Fire Occurrence in Hemi-Boreal Forests: Exploring Natural and Cultural Scots Pine Fire Regimes Using Dendrochronology in Lithuania

Abstract

Fire is an important natural disturbance and a driver of hemi-boreal forest successional trajectories, structural complexity, and biodiversity. Understanding the historic fire regime is an important step towards sustainable forest management. Focusing on Lithuania’s hemi-boreal forests, we first mapped the potential natural fire regimes based on the relationship between site conditions, vegetation, and fire frequency using the ASIO model. The ASIO model revealed that all the fire frequency categories (Absent, Seldom, Intermittent, Often) are found in Lithuania. Scots pine forests dominated the often fire frequency category (92%). Secondly, focusing on a fire-prone forest landscape, Dzūkija, we analyzed the fire occurrence of Scots pine forest types using dendrochronological records. We sampled and cross-dated 132 Scots pine samples with fire scars from four dry forest stands (n = 92) and four peatland forest stands (n = 40), respectively. In total, the fire history analysis revealed 455 fire scars and 213 fire events during the period of 1742–2019. The Weibull median fire intervals were 2.7 years (range 1–34) for the dry forest types and 6.3 years (range 1–27) for the peatland forest types. Analysis pre- and post-1950 showed the Weibull median fire interval increased from 2.2 to 7.2 for the dry forest types but decreased from 6.2 to 5.2. for the peatland forest types. A superposed epoch analysis revealed significant precipitation fluxes prior to the fire events after 1950. Thus, the Dzūkija landscape of Lithuania has been strongly shaped by both human and naturally induced fires. The combination of theory (the ASIO model) with the examination of biological archives can be used to help guide sustainable forest management to emulate forest disturbances related to fire. As traditional forest management focusing on wood production has eliminated fire, and effectively simplified forest ecosystems, we recommend introducing educational programs to communicate the benefits and history of forest fires as well as adaptive management trials that use low-intensity prescribed burning of Scots pine stands.

Adaptive Relationships in Hemi-Boreal Forests: Tree Species Responses to Competition, Stress, and Disturbance

“…Moreover, a diverse spectrum of forest vegetation communities is at risk of being lost due to widespread even-aged clearcutting practices, i.e., maximum sustained yield [ 24 ], and early age harvesting [ 2 ]. Subsequent re-establishment practices of deep mechanical scarification and planting of singular tree species continue to place increased pressure on Lithuania’s hemi-boreal forests as functionally integrated complex adaptive dynamical systems [ 1 , 25 ]. In Lithuania, “high forestry” is still associated with the growing use of stem wood regardless of species and tree age [ 26 , 27 ].…”

Challenges and Solutions for Forest Biodiversity Conservation in Sweden: Assessment of Policy, Implementation Outputs, and Consequences

“…Migratory fish and their relationship to water flow regimes and dynamics of other species in entire catchments is another [314,315]. Another example is the interaction between forest fires and species that depend on them [316,317]. The highest level of ambition represents resilience, which means to maintain a system's ability to recover from large-scale disturbances [318].…”

Deep Ecology, Biodiversity and Assisted Natural Regeneration of European Hemiboreal Forests

“…We focused on the European hemiboreal forests of Lithuania because it is one of only two countries (Latvia and Lithuania) that falls completely within the hemiboreal forest zone in Europe [17]. The hemiboreal forest zone is the flux zone between the temperate forest zone to the south and boreal zone to the north.…”

“…Lithuania's hemiboreal forest site types (as well as the 13 Natura 2000 forest habitat types of European Community) can be classified into three main forest habitat types based on the concept of potential vegetation and soils [14,18,19]: (1) mixed broadleaved forests on rich sites; (2) mixed species forests on mesic sites dominated by Norway spruce; and (3) Scots pine (Pinus sylvestris) forests on poor sites. Soil moisture and fertility of Lithuania's forests are considered the main drivers of forest disturbances and succession [17]. As such, Lithuania's forests have been classified by the Food and Agriculture Organisation (FAO, Rome, Italy) soil classification system [20,21] based on soil typological groups (Figure 1).…”

“…Scots pine forests grow on highly oligotrophic, strongly acid-to base-rich soils, on very shallow and dry substrates to wet and oxygen-poor mires, on mineral and peat wetlands. Within peatland forests, vegetation communities show that a high-water table and nutrient poor environment affects tree growth [17]. The species composition of Lithuanian hemiboreal pine forests is often a mixture of species from various vegetation formations but can be remarkably similar to boreal pine forests (especially on infertile sites).…”