Structural variation of forest edges across Europe

Abstract

Forest edges are interfaces between forest interiors and adjacent land cover types. They are important elements in the landscape with almost 20 % of the global forest area located within 100 m of the edge.Edges are structurally different from forest interiors, which results in unique edge influences on microclimate, functioning and biodiversity. These edge influences have been studied for multiple decades, yet there is only limited information available on how forest edge structure varies at the continental scale, and which factors drive this potential structural diversity. Here we quantified the structural variation along 45 edge-to-interior transects situated along latitudinal, elevational and management gradients across Europe. We combined state-of-the-art terrestrial laser scanning and conventional forest inventory techniques to investigate how the forest edge structure (e.g. plant area index, stem density, canopy height and foliage height diversity) varies and which factors affect this forest edge structural variability. Macroclimate, management, distance to the forest edge and tree community composition all influenced the forest edge structural variability and interestingly we detected interactive effects of our predictors as well. We found more abrupt edge-to-interior gradients (i.e. steeper slopes) in the plant area index in regularly thinned forests. In addition, latitude, mean annual temperature and humidity all affected edge-to-interior gradients in stem density. We also detected a simultaneous impact of both humidity and management, and humidity and distance to the forest edge, on the canopy height and foliage height diversity. These results contribute to our understanding of how environmental conditions and management shape the forest edge structure. Our findings stress the need for site-specific recommendations on forest edge management instead of generalized recommendations as the macroclimate substantially influences the forest edge structure.Only then, the forest edge microclimate, functioning and biodiversity can be conserved at a local scale.

Drivers of carbon stocks in forest edges across Europe

“…continuously forested since the oldest available land use maps, which is typically at least 150-300 years ago). For further details regarding the study design, forest structure and site selection see Govaert et al (2020) and Meeussen et al (2020).…”

“…The plant area index was determined (May and July 2018, leaf-on conditions) with a RIEGL VZ-400 terrestrial laser scanner and was calculated as the integral of the plant area per volume density (m 2 m −3 ) over the canopy height. More technical details on the terrestrial laser scanning campaign and data processing can be found in Meeussen et al (2020). During the growing season, the plant area index is mainly determined by the amount of foliage biomass; typical ratios of the woody to total plant area are less than 0.4 (Gower et al, 1999;Kalácska et al, 2005).…”

“…However, up to 20% of the global forested area lies within 100 m of a forest edge (Haddad et al, 2015) and is subject to strong edge influences that penetrate far towards the interior (Schmidt et al, 2017). Forest edges differ in vegetation structure and composition compared to interiors (Harper et al, 2005;Meeussen et al, 2020). Furthermore, due to the strong differences in structure between forest edges and adjacent lands, edges further receive higher levels of atmospheric N-deposition (Weathers et al, 2001;Devlaeminck et al, 2005;De Schrijver et al, 2007;Wuyts et al, 2008).…”

Small scale environmental variation modulates plant defence syndromes of understorey plants in deciduous forests of Europe

“…Future research addressing the inducibility of both defence and tolerance traits in response to herbivore feeding will contribute to a better understanding of the importance of induced trait responses in shaping patterns along environmental gradients. Forest edge-to-core transects can in this context act as an extremely useful study system as they are characterized by strong biotic and abiotic clines over a small spatial scale (De Frenne et al, 2019;De Smedt et al, 2019;Govaert et al, 2020;Lantman et al, 2019;Meeussen et al, 2020;Murcia, 1995;Remy et al, 2016).…”

“…The spatial scale of sampling along latitudinal or elevational gradients (partly) mismatches the spatial scale of evolutionary processes that are postulated to drive variation in defence traits (Gaston, 2000). Forest edge-to-core transects, for example, are characterized by strong abiotic clines in temperature, humidity, light and soil nutrient availability (De Frenne et al, 2019;Meeussen et al, 2020;Murcia, 1995;Remy et al, 2016), as well as biotic clines in the floral, arthropod and gastropod community composition over less than 100 m (De Smedt et al, 2019;Govaert et al, 2020;Lantman et al, 2019).…”