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1. A central challenge of today's ecological research is predicting how ecosystems will develop under future global change. Accurate predictions are complicated by (a) simultaneous effects of different drivers, such as climate change, nitrogen deposition and management changes; and (b) legacy effects from previous land use. 2. We tested whether herb layer biodiversity (i.e. richness, Shannon diversity and evenness) and functional (i.e. herb cover, specific leaf area [SLA] and plant height) responses to environmental change drivers depended on land-use history. We used resurvey data from 192 plots across nineteen European temperate forest regions, with large spatial variability in environmental change factors. We tested for interactions between land-use history, distinguishing ancient and recent (i.e. post-agricultural) forests and four drivers: temperature, nitrogen deposition, and aridity at the regional scale and light dynamics at the plot-scale. 3. Land-use history significantly modulated global change effects on the functional signature of the herb layer (i.e. cover, SLA and plant height). Light availability was the main environmental driver of change interacting with land-use history. We found greater herb cover and plant height decreases and SLA increases with

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Saving the remaining natural forests in northern Europe has been one of the main goals to halt the ongoing decline of forest biodiversity. To facilitate the recognition, mapping and efficient conservation of natural forests, there is an urgent need for a general formulation, based on ecological patterns and processes, of the concept of "forest naturalness". However, complexity, structural idiosyncracy and dynamical features of unmanaged forest ecosystems at various spatio-temporal scales pose major challenges for such a formulation. The definitions hitherto used for the concept of forest naturalness can be fruitfully grouped into three dimensions: 1) structure-based concepts of natural forest, 2) species-based concepts of natural forest and 3) process-based concepts of natural forest. We propose that explicit and simultaneous consideration of all these three dimensions of naturalness can better cope with the natural variability of forest states and also aid in developing strategies for forest conservation and management in different situations. To become operational, criteria and indicators of forest naturalness need to integrate the three dimensions by combining species (e.g. red-listed-, indicator-and umbrella species) with stand and landscape level structural features that are indicative of disturbance and succession processes.

Functional traits respond to environmental drivers, hence evaluating trait-environment relationships across spatial environmental gradients can help to understand how multiple drivers influence plant communities. Global-change drivers such as changes in atmospheric nitrogen deposition occur worldwide, but affect community trait distributions at the local scale, where resources (e.g. light availability) and conditions (e.g. soil pH) also influence plant communities.• We investigate how multiple environmental drivers affect community trait responses related to resource acquisition (plant height, specific leaf area (SLA), woodiness, and mycorrhizal status) and regeneration (seed mass, lateral spread) of European temperate deciduous forest understoreys. We sampled understorey communities and derived trait responses across spatial gradients of global-change drivers (temperature, precipitation, nitrogen deposition, and past land use), while integrating in-situ plot measurements on resources and conditions (soil type, Olsen phosphorus (P), Ellenberg soil moisture, light, litter mass, and litter quality).• Among the global-change drivers, mean annual temperature strongly influenced traits related to resource acquisition. Higher temperatures were associated with taller understoreys producing leaves with lower SLA, and a higher proportional cover of woody and obligate mycorrhizal (OM) species. Communities in plots with higher Ellenberg soil moisture content had smaller seeds and lower proportional cover of woody and OM species. Finally, plots with thicker litter layers hosted taller understoreys with larger seeds and a higher proportional cover of OM species.• Our findings suggest potential community shifts in temperate forest understoreys with global warming, and highlight the importance of local resources and conditions as well as global-change drivers for community trait variation. Hansen et al., 2001;Walther, 2010;De Frenne et al., 2011;Bernhardt-R€ omermann et al., 2015;Bjorkman et al., 2018). Important global change drivers affecting temperate plant communities include increased temperatures, changes in Plant Biology 22 (2020) 410-424

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Abandonment of agriculture land and subsequent natural afforestation have been common features of the contemporary Latvian rural landscape, particularly in the period since 1990. This process affects the structure, ecology and visual qualities of the landscape. The study examines spatial characteristics of afforestation in relation to various environmental factors. The study was conducted in the central part of Latvia, where there is abundant abandoned agriculture land and a great variety of spatial afforestation patterns. The most typical patterns in this area were linear, mosaic, and continuous afforestation, as well as development of afforestation from the forest edge. The results of the study show that the spatial patterns of natural afforestation of abandoned agriculture fields can be very diverse, and do not follow the classical secondary succession model. Afforestation can be delayed by a dense cover of herbaceous vegetation for a period of up to 20 years. There are many interacting factors that affect succession and development of afforestation patterns, such as soil properties, size and configuration of fields, previous land use and also the random nature of plant colonization by seed. Further studies on afforestation patterns would help to understand better their ecological, economic and social effects as well as to determine optimal solutions for the use of abandoned agriculture land.