DOI: 10.5061/dryad.2547d7wng
title: Data from: Norway and Sweden Green Roof (GF) plant data

description: Standard succulent vegetation mixes developed mostly in temperate climates
 are being increasingly used on green roofs in different climate zones with
 uncertain outcome regarding vegetation survival and cover. We investigated
 vegetation on green roofs at nine temperate, cold and/or wet locations in
 Norway and Sweden covering wide ranges of latitude, mean annual
 temperature, annual precipitation, frequencies of freeze-thaw cycles and
 longest annual dry period. The vegetation on the roofs were surveyed in
 two consecutive years, and weather data were compiled from meteorological
 databases. At all sites we detected a significant decline in species
 compared to originally intended (planted/sown) species. Both the survival
 rate and cover of the intended vegetation were positively related to the
 mean annual temperature. Contrary to a hypothesis, we found that intended
 vegetation cover was negatively rather than positively related to mean
 annual precipitation. Conversely, the unintended (spontaneous) vegetation
 was favoured by high mean annual precipitation, and low mean annual
 temperature, possibly by enabling it to colonise bare patches and
 outcompete the intended vegetation. When there is high mortality and
 variation in cover of the intended vegetation, predicting the strength of
 ecosystem services the vegetation provides on green roofs is difficult.
 The results highlight the needs for further investigation on species
 traits and the local factors driving extinction and colonisations in order
 to improve survivability and ensure a dense vegetation throughout the
 successional stages of a green roof.
description: <b>Survey
 methods</b> We monitored vegetation cover and
 species presence/absence in permanent 1 x 1 m quadrats placed in transects
 with evenly spaced quadrats reflecting the surface area of the roof and
 avoiding edge zones and shaded areas. The total intended vegetation cover,
 total unintended vegetation cover, total moss cover and total bare
 vegetation cover as well as the percentage cover of each individual
 intended vascular plant species was recorded in each quadrat. Each quadrat
 was divided into smaller 0.1 x 0.1 m squares, corresponding to 1% cover,
 to facilitate estimation of plant cover. The exact locations of quadrats
 were recorded so that successional changes at the same spots could be
 monitored by surveys in consecutive years. Due to the difficulties of
 differentiating <i>Phedimus</i> <i>hybridus</i>
 from <em>P. kamtschaticus when not in
 flower the two species were merged and are referred to as P. coll
 hereafter.</em>   <b>Weather
 variables</b> Weather time series for the years
 prior to the surveys were collected from the Norwegian Meteorological
 Institute (MET Norway) and Swedish Meteorological and Hydrological
 Institute (SMHI) as daily averages for precipitation and 6 h averages for
 temperature. To acquire complete full time series of data for all sites,
 weather data from several weather stations in the same town were merged
 when data were incomplete. All weather variables were compiled from July
 15 until the same date of the following year when surveys were conducted.
 Since relevant weather indices are often highly correlated (Johannessen et
 al. 2017), we selected a subset to represent major gradients. Freeze-thaw
 cycles were defined as all changes between negative and positive
 temperatures recorded with six-hour resolution, irrespective of snow cover
 since such data were incomplete. The duration of the longest drought
 episode was defined as the longest consecutive sequence of days without
 precipitation (recorded in days), and mean annual temperature as the mean
 temperature recorded between July 15 and July 15 the following year. Total
 precipitation was the total precipitation during the time from July 15 in
 the preceding year until July 15 in the year of the survey. Samples from
 2016 and 2017 were treated as separate replicates to account for the
 variability in weather and vegetation between the years.