Life‐form diversity across temperate deciduous forests of Western Eurasia: A different story in the understory

Abstract

Aim To analyse the biogeographic patterns of Temperate Deciduous Forests (TDFs) in Western Eurasia based on different life‐forms and forests layers and explore their relationships with the current climate, Last Glacial Maximum (LGM) climate and topography. Location Western Eurasia. Taxon Vascular plants. Methods We delimited nine regions encompassing the variability of TDFs in Western Eurasia and collected 1000 vegetation plots from each. We deconstructed the plant communities into three layers, tree, shrub and floor. We used (i) generalized linear mixed models (GLMM) to analyse the influence of current climate, historical climate and topography on species richness by accounting for regional effects and (ii) redundancy analysis (RDA) with variance partitioning to describe the variation in life forms along abiotic gradients. The three forest layers were analysed jointly and separately. Results The Balkans, Alps and Carpathians appeared to be the richest in plant species, whereas the British Isles and the Hyrcanian region were the poorest. Annual temperature range and annual mean temperature were the best predictors of species richness for the whole dataset and for the shrub layer. The tree layer richness was mainly explained by the annual temperature range and by elevation, whereas the forest floor richness was more related to the annual temperature range and the annual mean temperature differences between the LGM and current climate. The current climate was the main predictor of the composition of the whole community, the tree layer and the floor layer, while the shrub layer was also influenced by historical climate. Main conclusions Our overview of the diversity of temperate deciduous forests in Western Eurasia demonstrates different patterns and drivers across life‐forms and forest layers. While the diversity of trees is mainly linked to current climatic conditions, the shrub layer is also driven by postglacial‐glacial climatic stability, suggesting a different origin from forest trees.

Climatic definitions of the world’s terrestrial biomes

“…In Western Eurasia this biome covers a large area encompassing most of Europe, a strip in central-western Siberia, the Caucasus piedmonts and the eastern and southern coastal fringe around the Black Sea (Euxinian) and south Caspian Sea (Hyrcanian), a vast area limited by the boreal forest in the north and the Mediterranean and steppic regions in the south (Jahn 1991;Loidi et al 2021). The summer rains are provided by the westerlies coming from the Atlantic, which drag a succession of lows with fronts, which form part of the Polar Front system.…”

Solutions to fire and shade: resprouting, growing tall and the origin of Eurasian temperate broadleaved forest

“…Mechanical defences such as spinescence, consistent with herbivore regulation (Bakker et al ., 2004; Vera et al ., 2006; Bakker et al ., 2016), tend to be associated with shrubs. Herbaceous plants are the most species‐rich component of western Eurasian forests (Loidi et al ., 2021). However, classified according to the Raunkiær plant life‐form system, these ground‐layer plants bear fire‐avoiding traits that are adaptive under consumer regulation in open environments: chamaephytes (perennating buds at ground level), geophytes (below‐ground storage), hemicryptophytes (herbaceous perennials with bud renewal at ground level) and therophytes (annuals).…”

“…Fire and drought have been key historical drivers shaping the development of the forest‐steppe (Feurdean et al ., 2015; Feurdean & Vasiliev, 2019; Butiseacă et al ., 2021). Compared with herbaceous growth forms, the woody component is impoverished (Klimešová et al ., 2017; Loidi et al ., 2021), evidence of antiquity and diversification in the former and strong environmental filtering in the latter.…”

“…Mechanical defences such as spinescence, consistent with herbivore regulation (Bakker et al, 2004;Vera et al, 2006;Bakker et al, 2016), tend to be associated with shrubs. Herbaceous plants are the most species-rich component of western Eurasian forests (Loidi et al, 2021). However, classified according to the Raunkiaer plant life-form system, these ground-layer plants bear fire-avoiding traits that are adaptive…”

The combined effects of climate and canopy cover changes on understorey plants of the Hyrcanian forest biodiversity hotspot in northern Iran

“…The forests harbor the southeasternmost populations of several European tree species, such as Carpinus betulus , Fraxinus excelsior , Sorbus torminalis, and Ulmus glabra (Akhani et al, 2010). These isolated forests have a heterogeneous structure (Ehlers, 2012), comprise almost half of the plant diversity of the Caucasus biodiversity hotspot (Mittermeier et al, 2011), harbor many endangered, and regionally and locally endemic plant species, and thus contribute to the high conservation value of the region (Akhani et al, 2010; Loidi et al, 2021; Noroozi et al, 2019).…”