Natural regeneration and development of Scots pine seedlings in continuous cover forestry in northern Finland

Improved forest management (IFM), particularly the transition of even-aged forests to continuous cover forestry (CCF), is gaining attention as a management approach that may contribute to climate change mitigation by enhancing forest carbon sequestration and maintaining soil carbon storage. CCF aims to maintain continuous tree cover over time by using selective harvesting and natural regeneration instead of clear-cutting (CC), and is promoted as a forest management method that enhances productivity, ecological, and social benefits. Using a Scots pine stand management in Poland, we evaluated the profitability, harvest rates, and carbon fluxes of CCF compared to traditional CC. We used discounted cash flow models to assess the potential benefits of transitioning even-aged Scots pine stands to a CCF regime. At the assumed 5% discount rate, CC management had higher Land Expectation Values (LEVs), while CCF had higher internal rates of return (IRR) for lower land acquisition prices of 8,000 EUR or less. For land prices ranging from 9,000 to 11,000 EUR, IRRs varied considerably depending on the age at which the stand was transitioned to CCF. Purchasing older forests, which then produced earlier harvest revenues, was more profitable. CC management consistently produced more wood per hectare than CCF, but since CCF had lower input costs, the costs per tonne of CO2e were similar between the two management regimes, as were the wood production costs. Our findings highlight important trade-offs, suggesting that while CCF may not always maximize wood yields, it can offer competitive financial performance under favorable land prices while simultaneously supporting climate mitigation objectives.

Comparison of breeding bird assemblages in conifer plantations managed by continuous cover forestry and clearfelling

To date there are no studies comparing RF and CCF on peatlands with stand-level optimization. This study fills this gap and introduces the effect of genetic gain into analyses, covering different locations and two site types on peatlands. Two different data sets are applied: (1) six experimental plots which had been treated by conducting thinnings from below (RF management) and (2) identical locations and site types to those six plots representing bare land cases. A stand-level optimization was applied to achieve maximum net present value according to CCF and RF. The results demonstrated the superiority of RF with genetic gains to other options: RF without genetic gain and CCF when the starting point was an ongoing rotation. The results were valid regardless of location (southern, northern Finland), site type (Vaccinium myrtillus type I, herb-rich) and interest rate (3%, 5%). When starting from a bare land in northern Finland CCF became financially more profitable than RF (with or without genetic gain) with a 5% interest rate. This is mainly due to poorer growth potential in northern compared to southern Finland and the fact that the stand establishment costs associated with RF differ only slightly between southern and northern Finland.

There is increasing interest across Europe in adopting forest management strategies, which promote species and structural diversity through the use of irregular silvicultural systems, an approach often described as continuous cover forestry (CCF). However, there is little information about the proportion of CCF practised across the continent or about the knowledge gaps and other obstacles that limit its use. A survey of respondents in 33 European countries sought to address these issues. The results indicated that the silvicultural systems associated with CCF were single stem, group selection and irregular shelterwood. Rotational forest management (RFM) was more frequent than CCF in about 66 per cent of countries, whereas in 25 per cent the reverse was true. We estimated that between 22 and 30 per cent of European forests are managed through CCF, although good data are lacking. The main knowledge gaps were: uncertainties arising from climate change (e.g. appropriate species choice, carbon storage in CCF), using CCF to increase forest resilience, deployment of mechanized harvesting systems, lack of knowledge about CCF amongst professional foresters and better information on economic implications of this approach. Major obstacles included: little awareness of CCF amongst forest owners, limited competence in CCF within the forestry profession and a scarcity of skilled forest workers to implement this approach, high ungulate populations damaging natural regeneration, a sawmilling sector geared to processing medium-sized logs, subsidy regimes favouring practices associated with RFM and a lack of experience in transforming plantation forests to more diverse structures. Better information on the use of different silvicultural systems is essential to allow policymakers and other stakeholders to monitor progress in diversifying forests. Establishment of a continental network of long-term operational trials (e.g. expanding the existing Association Futaie Irrégulière network) would improve professional understanding of CCF, would demonstrate this approach to forest owners and other stakeholders and could provide a valuable platform for supporting research.

Boreal peatlands comprise one of the largest terrestrial carbon pools, provide a variety of ecosystem services, and are important for biodiversity. The characteristic multifunctionality of peatland forests calls for research that is able to assess trade-offs between marketed (timber) and non-marketed (water quality, greenhouse gas balance) public goods. Once the trade-offs are revealed, it becomes feasible to pursue sustainable forest management. An openly available database was used to derive an empirical dataset representing a miniature of the Kiiminkijoki catchment in northern Finland, which was used for stand-level simulations (Motti stand simulator) and landscape-level optimisation in drained peatland forests. For each initial state, stand projections were simulated for rotation forestry (RF) and continuous cover forestry (CCF) management. The rationale was to investigate trade-offs between nutrient export, greenhouse gas balance and net present value (NPV). The cost efficiency of reducing greenhouse gas emissions and nutrient export was calculated by optimising forest management (both RF and CCF) within the Kiiminkijoki catchment. The results suggested that applying both RF and CCF in drained peatlands constitutes a highly cost-effective way to reduce greenhouse gas emissions, the cost range being € ~5–20 per tonne of CO2. However, the nitrogen equivalent (NE) cost of reducing nutrient export tends to be quite high (€ 17–58 kg-1) compared to values for mineral soils provided by existing literature.

Abstract: Natural regeneration is crucial for silvicultural approaches based on the continuous presence of a forest cover, or Continuous Cover Forestry (CCF). Sitka spruce (Picea sitchensis) is the main commercial species in the United Kingdom (UK), and its potential for CCF has been demonstrated in various studies. However, there are no quantitative models available to predict its natural regeneration in the country. We describe models for Sitka spruce seedlings presence and density under canopy cover in the UK forests, to be used as a substitution of a regeneration survey. Using a natural regeneration dataset comprised of 340 plots, a Generalized Linear Mixed Model (GLMM) was calibrated to estimate the likelihood of regeneration presence at plot level. Seedling density was simulated in a subsequent step using only the subset of data with regeneration presence (138 plots): we compared methods based on GLMMs calibrated to the observed seedling density, and the simple generation of random numbers similar in distribution to the observed values. We validated the models with a cross-validation method using the calibration dataset and with an independent dataset of 78 plots collected in forests already in the process of transformation to CCF. The best GLMM for regeneration presence included age of the plantation, time after last thinning, favourable ground cover and basal area. After the cross-validation, 73% of the plots were correctly estimated (76% for presence of regeneration and 71% for the absence). After the independent validation process, 82% of the plots were correctly estimated, although 100% for presence of regeneration and only 12% for the absence. Both methods for estimating seedling density had a poor performance, both with the cross-validation and independent validation. The results showed that the tools here described are appropriate for estimating regeneration presence in traditional Sitka spruce plantations. However, alternative methods are required for forests already in an advanced stage of transformation to CCF systems.

Could continuous cover forestry be an economically and environmentally feasible management option on drained boreal peatlands?

In the northern boreal region, tree growth, timber yields and economic returns are low, meaning low regeneration costs are the basis of profitable forestry. If natural regeneration is successful, it may be favoured over expensive planting or seeding. We studied the regeneration success and early growth of Scots pine in gaps in terms of seedling density and height 10 years after gap cuttings in central Finnish Lapland. Three gap sizes (diameters of 20, 40, and 80 m) were studied on patch scarified xeric and sub-xeric sites in six random blocks and a total of 18 replicates of each. The number of pine seedlings was high across the gap sizes. The proportion of empty regeneration plots (size 5 m2) was ∼ 2%. Site preparation substantially increased the number of seedlings. The growth of seedlings was faster in larger gaps, but a high proportion of exposed mineral soil decreased it. The results suggest that all studied gap sizes regenerated naturally well, and that soil scarification exposing 10–20% of the surface area or even less can be enough to achieve regeneration goals. Gaps of a diameter of 40 m or more are required to achieve an optimal balance between seedling density and growth.

Genetic effects of continuous cover forestry (CCF) are not well known. We need more research, especially on the genetics of spruce-dominated CCF sites. Levels of relatedness are of interest, as are estimates of safe limits for the intensity and duration of CCF practices that secure genetic potential for good growth and quality. With even-aged forestry, genetically improved regeneration material can be used to mitigate climate change-related risks through breeding and deployment recommendations. In CCF, currently based on natural regeneration, we assume that enough seedlings establish, and that sites contain enough genetic variation to enable natural selection and evolutionary processes. Based on research in other regions, the number of reproducing trees must be kept large to avoid excessive levels of relatedness and inbreeding and to maintain sufficient levels of genetic diversity. In some well-documented long-term experiments in other regions, intensive high-grading has led to slower growth rates, which could partly be due to genetic degradation of the stand. If contemporary recommendations for selection cutting are followed, negative genetic effects should be unlikely.

We study the effect of forest stand growth models on the economically optimal management of boreal mixed-species forests. Our size-structured economic–ecological model includes the optimization of harvest timing, harvesting intensities, rotation periods, and the choice between rotation forestry and continuous cover forestry. We carry out a systemic comparison of economically optimal solutions obtained with three statistical–empirical stand growth models for both single- and mixed-species stands with up to four tree species. Given a 1% interest rate, the optimal choice between continuous cover and rotation forestry depends on the applied growth model. However, under a 3% interest rate, the optimal management regime is always continuous cover forestry. The optimal solution details are highly dependent on the growth models. With a 1% interest rate, it may become optimal to apply intensive close-to-clearcut harvesting that results in a dominant species change via natural regeneration. However, the level of natural regeneration varies strongly between the growth models. The economic superiority of a species mixture cannot be determined from overyielding differences. Mixed-species stands have higher maximum sustainable yields, bare land values, and average net revenues compared with monocultures.

Continuous cover forestry (CCF) is forest management based on ecological and biological principles. CCF particularly requires the abandonment of clearfelling practices in favour of more natural approaches of regeneration. Recently, CCF has been identified as a way to mitigate climate change, to bring about forest conservation and to meet the diverse requirements of recreation forests. EU strategies support the use of CCF and Sweden is committed to the transformation of 20% of its plantation forest land to CCF. This policy change meets the Swedish forest industry rather unprepared. CCF training is therefore urgently required and we applied marteloscope techniques to begin with establishing a benchmark of training requirements. A marteloscope is a forest research plot where all trees are measured and have clearly visible numbers on the stem surface. We carried out a first marteloscope experiment at the Svartberget experimental forest near Umeå in Northern Sweden involving 13 test persons that we asked to carry out CCF management by selecting trees that are supposed to stay behind and others that are to be taken out in order to achieve CCF objectives. We applied specialised statistics to analyse the trainees’ choices and thus to measure their current state of silvicultural knowledge and experience. The results were interpreted in the context of data previously obtained from 26 comparable marteloscope experiments in Britain. The Svartberget results were in parts similar to and sometimes even closer to theoretical expectations than the British results, but also revealed that more intensive training was required in individual-based forest management, which is an important part of CCF. A new didactic technique, the competitor-for-frame tree rule, tightening the link between evicted and residual trees has contributed to the good tree-selection performance at Svartberget.

Under a changing climate, the use of different forest management practices needs to be critically assessed to ensure functional forest stands. In rotational forestry (RF), similar-aged trees are planted in the stand, thinned several times during the rotation period, followed by a final clear-cut. Recently, the use of RF has caused a wide discussion in Fennoscandia since it has been shown to impact the microclimate, the ecosystem functioning and reduce the biodiversity compared to unmanaged forests. At the same time, alternative forest management options like continuous-cover forestry (CCF) have gained more interest. In CCF, only singular trees (single-tree selection) or groups of trees (gap-cutting) are harvested. The hypothesis is that CCF could maintain a higher biodiversity while it could mitigate the change in ecosystem functioning and microclimate. However, there is still a lack of scientific evidence on how different methods of CCF impact the forest microclimate, its spatial variation, and how that affects the understory vegetation including ericoid dwarf shrubs. Ericoid dwarf shrubs are an essential bioindicator of forests since they provide a habitat for wildlife, contribute to biodiversity, and impact the regeneration of tree seedlings. We have found contrasting results in the literature on how different forest management methods affect the growth patterns of ericoid dwarf shrubs in boreal forests. While some studies revealed that the shoot mortality of bilberry increased in clear-cut compared to uncut sites (Atlegrim and Sjöberg 1996), more recent studies have recorded an increased shoot growth and increased biomass in clear-cutting compared to mature RF stands (Nielsen et al. 2007, Nybakken et al. 2013). Thus, we aimed to shed light into the question on how RF and different methods of CCF (single-tree selection and gap-cutting) affect the forest floor microclimate and the morphology of two common dwarf shrub species (Vaccinium myrtillus and Vaccinium vitis-idaea) in boreal forest. We conducted our study in two different experimental research areas in Southern Finland. In the first area, we studied four RF and six CCF stands. We classified the stands managed by RF according to the time since the last clear cut, into the age classes ‘clear-cut’, ‘young’, ‘immature’, and ‘mature’. The CCF stands were managed by single-tree selection. In the second area, 50 km north from the first area, we studied five stands managed by gap-cuttings, collecting material in six gaps and their surrounding forests. We installed microclimate sensors in all the sites and recorded the soil moisture and soil temperature. In the beginning of August 2022, we sampled one V. myrtillus and V. vitis-idaea ramet adjacent to each microclimate sensor and recorded the canopy cover of the surrounding forest above each shrub pair. We calculated from each dwarf shrub ramet the specific leaf area (SLA), basal area increment (BAI), mean shoot elongation and total shoot elongation. Ramets of both species showed higher specific leaf areas in young RF stands than in clear-cut stands and ramets of V. vitis-idaea showed enhanced BAI in clear-cut stands compared to all other RF age classes and to single-tree selection. Growth traits of both species did not differ between ramets that grew in gap-centre and the surrounding forest. Within gaps, however, V. myrtillus showed an enlarged total shoot elongation at the northern-edge compared to gap-centre, and southern edge. We further observed that single-tree selection maintained more similar soil temperatures and soil moistures than mature RF stands, while the microclimate in clear-cut and young RF stands were altered compared to mature and immature RF stands. Gaps showed differing soil temperatures during the winter months, and differing soil moistures over the growing season. Since we could show that growth traits of ericoid dwarf shrubs were affected by forest management methods and by microclimate, we conclude further studies are needed to validate our findings and to ensure a successful forest regeneration.

Many well established techniques such as yield tables and age-based growth models are not applicable in continuous cover forestry (CCF). A further complexity in CCF is the need to predict regeneration. It is possible to model CCF using stand-based approaches such as transition matrices and stand table projection but the utility of these approaches is limited. Individual-based approaches are the most promising and may take two forms: cohort-based and single-tree models. While the utility and limitations of site indices based on age and dominant height is well established for plantation situations, there is no dominant paradigm for dealing with site productivity in stands managed as CCF. Alternatives include dendrometric approaches, indicator species and site descriptors such as elevation, slope and soil depth. In even-aged forests, the self-thinning line provides an effective way to estimate mortality in forest stands, but the concept is of limited utility in CCF. With CCF, the best option is to predict individual-tree survival from the resources deemed to be available to each tree. Fertile areas for further research include site productivity assessment and the modelling of regeneration and species interactions.

High boreal forest multifunctionality requires continuous cover forestry as a dominant management

In Finland, the new Forest Act in 2014 made continuous cover forestry (CCF) a possible forest management option. This triggered research on how forest owners and forestry professionals perceive CCF. In Sweden and Norway, the CCF method has been legal but not encouraged. Research on stakeholder views on CCF has only recently emerged, so only a few studies have been published on the topic. In Finland, according to surveys, less than 10% of forest owners have converted to CCF in all their forests and around 20–25% in part of their forests. About a fifth of forest owners expressed an interest in testing it. In the Finnish studies, CCF has been of particular interest to forest owners whose holdings are smaller than average and where they have recreational objectives. The interest of forest owners clearly increased if they were compensated for converting to CCF. Forestry companies, as well as their associations in Sweden and Finland, promote CCF as an alternative forest management method, according to statements on their official websites. How well this supportive attitude will materialise in their actions remains an open question. The current forestry culture, the power of industrial networks, uncertainties concerning economic profitability and ecological outcomes, as well as current forestry education and technical knowledge, are the main barriers for CCF.