Grantee Research Project Results
2001 Progress Report: Regional Analysis of Net Ecosystem Productivity of Pacific Northwest Forests: Scaling Methods, Validation and Results Across Major Forest Types and Age Classes
EPA Grant Number: R828309Title: Regional Analysis of Net Ecosystem Productivity of Pacific Northwest Forests: Scaling Methods, Validation and Results Across Major Forest Types and Age Classes
Investigators: Law, B. E. , Harmon, M. E. , Daly, Christopher , Turner, D. , Unsworth, M. , Cohen, W.
Institution: Oregon State University
EPA Project Officer: Packard, Benjamin H
Project Period: July 1, 2000 through June 30, 2003 (Extended to June 30, 2004)
Project Period Covered by this Report: July 1, 2001 through June 30, 2002
Project Amount: $1,848,927
RFA: Regional Scale Analysis and Assessment (1999) RFA Text | Recipients Lists
Research Category: Aquatic Ecosystems , Ecological Indicators/Assessment/Restoration
Objective:
The objectives of this research project are to: (1) develop and test a regional scale approach that combines modeling, data from remote sensing, sample surveys, and intensive research sites to better estimate variation in the carbon balance of forest ecosystems in the Pacific Northwest; and (2) apply our strategy to investigate how processes controlling variation in net ecosystem productivity are influenced by forest development, disturbances, and contrasting climatic conditions.
Progress Summary:
Field Data Findings
Foliar, litter, and soil chemistry data, which we analyzed for 96 plots across OR, are important for scaling estimates of productivity and carbon storage to region. Foliar chemistry data are used to parameterize ecosystem models, but default values for a given species or life form typically are used rather than actual data from the study area. We found that leaf mass per unit leaf area (LMA) significantly differed (P < 0.0001) between species, with the differences affected by the broad geographical regions. Geographically: EOR > CASC and SWOR > COAS (EOR = eastern OR, CASC = Cascade Mountains, SWOR = southwest OR, COAS = coastal forests). The foliar C:N ratio was highly specific (P < 0.0001) to species and the broad geographical regions (CASC > EOR and SOR > COAS), and the soil C:N ratio was CASC SWOR EOR > COAS, where indicates no statistical significance. The canopy C:N ratio linearly was correlated with the soil C:N ratio (see Figure 1), which suggests that there is coupling between the above and below ground carbon and nitrogen processes, as assumed in process models. Sensitivity analysis in previous scaling work suggests that the model is very sensitive to foliar C:N. Our preliminary analysis suggests that our estimates of productivity and biomass are improved by using field measurements of foliar chemistry to parameterize Biome-BioGeochemical Cycles (BGC) for geo-regions of conifers in OR.
Figure 1. Canopy C:N Ratio (Weighted by Species and Needle Age Classes) is Linearly Related to Soil C:N Ratio. The dotted line indicates 1:1 relationship.
We are preparing a paper on Forest Inventory and Analysis (FIA) and Current Vegetation Survey (CVS) inventory data, entitled "How carbon fluxes and storage vary across OR forests-an assessment with inventory and intensive plot data." Using a combination of forest inventory data, intensive inventory sites, and remote sensing, we estimated forest biomass and net primary production for the forested region of OR. Plot level forest inventory data were provided by the U.S. Department of Agriculture Forest Service through their FIA (1,100 plots) and CVS (4,300 plots) programs. Stand age ranged from 0 to 750 years across the study area. The forest age distributions differed by geographic location with fewer old stands in coastal and eastern OR, and a relatively even distribution of ages from 0 to 750 in the Cascade Mountains (see Figure 2). Interestingly, age distribution differed by land ownership, with fewer old stands on federal lands than on non-federal lands across the entire study area. Forest biomass increased steeply in early development with the trajectory leveling out at about 200 years. Peak biomass generally was lower in eastern OR than in other areas (median biomass at asymptote ~10,000 g cm-2 and ~30,000 g cm-2 respectively), possibly due to water availability constraints. The timing and magnitude of the peak in net primary productivity (NPP) varied by geographic location within the study area with high-productivity sites (coastal OR) exhibiting a relatively high peak (median NPP ~1,000 g cm-2 y-1) around 30 years and low-productivity sites (eastern OR) exhibiting a relatively low peak (median NPP ~250 g cm-2 y-1) between 80 and 100 years (see Figure 3). Productivity tended to decline after the peak and stabilize at about 50 percent of the peak by about age 200. Measurements of additional carbon budget components combined with inventory data provided estimates of carbon storage and fluxes that may be useful for forest management and validation of Biome-pBGC across the region.
Figure 2. Frequency Distributions of Stand Age by Geographic and Data Type. Forests in western OR tend to have fewer old stands on non-federal FIA lands than on federal, CVS lands. This trend is apparent in all geographic areas and may reflect forest management practices on non-federal lands that tend to have short rotation periods of 50 to 100 years.
Figure 3. Changes in Wood NPP (Aboveground and Coarse Root) With Stand Age on CVS and FIA Forest Inventory Plots. Plots are grouped into 10-year age classes and box plots were made for each age class. Bars represent the interquartile range (25 percent to 75 percent) and lines represent 0 to 25 percent and 75 to 100 percent. The black bar indicates the median of each age class.
We submitted a paper to Global Change Biology for publication, entitled "Changes in carbon storage and fluxes in a chronosequence of ponderosa pine." The paper evaluates differences in carbon budget components across 12 stands ranging from 9 to greater than 300 years. NPP, heterotrophic respiration, and net ecosystem production (NEP) were lowest in young stands, highest in stands from 100 to 150 years old, and slightly lower in stands greater than 200 years old (see Figure 4). NEP averaged 141 g cm-2 y-1 (SD 111). Carbon storage in live mass reached a maximum of 17.4 kg cm-2 by age 150 to 200, and was not lower in older stands, contrary to the belief that mortality leads to decreased live mass of old stands. Total ecosystem carbon storage and the fraction of ecosystem carbon in aboveground wood mass increased rapidly until 150 to 200 years, and also did not decline in older stands. Forest inventory data (FIA, CVS) on 950 ponderosa pine plots in OR showed that the greatest proportion of plots exist in stands approximately 100 years old, indicating that a majority of stands are approaching maximum carbon storage and net carbon uptake. Our data suggest that NEP averages approximately 150 g cm-2 y-1 for ponderosa pine forests in OR. About 85 percent of the total carbon storage in biomass on the survey plots exists in stands greater than 100 years, which has implications for managing forests for carbon sequestration.
Figure 4. Simulated NEP as a Function of Stand Age in Ponderosa Pine (Crosses, Vertical Bars Show One Standard Deviation Range of Climate-driven Interannual Variability). Observed values shown for comparison (squares).
Modeling Findings
Pine Chronosequence Study on Disturbance Effects. We used the model, Biome-BGC, to simulate the historical patterns of disturbance and recovery at each of the ponderosa pine chronosequence sites (Law, et al., submitted). With the observations from the chronosequence, we were able to construct simple relationships describing the variation of allocation parameters with stand age, and we tested the hypothesis that this variation reduces model bias in both state and flux variable comparisons to observations. We used these model results to develop an additional hypothesis regarding variation in leaf nitrogen allocation to the RuBisCO enzyme as a function of time following disturbance. We also explored the variability in disturbance recovery responses related to atmospheric CO2 concentration during recovery. The timing of initiation of young stands following stand-replacing disturbance had a significant effect on model estimates of NEP in the early years of stand development (see Figure 4). The simulated response in NEP during the first 100 years following disturbance had a strong dependence on the atmospheric concentration of CO2, which varied according to the historical timing of disturbances at different stands in the chronosequence. The peak carbon sink strength was higher and occurred sooner following disturbance for the more recently disturbed stands. The time required to replace the carbon lost as a result of disturbance was shorter in these stands, and the total carbon lost before the stands switched from sources to sinks of carbon was less. The effect of CO2 on carbon cycling interacts strongly with the variation in available soil mineral nitrogen, which increases after disturbance due to reduced plant demand. The simulated NEP response to increasing atmospheric CO2 in the oldest undisturbed stand (plot 35) is very small and is proportional to the rate of change in CO2 concentration. The observations suggested new parameterizations that have improved our ability to simultaneously estimate carbon pools and fluxes in this system. We found that accurate simulation requires a dynamic parameterization for biomass allocation that depends on stand age, and also should include a representation of competition between multiple plant functional types for space, water, and nutrients. These modifications now stand as new hypotheses to be tested for generality in other systems and with additional types of observations.
Scaling Issues Evaluated at the H.J. Andrews LTER Site. In this study, a fine scale (25 m grid) analysis of NEP over a 164-km2 area of the H.J. Andrews Long-Term Ecology Research (LTER) site, where coniferous forests are some of the most productive in the Pacific Northwest Region (Turner, et al., 2002). We evaluated the effects of including fine scale information in landscape-scale NEP assessments. The Enhanced Thematic Mapper (ETM+) sensor resolved five cover classes in the study area and further differentiated between young, mature, and old-growth conifer stands (see Figure 5). ETM+ also was used to map current leaf area index (LAI) based on an empirical relationship of observed LAI to spectral vegetation indices. A daily time step climatology, based on 18 years of meteorological observations, was distributed (1 km resolution) over the mountainous terrain of the study area using the DAYMET model. Estimates of carbon pools and flux associated with soil, litter, coarse woody debris, and live trees then were generated by running the Biome-BGC model to a state that reflected the current successional status and LAI of each grid cell, as indicated by the remote sensing observations. Estimated annual NEP for 1997 over the complete study area averaged 230 gCm-2 with most of the area acting as a carbon sink (see Figure 6). The area-wide NEP strongly is positive because of reduced harvesting in the last decade and the recovery of areas harvested between 1940 and 1990. The average value was greater than would be indicated if the entire area was assumed to be a mature conifer stand, as in a coarse scale analysis. The mean NEP varied interannually by more than a factor of two. This variation was 38 percent less than the interannual variation for a single point. The integration of the process model with ground surface information provided by remote sensing offers a framework for investigating mechanisms regulating NEP and evaluating coarse resolution globally-applied NEP scaling efforts.
Figure 5. (a) Land Cover Data Layer for the H. J. Andrews Study Area, (b) LAI Reference Data Layer for the H.J. Andrews Study Area. The location of the site headquarters is in the lower left corner of the figures, at 44 12 N, 122 14 W.
Figure 6. Mean NEP by Cover Type in the H.J. Andrews LTER from Biome-BGC Simulations.
Remote Sensing Findings. The role of remote sensing in this project was to develop methods for estimating stand age and LAI, and to provide spatial estimates of forest type, age, and LAI for the spatially explicit modeling of productivity and NEP. First, we developed spectral regressions for estimating LAI. There is a strong, linear relationship between a number of satellite vegetation indices and LAI measured using the LAI-2,000 optical instrument during the summer of 2001 (see Figure 7). When we evaluated remotely sensed LAI with the remaining field data points for the east and west side of the Cascade Mountains separately, we found that the ETM+ was more sensitive to the low LAIs found on the dry east side of the Cascades, and that it tended to saturate at high LAIs on the west site. Conversely, stand age derived from ETM+ was more accurate on the west side than the east side of the Cascades. Thus, we were limited to distinguishing only 3 to 5 age classes on the west side. Accuracies for the mapping of disturbance (age) generally exceeded 90 percent. We completed mapping of stand age, LAI, and forest type with the ETM+ imagery in OR.
Figure 7. ETM+ Predicted Versus Observed LAI From Field Data in the H.J. Andrews LTER Site in the Cascade Mountains.
Future Activities:
We will continue to acquire flux tower gross primary production (GPP) and NEP estimates as they become available, and compare them to our model simulations. As site-specific estimates of the bole carbon stocks and production become available from the inventory data and plot data, we will make comparisons with simulated values derived from the Biome-BGC and LANDCARB models.
Journal Articles on this Report : 12 Displayed | Download in RIS Format
Other project views: | All 38 publications | 25 publications in selected types | All 24 journal articles |
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Campbell JL, Sun OJ, Law BE. Supply-side controls on soil respiration among Oregon forests. Global Change Biology 2004;10(11):1857-1869. |
R828309 (2000) R828309 (2001) R828309 (2002) R828309 (Final) |
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Cohen WB, Maiersperger TK, Spies TA, Oetter DR. Modelling forest cover attributes as continuous variables in a regional context with Thematic Mapper data. International Journal of Remote Sensing 2001;22(12):2279-2310. |
R828309 (2000) R828309 (2001) R828309 (Final) |
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Cohen WB, Spies TA, Alig RJ, Oetter DR, Maiersperger TK, Fiorella M. Characterizing 23 years (1972-95) of stand replacement disturbance in western Oregon forests with Landsat imagery. Ecosystems 2002;5(2):122-137. |
R828309 (2000) R828309 (2001) R828309 (2002) R828309 (Final) |
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Davidson EA, Savage K, Bolstad P, Clark DA, Curtis PS, Ellsworth DS, Hanson PJ, Law BE, Luo Y, Pregitzer KS, Randolph JC, Zak D. Belowground carbon allocation in forests estimated from litterfall and IRGA-based soil respiration measurements. Agricultural and Forest Meteorology 2002;113(1-4):39-51. |
R828309 (2000) R828309 (2001) |
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Harding DJ, Lefsky MA, Parker GG, Blair JB. Laser altimeter canopy height profiles--methods and validation for closed-canopy, broadleaf forests. Remote Sensing of Environment 2001;76(3):283-297. |
R828309 (2000) R828309 (2001) |
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Law BE, Van Tuyl S, Cescatti A, Baldocchi DD. Estimation of leaf area index in open-canopy Ponderosa pine forests at different successional stages and management regimes in Oregon. Agricultural and Forest Meteorology 2001;108(1):1-14. |
R828309 (2000) R828309 (2001) |
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Law BE, Sun OJ, Campbell J, Van Tuyl S, Thornton PE. Changes in carbon storage and fluxes in a chronosequence of Ponderosa pine. Global Change Biology 2003;9(4):510-524. |
R828309 (2000) R828309 (2001) |
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Law BE, Turner D, Campbell J, Sun OJ, Van Tuyl S, Ritts WD, Cohen WB. Disturbance and climate effects on carbon stocks and fluxes across Western Oregon USA. Global Change Biology 2004;10(9):1429-1444. |
R828309 (2000) R828309 (2001) R828309 (2002) |
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Lefsky MA, Cohen WB, Spies TA. An evaluation of alternate remote sensing products for forest inventory, monitoring, and mapping of Douglas-fir forests in western Oregon. Canadian Journal of Forest Research 2001;31(1):78-87. |
R828309 (2000) R828309 (2001) R828309 (Final) |
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Lefsky MA, Cohen WB, Parker GG, Harding DJ. Lidar Remote Sensing for Ecosystem Studies: Lidar, an emerging remote sensing technology that directly measures the three-dimensional distribution of plant canopies, can accurately estimate vegetation structural attributes and should be of particular interest to forest, landscape, and global ecologists. Bioscience 2002;52(1):19-30. |
R828309 (2000) R828309 (2001) |
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Parker GG, Lefsky MA, Harding DJ. Light transmittance in forest canopies determined from airborne laser altimetry and in-canopy quantum measurements. Remote Sensing of Environment 2001;76(3):298-309. |
R828309 (2000) R828309 (2001) |
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Sun OJ, Campbell J, Law BE, Wolf V. Dynamics of carbon stocks in soils and detritus across chronosequences of different forest types in the Pacific Northwest, USA. Global Change Biology 2004;10(9):1470-1481. |
R828309 (2000) R828309 (2001) R828309 (2002) R828309 (Final) |
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Supplemental Keywords:
atmosphere, land, soil, global climate, ecosystem, regionalization, scaling, terrestrial, integrated assessment, ecology, modeling, monitoring, analytical, surveys, measurement methods, climate models, satellite, landsat, remote sensing, Pacific Northwest., RFA, Scientific Discipline, Air, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Ecology, Ecosystem/Assessment/Indicators, Ecosystem Protection, Environmental Chemistry, climate change, State, Ecological Effects - Environmental Exposure & Risk, Forestry, Regional/Scaling, Pacific Northwest, anthropogenic stresses, ecological effects, ecological exposure, carbon allocation, semi-arid environments, ecosystem assessment, survey data, Oregon, forest ecosystems, natural stressors, forest inventory and analysis, climate, Washington (WA), ecosystem indicators, regional scale impacts, forests, forest resources, ecosystem stress, remote sensing imagery, ecological response, validation, carbon stress index, scaling methodsRelevant Websites:
http://www.fsl.orst.edu/terra Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.