Dustin L. Herrmann

The role of trees in urban stormwater management

Urban impervious surfaces convert precipitation to stormwater runoff, which causes water quality and quantity problems. While traditional stormwater management has relied on gray infrastructure such as piped conveyances to collect and convey stormwater to wastewater treatment facilities or into surface waters, cities are exploring green infrastructure to manage stormwater at its source. Decentralized green infrastructure leverages the capabilities of soil and vegetation to infiltrate, redistribute, and otherwise store stormwater volume, with the potential to realize ancillary environmental, social, and economic benefits. To date, green infrastructure science and practice have largely focused on infiltration-based technologies that include rain gardens, bioswales, and permeable pavements. However, a narrow focus on infiltration overlooks other losses from the hydrologic cycle, and we propose that arboriculture - the cultivation of trees and other woody plants - deserves additional consideration as a stormwater control measure. Trees interact with the urban hydrologic cycle by intercepting incoming precipitation, removing water from the soil via transpiration, enhancing infiltration, and bolstering the performance of other green infrastructure technologies. However, many of these interactions are inadequately understood, particularly at spatial and temporal scales relevant to stormwater management. As such, the reliable use of trees for stormwater control depends on improved understanding of how and to what extent trees interact with stormwater, and the context-specific consideration of optimal arboricultural practices and institutional frameworks to maximize the stormwater benefits trees can provide.

Biological invasions, ecological resilience and adaptive governance

In a world of increasing interconnections in global trade as well as rapid change in climate and land cover, the accelerating introduction and spread of invasive species is a critical concern due to associated negative social and ecological impacts, both real and perceived. Much of the societal response to invasive species to date has been associated with negative economic consequences of invasions. This response has shaped a war-like approach to addressing invasions, one with an agenda of eradications and intense ecological restoration efforts towards prior or more desirable ecological regimes. This trajectory often ignores the concept of ecological resilience and associated approaches of resilience-based governance. We argue that the relationship between ecological resilience and invasive species has been understudied to the detriment of attempts to govern invasions, and that most management actions fail, primarily because they do not incorporate adaptive, learning-based approaches. Invasive species can decrease resilience by reducing the biodiversity that underpins ecological functions and processes, making ecosystems more prone to regime shifts. However, invasions do not always result in a shift to an alternative regime; invasions can also increase resilience by introducing novelty, replacing lost ecological functions or adding redundancy that strengthens already existing structures and processes in an ecosystem. This paper examines the potential impacts of species invasions on the resilience of ecosystems and suggests that resilience-based approaches can inform policy by linking the governance of biological invasions to the negotiation of tradeoffs between ecosystem services.

Vacant urban lot soils and their potential to support ecosystem services

AimsUrban soils are the basis of many ecosystem services in cities. Here, we examine formerly residential vacant lot soils in Cleveland, Ohio and Detroit, Michigan, USA for their potential to provide multiple ecosystem services. We examine two key contrasts: 1) differences between cities and 2) differences within vacant lots created during demolition, specifically pre-existing (i.e., prior to demolition) soils outside of the building footprint and fill soils added within the former building’s footprint.MethodsDeep soil cores were collected from vacant lots in Cleveland and Detroit. Soil properties that are proxies for three ecosystem services were measured: hydraulic conductivity for stormwater retention, topsoil depth and soil nitrogen (N) level for support for plant growth, and soil carbon (C) content for C storage.ResultsBoth city and soil group contrasts created distinct ecosystem service provisioning based on proxy measures. Cleveland soils had greater hydraulic conductivity and greater soil C and N levels but thinner topsoil layers than Detroit. Within vacant lots of both cities, pre-existing soils had greater soil C and N levels, but lower hydraulic conductivity values than fill soils.ConclusionsSoil properties of vacant lots were generally suitable for providing multiple ecosystem services. City-level differences in soil properties created differences in ecosystem service potential between cities and these differences were evident in pre-existing and fill soils. When comparing between cities, though, fill soils were more similar than pre-existing soils indicating some homogenization of ecosystem service potential with greater redistribution of soil.

Leaf phenology mediates provenance differences in herbivore populations on valley oaks in a common garden

1. Plants from different populations often display a variation in herbivore resistance. However, it is rarely understood what plant traits mediate such differences.

Data for: Pearse et al 2015 Ecological Entomology "Leaf phenology mediates provenance differences in herbivore populations on valley oaks in a common garden"

1. Plants from different populations often display a variation in herbivore resistance. However, it is rarely understood what plant traits mediate such differences.

Widespread loss of intermediate soil horizons in urban landscapes

Significance As societies move toward nature-based infrastructure to provide ecosystem services for sustainable urban environmental management, knowledge of urban soils remains a critical gap. An 11-city comparison of urban to reference preurban soil profiles revealed how urbanization modifies the presence and ordering of soil layers and its properties. Urban soils had fewer horizons than their preurban counterparts, with a predominant absence of intermediate B horizons. The loss of B horizons, which are not easily replaced, as they form over decades to millennia, can affect ecosystem functions, with potentially wide-ranging consequences for ecosystem services in cities. Soils support terrestrial ecosystem function and therefore are critical urban infrastructure for generating ecosystem services. Urbanization processes modify ecosystem function by changing the layers of soils identified as soil horizons. Soil horizons are integrative proxies for suites of soil properties and as such can be used as an observable unit to track modifications within soil profiles. Here, in an analysis of 11 cities representing 10 of the 12 soil orders, we show that urban soils have ∼50% fewer soil horizons than preurban soils. Specifically, B horizons were much less common in urban soils and were replaced by a deepening of A horizons and a shallowing of C horizons. This shift is likely due to two processes: (i) local management, i.e., soil removal, mixing, and fill additions, and (ii) soil development timelines, i.e., urbanized soils are young and have had short time periods for soil horizon development since urbanization (decades to centuries) relative to soil formation before urbanization (centuries to millennia). Urban soils also deviated from the standard A-B-C horizon ordering at a much greater frequency than preurban soils. Overall, our finding of common shifts in urban soil profiles across soil orders and cities suggests that urban soils may function differently from their preurban antecedents. This work introduces a basis for improving our understanding of soil modifications by urbanization and its potential effects on ecosystem functioning and thereby has implications for ecosystem services derived from urban landscapes.

Abiotic Drivers of Ecological Structure and Function in Urban Systems

The interactions between abiotic (nonliving) and biotic (living) factors define ecosystem ecology, and form an essential foundation for any effort to understand urban wildlife. The study of ecosystems considers the flow of energy and materials between organisms and their physical environment. For instance, how much energy enters an ecosystem through the process of primary production—the conversion of CO2, water, and solar energy into biomass—by plants significantly influences how many organisms an ecosystem can support. The interactions between abiotic and biotic components of urban systems are both fundamental to understanding the ecological functioning of cities and are used to explain wildlife-related phenomena, including trophic cascades, biodiversity, and species distribution across the landscape.