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The PnET family of models was originally developed at the University of New Hampshire by John Aber and colleagues. Support for this development was provided by public agencies and hence the model, data files and results should be considered public property and available free of charge. Recipients also have a responsibility which we outline below.

Summary:

PnET (Photosynthetic EvapoTranspiration model) has been developed and validated in the Northeastern U.S. at both the site and grid level (to 1 km resolution). Some datasets available from this model include a landuse classification map for New England, grids of climate variables, monthly (e.g. precipitation), grids of annual N and S (sulfur) atmospheric deposition, forest NPP and runoff at ambient and twice CO2 levels and a map of steady state N cycling rates.

All the PnET datasets are long term means except the landuse and landcover dataset, which has a temporal scale of 1989 - 1990. This landuse and landcover dataset is from a 1989 AVHRR scene, augmented by USFS field work in a database called CONUS.

PnET (net photosynthesis / evapotranspiration) is a nested series of models of carbon (C), water and nitrogen dynamics in forest ecosystems. The models can be used to predict transient responses in net primary production (NPP), carbon and water balances, net N mineralization and nitrification and N leaching losses, resulting from changes in climate, N deposition, tropospheric ozone and land use as well as variation in species composition. The models use generalized representations of physiological and ecosystem processes and were designed to be run with relatively few input parameters that require no calibration. At the core of each version is a multi-layered canopy model of phenology and photosynthesis (PnET-Day) that was designed to simulate daily canopy carbon exchange.

The PnET-II model is a canopy-to-stand-level model of monthly carbon and water balances for temperate and boreal forest ecosystems. Central to the model are relationships between foliar nitrogen and maximum leaf photosynthesis, and between actual photosynthesis and stomatal conductance. Together, these provide a link between the carbon and water balance portions of the model in that transpiration is determined as a function of canopy photosynthesis. The model has been applied and validated regionally in the northeastern US and elsewhere using input parameters that reflect typical deciduous and coniferous forests. PnET-II outputs include annual net primary productivity (NPP), wood production and runoff under current and climate change conditions (+6 degrees C, -15% precipitation and 2X CO₂). Climate change predictions are presented as ratios of future to current values.

The PnET-CN model adds live biomass, litter and soil organic matter compartments to the structure of PnET-II and simulates temporal changes in both plant and soil C and N pools. Nitrogen is included in all compartments and fluxes, as well as N mineralization and nitrification, plant N uptake and leaching losses to produce complete cycles for water, carbon and nitrogen. Canopy and soil processes interact through C:N ratios in foliage and litter. Foliar N concentrations vary with the availability of C and N in plants. Tissue C:N ratios are reflected in litter, and high C/N ratios decrease net N mineralization. PnET-CN can be applied transiently where site history information is available. PnET-CN outputs presented here are regional predictions of equilibrium N cycling.

For more information on the Pnet models, visit the PnET web site.

The table below lists the datasets related to the PnET model, primarily output data with links to journal articles with results drawn from these datasets. Some of the datasets vary only in their spatial resolution, 1 km or 2 km. The area modeled and validated is New England and northern New York, and a small portion of northern New Jersey and northern Pennsylvania. Datasets without a "PnET" source are inputs to the model rather than outputs. The PnET-2 sources are run with parameters to model water and carbon balances. The PnET CN model adds nitrogen cycling to the water and carbon balances in the PnET 2 model.

More information about the specific dataset can be found by linking through the "Dataset" column in this table. The associated abstract can be displayed by linking through the "Publication" column.

PnET Dataset Descriptions:

Precipitation

Precipitation data were generated with the CLIMCALC model, which is described in the publication "Modeling Physical and Chemical Climate of Northeastern United States for a Geographic Information System," by Scott V. Ollinger, John D. Aber, C. Anthony Federer, Gary M. Lovett and Jennifer M. Ellis, USFS, General Technical Report NE-191, Feb 1995. The model combines latitude, longitude and elevation gradients in monthly precipitation (derived from 30 year mean weather station data) with a digital elevation model to yield monthly precipitation data planes for the northeast region. The model has been used as input to the PnET forest ecosystem models at 30 and 60 arc second resolution for regional analyses of forest ecosystem function. The units are cm/yr and the min and max values are 30 cm and 219 cm/yr. Background values for areas outside the study region are 0. The spatial resolution of data available here is 60 arc seconds (about 2 km) and the grid dimensions are 660 x 600 pixels, ranging from 38 to 48 degrees N latitude and from 66 to 77 degrees W longitude.

Runoff

Runoff data were generated with the PnET-2 forest carbon and water balance model using monthly climate inputs provided by CLIMCALC and the Lathrop and Bognar (1994) land cover map. Model parameters are provided as part of the auxiliary data downloaded with data from EOS-WEBSTER. This variable is mean annual runoff. The units are mm/yr. The min and max values are 235 and 1545. The fill value is 0, representing non-forested grid cells and areas that lie outside the region. Complete description of the methods, interpretation of results and validation against measured runoff at USGS gauged watersheds are given in Ollinger et al. 1998. (Landscape Ecology 13, pp. 323-334). The area represented is 38 to 48 degrees N and 66 to 77 degrees W. The spatial resolution is 30 arc seconds (approximately 1 km) and grid dimensions are 1320 by 1200 pixels.

Climate Change Runoff

These data indicate the change in runoff predicted by PnET-2 under a climate change scenario of +6 degrees C, -15% precipitation and 2X CO2. Values shown are the ratio of predicted runoff under climate change to that under current conditions, scaled by a factor of 100. Hence, a value of 130 represents a 30% increase in runoff under climate change and a value of 70 represents a 30% decrease. Predictions range from 62 to 133, although the majority of pixels lie between 75 and 90, indicating a decrease in runoff regionally. Model parameters used in these simulations are provided as part of the auxiliary data downloaded with the data from EOS-WEBSTER. The fill value (non-forested pixels and areas outside the region) is 0. The data are described more completely in Aber et al. 1995 (Climate Research 5, pp. 207-222). The area represented is 38 to 48 degrees N latitude and 66 to 77 degrees W longitude. The spatial resolution is 60 arc seconds (approximately 2 km) and the grid dimensions are 660 x 600 pixels.

Climate Change NPP

These data indicate the change in annual Net Primary Production predicted by PnET-2 under a climate change scenario of +6 degrees C, -15% precipitation and 2X CO2. Values shown are the ratio of predicted NPP under climate change to that under current conditions, scaled by a factor of 100. Hence, a value of 130 represents a 30% increase under climate change and a value of 70 represents a 30% decrease. Predictions range from 70 to 175, although the majority of pixels lie between 100 and 150, indicating an increase in NPP regionally. Model parameters used in these simulations are provided as part of the auxiliary data downloaded with the data from EOS-WEBSTER. The fill value (non-forested pixels and areas outside the region) is 0. The data are described more completely in Aber et al. 1995 (Climate Research 5, pp. 207-222). The area represented is 38 to 48 degrees N latitude and 66 to 77 degrees W longitude. The spatial resolution is 60 arc seconds (approximately 2 km) and the grid dimensions are 660 x 600 pixels.

Net Ecosystem Production

These data represent predictions of Net Ecosystem Production (NEP), or Ecosystem Carbon Flux predicted by the PnET-2 model. Model parameters are part of the auxiliary data downloaded with the data from EOS-WEBSTER. These predictions are the result of a PnET-2 simulation under current climate conditions, with climate inputs provided by CLIMCALC (Ollinger et al. 1995, USFS General Technical Report NE-191. NEP units are g C/m2/yr. The min and max values are -376 to 235. The fill value is 0. All actual NEP values are non-zero here. The data are described in Aber et al. 1995 (Climate Research 5, 1995, pp. 207-222). The area represented is 38 to 48 degrees N and 66 to 77 degrees W. The resolution is 60 arc seconds (approximately 2 km) and the grid dimensions are 660 x 600 pixels.

Land Use & Land Cover

This land cover data set is used as input to the PnET models for regional predictions of forest productivity, runoff and N cycling in a region comprised of New England and eastern New York State. It was developed from AVHRR imagery and USGS Land Use/Land Cover data by R. G. Lathrop Jr. and J. A. Bognar (International Journal of Remote Sensing 15, 1994, no 13, pp. 2695-2702) and later reclassified to 11 major land cover categories. The lookup table is part of the auxiliary data downloaded with the data from EOS-WEBSTER. Background values are 0. The spatial resolution is 30 arc seconds (about 1 km) and the grid dimensions are 1320 x 1200, covering the area from 38 to 48 degrees N latitude, and from 66 to 77 degrees W longitude.

NPP

Annual NPP data were generated with the PnET-2 forest carbon and water balance model using monthly climate inputs provided by CLIMCALC and the Lathrop and Bognar (1994) land cover map. Model parameters are provided as part of the auxiliary data downloaded with the data from EOS-WEBSTER. The units are g/m2/yr. The min and max values are 114 to 1452. The fill value is 0. Complete description of the methods, interpretation of results and validation against measured data are given in Ollinger et al. 1998. (Landscape Ecology 13, pp. 323-334). The area represented is 38 to 48 degrees N and 66 to 77 degrees W. The spatial resolution is 30 arc seconds (approximately 1 km) and grid dimensions are 1320 by 1200 pixels.

Wood Production

Annual wood production data were generated with the PnET-2 forest carbon and water balance model using monthly climate inputs provided by CLIMCALC and the Lathrop and Bognar (1994) land cover map. Model parameters are provided as part of the auxiliary data downloaded with the data from EOS-WEBSTER. The units are g/m2/yr. The min and max values are 45 to 865. The fill value is 0. Complete description of the methods, interpretation of results and validation against measured data are given in Ollinger et al. 1998. (Landscape Ecology 13, pp. 323-334). The area represented is 38 to 48 degrees N and 66 to 77 degrees W. The spatial resolution is 30 arc seconds (approximately 1 km) and grid dimensions are 1320 by 1200 pixels.

Nitrogen and Sulfur Atmospheric Deposition

Atmospheric deposition of nitrogen and sulfur was estimated by combining regional gradients in wet plus dry deposition. For wet deposition, regional patterns of ion concentrations in rainfall were evaluated using 2-11 years of data from 26 National Atmospheric Deposition Program/National Trends Network (NADP/NTN) stations. These patterns were combined with CLIMCALC precipitation estimates to yield gridded estimates of wet deposition amount. For dry deposition, latitude and longitude gradients in air concentrations were evaluated using data from the National Dry Deposition Network (NDDN) and combined with modeled estimates of dry deposition velocities.

For wet deposition, a more than two-fold linear decrease occurs along a longitude gradient from western New York to eastern Maine, suggesting that the dominant sources lie outside the region to the west. In contrast, dry deposition declines along a steep latitude gradient, suggesting more local sources - urban areas across the southern portion of the region. The combination of wet plus dry deposition produces southwest to northeast gradients in total deposition.

Nitrogen deposition is used as an input to the PnET-CN model to determine the effects of N deposition on forest ecosystem function. Sulfur deposition may be added to a future version which adds complete biogeochemical cycles. Deposition rates range from 3.15 to 12.7 kg/ha/yr for nitrogen and from 4.43 to 19.05 kg/ha/yr for sulfur. The fill value is 0. Complete data description can be found in Ollinger et al. 1993 (Ecological Applications 3(3), pp. 459-472) and Ollinger et al. 1995 (USFS, General Technical Report NE-191, Feb 1995). The area represented is 38 to 48 degrees N latitude and 66 to 77 degrees W longitude. The spatial resolution is 30 arc seconds (approximately 1 km), corresponding to grid dimensions of 1320 by 1200 pixels.

Equilibrium N Cycling

N cycling data are from the PnET-CN carbon, water and nitrogen balances model. Data available here reflect spatial trends in maximum, or equilibrium N cycling and not actual N cycling, which depends on the disturbance history of individual sites. Spatial trends were determined by comparing model predictions with summary climate variables. Across hardwood forest types, N cycling was strongly related to patterns of precipitation, suggesting limitations by moisture availability. Among coniferous forests, N cycling followed patterns of growing degree days, suggesting energy limitations. Model parameters are part of the auxiliary data downloaded with the data from EOS-WEBSTER. The min and max values are 2.5 and 10.6 g/m2/yr. The fill value is 0. Complete description can be found in Aber et al. 1997 (Ecological Modelling 101, pp. 61-78, 1997). The area represented is 38 to 48 degrees N latitude and 66 to 77 degrees W longitude. The spatial resolution is approximately 2 km (60 arc sec), corresponding to a grid of 660 x 600 pixels.

Data Providers:

John Aber, Scott Ollinger and Rita Freuder, Complex Systems Research Center, Institute for the Study of Earth, Oceans, and Space, Morse Hall, University of New Hampshire, Durham, New Hampshire, USA. Ph: 603.862.1792, Fax: 603.862.0188, Email: rita.freuder@unh.edu.

Last Data Update:

2/29/2000

Last Doc. Updated:

9/21/2001

Doc. Updated By:

Rita Freuder

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