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For carbon (C) trading or any other verifiable C reports, it would be reasonable to identify and quantify continuous changes in carbon stocks at regional scales without high investments into additional C-specific, time- and labor-intensive inventories. Our study demonstrates the potential of using routine stand taxation data from large scale forestry inventories for verifiable quantification of tree biomass C stocks, C stock change rates, and associated uncertainties. Empirical models, parameters, and equations of uncertainty propagation have been assembled and applied to data from a forest management unit in Central Germany (550 000 ha), using stand taxation inventories collected between 1993 and 2006. The study showed: 1) The use of stand taxation data resulted in a verifiable and sufficiently precise (cv = 7%) quantification of tree biomass carbon stocks and their changes at the level of growth-regions (1700 to 140 000Â ha). 2) The forest of the test region accumulated carbon in tree biomass at a mean annual rate of 1.8 (â0.9 to 4.5) tC/ha/yr over the studied period. 3) The taxation inventory data can reveal spatial patterns of rates of C stock changes, specifically low rates of 0.4 tC/ha/yr in the northwest and high rates of 3.0 tC/ha/yr in the south of the study region.

Estimates of litter production are a prerequisite for modeling soil carbon stocks and its changes at regional to national scale. However, the required data on biomass removal is often available only for the recent past. In this study we used yield tables as a source of probable past forest management to drive a single tree based stand growth model. Next, simulated growth and timber volume was converted to tree compartment carbon stocks and biomass turnover. The study explicitly accounted for differences in site quality between stands. In addition we performed a Monte Carlo uncertainty and sensitivity analysis. We exemplify the approach by calculating long-term means of past litter production for 10 species by using yield tables that have been applied in Central Germany during the last century. We found that litter production resulting from harvest residues was almost as large as the one from biomass turnover. Differences in site quality caused large differences in litter production. At a given site quality, the uncertainty in soil carbon inputs were 14%, 17%, and 25% for beech, spruce, and pine stands, respectively. The sensitivity analysis showed that the most influential parameters were associated with foliage biomass and turnover. We conclude that rates of mean past litter production and their uncertainties can reliably be modeled on the basis of yield tables if the model accounts for 1) full rotation length including thinning and final harvest, 2) differences in site quality, and 3) environmental dependency of foliage biomass and foliage turnover.

Mixed-species forests are, for multiple reasons, promising options for forest management in Central Europe. However, the extent to which interspecific competition affects tree hydrological processes is not clear. High-resolution dendrometers capture subdaily variations in stem diameter; they can simultaneously monitor stem growth (irreversible changes in diameter) and water status (reversible changes) of individual trees. Using the information on water status, we aimed to assess potential effects of tree species mixture, expressed as local neighborhood identity, on night-time rehydration and water stress. We deployed 112 sensors in pure and mixed forest stands of European beech, Norway spruce and Douglas fir on four sites in the northwestern Germany, measuring stem diameter in 10-min intervals for a period of four years (2019–2022). In a mixture distribution model, we used environmental variables, namely soil matric potential, atmospheric vapor pressure deficit, temperature, precipitation and neighborhood identity to explain night-time rehydration, measured as the daily minimum tree water deficit (TWDmin). TWDmin was used as a daily indicator of water stress and the daily occurrence of sufficient water supply, allowing for stem growth (potential growth). We found that species and neighborhood identity affected night-time rehydration, but the impacts varied depending on soil water availability. While there was no effect at high water availability, increasing drought revealed species-specific patterns. Beech improved night-time rehydration in mixture with Douglas fir, but not in mixture with spruce. Douglas fir, however, only improved rehydration at a smaller share of beech in the neighborhood, while beech dominance tended to reverse this effect. Spruce was adversely affected when mixed with beech. At species level and under dry conditions, we found that night-time rehydration was reduced in all species, but beech had a greater capacity to rehydrate under high to moderate soil water availability than the conifers, even under high atmospheric water demand. Our study gives new insights into neighborhood effects on tree water status and highlights the importance of species-specific characteristics for tree-water relations in mixed-species forests. It shows that drought stress of European beech can be reduced by admixing Douglas fir, which may point towards a strategy to adapt beech stands to climate change. [ABSTRACT FROM AUTHOR]

Climate change effects on tree reproduction are poorly understood, even though the resilience of populations relies on sufficient regeneration to balance increasing rates of mortality. Forest‐forming tree species often mast, i.e. reproduce through synchronised year‐to‐year variation in seed production, which improves pollination and reduces seed predation. Recent observations in European beech show, however, that current climate change can dampen interannual variation and synchrony of seed production and that this masting breakdown drastically reduces the viability of seed crops. Importantly, it is unclear under which conditions masting breakdown occurs and how widespread breakdown is in this pan‐European species. Here, we analysed 50 long‐term datasets of population‐level seed production, sampled across the distribution of European beech, and identified increasing summer temperatures as the general driver of masting breakdown. Specifically, increases in site‐specific mean maximum temperatures during June and July were observed across most of the species range, while the interannual variability of population‐level seed production (CVp) decreased. The declines in CVp were greatest, where temperatures increased most rapidly. Additionally, the occurrence of crop failures and low seed years has decreased during the last four decades, signalling altered starvation effects of masting on seed predators. Notably, CVp did not vary among sites according to site mean summer temperature. Instead, masting breakdown occurs in response to warming local temperatures (i.e. increasing relative temperatures), such that the risk is not restricted to populations growing in warm average conditions. As lowered CVp can reduce viable seed production despite the overall increase in seed count, our results warn that a covert mechanism is underway that may hinder the regeneration potential of European beech under climate change, with great potential to alter forest functioning and community dynamics. [ABSTRACT FROM AUTHOR]

Droughts affect terrestrial ecosystems directly and concurrently, and can additionally induce lagged effects in subsequent seasons and years. Such legacy effects of drought on vegetation growth and state have been widely studied in tree-ring records and satellite-based vegetation greenness, while legacies on ecosystem carbon fluxes are still poorly quantified and understood. Here, we focus on two ecosystem monitoring sites in central Germany with similar climate but characterized by different species and age structures. Using eddy-covariance measurements, we detect legacies on gross primary productivity (GPP) by calculating the difference between random-forest model estimates of potential GPP and observed GPP. Our results showed that at both sites, droughts caused significant legacy effects on GPP at seasonal and annual time scales which were partly explained by reduced leaf development. The GPP reduction due to drought legacy effects is of comparable magnitude to the concurrent drought effects, but differed between two neighbouring forests with divergent species and age structures. The methodology proposed here allows quantifying the temporal dynamics of legacy effects at the sub-seasonal scale and separating legacy effects from model uncertainties. Application of the methodology at a larger range of sites will help quantify whether the identified lag effects are general and on which factors they may depend. [ABSTRACT FROM AUTHOR]

This study reviews the effects of changes in land use and land management on SOC pools in forest soils. In the 1990s, deforestation remained the most important land-use change in tropical regions (-142 x 10(6) ha per year). In non-tropical regions the forested area increased in developed countries as a result of natural reforestation (+26 x 10(6) ha per year). Deforestation also continued in under-developed countries in temperate regions. Without intensive site preparation, harvest followed by natural regeneration or reforestation has little impact on SOC pools in the mineral topsoil (0-0.3 m). Intensive site preparation results in losses of 6-13% of the initial SOC from the topsoil in the first decades. On average, deforestation followed by conversion to cropland results in SOC losses of 42% (or 0.1-1500 g (C) m(-2)) from the mineral topsoil, whereas conversion to pasture results in gains of 8%. The largest changes in SOC storage occur within the first two decades. After reforestation, SOC accumulation depends on the kind of managed forest established. Under productive deciduous reforestation (excluding eucalypts), SOC in the mineral topsoil accumulates at a rate of 20-50 g (C) m(-2) per year, and SOC pools could recover from cultivation-induced losses within 40 years. Under coniferous reforestation, the rate of accumulation of carbon is highest (95 g (C) m(-2) per year) in the organic layer, which is very susceptible to site preparation practices. In the mineral topsoil, the rate of accumulation is much lower (4 g (C) m(-2) per year), and recovery of the initial SOC pools might take several hundred years. The resulting land-use 'memory effect' has introduced large variation of the SOC pools in contemporary carbon budget studies. Thus, there seems to be a large temporal asymmetry between the period of time over which depletion of SOC occurs and the time needed for recovery of the SOC pools in the mineral soil. This should be taken into account when considering land-use and land-management activities to decrease atmospheric CO2 concentrations over this century.