Learning from the ecological degradation of European forests for future conservation
The 1.8 million ha of forest south of the Caspian Sea is a relict of intact Eurasian temperate forest characterized by numerous old-growth features. The forest shares a large proportion of species with Central European forests, but in Europe, forests are ecologically degraded due to millennia of human pressure. Recently, a law was enacted , protecting Caspian forests, but permits the extraction of damaged and dying trees to fulfill timber demands. In Europe, the extraction of dead wood was a major factor driving the ecological degradation of forests. By learning from the history of European forests, a degradation of Caspian forests similar to that of European forests may be prevented. To identify structural features crucial for biodiversity and ecological processes behind the decline of species, we modeled the Red List categories of 1,025 saproxylic beetles in Central Europe using a proportional-odds linear mixed-effects model. The model included traits characterizing species biology, required resources, and distribution as fixed-effects and phylogenetically correlated random intercepts. Our model allowed predictions of extinction risk for Caspian species if the ecological degradation continues. Furthermore, we assessed richness of saproxylic beetles in the Caspian region relative to environmental factors to evaluate to importance of dead-wood volumes.
For Central Europe, our model revealed a higher extinction risk for lowland and large species as well as for species that rely on wood of large diameter, broad-leaved trees, or open canopy. These results mirror well the centuries of ecological degradation of European forests caused by modern forestry, i.e., the conversion of natural broad-leaved forests to dense conifer-dominated forests, and the loss of over-mature trees and dead wood. In Caspian forests, these structures are still abundant and many species that are threatened or extinct in Europe due to the long history of forest management were frequently encountered on our plots in the Caspian forest. These species can thus be used as indicators for monitoring the status of saproxylic biodiversity. Similar to findings in Europe, dead-wood amount best explained species richness and composition of saproxylic beetle assemblages in Caspian forests. Considering these findings and learning from the history of forest degradation in Europe, we urge local authorities to stop the harvest of valuable dead-wood habitat in Caspian forests and to maintain habitat structures crucial for saproxylic biodiversity. Otherwise, a similar ecological degradation as experienced in European forests can be expected.