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Effects of land-use changes on sources, sinks and fluxes of carbon in European mountain areas

Deliverables

The aim of this result is to evaluate the annual carbon balances for landscape sections in order to estimate the effects of likely future land-use scenarios on landscape carbon sequestration. A GIS database has been elaborated for the selected target landscapes, defining vegetation and soil parameters for each pixel. To obtain and/ or complement already existing spatial data sets a novel remote sensing technique has been tested and applied (see result airborne remote sensing system). As for the modelling approach, the one-dimensional SVAT model developed (see result SVAT modelling software) will be integrated into a spatial framework that allows the landscape carbon balance to be derived from integration of the CO2 exchange of each pixel (see result landscape modelling software). Scenarios of likely policy effects on land use have been defined by focus groups, comprising environmental scientists and local and regional stakeholders, which have been set up in each study site. The focus groups defined scenarios of likely policy effects on land use and thus helped to provide a link between detailed process studies and the modelling of impacts of policies at landscape scale. Three contrasting policy scenarios, based on stakeholder consultations, as well as a farm-level agro-economic model, have been taken into account to derive scenarios of likely future land use. From these scenarios the following conclusions can be derived: - Since mountain farming in Europe is generally at its economic limits, all scenarios predict a pronounced decline of agricultural activities, accompanied by an increase in forest cover. - Simulations of landscape-scale CO2 exchange and carbon pools under these likely future land-use scenarios suggest a decrease in mountain grassland carbon sequestration due to reduced management, which at the landscape-scale, however, is compensated by an increase in forest carbon stocks. - Land-use history is a crucial parameter for obtaining realistic estimates of carbon sequestration under changing climatic conditions and land-use practices. More information on the CARBOMONT project can be found at: http://carbomont.uibk.ac.at
The SVAT model developed is a 1-dimensional, multi-layer representation of the soil-vegetation-atmosphere continuum and calculates the fluxes of CO2 and energy between the soil-vegetation system and a specified reference height above the canopy. It consists of coupled micrometeorological and physiological modules: The micrometeorological modules compute radiative transfer, the interception of precipitation, the transfer of momentum and the turbulent dispersion CO2, H2O and sensible heat within and above the canopy using a random-flight scheme. Turbulence statistics required for the turbulent dispersion calculations are derived from a second-order closure model. Soil heat and water fluxes and soil respiration are modelled in the soil module. The environmental variables computed in the micrometeorological modules represent the driving forces for the energy balance model, which partitions absorbed energy into emitted long-wave radiation, latent and sensible heat fluxes. Net photosynthesis, respiration, and stomatal conductance are calculated in a sub-module of the energy balance. Given the necessary abiotic and biotic input data are supplied, the model allows the simulation of CO2, H2O and energy exchange between any ecosystem and the atmosphere. Due to its mechanistic basic the model allows to study the various component processes, their interactions and the way these are influenced by land-use changes. More information on the CARBOMONT project can be found at: http://carbomont.uibk.ac.at
The potential impact of likely future land-use changes depends inter alia on the size of the various ecosystem carbon and nitrogen pools. CARBOMONT delivers the various carbon and nitrogen pool sizes for differently managed mountain grassland ecosystem across Europe, which up to now are missing. Management was an important determinant of plant standing biomasses and carbon and nitrogen pools. CARBOMONT has shown that abandonment increases both the aboveground phytomass, carbon and nitrogen pool size as compared to meadows and pastures. More than 95% of the grassland carbon pools are located belowground and reflect land-use history more than current land use. More information on the CARBOMONT project can be found at: http://carbomont.uibk.ac.at
The net ecosystem exchange of CO2 consists of several component processes, eg. above- and below-ground, auto- and heterotrophic. Understanding net ecosystem CO2 exchange under current climatic conditions and land use, and predicting net ecosystem exchange under likely future climatic conditions and land-use requires a quantification of the contribution of the various component processes and their interactions. This result delivers the required information on the component processes of the net ecosystem CO2 exchange of differently managed mountain grassland ecosystems in Europe. In the case of managed ecosystems CARBOMONT also quantifies off-site carbon losses, which need to be taken into account for an assessment of the carbon balance of managed (mowed or grazed) mountain grassland ecosystems. - Leaf photosynthesis and respiration change with species/ functional group, nitrogen concentration, phenology and plant age. Thus, shifts in nitrogen supply, species composition and plant age structure as related to land-use changes immediately affect the physiological basis for gross primary production. A general relationship between the two main biochemical parameters used for modelling photosynthesis was confirmed. - Variation among sites at different latitudes and elevations in the plant state spectrum was found to be the primary determinant of the apparent climatic sensitivity of functional leaf structure versus photosynthesis relations. - Soil respiration is a major determinant of the carbon balance of grasslands, contributing the largest proportion to CO2 efflux from the ecosystems. Water-limited and water-logged sites exhibit distinct reductions of soil CO2 efflux. Management (mowing, grazing) may lead to a transient decrease of soil respiration. - The proportion of root versus microbial contribution to soil respiration vary with site and type of land use and in response to management practices (e.g. cutting). Root diameter and nitrogen concentration affect the temperature sensitivity of root respiration and thus alter soil CO2 flux partitioning. - The carbon cycle and its components are intimately linked to the nitrogen cycle, which depends on atmospheric deposition of nitrogen at a regional and fertiliser application at a local scale, both exhibiting peak values at the Central European sites. On intensively managed grasslands high N inputs result in the highest productivity, whose effect on net biome production is, however, counterbalanced by higher off-site C losses. More information on the CARBOMONT project an be found at: http://carbomont.uibk.ac.at
The following describes the general concept for the landscape model PROXELLS (Process Pixel Landscape) as currently planned for CARBOMONT: Intention is to provide input layers pixel-wise to the core model (1-D SVAT) which calculates land surface to atmosphere fluxes for water vapour and carbon dioxide. The critical information provided in these layers is the following: - Solar energy in dependence on topography and elevation (direct and diffuse); - Parameters for canopy conductance along elevation gradients; - Leaf area index in both forest and grassland stands along elevation gradients; - Meteorological driver variables along elevation gradients. Flexibility is obtained for a general spatial model by providing input as a series of matrices with specific pixel-based information. Pre-processing is required by a sophisticated radiation model that provides fields for both direct and diffuse radiation fluxes on an hourly basis. Fields of meteorological input are obtained from regression models fitted to long-term observations at meteorological stations. Finally, results from field studies that define a small number of key ecosystem functional variables are again stored in input layers such that specific ecosystem properties (according to experience) may be imported to the model. Topography dependent lateral transfer of water within the mountain landscape is included very crudely at present (exploratory sub-model of PROXELLS), but is planned to be improved in the future. Currently a version of the model is running in FORTRAN and under LINUX for a test landscape. The test version, however, estimates direct and diffuse radiation at each point hourly during simulation runs. It also uses a relatively fixed structure and physiology along elevation gradients (changes stepwise in limited number of categories). A preliminary lateral transfer component is included. Data related to the meteorology and ecosystem layers are currently being analysed for the Berchtesgaden site. More information on the CARBOMONT project can be found at: http://carbomont.uibk.ac.at
The time-rate-of-change of the atmospheric CO2 concentration depends inter alia on the net exchange of CO2 between terrestrial ecosystems and the atmosphere. If terrestrial ecosystems are a net source of CO2 atmospheric CO2 concentrations are likely to rise and vice versa. CARBOMONT delivers the first data on the net ecosystem CO2 exchange (NEE) of non-forest mountain ecosystems, which up to now are missing in the European carbon inventory. In the future this data will allow to better assessing the status quo and potential effects of land-use changes on the source/sink relationships of non-forest mountain ecosystems with reference to the Kyoto-protocol. The investigated mountain grassland ecosystems may be separated into two groups: - The NEE of managed ecosystems (meadows and pastures) shows to be highly sensitive to the timing and duration of management practises, such as mowing, grazing and fertiliser application. The NEE of these ecosystems ranges from appreciable sinks to large sources of CO2. On average the investigated managed mountain grassland ecosystems absorb 48+/-136 g C m-2 y-1. Soil water availability is a critical factor for the NEE, not only at the sites influenced by the Mediterranean and Continental climates, but as well in the Alps, resulting in larger carbon losses during dry years. Given the balanced carbon cycle of mountain grasslands the ratio of carbon imports (manure) to exports (hay) critically determines whether these ecosystems act as sinks or sources of carbon in terms of their net biome production. - The NEE of natural, unmanaged ecosystems, which are exclusively associated with high latitudes within the CARBOMONT project, is driven mainly by environmental forcing variables, in particular temperature. These ecosystems act as small sinks for CO2 absorbing on average 20+/-32g Cm-2 y-1. More information on the CARBOMONT project can be found at: http://carbomont.uibk.ac.at
ASPIS (Advanced SPectroscopic Imaging System) is a novel airborne digital multispectral imaging system for research and monitoring of agricultural and forest environment and consists of: - Four digital cameras with two dimensional CCD (512x768 pixel) with quantum efficiency in the spectral range of 0.4 a 1.0 nm, radiometric resolution of 14bit (16384 grey levels) and cooled Peltier cell (- 40°C); - Spectral bands are selected by interferential filters on fly; - Four lens12 mm, f/2, FOV 38°; - A panchromatic digital cinecamera; - GPS; - Monitor 12” LCD and computer Pentium III 750 MHz. The aircraft is a certificated airborne (JAR-VLA), named Sky Arrow 650tc. ASPIS acquires four digital images at the same time, each one in the selected spectral band. The digital panchromatic cinecamera allows to view and to record wide area film at true colour. The GPS acquires the geographic coordinates of the image. Aircraft measurements are made at 800-1000m above ground level, to obtain an average spatial resolution of 60-70cm/pixel. Acquired spectral bands are: 550, 680, 700, 699.8, 719.3, 733.5, 748.5 and 780nm. At same time of the flights, total phytomass, divided in dead and live material, and plant area index (LAI) are sampled in 10x10m plots at each site. The plots are characterised by different species composition and biomass levels, and provide ground truth data for comparison with remote sensing data. More information on the CARBOMONT project can be found at: http://carbomont.uibk.ac.at

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