Bibliography - J. P. Caspersen
- Lichstein, J W., J. Dushoff, Kiona Ogle, Anping Chen, D. W. Purves, J. P. Caspersen, and Stephen W. Pacala, 2010: Unlocking the forest inventory data: relating individual tree performance to unmeasured environmental factors. Ecological Applications, (20(3)), doi:10.1890/08-2334.1 684-699
[ Abstract ]Geographically extensive forest inventories, such as the USDA Forest Service's Forest Inventory and Analysis (FIA) program, contain millions of individual tree growth and mortality records that could be used to develop broad-scale models of forest dynamics. A limitation of inventory data, however, is that individual-level measurements of light (L) and other environmental factors are typically absent. Thus, inventory data alone cannot be used to parameterize mechanistic models of forest dynamics in which individual performance depends on light, water, nutrients, etc. To overcome this limitation, we developed methods to estimate species-specific parameters (θG) relating sapling growth (G) to L using data sets in which G, but not L, is observed for each sapling. Our approach involves: (1) using calibration data that we collected in both eastern and western North America to quantify the probability that saplings receive different amounts of light, conditional on covariates x that can be obtained from inventory data (e.g., sapling crown class and neighborhood crowding); and (2) combining these probability distributions with observed G and x to estimate θG using Bayesian computational methods. Here, we present a test case using a data set in which G, L, and x were observed for saplings of nine species. This test data set allowed us to compare estimates of θG obtained from the standard approach (where G and L are observed for each sapling) to our method (where G and x, but not L, are observed). For all species, estimates of θG obtained from analyses with and without observed L were similar. This suggests that our approach should be useful for estimating light-dependent growth functions from inventory data that lack direct measurements of L. Our approach could be extended to estimate parameters relating sapling mortality to L from inventory data, as well as to deal with uncertainty in other resources (e.g., water or nutrients) or environmental factors (e.g., temperature).
- Shevliakova, E., Stephen W. Pacala, S. Malyshev, G. C. Hurtt, P.C.D. Milly, J. P. Caspersen, L. T. Sentman, J. P. Fisk, C. Wirth, and C. Crevoisier, 2009: Carbon Cycling Under 300 Years of Land-Use Change: The Importance of the Secondary Vegetation Sink. Global Biogeochemical Cycles, doi:10.1029/2007GB003176
[ Abstract ]We have developed a dynamic land model (LM3V) able to simulate ecosystem dynamics and exchanges of water, energy, and CO2 between land and atmosphere. LM3V is specifically designed to address the consequences of land use and land management changes including cropland and pasture dynamics, shifting cultivation, logging, fire, and resulting patterns of secondary regrowth. Here we analyze the behavior of LM3V, forced with the output from the Geophysical Fluid Dynamics Laboratory (GFDL) atmospheric model AM2, observed precipitation data, and four historic scenarios of land use change for 1700–2000. Our analysis suggests a net terrestrial carbon source due to land use activities from 1.1 to 1.3 GtC/a during the 1990s, where the range is due to the difference in the historic cropland distribution. This magnitude is substantially smaller than previous estimates from other models, largely due to our estimates of a secondary vegetation sink of 0.35 to 0.6 GtC/a in the 1990s and decelerating agricultural land clearing since the 1960s. For the 1990s, our estimates for the pastures’ carbon flux vary from a source of 0.37 to a sink of 0.15 GtC/a, and for the croplands our model shows a carbon source of 0.6 to 0.9 GtC/a. Our process-based model suggests a smaller net deforestation source than earlier bookkeeping models because it accounts for decelerated net conversion of primary forest to agriculture and for stronger secondary vegetation regrowth in tropical regions. The overall uncertainty is likely to be higher than the range reported here because of uncertainty in the biomass recovery under changing ambient conditions, including atmospheric CO2 concentration, nutrients availability, and climate.
- Pacala, Stephen W., and J. P. Caspersen, et al., 2004: Forest Inventory Data Falsify Ecosystem Models of CO2 Fertilization. ,
[ Abstract ]We analyze tree growth data from Wisconsin forest inventories completed in 1968, 1983, 1996 and 2002. These show that the rate of forest growth decreased steadily over the period, in contrast to the increases predicted by CO2 fertilization models. Measured growth rate changed an average of -0.27% y-1 (95% confidence range: -0.05% to -0.49% y-1), whereas the prediction for CO2 fertilization is 0.16% y-1 (corresponding to a ß of 0.36). The high statistical precision is due both to large sample sizes and positive correlations among the growth rates from different time periods within the same plot. Decreased growth occurred in stands of all ages, and so our results are not caused by age-related declines in growth (although highly significant age-related declines were also detected).
Data allowing a direct examination of growth rates over several decades are available only for Wisconsin, but Caspersen et al. (2000) introduced an indirect method for detecting past changes in growth rate using only two sequential inventories. This method was criticized by Joos et al. (2002), who claimed that it lacked the statistical power to falsify state-of–the-art ecosystem models of CO2 fertilization. We explain both the sound points and the critical errors in Joos et al.’s argument, introduce a transparent and analytically tractable version of Caspersen et al.’s method, and check its ability to detect the decreasing growth rates in the Wisconsin data. The results show that the indirect method accurately characterizes the past changes that actually occurred, and has sufficient statistical power to falsify CO2 fertilization models, including the model in Joos et al. (2002).
We discuss the implications of decreasing Wisconsin growth rates, together with other reasons for skepticism about the future magnitude of CO2 fertilization. In particular, the steep reductions in fossil fuel emissions required to stabilize atmospheric CO2 at 500 ppm must begin more than a decade sooner if the predictions of the CO2 fertilization models in the IPCC Third Assessment (Prentice et al. 2001) are incorrect. The difference between a terrestrial carbon sink that grows because of CO2 fertilization, and one that shrinks because it is caused by recovery from past land use, is the difference between the luxury of a substantial delay and the need to act now. - Purves, D. W., J. P. Caspersen, P. R. Moorcroft, G. C. Hurtt, and Stephen W. Pacala, 2004: Human-induced Changes in U.S. Biogenic Volatile Organic Compound Emissions: evidence from long-term forest inventory data. Global Change Biology, 10(10), doi:10.1111/j.1365-2486.2004.00844.x 1737-1755
[ Abstract ]Volatile organic compounds (VOCs) emitted by woody vegetation influence global climate forcing and the formation of tropospheric ozone. We use data from over 250 000 re-surveyed forest plots in the eastern US to estimate emission rates for the two most important biogenic VOCs (isoprene and monoterpenes) in the 1980s and 1990s, and then compare these estimates to give a decadal change in emission rate. Over much of the region, particularly the southeast, we estimate that there were large changes in biogenic VOC emissions: half of the grid cells (1° X 1°) had decadal changes in emission rate outside the range -2.3% to +16.8% for isoprene, and outside the range 0.2–17.1% for monoterpenes. For an average grid cell the estimated decadal change in heatwave biogenic VOC emissions (usually an increase) was three times greater than the decadal change in heatwave anthropogenic VOC emissions (usually a decrease, caused by legislation). Leaf-area increases in forests, caused by anthropogenic disturbance, were the most important process increasing biogenic VOC emissions. However, in the southeast, which had the largest estimated changes, there were substantial effects of ecological succession (which decreased monoterpene emissions and had location-specific effects on isoprene emissions), harvesting (which decreased monoterpene emissions and increased isoprene emissions) and plantation management (which increased isoprene emissions, and decreased monoterpene emissions in some states but increased monoterpene emissions in others). In any given region, changes in a very few tree species caused most of the changes in emissions: the rapid changes in the southeast were caused almost entirely by increases in sweetgum (Liquidambar styraciflua) and a few pine species. Therefore, in these regions, a more detailed ecological understanding of just a few species could greatly improve our understanding of the relationship between natural ecological processes, forest management, and biogenic VOC emissions.
- Pacala, Stephen W., G. C. Hurtt, P. R. Moorcroft, and J. P. Caspersen, 2001: Carbon storage in the US caused by land use change. The Present and Future of Modeling Global Environmental Change, Terra Scientific Publishing, Tokyo, Japan, http://www.terrapub.co.jp/e-library/toyota/pdf/145.pdf, 145-172
[ Abstract ]Here we examine the cause, size and future of the U.S. carbon sink. To estimate the size of the U.S. carbon sink we review a comprehensive land-based analysis of the carbon sink in the coterminous U.S. For the 1980s, the sink is between 1/3 and 2/3 PgC y-1, and is split approximately evenly between forest and non-forest sectors. The non-forest sink is caused by fire suppression on non-forested lands, sediment burial in reservoirs, alluvium and colluvium, and agricultural practices.
The forest sink has been attributed to changes in land use and the enhancement of plant growth by CO2 fertilization, N deposition and climate change. To estimate the relative contribution of land use and growth enhancement in forest ecosystems, we use forest inventory data from five states spanning a latitudinal gradient in the eastern U.S. Land use is the dominant factor governing the rate of carbon accumulation in forests in these states, with growth enhancement contributing far less than previously reported. The estimated fraction of above-ground net ecosystem production due to growth enhancement is 2.0 ± – 4.4%, with the remainder due to land use.
To forecast the future of the U.S. carbon sink, we used the Ecosystem Demography Model (ED). We first modeled carbon sources and sinks from 1700–1990, and then projected patterns to 2100. Our projections indicate that the land-use portion of the U.S. carbon sink will decrease in the future, with a half-life of approximately 50 years, as U.S. ecosystems gradually equilibrate with current patterns of natural and anthropogenic disturbance.
Inventories of terrestrial carbon storage in the coterminous United States (the U.S. minus Alaska and Hawaii) appear to support the conclusion that the sink is small (4). However, inventories in the Northern Hemisphere have been able to account for only a third or less of the 1–2 PgC y-1 indicated strongly by other lines of evidence (5). Moreover, the two primary groups of U.S. inventory studies strongly disagree about cause of the U.S. sink. Houghton and his colleagues (6) used historical records of land use change, timber production, soil conservation, wildfire rates, and simple models of carbon gains and losses in vegetation, soils and wood products. They estimated a sink for the coterminous U.S. averaging 0.39 PgC y-1 from 1950–1990, and caused primarily by increases in crop productivity and changes in the management of agricultural soils (0.15 PgC), and by fire suppression on non-forested land (0.13 Pg C). They concluded that the entire forest sector contributed only 0.07–0.12 PgC y-1.
The U.S. Forest Service (USFS) estimated a coterminous U.S. sink averaging 0.33 PgC y–1 from 1952–1992, using census and tree measurement data from the over 100,000 plots in their Forest Inventory and Analysis (FIA) network, together with models of soil carbon and the fate of wood products (7). Although 0.33 Pg is close to 0.39 Pg, the entire USFS estimate is for the forest sector. If all of the carbon identified in both (6) and (7) were real, then the annual sink for the coterminous U.S. would be 0.60–0.65 PgC (0.33 from (7) plus 0.39 from (6) minus the forest sector estimates from (6)) and thus the overlap between the two estimates is only 11–20% of the total (0.07/0.65 to 0.12/0.60).
The FIA data base shows that the increase of carbon in trees has remained remarkably steady from 1952 to 1992, at approximately 0.10 + 0.02 PgC y-1, because regrowth in the eastern half of the U.S. consistently exceeds harvest by about 0.1 PgC (7). This value is approximately double the increase in living forest carbon modeled in (6). To first order, differences among published inventories based on FIA data are caused by differences in the modeling of all forms of dead organic matter (including slash, wood products, standing dead trees, and soil carbon). For example, one study produced an estimate of only 0.08 PgC y-1 for the 1980’s, because its modeling assumptions led to negligible accumulation of nonliving carbon (8). In contrast, the assumptions behind the USFS estimate of 0.33 PgC y-1 implied that soil carbon accumulated twice as fast as living carbon in trees. In addition, no comprehensive inventory has as yet included the carbon sink caused by sediment burial in reservoirs, alluvium and colluvium and by the transport of carbon into the oceans by rivers. At least one study suggests that sediment burial and river transport may be significant (9). Finally, no comprehensive inventory accounts for net export of carbon in agricultural and wood products.
Ecosystem models provide the final source of information about the terrestrial carbon sink and generally produce small estimates for the coterminous U.S. For example, the models in the recently published VEMAP comparison produced estimates of 0.08 + 0.02 PgC y-1 for the period from 1980–1993 (10). However, none of these models includes the land use changes (i.e. agricultural abandonment, fire suppression, forest harvesting and regrowth, no-till agriculture) that play such a dominant role in the inventory analyses. The models focus instead on the effects of climate change and CO2 and nitrogen fertilization.
In what follows, we first summarize the results of a new inventory-based analysis of the coterminous U.S. carbon sink, which shows that the sink averages between one third and two thirds Pg annually (11). These estimates and smaller than the 0.81–0.84 PgC y-1 in the controversial study (2) (see 11 for a discussion of the portion of estimates in (2) that correspond to the coterminous U.S.). However, they are significantly larger than the previously published range (one tenth to one third PgC y-1). The analysis in (11) shows that approximately half the sink can be unambiguously ascribed to land use and management. We then summarize a recently published analysis (12) of the FIA data showing that the other half of the U.S. carbon sink is also overwhelmingly caused by land use and management.
Given that human land use rather than CO2 or nitrogen fertilization or climate change causes the sink, it is interesting to consider the sink’s future. We then turn to two additional studies. The first (13), introduces a new model that incorporates the sub grid-scale heterogeneity necessary to simulate land use. The second (14), applies this model for the past 300 years of land use in the coterminous U.S., and shows that the U.S. sink will decrease throughout the coming century. Unlike sinks caused by fertilization or climate change that might increase, the land use sink will decrease as U.S. ecosystems adjust to the altered disturbance regimes created by land use and management. - Pacala, Stephen W., G. C. Hurtt, D. Baker, P. Peylin, R. A. Houghton, R. A. Birdsey, L. Heath, E. T. Sundquist, R. F. Stallard, P. Ciais, P. R. Moorcroft, J. P. Caspersen, and E. Shevliakova, et al., 2001: Consistent Land- and Atmosphere-Based U.S. Carbon Sink Estimates. Science, 292, doi:10.1126/science.1057320 2316-2320
[ Abstract ]For the period 1980-89, we estimate a carbon sink in the coterminous United States between 0.30 and 0.58 petagrams of carbon per year (petagrams of carbon = 1015 grams of carbon). The net carbon ßux from the atmosphere to the land was higher, 0.37 to 0.71 petagrams of carbon per year, because a net ßux of 0.07 to 0.13 petagrams of carbon per year was exported by rivers and commerce and returned to the atmosphere elsewhere. These land-based estimates are larger than those from previous studies (0.08 to 0.35 petagrams of carbon per year) because of the inclusion of additional processes and revised estimates of some component fluxes. Although component estimates are uncertain, about one-half of the total is outside the forest sector. We also estimated the sink using atmospheric models and the atmospheric concentration of carbon dioxide (the tracer-transport inversion method). The range of results from the atmosphere-based inversions contains the land-based estimates. Atmosphere- and land-based estimates are thus consistent, within the large ranges of uncertainty for both methods. Atmosphere-based results for 1980-89 are similar to those for 1985-89 and 1990-94, indicating a relatively stable U.S. sink throughout the period.
- Hurtt, G. C., Stephen W. Pacala, P. R. Moorcroft, J. P. Caspersen, E. Shevliakova, R. A. Houghton, and B. Moore III, 0000: Projecting the Future of the U.S. Carbon Sink. Proceedings of the National Academy of Sciences of the United States of America, 99(3), doi:10.1073/pnas.012249999 1389-1394
[ Abstract ]Atmospheric and ground-based methods agree on the presence of a carbon sink in the coterminous United States (the United States minus Alaska and Hawaii), and the primary causes for the sink recently have been identified. Projecting the future behavior of the sink is necessary for projecting future net emissions. Here we use two models, the Ecosystem Demography model and a second simpler empirically based model (Miami Land Use History), to estimate the spatio-temporal patterns of ecosystem carbon stocks and fluxes resulting from land-use changes and fire suppression from 1700 to 2100. Our results are compared with other historical reconstructions of ecosystem carbon fluxes and to a detailed carbon budget for the 1980s. Our projections indicate that the ecosystem recovery processes that are primarily responsible for the contemporary U.S. carbon sink will slow over the next century, resulting in a significant reduction of the sink. The projected rate of decrease depends strongly on scenarios of future land use and the long-term effectiveness of fire suppression.
Direct link to page: http://cmi.princeton.edu/bibliography/results.php?author=4226
