Consequences of rewetting and ditch cleaning on hydrology, water quality and greenhouse gas balance in a drained northern landscape

Drainage for forestry has created ~ 1 million km of artificial waterways in Sweden, making it one of the largest human-induced environmental disturbances in the country. These extensive modifications of both peatland and mineral soil dominated landscapes still carry largely unknown, but potentially enormous environmental legacy effects. However, the consequences of contemporary ditch management strategies, such as hydrological restoration via ditch blocking or enhancing forest drainage to promote biomass production via ditch cleaning, on water resources and greenhouse gas (GHG) fluxes are unclear. To close the gap between science and management, we have developed a unique field research platform to experimentally evaluate key environmental strategies for drained northern landscapes with the aim to avoid further environmental degeneration. The Trollberget Experimental Area (TEA) includes replicated and controlled treatments applied at the catchment scale based on a BACI approach (before-after and control-impact). The treatments represent the dominant ecosystem types impacted by ditching in Sweden and the boreal zone: (1) rewetting of a drained peatland, (2) ditch cleaning in productive upland forests and (3) leaving these ditches unmanaged. Here we describe the TEA platform, report initial results, suggest ways forward for how to best manage this historical large-scale alteration of the boreal landscape, as well as warn against applying these treatments broadly before more long-term results are reported.

Short-term responses of the soil microbiome and its environment indicate an uncertain future of restored peatland forests

Restoring peatland ecosystems involves significant uncertainty due to complex ecological and socio-economic feedbacks as well as alternative stable ecological states. The primary aim of this study was to investigate to what extent the natural functioning of drainage-affected peat soils can be restored, and to examine role of soil microbiota in this recovery process. To address these questions, a large-scale before-after-control-impact (BACI) experiment was conducted in drained peatland forests in Estonia. The restoration treatments included ditch closure and partial tree cutting to raise the water table and restore stand structure. Soil samples and environmental data were collected before and 3-4 years after the treatments; the samples were subjected to metabarcoding to assess fungal and bacterial communities and analysed for their chemical properties. The study revealed some indicators of a shift toward the reference state (natural mixotrophic bog-forests): the spatial heterogeneity in soil fungi and bacteria increased, as well as the relative abundance of saprotrophic fungi; while nitrogen content in the soil decreased significantly. However, a general stability of other physico-chemical properties (including pH remaining elevated by ca. one unit) and annual fluctuations in the microbiome suggested that soil recovery will remain incomplete and patchy for decades. The main implication is the necessity to manage hydrologically restored peatland forests while explicitly considering an uncertain future and diverse outcomes. This includes their continuous monitoring and the adoption of a precautionary approach to prevent further damage both to these ecosystems and to surrounding intact peatlands.

Utilizing historical maps in identification of long-term land use and land cover changes

Knowledge in the magnitude and historical trends in land use and land cover (LULC) is needed to understand the changing status of the key elements of the landscape and to better target management efforts. However, this information is not easily available before the start of satellite campaign missions. Scanned historical maps are a valuable but underused source of LULC information. As a case study, we used U-Net to automatically extract fields, mires, roads, watercourses, and water bodies from scanned historical maps, dated 1965, 1984 and 1985 for our 900 km[Formula: see text] study area in Southern Finland. We then used these data, along with the topographic databases from 2005 and 2022, to quantify the LULC changes for the past 57 years. For example, the total area of fields decreased by around 27 km[Formula: see text], and the total length of watercourses increased by around 2250 km in our study area.

Peat loss collocates with a threshold in plant-mycorrhizal associations in drained peatlands encroached by trees

Drainage-induced encroachment by trees may have major effects on the carbon balance of northern peatlands, and responses of microbial communities are likely to play a central mechanistic role. We profiled the soil fungal community and estimated its genetic potential for the decay of lignin and phenolics (class II peroxidase potential) along peatland drainage gradients stretching from interior locations (undrained, open) to ditched locations (drained, forested). Mycorrhizal fungi dominated the community across the gradients. When moving towards ditches, the dominant type of mycorrhizal association abruptly shifted from ericoid mycorrhiza to ectomycorrhiza at c. 120 m from the ditches. This distance corresponded with increased peat loss, from which more than half may be attributed to oxidation. The ectomycorrhizal genus Cortinarius dominated at the drained end of the gradients and its relatively higher genetic potential to produce class II peroxidases (together with Mycena) was positively associated with peat humification and negatively with carbon-to-nitrogen ratio. Our study is consistent with a plant-soil feedback mechanism, driven by a shift in the mycorrhizal type of vegetation, that potentially mediates changes in aerobic decomposition during postdrainage succession. Such feedback may have long-term legacy effects upon postdrainage restoration efforts and implication for tree encroachment onto carbon-rich soils globally.

Trading wood for water and carbon in peatland forests? Rewetting is worth more than wood production

While traditional forest management systems aim at maximizing timber production, sustainable forest management focuses on the multiple benefits of entire forest landscapes. The latter is now at the top of policy agendas. This calls for learning through evaluation to support the implementation of policies aiming towards multi-functional forest landscapes. The aim of this study is to quantify the economic trade-offs among natural, current, and re-wetted peatland forests using seven indicators, viz. drainage maintenance, rewetting, water retention, wood production, and three types of carbon sequestration as economic indicators. We discuss ways to adapt to and mitigate effect of forest draining on climate change toward securing multi-functional forest landscapes. The cost benefit analysis showed that in a potential natural state, Lithuania's peatland forests would deliver an economic benefit of ∼€176.1 million annually. In contrast, compared to natural peatland forests, the drainage of peatland forests for wood production has caused a loss of ∼€309 million annually. In comparison, peatland forest rewetting is estimated to increase the economic value by ∼€170 million annually. This study shows that satisfying different ecosystem services is a balancing act, and that a focus on wood production has resulted in net losses when foregone values of water storage and carbon sequestration are considered. Valuation of different sets of ecosystems service benefits and disservices must be assessed, and can be used as a tool towards creating, implementing and monitoring consequences of policies on both sustainability and biodiversity.

What does FSC forest certification contribute to biodiversity conservation in relation to national legislation?

Forest certification has emerged as a voluntary, market-driven tool for sustainable forest management (SFM). Its legitimacy depends on its ability to achieve its objectives and to retain the support of stakeholders such as NGOs and the companies that adopt it. This study presents a novel approach for assessing the contributions of forest certification to biodiversity conservation, based on Forest Stewardship Council (FSC) certification in four northern European countries (Finland, Sweden, Estonia, Latvia). In each case, national FSC certification requirements related to specific biodiversity targets were compared with requirements in national legislation. Nearly 80% of the assessed certification requirements were more prescriptive than the national legislation. One-third of these requirements (3-8 per country) were assessed to have a positive contribution to biodiversity conservation, whereas four requirements (up to 2 per country) were assessed to have a low positive contribution. FSC requirements to protect Woodland Key Habitats were identified as having a positive contribution in all four countries, whereas requirements regarding live tree retention in harvests and preserving dead wood had a positive contribution in three countries each. Despite often prescribing similar measures, the other requirements with positive contributions varied between countries depending on the national legislative baseline. The remaining requirements could not be assessed through expert evaluation, indicating the need for additional empirical research to evaluate how the normative requirements translate to impacts in the field, and how the national context may affect their implementation. The approach is globally applicable, repeatable, and provides a basis for designing systematic empirical assessments of the certification impact.

Multiple stressors in small streams in the forestry context of Fennoscandia: The effects in time and space

In this paper we describe how forest management practices in Fennoscandian countries, namely Sweden and Finland, expose streams to multiple stressors over space and time. In this region, forestry includes several different management actions and we explore how these may successively disturb the same location over 60-100 year long rotation periods. Of these actions, final harvest and associated road construction, soil scarification, and/or ditch network maintenance are the most obvious sources of stressors to aquatic ecosystems. Yet, more subtle actions such as planting, thinning of competing saplings and trees, and removing logging residues also represent disturbances around waterways in these landscapes. We review literature about how these different forestry practices may introduce a combination of physicochemical stressors, including hydrological change, increased sediment transport, altered thermal and light regimes, and water quality deterioration. We further elaborate on how the single stressors may combine and interact and we consequently hypothesise how these interactions may affect aquatic communities and processes. Because production forestry is practiced on a large area in both countries, the various stressors appear multiple times during the rotation cycles and potentially affect the majority of the stream network length within most catchments. We concluded that forestry practices have traditionally not been the focus of multiple stressor studies and should be investigated further in both observational and experimental fashion. Stressors accumulate across time and space in forestry dominated landscapes, and may interact in unpredictable ways, limiting our current understanding of what forested stream networks are exposed to and how we can design and apply best management practices.

Long Term Interferometric Temporal Coherence and DInSAR Phase in Northern Peatlands

Peatlands of northern temperate and cold climates are significant pools of stored carbon. Understanding seasonal dynamics of peatland surface height and volume, often referred to as mire breathing or oscillation, is the key to improve spatial models of material flow and gas exchange. The monitoring of this type of dynamics over large areas is only feasible by remote sensing instruments. The objective of this study is to examine the applicability of Sentinel-1 synthetic aperture radar interferometry (InSAR) to characterize seasonal dynamics of peatland surface height and water table (WT) over open raised bog areas in Endla mire complex in central Estonia, characteristic for northern temperate bogs. Our results show that InSAR temporal coherence, sufficient for differential InSAR (DInSAR), is preserved in the open bog over more than six months of temporal baseline. Moreover, the coherence which is lost in a dry summer, make a recovery in autumn correlate with WT dynamics. The relationship between the coherence from a single master image and the corresponding WT difference is described by the second degree polynomial regression model (Root Mean Squared Error RMSE = 0.041 for coherence magnitude). It is also demonstrated that DInSAR phase is connected to bog surface dynamics and reveals differences between bogs and for ecotopes within a bog. These findings suggest that InSAR long term temporal coherence could be used to describe seasonal bog WT dynamics and differentiate between mire types and ecotopes within a bog. Moreover, DInSAR analysis has the potential to characterize seasonal mire surface oscillation which may be important for assessing the capacity of water storage or restoration success in northern temperate bogs.

Restoration dilemmas between future ecosystem and current species values: The concept and a practical approach in Estonian mires

Ecosystem restoration is gaining political and economic support worldwide, but its exact targets and costs often remain unclear. A key issue, both for predicting restoration success and assessing the costs, is the uncertainty of post-restoration development of the ecosystem. A specific combination of uncertainties emerges when ecosystem restoration would negatively affect pre-restoration species conservation values. Such dilemma appears to be common, but largely ignored in restoration planning; for example, in historically degraded forests, wetlands and grasslands that provide novel habitats for some threatened species. We present a framework of linked options for resolving the dilemma, and exemplify its application in extensive mire restoration in Estonia. The broad options include: redistributing the risks by timing; relocating restoration sites; modifying restoration techniques; and managing for future habitats of the species involved. In Estonia, we assessed these options based on spatially explicit mapping of expected future states of the ecosystem, their uncertainty, and the distribution of species at risk. Such planning documentation, combined with follow-up monitoring and experimentation, can be used for adaptive management, by funding organizations and for academic research.

A simple survey protocol for assessing terrestrial biodiversity in a broad range of ecosystems

Finding standard cost-effective methods for monitoring biodiversity is challenging due to trade-offs between survey costs (including expertise), specificity, and range of applicability. These trade-offs cause a lack of comparability among datasets collected by ecologists and conservationists, which is most regrettable in taxonomically demanding work on megadiverse inconspicuous taxon groups. We have developed a site-scale survey method for diverse sessile land organisms, which can be analyzed over multiple scales and linked with ecological insights and management. The core idea is that field experts can effectively allocate observation effort when the time, area, and priority sequence of tasks are fixed. We present the protocol, explain its specifications (taxon group; expert qualification; plot size; effort) and applications based on >800 original surveys of four taxon groups; and we analyze its effectiveness using data on polypores in hemiboreal and tropical forests. We demonstrate consistent effort-species richness curves and among-survey variation in contrasting ecosystems, and high effectiveness compared with casual observations both at local and regional scales. Bias related to observer experience appeared negligible compared with typical assemblage variation. Being flexible in terms of sampling design, the method has enabled us to compile data from various projects to assess conservation status and habitat requirements of most species (specifically rarities and including discovery of new species); also, when linked with site descriptions, to complete environmental assessments and select indicator species for management. We conclude that simple rules can significantly improve expert-based biodiversity surveys. Ideally, define (i) a common plot size that addresses multiple taxon groups and management goals; (ii) taxon groups based on field expertise and feasible number of species; (iii) sufficient and practical search time; (iv) a procedure for recording within-plot heterogeneity. Such a framework, combined with freedom to allocate effort on-site, helps utilizing full expertise of observers without losing technical rigor.

Identifying and assessing the potential hydrological function of past artificial forest drainage

Drainage of forested wetlands for increased timber production has profoundly altered the hydrology and water quality of their downstream waterways. Some ditches need network maintenance (DNM), but potential positive effects on tree productivity must be balanced against environmental impacts. Currently, no clear guidelines exist for DNM that strike this balance. Our study helps begin to prioritise DNM by: (1) quantifying ditches by soil type in the 68 km² Krycklan Catchment Study in northern Sweden and (2) using upslope catchment area algorithms on new high-resolution digital elevation models to determine their likelihood to drain water. Ditches nearly doubled the size of the stream network (178-327 km) and 17% of ditches occurred on well-draining sedimentary soils, presumably making DNM unwarranted. Modelling results suggest that 25-50% of ditches may never support flow. With new laser scanning technology, simple mapping and modelling methods can locate ditches and model their function, facilitating efforts to balance DNM with environmental impacts.