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Terrestrial biosphere models are important tools for diagnosing both the current state of the terrestrial carbon cycle and forecasting terrestrial ecosystem responses to global change. While there are a number of ongoing assessments of the short-term predictive capabilities of terrestrial biosphere models using flux-tower measurements, to date there have been relatively few assessments of their ability to predict longer term, decadal-scale biomass dynamics. Here, we present the results of a regional-scale evaluation of the Ecosystem Demography version 2 (ED2)-structured terrestrial biosphere model, evaluating the model's predictions against forest inventory measurements for the northeast USA and Quebec from 1985 to 1995. Simulations were conducted using a default parametrization, which used parameter values from the literature, and a constrained model parametrization, which had been developed by constraining the model's predictions against 2 years of measurements from a single site, Harvard Forest (42.5° N, 72.1° W). The analysis shows that the constrained model parametrization offered marked improvements over the default model formulation, capturing large-scale variation in patterns of biomass dynamics despite marked differences in climate forcing, land-use history and species-composition across the region. These results imply that data-constrained parametrizations of structured biosphere models such as ED2 can be successfully used for regional-scale ecosystem prediction and forecasting. We also assess the model's ability to capture sub-grid scale heterogeneity in the dynamics of biomass growth and mortality of different sizes and types of trees, and then discuss the implications of these analyses for further reducing the remaining biases in the model's predictions.

The Amazon basin is likely to be increasingly affected by environmental changes: higher temperatures, changes in precipitation, CO2 fertilization and habitat fragmentation. To examine the important ecological and biogeochemical consequences of these changes, we are developing an international network, RAINFOR, which aims to monitor forest biomass and dynamics across Amazonia in a co-ordinated fashion in order to understand their relationship to soil and climate. The network will focus on sample plots established by independent researchers, some providing data extending back several decades. We will also conduct rapid transect studies of poorly monitored regions. Field expeditions analysed local soil and plant properties in the first phase (2001–2002). Initial results suggest that the network has the potential to reveal much information on the continental-scale relations between forest and environment. The network will also serve as a forum for discussion between researchers, with the aim of standardising sampling techniques and methodologies that will enable Amazonian forests to be monitored in a coherent manner in the coming decades. Abbreviation: PSP = Permanent sample plot.

The responses of high latitude ecosystems to global change involve complex interactions among environmental variables, vegetation distribution, carbon dynamics, and water and energy exchange. These responses may have important consequences for the earth system. In this study, we evaluated how vegetation distribution, carbon stocks and turnover, and water and energy exchange are related to environmental variation spanned by the network of the IGBP high latitude transects. While the most notable feature of the high latitude transects is that they generally span temperature gradients from southern to northern latitudes, there are substantial differences in temperature among the transects. Also, along each transect temperature co-varies with precipitation and photosynthetically active radiation, which are also variable among the transects. Both climate and disturbance interact to influence latitudinal patterns of vegetation and soil carbon storage among the transects, and vegetation distribution appears to interact with climate to determine exchanges of heat and moisture in high latitudes. Despite limitations imposed by the data we assembled, the analyses in this study have taken an important step toward clarifying the complexity of interactions among environmental variables, vegetation distribution, carbon stocks and turnover, and water and energy exchange in high latitude regions. This study reveals the need to conduct coordinated global change studies in high latitudes to further elucidate how interactions among climate, disturbance, and vegetation distribution influence carbon dynamics and water and energy exchange in high latitudes.

We evaluated the balance of production and decomposition in natural ecosystems of Pinus sylvestris, Larix sibirica and Betula pendulain the southern boreal forests of central Siberia, using the Yenisei transect. We also investigated whether anthropogenic disturbances (logging, fire and recreation pressure) influence the carbon budget. Pinus and Larix stands up to age class VI act as a net sink for atmospheric carbon. Mineralization rates in young Betulaforests exceed rates of uptake via photosynthesis assimilation. Old-growth stands of all three forest types are CO2 sources to the atmosphere. The prevalence of old-growth Larix in the southern taiga suggests that Larix stands are a net source of CO2. The CO2 flux to the atmosphere exceeds the uptake of atmospheric carbon via photosynthesis by 0.23 t C.ha−1.yr−1 (47%). Betula and Pinus forests are net sinks, as photosynthesis exceeds respiration by 13% and 16% respectively. The total carbon flux from Pinus, Larix and Betula ecosystems to the atmosphere is 10 387 thousand tons C.yr−1. Net Primary Production (0.935 t-C.ha−1) exceeds carbon release from decomposition of labile and mobile soil organic matter (Rh) by 767 thousand tons C (0.064 t-C.ha−1), so that these forests are net C-sinks. The emissions due to decomposition of slash (101 thousand tons C; 1.0%) and from fires (0.21%) are very small. The carbon balance of human-disturbed forests is significantly different. A sharp decrease in biomass stored in Pinus and Betula ecosystems leads to decreased production. As a result, the labile organic matter pool decreased by 6–8 times; course plant residues with a low decomposition rate thus dominate this pool. Annual carbon emissions to the atmosphere from these ecosystems are determined primarily by decomposing fresh litterfall. This source comprises 40–79% of the emissions from disturbed forests compared to only 13–28% in undisturbed forests. The ratio of emissions to production (NPP) is 20–30% in disturbed and 52–76% in undisturbed forests. Abbreviations: LOM = Labile organic matter; MOM = mobile organic matter; NPP = Net primary production; Rh = Heterotrophic respiration; SOM = Soil organic matter.

Europe is characterized not only by large geomorphological variability but also by a long history of land use. This resulted in a highly variegated landscape. Based on the IGBP-transect initiative, a north south transect was established across Europe ranging from north Sweden to central Italy in order to study effects of global change. Mainly process oriented studies were established on plots along the transect, and these were used to establish functional relationships as basis for landscape integration. However, it became apparent that the transect approach was not sufficient to mirror the European environment. From early on, the assessment of land cover was not constrained to this transect but complemented with measurements focused on Europe at a continental scale. Also, continental networks of flux measurements and ecosystem experiments were established, because these were able to encompass a larger inherent variability of climate, geology and land use. Resulting from the Kyoto protocol emphasis moved stronger from observations along transects towards a continental scale quantification of fluxes given the reporting needs. In this process the transect and the networks merged into research clusters, which provided a scaling and verification mechanism. Thus, the European situation may serve as an example of how the initial idea of transects has further evolved and broadened to continental scale studies in a region where anthropogenic land use dominates over climate change. Abbreviations: GPP = Gross primary production; IGBP = International Geosphere Biosphere Programme; NBP = net biome productivity; NEE = Net ecosystem exchange; NEP = Net ecosystem productivity; NPP = Net primary productivity.

The Northeast China Transect (NECT) has been used to study how water availability influences the composition of plant functional types, soil organic matter, net primary production, trace gas flux, and land-use patterns. We discuss relations of plant species number, soil C and N and above-ground biomass with a precipitation gradient and interactions with land-use practices (grassland fencing, mowing and grazing), on the basis of data from the west part of NECT. The results indicate: 1. The above-ground biomass of grassland communities has a linear relationship with precipitation under three land-use practices, while plant species number, soil C, and total soil N have linear relationships with precipitation under fencing and mowing; under grazing the relationships are non-linear. 2. Plant species number, soil C and total soil N have strong linear relationships with above-ground biomass under both fencing and mowing, while they seem to have non-linear relationships under grazing. 3. Land-use practices along the precipitation gradient result not only in changes in grassland communities but also in qualitative changes of their structure and function. 4. Grasslands are more vulnerable to changes in climate under mowing than under fencing, and are more capable to store C in soil and plants. 5. At a given precipitation level, number of plant species, above-ground biomass, and soil C are higher under low to medium intensity of human activities (mowing and grazing). A better understanding of how different intensities of human activities will affect the structure and function of grassland will require further research. Abbreviations: NECT = Northeast China Transect; NPP = Net primary production; GCTE = Global Change and Terrestrial Ecosystems; IGBP = International Geosphere-Biosphere Programme.

The central grassland region of North America is characterized by large gradients of temperature and precipitation. These climatic variables are important determinants of the distribution of plant species, and strongly influence plant morphology and tissue chemistry. We analysed regional patterns of plant litter quality as they vary with climate in grassland ecosystems throughout central North America including tall-grass prairie, mixed grass prairie, shortgrass steppe, and hot desert grasslands. An extensive database from the International Biological Program and the Long-Term Ecological Research Program allowed us to isolate the effects of climate from those of plant functional types on litter quality. Our analysis of grass species confirms a previously recognized positive correlation between C/N ratios and precipitation. Precipitation exhibited a similar positive relationship with lignin/N and percent lignin. Although there was no significant correlation between temperature and C/N, there was a significant positive relationship between temperature and both percent lignin and lignin/N. Among functional types, C3 grasses had a slightly lower C/N ratio than C4 grasses. Tall grass species exhibited higher C/N, lignin/N, and percent lignin than short grass species. This understanding of the regional patterns of litter quality and the factors controlling them provides us with a greater knowledge of the effect that global change and the accompanying feedbacks may have on ecosystem processes. Abbreviations: LTER = Long-Term Ecological Research; NUE = Nutrient use efficiency.

Two-weekly AVHRR images were used to examine spatial patterns of the normalized difference vegetation index (NDVI) and their relationships with environmental variables for moist acidic tundra (MAT) and moist non-acidic tundra (MNT) along two latitudinal transects in northern Alaska. The NDVI database was derived from a 5-yr time series (1995–1999) of two-weekly AVHRR composites for Alaska. A digital climate map, digital elevation map and vegetation map were processed and overlain with the NDVI grid. Homogeneous vegetation patches for both MAT and MNT were defined as sample sites using infrared aerial photos, MSS images and the vegetation map along the transects. Linear and non-linear regression modeling were performed between NDVI indices and environmental variables, total summer warmth (TSW) and elevation. It was demonstrated that along both western and eastern transects, there were obvious latitudinal trends of peak NDVI (AP-NDVI), average growing season NDVI (GS-NDVI), and early June NDVI (EJ-NDVI). In most cases, MNT had lower NDVI values than MAT throughout the year. There were significant (p < 0.01) relations between NDVI (AP-NDVI, GS-NDVI and EJ-NDVI) and total summer warmth (TSW) and elevation in the region. EJ-NDVI showed the strongest correlation with TSW or elevation, making it the most sensitive NDVI indicator along environmental gradients in northern Alaska. NDVI was likely controlled by TSW and elevation, with the former being dominant. Nomenclature: Yurtsev (1994). Abbreviations: AK = Alaska; AP-NDVI = Annual peak NDVI; AVHRR = Advanced Very High Resolution Radiometer; DEM = Digital elevation model; EJ-NDVI = Early June NDVI; GS-NDVI = Growing season NDVI; LAI = Leaf-area index; MAT = Moist acidic tundra; MNT = Moist non-acidic tundra; NDVI = Normalized difference vegetation index; TSW = Total summer warmth.

The decline in tree density on sandy soils in savannas is highly correlated with declining mean annual rainfall along the North Australian Tropical Transect (NATT). We re-analyse various data on water use by individual trees and argue that a common relationship can be used to estimate annual water use by tree stands along the NATT from ca. 600 mm mean annual rainfall to at least 1600 mm. Where rainfall is less than 600 mm, trees of a given size use less water than at sites where rainfall is higher. We use these relationships to relate water use at the stand scale with mean annual rainfall along the NATT. From this we show that the empirical data imply that the minimum depth of sandy soil that needs to be exploited by trees declines with increasing aridity along the NATT from more than 5 m to less than 1 m. This finding is consistent with other observations and the pattern that with increasing aridity, an increasing proportion of rainfall coming from isolated storms rather than from periods of extended monsoon activity. Abbreviation: NATT = North Australian Tropical Transect.

Both ecosystem carbon gain and nutrient availability are largely constrained by the magnitude and seasonality of precipitation in arid and semi-arid ecosystems. We investigated the role of precipitation on ecosystem processes along an International Geosphere Biosphere Programme (IGBP) transect in temperate South America. The transect consists of a contiguous precipitation gradient in the southern region of Argentinean Patagonia (44–45° S), from 100 mm to 800 mm mean annual precipitation (MAP) and vegetation ranging from desert scrub to closed canopy forest. Gravimetric soil water content tracked changes in seasonal and annual precipitation, with a linear increase in soil water content with increasing MAP. Above-ground net primary production (ANPP) increased linearly along the gradient of precipitation (ANPP = − 31.2 + 0.52 MAP, r2 = 0.84, p = 0.028), supporting the relationship that carbon assimilation is largely controlled by available water in these sites, and was in general agreement with regional models of ANPP and rainfall. However, inorganic soil nitrogen was also highly linearly correlated with both MAP ([N] = 0.19 MAP − 32, r2 = 0.96, p = 0.003) and ANPP (ANPP = 2.6 [Ninorganic]+59.4, r2 = 0.79, p = 0.042), suggesting a direct control of precipitation on nitrogen turnover and an interaction with nitrogen availability in controlling carbon gain. The asynchrony of precipitation and changes in dominant vegetation may play important roles in determining the carbon-nitrogen interactions along this rainfall gradient. Nomenclature: Correa (1971); Dimitri (1972). Abbreviations: ANPP = Above-ground net primary production, IGBP = International Geosphere Biosphere Programme; MAP = Mean annual precipitation.