Vegetation development over four years on two green roofs in the UK
- Authors: Bates, Adam , Sadler, Jon , Mackay, Rae
- Date: 2013
- Type: Text , Journal article
- Relation: Forestry sciences Vol. 12, no. 1 (2013), p. 98-108
- Full Text: false
- Reviewed:
- Description: Carefully designed green roofs have the potential to be used as mitigation for habitats lost at ground level. The development of plant assemblages on two green roofs designed to emulate diverse brownfield habitats (brown roofs), by using recycled demolition aggregate as part of a low-fertility growth substrate, were studied over the first four years of their development. The cover-abundance of flowering plants and habitat structural components (e.g. bare ground, moss) were measured on the Domin-Krajina scale within all identified microhabitats. Drought disturbance was one of the main controlling factors on assemblage development. Annual plants were abundant and successful in the first growth season, and thereafter only re-appeared in any numbers following drought disturbances in subsequent years. Moss and Sedum acre L. increased through the study period until these plants dominated coverage. The cover-abundance of perennial wildflower species was strongly influenced by drought disturbance. The influence of drought disturbance varied between different brown roof microhabitats, with plant assemblages in coarser and less fertile microhabitats more resistant to these disturbances. Observed responses to drought were consistent with the following two hypotheses: (i) Areas of coarse substrate can act as disturbance refugia for plants during drought by helping preserve pockets of water under large clasts and within absorbent materials such as brick. (ii) The plant assemblages living in areas of more fertile substrates, which grow more luxuriantly when water availability is high, are more vulnerable to drought disturbance. Green roofs should be designed to include a range of substrate types to create several microhabitats that will collectively support more species than any single microhabitat.
An initial experimental assessment of the influence of substrate depth on floral assemblage for extensive green roofs
- Authors: Olly, Luke , Bates, Adam , Sadler, Jon , Mackay, Rae
- Date: 2011
- Type: Text , Journal article
- Relation: Urban Forestry and Urban Greening Vol. 10, no. 4 (2011), p. 311-316
- Full Text: false
- Reviewed:
- Description: Extensive green roofs have the potential to be used as mitigation tools to compensate for urban habitat loss, but there is little information about how closely these systems emulate ground-based habitats. This study investigated the effect of limited substrate depth on plant assemblages in the initial phase of growth in extensive green roof substrates. Five replicate mesocosms (1m 2) for each of three design treatments: (A) 10cm aggregate depth with green roof drainage and solid floor, (B) 15cm aggregate depth with green roof drainage and solid floor, and (C) 15cm aggregate depth on top of bare earth; were positioned at ground level. Each mesocosm had an identical growth substrate and was seeded with the same seed mix. Plant assemblages were analysed using point-quadrat methods. Significant differences in species composition were observed between treatments that seemed to be related to water availability. Even the deep (15cm) solid floor green roof treatment showed many significant differences in floral assemblage compared to the identical treatment (C) where plants had access to water in the soil profile. Therefore, it is not possible to exactly recreate most ground-based urban habitats on roofs by simply copying the soil characteristics and floral composition found on the ground. Like for mitigation for habitat loss using extensive green roofs requires the careful manipulation of design elements in order to counteract the limited water availability on green roofs. © 2011 Elsevier GmbH.