DOI: 10.5061/dryad.1g1jwsv1t
title: Forest edge effects on moss growth are amplified by drought

description: Forest fragmentation increases the amount of edges in the landscape.
 Differences in wind, radiation and vegetation structure create
 edge-to-interior gradients in forest microclimate, and these gradients are
 likely to be more pronounced during droughts and heatwaves. Although the
 effects of climate extremes on edge influences have potentially strong and
 long-lasting impacts on forest understory biodiversity, they are not well
 understood and are not often considered in management and landscape
 planning. Here we used a novel method of retrospectively quantifying
 growth to assess biologically relevant edge influences likely caused by
 microclimate using Hylocomium splendens, a moss with annual segments. We
 examined how spatio-temporal variation in drought across three years and
 46 sites in central Sweden, affected the depth and magnitude of edge
 influences. We also investigated whether edge effects during drought are
 influenced by differences in forest structure. Edge effects were almost
 twice as strong in the drought year as in the non-drought years, but we
 did not find clear evidence that they penetrated deeper into the forest in
 the drought year. Edge influences were also greater in areas that had
 fewer days with rain during the drought year. Higher levels of forest
 canopy cover and tree height buffered the magnitude of edge influence in
 times of drought. Our results demonstrate that edge effects are amplified
 by drought, suggesting that fragmentation effects are aggravated when
 droughts become more frequent and severe. Our results suggest that dense
 edges and buffer zones with high canopy cover can be important ways to
 mitigate negative drought impacts in forest edges.
description: The data is from 46 boreal
 forest edges in central Sweden. The datasets consist of measurements of
 yearly growth of the moss <em>Hylocomium splendens</em> along
 edge-to-interior transects, as well as data on site-level, including
 canopy cover, tree height and drought intensity. 
 Moss measurements: At each
 forest edge, we collected shoots of the moss<em> H.
 splendens</em> along edge-to-interior transects at the following
 distances: 0, 5, 10, 20, 30 and 50 m. We collected three moss samples
 (minimum 7 shoots) perpendicular to the transect at each distance. We
 measured yearly growth three years back in time (2016, 2017 and 2018, one
 segment per year) of 21 moss-shoots at each distance, resulting in a total
 of 17 293 measurements. A more extensive explanation of these measurements
 is found in the method section of the article.
 Site-level data: Forest
 structural variables were measured at five locations in the forest
 interior. These five locations were approximately 10 m apart along a
 transect parallel to the edge. Canopy cover was calculated based on
 hemispherical photos, using the software ImageJ v. 1.53A with the plug-in
 Hemisperical 2.0. Tree height was measured with a clinometer and
 measure-tape. Spatial variation in drought intensity was
 calculated using a novel high temporal-spatial resolution dataset called
 HIPRAD (HIgh-resolution Precipitation from gauge-adjusted weather RADar).
 We calculated two drought indices: First, we summed the total
 precipitation during the period 1st May–31st August 2018. Second, we
 counted the number of days with rainfall over 3 mm during this
 period.
description: R and Excel are required for the files.