Is there more than meets the eye? Seed bank analysis of a typical novel ecosystem, the extensive green roof

Abstract

Questions: (a) Will seed banks develop on extensive green roofs (EGRs) -prime examples of novel ecosystems -as in (semi-)natural systems? If so, which type of seed bank (transient or persistent) can be expected? (b) Do EGR characteristics, such as roof age and substrate depth, influence seed bank seed density and species richness? (c) Can differences in successional stages be noticed in the seed bank and vegetation on EGRs? Location: Flanders and Brussels regions of Belgium. Methods:We conducted a field sampling campaign in which the vegetation and seed bank of 109 EGRs were sampled. Information on roof characteristics (e.g. age, substrate depth) was also collected. Seedling emergence was monitored under standardized greenhouse conditions. Species traits were collected from several existing databases. Data analysis consisted of (generalized) linear mixed modelling.Results: A total of 18,466 seedlings from 139 different species emerged in the seed bank analysis. Average similarity between vegetation and the seed bank was low, and the majority of species could be considered spontaneous colonizers. Most species were classified as having a transient seed bank. Life forms were shown to be significantly different between vegetation and seed bank. Older EGRs had higher seed bank species richness and seed density, both of which were also positively influenced by sampling date and the vegetation species richness. A discrepancy between seed bank and vegetation successional state, characterized by functional signatures, was present for EGRs. Conclusions:EGRs do develop seed banks and show parallels with seed banks in other novel ecosystems. Seed bank species richness and seed density are influenced by temporal and vegetation related factors. We can also confirm EGR seed bank succession and the discrepancy between seed bank and vegetation successional state, as often observed in natural and novel systems. Furthermore, we argue that seed banks can function as biodiversity reservoirs, which can be considered in EGR vegetation restoration if a set of several conditions is fulfilled. Overall, this study explores seed bank analysis on EGR as a novel ecosystem model. It thereby provides multiple insights in processes impacting EGR plant species diversity, both on and in the soil. 420 |

Adaptive strategy biases in engineered ecosystems: Implications for plant community dynamics and the provisioning of ecosystem services to people

“…Ruderals are expected to play an important role in designed, novel ecosystems, given their ability to colonize and re‐colonize space, providing a means for green infrastructure to self‐repair; cast in this light, ruderals become a way to preserve plant cover when competitive or stress tolerant plants die, providing a gap filling service with tangible benefits that makes them more than just ‘weeds’ (Dunnett, 2015; Vanstockem et al, 2019). This is not to say that we want to turn a blind eye to gap dynamics and let all pioneer species (invasive or otherwise) take root in biofilters, rather that there may be value in anticipating and planning for such dynamics, perhaps by populating biofilter seed banks with desirable ruderals (including annuals; see Vanstockem et al, 2018) that self‐seed once established (Dunnett, 2015; Koppler et al, 2014). A variety of commercially available biofilter seed mixes exist that might be modified and used for this purpose, and most design guidelines allow for application of seed provided container plants are used to establish an initial vegetation presence (MSM Wiki, 2003, SoCal LID, 2010).…”

Community assembly on extensive green roofs: Effects of dispersal‐, abiotic‐ and biotic filtering on the spontaneous species‐ and functional diversity

“…Within this abiotic context, the RDA results show that increased SVF leads to higher seed persistence and lower seed mass, both suggesting that stressful environments favor temporal bet-hedging species. The importance of soil seed banks for vegetation composition has not only been shown for EGRs (Vanstockem et al, 2018), but also for urban wastelands (Albrecht, Eder, Langbehn, & Tschiersch, 2011).…”

“…30%, e.g., succulent species), and a large fraction of spontaneous colonizers (ca. 70%) (Dunnett, Nagase, & Hallam, 2008;Lysens, 2004;Vanstockem, Ceusters, Van Dyck, Somers, & Hermy, 2018).…”

Quantifying the relationship between soil seed bank and plant community assemblage in sites harboring the threatened Ivesia webberi in the western Great Basin Desert

“…Therefore, we asked the following questions: (a) what is the degree of similarity between the species assemblage in the above‐ground vegetation and the soil seed bank of the sites where Ivesia webberi occur; (b) is there a significant relationship between the soil seed bank and the above‐ground plant communities in these sites; and (c) if so, what proportion of the above‐ground plant community structure is explained by the soil seed bank in comparison to other environmental variables? Given a high density of non‐native and invasive annual plant species in the study sites, and based on existing literature (e.g., Humphrey and Schupp, 2001; Hopfensperger, 2007; Barga and Leger, 2018; Vanstockem et al, 2018), we predict high dissimilarity between the above‐ground vegetation and the soil seed bank in these relatively undisturbed sites. We defined the soil seed bank as a collection of viable but ungerminated seeds, originating from standing, but also locally extirpated plants and vegetation from neighboring sites (Baskin and Baskin, 1998; Boussyt and Honnay, 2008; Solomon, 2011).…”

“…Given a high density of non-native and invasive annual plant species in the study sites, and based on existing literature (e.g., Humphrey and Schupp, 2001;Hopfensperger, 2007;Barga and Leger, 2018;Vanstockem et al, 2018), we predict high dissimilarity between the above-ground vegetation and the soil seed bank in these relatively undisturbed sites. We defined the soil seed bank as a collection of viable but ungerminated seeds, originating from standing, but also locally extirpated plants and vegetation from neighboring sites (Baskin and Baskin, 1998;Boussyt and Honnay, 2008;Solomon, 2011).…”