Abstract
Key messageFrom 1973 to 1991, Polish SO2emissions above 3250 Gg/year resulted in a decline of firAbies albaMill. After stresses connected with these emissions, five main diameter at breast height (DBH) structural types were described. This type of heterogeneous forest structure is supposed to increase forest resistance and resilience to abiotic, biotic and anthropogenic disturbances.ContextThe analyses of forest structure are important under the current scenario of global change, since heterogeneous structures allow for better responses to disturbances. Forests with more complex structures should present greater vitality.AimsThe main hypotheses were as follows: (1) the temporal changes of atmospheric SO2 emissions caused (a) the abrupt changes in the tree DBH radial increment and (b) the death of fir trees; and (2) atmospheric SO2 emissions and related fir decline and recovery processes ultimately result in the development of stands characterised by diverse DBH structures.MethodsRadial growth trends of 49 and 215 fir trees in the older and younger generations, respectively, and 85 dead fir trees were evaluated. Using data collected in 32 stands, the DBH structural types were identified, and the shapes of these types were illustrated.ResultsThe structural diversification of forest patches may influence forest resistance and resilience to disturbances; five main structural types were identified: ML1 and ML2 represent DBH distributions of multi-layered stands, and OS, TS1 and TS2 represent DBH distributions of one- and two-storied stands.ConclusionStructural diversity of forests was a response to SO2 emissions; fir trees had the ability to increase their radial growth, although there were still high SO2 emissions.
Highlights
Considering only the tree components of a forest, structural diversity can be observed in the heterogeneity of forest patches, primarily as a variation in tree diameter at breast height (DBH) distributions
The following stand and DBH distribution variables were calculated for each sample plot: share of fir assessed on the basis of a basal area, number of trees per hectare (N), stand basal area (G), minimum DBH, average DBH (d ), maximum DBH, 1 quartile DBH (d0.25), 2 quartile DBH (≡median) (d0.50) and 3 quartile DBH (d0.75)
The radial growth trends and the relationships between tree ring widths and SO2 emissions for fir trees were similar, but the greater and longer decrease occurred in fir trees from the older generation compared to that of the fir trees from the younger generation (Figs. 4, 5 and 6)
Summary
Considering only the tree components of a forest, structural diversity can be observed in the heterogeneity of forest patches, primarily as a variation in tree diameter at breast height (DBH) distributions. Structural diversity plays an important role in the analysis of biological processes and functions, e.g. in explaining forest dynamics (Korpeľ 1995). The multifactorial nature of tree mortality means that simple associations among variables such as various anthropogenic factors, or climate changes and forest dynamics, may be often unrealistic (Lloret et al 2012). Forest ecosystems use ecophysiological and demographic-stabilising mechanisms, which can compensate for dying. Such mechanisms should not underestimate the potential of these events to induce dramatic changes, especially if they are more frequent
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