Forest vegetation in western Romania in relation to climate variables: Does community composition reflect modelled tree species distribution?

Abstract

Abstract. European beech (Fagus sylvatica L.) is the prevailing tree species of mesic forests in Central Europe. Increasing summer temperatures and decreasing precipitation, as climate change scenarios predict, may, however, negatively influence beech growth and induce a shift to more thermophilous forest communities. Temperatures as expected in the future for western Central Europe are currently found in parts of western Romania. In light of this climate analogy we investigated forest vegetation as an indicator for future vegetation changes in five regions of western Romania representing a climatic gradient. We related species composition to climate variables and examined if tree and understorey species composition respond similarly to the climatic gradient. We further analysed if tree species occurrences correspond with their modelled distance to the rear niche edge. We found evidence for climatic effects on vegetation composition among regions as well as within deciduous and pine forests, respectively. This underlines that vegetation composition is a useful indicator for environmental change. Tree and understorey species compositions were closely linked showing that community-based characterization of forest stands can provide additional information on tree species suitability along environmental gradients. Both, vegetation composition and a climatic marginality index demonstrate the rear niche edge occurrence of beech in the studied sites of Romania and can predict the site suitability for different tree species. While vegetation surveys indicate Quercus petraea to be associated to moderately mesic forests, the marginality index suggested an inner niche position of sessile oak along the climatic gradient. Phytosociological relevés that differentiate between subspecies (or microspecies) of sessile oak with differing habitat requirements should be considered to complement national forest inventories and species distribution maps when modelling rear distribution edges. We conclude that climate driven forest vegetation composition in western Romania is a suitable analogon and may indicate future forest development in western Central Europe.

Climate warming-induced replacement of mesic beech by thermophilic oak forests will reduce the carbon storage potential in aboveground biomass and soil

“…Earlier studies of forest structure and community composition in the western Romanian study region have shown that the beech forests are in many structural aspects very similar to Central European beech forests of the Galio-Fagion, and the oak-rich forests resemble Central European communities of the Quercetalia pubescenti-petraeae (thermophilic mixed oak forests) and Carpinetalia betuli (oak-hornbeam forests), despite the admixture of additional tree species with sub-Mediterranean and southeast European origin (Heinrichs et al, 2016;Indreica et al, 2017Indreica et al, , 2019Walentowski et al, 2015). The forest inventory and soil chemical data show that the three transects are located on mesic to eutric soils, and they are more or less comparable amongst the transects.…”

Ecological analysis of large floristic and plant-sociological datasets – opportunities and limitations

“…by excluding unsuitable records from isolated sub-populations. Another procedure to improve extrapolation results involves the restriction of the model area, to train the model only on the cells having a common climatic range on both islands, as applied in other studies (Heinrichs et al 2016;Horsák et al 2010). We found no significant improvement in the model's predictions, due to data abatement and to loss in the ecological response curves of the training data and therewith support the findings of other studies (Thuiller et al 2004).…”

Suitability of Fagus orientalis Lipsky at marginal Fagus sylvatica L. forest sites in Southern Germany

“…The CMI is more meaningful in climate change studies compared to other habitat suitability indices (HSI - Mellert et al 2016) as it distinguishes between the rear and the leading edge of the climatic range for a species. Recently, it has been used in many studies (Mellert et al 2015, Heinrichs et al 2016, Dorado-Liñán et al 2019, Walentowski 2019, Kasper et al 2021, Sánchez De Dios et al 2021). The CMI obtained in this study allowed a subdivision of the species niches into five meaningful zones along the gradient from the rear to the leading edge (see Fig.…”