Lutz Breuer

Plant parameter values for models in temperate climates

Abstract Ecological, and especially hydrological models used to assess the effects of land cover changes require various input parameters for plants. Regional model applications rely on detailed information about the properties of the vegetation, especially if process-based approaches are chosen. As raising acceptable data is a time consuming issue, scientists often use globally approximated plant parameter ranges, rather than considering published data sets. The plant parameters summarised in this overview, i.e. albedo, interception capacity, maximum leaf area index, rooting depth, plant height and stomatal conductance, can be used as data for a wide range of published ecological and hydrological models. We concentrate on a presentation of values for temperate regions in order to list a manageable amount of data. Information on plant species is grouped into four main land cover types, crops, pasture (herbs, forbs, grasses), coniferous and deciduous trees. Overall, more than 1300 values for the described parameters have been gathered and present a solid data base for future applications. Further properties of species and sites, such as stand age, basal area, stock density, plant height, mean annual precipitation, mean annual temperature, coordinates and country are given, if available. In many cases of model applications scientists used parameter spans, with no further information or testing of the distribution of data. Twenty-two of the total of 26 data sets subsumed in this data base contained sufficient values to perform a Kolmogorov–Smirnov-test. Twenty of these 22 data sets are normally distributed. In order to investigate spatial differences, the data for stomatal conductance, leaf area index and interception capacity were grouped into North American and European land cover species. Significant differences could only be determined for the leaf area index of deciduous trees and pasture species between the continents.

Fluxes of NO and N2O from temperate forest soils: impact of forest type, N deposition and of liming on the NO and N2O emissions

Annual cycles of NO, NO2 and N2O emission rates from soil were determined with high temporal resolution at a spruce (control and limed plot) and beech forest site (“Höglwald”) in Southern Germany (Bavaria) by use of fully automated measuring systems. The fully automated measuring system used for the determination of NO and NO2 flux rates is described in detail. In addition, NO, NO2 and N2O emission rates from soils of different pine forest ecosystems of Northeastern Germany (Brandenburg) were determined during 2 measuring campaigns in 1995. Mean monthly NO and N2O emission rates (July 1994–June 1995) of the untreated spruce plot at the Höglwald site were in the range of 20–130 µg NO-N m-2 h-1 and 3.5–16.4 µg N2O-N m-2 h-1, respectively. Generally, NO emission exceeded N2O emission. Liming of a spruce plot resulted in a reduction of NO emission rates (monthly means: 15–140 µg NO-N m-2 h-1) by 25-30% as compared to the control spruce plot. On the other hand, liming of a spruce plot significantly enhanced over the entire observation period N2O emission rates (monthly means: 6.2–22.1 µg N2O-N m-2 h-1). Contrary to the spruce stand, mean monthly N2O emission rates from soil of the beech plot (range: 7.9–102 µg N2O-N m-2 h-1) were generally significantly higher than NO emission rates (range: 6.1–47.0 µg NO-N m-2 h-1). Results obtained from measuring campaigns in three different pine forest ecosystems revealed mean N2O emission rates between 6.0 and 53.0 µg N2O-N m-2 h-1 and mean NO emission rates between 2.6 and 31.1 µg NO-N m-2 h-1. The NO and N2O flux rates reported here for the different measuring sites are high compared to other reported fluxes from temperate forests. Ratios of NO/N2O emission rates were >> 1 for the spruce control and limed plot of the Höglwald site and << 1 for the beech plot. The pine forest ecosystems showed ratios of NO/N2O emission rates of 0.9 ± 0.4. These results indicate a strong differentiating impact of tree species on the ratio of NO to N2O emitted from soil.

N2O emission from tropical forest soils of Australia

Three different tropical rain forest sites (Kauri Creek, Lake Eacham, and Massey Creek) on the Atherton Tablelands, Queensland, Australia, were investigated for the magnitude of N 2 O emission from soils during different seasons, that is, wet season, dry season, and transition periods. Highest mean N 2 O emission rates were observed for soils derived from granite at the Kauri Creek site with 74.5 ± 25.2 μg N 2 O-N m -2 h -1 , whereas for soils derived from Metamorphics (Lake Eacham site) mean N 2 O emission rates were much lower (13.1 ± 1.1 μg N 2 O-N m -2 h -1 ). For the Massey Creek site, with soils derived from Rhyolite, a mean annual N 2 O emission rate of 46.2 ± 1.1 μg N 2 O-N m -2 h -1 was calculated. The mean annual N 2 O emission rate calculated for all three sites over the entire observation period was 39.0 μg N 2 O-N m -2 h -1 and thus at the high end of reports from tropical rain forest soils. N 2 O emission rates showed at all sites pronounced temporal as well as spatial variability. The magnitude of N 2 O emissions was strongly linked to rainfall events; that is, N 2 O emissions strongly increased approximately 6-8 hours after precipitation. Correlation analysis confirmed the strong dependency of N 2 O emissions on changes in soil moisture, whereas changes in soil temperature did not mediate considerable changes in N 2 O fluxes. Spatial variability of N 2 O fluxes on a site scale could be explained best by differences in water-filled pore space, CO 2 emission, and C/N ratio of the soil. On the basis of all published N 2 O flux rates from tropical rain forest soils we recalculated the contribution of such forests to the global atmospheric N 2 O budget and come up with a figure of 3.55 Tg N 2 O-N yr -1 , which is approximately 50% higher than reported by others.

Parameter uncertainty and the significance of simulated land use change effects

Abstract Uncertainty in parameters characterising different land covers leads to uncertainty in model predictions of land use change effects. In this study, a new approach is presented which allows a model to be assessed to see whether it is suitable for investigating land use change scenarios in the sense that different land covers can be significantly distinguished in their effects on model output. It consists of the following steps: (a) The uncertainty in land cover-dependent parameters is quantified. (b) The model of an artificial catchment with representative characteristics and uniform land cover is established. (c) Using this artificial catchment, Monte Carlo simulations are carried out to determine the uncertainty in the model response to different land covers. (d) By comparing the results for two covers, respectively, a dimensionless test statistic, the distinction level, is calculated. The distinction level is a normalised probability that two independent realisations of land covers which are parameterised within their range of natural uncertainty will yield distinct model responses. If the distinction level is greater than or equal to 90%, the land covers are assumed to have a significantly different effect on the model output. An example of the application of the new method is provided using the eco-hydrologic model SWAT-G. The land covers forest, pasture and arable land can be significantly distinguished by their long-term means of surface runoff, groundwater recharge and streamflow. The minimum proportion of the catchment area on which land cover must change in order to obtain significantly distinct model responses depends on the land covers involved and the considered hydrologic variable. In the case of a change between pasture and forest and with regard to average streamflow, this minimum proportion amounts to about 25%, a value that compares well with the results of paired catchment studies.

LandscapeDNDC: a process model for simulation of biosphere–atmosphere–hydrosphere exchange processes at site and regional scale

We present a new model system, which facilitates scaling of ecosystem processes from the site to regional simulation domains. The new framework LandscapeDNDC—partly based on the biogeochemical site scale model DNDC—inherits a series of new features with regard to process descriptions, model structure and data I/O functionality. LandscapeDNDC incorporates different vegetation types and management systems for simulating carbon, nitrogen and water related biosphere–atmosphere–hydrosphere fluxes in forest, arable and grassland ecosystems and allows the dynamic simulation of land use changes. The modeling concept divides ecosystems into six substates (canopy air chemistry, microclimate, physiology, water cycle, vegetation structure, and soil biogeochemistry) and provides alternative modules dealing with these substates. The model can be applied on the site scale, as well as for three-dimensional regional simulations. For regional applications LandscapeDNDC integrates all grid cells synchronously forward in time. This allows easy coupling to other spatially distributed models (e.g. for hydrology or atmospheric chemistry) and efficient two-way exchange of states. This paper describes the fundamental design concept of the model and its object-oriented software implementation. Two example applications are presented. First, calculation of a nitrous oxide emission inventory from agricultural soils for the State of Saxaony (Germany), including data preprocessing of the regional model input data. The computational effort for the LandscapeDNDC preprocessing and simulation could be speed up by a factor of almost 100 compared to the approach using the original DNDC version 9.3. Calculated N2O emissions for Saxony with LandscapeDNDC (2693 t N2O–N/a) were compared with the original DNDC model (2725 t N2O–N/a), the IPCC Tier I methodology (1107 t N2O–N/a), and the German National Inventory Report (equal to IPCC Tier II, 2100 t N2O–N/a). The second example illustrates the capabilities of LandscapeDNDC for building a fully coupled three-dimensional model system on the landscape scale. Therefore we coupled the biogeochemical and plant growth calculations to a hydrological transport model and demonstrate the transport of nitrogen along a virtual hillslope and associated formation of indirect nitrous oxide emissions.

Software, Data and Modelling News: CMF: A Hydrological Programming Language Extension For Integrated Catchment Models

Hydrological models are created for a wide range of scales and intents. The Catchment Modelling Framework (CMF) extends the Python programming language with hydrology specific language elements, to setup specific hydrological models adapted to the scientific problems and the dominant flow processes of a particular study area. CMF provides a straightforward method to test hydrological theories and serve as a transport module in integrated, interdisciplinary catchment model approaches.

Afforestation or intense pasturing improve the ecological and economic value of abandoned tropical farmlands

Increasing demands for livelihood resources in tropical rural areas have led to progressive clearing of biodiverse natural forests. Restoration of abandoned farmlands could counter this process. However, as aims and modes of restoration differ in their ecological and socio-economic value, the assessment of achievable ecosystem functions and benefits requires holistic investigation. Here we combine the results from multidisciplinary research for a unique assessment based on a normalization of 23 ecological, economic and social indicators for four restoration options in the tropical Andes of Ecuador. A comparison of the outcomes among afforestation with native alder or exotic pine, pasture restoration with either low-input or intense management and the abandoned status quo shows that both variants of afforestation and intense pasture use improve the ecological value, but low-input pasture does not. Economic indicators favour either afforestation or intense pasturing. Both Mestizo and indigenous Saraguro settlers are more inclined to opt for afforestation.

Current concepts in nitrogen dynamics for mesoscale catchments

Abstract The study of global change impacts on nitrogen dynamics in mesoscale catchments remains an important topic. The primary mechanisms of change can be grouped broadly into those focused on land management, land use, climatic change, as well as on N deposition patterns. The current state of mesoscale studies of N dynamics is outlined in an effort to present the potential tools and methods available to researchers, as well as to outline future directions for additional research. This review focuses on a comparison of the common model approaches that are used to simulate the N cycle in catchments. The review is not meant as an exhaustive list of all models that might include N cycling, but instead outlines a classification framework as a means of better understanding key differences between common modelling strategies. We conclude with a blueprint of what hydro-biogeochemical models should be capable of, and which additional efforts should be considered in the course of model development and verification.

Compositional diversity of rehabilitated tropical lands supports multiple ecosystem services and buffers uncertainties

High landscape diversity is assumed to increase the number and level of ecosystem services. However, the interactions between ecosystem service provision, disturbance and landscape composition are poorly understood. Here we present a novel approach to include uncertainty in the optimization of land allocation for improving the provision of multiple ecosystem services. We refer to the rehabilitation of abandoned agricultural lands in Ecuador including two types of both afforestation and pasture rehabilitation, together with a succession option. Our results show that high compositional landscape diversity supports multiple ecosystem services (multifunction effect). This implicitly provides a buffer against uncertainty. Our work shows that active integration of uncertainty is only important when optimizing single or highly correlated ecosystem services and that the multifunction effect on landscape diversity is stronger than the uncertainty effect. This is an important insight to support a land-use planning based on ecosystem services.

Deforestation and benthic indicators: how much vegetation cover is needed to sustain healthy Andean streams?

Deforestation in the tropical Andes is affecting ecological conditions of streams, and determination of how much forest should be retained is a pressing task for conservation, restoration and management strategies. We calculated and analyzed eight benthic metrics (structural, compositional and water quality indices) and a physical-chemical composite index with gradients of vegetation cover to assess the effects of deforestation on macroinvertebrate communities and water quality of 23 streams in southern Ecuadorian Andes. Using a geographical information system (GIS), we quantified vegetation cover at three spatial scales: the entire catchment, the riparian buffer of 30 m width extending the entire stream length, and the local scale defined for a stream reach of 100 m in length and similar buffer width. Macroinvertebrate and water quality metrics had the strongest relationships with vegetation cover at catchment and riparian scales, while vegetation cover did not show any association with the macroinvertebrate metrics at local scale. At catchment scale, the water quality metrics indicate that ecological condition of Andean streams is good when vegetation cover is over 70%. Further, macroinvertebrate community assemblages were more diverse and related in catchments largely covered by native vegetation (>70%). Our results suggest that retaining an important quantity of native vegetation cover within the catchments and a linkage between headwater and riparian forests help to maintain and improve stream biodiversity and water quality in Andean streams affected by deforestation. This research proposes that a strong regulation focused to the management of riparian buffers can be successful when decision making is addressed to conservation/restoration of Andean catchments.