The decision on how to manage a forest under climate change is subject to deep and dynamic uncertainties. The classic approach to analyze this decision adopts a predefined strategy, tests its ...robustness to uncertainties, but neglects their dynamic nature (i.e., that decision-makers can learn and adjust the strategy). Accounting for learning through dynamic adaptive strategies (DAS) can drastically improve expected performance and robustness to deep uncertainties. The benefits of considering DAS hinge on identifying critical uncertainties and translating them to detectable signposts to signal when to change course. This study advances the DAS approach to forest management as a novel application domain by showcasing methods to identify potential signposts for adaptation on a case study of a classic European beech management strategy in South-West Germany. We analyze the strategy’s robustness to uncertainties about model forcings and parameters. We then identify uncertainties that critically impact its economic and ecological performance by confronting a forest growth model with a large sample of time-varying scenarios. The case study results illustrate the potential of designing DAS for forest management and provide insights on key uncertainties and potential signposts. Specifically, economic uncertainties are the main driver of the strategy’s robustness and impact the strategy’s performance more critically than climate uncertainty. Besides economic metrics, the forest stand’s past volume growth is a promising signpost metric. It mirrors the effect of both climatic and model parameter uncertainty. The regular forest inventory and planning cycle provides an ideal basis for adapting a strategy in response to these signposts.
Key message
Managing forest risks in uncertain times of climate change necessitates novel and adaptive forest decision approaches. Multiple risks (biotic and abiotic) and sources of uncertainty ...should be identified, and their quantities over decision horizon should be propagated in searching for robust solutions. The solutions may ask for changes in classical forest decisions, e.g., rotation age or beyond, e.g., forest insurance.
Tropical forests represent important supporting pillars for society, supplying global ecosystem services (ES), e.g., as carbon sinks for climate regulation and as crucial habitats for unique ...biodiversity. However, climate change impacts including implications for the economic value of these services have been rarely explored before. Here, we derive monetary estimates for the effect of climate change on climate regulation and habitat services for the forests of Central America. Our results projected ES declines in 24-62% of the study region with associated economic costs of $51-314 billion/year until 2100. These declines particularly affected montane and dry forests and had strong economic implications for Central America's lower-middle income countries (losses of up to 335% gross domestic product). In addition, economic losses were mostly higher for habitat services than for climate regulation. This highlights the need to expand the focus from mere maximization of CO
sequestration and avoid false incentives from carbon markets.
•Thinning affects ecohydrological processes under different biophysical conditions, silvicultural systems, and time scales.•Throughfall, net precipitation, soil moisture and tree-level water use ...increase after thinning by 1.19, 1.14 and 1.56 relative to the control, respectively.•Stemflow and stand transpiration decrease after thinning by 0.42 and 0.6 relative to the control, respectively.•Thinning enhances runoff and groundwater recharge and mitigates the effects of drought through increasing Water Use Efficiency.•Thinning intensity of about 50% of the stand density is determined as the threshold at or over which hydrological processes are significantly affected.•The duration of thinning effect can be set between 2.6 and 4.3 (throughfall) and 3.1–8.6 years (soil moisture and transpiration).
Forest thinning can significantly affect hydrological processes. However, these effects largely vary with forest types, climate, thinning intensity, and hydrological variables of interest. Understanding these effects and their variations can significantly support thinning treatments' design and selection to ensure desired hydrological benefits. In this global-level review paper, we report the first comprehensive meta-analysis on the effects of thinning on major hydrological processes with an emphasis on rainfall partitioning, soil moisture and evapotranspiration processes. The synthesized and reviewed studies encompass different biophysical conditions (climate and forest ecosystems), silvicultural systems, and time scales (from weeks to decades) across continents. The results showed a significant increase in net precipitation, soil moisture and tree-level water use after thinning (the effect sizes are 1.19, 1.14 and 1.56 relative to the value of the control, respectively), while decreases in stemflow and transpiration (the effect sizes of 0.42 and 0.6 relative to the value of the control, respectively). Thinning intensity of about 50% of the stand density is determined as the threshold at or over which hydrological processes are significantly affected. The duration of thinning effect can be set between 2.6 and 4.3 (throughfall) and 3.1–8.6 years (soil moisture and transpiration), asking for repeated thinning in order to effectively sustain these effects. These global averages can serve as benchmarks for assessment and comparisons, but the effects of thinning depend on local biophysical conditions and thinning treatments. The literature review on the rest of the studied hydrological variables suggests that thinning generally enhance runoff to increase water yield and groundwater recharge. Thinning can also have a positive or limited role in water use efficiency (WUE), but it mitigates the effects of drought through increasing WUE. Moderate adverse effects on water quality can be prevented by adequate forest managements to prevent soil degradation. Nevertheless, more researches at relatively less studied regions are needed to support a more robust analysis of these reviewed hydrological variables. The management implications of the synthesized and reviewed results are suggested and discussed within the context of climate change.
Abstract
Central America hosts many key biodiversity areas (KBAs), areas which represent unique and irreplaceable ecosystems of global importance for species conservation. However, large extents of ...these areas are not under legal protection and could be threatened by pressures from land use change (e.g. deforestation and agricultural expansion), high human population density (e.g. population growth and urban sprawl) and climate-driven biome shifts. Here, we simulated future biome stability under the influence of climate change across KBAs in the Mesoamerican biodiversity hot spot and combined the results with projections of land use and population density up to the end of the 21st century. We applied four forcing scenarios based on two global climate models (GFDL-ESM4 and IPSL-CM6A-LR) and two shared socio-economic pathways (SSP1-2.6 and SSP3-7.0), which represent a range from low to high emission pathways. Our model projected decreased biome stability in 39%–46% of protected areas in KBAs, whereas this number even increased to 59%–60% for unprotected areas in KBAs (depending on the climate scenario). While human interferences in protected parts of KBAs are expected to be limited, large parts of unprotected areas in KBAs were projected to be pressured by multiple factors at once and are reason for concern. In particular, high human population pressures (>10 people km
−2
) emerged as a main threat over 30%–44% of the unprotected area in KBAs. These were largely accompanied by pressures from land use and sporadically reinforced by pressures from climate-driven biome shifts. Among the hot spots facing multiple high pressures are some of the last tropical dry and montane forest ecosystems in Central America, which stresses the need for urgent conservation action.
Abstract
Key message
By calibrating and validating a forest growth model for seven species in Germany and coupling it with a wind damage simulator, we specifically estimated the impact of wind damage ...on the net present value of Norway spruce and European beech in mixture and monoculture. Under risk, the net present value of spruce managements saw the sharpest declines, although the highest end net present value was still obtained through a heavily thinned spruce monoculture.
Context
Wind damage is one of the most important risks to Central European forests, and adaptation measures are essential.
Aim
Adaptive management strategies should simultaneously account for forest production and wind risk. We simulated the effect of adaptive measures on wind-risk in German forests.
Methods
A process-based forest growth model, “3-PG Mix”, was recalibrated and coupled with the storm damage risk model “Lothar”. We investigated the effect of thinning regimes on wind risk in monoculture and mixed species stands. The net present value of the simulated regimes was calculated and compared (risk vs. no risk).
Results
Spruce regimes achieved the highest net present values when risk was not considered. Considering risk in spruce and beech mixtures and monoculture, all regimes reached values below 3000 € ha
−1
by year 120. The exception was a heavily thinned spruce monoculture at 4507 € ha
−1
, being the most profitable regime under risk.
Conclusion
We conclude, on the basis of this modelling study, that heavy thinning reduced storm risk and maintained a higher net present value in spruce. Species mixture of beech and spruce saw net present values levels remain more constant under risk, while beech monoculture increased.
Abstract
Key message
Drought severely worsened till 2100 and eventually outplayed growth-enhancing CO
2
fertilization turning productivity gains into losses for beech and fir. Most scenarios ...generated notable losses in profitability but economic tipping points were later than for productivity due to lag effects related to discounting. Time mixture of fir and shortening rotation can counteract economic risks under climate change, but requires early admixture and moderate establishment costs.
Context
Adaptation strategies to climate change (CC) such as establishing mixed forests are often based on ecological understanding while economic rationale is often disregarded.
Aims
This paper studies CC uncertainty on productivity and profitability of European beech (
Fagus sylvatica
L.) and Silver fir (
Abies alba
Mill.). Besides, the economic consequences to actively adapt beech forests by admixing Silver fir are investigated.
Methods
We used the process-based forest growth model GOTILWA + to simulate RCP2.6, RCP4.5 and RCP8.5 climatic projection by the MPI-ESM-LR global circulation model (MPI-ESM-LR) with the CO
2
fertilization effect (eCO
2
) switched on and off. We analysed the sensitivity of the land expectation value (LEV) on CC and economic parameters.
Results
CC initially increased productivity, but declined after a tipping point (2040–2070) and later also profitability (2045–2100). RCP8.5 had positive, RCP2.6 negative and RCP4.5 neutral effects on LEV. Switching off eCO
2
turned RCP8.5 from the most profitable to the least profitable scenario and the opposite for RCP2.6. CC generally reduced optimal rotation (
R
opt
) being scenario dependant, but comparatively more for fir than beech. Admixing fir created an economic benefit when implemented before stand age 50 of beech. This benefit was nullified with protection costs for browsing control (fencing or tree shelters).
Conclusions
Economic parameters (not CC) were the major source of uncertainty stemming from discounting factors and establishment costs. Admixture of fir and shortening rotation can provide a solution to tackle economic and climate uncertainties, but requires early admixture and browsing control.
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•BFAST was developed to reconstruct historical forest disturbance events.•Fires, extreme cold events, and droughts were identified.•Fires led to largest damages and altered regular ...phenology.•Legacy effects existed 1–2 years after cold and drought events.•Ambient climate contributed to modulating post-disturbance effects.
Forest disturbances significantly affect the global carbon cycle by, for example, vegetation loss or changing forest phenology. However, the lack of historical disturbance events constitutes a challenge for in-depth temporal and spatial analysis. Available remote sensing time series and combined climate data may have great potential to quickly and consistently detect and identify forest disturbances events. We employed time-series data (2001–2014) of a vegetation index (normalized difference vegetation index, NDVI) and a change detection algorithm (the breaks for additive seasonal and trend, BFAST) to detect forest disturbances in a sub-tropical area located in Southwest China. Remote sensing and meteorological data were combined to distinguish among the typical forest disturbances: fires, extreme cold events in winter (ECE), and droughts. With the reconstructed historical disturbance events, post-disturbance vegetation loss, short-term vegetation cover, and phenology changes were analyzed. Our results show that fires and droughts caused severe damage to forest cover (NDVI anomalies can reach up to −1.84 and −1.11, respectively). Fire changed the regular phenological periods which last 3–4 years, and it also took 1–2 years for vegetation greenness to recover after ECE and droughts, which triggered carbon emissions and reduced forest stocks. Warmer areas were vulnerable to ECE effects as well and should be paid more attention. Post-disturbance effects show complex patterns: characteristics of disturbances, climatic conditions, and multiple events overlaying contribute to modifying forest vegetation. Hence, forest disturbances cannot be neglected but should be emphasized in future forest ecosystem modeling or analyzing. The approach used in the study can be a crucial step in detecting and assessing the effects of various disturbances on forest vegetation and phenology and, thereby, contributes to improved risk analysis and management in forestry.
Key message
We applied a modified forest gap model (ForClim) to depict changes in stand water transpiration via density reduction as a forest adaptation strategy. This approach is the key to ...analyzing the ecological resilience to drought, stress-induced mortality, and economic efficiency of managed mixed forest stands in Central Europe. The results show that specific geographic conditions and forest composition define the optimal stand density of drought-resilient forests
.
Context
Reducing stand density has been recognized as a valid strategy to increase forest resilience to drought. Moreover, to develop adaptive management strategies (AMS) under climate change, it is crucial to consider not only drought resilience but also the economic efficiency of alternative AMS proposed to alleviate drought effects.
Aims
To analyze how decreased inter-tree competition among overstorey trees affects stand vulnerability to drought and its expected yield.
Methods
We integrated experimental thinning data and historical responses to drought years in a climate-sensitive forest gap model, ForClim. We tested a business as usual (BAU) and three alternative AMS (“do-nothing,” low- and high-intensity overstorey removal) in mixed stands of Norway spruce (
Picea abies
), silver fir (
Abies alba
), and European beech (
Fagus sylvatica
) along an elevational gradient of 520–1020 m a.s.l. in Central Europe.
Results
High-intensity overstorey removal in mixed stands of all three species considerably increased forest volume growth resilience to drought and decreased stress-induced mortality by two-thirds vis à vis a “do-nothing” strategy. In sites including only conifer species, forest resilience was equally improved by high- and low-intensity overstorey removal compared to that in the BAU strategy. Regarding the timber economy, high-intensity overstorey removal resulted in a higher economic revenue of mixed stands (~ 22% higher net present value than other strategies) on the high-elevation sites (> 1000 m a.s.l.).
Conclusion
Modifying forest density and structure by overstorey removal is principally suitable to increase forest resilience to drought and improve its economic efficiency. The magnitude of the effect however depends on the geographical setting and forest composition.
Forest growth function and water cycle are affected by climatic conditions, making climate-sensitive models, e.g., process-based, crucial to the simulation of dynamics of forest and water ...interactions. A rewarded and widely applied model for forest growth analysis and management, 3PG, is a physiological process-based forest stand model that predicts growth. However, the model runs on a monthly basis and uses a simple soil-water module. Therefore, we downscale the temporal resolution to operate daily, improve the growth modifiers and add a responsive hydrological sub-model to represents the key features of a snow routine, a detailed soil-water model and a separated soil-evaporation calculation. Thereby, we aim to more precisely analyze the effects of thinning events on forest productivity and water services. The novel calibrated 3PG-Hydro model was validated in Norway spruce sites in Southern Germany and confirmed improvements in building forest processes (evapotranspiration) and predicting forest growth (biomass, diameter, volume), as well as water processes and services (water recharge). The model is more sensitive to forest management measures and variability in soil water by (1) individualization of each site’s soil, (2) simulation of percolation and runoff processes, (3) separation of transpiration and evapotranspiration to predict good evapotranspiration even if high thinning is applied, (4) calculation in daily time steps to better simulate variation and especially drought and (5) an improved soil-water modifier. The new 3PG-Hydro model can, in general, better simulate forest growth (stand volume, average diameter), as well as details of soil and water processes after thinning events. The novel developments add complexity to the model, but the additions are crucial and relevant, and the model remains an easy-to-handle forest simulation tool.
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