Shifting forward: Urban ecology in perspective.

The world has become urban; cities increasingly shape our worldviews, relation to other species, and the large-scale, long-term decisions we make. Cities are nature, but they need to align better with other ecosystems to avoid accelerating climate change and loss of biodiversity. We need a science to guide urban development across the diverse realities of global cities. This need can be met, in part, by shifts in urban ecology and its linkages to related sciences. This perspective is a "synthesis of syntheses", consolidating ideas from the other articles in the Special Section. It re-examines the role of urban ecology, and explores its integration with other disciplines that study cities. We conclude by summarizing the next steps in the ongoing shift in urban ecology, which is fast becoming an integral part of urban studies.

The relational shift in urban ecology: From place and structures to multiple modes of coproduction for positive urban futures.

This perspective emerged from ongoing dialogue among ecologists initiated by a virtual workshop in 2021. A transdisciplinary group of researchers and practitioners conclude that urban ecology as a science can better contribute to positive futures by focusing on relationships, rather than prioritizing urban structures. Insights from other relational disciplines, such as political ecology, governance, urban design, and conservation also contribute. Relationality is especially powerful given the need to rapidly adapt to the changing social and biophysical drivers of global urban systems. These unprecedented dynamics are better understood through a relational lens than traditional structural questions. We use three kinds of coproduction-of the social-ecological world, of science, and of actionable knowledge-to identify key processes of coproduction within urban places. Connectivity is crucial to relational urban ecology. Eight themes emerge from the joint explorations of the paper and point toward social action for improving life and environment in urban futures.

A transformative shift in urban ecology toward a more active and relevant future for the field and for cities.

This paper builds on the expansion of urban ecology from a biologically based discipline-ecology in the city-to an increasingly interdisciplinary field-ecology of the city-to a transdisciplinary, knowledge to action endeavor-an ecology for and with the city. We build on this "prepositional journey" by proposing a transformative shift in urban ecology, and we present a framework for how the field may continue this shift. We conceptualize that urban ecology is in a state of flux, and that this shift is needed to transform urban ecology into a more engaged and action based field, and one that includes a diversity of actors willing to participate in the future of their cities. In this transformative shift, these actors will engage, collaborate, and participate in a continuous spiral of knowledge → action → knowledge spiral and back to knowledge loop, with the goal of co producing sustainable and resilient solutions to myriad urban challenges. Our framework for this transformative shift includes three pathways: (1) a repeating knowledge → action → knowledge spiral of ideas, information, and solutions produced by a diverse community of agents of urban change working together in an "urban sandbox"; (2) incorporation of a social-ecological-technological systems framework in this spiral and expanding the spiral temporally to include the "deep future," where future scenarios are based on a visioning of seemingly unimaginable or plausible future states of cities that are sustainable and resilient; and (3) the expansion of the spiral in space, to include rural areas and places that are not yet cities. The three interrelated pathways that define the transformative shift demonstrate the power of an urban ecology that has moved beyond urban systems science and into a realm where collaborations among diverse knowledges and voices are working together to understand cities and what is urban while producing sustainable solutions to contemporary challenges and envisioning futures of socially, ecologically, and technologically resilient cities. We present case study examples of each of the three pathways that make up this transformative shift in urban ecology and discuss both limitations and opportunities for future research and action with this transdisciplinary broadening of the field.

Cross-Site Comparisons of Dryland Ecosystem Response to Climate Change in the US Long-Term Ecological Research Network.

Long-term observations and experiments in diverse drylands reveal how ecosystems and services are responding to climate change. To develop generalities about climate change impacts at dryland sites, we compared broadscale patterns in climate and synthesized primary production responses among the eight terrestrial, nonforested sites of the United States Long-Term Ecological Research (US LTER) Network located in temperate (Southwest and Midwest) and polar (Arctic and Antarctic) regions. All sites experienced warming in recent decades, whereas drought varied regionally with multidecadal phases. Multiple years of wet or dry conditions had larger effects than single years on primary production. Droughts, floods, and wildfires altered resource availability and restructured plant communities, with greater impacts on primary production than warming alone. During severe regional droughts, air pollution from wildfire and dust events peaked. Studies at US LTER drylands over more than 40 years demonstrate reciprocal links and feedbacks among dryland ecosystems, climate-driven disturbance events, and climate change.

Plant transpiration in constructed treatment wetland: Effects on water budget and management consequences.

Plant transpiration is an important feature of wetlands with biological and hydraulic impacts. The global objective of this study was to question the influence of transpirational water losses on constructed treatment wetland water budget for a variety of wetland design and time of the year. Biomass and transpiration field measurements were carried out in constructed treatment wetlands (CTWs) submitted to oceanic climate and used for waste- or stormwater management. Measurements were carried out during spring, summer and fall. Biomass and transpiration rate were both significantly affected by season and site configuration, although the effect appears more sharply for season than for site. Transpiration can reach 26% of the incoming flow during the warmest part of the year for wastewater management CTW, when the effect on adjacent water courses is likely to be the most significant. The impact on multi-monthly water budget plummets to 2% of the incoming water volume. For stormwater CTW, transpiration can lead to strong water scarcity, virtually emptying all available water in these stochastically fed systems. As transpiration also plays a significant role in biogeochemical processes in wetlands, it seems important to design this type of ecological infrastructure in close relation with the pursued objectives, be it either the quality of outlet water (emphasis on treatment efficiency) or the quantity of outlet water (emphasis on flow regulation).

Phosphorus in Phoenix: a budget and spatial representation of phosphorus in an urban ecosystem.

As urban environments dominate the landscape, we need to examine how limiting nutrients such as phosphorus (P) cycle in these novel ecosystems. Sustainable management of P resources is necessary to ensure global food security and to minimize freshwater pollution. We used a spatially explicit budget to quantify the pools and fluxes of P in the Greater Phoenix Area in Arizona, USA, using the boundaries of the Central Arizona-Phoenix Long-Term Ecological Research site. Inputs were dominated by direct imports of food and fertilizer for local agriculture, while most outputs were small, including water, crops, and material destined for recycling. Internally, fluxes were dominated by transfers of food and feed from local agriculture and the recycling of human and animal excretion. Spatial correction of P dynamics across the city showed that human density and associated infrastructure, especially asphalt, dominated the distribution of P pools across the landscape. Phosphorus fluxes were dominated by agricultural production, with agricultural soils accumulating P. Human features (infrastructure, technology, and waste management decisions) and biophysical characteristics (soil properties, water fluxes, and storage) mediated P dynamics in Phoenix. P cycling was most notably affected by water management practices that conserve and recycle water, preventing the loss of waterborne P from the ecosystem. P is not intentionally managed, and as a result, changes in land use and demographics, particularly increased urbanization and declining agriculture, may lead to increased losses of P from this system. We suggest that city managers should minimize cross-boundary fluxes of P to the city. Reduced P fluxes may be accomplished through more efficient recycling of waste, therefore decreasing dependence on external nonrenewable P resources and minimizing aquatic pollution. Our spatial approach and consideration of both pools and fluxes across a heterogeneous urban ecosystem increases the utility of nutrient budgets for city managers. Our budget explicitly links processes that affect P cycling across space with the management of other resources (e.g., water). A holistic management strategy that deliberately couples the management of P and other resources should be a priority for cities in achieving urban sustainability.

Seasonal plant water uptake patterns in the saline southeast Everglades ecotone.

The purpose of this study was to determine the seasonal water use patterns of dominant macrophytes coexisting in the coastal Everglades ecotone. We measured the stable isotope signatures in plant xylem water of Rhizophora mangle, Cladium jamaicense, and Sesuvium portulacastrum during the dry (DS) and wet (WS) seasons in the estuarine ecotone along Taylor River in Everglades National Park, FL, USA. Shallow soilwater and deeper groundwater salinity was also measured to extrapolate the salinity encountered by plants at their rooting zone. Average soil water oxygen isotope ratios (delta(18)O) was enriched (4.8 +/- 0.2 per thousand) in the DS relative to the WS (0.0 +/- 0.1 per thousand), but groundwater delta(18)O remained constant between seasons (DS: 2.2 +/- 0.4 per thousand; WS: 2.1 +/- 0.1 per thousand). There was an inversion in interstitial salinity patterns across the soil profile between seasons. In the DS, shallow water was euhaline [i.e., 43 practical salinity units (PSU)] while groundwater was less saline (18 PSU). In the WS, however, shallow water was fresh (i.e., 0 PSU) but groundwater remained brackish (14 PSU). All plants utilized 100% (shallow) freshwater during the WS, but in the DS R. mangle switched to a soil-groundwater mix (delta 55% groundwater) while C. jamaicense and S. portulacastrum continued to use euhaline shallow water. In the DS, based on delta(18)O data, the roots of R. mangle roots were exposed to salinities of 25.4 +/- 1.4 PSU, less saline than either C. jamaicense (39.1 +/- 2.2 PSU) or S. portulacastrum (38.6 +/- 2.5 PSU). Although the salinity tolerance of C. jamaicense is not known, it is unlikely that long-term exposure to high salinity is conducive to the persistence of this freshwater marsh sedge. This study increases our ecological understanding of how water uptake patterns of individual plants can contribute to ecosystem levels changes, not only in the southeast saline Everglades, but also in estuaries in general in response to global sea level rise and human-induced changes in freshwater flows.

Cascading ecological effects of low-level phosphorus enrichment in the Florida everglades.

Few studies have examined long-term ecological effects of sustained low-level nutrient enhancement on wetland biota. To determine sustained effects of phosphorus (P) addition on Everglades marshes we added P at low levels (5, 15, and 30 microg L(-1) above ambient) for 5 yr to triplicate 100-m flow-through channels in pristine marsh. A cascade of ecological responses occurred in similar sequence among treatments. Although the rate of change increased with dosing level, treatments converged to similar enriched endpoints, characterized most notably by a doubling of plant biomass and elimination of native, calcareous periphyton mats. The full sequence of biological changes occurred without an increase in water total P concentration, which remained near ambient levels until Year 5. This study indicates that Everglades marshes have a near-zero assimilative capacity for P without a state change, that ecosystem responses to enrichment accumulate over time, and that downstream P transport mainly occurs through biota rather than the water column.

Ecological effects of low-level phosphorus additions on two plant communities in a neotropical freshwater wetland ecosystem.

We conducted a low-level phosphorus (P) enrichment study in two oligotrophic freshwater wetland communities (wet prairies [WP] and sawgrass marsh [SAW]) of the neotropical Florida Everglades. The experiment included three P addition levels (0, 3.33, and 33.3 mg P m(-2) month(-1)), added over 2 years, and used in situ mesocosms located in northeastern Everglades National Park, Fla., USA. The calcareous periphyton mat in both communities degraded quickly and was replaced by green algae. In the WP community, we observed significant increases in net aboveground primary production (NAPP) and belowground biomass. Aboveground live standing crop (ALSC) did not show a treatment effect, though, because stem turnover rates of Eleocharis spp., the dominant emergent macrophyte in this community, increased significantly. Eleocharis spp. leaf tissue P content decreased with P additions, causing higher C:P and N:P ratios in enriched versus unenriched plots. In the SAW community, NAPP, ALSC, and belowground biomass all increased significantly in response to P additions. Cladium jamaicense leaf turnover rates and tissue nutrient content did not show treatment effects. The two oligotrophic communities responded differentially to P enrichment. Periphyton which was more abundant in the WP community, appeared to act as a P buffer that delayed the response of other ecosystem components until after the periphyton mat had disappeared. Periphyton played a smaller role in controlling ecosystem dynamics and community structure in the SAW community. Our data suggested a reduced reliance on internal stores of P by emergent macrophytes in the WP that were exposed to P enrichment. Eleocharis spp. rapidly recycled P through more rapid aboveground turnover. In contrast, C. jamaicense stored added P by initially investing in belowground biomass, then shifting growth allocation to aboveground tissue without increasing leaf turnover rates. Our results suggest that calcareous wetland systems throughout the Caribbean, and oligotrophic ecosystems in general, respond rapidly to low-level additions of their limiting nutrient.

Decadal change in vegetation and soil phosphorus pattern across the Everglades landscape.

Wetlands respond to nutrient enrichment with characteristic increases in soil nutrients and shifts in plant community composition. These responses to eutrophication tend to be more rapid and longer lasting in oligotrophic systems. In this study, we documented changes associated with water quality from 1989 to 1999 in oligotrophic Everglades wetlands. We accomplished this by resampling soils and macrophytes along four transects in 1999 that were originally sampled in 1989. In addition to documenting soil phosphorus (P) levels and decadal changes in plant species composition at the same sites, we report macrophyte tissue nutrient and biomass data from 1999 for future temporal comparisons. Water quality improved throughout much of the Everglades in the 1990s. In spite of this improvement, though, we found that water quality impacts worsened during this time in areas of the northern Everglades (western Loxahatchee National Wildlife Refuge [NWR] and Water Conservation Area [WCA] 2A). Zones of high soil P (exceeding 700 mg P kg(-1) dry wt. soil) increased to more than 1 km from the western margin canal into the Loxahatchee NWR and more than 4 km from northern boundary canal into WCA-2A. This doubling of the high soil P zones since 1989 was paralleled with an expansion of cattail (Typha spp.)-dominated marsh in both regions. Macrophyte species richness declined in both areas from 1989 to 1999 (27% in the Loxahatchee NWR and 33% in WCA-2A). In contrast, areas well south of the Everglades Agricultural Area, induding WCA-3A and Everglades National Park (ENP), did not decline during this time. We found no significant decadal change in plant community patterns from 1989 and 1999 along transects in southern WCA-3A or Shark River Slough (ENP). Our 1999 sampling also included a new transect in Taylor Slough (ENP), which will allow change analysis here in the future. Regular sampling of these transects, to verify decadal-scale environmental impacts or improvements, will continue to be an important tool for long-term management and restoration of the Everglades.