Vegetation composition, structure and soil properties across coastal forest–barren ecotones

Accepted VersionCoastal barrens support rare plant species but may be threatened by forest encroachment. We determined whether trees spread into coastal barren habitat from forest patches and assessed plant species composition and soil properties across the forest–barren ecotone. We quantified tree age and height, soil properties, and vascular plant, bryophyte and lichen species composition along transects perpendicular to the edges of tree patches within the forest–barren ecotone in coastal Nova Scotia. Randomization tests assessed whether the vegetation and environmental characteristics were significantly different in the transition zone compared to one or both adjoining ecosystems. We used ordination to examine trends in species composition across the ecotone and the relationship to environmental variables. Tree age and height decreased continuously from the forest towards the edge of the forest patches. There were also trends in vegetation composition and structure from the forest into the open barrens. Many species were most abundant within the transition zone, although not always significantly. Soil properties were relatively uniform across the ecotone. The structure and vegetation of the forest–barren ecotone suggests that forest patches act as nuclei for forest expansion on barrens with a typical successional pathway where coastal barren vegetation is gradually replaced by forest species. This encroachment may pose a threat to rare barrens communities. While landscape factors such as salt spray and wind exposure may determine the general locations where forest can establish, biotic processes of growth and dispersal appear to govern the fine-scale expansion of tree patches

Leaf and life history traits predict plant growth in a green roof ecosystem

Publisher's Version/PDFGreen roof ecosystems are constructed to provide services such as stormwater retention and urban temperature reductions. Green roofs with shallow growing media represent stressful conditions for plant survival, thus plants that survive and grow are important for maximizing economic and ecological benefits. While field trials are essential for selecting appropriate green roof plants, we wanted to determine whether plant leaf traits could predict changes in abundance (growth) to provide a more general framework for plant selection. We quantified leaf traits and derived life-history traits (Grime's C-S-R strategies) for 13 species used in a four-year green roof experiment involving five plant life forms. Changes in canopy density in monocultures and mixtures containing one to five life forms were determined and related to plant traits using multiple regression. We expected traits related to stress-tolerance would characterize the species that best grew in this relatively harsh setting. While all species survived to the end of the experiment, canopy species diversity in mixture treatments was usually much lower than originally planted. Most species grew slower in mixture compared to monoculture, suggesting that interspecific competition reduced canopy diversity. Species dominant in mixture treatments tended to be fast-growing ruderals and included both native and non-native species. Specific leaf area was a consistently strong predictor of final biomass and the change in abundance in both monoculture and mixture treatments. Some species in contrasting life-form groups showed compensatory dynamics, suggesting that life-form mixtures can maximize resilience of cover and biomass in the face of environmental fluctuations. This study confirms that plant traits can be used to predict growth performance in green roof ecosystems. While rapid canopy growth is desirable for green roofs, maintenance of species diversity may require engineering of conditions that favor less aggressive species

Saxicolous lichens on a Nova Scotian coastal barren

Publisher's Version/PDFSaxicolous lichens of a coastal barren were surveyed in Nova Scotia, Canada. Forty-three species were found, including Rhizocarpon suomiense, new to North America, and five other species new to the province. The response of saxicolous lichens to the maritime influence was assessed along transects perpendicular to the shoreline, as well as on three faces of the boulders: facing towards the coast, upwards, and away from the coast. Boulder face did not significantly affect lichen species richness; however, cover significantly increased from front to top to back faces. Lichen species richness and cover increased significantly with increasing distance from the shoreline. The ecology of selected species with respect to the maritime gradient is discussed

Global urban environmental change drives adaptation in white clover

Urbanization transforms environments in ways that alter biological evolution. We examined whether urban environmental change drives parallel evolution by sampling 110,019 white clover plants from 6169 populations in 160 cities globally. Plants were assayed for a Mendelian antiherbivore defense that also affects tolerance to abiotic stressors. Urban-rural gradients were associated with the evolution of clines in defense in 47% of cities throughout the world. Variation in the strength of clines was explained by environmental changes in drought stress and vegetation cover that varied among cities. Sequencing 2074 genomes from 26 cities revealed that the evolution of urban-rural clines was best explained by adaptive evolution, but the degree of parallel adaptation varied among cities. Our results demonstrate that urbanization leads to adaptation at a global scale

The ecology and evolution of constructed ecosystems as green infrastructure

Publisher's version/PDFGreen infrastructure consists of ecosystems that provide valuable services to urban areas. Constructed ecosystems, including green roofs, bioretention systems, constructed wetlands and bioreactors are artificial, custom-built components of green infrastructure that are becoming more common in cities. Small size, strong spatial boundaries, ecological novelty and the role of human design characterize all constructed ecosystems, influencing their functions and interactions with other urban ecosystems. Here I outline the relevance of ecology and evolution in understanding the functioning of constructed ecosystems. In turn, a research focus on the distinctive aspects of constructed ecosystems can contribute to fundamental science

Cladonia lichens on extensive green roofs: evapotranspiration, substrate temperature, and albedo

Publisher's Version/PDFGreen roofs are constructed ecosystems that provide ecosystem services in urban environments. Shallow substrate green roofs subject the vegetation layer to desiccation and other environmental extremes, so researchers have evaluated a variety of stress-tolerant vegetation types for green roof applications. Lichens can be found in most terrestrial habitats. They are able to survive extremely harsh conditions, including frequent cycles of desiccation and rehydration, nutrient-poor soil, fluctuating temperatures, and high UV intensities. Extensive green roofs (substrate depth <20cm) exhibit these harsh conditions, making lichens possible candidates for incorporation into the vegetation layer on extensive green roofs. In a modular green roof system, we tested the effect of Cladonia lichens on substrate temperature, water loss, and albedo compared to a substrate-only control. Overall, the Cladonia modules had significantly cooler substrate temperatures during the summer and significantly warmer temperatures during the fall. Additionally, the Cladonia modules lost significantly less water than the substrate-only control. This implies that they may be able to benefit neighboring vascular plant species by reducing water loss and maintaining favorable substrate temperatures

Atrium green roof temperature, moisture, seedling density, and species richness 2014 data

Data pertaining to Tables 2 & 3 and Figure 4. Includes data from the Atrium green roof collected in June and September of 2014. Data measured per quadrat (100cm2), with experimental quadrats assigned to 12 distinct microsite types relating to substrate depth (shallow, control, deep) and substrate features (none, logs, pebble pile center, pebble pile edge); abiotic data: substrate temperature (degrees Celsius), substrate volumetric water content (VWC, %), biotic data: seedling density (number of seedlings/100cm2), and species richness (species/100cm2). Covariate data (% cover of vegetation, total solar radiation) are also included here

glasshouse module temperature, moisture, seedling density, species richness 2015

Data from glasshouse modules, used to create Figure 6. Contains data according to treatment (surface feature type) and time, including substrate temperature (degrees Celsius), volumetric moisture content (VWC, %), seedling density (seedlings/1296 cm2), and species richness (per 1296 cm2)

Data from: Designed habitat heterogeneity on green roofs increases seedling survival but not plant species diversity

Urban areas benefit from the ecosystem services provided by low input green roofs. However, limited substrate depth on these green roofs creates challenging conditions for plant establishment and survival, leading to industry reliance on non-native succulents. Through a green roof and glasshouse study, we assessed the impact of simple design modifications to the green roof surface, including redistribution of substrate and addition of logs and pebble piles, on both substrate temperature and moisture content. We added seeds of 26 native species and quantified seedling density, species richness and composition over a single growing season. Overall effects of microsite heterogeneity on species diversity were assessed using species accumulation curves. The modifications altered substrate temperature and moisture. Deep substrate (10-12 cm) and the presence of surface features reduced temperature by 14.6°C and, while surface features had mixed effects on substrate moisture on the green roof, pebble piles slowed moisture loss during a six-week drought in the glasshouse. Following drought conditions, seedling density and species richness was greatest, relative to seeded controls, where substrate was deep on the green roof and where pebbles were present in glasshouse modules, despite high mortality overall. Design modifications did not result in differentiation of seedling communities among different microsite types. Species accumulation curves showed no difference in species richness between aggregates of modified vs. unaltered microsites. Synthesis and applications. Redistribution of green roof substrate and the addition of logs and pebble piles altered microsite conditions and created habitat heterogeneity on a green roof. These design modifications represent a minimalist strategy to ameliorate growing conditions, improve seedling survival and decrease species loss on shallow substrate green roofs

Atrium green roof species richness data 2014 - EstimateS output

Species richness output from EstimateS - used to create Figure 5. Microsites categorized as seeded controls (homogeneous conditions) or heterogeneous (mixed microsites). Combined homogeneous area sampled = 2400 cm2, combined heterogeneous area sampled = 9600 cm2