Temperatures and precipitation affect vegetation dynamics on Scandinavian extensive green roofs

Abstract

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 colonize 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 colonizations in order to improve survivability and ensure a dense vegetation throughout the successional stages of a green roof.

Seasonal variation in preference for green roof vegetation

“…The limited research to date has suggested that important changes are likely occurring over time in the green roof plant communities, changes that may influence ecosystem service provision (e.g. Lönnqvist et al, 2021, Gabrych et al, 2016. After establishment, temporal variation in green roof plant communities is to be expected, and shifts in the plant community have been observed when young and old roofs are compared (e.g., Köhler and Poll, 2010;Gabrych et al, 2016;Mitchell et al, 2021).…”

“…Variation in green roof plant communities over time has emerged as a clear theme across studies (e.g. Gabrych et al, 2016;Lönnqvist et al, 2021), with some studies suggesting a negative relationship between roof age and species richness (Köhler and Poll, 2010;Thuring and Dunnett, 2014) and others a positive relationship (Catalano et al, 2016;Gabrych et al, 2016) or no relationship (Mitchell et al, 2021).…”

The role of green roofs as urban habitats for biodiversity modulated by their design: a review

“…From a geographical point of view, the majority of these studies were carried out in the countries of the northern hemisphere (figure 2) with about 36% in North America and Europe, followed by 23% in Asia. Only four studies described roofs in different countries; all being located in Europe (Bubnova et al 2012, Van Mechelen et al 2015, Nicolaisen et al 2017, Lönnqvist et al 2021. Moreover, no study on this subject was referenced in Africa.…”

Blue-Green Infrastructure for All Seasons: The Need for Multicolored Thinking

“…3, where the snow stored on the swale is prepared as a ski track. Technical Functionality of BGWI Concerns over the technical functionality of BGI in cold climates have been raised, and a range of impacts have been identified, e.g., ice covers in ponds and wetlands leading to oxygen depletion and changed flow patterns (German et al 2003), less efficient (bio) chemical processes in bioretention cells (Muthanna et al 2007), the limited number of adapted plant species (Lönnqvist et al 2021), road salt affecting BGI functionality (Søberg et al 2014), less evapotranspiration during cold seasons (Johannessen et al 2017), and reduced infiltration due to clogging caused by abrasives used for winter road maintenance or frozen facilities (Moghadas et al 2016). However, studies have also shown that despite these impacts, a range of BGI (e.g., ponds, bioretention cells, and green roofs) continue to have a positive impact on stormwater quality and quantity objectives (e.g., Marsalek et al 2003;Muthanna et al 2007;Johannessen et al 2017;Kratky et al 2017;Søberg et al 2014;Tahvonen 2018;Kuoppamäki 2021).…”