The leaf economic and plant size spectra of European forest understory vegetation

Abstract

Forest understories play a vital role in ecosystem functioning and the provision of ecosystem services. However, the extent to which environmental conditions drive dominant ecological strategies in forest understories at the continental scale remains understudied. Here, we used ~29 500 forest vegetation plots sampled across Europe and classified into 25 forest types to explore the relative role of macroclimate, soil pH and tree canopy cover in driving abundance‐weighted patterns in the leaf economic spectrum (LES) and plant size spectrum (PSS) of forest understories (shrub and herb layers). We calculated LES using specific leaf area (SLA) and leaf dry matter content (LDMC) and PSS using plant height and seed mass of vascular plant species found in the understories. We found that forest understories had more conservative leaf economics in areas with more extreme mean annual temperatures (mainly Fennoscandia and the Mediterranean Basin), more extreme soil pH and under more open canopies. Warm and summer‐dry regions around the Mediterranean Basin and areas of Atlantic Europe also had taller understories with heavier seeds than continental temperate or boreal areas. Understories of broadleaved deciduous forests, such as Fagus forests on non‐acid soils, or ravine forests, more commonly hosted species with acquisitive leaf economics. In contrast, some coniferous forests, such as Pinus, Larix and Picea mire forests, or Pinus sylvestris light taiga and sclerophyllous forests, more commonly hosted species with conservative leaf economics. Our findings highlight the importance of macroclimate and soil factors in driving trait variation of understory communities at the continental scale and the mediator effect of canopy cover on these relationships. We also provide the first maps and analyses of LES and PSS of forest understories across Europe and give evidence that the understories of European forest types are differently positioned along major axes of trait variation.

Variation in floristic and trait composition along environmental gradients in the herb layer of temperate forests in the transition zone between Central and SE Europe

“…This group of species also have a very short flowering period compared to other species and can be additionally differentiated in terms of some key functional traits related to leaf economics and plant size spectra (e.g. specific leaf area, leaf dry matter content, plant height, seed mass) (Durak and Durak 2021;Cubino et al 2021). In addition, phenological traits of understory communities perhaps depend more on species (i.e.…”

“…Beech forest species show a rather narrow spectrum of ecological niches (higher requirements for soil nutrients and moisture) and share similar functional traits associated with a competitive and/or stress-tolerant strategy but limited dispersal ability (Willner et al 2009). Understories of broadleaved deciduous European forests (such as beech forests on non-acid soils or ravine forests) more commonly host species with acquisitive leaf economics (Cubino et al 2021). Such a pattern can also be interpreted with respect to shade-tolerant competitive tree species (e.g.…”

“…Since functional composition largely reflects floristic composition, similar effects of future climate shifts can be expected for community trait patterns (Felsmann et al 2018). As highlighted by Cubino et al (2021), trait variation of understory plant communities at the continental scale is driven by macroclimate and soil factors and modulated by overstory canopy cover. All these factors (or their surrogates) were addressed also in our study.…”

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

“…Forest canopy cover, besides temperature, can greatly influence the distribution of graminoids likely due to amount of light availability offered (Cubino et al, 2021; De Frenne et al, 2019; cf. Depauw et al, 2020).…”

“…Conversely, shade‐adapted species which are more concentrated in higher elevations (positive Spearman correlation between shade‐adapted and cold‐adapted species; r = 0.436) more strongly declined (Table 2). However, the full mechanisms of future climate adaption of species are not clearly known and it seems that other important factors attributed to specific habitat peculiarities of species, current distribution, reproduction strategy, and functional trait peculiarities (i.e., conservative resource use vs. acquisitive resource use; Cubino et al, 2021) of each individual species can influence the way they cope with climate change.…”