Evaluation of three different regional climate change scenarios for the application of a water balance model in a mesoscale catchment in Northeast Germany

Future climate changes might have some impacts on catchment hydrology. An assessment of such impacts on e.g. ground water recharge is required to derive adaptation strategies for future water resources management. The main objective of our study was an analysis of three different regional climate change scenarios for a catchment with an area of 2415 km² located in the Northeastern German lowlands. These data sets consist of the STAR-scenario with a time period 1951–2055, the WettReg-scenario covering the period 1961–2100 and the grid based REMO-scenario for the time span 1950–2100. All three data sets are based on the SRES scenario A1B of the IPCC. In our analysis, we compared the meteorological data for the control period obtained from the regional climate change scenarios with corresponding data measured at meteorological stations in the catchment. The results of this analysis indicated, that there are high differences between the different regional climate change scenarios regarding the temporal dynamics and the amount of precipitation. In addition, we applied a water balance model using input data obtained from the different climate change scenarios and analyzed the impact of these different input data on the model output groundwater recharge. The results of our study indicated, that these regional climate change scenarios due to the uncertainties in the projections of precipitation show only a limited suitability for hydrologic impact analysis used for the establishment of future concrete water management procedures in their present state

Global transpiration data from sap flow measurements : the SAPFLUXNET database

Plant transpiration links physiological responses of vegetation to water supply and demand with hydrological, energy, and carbon budgets at the land-atmosphere interface. However, despite being the main land evaporative flux at the global scale, transpiration and its response to environmental drivers are currently not well constrained by observations. Here we introduce the first global compilation of whole-plant transpiration data from sap flow measurements (SAPFLUXNET, https://sapfluxnet.creaf.cat/, last access: 8 June 2021). We harmonized and quality-controlled individual datasets supplied by contributors worldwide in a semi-automatic data workflow implemented in the R programming language. Datasets include sub-daily time series of sap flow and hydrometeorological drivers for one or more growing seasons, as well as metadata on the stand characteristics, plant attributes, and technical details of the measurements. SAPFLUXNET contains 202 globally distributed datasets with sap flow time series for 2714 plants, mostly trees, of 174 species. SAPFLUXNET has a broad bioclimatic coverage, with woodland/shrubland and temperate forest biomes especially well represented (80 % of the datasets). The measurements cover a wide variety of stand structural characteristics and plant sizes. The datasets encompass the period between 1995 and 2018, with 50 % of the datasets being at least 3 years long. Accompanying radiation and vapour pressure deficit data are available for most of the datasets, while on-site soil water content is available for 56 % of the datasets. Many datasets contain data for species that make up 90 % or more of the total stand basal area, allowing the estimation of stand transpiration in diverse ecological settings. SAPFLUXNET adds to existing plant trait datasets, ecosystem flux networks, and remote sensing products to help increase our understanding of plant water use, plant responses to drought, and ecohydrological processes. SAPFLUXNET version 0.1.5 is freely available from the Zenodo repository (https://doi.org/10.5281/zenodo.3971689; Poyatos et al., 2020a). The "sapfluxnetr" R package - designed to access, visualize, and process SAPFLUXNET data - is available from CRAN.Peer reviewe

Drought primarily reduces canopy transpiration of exposed beech trees and decreases the share of water uptake from deeper soil layers

Research Highlights: During drought, reduced soil water availability and increased vapor pressure deficit diminished transpiration in a mature beech stand (Fagus sylvatica L.). Dominant trees were more affected than suppressed trees. The share of soil water uptake from deeper layers decreased. The ability of individual trees in the forest stand to save water during drought was apparently dependent on their social status. This would be relevant for forest management. Objectives: We investigated which basal area classes of trees contribute more or less to total transpiration under wet and dry conditions, and from which soil layers they took up water. We hypothesized that dominant trees have a better adaptability to drought and diminish transpiration more than suppressed trees. Methods: The water budget of the forest stand was continuously monitored throughout the entire observation period. Xylem sap flux measurements using thermal dissipation probes were performed during the vegetation period at different depths in the trunks of ten representative trees. A radial distribution model of the sap flow density pattern was used to compute whole-tree and stand transpiration. Water budget was simulated using a physiology-based model. Results: During drought, the fraction of suppressed trees to whole-canopy transpiration of the forest stand increased and the share of soil water uptake from deeper layers decreased. Conclusions: The behavior of dominant trees under drought conditions could be interpreted as a water-conserving strategy. Thinning by removing suppressed trees should be employed to stabilize forests

Stem distance as an explanatory variable for the spatial distribution and chemical conditions of stand precipitation and soil solution under beech (Fagus sylvatica L.) trees

The partitioning of bulk precipitation (PR) in forest ecosystems and its chemical composition depends on both meteorological factors, such as precipitation amount and intensity, evaporation rate, and wind speed, and stand structural factors, such as stand density, canopy structure, bark texture, and spatiotemporal distribution and density of foliage. We analysed fluxes of water and element contained therein of a mature European beech (Fagus sylvatica L.) forest stand on sandy soils in northeastern Germany. We applied a radially symmetrical setup within a stem distance gradient to measure stand precipitation (SP) with its components of throughfall (TF) and stemflow (SF), as well as to measure soil moisture, the chemical composition of the soil solution, the soil chemistry, and the fine root distribution. The chemical analysis of the constituents covered the macroelements (Ca, Mg, K, Na, Al, Fe, Mn, Si, S, P), the cations and anions NH4+, NO3–, Cl-, SO42-, and a few heavy metals (Cu, Pb, Zn). With an average PR of 620 mm a-1, the partitioning resulted in 79% TF, 6% SF, and 15% canopy interception. TF volume increased with distance to stem during summer, but decreased during winter. Clear spatial gradients with increasing concentrations from PR, to different classes of TF as the distance from the trunk decreased, to SF were observed for nearly all elements. The contact of precipitation with leaves and the canopy structures alters the chemical composition of TF and SF by transferring elements from dry deposition or leaching of intracellular materials from the canopy and leads to the input of larger amounts of macroelements and heavy metals with the SP into the soil. Spatial patterns of canopy structures thus affect the spatial variation of TF and its constituents, which also affects the spatial distribution of roots and, at least in phases, the chemical composition of the topsoil solution

Modelling carbon stocks and fluxes in the wood product sector: a comparative review

In addition to forest ecosystems, wood products are carbon pools that can be strategically managed to mitigate climate change. Wood product models (WPMs) simulating the carbon balance of wood production, use and end of life can complement forest growth models to evaluate the mitigation potential of the forest sector as a whole. WPMs can be used to compare scenarios of product use and explore mitigation strategies. A considerable number of WPMs have been developed in the last three decades, but there is no review available analysing their functionality and performance. This study analyses and compares 41 WPMs. One surprising initial result was that we discovered the erroneous implementation of a few concepts and assumptions in some of the models. We further described and compared the models using six model characteristics (bucking allocation, industrial processes, carbon pools, product removal, recycling and substitution effects) and three model-use characteristics (system boundaries, model initialization and evaluation of results). Using a set of indicators based on the model characteristics, we classified models using a hierarchical clustering technique and differentiated them according to their increasing degrees of complexity and varying levels of user support. For purposes of simulating carbon stock in wood products, models with a simple structure may be sufficient, but to compare climate change mitigation options, complex models are needed. The number of models has increased substantially over the last ten years, introducing more diversity and accuracy. Calculation of substitution effects and recycling has also become more prominent. However, the lack of data is still an important constraint for a more realistic estimation of carbon stocks and fluxes. Therefore, if the sector wants to demonstrate the environmental quality of its products, it should make it a priority to provide reliable life cycle inventory data, particularly regarding aspects of time and location

Effect of cascade use on the carbon balance of the German and European wood sectors

status: publishe

Effect of cascade use on the carbon balance of the German and European wood sectors

Wood product models have often been used to estimate the carbon dynamics of wood products and evaluate their effects on the mitigation of climate change. Their increasing complexity allows for advanced analysis of industrial product conversion efficiency, product lifespan and recycling rate, although data availability for such analyses is very often problematic. In spite of the widely recognised importance of cascade chains from one wood product to another, some wood product models represent them with recycling parameters that allocate part of the recycled wood to the same product category. Consequently, the infinite repetition of these loops overestimates carbon stock. This study analyses and benchmarks the effect on carbon stock in wood products for the German wood sector, when infinite recycling loops in wood product models are replaced by cascade chains. Different scenarios were simulated to analyse the effect of enhanced cascade chains. We estimated the carbon stock in the German wood product sector at 22.17 ± 3.82 t C per hectare of forest in the most realistic current scenario, an amount that is overestimated by 15.8% if infinite recycling loops were used instead. The deviation on the estimated carbon stock was derived from the uncertainty of allocation parameters. Then we estimated the carbon stock in the European wood product sector (EU-28) at 1231.76 t C, representing 9.16 t C per hectare of forest. The carbon stock in German wood product sector estimated for the high quality wood benchmark scenario (103.17 t C per hectare of forest) indicated that strategies to promote the development of new product designs and material technologies to enhance cascading may have the highest impact on carbon stock in the wood product sector. Studies aiming at reducing uncertainty on results are urgent, because the use of wood products is becoming an important strategy of the international community to mitigate climate change. At the same time, a correct representation of cascade use in wood product models is important because cascade practices are being promoted by governments and will probably become more common in the near future

Climate mitigation by energy and material substitution of wood products has an expiry date

The expected increased share of renewables due to the ongoing energy transition may reduce the estimated potential mitigation effect of wood. Here, we estimated the climate change mitigation effect for five scenarios of wood products use in Europe applying dynamic substitution factors embracing a future energy mix with an increasing share of renewables in accordance with the emission reductions necessary to achieve the Paris Agreement targets. Our innovative modelling approach also included the elimination of eternal recycling loops, the inclusion of more realistic wood use cascading scenarios, and adoption of a more realistic marginal (ceteris paribus) substitution approach. Results show that the mitigation effect derived from material substitution is 33% lower in 2030 than previously predicted, and even 96% lower in 2100, showing its expiry date by the end of the century. Nevertheless, the mitigation effect of wood product use, in addition to mitigation by forests, may represent 3.3% of the European emission reduction targets by 2030