Patterns of Understory Community Assembly and Plant Trait-Environment Relationships in Temperate SE European Forests

Abstract

We analyzed variation in the functional composition and diversity of understory plant communities across different forest vegetation types in Slovenia. The study area comprises 10 representative forest sites covering broad gradients of environmental conditions (altitude, geology, light availability, soil type and reaction, nutrient availability, soil moisture), stand structural features and community attributes. The mean and variation of the trait values were quantified by community-weighted means and functional dispersion for four key plant functional traits: plant height, seed mass, specific leaf area and leaf dry matter content. At each study site, forest vegetation was surveyed at two different spatial scales (4 and 100 m 2 ) in order to infer scale-dependent assembly rules. Patterns of community assembly were tested with a null model approach. We found that both trait means and diversity values responded to conspicuous gradients in environmental conditions and species composition across the studied forests. Our results mainly support the idea of abiotic filtering: more stressful environmental conditions (e.g., high altitude, low soil pH and low nutrient content) were occupied by communities of low functional diversity (trait convergence), which suggests a selective effect for species with traits adapted to such harsh conditions. However, trait convergence was also detected in some more resource-rich forest sites (e.g., low altitude, high soil productivity), most likely due to the presence of competitive understory species with high abundance domination. This could, at least to some extent, indicate the filtering effect of competitive interactions. Overall, we observed weak and inconsistent patterns regarding the impact of spatial scale, suggesting that similar assembly mechanisms are operating at both investigated spatial scales. Our findings contribute to the baseline understanding of the role of both abiotic and biotic constraints in forest community assembly, as evidenced by the non-random patterns in the functional structure of distinct temperate forest understories.

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

“…Level I plots are systematically distributed in a 16 km 9 16 km grid across Slovenia (Kutnar 2011). Level II plots were established in 11 different locations, representative of the heterogeneity of Slovenian forest types (Urbanc ˇic ˇet al 2016; Kermavnar and Kutnar 2020). We collected plant community and environmental data in 50 monitoring plots of 400 m 2 in size.…”

Disentangling the Ecological Determinants of Species and Functional Trait Diversity in Herb-Layer Plant Communities in European Temperate Forests

“…Level II plots were established in 11 different locations, representative of the heterogeneity of Slovenian forest types [53]. Detailed information on Intensive Monitoring plots is reported in the work of [39] and in [54]. Collectively, Level I and Level II plots were located in forest sites with a wide variety of climatic, geological, edaphic and topographical conditions as well as a broad range of forest vegetation composition.…”

Empirical Approach for Modelling Tree Phenology in Mixed Forests Using Remote Sensing

“…Slovenia is characterised by fairly large gradients of climatic factors due to its position between the Alps, the Mediterranean and continental Europe [43,44]. Consequently, a great variety of forest habitats, from the lowlands to the high mountains, can be found in the country [45]. Six broadleaved tree species/groups with more than ten years of available phenological observations provided by the NPN were included in this study: European beech (Fagus sylvatica), silver birch (Betula pendula), lime tree (mainly Tilia platyphyllos), common ash (Fraxinus excelsior), oak (pedunculate oak and sessile oak, i.e., Quercus robur and Quercus petraea, respectively) and aspen (Populus tremula).…”