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Accurate characterization of leaf area index (LAI) is required to quantify the exchange of energy, water, and carbon between terrestrial ecosystems and the atmosphere. The objective of this study was to use a cyclic sampling design to compare the spatial patterns of LAI of the dominant terrestrial ecosystems that comprised the area around the 447-m WLEF television tower, equipped with an eddy flux system, near Park Falls, Wisconsin, USA. A second objective was to compare the efficiency of cyclic, random, and uniform sampling designs in terms of the precision of spatial information derived per unit sampling effort. The vegetation surrounding the tower was comprised (more than 80%) of four major forest cover types: forested wetlands, upland aspen forests, upland northern hardwood forests, and upland pine forests, and a fifth, nonforested cover type, grass (open meadow). LAI differed significantly among the five cover types and averaged 3.45, 3.57, 3.82, 3.99, and 1.14 for northern hardwoods, aspen, forested wetlands, upland conifers, and grass, respectively. The cyclic sampling design maximized information about the variance of vegetation characteristics of the heterogeneous landscape and decreased by 60% the number of plots needed to obtain the same confidence interval width using a random sampling design. The range of spatial autocorrelation for LAI was 147 m, but it was decreased to 117 m when vegetation cover was included as a covariate. The cyclic sampling design has several important advantages over other sampling designs. The cyclic sampling design increased the sampling efficiency by optimizing the placement of plots so they were distributed more efficiently for geostatistical analyses such as semi-variograms, correlograms, and spatial regression and can incorporate covariates (for example, vegetation cover, soil properties, and so on) that may explain the sources of spatial patterns. The cyclic sampling design was used to derive a spatial map of LAI and the average LAI for the 3 × 2 km area centered on the flux tower was 3.51 ± 0.89 (with a minimum of 0 and a maximum of 6.35). Airborne and satellite reflectance data have also been used to characterize LAI, but in this region, and many other forests of the world, remotely sensed vegetation indexes saturate in forests with an LAI greater than 3–5. The cyclic sampling design also provides a general ecological sampling approach that can be used at multiple scales.

The Moderate Resolution Imaging Radiometer (MODIS) is the primary instrument in the NASA Earth Observing System for monitoring the seasonality of global terrestrial vegetation. Estimates of 8-day mean daily gross primary production (GPP) at the 1 km spatial resolution are now operationally produced by the MODIS Land Science Team for the global terrestrial surface using a production efficiency approach. In this study, the 2001 MODIS GPP product was compared with scaled GPP estimates (25 km 2 ) based on ground measurements at two forested sites. The ground-based GPP scaling approach relied on a carbon cycle process model run in a spatially distributed mode. Land cover classification and maximum annual leaf area index, as derived from Landsat ETM+ imagery, were used in model initiation. The model was driven by daily meteorological observations from an eddy covariance flux tower situated at the center of each site. Model simulated GPPs were corroborated with daily GPP estimates from the flux tower. At the hardwood forest site, the MODIS GPP phenology started earlier than was indicated by the scaled GPP, and the summertime GPP from MODIS was generally lower than the scaled GPP values. The fall-off in production at the end of the growing season was similar to the validation data. At the boreal forest site, the GPP phenologies generally agreed because both responded to the strong signal associated with minimum temperature. The midsummer MODIS GPP there was generally higher than the ground-based GPP. The differences between the MODIS GPP products and the ground-based GPPs were driven by differences in the timing of FPAR and the magnitude of light use efficiency as well as by differences in other inputs to the MODIS GPP algorithm—daily incident PAR, minimum temperature, and vapor pressure deficit. Ground-based scaling of GPP has the potential to improve the parameterization of light use efficiency in satellite-based GPP monitoring algorithms.

Forests are an important source for fiber and fuel for humans and contain the majority of the total terrestrial carbon (C). The amount of C stored in the vegetation and soil are strongly influenced by environmental constraints on annual C uptake and decomposition and time since disturbance. Increasing concentrations of atmospheric carbon dioxide (CO2), nitrogen deposition, and climate warming induced by greater greenhouse gas (GHG) concentrations in the atmosphere influence C accumulation rates of forests, but their effects will likely differ in direction and magnitude among forest ecosystems. The net interactive effect of global change on the forest C cycle is poorly understood. The growing demand for wood fiber and fuel by humans and the ongoing anthropogenic perturbations of the climate have changed the natural disturbance regimes (i.e., frequency and intensity); these changes influence the net exchange of CO2 between forests and the atmosphere. To date, the role of forest products in the global C cycle have largely been ignored, and important emissions associated with the production, transport, and utilization of the forest products have been excluded, leading to erroneous conclusions about net C storage in forest products.

Quantifying forest net primary production (NPP) is critical to understanding the global carbon cycle because forests are responsible for a large portion of the total terrestrial NPP. The objectives of this study were to measure above ground NPP (NPPA) for a land surface in northern Wisconsin, examine the spatial patterns of NPPA and its components, and correlate NPPA with vegetation cover types and leaf area index. Mean NPPA for aspen, hardwoods, mixed forest, upland conifers, nonforested wetlands, and forested wetlands was 7.8, 7.2, 5.7, 4.9, 5.0, and 4.5 t dry mass·ha–1·year–1, respectively. There were significant (p = 0.01) spatial patterns in wood, foliage, and understory NPP components and NPPA (p = 0.03) when the vegetation cover type was included in the model. The spatial range estimates for the three NPP components and NPPA differed significantly from each other, suggesting that different factors are influencing the components of NPP. NPPA was significantly correlated with leaf area index (p = 0.01) for the major vegetation cover types. The mean NPPA for the 3 km × 2 km site was 5.8 t dry mass·ha–1·year–1.

Interpretation of elemental balances requires careful assessment of component terms and their errors, especially for the major terms of the nitrogen (N) budget which has implications for environmental health. This study reports results from independent field measurements of major annual N-budget components, including atmospheric deposition, fertilizer added, net mineralization, residue returned, soil storage changes of inorganic N, leaching, and plant uptake. Measurements were made in a restored tallgrass prairie and optimally and deficiently N-fertilized, no-tillage and chisel-plowed maize (Zea mays L.) agroecosystems on Plano silt loam soil (fine-silty, mixed, superactive, mesic Typic Argiudoll (USDA); Haplic Phaeozem (approximate FAO)) in Wisconsin between 1995 and 1999. Denitrification and N losses due to runoff were assumed negligible and bulk density was assumed uniform with depth and across ecosystems. Annual inorganic N leaching was negligible in the restored prairie, but represented 3–57% of the amount of fertilizer-N applied in the optimally N-fertilized agroecosystems. On an annual basis, closure of the inorganic-N budget yielded cumulative errors that were often undesirably large; indicating methodological problems with quantifying ecosystem N cycling in situ. Increased spatial sampling is required to reduce individual measurement errors of two components with large uncertainties; namely net N-mineralization and soil inorganic N changes. Profile-scaled net N-mineralization generally did not balance with the residue N input from the previous year, but the imbalance agreed with the N-budget imbalance. Both results suggest that the prairie is accumulating N slowly, the deficiently N-fertilized maize plots are losing N more rapidly, and the optimally N-fertilized maize plots have too large an uncertainty to be interpreted confidently. Nitrogen-use efficiency, defined on a N-uptake basis, did not differ among the prairie and deficiently N-fertilized maize for 3 out of 5 years, but the prairie was significantly more efficient than the optimally N-fertilized maize.

Black spruce (Picea mariana [Mill.] BSP) is the most dominant forest ecosystem in the North American boreal region. There are at least two contrasting boreal black spruce forest communities: open-canopy black spruce overstory with Sphagnum ground cover (BSSP) and closed-canopy black spruce overstory with feathermoss ground cover (BSFM). The objectives of this study were (a) to compare net primary production (NPP) and light-use efficiency (LUE) for the two contrasting black spruce communities, and (b) to quantify the contribution of different vegetation strata (bryophytes, understory, overstory, and belowground) to total NPP and LUE in a mature black spruce forest stand in central Saskatchewan, Canada.Total NPP for the BSFM community (446 g biomass m -2 y -1 ) was significantly greater (P = 0.04) than the BSSP community (276 g biomass m -2 y -1 ). Bryophyte and under-story NPP together comprised the greatest fraction of total (overstory, understory, bryophytes, and belowground) NPP in the BSSP community (51%), whereas overstory NPP comprised the largest fraction of total NPP (86%) for the BSFM community. Overstory LUE was similar (P = 0.87) for the two communities (0.20-0.21 g MJ -1 annual absorbed photosynthetic active radiation [APAR]), but ecosystem LUE was significantly greater (P = 0.03) for the BSFM community (0.20 g MJ -1 annual APAR) than the BSSP community (0.15 g MJ -1 annual APAR). The results from this study demonstrate that all vegetation components must be measured to accurately estimate NPP and LUE of boreal black spruce ecosystems, and community-specific LUE coefficients increase the accuracy of LUE models.

The objective of this study was to compare the carbon (C) budgets of two similar-aged boreal black spruce (Picea mariana [Mill.] BSP) forest communities: closed-canopy black spruce with feathermoss ground cover (BSFM) on moderately drained soils and open-canopy black spruce with Sphagnum ground cover (BSSP) on poorly drained soils. C content, soil surface carbon dioxide (CO 2 ) flux (R s ), heterotrophic respiration (R H ), net primary production (NPP), and net ecosystem production (NEP) were measured or estimated. The total C content for the two communities (BSFM, 113 Mg C ha -1 ; BSSP, 107 Mg C ha -1 ) did not differ significantly (P = 0.95). However, annual R s was significantly greater (P < 0.0001) for the BSFM (564 g C m -2 y -1 ) than the BSSP (319 g C m -2 y -1 ) community. The greater R H in the BSFM (440 g C m -2 y -1 ) than the BSSP community (264 g C m -2 y -1 ) and the higher peat C content for the BSSP (84 Mg C ha -1 ) than the BSFM (34 Mg C ha -1 ) community provided evidence that the BSSP community had a lower decomposition rate than the BSFM community. NEP was significantly (P = 0.04) more negative for the BSFM community (-222 ± 35 g C m -2 y -1 ) than the BSSP community (-128 ± 14 g C m -2 y -1 ), but both communities were C sources to the atmosphere. The results from this study illustrate the influence of small differences in edaphic conditions on ecosystem C accumulation.

Aboveground net primary productivity (ANPP) and soil and vegetation nutrient concentrations were measured in pole-sized northern hardwood and aspen forests to quantify the potential for various nutrient amendments to increase tree growth, as well as potential deleterious effects on vegetation. Four blocks were installed in each forest type containing the following treatments: control, N+Ca+Mg+K+P+S (complete), wood-fired boiler ash (ash), N+wood-fired boiler ash (N+ash), and two rates of paper mill sludge (sludge and 2× sludge). The northern hardwood forests had three additional treatments: N, Ca+Mg+K (base cations), and N+Ca+Mg+K (N+base cations). Fertilizer treatments were designed to provide N at a rate of 100 kg ha−1. Other nutrients were applied in proportion to N so that N, P, K, S, Mg, and Ca were applied at a ratio of 100:50:33:9:5:4, respectively. Total ANPP was not significantly different among treatments for the maple stands, but plots treated with wood ash were 10% greater than controls. ANPP was greater in 1998 and 1999 for aspen plots receiving N+ash, but results were only statistically significant (p=0.013) in 1999. Basal area differed by 40–60% among experimental plots within any given block and was positively correlated to wood increment. Wood increment, adjusted for basal area, did not differ significantly among treatments for the aspen stands, but the N+ash treatment was 30% greater than the control. A two-way factorial comparison indicated that ash had a significant (p=0.024) positive effect on wood increment and N had a significant (p=0.044) negative effect on wood increment for the maple stands. Tree growth was not correlated to foliar nutrient concentrations, but ratios of K to other elements (K:Ca, K:Mg, K:N, and K:P) were highest, on average, for wood ash plots. These differences were not statistically significant with the exception of K:N for the aspen stands and K:Ca for the maple stands. We did not observe any beneficial effects of paper mill sludge on forest growth, but there was some evidence that wood ash increased annual wood production.

Empirical models are important tools for relating field-measured biophysical variables to remote sensing data. Regression analysis has been a popular empirical method of linking these two types of data to provide continuous estimates for variables such as biomass, percent woody canopy cover, and leaf area index (LAI). Traditional methods of regression are not sufficient when resulting biophysical surfaces derived from remote sensing are subsequently used to drive ecosystem process models. Most regression analyses in remote sensing rely on a single spectral vegetation index (SVI) based on red and near-infrared reflectance from a single date of imagery. There are compelling reasons for utilizing greater spectral dimensionality, and for including SVIs from multiple dates in a regression analysis. Moreover, when including multiple SVIs and/or dates, it is useful to integrate these into a single index for regression modeling. Selection of an appropriate regression model, use of multiple SVIs from multiple dates of imagery as predictor variables, and employment of canonical correlation analysis (CCA) to integrate these multiple indices into a single index represent a significant strategic improvement over existing uses of regression analysis in remote sensing. To demonstrate this improved strategy, we compared three different types of regression models to predict LAI for an agro-ecosystem and live tree canopy cover for a needleleaf evergreen boreal forest: traditional (Yon X) ordinary least squares (OLS) regression, inverse (X on Y) OLS regression, and an orthogonal regression method called reduced major axis (RMA). Each model incorporated multiple SVIs from multiple dates and CCA was used to integrate these. For a given dataset, the three regression-modeling approaches produced identical coefficients of determination and intercepts, but different slopes, giving rise to divergent predictive characteristics. The traditional approach yielded the lowest root mean square error (RMSE), but the variance in the predictions was lower than the variance in the observed dataset. The inverse method had the highest RMSE and the variance was inflated relative to the variance of the observed dataset. RMA provided an intermediate set of predictions in terms of the RMSE, and the variance in the observations was preserved in the predictions. These results are predictable from regression theory, but that theory has been essentially ignored within the discipline of remote sensing. D 2002 Elsevier Science Inc. All rights reserved.

We examined physiological parameter tradeoffs in modeling stomatal control of transpiration from a number of forest species. Measurements of sapflux, micrometeorology, and leaf area index were made in stands representing 85% of the forest ecosystems around the WLEF eddy flux tower in northern Wisconsin. A Jarvis-based canopy conductance model was used to simulate canopy transpiration (EC) for five tree species from these stands. They consisted of conifers and deciduous species in both upland and wetland locations. Parameter estimation was used to assess the tradeoffs between physiological parameters used in the calculation of stomatal conductance. These tradeoffs were then evaluated against current theory on stomatal regulation of leaf water potential. The results showthat the best simulations of EC were obtained with values of maximum stomatal conductance (gSmax) and stomatal sensitivity to vapor pressure deficit (d) that closely followed this hydraulic theory. The model predictions reveal a large variation in the strategies used to regulate water potential among species. Aspen showed the greatest tendency towards efficiency, indicating that it has high EC under lowvapor pressure deficit ( D) conditions, but is susceptible to rapid EC decline at moderate to high D. Other species showed more conservative water use. The results indicate that inter-specific differences in dynamic response to D can produce large spatial variation in EC under typical environmental conditions. 2002 Elsevier Science Ltd. All rights reserved.

Knowledge of foliar surface area is important in many fields, but estimating the area of nonflat conifer needles is difficult. The primary goal of this study was to use optical scanning and immersion methods to test and refine the standard cross-sectional geometries assumed for black spruce (Picea mariana (Mill.) BSP) and jack pine (Pinus banksiana Lamb.) needles. Projected leaf area (PLA, measured using a flatbed scanner), and hemisurface leaf area (HSLA, estimated from water immersion) were compared for conifer samples from a 37-year-old even-aged stand in northern Manitoba, Canada. The HSLA–PLA relationship was used to infer information about needle cross-sectional geometry after assuming a basic form (rhombus for black spruce and hemiellipse for jack pine). The cross section of black spruce needles was best approximated as a rhombus with a major/minor diagonal ratio of 1.35. Jack pine needles were best described by a hemiellipse with major/minor axis ratio of 1.30. Minor but incorrect assumptions of needle cross-sectional geometry resulted in foliar area errors of 6–8% using scanning methods and 1–2% using immersion methods. Simple equations are presented to calculate hemisurface needle area from volume or projected needle area based on these refined parameters.

Nitrogen (N) mineralization is a spatially variable and difficult component of the N cycle to quantify accurately under field conditions. Net N-mineralization was compared by direct measurement, indirect estimate, and laboratory incubation for a restored tallgrass prairie and for deficiently and optimally N-fertilized, no-tillage (NT) and chisel-plowed (CP) maize (Zea mays L.) agroecosystems on Plano silt loam soil (fine-silty, mixed, superactive, mesic Typic Argiudoll) in Wisconsin, USA. Four years of in-situ field measurements using an incubated-soil-core/ion-exchange-resin-bag technique showed that land use significantly affected net N-mineralization. Net N-mineralization was consistently smaller in the restored prairie than in the maize agroecosystems and typically larger in the CP than in the NT maize agroecosystems. Three independent methods for indirectly estimating annual net N-mineralization (i.e., N budget residual, deficiently N-fertilized plant N uptake, and profile-scaled in-situ field measurements) were relatively consistent at capturing land-use and tillage effects on net N-mineralization. Laboratory incubation and periodic leaching of Fall-sampled soils demonstrated that both mineralized N and labile C were co-limiting factors influencing N-mineralization in agricultural soils and generally supported field measurements by showing a significant difference in net N-mineralization with and without added fertilizer-N.

Forest management presents challenges to accurate prediction of water and carbon exchange between the land surface and atmosphere, due to its alteration of forest structure and composition. We examined how forest species types in northern Wisconsin affect landscape scale water fluxes predicted from models driven by remotely sensed forest classification. A site-specific classification was developed for the study site. Using this information and a digital soils database produced for the site we identified four key forest stand types: red pine, northern hardwoods, aspen, and forested wetland. Within these stand types, 64 trees representing 7 species were continuously monitored with sap flux sensors. Scaled stand-level transpiration from sap flux was combined with a two-source soil evaporation model and then applied over a 2.5 km × 3.0 km area around the WLEF AmeriFlux tower (Park Falls, Wisconsin) to estimate evapotranspiration. Water flux data at the tower was used as a check against these estimates. Then, experiments were conducted to determine the effects of aggregating vegetation types to International Geosphere– Biosphere Program (IGBP) level on water flux predictions. Taxonomic aggregation resulting in loss of species level information significantly altered landscape water flux predictions. However, daily water fluxes were not significantly affected by spatial aggregation when forested wetland evaporation was included. The results demonstrate the importance of aspen, which has a higher transpiration rate per unit leaf area than other forest species. However, more significant uncertainty results from not including forested wetland with its high rates of evaporation during wet summers.

Specific leaf area (SLA) and leaf area index (LAI) were estimated using site-specific allometric equations for a boreal black spruce (Picea mariana (Mill.) BSP) fire chronosequence in northern Manitoba, Canada. Stands ranged from 3 to 131 years in age and had soils that were categorized as well or poorly drained. The goals of the study were to: (i) measure SLA for the dominant tree and understory species of boreal black spruce-dominated stands, and examine the effect of various biophysical conditions on SLA; and (ii) examine leaf area dynamics of both understory and overstory for well- and poorly drained stands in the chronosequence. Overall, average SLA values for black spruce (n = 215), jack pine (Pinus banksiana Lamb., n = 72) and trembling aspen (Populus tremuloides Michx., n = 27) were 5.82 +/- 1.91, 5.76 +/- 1.91 and 17.42 +/- 2.21 m2 x kg-1, respectively. Foliage age, stand age, vertical position in the canopy and soil drainage had significant effects on SLA. Black spruce dominated overstory LAI in the older stands. Well-drained stands had significantly higher overstory LAI (P0.001), but lower understory LAI (P = 0.022), than poorly drained stands. Overstory LAI was negligible in the recent (3-12 years old) burn sites and highest in the 70-year-old burn site (6.8 and 3.0 in the well- and poorly drained stands, respectively), declining significantly (by 30-50%) from this peak in the oldest stands. Understory leaf area represented a significant portion (40%) of total leaf area in all stands except the oldest.

Carbon dioxide flux from coarse woody debris (CWD) is an important source of CO2 in forests with moderate to large amounts of CWD. A process-based understanding of environmental controls on CWD CO2 flux (RCWD) is needed to accurately model carbon exchange between forests and the atmosphere. The objectives of this study were to: (1) use a laboratory incubation factorial experiment to quantify the effect of temperature (TCWD), water content (WC), decay status, and their interactions on RCWD for black spruce [Picea mariana (Mill.) BSP] CWD; (2) measure and model spatial and temporal dynamics in TCWD for a boreal black spruce fire chronosequence; and (3) validate the RCWD model with field measurements, and quantify potential errors in estimating annual RCWD from this model on various time steps. The RCWD was positively correlated to TCWD (R2=0.37, P

Midwestern grasslands have undergone dramatic changes in land use and management practices, but the effects of these changes on terrestrial carbon budgets are poorly understood. This study compared, for five years, the effects of land-use type on components of the carbon (C) budget (above- and belowground net primary production [NPP], C leaching, soil surface CO2 flux, vegetation and soil C contents, and C export from burning and grain removal) of a restored tallgrass prairie and maize agroecosystems on a silt loam soil. Interannual variation of the C budget was addressed by correlating annual fluctuations of environmental variables and soil properties with C-budget components. The C losses we estimated, in order of increasing magnitude, were C leaching, grain C removal from the maize agroecosystems, and soil surface CO2 flux. NPP was significantly greater for N-fertilized maize (10.4 Mg C·ha−1·yr−1) than unfertilized maize agroecosystems (6.2 Mg C·ha−1·yr−1), and both were significantly greater than rest...

Allometric equations were developed relating aboveground biomass, coarse root biomass, and sapwood area to stem diameter at 17 study sites located in the boreal forests near Thompson, Man. The six species studied were trembling aspen (Populus tremuloides Michx.), paper birch (Betula papyrifera Marsh.), black spruce (Picea mariana (Mill.) BSP), jack pine (Pinus banksiana Lamb.), tamarack (Larix laricina (Du Roi) Koch.), and willow (Salix spp.). Stands ranged in age from 4 to 130 years and were categorized as well or poorly drained. Stem diameter ranged from 0.1 to 23.7 cm. Stem diameter was measured at both the soil surface (D0) and breast height (DBH). The relationship between biomass and diameter, fitted on a log–log scale, changed significantly at ~3 cm DBH, suggesting that allometry differed between saplings and older trees. To eliminate this nonlinearity, a model of form log10 Y = a + b(log10 D) + c(AGE) + d(log10 D × AGE) was used, where D is stem diameter, AGE is stand age, and the cross product is the interaction between diameter and age. Most aboveground biomass equations (N = 326) exhibited excellent fits (R2 > 0.95). Coarse root biomass equations (N = 205) exhibited good fits (R2 > 0.90). Both D0 and DBH were excellent (R2 > 0.95) sapwood area predictors (N = 413). Faster growing species had significantly higher ratios of sapwood area to stem area than did slower growing species. Nonlinear aspects of some of the pooled biomass equations serve as a caution against extrapolating allometric equations beyond the original sample diameter range.

Prescribed burning recycles essential plant nutrients and stimulates growth in prairie restoration. While reducing the content of nutrients in dry matter, prescribed burning may also alter the spatial variability and distribution of nutrients, which in turn could negatively impact long-term productivity. A study was conducted in a tallgrass prairie restoration at the Audubon Society's Goose Pond Sanctuary near Arlington, Wisconsin to characterize the content and spatial variability and distribution of macro- (i.e., N, C, P, K, Ca, Mg and S) and micro-nutrients (i.e., Zn, B, Mn, Cu, Fe, Al and Na) in the aboveground litter before burning and in the ash after burning following 3- and 6-y burn intervals. Aboveground litter mass was significantly higher in 2001 after the 3-y burn interval than in 1998 after the 6-y burn interval. The amount of preburn litter was consistently reduced by >90% for both burn intervals, but the reduction of dry matter and the reductions in mass of N, C, P, K and S were significantly higher in 2001 than in 1998. The 6-y burn interval resulted in nutrient export that was similar to nutrient inputs from atmospheric wet deposition, whereas the 3-y burn interval resulted in the export of N, K, Ca and Mg faster than they were replenished. Prescribed burning significantly affected the spatial variability of dry matter and the concentration and content of most macro- and micronutrients. However, prescribed burning had little effect on the pre- and postburn spatial distributions of macro- and micro-nutrient masses, which were similar to pre- and postburn spatial distributions of litter and ash masses, except for Fe and Al which had atypically large concentration variances.

Light use efficiency (LUE) algorithms are a potentially effective approach to monitoring global net primary production (NPP) using satellite-borne sensors such as the Moderate Resolution Imaging Spectroradiometer (MODIS). However, these algorithms are applied at relatively coarse spatial resolutions ( � 1 km), which may subsume significant heterogeneity in vegetation LUE (en, gM J � 1 ) and, hence, introduce error. To examine the effects of spatial heterogeneity on a LUE algorithm, imagery from the Advanced Very High Resolution Radiometer (AVHRR) at � 1-km resolution was used to implement a LUE approach for NPP estimation over a 25-km 2 area of corn (Zea mays L.) and soybean (Glycine max Merr.) in central Illinois, USA. Results from several en formulations were compared with a NPP reference surface based on measured NPPs and a high spatial resolution land cover surface derived from Landsat ETM+. Determination of en based on measurements of biomass production and monitoring of absorbed photosynthetically active radiation (APAR) revealed that en of soybean was 68% of that for corn. When a LUE algorithm for estimating NPP was implemented in the study area using the assumption of homogeneous cropland and the en for corn, the estimate for total biomass production was 126% of that from the NPP reference surface. Because of counteracting errors, total biomass production using the soybean en was closer (86%) to that from the NPP reference surface. Retention of high spatial resolution land cover to assign en resulted in a total NPP very similar to the reference NPP because differences in leaf phenology between the crop types were small except early in the growing season. These results suggest several alternative approaches to accounting for land cover heterogeneity in en when implementing LUE algorithms at coarse resolution. D 2002 Elsevier Science Inc. All rights reserved.

The three objectives of this paper were: to summarize net primary production (NPP) and carbon allocation patterns for boreal forests, to examine relationships between climatic and biological variables and NPP, and to examine carbon allocation coefficients for all boreal forests or types of boreal forests that can be used to estimate NPP from easily measured components of NPP. Twenty-four Class I stands (complete NPP budgets) and 45 Class II boreal forest stands (aboveground NPP [NPPA] and budget only) were identified. The geographic distribution of the Class I stands was not uniform; 46% of the stands were from two studies in North America, and only one stand was from the important larch forests of Eurasia. Total (above- and belowground) net primary production (NPPT) ranged from 52 to 868 g C·m−2·yr−1 and averaged 424 g C·m−2·yr−1. NPPA was consistently larger for deciduous than for evergreen boreal forests in each of the major boreal regions, especially for boreal forests in Alaska. Belowground net prima...

Boreal black spruce forests typically have a dense ground cover of bryophytes. The two main bryophyte groups in boreal black spruce forests, feathermoss and Sphagnum, have ecophysiological characteristics that influence the biogeochemical cycles of black spruce forests differently. The objective of this study was to examine the environmental controls of ground cover composition and net primary production (NPP) of feathermoss and Sphagnum in a boreal black spruce forest in central Saskatchewan. The fraction of Sphagnum ground cover was positively correlated to canopy photosynthetically active radiation (PAR) transmittance (r2=0.48, P=0.03), but the fraction of feathermoss ground cover was negatively correlated to canopy PAR transmittance in plots where Sphagnum was present (r2=0.87, P

The boreal larch forest of Eurasia is a widespread forest ecosystem and plays an important role in the carbon budget of boreal forests. However, few carbon budgets exist for these forests, and the effects of wildfire, the dominant natural disturbance in this region, on carbon budgets are poorly understood. The objective of this study was to quantify the effects of wildfire on carbon distribution and net primary production (NPP) for three major Dahurian larch (Larix gmelinii Rupr.) forest ecosystems in Tahe, Daxing’anling, north-eastern China: Larix gmelinii‐Ledum palustre, Larix gmelinii‐grass and Larix gmelinii‐Rhododendron dahurica forests. The experimental design included mature forests (unburned), and lightly and heavily burned forests from the 1.3-million-ha 1987 wildfire. We measured carbon distribution and above-ground NPP, and estimated fine root production from literature values. Total ecosystem carbon content for the mature forests was greatest for Larix‐ Ledum forests (251.4 t C ha ‐1 ) and smallest for Larix‐grass forests (123.8 t C ha ‐1 ). Larix‐Ledum forests contained the smallest vegetation carbon (13.5%), while Larix‐Rhododendron contained the largest vegetation carbon (63.1%). Fires tended to transfer carbon from vegetation to detritus and soil. Total NPP did not differ significantly between the lightly burned and unburned stands, and averaged 1.58, 1.29 and 1.01 t C ha ‐1 year ‐1 for Larix‐grass, Larix‐Rhododendron and Larix‐Ledum lightly burned stands, respectively. Above-ground net primary production (ANPP) of heavily burned stands was 92‐95% less than unburned and lightly burned stands. The estimated carbon loss during the 1987 fire showed substantial variability among forest types and fire severity levels. Depending upon the assumptions made about the fraction of the landscape occupied by the three larch forest types, the 1987 conflagration in north-east China released 2.5 3 10 7 ‐ 4.9 3 10 7 t C to the atmosphere. This study illustrates the need to distinguish

Landmanagement practices such as no-tillage agriculture and tallgrass prairie restoration have been proposed as a possible means to sequester atmospheric carbon, helping to refurbish soil fertility and replenish organic matter lost as a result of previous agricultural management practices. However, the relationship between land-use changes and ecosystem structure and functioning is not yet understood. We studied soil and vegetation properties over a 4-year period (1995–98), and assembled measurements of microbial biomass, soil organic carbon (SOC) and nitrogen (N), N-mineralization, soil surface carbon dioxide (CO2) flux, and leached C and N in managed (maize; Zea mays L.) and natural (prairie) ecosystems near the University of Wisconsin Agricultural Research Station at Arlington. Field data show that different management practices (tillage and fertilization) and ecosystem type (prairie vs maize) have a profound influence on biogeochemistry and water budgets between sites. These measurements were used in conjunction with a dynamic terrestrial ecosystem model, called IBIS (the Integrated Biosphere Simulator), to examine the long-term effects of land-use changes on biogeochemical cycling. Field data and modeling suggest that agricultural land management near Arlington between 1860 and 1950 caused SOC to be depleted by as much as 63% (native SOC approximately 25.1 kg C m−2). Reductions in N-mineralization and microbial biomass were also observed. Although IBIS simulations depict SOC recovery in no-tillage maize since the 1950s and also in the Arlington prairie since its restoration was initiated in 1976, field data suggest otherwise for the prairie. This restoration appears to have done little to increase SOC over the past 24 years. Measurements show that this prairie contained between 28% and 42% less SOC (in the top 1 m) than the no-tillage maize plots and 40%–47% less than simulated potential SOC for the site in 1999. Because IBIS simulates competition between C3 and C4 grass species, we hypothesized that current restored prairies, which include many forbs not characterized by the model, could be less capable of sequestering C than agricultural land planted entirely in monocultural grass in this region. Model output and field measurements show a potential 0.4 kg C m−2 y−1 difference in prairie net primary production (NPP). This study indicates that high-productivity C4 grasslands (NPP = 0.63 kg C m−2 y−1) and high-yield maize agroecosystems (10 Mg ha−1) have the potential to sequester C at a rate of 74.5 g C m−2 y−1 and 86.3 g C m−2 y−1, respectively, during the next 50 years across southern Wisconsin.

The drainage of water and leaching of dissolved constituents represent major components of agroecosystem mass budgets that have been exceedingly difficult to measure. Equilibrium-tension lysimeters (ETLs) were used to monitor drainage, nitrogen (N), and carbon (C) leaching through Piano silt loam (fine-silty, mixed, superactive, mesic Typic Argiudoll) for a 4-yr period in a restored prairie and N-fertilized no-tillage and chisel-plowed maize (Zea mays L.) agroecosystems. Mean drainage recorded during 4 yr for the prairie, no-tillage, and chisel-plowed ecosystems totaled 461, 1116, and 1575 mm and represented 16, 33, and 47% of precipitation plus melting of drifted snow received, respectively. Total inorganic N leaching losses during the 4-yr period for the prairie, no-tillage, and chisel-plowed ecosystems were 0.6, 201, and 179 kg N ha -1 , respectively. Inorganic N leaching represented 26 and 24% of applied fertilizer N additions to the no-tillage and chisel-plowed agroecosystems. Total dissolved C leaching losses were 119, 435, and 502 kg C ha -1 for the prairie, no-tillage, and chisel-plowed ecosystems, respectively. Sufficient dissolved organic carbon (DOC) and nitrate N (NO 3 - -N) existed in the prairie and agroecosystems to support subsoil denitrification. Potential denitrification, however, was limited by insufficient lengths of saturated soil conditions in all three ecosystems, the supply of DOC in the agroecosystems, and the supply of nitrate N in the prairie. Based on available DOC and nitrate N, the maximum contribution of denitrification below the root zone in the agroecosystems was less than 25% of the total amount of leached nitrate N and the probable contribution of denitrification was much less.

To reconcile observations of decomposition rates, carbon inventories, and net primary production (NPP), we estimated long-term averages for C exchange in boreal forests near Thompson, Manitoba. Soil drainage as defined by water table, moss cover, and permafrost dynamics, is the dominant control on direct fire emissions. In upland forests, an average of about 10-30% of annual NPP was likely consumed by fire over the past 6500 years since these landforms and ecosystems were established. This long-term, average fire emission is much larger than has been accounted for in global C cycle models and may forecast an increase in fire activity for this region. While over decadal to century times these boreal forests may be acting as slight net sinks for C from the atmosphere to land, periods of drought and severe fire activity may result in net sources of C from these systems.

While a new class of Dynamic Global Ecosystem Models (DGEMs) has emerged in the past few years as an important tool for describing global biogeochemical cycles and atmosphere-biosphere interactions, these models are still largely untested. Here we analyze the behavior of a new DGEM and compare the results to global-scale observations of water balance, carbon balance, and vegetation structure. In this study, we use version 2 of the Integrated Biosphere Simulator (IBIS), which includes several major improvements and additions to the prototype model developed by Foley et al. [1996]. IBIS is designed to be a comprehensive model of the terrestrial biosphere; the model represents a wide range of processes, including land surface physics, canopy physiology, plant phenology, vegetation dynamics and competition, and carbon and nutrient cycling. The model generates global simulations of the surface water balance (e.g., runoff), the terrestrial carbon balance (e.g., net primary production, net ecosystem exchange, soil carbon, aboveground and belowground litter, and soil CO2 fluxes), and vegetation structure (e.g., biomass, leaf area index, and vegetation composition). In order to test the performance of the model, we have assembled a wide range of continental and global-scale data, including measurements of river discharge, net primary production, vegetation structure, root biomass, soil carbon, litter carbon, and soil CO2 flux. Using these field data and model results for the contemporary biosphere (1965–1994), our evaluation shows that simulated patterns of runoff, NPP, biomass, leaf area index, soil carbon, and total soil CO2 flux agree reasonably well with measurements that have been compiled from numerous ecosystems. These results also compare favorably to other global model results.

1. We compared leaf-level carbon, nitrogen and water use for a deciduous (Larix occidentalis Nutt.) and sympatric evergreen (Pseudotsuga menziesii, Beissn., Franco, or Pinus contorta Engelm.) conifer along a resource availability gradient spanning the natural range of L. occidentalis in western Montana, USA. 2. We hypothesized that leaf photosynthesis (A), respiration (r), specific leaf area (SLA) and foliar nitrogen concentration (N) would be higher for deciduous than sympatric evergreen conifers in mixed stands, and that these interspecies differences would increase from high to low resource availability. We also hypothesized that leaf-level nitrogen and water-use efficiency would be higher for the co-occurring evergreen conifer than L. occidentalis. 3. In general, mass-based photosynthesis (Am) was significantly higher for L. occidentalis than co-occurring evergreen conifers in the drier sites, but Am was similar for evergreen and deciduous conifers at the mesic site. 4. Mass-based foliar nitrogen concentration (Nm) was positively correlated to SLA for all species combined across the gradient (R2 = 0·64), but the relationship was very weak (R2 = 0·08–0·34) for evergreen and deciduous species separately. Mass-based Am and rm were poorly correlated to Nm for all species combined across the gradient (R2 = 0·28 and 0·04, respectively). 5. For each site-species combination, daily maximum Am was negatively correlated to vapour pressure deficit (VPD) (R2 = 0·36–0·59), but was poorly correlated to twig predawn water potential (R2

To examine the linkage between forest cover type, litter inputs, and patterns of net N mineralization versus the turnover of N among soil microbes, we measured both the net and gross rates of N mineralization in replicated, adjacent old-growth eastern hemlock [Tsuga canadensis(L.) Carr.] or sugar maple (Acer saccharum Marsh.) stands in upper Michigan. Mean aboveground net primary production and annual litterfall mass were significantly higher (P 0.10) between the two forest types. In situ gross rates of N mineralization were higher (P < 0.06) in the maple forests than in the hemlock forests (7.5 and 6.1 mg N·kg soil-1·d-1 respectively), but in situ net N mineralization varied independently of forest type and stand-level litterfall N concentration. Cover type–dependent differences in detritus production and detritus C quality appear to result in different N turnover rates, but the balance between gross mineralization and immobilization of N is very sensitive to within stand variability and varies at a scale smaller than cover type alone can predict.

Understanding terrestrial carbon metabolism is critical because terrestrial ecosystems play a major role in the global carbon cycle. Furthermore, humans have severely disrupted the carbon cycle in ways that will alter the climate system and directly affect terrestrial metabolism. Changes in terrestrial metabolism may well be as important an indicator of global change as the changing temperature signal. Improving our understanding of the carbon cycle at various spatial and temporal scales will require the integration of multiple, complementary and independent methods that are used by different research communities. Tools such as air sampling networks, inverse numerical methods, and satellite data (top-down approaches) allow us to study the strength and location of the global- and continental-scale carbon sources and sinks. Bottom-up studies provide estimates of carbon fluxes at finer spatial scales and examine the mechanisms that control fluxes at the ecosystem, landscape, and regional scales. Bottom-up approaches include comparative and process studies (for example, ecosystem manipulative experiments) that provide the necessary mechanistic information to develop and validate terrestrial biospheric models. An iteration and reiteration of top-down and bottom-up approaches will be necessary to help constrain measurements at various scales. We propose a major international effort to coordinate and lead research programs of global scope of the carbon cycle.

Annual monitoring of water-budget components is useful for comparing the fate of water inputs among ecosystems. Land-use changes from natural prairies to managed agroecosystems alter water-budget components. Weekly hydrological budgets for a restored natural prairie and maize (Zea mays L.) agroecosystems (no-tillage and chisel-plow) were constructed for 132 consecutive wk between June 1995 and January 1998. Precipitation, drainage, soil water-storage changes, and snow-cover changes were measured on Plano silt loam soil (fine-silty, mixed, superactive, mesic Typic Argiudoll) at agricultural and prairie sites. Compared with the maize ecosystems, the prairie maintained greater soil water contents deeper in the soil profile (0.8-1.4 m), somewhat larger evapotranspiration (Et), and significantly less drainage because of considerable interception of precipitation by a residue layer. Soil water storage in the no-tillage maize setting was more similar to the prairie, while Et, net primary productivity, and drainage were more comparable to the chisel-plow agroecosystem. Total drainage measured with equilibrium-tension lysimeters was 199 mm of water (coefficient of variation [CV] = 5.7%) for the prairie ecosystem, 563 mm of water (CV = 13.6%) for the no-tillage maize ecosystem, and 793 mm of water (CV = 18.5%) for the chisel-plow maize ecosystem. Residue interception for the prairie was 477 mm, compared with 681 mm of precipitation during the growing senson of 1997, which contributed to lower prairie drainage. The combination of similar productivity, higher soil water contents, and less drainage than the chisel-plow ecosystem suggests that a no-tillage ecosystem is more sustainable than the chisel-plow agroecosystem in terms of reducing potential adverse environmental impacts associated with soil water movement.

Accurate monitoring of global scale changes in the terrestrial biosphere has become acutely important as the scope of human impacts on biological systems and atmospheric chemistry grows. For example, the Kyoto Protocol of 1997 signals some of the dramatic socioeconomic and political decisions that may lie ahead concerning CO2 emissions and global carbon cycle impacts. These decisions will rely heavily on accurate measures of global biospheric changes Schimel 1998 , IGBP TCWG 1998 . An array of national and international programs have inaugurated global satellite observations, critical field measurements of carbon and water fluxes, and global model development for the purposes of beginning to monitor the biosphere. The detection by these programs of interannual variability of ecosystem fluxes and of longer term trends will permit early indication of fundamental biospheric changes which might otherwise go undetected until major biome conversion begins. This article describes a blueprint for more comprehensive coordination of the various flux measurement and modeling activities into a global terrestrial monitoring network that will have direct relevance to the political decision making of global change.

A primary objective of the Earth Observing System (EOS) is to develop and validate algorithms to estimate leaf area index (L), fraction of absorbed photosynthetically active radiation (fAPAR), and net primary production (NPP) from remotely sensed products. These three products are important because they relate to or are components of the metabolism of the biosphere and can be determined for terrestrial ecosystems from satellite-borne sensors. The importance of these products in the EOS program necessitates the need to use standard methods to obtain accurate ground truth estimates of L, fAPAR, and NPP that are correlated to satellite-derived estimates. The objective of this article is to review direct and indirect methods used to estimate L, fAPAR, and NPP in terrestrial ecosystems. Direct estimates of L, biomass, and NPP can be obtained by harvesting individual plants, developing allometric equations, and applying these equations to all individuals in the stand. Using non-site-specific allometric equations to estimate L and foliage production can cause large errors because carbon allocation to foliage is influenced by numerous environmental and ecological factors. All of the optical instruments that indirectly estimate L actually estimate “effective” leaf area index (LE) and underestimate L when foliage in the canopy is nonrandomly distributed (i.e., clumped). We discuss several methods, ranging from simple to complex in terms of data needs, that can be used to correct estimates of L when foliage is clumped. Direct estimates of above-ground and below-ground net primary production (NPPA and NPPB, respectively) are laborious, expensive and can only be carried out for small plots, yet there is a great need to obtain global estimates of NPP. Process models, driven by remotely sensed input parameters, are useful tools to examine the influence of global change on the metabolism of terrestrial ecosystems, but an incomplete understanding of carbon allocation continues to hamper development of more accurate NPP models. We summarize carbon allocation patterns for major terrestrial biomes and discuss emerging allocation patterns that can be incorporated into global NPP models. One common process model, light use efficiency or epsilon model, uses remotely sensed fAPAR, light use efficiency (LUE) and carbon allocation coefficients, and other meteorological data to estimates NPP. Such models require reliable estimates of LUE. We summarize the literature and provide LUE coefficients for the major biomes, being careful to correct for inconsistencies in radiation, dry matter and carbon allocation units.

It has been suggested that a feedback exists between the vegetation and soil whereby fertile (vs infertile) sites support species with shorter leaf life spans and higher quality litter which promotes rapid decomposition and higher soil nutrient availability. The objectives of this study were to (1) characterize and compare the C and N dynamics of dominant upland forest ecosystems in north central Wisconsin, (2) compare the nutrient use efficiency (NUE) of these forests, and (3) examine the relationship between NUE and site characteristics. Analyzing data from 24 stands spanning a moisture / nutrient gradient, we found that resource-poor stands transferred less C and N from the vegetation to the forest floor, and that N remained in the forest floor at least four times longer than in more resource-rich stands. Analyzing data by leaf habit, we found that less N was transferred to the forest floor annually via litterfall in conifer stands, and that N remained in the forest floor of these stands nearly three times longer than in hardwood stands. NUE did not differ among forests with different resource availabilities, but was greater for conifers than for hardwoods. Vitousek's (1982) index of nutrient use efficiency (INUE1 = leaf litterfall biomass / leaf litterfall N) was most closely correlated to litterfall specific leaf area and percent hardwood leaf area index, suggesting that differences in species composition may have been responsible for the differences in NUE among our stands. NUE2, defined as ANPP / leaf litterfall N, was not closely correlated to any of the site characteristics included in this analysis.

An equilibrium tension lysimeter (ETL) was designed to maintain equilibrium between lysimeter suction and soil matric potential. Equilibrium tension lysimeter replicates were installed in a natural prairie, and N-fertilized no-tillage and chisel-plow agroecosystems to measure drainage through undisturbed soil. The ETLs were used to monitor drainage continuously at 1,4 m below the soil surface through a 0.2-μm pore diameter stainless steel porous plate (0.19 m 2 ). Heat dissipation sensors were used to record variations in matric potential inside and outside the ETL's sampling area. Suction was maintained on lysimeters according to the matric potential experienced by the surrounding bulk soil. Cumulative lysimeter drainage was 199, 563, and 793 mm for the prairie, fertilized no-tillage, and fertilized chisel-plow agroecosystems for 132 wk between 25 June 1995 and 3 Jan. 1998. Drainage accounted for 11, 31, and 44% of precipitation inputs for the prairie, fertilized no-tillage, and fertilized chisel plow systems. Variability between lysimeter replicates was smallest for the prairie, where the coefficient of variation (CV) was 8.2%, and largest for the N-fertilized no-tillage agroecosystem (CV = 36.6%).

Many of the native prairies in southern Wisconsin, and the midwestern United States in general, have been replaced by conventional till (chisel plow) and no-tillage corn agroecosystems. However, knowledge of the influence of land use change on the structure and function of ecosystems is incomplete. Soil surface CO 2 flux is a major transfer of carbon from terrestrial ecosystems to the atmosphere and varies greatly among vegetation types. We measured soil surface CO 2 flux and microbial biomass in tilled and no-till corn agroecosystems and a restored prairie ecosystem, examined the influence of various environmental factors on soil surface CO 2 flux in these ecosystems, and estimated annual soil surface CO 2 flux for the natural and managed ecosystems. Soil surface CO 2 flux is significantly greater for prairie and conventional tilled corn than for no-till corn in the spring, greater for prairie than tilled and no-till corn from July to early October, and is similar for all three ecosystems in the late fall and winter. Soil surface CO 2 flux is positively correlated to soil temperature at 10 cm for all three ecosystems ( r 2 =0.43–0.60, P 2 flux from 10 cm soil temperatures, we estimate annual soil surface CO 2 fluxes of 508, 535 and 719 (g C m −2 y −1 ) for the tilled and no-till corn and restored prairie ecosystems, respectively, demonstrating that land use practices significantly affect soil surface CO 2 flux.

We compared the species composition, structure and selected components of the carbon (C) and nitrogen (N) budgets of similar-aged, mature boreal jack pine (Pinus banksiana Lamb.) forests with and without green alder [Alnus crispa (Ait.) Pursh.] in two different boreal environments. The C and N content of the overstory biomass components (for example, stem, branch, and foliage), total vegetation, forest floor, and mineral soil were greater (P= 0.05 to P= 0.10) for jack pine with alder (JPA) stands than for jack pine without alder (JP) stands at both study areas. Jack pine foliage N isotopic discrimination (δ15N) and annual litterfall N content were significantly greater (P < 0.05) in the JPA than the JP stands at both study areas, suggesting that alder was fixing N and that N availability was greater in the JPA than the JP stands. The greater leaf area index (LAI) and overstory C accumulation in the JPA than the JP stands (P < 0.05) is likely because of the greater N availability in the JPA stands, but the effect of soil texture discontinuity on water availability in the JPA stands can not be dismissed. Percent ground cover by feathermoss varied among the jack pine communities and was positively correlated with overstory LAI (r 2= 0.83, P< 0.05). One index of N-use efficiency (NUE), defined as aboveground net primary productivity (ANPP) per litterfall N, was significantly greater (P < 0.05) for the JP than the JPA stands, but a second index of NUE, ANPP/N uptake, did not differ between the two jack pine communities. Jack pine trees growing without alder produced more organic matter per unit of N, but percent N retranslocation from senescing foliage and N mean residence time in the overstory did not differ between the JPA and the JP stands. A conceptual model is presented that illustrates the potential influence of alder on the species composition, structure, and function of boreal jack pine forests.

Habitat type classification is a natural classification system that uses the co-occurrence of ground flora and tree species to formulate taxa that can be used to identify sites which support similar plant communities or associations at climax. In 1988 a habitat type classification was developed for northern Wisconsin forests, but scientists have yet to determine whether important soil and vegetation characteristics are similar within a habitat type and if they exhibit consistent differences among habitat types. We compared the soil and vegetation characteristics of 24 sites from the 6 major habitat types in north central Wisconsin. Total soil nitrogen and organic matter concentrations, soil available potassium, soil silt fraction, and soil water-holding capacity all generally increased in the order: Quercus-Acer/Epigaea (QAE) < Acer-Quercus/Vaccinium (AQV) < Pinus/Maianthemum-Vaccinium (PMV) < Acer/Vaccinium-Viburnum (AVVib) < Acer-Tsuga/Dryopteris (ATD) < Acer/Viola-Osmorhiza (AViO). In addition, we observed positive trends (QAE < AQV < PMV < AVVib < ATD < AViO) in leaf area index (leaf area per unit ground area )and forest net primary productivity, both of which are expressions of total resource availability. North. J. Appl. For. 15(2):69-76.

Estimates of leaf area index obtained with indirect measurement techniques, which are replacing more arduous destructive sampling methods, are frequently questioned due to light interception by woody elements and a non-random distribution of foliage elements. Usually, branches are assumed to be positioned randomly with respect to leaves or shoots in the canopy. However, in this study of boreal forest architecture, branches are shown to be preferentially shaded by other non-woody elements (e.g. shoots or leaves) in both coniferous and deciduous species of the boreal region. A new instrument called a Multiband Vegetation Imager (MVI) is used to capture two-band (Visible, 400–620 nm and Near-Infrared, 720–950 nm) image pairs of contrasting Canadian boreal forest canopies during the BOReal Ecosystem-Atmosphere Study (BOREAS). The spatial relationship of branches and photosynthetically active foliage is studied to estimate the fraction of the effective branch hemi-surface area index ( B e ) that is masked by leaves and shoots. We suggest an approach that corrects indirect LAI measurements using the LAI-2000 or a similar instrument by correcting for the following biases: (1) the effective canopy branch hemi-surface area that is not masked by leaves or shoots in the canopy, (2) the amount of stem hemi-surface area beneath crowns, (3) leaf (or shoot) (Ω e ( θ )) and branch (Ω b ( θ )) non-random spatial distributions in the canopy, and (4) the fraction of maximum LAI resulting from defoliation in the canopy. In boreal aspen, MVI image analysis shows that 95% of the effective branch hemi-surface area is masked by other foliage in the canopy. In jack pine and black spruce forests, 80–90% of the effective branch hemi-surface area is masked by other foliage in the canopy. These estimates suggest the fraction of indirect LAI that consists of branches intercepting light is less than 10%. Therefore, branches generally do not intercept a significant amount of beam radiation in boreal forests, and do not significantly bias indirect LAI measurements. However, stems, which comprise 30–50% of the total woody area in this study, may not be preferentially shaded by leafy foliage. Therefore, stem contribution to indirect LAI estimates measured with the LAI-2000 or a similar instrument cannot be overlooked. MVI estimates of the total branch hemi-surface area index agree to within 10–40% of direct measurements made in similar species; however, the error between indirect and direct measurements may be due largely to difficulties associated with obtaining adequate sampling so that the error may fall within the noise level of measurements.

A new instrument called a Multiband Vegetation Imager (MVI) (Kucharik et al., 1997), which uses a 16-bit charge-coupled device (CCD) camera and filter exchange mechanism to capture 2-band (visible and near-infrared) image pairs of plant canopies, has been used to measure the light distribution over sunlit leaves and indirectly infer leaf area index (LAI), sunlit LAI and leaf angle distribution (LAD) in a boreal aspen (Populus tremuloides) forest during the Boreal Ecosystem‐ Atmosphere Study (BOREAS). One purpose of this study is to demonstrate that by combining MVI measurements with numerical Monte Carlo simulations of forest canopy architecture, the LAD and sunlit LAI of aspen can be obtained indirectly. Our results show that this boreal aspen stand exemplifies an erectophile LAD, with a mean leaf inclination angle near 708 .W e also find that the values of the measured and modeled sunlit leaf area in aspen do not change dramatically for typical northern boreal latitude solar zenith angles (i.e. 30‐708). A major problem with determining the sunlit LAI is deciding what range of light intensities constitute a sunlit leaf because penumbra create a smooth continuum of light intensities over sunlit and shaded leaves in the canopy. Therefore, we show that the upper and lower limits can be placed on sunlit LAI values in aspen by using different leaf illumination threshold levels to determine sunlit and shaded LAI in the canopy. Typically, sunlit LAI values in aspen (LAIa3.3) range between 0.8‐1.0 at a 708 sun zenith angle and 1.1‐1.6 at a 308 sun zenith angle. Monte Carlo simulations and MVI measurements suggest that canopy sunlit leaf area estimates are possible from below the canopy at modest LAI values ( 5.0). Since a substantial fraction of the total sunlit leaf area can be viewed from below the canopy in aspen (40‐60% of the total sunlit LAI), a representative light distribution can be measured and used to quantify the canopy leaf angle distribution. # 1998 Elsevier Science B.V. All rights reserved.

We used eddy covariance; gas-exchange chambers; radiocarbon analysis; wood, moss, and soil inventories; and laboratory incubations to measure the carbon balance of a 120-year-old black spruce forest in Manitoba, Canada. The site lost 0.3 ± 0.5 metric ton of carbon per hectare per year (ton C ha −1 year −1 ) from 1994 to 1997, with a gain of 0.6 ± 0.2 ton C ha −1 year −1 in moss and wood offset by a loss of 0.8 ± 0.5 ton C ha −1 year −1 from the soil. The soil remained frozen most of the year, and the decomposition of organic matter in the soil increased 10-fold upon thawing. The stability of the soil carbon pool (∼150 tons C ha −1 ) appears sensitive to the depth and duration of thaw, and climatic changes that promote thaw are likely to cause a net efflux of carbon dioxide from the site.

Since the late 1980's the productivity of monocultures vs. mixed-species forests has been the subject of studies by forest managers and ecologists. Mixed plantations have been established in different proportions to determine if mixtures could provide greater yields and more benefits than monocultures of the component species, as well as to understand if they could be an interesting economic option. An experimental design trial was set up in the north of Portugal in a replacement series with pure and mixed Castanea sativa Mill. and Pseudotsuga menziesii (Mirb.) Franco. The objective of this study was to assess growth dynamics and compare the aboveground biomass and net primary production of the two species in pure and mixed treatments in proportions 1:1 and 1:3. The growth was measured at 7, 11, 15, 17, 19, 27 and 28 years after planting and aboveground net primary production was estimated at age 28. As a component of the mixed treatments, P. menziesii exhibited greater height, diameter and aboveground biomass than C. sativa. Relative yield total indicated a higher productivity in the mixtures compared with the pure treatments. Early in the development, pure treatments and mixtures had similar aboveground biomass per hectare, but later the mixtures showed higher yield than pure treatments. The mixture productivity increase through time appears to be the result of both canopy stratification and better use of site resources. The aboveground net primary production was also higher in mixed than in the pure treatments. We are most grateful to Carlos Fernandes and Carlos Brito for their help with the field data collection, to Armindo Teixeira and Helena Ferreira for their help in the laboratory. This study was funded by FCT research in project PTDC/AGR-CF/68186/2006 and FCT Program SFRH/PROTEC/50127/2009 info:eu-repo/semantics/publishedVersion

The effects of forest management on soil carbon (C) and nitrogen (N) dynamics vary by harvest type and species. We simulated long-term effects of bole-only harvesting of aspen (Populus tremuloides) on stand productivity and interaction of CN cycles with a multiple model approach. Five models, Biome-BGC, CENTURY, FORECAST, LANDIS-II with Century-based soil dynamics, and PnET-CN, were run for 350 yr with seven harvesting events on nutrient-poor, sandy soils representing northwestern Wisconsin, United States. Twenty CN state and flux variables were summarized from the models' outputs and statistically analyzed using ordination and variance analysis methods. The multiple models' averages suggest that bole-only harvest would not significantly affect long-term site productivity of aspen, though declines in soil organic matter and soil N were significant. Along with direct N removal by harvesting, extensive leaching after harvesting before canopy closure was another major cause of N depletion. These five models were notably different in output values of the 20 variables examined, although there were some similarities for certain variables. PnET-CN produced unique results for every variable, and CENTURY showed fewer outliers and similar temporal patterns to the mean of all models. In general, we demonstrated that when there are no site-specific data for fine-scale calibration and evaluation of a single model, the multiple model approach may be a more robust approach for long-term simulations. In addition, multimodeling may also improve the calibration and evaluation of an individual model.

This report assesses past and prospective carbon stocks for 4.5 million ha of forest land in northern Wisconsin, including a baseline assessment and analysis of the impacts of disturbance and management on carbon stocks. Carbon density (amount of carbon stock per unit area) averages 237 megagrams (Mg) per ha, with the National Forest lands having slightly higher carbon density than other ownership classes. Over the last decade, carbon stocks of northern Wisconsin forests have been increasing by about one teragram (Tg) per year or 0.22 megagrams per ha per year, with most of the increase in live biomass. Harvest, wind, and fire have been principal drivers of forest carbon dynamics over the last century. For all forest types in northern Wisconsin, there is potential to increase stocking on the land by allowing more of the forested area to reach older age classes or by increasing productivity. Opportunities to increase afforestation and reduce deforestation are limited, but the potential exists for utilizing biomass energy as a substitute for fossil fuels. There are several options for private landowners to participate in carbon markets or greenhouse gas registries and receive some credit for additional actions to reduce emissions or increase sequestration of carbon. The methods used here can be adapted for use by other regions or forests to assess carbon stocks and effects of management on future carbon stocks.

Studies about the productivity of forest ecosystems help to quantify sequestered carbon and provide data that are used in forest management. Forests in northern Portugal are an important economic resource, but their productivity in scenarios of future climate change is not yetwell understood. The objectives of this study were to evaluate and compare simulated net primary production (NPP) andNPPbased onmeasured data of twotree species located in the Vila Real district forests, pine (Pinus pinaster Aiton) and oak (Quercus pyrenaica Willd.) and assess their simulatedNPPin diverse climate conditions, including future climate scenariosandincreasing atmospheric CO2 concentrations. An ecosystem process model, Biome-BGC, which simulates carbon, nitrogen and water cycles of forest ecosystems close to equilibrium conditions, was used to examine the importance of site and ecophysiological factors on the productivity of these forests. Climate change scenarios and increased CO2 concentrations were tested to explore potential responses of the studied species. The model provided good estimates of NPP. There was a strong correlation between the simulated and measured NPP values in the pine (15) and oak (15) stands. The NPP of these forests are predicted to increase in the future with a CO2 increase whereas in a climate with higher temperature and lower soil moisture, the NPP will decrease. These results confirm that precipitation is a very important climate variable to growth and productivity in the Mediterranean forest ecosystems. This study also demonstrated the ability of Biome-BGC to accurately simulate forest ecosystems behaviour and encourages the application of model simulations in Portugal info:eu-repo/semantics/publishedVersion

Measurements of soil-surface CO2 fluxes are important for characterizing the carbon budget of boreal forests because these fluxes can be the second largest component of the budget. Several methods for measuring soil-surface CO2 fluxes are available: (1) closed-dynamic-chamber systems, (2) closed-static-chamber systems, (3) open-chamber systems, and (4) eddy covariance systems. This paper presents a field comparison of six individual systems for measuring soil-surface CO2 fluxes with each of the four basic system types represented. A single system is used as a reference and compared to each of the other systems individually in black spruce (Picea mariana), jack pine (Pinus banksiana), or aspen (Populus tremuloides) forests. Fluxes vary from 1 to 10 μmol CO2 m−2 s−1. Adjustment factors to bring all of the systems into agreement vary from 0.93 to 1.45 with an uncertainty of about 10–15%.

A new method for measuring plant canopy nonrandomness and other architectural components has been developed using a 16 bit (65535 gray scale levels) charged-coupled device (CCD) camera that captures images of plant canopies in two wavelength bands. This complete system is referred to as a multiband vegetation imager (MVI). The use of two wavelength bands (visible (VIS) 400–620 nm and near infrared (NIR) 720–950 nm) permits identification of sunlit and shaded foliage, sunlit and shaded branch area, clouds, and blue sky based on the camera's resolution, and the varying spectral properties that scene components have in the two wavelength bands. This approach is different from other canopy imaging methods (such as fish-eye photography) because it emphasizes measuring the fraction of an image occupied by various scene components (branches, shaded leaves, sunlit leaves) under different sky conditions rather than simply the canopy gap fraction under uniform sky conditions. The MVI has been used during the Boreal Ecosystem-Atmosphere Study (BOREAS) in aspen (Populus tremuloides) and balsam poplar (Populus balsamifera) to estimate architectural characteristics of each canopy. The leaf area index (LAI), sunlit LAI, and degree of nonrandomness within a canopy are architectural properties that have been measured with the MVI. Using a crown-based Monte Carlo model for nonrandom canopies, nonrandomness factors are calculated from MVI data using two approaches (gap fraction and gap-size distribution theories) to correct total and sunlit LAI estimates from indirect methods that assume random foliage distributions. Canopy nonrandomness factors obtained from analyzing the gap-size distribution in a Monte Carlo model are shown to be a function of path length (angle) through the canopy (Ωe(θ)); thus we suggest that LAI-2000 indirect measurements of LAI be adjusted with the value of Ωe(θ) at θ=35° because this is the mean angle at which the canopy gap fraction is measured by the LAI-2000. In this study, values of Ωe(35)=0.69 in an aspen forest. Alternatively, corrections to indirect LAI measurements obtained with the MVI in this study are made using the value of Ωe(0) because the MVI is used to measure the canopy gap-size distribution and gap fraction within 15° of the zenith. Values of Ωe(0) obtained with the MVI in aspen are typically between 0.55 and 0.65; while in balsam poplar, average values of Ωe(0) are equal to 0.82. This study shows that the MVI provides an attractive indirect measurement technique to obtain accurate estimates of total LAI in aspen. Corrected canopy LAI and direct LAI measurements are greater than indirect estimates based on assuming the foliage to be randomly distributed: In aspen, total LAI is 45% larger (3.3 versus 2.0) and sunlit LAI (40° Sun zenith angle) 10% larger, while in balsam poplar, total LAI is 17% larger (2.3 versus 1.9) and sunlit LAI is only 1% larger. The importance of these clumping characteristics is best appreciated with estimates of canopy net CO2 assimilation derived from scaling leaf photosynthesis versus light relations. Aspen canopy assimilation accounting for clumping is 39% larger than estimates based on indirect measurements of total LAI and the assumption that foliage is randomly distributed.

Leaf area index (LAI) is a key structural characteristic of forest ecosystems because of the role of green leaves in controlling many biological and physical processes in plant canopies. Accurate LAI estimates are required in studies of ecophysiology, atmosphere-ecosystem interactions, and global change. The objective of this paper is to evaluate LAI values obtained by several research teams using different methods for a broad spectrum of boreal forest types in support of the international Boreal Ecosystem-Atmosphere Study (BOREAS). These methods include destructive sampling and optical instruments: the tracing radiation and architecture of canopies (TRAC), the LAI-2000 plant canopy analyzer, hemispherical photography, and the Sunfleck Ceptometer. The latter three calculate LAI from measured radiation transmittance (gap fraction) using inversion models that assume a random spatial distribution of leaves. It is shown that these instruments underestimate LAI of boreal forest stands where the foliage is clumped. The TRAC quantifies the clumping effect by measuring the canopy gap size distribution. For deciduous stands the clumping index measured from TRAC includes the clumping effect at all scales, but for conifer stands it only resolves the clumping effect at scales larger than the shoot (the basic collection of needles). To determine foliage clumping within conifer shoots, a video camera and rotational light table system was used. The major difficulties in determining the surface area of small conifer needles have been largely overcome by the use of an accurate volume displacement method. Hemispherical photography has the advantage that it also provides a permanent image record of the canopies. Typically, LAI falls in the range from 1 to 4 for jack pine and aspen forests and from 1 to 6 for black spruce. Our comparative studies provide the most comprehensive set of LAI estimates available for boreal forests and demonstrate that optical techniques, combined with limited direct foliage sampling, can be used to obtain quick and accurate LAI measurements.

(1997). Regionalization of long-term ecological research (LTER) on north temperate lakes. SIL Proceedings, 1922-2010: Vol. 26, No. 2, pp. 522-528.