Long-term ecological research is faced with seemingly
contradictory constraints: It must maintain a consistent stream of rigorously
comparable data over time while at the same time responding to conceptual and
theoretical changes in the disciplines underlying those data. How can such opposing constraints be reconciled?
BES has faced this challenge in developing its most recent
proposal. It was required to shift from
a framework that -- although it highlighted a frontier topic in the
understanding of social-ecological systems -- proved to be problematical for
many readers. In response, members of
the project management team took a step back and sought ways to improve the
conceptual framework. First, they wanted
to simplify the conceptual framework.
Second, they wanted to increase its parallelism with frameworks of other
LTER sites. Finally, they wanted to
emphasize the interactions on multiple scales that caused the changes in urban
social-ecological systems over time.
This stepping back took us to the foundations of BES. The project was founded to examine the basic
biophysical structures and functions in an urban system, and how they
interacted with social processes, all in a context of change.
The Founding Ideas of BES
So the founding question of BES asked: How do biological and
social patch dynamics combine to shape and change a metropolitan area? This question was operationalized by applying
the watershed concept in a city-suburban-exurban matrix, and by examining nested
hierarchies of social, biological, soil, and hydrological processes as
potential causes of urban change.
In revisiting the framework, we looked at what the first
three phases of BES had accomplished, and what they suggested about refinements
in the concepts. Furthermore, we looked
at the improved understanding of climate change and globalization that had
developed over the nearly 20 year history of BES, to see what those insights
suggested about revision of our framework.
New Pressures in the System
It was clear that effects of climate change through sea
level rise, increases in storm intensity and frequency, risk of drought,
increase in heat waves, and shifts in species ranges were likely to alter the
structure and functioning of our urban ecosystem. Furthermore, globalization was likely to
alter human migrations, increase the pressure from introduced and/or invasive
plants, animals, pests, and diseases, as well as work continuing
social-demographic changes within our region.
These ideas had not played significant roles in the initial
conceptualization of BES, which was concerned primarily with testing how well ecological
approaches worked in an environment where they had not been tried previously.
Conceptual Refinement about Urban Ecosystems
An additional refinement emerging from BES and other urban
social-ecological research also played a role in the evolving framework. Early on, leaders of BES and its sibling
LTER, the Central Arizona Phoenix project, had pointed out the difference in
studying ecology in the city versus studying ecology of the city. The latter approach required an integrative,
interdisciplinary stance and investigated all habitats in an
urban-suburban-exurban matrix, not just the conspicuously green patches.
Taking ecology of
the city seriously generated a new land cover conceptualization and
classification, and required examining the intimate feedbacks between social
and biophysical processes over various temporal scales. Indeed, the urban ecosystem is now seen as
"coproduced" by natural and social processes, and consequently, to
possess a hybrid social-ecological-technological structure (Rademacher et al.
2018).
Key Features of a New Framework
These insights, empirical advances, and conceptual
refinements have led us to propose a new framework to support our continued
collection and analysis of long-term data in the urban ecosystem. The framework divides the research concerns
into 1) exogenous drivers of change, 2) the structure of the urban ecosystem,
consisting of biological, physical, constructed, and social components, and 3)
the functional responses of the urban ecosystem. All of these aspects -- drivers, structure,
and responses -- interact with each other through time. In addition, the functional responses of the
urban ecosystem feed back onto its structure.
In a system that includes humans as individuals, groups, and
institutions, the feedbacks may involve learning and adaptation or adjustment.
Exogenous Drivers.
Exogenous drivers are those that originate or are controlled from outside of
the local or regional urban mosaic.
Climate change is clearly exogenous, as are regional patterns of
atmospheric deposition of gasses and particulate pollution. Much of the economy of urban regions is
driven by national and international investments, policy, allocation of jobs,
and movement of resources and commodities.
Governance anchored beyond the city, such as requirements of regional
compacts, state law and regulation, federal regulations, and private-public
interactions, can affect a metropolis or its parts. Technology emerging elsewhere may also alter
the fluxes of matter and energy available to a city, and human population can
be altered by regional, national, or international migration numbers and
directions.
Some of the factors enumerated as "exogenous" may,
if they are managed or shaped within the city or metropolis, act as local or
endogenous factors. It is the origin and
distance which determines exogeneity, not the specific type of flux or
influence. For example, the movement of
people within a metropolis could reflect local environmental perceptions,
behaviors, and organizational networks.
Ecosystem Structure.
Exogenous and internal influences come together in the structure of the urban
ecosystem. Like all human ecosystems,
urban areas consist of the biological organisms and the physical environment,
but also of the various human and social structures, and the constructed
environment. The interactions among
these four components drive the functional responses of the urban
ecosystem. All four urban ecosystem
components are reflected in the ecosystem function.
Functional Responses.
The functional responses are divided into three linked process realms, long
used to organize BES data collection. Watershed biogeochemistry addresses the
amount and content of water flowing through constructed infrastructure and
biophysical features of catchments. Local
ecosystem production and nutrient transformations are driven by the biota,
represented by plant, animal, and microbial communities. These are indexed by
key sentinel species. Human
environmental perceptions, behaviors, and the actions of organizations
constitute the social functions of the urban ecosystem. Clearly, all three functional realms interact
with each other. Equally clearly, the
functional interactions feed back on the structural filter by which external
drivers impact the system.
Similarity with Other LTER Site Frameworks
This new framework is intended to be readily interpretable
by ecologists working outside of urban areas as well as those who focus on
urban places. In fact, the general
schema for the framework is very similar to that of the Hubbard Brook Ecosystem
Study LTER, located in the forests of the White Mountains of New
Hampshire. Hubbard Brook is one of the
oldest LTER projects, and focuses on understanding the dynamics of forested
watersheds under the influence of exogenous factors and local management
choices and ecological succession.
Exogenous factors are well illustrated by the Hubbard Brook study, where
acid rain from distant sources was first identified in North America. Current examples of climate changes include
the role of reduced snow cover, and intensification of winter storms. Of the existing LTER sites, the vast majority
include some sort of exogenous factors in their roster of drivers. Climate change, sea level rise, and human
generated land use change are commonly identified as exogenous drivers.
Accommodating Long-Term Data
For nearly 20 years, BES has collected continuous or
repeated data sets on climate and weather, watershed hydrology, nutrient
export, water quality, biodiversity and
key biotic populations, soil processes, land cover and land use, social
structures, and social dynamics. These
data sets are arrayed across the seven core areas required of urban LTER sites,
as stated in NSF's original request for proposals in 1997 (Table 1).
Table 1.
Major BES research areas and their distribution across the LTER core research
areas.
BES has revised its conceptual framework by identifying the
fundamental ecosystem structures and processes represented by its ongoing,
long-term data collection, while at the same time organizing the structures and
processes differently than in its original conception. In this way, we hope to have clarified the
big ideas that motivate and tie together the data streams emerging from a still
under-studied ecosystem type. The
framework combines some of the most fundamental ideas from ecosystem science
with the novel structure and large changes represented by urban systems.
Steward Pickett and Emma Rosi
Background Literature
Cadenasso, M. L., S. T. A.
Pickett, and J. M. Grove. 2006. Integrative approaches to investigating
human-natural systems: the Baltimore ecosystem study. Natures Sciences Societes
14:4–14.
Pickett, S. T. A., M. L.
Cadenasso, E. J. Rosi-Marshall, K. T. Belt, P. M. Groffman, J. M. Grove, E. G.
Irwin, S. S. Kaushal, S. L. LaDeau, C. H. Nilon, C. M. Swan, and P. S. Warren.
2017. Dynamic heterogeneity: a framework to promote ecological integration and
hypothesis generation in urban systems. Urban Ecosystems 20:1–14. DOI: 10.1007/s11252-016-0574-9
Rademacher, A., M. L. Cadenasso,
and S. T. A. Pickett. 2018. From feedbacks to coproduction: Toward an
integrated conceptual framework for urban ecosystems. Urban Ecosystems. DOI: 10.1007/s11252-018-0751-0
Zhou, W., S. T. A. Pickett, and
M. L. Cadenasso. 2017. Shifting concepts of urban spatial heterogeneity and
their implications for sustainability. Landscape Ecology 32:15–30. DOI: 10.1007/s10980-016-0432-4
