The increasing use of fossil fuels and the resulting drastic changes in global and local climate positions humanity in front of one of the most severe crises in history. Solutions pointing to carbon-neutral provisioning of energy and material resources have to be developed swiftly and on all spatial scales (IPCC, 2022; IUCN, 2022). Regional and local use of wood for energy and as building material is seen as one component of a more sustainable economy (EU, 2018; UK, 2012). In Germany, half of the country’s forested area is privately owned, distributed equally among owners possessing at least 20 ha, and small-scale private forest (SPF) owners with forest parcels under 20 ha (BMEL, 2014). While forestry in owner groups with larger properties (state and federal forests, communal forests, and larger private properties) has undergone increased mechanization and orientation towards economic objectives in the past, SPF owners have often been less inclined to extract wood from their forests. Furthermore, many SPFs in Germany are of very small sizes (average private forest parcel size of 3 ha) (BMEL, 2014), often precluding economic use, especially by heavy machinery, and leading to significantly different forest structures in SPFs compared to other ownership types (Mölder et al., 2021). Most notably, SPFs have been shown to feature higher structural diversity (Maltamo et al., 1997; Rendenieks et al., 2015; Schaich and Plieninger, 2013) and biodiversity (Torras et al., 2012). Certain structures and habitats that are considered especially important for nature conservation have been shown to occur there more frequently, like tree-related microhabitats (TreMs) (Johann and Schaich, 2016) and deadwood (Schaich and Plieninger, 2013)
With changing economic parameters like rising wood prices and increasing demand for sustainable fuels, increasing forest management intensity is becoming more and more interesting for many SPF owners. Extension services offered by state and private forestry associations are also increasingly encouraging wood extraction from small parcels (Takala et al., 2022), even though this might be questionable considering the carbon impact (Norton et al., 2019; Sterman et al., 2022). Another aspect to consider are the consequences for valuable habitat structures and the species that depend on them (Kjučukov et al., 2022). TreMs have been recognized as valuable for a plethora of species groups (Asbeck et al., 2021a). They are relatively easy to survey and can be used as a proxy for the occurrence of species groups like saproxylic beetles, spiders, bats, birds, fungi and lichens (Martin et al., 2022). Many TreMs are known to develop over long time spans (Kõrkjas et al., 2021) and are therefore rare in conventionally managed forests, where trees are mostly harvested before they can develop features like accumulated crown deadwood or tree hollows (Ranius et al., 2009). Due to lower management intensity, TreMs have a higher chance to develop in SPFs, but are now experiencing increased pressure with rising timber and particularly firewood extraction. Another feature of central importance to multiple forest functions is deadwood, which improves forest soils, has a beneficial impact on water retention, and serves as medium-term carbon sink (Chivulescu et al., 2022; Parisi et al., 2018; Piaszczyk et al., 2021). Deadwood also provides the substrate and habitat for a range of organism groups, many of which are endangered and protected. Examples include bryophytes, lichens, fungi, invertebrates, small mammals and birds (Bujoczek et al., 2021). Similar to TreMs, deadwood supplies in SPFs and related biodiversity can be put under pressure with increasing forest management intensity.
SPF owners are a heterogeneous group of people with a diverse set of motivations and goals concerning their land, resulting in a variety of strategies when managing their forests (Tiebel et al., 2023; Westin et al., 2023) While SPF owners are often assumed to have predominantly economic interests, there is actually a large variety in motivations. A substantial group of SPF owners is strongly interested in nature and cultural heritage conservation (Weiss et al., 2019). Likewise, the management activities of SPF owners are diverse and may comprise a wide range from industrialized wood harvesting, logging by horses, manually extracting single small stems as firewood for personal consumption, or even ceasing all felling activities for the sake of nature conservation, or due to lack of interest or long distances to their property (Bieling, 2004; Tiebel et al., 2021; Weiss et al., 2019).
Many structures of conservation value in forests take a long time to develop (Kõrkjas et al., 2021) or may depend on random, unpredictable events (breaking of stems or parts of the crown, injuries, colonization by animals; Larrieu et al. (2022)). Therefore, it seems not to be easy to relate structures and habitats to current motivations and management goals of forest owners. The time span during which individual forest owners actively influence their forests is often short compared to natural processes in the forest ecosystem, and long-term influences for example from topographical characteristics of the forest parcel (elevation, slope, water and soil parameters) or the surrounding landscape (fragmentation or location in large, closed forests) may play an equally important role in the development of valuable structures (Bujoczek and Bujoczek, 2022; Kapusta et al., 2020; Kennedy et al., 2008).
To our knowledge, the relationships between small-scale private forest owner goals and activities, and structures and habitats in their respective forest parcels have not been investigated yet. To address this research gap, we performed analyses in SPFs smaller than 5 ha in a model region, the Lower Saxon Hills in northwest Germany (see Fig. 1). We used the following data sets: (a) quantitative survey data about SPF owners’ goals and activities; (b) field data collected on their parcels (data on forest structure and nature conservation values); and (c) data on the topographical parameters of the parcels to address the following research questions:
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What are the characteristics of the SPF parcels in our model region concerning stand structure variables and the distribution of valuable habitats?
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What are the respective influences of owner goals and activities, and topographical parameters on these variables?
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How can the possibly varying influences be explained, and which conclusions for integrative forest and conservation management in SPFs can be drawn?