considering the interactions among land-use practices, energy options, and climate change. 5 176 CLIMATE CHANGE IMPACTS IN THE UNITED STATES Key Message 1: Increasing Forest Disturbances Climate change is increasing the vulnerability of many forests to ecosystem changes and tree mortality through fire, insect infestations, drought, and disease outbreaks. Insect and pathogen outbreaks, invasive species, wildfires, and extreme events such as droughts, high winds, ice storms, hurricanes, and landslides induced by storms 8 are all disturbances that affect U.S. forests and their management (Figure 7.1). These disturbances are part of forest dynamics, are often interrelated, and can be amplified by underlying trends-for example, decades of rising average temperatures can increase damage to forests when a drought occurs. 9 Disturbances that affect large portions of forest ecosystems occur relatively infrequently and in response to climate extremes. Changes in climate in the absence of extreme climate events (and the forest disturbances they trigger) may result in increased forest productivity, but extreme climate events can potentially overturn such patterns. 10 Factors affecting tree death-such as drought, physiological water stress, higher temperatures, and/or pests and pathogens-are often interrelated, which means that isolating a single cause of mortality is rare. 11,12,13 However, in western forests there have been recent large-scale die-off events due to one or more of these factors, 14,15,16 and rates of tree mortality are well correlated with both rising temperatures and associated increases in evaporative water demand. 17 In eastern forests, tree mortality at large spatial scales was more sensitive Figure 7.1. An example of the variability and distribution of major ecosystem disturbance types in North America, compiled from 2005 to 2009. Forest disturbance varies by topography, vegetation, weather patterns, climate gradients, and proximity to human settlement. Severity is mapped as a percent change in a satellite-derived Disturbance Index. White areas represent natural annual variability, orange represents moderate severity, and red represents high severity. 6 Fire dominates much of the western forest ecosystems, and storms affect the Gulf Coast. Insect damage is widespread but currently concentrated in western regions, and timber harvest is predominant in the Southeast. (Figure source: modified from Goetz et al. 2012; 7 Copyright 2012 American Geophysical Union). Forest Ecosystem Disturbances A Montana saw mill owner inspects a lodgepole pine covered in pitch tubes that show the tree trying, unsuccessfully, to defend itself against the bark beetle. The bark beetle is killing lodgepole pines throughout the western U.S. Warmer winters allow more insects to survive the cold season, and a longer summer allows some insects to complete two life cycles in a year instead of one. Drought stress reduces trees' ability to defend against boring insects. Above, beetle-killed trees in Rocky Mountain National Park in Colorado.
A biophysical soil-site model for estimating potential productivity of forested landscapes
Can J Forest Res, 1996
A biophysical soil–site model is presented for predicting potential forest productivity, defined ... more A biophysical soil–site model is presented for predicting potential forest productivity, defined as cubic metres per hectare per year at culmination of mean annual increment (CMAI), for use in forest taxation by the state of Montana. The model combines soil, climate, and topographic data layers within a geographic information system; a climate model (MT-CLIM); and an ecosystem carbon–water balance model (Forest-BGC) to generate estimates of potential forest productivity for all forested sites in the state. Weather station data were used to define base climate regions within the state, and to build regional precipitation models. Hydrologic equilibrium theory was used to estimate maximum leaf area from climate and soil water availability. Forest-BGC was initialized with estimates of the stem, leaf, and root carbon pools (kg C/ha) at CMAI and the 1-year prediction of stem carbon increment (kg C•ha−1•year−1) was taken as the initial estimate of potential productivity. The gross stem carbon increment was then converted to wood increment, reduced for branch wood growth, and finally adjusted for mortality rates found in regional yield tables. Other model adjustments included stockability factors for low-elevation forest–grassland sites, and modification of a photosynthesis rate parameter for north aspects. Response surfaces show potential productivity to vary as expected with precipitation, soil water, and temperature. Despite rather gross resolution of model inputs, regressions of site index on model predictions showed R2 values and standard errors comparable with those found when fitting empirical soil–site equations in the region.
Documentation and preliminary validation of H2OTRANS and DAYTRANS, two models for predicting transpiration and water stress in western coniferous forests
Research Paper Rocky Mountain Forest and Range Experiment Station Usda Forest Service, 1984
Trends and constraints in global terrestrial primary productivity
We present a reformulation of the Bristow±Campbell model for daily solar radiation, developed usi... more We present a reformulation of the Bristow±Campbell model for daily solar radiation, developed using daily observations of radiation, temperature, humidity, and precipitation, from 40 stations in contrasting climates. By expanding the original model to include a spatially and temporally variable estimate of clear-sky transmittance, and applying a small number of other minor modi®cations, the new model produces better results than the original over a wider range of climates. Our method does not require reparameterization on a site-by-site basis, a distinct advantage over the original approach. We do require observations of dewpoint temperature, which the original model does not, but we suggest a method that could eliminate this dependency. Mean absolute error (MAE) for predictions of clear-sky transmittance was improved by 28% compared to the original model formulation. Aerosols and snowcover probably contribute to variation in clear-sky transmittance that remains unexplained by our method. MAE and bias for prediction of daily incident radiation were about 2.4 MJ m À2 day À1 and 0.5 MJ m À2 day À1 , respectively. As a percent of the average observed values of incident radiation, MAE and bias are about 15% and 4%, respectively. The lowest errors and smallest biases (percent basis) occurred during the summer. The highest prediction biases were associated with stations having a strong seasonal concentration of precipitation, with underpredictions at summerprecipitation stations, and overpredictions at winter-precipitation stations. Further study is required to characterize the behavior of this method for tropical climates.
Regional Hydrological and Carbon Balance Response of Forests Resulting from Potential Climate Change
Forest ecosystem processes at the watershed scale: sensitivity to remotely-sensed Leaf Area Index estimates
Http Dx Doi Org 10 1080 01431169308904290, Apr 25, 2007
ABSTRACT
Regional implications of climate change: Summer stream discharge trends in the Northern Rockies
ABSTRACT Background/Question/Methods Semi-arid continental climates in the northern hemisphere ar... more ABSTRACT Background/Question/Methods Semi-arid continental climates in the northern hemisphere are experiencing large increases in surface temperatures due to climate change; however, to date there has been limited effort to evaluate stream flow trends in the Northern Rockies region. Cool in-stream temperatures are of great importance to the health and function of aquatic ecosystems during summer months. While historic stream temperature data is quite uncommon, stream discharge records are prolific throughout the Northern Rockies and are related to stream temperature, snow pack, and precipitation trends. The purpose of this study was to determine if mean August stream discharge values are decreasing over the last half-century, if low discharge values are occurring more frequently and if this trend can be attributed to climate change. Using historic discharge data from United States Geological Survey’s (USGS’s) national water information system (NWIS) web interface we analyzed data for trends of at least 20-50 years. Combining of these records along with aerial photos (with <10m resolution) and water rights records we selected gauging sites based on the length and continuity of discharge records, amount of diversion and location of water storage devices. In addition we used temperature records and precipitation records to perform a correlation analysis with discharge trends over the last half century. Results/Conclusions Preliminary analyses demonstrate that watersheds in select locations throughout the Northern Rockies are experiencing significant declines in stream discharge over the last half century. These results are further supported by recent research that shows decreasing mountain snowpack, earlier succession of snowmelt and more winter rain events. This regional assessment of stream discharge trends will provide invaluable information for local, county and state conservation plans and help to predict the severity of action needed to address decreasing discharge in the future.
Various FLUXNET sites, where simultaneous observations of canopy structure, leaf area index devel... more Various FLUXNET sites, where simultaneous observations of canopy structure, leaf area index development, net ecosystem exchange and soil respiration are available, provide an excellent basis for validating the MODLAND products that are related to ecosystem structure and carbon and water balance. Here we present our ongoing effort to compare LAI and GPP estimated via MODIS algorithms with ground-observed data at
Eos, Transactions American Geophysical Union, 2004
In the $388 billion omnibus appropriations bill for fiscal year (FY) 2005 that the US. Congress a... more In the $388 billion omnibus appropriations bill for fiscal year (FY) 2005 that the US. Congress approved on 20 November, most agencies aside from NASA that fund Earth and space sciences face flat or declining budgets. All agencies covered in the omnibus bill face an additional 0.8% reduction agreed to by Congress and the Bush Administration, which is not calculated into the figures in this article.
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