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A species is conservation reliant when the threats that it faces cannot be eliminated, but only managed. There are two forms of conservation reliance: population- and threat-management reliance. We provide an overview of the concept and introduce a series of articles that examine it in the context of a range of taxa, threats, and habitats. If sufficient assurances can be provided that successful population and threat management will continue, conservation-reliant species may be either delisted or kept off the endangered species list. This may be advantageous because unlisted species provide more opportunities for a broader spectrum of federal, state, tribal, and private interests to participate in conservation. Even for currently listed species, the number of conservation-reliant species—84% of endangered and threatened species with recovery plans— and the magnitude of management actions needed to sustain the species at recovered levels raise questions about society's willingness to support necessary action.
Kirtland's warbler is one of many conservation-reliant species listed under the Endangered Species Act (ESA). This species has met recovery goals, but removing it from the protections of the ESA is problematic because of its reliance on ongoing conservation. We define conservation management agreements (CMAs) and describe how they may provide a mechanism to protect conservation-reliant species after delisting. We suggest that CMAs should include four major elements: (1) a conservation partnership capable of implementing management actions at conservation-relevant scales, (2) a conservation management plan based on the management actions in the species' successful recovery plan, (3) sufficient financial resources to provide the required conservation management, and (4) legal enforcement. We use the efforts of the Kirtland's Warbler Recovery Team as a case study of the application of CMAs to build and maintain public and private partnerships to ensure continuing management for this species after delisting.
One-third of the bird species listed under the US Endangered Species Act are endemic to Hawaii. One requirement of delisting a species is the elimination or abatement of threats to that species. More than 95% of Hawaii's threatened and endangered species face multiple threats that cannot be eliminated (e.g., alien mammalian predators, invasive alien plants that alter habitat structure, disease). However, because we can manage many of the threats at scales at which the achievement of recovery goals is possible, these species could be delisted if conservation partners committed to the implementation of stewardship agreements to maintain viable populations following those populations' delistings.
The Mojave desert tortoise was listed as threatened under the US Endangered Species Act (ESA) because of local population declines and an array of threats. Challenges to the recovery of this species include an incomplete understanding of the threats most responsible for its decline, insufficient information on the effectiveness of management actions, and the intractability of threats across a large geographical range and multiple jurisdictions. Recognition that these challenges require long-term conservation efforts to ensure the species' persistence—with or without the protections of the ESA—necessitates a more structured approach to recovery, including broad stakeholder participation. A conservation-reliant perspective will probably be increasingly relevant for additional species and for adapting land management in the face of climate change by improving regional coordination of management activities, broadening spatial and temporal points of view in management, and increasing the emphasis on addressing multiple threats simultaneously.
Valuation of ecosystem services can provide evidence of the importance of sustaining and enhancing those resources and the ecosystems that provide them. Long appreciated only as a commercial source of oysters, oyster reefs are now acknowledged for the other services they provide, such as enhancing water quality and stabilizing shorelines. We develop a framework to assess the value of these services. We conservatively estimate that the economic value of oyster reef services, excluding oyster harvesting, is between $5500 and $99,000 per hectare per year and that reefs recover their median restoration costs in 2–14 years. In contrast, when oyster reefs are subjected to destructive oyster harvesting, they do not recover the costs of restoration. Shoreline stabilization is the most valuable potential service, although this value varies greatly by reef location. Quantifying the economic values of ecosystem services provides guidance about when oyster reef restoration is a good use of funds.
Virtually all global energy forecasts include an expectation that bioenergy will be a substantial future energy source. However, the scale of this potential resource remains poorly understood because of uncertain land availability and yield expectations. Here, we used climate-constrained, satellite-derived net primary productivity data computed for 110 million square kilometers of terrestrial plant production as an upper-envelope constraint on primary bioenergy potential (PBP). We estimated the maximum PBP to realistically range from 12% to 35% of 2009 global primary energy consumption, with yield potential ranging from 6.6 to 18.8 megajoules per square meter per year—roughly four times lower than previous evaluations. Our results highlight many recent bioenergy evaluations as overoptimistic, which we attribute to a failure to adequately apply biophysical constraints in estimates of yield potential. We do not advocate bioenergy production at the levels reported in this analysis; instead, we simply report the ceiling for PBP based on current planetary productivity.