The legacy of management approaches and abandonment on old-growth attributes in hardwood floodplain forests in the Pannonian Ecoregion

Abstract

In the absence of primeval floodplain forests, near-natural remnants are key references for close-to-nature forestry and nature conservation. Old-growth forest characteristics (OGCs) were quantified in 16 managed (rotation or selection) and abandoned semi-natural floodplain forests by taking snapshot inventories of structural features. Principal component analysis revealed a short gradient from closed-canopy managed stands dominated by large trees (mainly oaks) and hornbeams, with less deadwood, to abandoned older stands with more gaps, very large trees and different kinds of deadwood. All the studied forests are mainly in the early and late biostatic phases of forest development, with innovation and degradation phases almost completely absent. Results showed that selection forests had significantly more very large trees compared to rotation stands. The difference in structure between abandoned selection stands and abandoned rotation stands was more pronounced than in their counterparts that are still managed. Based on diameter distribution and the amount of very large trees and deadwood, abandoned selection stands were closest to the structure of natural forests. Selection forests may recover certain OGCs more rapidly than rotation forests. We concluded that after 100-150 years of homogenising rotation forestry, OGCs are slow to develop in just 25 years of non-intervention. Based on our results, we recommend: (i) an increase in the rotation cycle with selective logging in order to restore and maintain OGCs in managed rotation forests and (ii) total abandonment in certain well-preserved, near-natural forests with natural flooding regimes. However, the failure of oak to regenerate naturally remains a challenge.

Relation between Topography and Gap Characteristics in a Mixed Sessile Oak–Beech Old-Growth Forest

“…However, natural competition between seedlings and the formation of strong roots are favored [94][95][96]. The relevance of gaps formed near ground level has been shown as important not only for species regeneration but also for the growth of light-demanding species saplings [44,49]. In larger gaps, species competition ability increases because they develop strong root systems that favor better uptake of nutrients from soil and a higher resistance to biotic and abiotic factors [16,97].…”

“…Nevertheless, tree death does not always lead to gap formation, with their occurrence also being controlled by the sub-canopy structure [24]. However, canopy gaps are extremely important for the regeneration and growth process, especially for shade-intolerant species [12,19,21,37,44]. Canopy gaps also control light conditions, nutrient availability, soil moisture and biological properties, thus, influencing forest ecology, diversity and dynamics by creating suitable conditions for tree species development [30,37,45,46].…”

“…Many studies carried out in Europe have focused on the structural characteristics of the stands, such as the size of the canopy gap distribution [48,[58][59][60][61][62][63], and only a few have focused on the relationship between gap characteristics and topography [9,26,64]. However, numerous studies regarding canopy gaps have focused on gaps formed near ground-level [25,26,44,60,65,66]. These kinds of gaps are important for forest regeneration and the sapling growth of light-demanding species [44,49].…”

“…However, numerous studies regarding canopy gaps have focused on gaps formed near ground-level [25,26,44,60,65,66]. These kinds of gaps are important for forest regeneration and the sapling growth of light-demanding species [44,49]. It is difficult to measure the gaps formed higher up in the canopy, but these gaps are important for the higher growth of larger trees [26,44,67].…”

Tracking tree history to understand better natural dynamics of old-growth forest stands

“…Similar processes take place in managed forests after abandonment. Differentiation of the age and diameter distribution of trees begins slowly, species composition and dominance relations change, and the number of large and standing dead trees increases (Demeter et al 2020;Lábusová et al 2019). After some decades, a conspicuous accumulation of dead trees shapes the formerly managed stands looking like ancient ones (Vandekerkhove et al 2009;Aszalós et al 2017;Meyer and Schmidt 2011;Meyer et al 2021).…”