Fine‐scale substrate heterogeneity in green roof plant communities: The constraint of size

Abstract

Heterogeneity–diversity relationship (HDR) is commonly shown to be positive in accordance with classic niche processes. However, recent soil‐based studies have often found neutral and even negative HDRs. Some of the suggested reasons for this discrepancy include the lack of resemblance between manipulated substrate and natural settings, the treated areas not being large enough to contain species' root span, and finally limited‐sized plots may not sustain focal species’ populations over time. Vegetated green roofs are a growing phenomenon in many cities that could be an ideal testing ground for this problem. Recent studies have focused on the ability of these roofs to sustain stable and diverse plant communities and substrate heterogeneity that would increase niches on the roof has been proposed as a method to attain this goal. We constructed an experimental design using green roof experimental modules (4 m2) where we manipulated mineral and organic substrate component heterogeneity in different subplots (0.25 m2) within the experimental module while maintaining the total sum of mineral and organic components. A local annual plant community was seeded in the modules and monitored over three growing seasons. We found that plant diversity and biomass were not affected by experimentally created substrate heterogeneity. In addition, we found that different treatments, as well as specific subplot substrates, had an effect on plant community assemblages during the first year but not during the second and third years. Substrate heterogeneity levels were mostly unchanged over time. The inability to retain plant community composition over the years despite the maintenance of substrate differences supports the hypothesis that maintenance of diversity is constrained at these spatial scales by unfavorable dispersal and increased stochastic events as opposed to predictions of classic niche processes.

Gründächer im urbanen Raum und ihre Ökosystemleistungen

“…Allein die Höhe von Häusern und ihr inselartiger Charakter führen dazu, dass viele Organismen die Dächer nicht erreichen, sich nur eingeschränkt von Dach zu Dach ausbreiten können und aufgrund zufälliger Ereignisse (z. B. Dürre, letale Parasitierung) leicht wieder von dort verschwinden (Vasl et al 2019).…”

Urban stormwater characterization, control, and treatment

“…As seen in the previous sections, there is much interest in the role of vegetation in the hydrologic function, and to a lesser extent water quality, of green roofs. Green roof vegetation can be impacted by factors such as shading (Aguiar, Robinson, & French, 2019), substrate heterogeneity (Vasl, Schindler, Kadas, & Blaustein, 2019), and temperature on and within the subsurface of the green roof (Baryła, Gnatowski, Karczmarczyk, & Szatyłowicz, 2019). The role of shading was found to be highly dependent on the species of vegetation.…”

“…Heterogeneity of mineral and organic substrates was also investigated under a dry Mediterranean climate. Although some impact on vegetation was noticed in the first year, no statistically significant difference was found in plant diversity and biomass over three growing seasons (Vasl et al, 2019).…”

The Process of Soil Nutrient Stabilization in Micro-Patches in Alpine Kobresia Meadows

“…In comparison, plants can find and colonize suitable micro-patches, possibly changing the composition and pattern of the plant community in the ecosystem [23] and leading to regime shifts during the plant community succession process [24]. From this perspective, soil nutrients play an important role in maintaining ecosystem components in a steady state [25][26][27][28]. Variations in the amount and stability of soil nutrients can reflect the history and characteristics of micro-patches and plant community succession [3,14].…”