DOI: 10.5061/dryad.pnvx0k6x4
title: Data from: Canopy cover and soil moisture influence forest understory plant responses to experimental summer drought

description: Extreme droughts are globally increasing in frequency and severity. Most
 research on drought in forests focuses on the response of trees, while
 less is known about the impacts of drought on forest understory species
 and how these effects are moderated by the local environment. We assessed
 the impacts of a 45-day experimental summer drought on the performance of
 six boreal forest understory plants, using a transplant experiment with
 rainout shelters replicated across 25 sites. We recorded growth, vitality
 and reproduction immediately, two months, and one year after the simulated
 drought, and examined how differences in ambient soil moisture and canopy
 cover among sites influenced the effects of drought on the performance of
 each species. Drought negatively affected the growth and/or vitality of
 all species, but the effects were stronger and more persistent in the
 bryophytes than in the vascular plants. The two species associated with
 older forests, the moss Hylocomiastrum umbratum and the orchid Goodyera
 repens, suffered larger effects than the more generalist species included
 in the experiment. The drought reduced reproductive output in the moss
 Hylocomium splendens in the next growing season, but increased
 reproduction in the graminoid Luzula pilosa. Higher ambient soil moisture
 reduced some negative effects of drought on vascular plants. Both denser
 canopy cover and higher soil moisture alleviated drought effects on
 bryophytes, likely through alleviating cellular damage. Our experiment
 shows that boreal understory species can be adversely affected by drought
 and that effects might be stronger for bryophytes and species associated
 with older forests. Our results indicate that the effects of drought can
 vary over small spatial scales and that forest landscapes can be actively
 managed to alleviate drought effects on boreal forest biodiversity. For
 example, by managing the tree canopy and protecting hydrological networks.
description: <em>Experimental set-up and site-level
 variables</em> We experimentally induced a summer
 drought at 25 sites, representing a range of ambient canopy cover and soil
 moisture levels, in a managed forest landscape in central Sweden (Ekopark
 Färna, Västmanland, Sweden). We experimentally induced a 45-day drought
 during the summer 2021 (2<sup>th</sup> of June -
 16<sup>th</sup> of July), by installing rainout shelters that
 completely intercepted all rainfall during this period over one of the
 plots at each site. The rainout shelters were 2 × 2 m, to allow for a 0.5
 m buffer zone on each side of the drought-treated plots. The control plots
 received ambient rainfall, which added up to 87 mm. In
 all treatment and control plots, we tracked soil moisture levels using
 TMS-4 loggers (TOMST). These loggers recorded soil moisture of the topsoil
 in the middle of each plot every 15 minutes. Raw soil moisture measures,
 which are based on conductivity pulses, were calibrated to percentage soil
 moisture volume. We calculated site-level measures of soil moisture and
 canopy cover, in order to test how among-site variation in these factors
 interacted with the drought. For soil moisture, we used the average value
 of moisture in May 2021, the month before the drought from both control
 and treatment plots (drought plots were at that time still untreated). To
 calculate canopy cover for each site, we used hemispherical photographs
 taken with a Lumix Panasonic camera (DMC-G80M) and a circular fisheye lens
 (MFT 4mm F2.8 210°). We used the Hemispherical 2.0 package in the software
 ImageJ (version 1.53 a) to process the photos into binary
 images. <em>Plant responses</em>
 <em> </em>We transplanted three vascular plant
 species (<em>Goodyera repens</em>, <em>Luzula
 pilosa</em>, <em>Oxalis acetosella</em>) and three
 bryophytes (<em>Hylocomiastrum umbratum, Barbilophozia
 lycopodioides, Hylocomium splendens</em>) under rainout shelters and
 in control plots. We recorded plant drought responses
 in terms of vitality, growth and reproductive output. We assessed the
 immediate post-drought effects, as well as the effects two months and one
 year after the drought. For the vascular plants, we calculated growth by
 taking the log-ratio of the difference in number of leaves (L) at t+1 and
 t, using the formula log(L<sub>t+1</sub>) –
 log(L<sub>t</sub>). We also calculated the specific leaf area
 (SLA) for a few leaves (if possible, 3 for each transplant, 9 per plot for
 each species) that were produced during the drought period, by dividing
 the leaf area (cm<sup>2</sup>) by its dry-mass (g). For the
 mosses <em>H. splendens</em> and <em>H. 
 umbratum</em>, we marked five shoots per transplant (15 per plot,
 750 shoots in total for the experiment). These mosses produce a distinct
 growth segment each year, on top of the previous years’ segment. We
 calculated growth by measuring the difference in length of the marked
 segment (from the start of the segment until the apical tip) over sampling
 intervals (t and t+1). We also measured the segment that was produced
 during the growing season one year after the drought. In addition, we
 recorded number of new segments produced in 2022 on the marked shoot as a
 measure of branching. For the liverwort <em>B.
 lycopodioides,</em> we measured growth as the relative increase in
 patch size (S<sub>t+1</sub> / S<sub>t</sub>). We
 photographed patches together with a scale bar and measured patch size by
 manually tracing the patches in ImageJ. Vitality was assessed for vascular
 plants and bryophytes using a scale from 1 to 7 developed by Dynesius et
 al. (2008) to describe vitality after exposure to drought: 1) dead; 2)
 some leaves green; 3) some shoots green; 4) half of the shoots alive; 5)
 alive but affected; 6) most of the shoots vigorous; and 7) the entire
 plant fresh and growing. We assessed reproductive output only for
 <em>L. pilosa</em> and <em>H. splendens</em>. For
 <em>L. pilosa</em>, we measured the number of inflorescences
 per transplant, mean number of fruits per inflorescence (based on fruit
 count of two inflorescences), the number of developed seeds per fruit, and
 the average weight of developed seeds. Developed seeds were distinguished
 from non-developed based on appearance. For <em>H.
 splendens</em>, we counted the number of sporophytes per transplant,
 the average number of spores per capsule, and the proportion of spores
 that were aborted.
description: # Data from: Canopy cover and soil moisture influence forest understory
 plant responses to experimental summer drought ## Dataset 1: sitelevel
 data Provides site-level data for the 25 sites Site_ID: Unique ID for each
 site Latitude: Latitudinal coordinate Longitude: Longitudinal cordinate
 gap_fraction: The % gap in the canopy (inverse of canopy cover).
 Canopy_cover: The % canopy cover TMS_may: Proportional soil moisture in
 May before the drought treatment ## Dataset 2: All_species_growth_sc
 Provides data on the scaled growth of the species over the different time
 intervals Site_ID: Unique ID for each site Treatment: Two level factor:
 drought treatment and ambient control Transplant: Transplant ID within
 each plot (3 transplant patches for each species) Species: Abbreviations
 of the six study species: Gr = Goodyera repens, Lp =Luzula pilosa, Oa =
 Oxalis acetosella, Hs = Hylocomium splendens, Hu = Hylcomiastrum umbratum,
 Bl = Barbilophozia lycopodioides Group: Two level factor: vascular plants
 (vasc) or bryophytes (bryo) Growth_July_sc: Scaled growth between the
 pre-drought and post-drought period. n/a values are due to missing data,
 for example destroyed transplants or missing markings for the moss shoots
 (see dataset 6). Growth_Sept_sc: Scaled growth between post-drought and
 two months after the drought. n/a values are due to missing data.
 Growth_2022_sc: Scaled growth between two months after the drought and one
 year after the drought. n/a values are due to missing data. Growth_Tot_sc:
 Scaled growth between pre-drought and one year after the drought. n/a
 values are due to missing data. Growth_22seg_sc: Scaled growth of the next
 seasons segment for the mosses H. umbratum and H. splendens. Only
 applicable to the mosses, n/a for the other species. ## Dataset 3:
 All_species_vit_sc Provides data on the scaled vitality of the species
 over the different time intervals Site_ID: Unique ID for each site
 Treatment: Two level factor: drought treatment and ambient control
 Transplant: Transplant ID within each plot (3 transplant patches for each
 species) Species: Abbreviations of the six study species: Gr = Goodyera
 repens, Lp =Luzula pilosa, Oa = Oxalis acetosella, Hs = Hylocomium
 splendens, Hu = Hylcomiastrum umbratum, Bl = Barbilophozia lycopodioides
 Group: Two level factor: vascular plants (vasc) or bryophytes (bryo)
 Vit_Before_sc: Scaled pre-drought vitality Vit_July_sc: Scaled vitality
 post-drought. n/a values are due to missing data, for example completely
 dead plants or destroyed transplants so that vitality could not be
 scored.  Vit_Sept_sc: Scaled vitality two months after the drought. n/a
 values are due to missing data. Vit_22_sc: Scaled vitality one year after
 the drought. n/a values are due to missing data. ## Dataset 4: SLA
 Provides data on the Specific Leaf Area for the vascular plants Site_ID:
 Unique ID for each site Treatment: Two level factor: drought treatment and
 ambient control Transplant: Transplant ID within each plot (3 transplant
 patches for each species) Species: Abbreviations of the three vascular
 plants: Gr = Goodyera repens, Lp =Luzula pilosa, Oa = Oxalis acetosella
 Leaf area (cm^2): Leaf area in cm^2, traced with the software ImageJ. n/a
 values are due to missing data, for example when there the plants were
 dead and no leaves could be collected. Dry weight (mg): Dry weight in mg.
 n/a values are due to missing data, for example when there the plants were
 dead and no leaves could be collected. Dry weight (g): Dry weight in g.
 n/a values are due to missing data, for example when there the plants were
 dead and no leaves could be collected. SLA (cm^2.g^-1): Specific leaf area
 in cm^2.g^-1 calculated by dividing the leaf area by weight in gram. n/a
 values are due to missing data, for example when there the plants were
 dead and no leaves could be collected. ## Dataset 5: Reproduction - Sheet
 HS Provides data on the reproductive output of Hylocomium splendens
 Site_ID: Unique ID for each site Treatment: Two level factor: T= drought
 treatment and C= ambient control Transplant: Transplant ID within each
 plot (3 transplant patches for each species) Sporophytes_produced: The
 number of sporophytes for each moss patch Spore_count: Number of spores
 counted on a sedgewick chamber. n/a values are due to missing data, for
 example there were no sporophytes produced. Aborted: the % of aborted
 spores. n/a values are due to missing data, for example there were no
 sporophytes produced. ## Dataset 5: Reproduction - Sheet LP Provides data
 on the reproductive output of Luzula pilosa Site_ID: Unique ID for each
 site Treatment: Two level factor: T= drought treatment and C= ambient
 control Transplant: Transplant ID within each plot (3 transplant patches
 for each species) Nr_leaves_22: Number of leaves at the time of
 reproductive effort scoring Weight: Average seed weight. n/a values are
 due to missing data, for example there were no fruits produced.
 Vital_seed_fruit: Average number of vital seeds per fruit (based on 10
 fruits). n/a values are due to missing data, for example there were no
 fruits produced. Nr_Infl: Number of inflorescenses.\ Avr_fruits_infl:
 Average number of fruits per inflorescence. ## Dataset 6: Species
 responses_raw - sheet Vasc plants Provides the raw data on the species
 vitality and size for each site, plot and transplant Site_ID: Unique ID
 for each site Treatment: Two level factor: drought treatment and ambient
 control Transplant: Transplant ID within each plot (3 transplant patches
 for each species) Species: Abbreviations of the study species: Gr =
 Goodyera repens, Lp =Luzula pilosa, Oa = Oxalis acetosella
 Nr_leaves_before: Number of leaves before the drought treatment (either
 April or June 2021) Vitality_before: Vitality (1-7 scale) before the
 drought treatment (either April or June 2021) Vitality_july: Vitality (1-7
 scale) in July 2021. Nr_leaves_July: Number of leaves in July 2021
 Vitality_sept: Vitality (1-7 scale) in September 2021. n/a values can
 occur when the plant was completely gone. Nr_leaves_sept: Number of leaves
 in September 2021 Vitality_22: Vitality (1-7 scale) in July 2022. n/a
 values can occur when the plant was completely gone. Nr_leaves_22: Number
 of leaves in July 2022 ## Dataset 6: Species responses_raw - sheet Mosses
 Provides the raw data on the species vitality and size for each site, plot
 and transplant Site_ID: Unique ID for each site Treatment: Two level
 factor: drought treatment and ambient control Transplant: Transplant ID
 within each plot (3 transplant patches for each species) Species:
 Abbreviations of the six study species: Hs = Hylocomium splendens, Hu =
 Hylcomiastrum umbratum Size_June: Segment size (mm) in June 2021 (before
 the drought treatment) Vitality_June: Vitality (1-7 scale) in June for
 each transplant patch (hence the vitality is written at the first row of
 each site-plot-transplant, rest is n/a) Size_July: Segment size (mm) in
 July 2022 (after the drought treatment) Growth_July: Growth from June 2021
 to July 2021 in mm. When rows are n/a it is because we lost the initially
 marked shoot, and marked a new one with the same color. Vitality_July:
 Vitality (1-7 scale) in July for each transplant patch (hence the vitality
 is written at the first row of each site-plot-transplant, rest is n/a)
 Size_September: Segment size (mm) in September 2022 Growth_September:
 Growth from July 2021 to September 2021 in mm. When rows are n/a it is
 because we lost the initially marked shoot, and marked a new one with the
 same color. Vitality_September: Vitality (1-7 scale) in September for each
 transplant patch (hence the vitality is written at the first row of each
 site-plot-transplant, rest is n/a) Size_2021: Size (mm) of the entire
 segment produced in 2021, measured in July 2022 Growth_sep_july22: Growth
 from September 2021 to July 2022 in mm. When rows are n/a it is because we
 lost the initially marked shoot, and marked a new one with the same color.
 Size_july_2022: Size (mm) of the segment produced in 2022 (growing from
 the 2021 segment). Vitality_2022: Vitality (1-7 scale) in July 2022 for
 each transplant patch (hence the vitality is written at the first row of
 each site-plot-transplant, rest is n/a) ## Dataset 6: Species
 responses_raw - sheet Bl Provides the raw data on the species vitality and
 size for each site, plot and transplant for the liverwort Barbilophozia
 lycopodioides n/a values can occur when the liverwort patch was gone
 (cannot scale vitality) or if we had a missing datapoint such as a loss of
 a photograph. Site_ID: Unique ID for each site Treatment: Two level
 factor: drought treatment and ambient control Transplant: Transplant ID
 within each plot (3 transplant patches for each species) Vitality_june:
 Vitality (1-7 scale) in June 2021 Patch_size_june: Path size (mm^2) in
 June 2021 Vitality_july: Vitality (1-7 scale) in July 2021
 Patch_size_july: Path size (mm^2) in July 2021 Vitality_sept: Vitality
 (1-7 scale) in September 2021 Patch_size_sept: Path size (mm^2) in
 September 2021 Patch_size_2022: Path size (mm^2) in July 2022
 Vitality_2022: Vitality (1-7 scale) in July 2022 ## Dataset 7:
 Hemispherical canopy cover photos (zip file) Hemispherical photos at each
 site and each plot from which we calculated canopy cover ## Dataset 8: TMS
 soil moisture raw (zip file) Excel files for each site and plot with raw
 (uncalibrated) soil moisture values, as well as temperature, at a temporal
 resolution of 10 minutes