One of the objectives of forest conservation is the set aside of unharvested areas. However, the fragmentation and lack of connectivity of protected areas make the integration of conservation measures in productive forests essential. Strategies to integrate conservation of saproxylic biodiversity in forest management have been developed, but often considering only specific aspects or remaining preliminary otherwise. As the impact of climate change and anthropogenic stresses increases, the development and the synthesis of this approach is crucial. We reviewed the key literature on forest management for biodiversity conservation, integrating forest science perspective to provide a practical management framework. Our goal is to present a management framework that could contribute to the effective preservation of forest insect biodiversity at the landscape scale, without high economic efforts, and addressing the conflicts that still jeopardize sustainable forest management. The results of our review support the creation of micro-reserves inside productive forests, to support large reserves in landscape conservation strategies. Micro-reserves increase the resilience of forest ecosystems to anthropogenic disturbances, through the development of a heterogeneous structure, maximizing microhabitat availability. Modeling forest management and harvest on local natural disturbance would extend the benefits of spatio-temporal heterogeneity in productive forests. Variable retention harvest systems, applied at the landscape scale, are a feasible and adaptable strategy to preserve and increase biodiversity, safeguarding structural legacies such as senescent trees and deadwood inside the productive matrix. The operational shift, from the stand to the forest landscape, is fundamental to extend the benefits of conservation measures. The Forest Biodiversity Artery, composed by several micro-reserves or
Changes in land-use confined old-growth forest to less than 0.5% of the forested area in Europe, United States and China (
Traditionally conservation efforts brought the employment of natural forest as a model for restoration (
Since the establishment in 1811 of the Royal Saxon Academy of Forestry in Tharandt by Heinrich Cotta, the concept of sustainability, in its former sense of a sustained yield of wood, has been a leading principle for managing forests in Europe (
For the selection of the reviewed studies,
After the 1970s, the idea that forests were constant and stable systems was abandoned, recognizing the complexity associated to the different kinds of disturbance (
Oldeman’s view roots on the subdivision of forests in eco-units, forest areas whose development started at a unique moment in time, and “which architecture, eco-physiological functioning and species composition are ordained by one set of trees until the end”. Even if the pathways of forest development are countless and influenced by chance, succession models have been derived to group them and summarize the involved processes (
A silvicultural practice based on the occurrence of the different eco-units or FDPs, established considering reference conditions, would sustain structural biodiversity conservation (
The maintenance of natural forest regeneration, together with the protection of soil productivity, represent the heart of nature-based silviculture (
Senescent and dead trees, together with snags and logs left on the forest floor, constitute what
Even if the threat represented by the management of a single forest stand is rather limited, the cumulative effect of these activities across a landscape may be significant (
In retention forestry, a part of trees and snags are left after the harvest, to create in young successional forests structures similar to those created by natural disturbance (
The general view on plantations is that they represent a sort of green desert. However, they can actually represent a potential habitat for biodiversity, since they resemble the structural complexity of natural forests more than other more intense land uses (
Conservation efforts in productive forests include the protection of “tree islands”, where no harvest takes place (
Saproxylic species assemblages that characterize forest environments live in association with their surroundings, depending on heterogeneous conditions in time and space (
The general definition of stand, as an area characterized by its internal uniformity in terms of “composition, age, arrangement or condition” (
For the effective preservation of forest biodiversity, an extensive strategy integrating reserves and matrix management must be developed (
Learning and inferring from natural models are key instruments to reach both economic production and biodiversity conservation (
Tree microhabitats are diverse (
The deadwood amount required to preserve biodiversity should be calibrated considering several taxonomical groups, taking into account the community composition rather than relying on the misleading species richness (
Forest restoration methods generally include tree girdling and felling to increase the availability of deadwood (
Patch-based conservation networks have been designed specifying a minimum number of required patches, having certain habitat conditions (
The application of predictive forest models to establish the IdS minimum size in beech (
The management system offered by the FBA ensures habitat continuity and the presence of a more complete set of eco-units, to preserve the saproxylic species that occur either as habitat-tracking meta-populations (
Nature-based silviculture relies on a thorough understanding of socio-economic and ecological components (
A heterogeneous range of substrate quality and management practices are essential to preserve saproxylic beetle diversity in productive forests (
Since the expansion of protected areas is limited by competing socio-economic goals, the shift towards the integration of reserves and structural legacies in production and protection forests (
Franco Mason was supported by the MiPAAF, Ministry of Agricultural Policy and Forestry, Italian National Forest Service, Central Biodiversity Office, Rome, in the framework of the LIFE Project ManFor C.BD. (LIFE09 ENV/IT/000078); Livia Zapponi was supported by the LIFE Project ManFor C.BD. We would like to thank our colleagues Serena Corezzola and Davide Badano, who kindly read an earlier version of the manuscript. We would like to thank Randy Rollins for language revision, and Zarina Dalla Santa Brown for the final reviewing of grammar and style. We thank Giorgio Matteucci for his constant support in the framework of the Life Project ManFor C.BD., Alessandro Bottacci, Marco Panella and Gianni Zanoni (Central Biodiversity Office of the Italian National Forest Service), Paola Favero (local Biodiversity Office of Vittorio Veneto, Italy) for the keen interest in applying for the first time in Italy the
Representation of the proposed management system: the Forest Biodiversity Artery (FBA). The FBA is embedded in the productive matrix, showing the Deadwood Corridors (DC) and the
Used term combinations for the literature search. (*): wildcard character used for boolean search.
Term 1 | - | Term 2: Management | - | Term 2: Conservation |
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Forest | - | Certification | - | Biodiversity |
Saproxylic* | AND | Disturbance | OR | Biodiversity conservation |
Dynamic | Deadwood | |||
Eco unit | Habitat tree* | |||
Gap harvest | Hollow tree* | |||
Landscape approach | Îlot* de sénescence | |||
Landscape management | Old-growth | |||
Plantation | Structural legacies | |||
Retention harvest | Tree retention | |||
Sustainable management | Tree microhabitat* |
Examples of gap based harvest with variable retention systems, applied to different forest types and various objectives.
Forest type | Aim | Harvest method | Unit size | Source |
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Boreal forest | Study the effect of green tree retention on forest biota | Retain 0, 10, 50 m3 ha-1 of the standing volume | 3-5 tree groups |
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Boreal mixed forests | Increase the density and vigour of spruce in aspen-dominated mixed woods | Alternate harvested and unharvested corridors | 10 m wide |
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Boreal mixed forests | Evaluate regeneration after partial cutting and natural disturbance | Remove 47.9-63.2% of pre-harvest basal area | 400 m2 |
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Boreal mixed forests | Emulate natural disturbance, maintain beetle diversity | Remove 10-20% of the canopy in harvest gaps | 0.1-0.2 ha |
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Boreal riparian forest | Emulate natural disturbance, increase habitat complexity through early succession forest regeneration | Partial harvest, up to 50% of basal area | 10 - 400 m2 |
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Floodplain forest | Natural reserve management emulating disturbances, saproxylic species conservation | Randomized small-gaps cutting with retention elements, waterlogging | 250-300 m 2 |
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Mixed hardwood forest | Restore and maintain ground-layer vascular plant diversity in a second-growth forest | Dormant season timber harvesting in the gap and thinning outside | 0 to 46 m of diameter |
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Mixed temperate forests and plantations | Limit environmental impact, emulate disturbance, re-establish multi-layer structure and re-naturalization of conifer plantations | Eco-units with retention of deadwood | 300-1000 m 2 |
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Spruce-fir ( |
Strengthen forest resilience to climate change increasing structural irregularity | Group selection with <50% of harvested trees (minimum diameter 52.5 cm) | 500 m2 |
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Lenga beech ( |
Assess regeneration under different microenvironmental conditions | Retain evenly distributed dominant trees between aggregates | 30 m radius aggregates |
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Key elements favoring the preservation of forest biodiversity at the landscape scale.
Element | Function | Characteristics | Source |
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Conserving biodiversity in commercial forests | Part of the sylvatic mosaic, size established considering local disturbance dynamics. High availability of deadwood and veteran trees, never harvested |
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Deadwood corridor (DC) | Favoring the connections and meta-community dynamics | Approximate interior forest conditions |
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Variable retention harvest (VRH) | Sustaining productive values without compromising ecosystem services | Gap harvest, with the retention of living structures and deadwood | See |
Structural legacies | Lowering critical trophic and raising microhabitat resources | Coarse woody debris: chablis or uprooted trees, volis or snags, high and low stumps | |
Habitat tree | Life boating for species and ecosystem processes | Green-tree retention in the harvested gaps, preserving over-mature trees (DBH>90 cm) in the matrix and, indefinitely in the FBA |
Types of the small patch cutting as reviewed by
Eco-units | Source | |
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Size (m2) | Shape | |
500-1000 | D = ½ H |
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< 400-500 | Circular |
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600-1500 | 1-1.5 H |
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NA | NA |
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500-1500 | NA |
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1000-1500 | D =1-1.5 H |
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NA | D = 2 H |
Characteristics that increase the probability of microhabitat and hollow formation.
Tree species | Characteristics | Focus | Source |
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Minimum DBH: beech>90 cm, fir>100 cm | Montane forests |
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Stage of senescence, tree form and DBH determine the occurrence of hollows | Model probability of hollow occurrence |
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Tree heights> 19 m, tree DBH>45 cm | Reptiles |
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DBH>110 cm | Reptiles |
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Minimum DBH: beech>72 cm, spruce>43 cm; the number of microhabitats increases for DBH>68 cm | Saproxylic beetles |
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Minimum DBH: beech>50 cm, spruce>65 cm | Saproxylic beetles |
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Snags host more microhabitats than living trees. More microhabitats on oaks than on the other species | Biodiversity |
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DBH 60.6 ± 16.4 cm | Birds |
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Minimum DBH for snags created from Scots pine to provide suitable cavity nest for birds and wildlife >40 cm | Birds and wildlife |
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DBH≥70 cm | Birds and mammals |
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Good predictors: time since last cutting, diameter class. Non-coniferous species have more microhabitats | Birds, mammals and saproxylic beetles |
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50% chance of hollow presence for trees 258 years old | Invertebrates, birds and mammals |
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Various | High DBH; balanced and pointed crown; straight trunk; dominant trees; local patterns related to altitude and slope | Wildlife conservation |
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Management recommendations for the preservation and increase of habitat and hollow trees.
Tree species | Recommendations | Focus | Source |
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Favor mixed forests:differentiate microhabitats. Allow that a part of the trees complete their natural cycle | Montane forests |
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Time lag in the use of hollow-bearing trees in harvested areas: ensure landscape availability | Mammals |
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Lag effects on the availability of hollows and conservation scenarios: model number of potential trees of high DBH/age | Birds |
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Take into account spatial distribution, avoiding safety conflicts | Saproxylic beetles |
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Include a sub-population (10-20% of the surface area) that will complete the natural silvigenetic cycle | Saproxylic beetles |
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Preserve and create pollard trees | Saproxylics |
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Microhabitat abundance is higher with low treatment history. Increase structural complexity: group harvest, small gap creation, retention of biological legacies | Birds and mammals |
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High stem density has a negative effect | Birds, mammals and saproxylic beetles |
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Hollows generated early in fast-growing trees | Invertebrates, birds and mammals |
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Guidelines for the artificial creation of microhabitats | Saproxylics |
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Pollarding increases the probability of hollows formation | Saproxylic beetles |
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Broadleaf species | Hollow tree spatial distribution less than 100 m | Saproxylic beetles |
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Maturing hardwood forests | Uneven-aged harvest with group selection had a lower impact on hollow availability | Harvest regimes |
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Various | Retain species with higher probability of developing hollows of survival | Wildlife |
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Various | Management guidelines in coppice | Insects |
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