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The impact of climate change on endangered plants and lichen [1]

['Amy Wrobleski', 'Department Of Anthropology', 'The Pennsylvania State University', 'University Park', 'Pennsylvania', 'United States Of America', 'Intercollege Graduate Degree Program In Ecology', 'Sydney Ernst', 'Theodore Weber', 'Defenders Of Wildlife']

Date: 2023-07 

The Endangered Species Act (ESA) was a landmark protection for rare organisms in the United States. Although the ESA is known for its protection of wildlife, a majority of listed species are actually plants and lichen. Climate change will impact species populations globally. Already-rare species, like those listed in the ESA, are at an even higher risk due to climate change. Despite this, the risk climate change poses to endangered plants has not been systematically evaluated in over a decade. To address this gap, we modified previously existing qualitative assessment toolkits used to examine the threat of climate change in federal documentation on listed wildlife. These modified toolkits were then applied to the 771 ESA listed plants. First, we evaluated how sensitive ESA listed plants and lichens were to climate change based on nine quantitative sensitivity factors. Then, we evaluated if climate change was recognized as a threat for a species, and if actions were being taken to address the threats of climate change. We found that all ESA listed plant and lichen species are at least slightly (score of 1) sensitive to climate change, and therefore all listed plants and lichens are threatened by climate change. While a majority of ESA listing and recovery documents recognized climate change as a threat, very few had actions being taken in their recovery plans to address climate change directly. While acknowledging the threat that climate change poses to rare plants is an important first step, direct action will need to be taken to ensure the recovery of many of these species.

Introduction

Since the publication of Linnaeus’ Species plantarum in 1753, over 600 plant species have become extinct globally [1, 2]. The true number is likely higher, as this estimate leaves out many plant groups that are data deficient, meaning that there is not enough known about these species to ascertain if they are threatened or at risk for extinction [3]. CO 2 emissions are the driving force of anthropogenic climate change and have been increasing in the earth’s atmosphere since 1850. While the growth rate of CO 2 emissions has slowed in recent decades, total emissions overall continue to rise [4]. Likewise, while the historic background extinction rate for plant species has been estimated between .05 and .15 extinctions per 10,000 species per 100 years [5–9], the global extinction rate for plants under anthropogenic climate change may be as high as .6 species extinctions per 10,000 species per 100 years [10]. Given this raised risk of extinction, species already considered rare may be at an even higher risk to shifting climatic conditions [11]. Species with low population numbers are vulnerable to catastrophic events as well as the long-term impacts of Allee effects, which complicate long-term recovery of a species after a catastrophic event. Additionally, many rare species may be abundant, but geographically restricted, meaning a whole species could be impacted by a single catastrophic event [12]. Therefore, while many if not most plants will be impacted by climate change, it is particularly important to understand the impacts on rare plants, as their potential for recovery is far less likely.

Although ecosystems continue to be threatened by climate change, substantial conservation actions could help to mitigate its worst effects [4]. This study seeks to understand how the Endangered Species Act (ESA) directs conservation actions and establishes regulations to address the threat of climate change on listed plant and lichen species and to assess the actions, if any, being taken to mitigate climate change threats for those species. Understanding how the ESA addresses the threat of climate change for listed endangered species is vital to the persistence of these species into the future, as the populations of many endangered species are already dwindling. Through evaluations such as these, agencies such as the US Fish and Wildlife Service (US FWS) can have a better understanding of where they currently stand on incorporating climate change into conservation and recovery goals, and what can potentially be done to improve recovery plans and reviews. If the ESA is not directing conservation actions and regulation to climate change threats, then it is likely that, on a larger scale, ecosystems are also at risk and actions are not being taken to address these threats. Alternatively, if the ESA is integrating climate change into conservation actions and regulations and highlights actions needed to address climate change impacts for endangered plant species, then it could be used as a model for other climate and conservation-based initiatives elsewhere.

Climate change risks and plants Climate change is predicted to impact a variety of global conditions, from shifting temperatures to changing precipitation patterns to sea level rise [4]. There has already been a 1.1°C global temperature increase from 2011–2020 when compared to 1850–1900 averages [13] Changes in atmospheric CO 2 levels have been shown to alter vegetation functional groups [14, 15]. Increased temperatures have been shown to largely impact plant reproductive success, with warm temperatures accelerating phenological development, and heat stress leading to impaired fertilization and the abortion of plant reproductive organs [16, 17]. Rising temperatures have been linked to competitive displacement, predation intensification, and new predator-prey interactions. Alternatively, climate change may also allow for coexistence between species that was not possible under previous conditions [14]. Sea levels are also expect to rise globally as temperatures warm, leading to the erosion of key coast dune habitat for plant species, shifting nutrient availability and flooding stress for coastal plants, and along with the stress from flooding, often increased salinity, which some species are not able to tolerate [18–20]. All of these components have impacts on biotic factors and therefore may impact plants. Climate is a major factor in determining the distribution of species [21]. Under the pressure of climate change, the distributions of plant species could be altered in the future. Fig 1 illustrates how climate change may impact the United States through changing temperature and precipitation regimes, and shows the broad distribution critical habitats for endangered and threatened species across the United States. All regions of the United States will be impacted by changing climatic conditions, but the directionality and intensity vary depending on the region, as will the impacts on endangered species. PPT PowerPoint slide

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TIFF original image Download: Fig 1. Critical habitat and data from the U.S. climate resilience toolkit climate explorer [ Critical habitat and data from the U.S. climate resilience toolkit climate explorer [ 22 ]. A. All land designated as critical habitat for both plants and animals under the Endangered Species Act is shaded in dark red. While not all endangered species are located on critical habitat, it does provide a rough distribution of endangered species. The light red circles indicate the relative number of plants in each US FWS region, with larger circles indicating a greater number of listed plants. The black outlines are US FWS regions, which are regulatory regions applied to enforcing the ESA. Region 1: Pacific, the largest circle of the map, also includes Hawai’i as well as other Pacific Islands, where most of the listed plants in this region are located. Layers used to create this map are the USFWS Region Layer (https://gis-fws.opendata.arcgis.com/datasets/c9d8cd103c5c444f9f65a1bc0dfe1b95_0/about), the USFWS Critical Habitat Layer (https://ecos.fws.gov/ecp/report/critical-habitat ), and the Base Layer “Outline Map” (https://www.arcgis.com/home/item.html?id=7da16f48c81f448fa972d4a52fdc1e4e). B. “Temperature” is the average daily maximum temperature. Under high emissions, the average daily maximum temperature will increase for most locations in the continental US. “Growing Degree Days” is an estimate of the growth and development of plants. A higher number of growing degree days indicates longer durations of warm conditions. Much like temperature, the number of growing degree days is projected to increase in all areas other than the highest elevations. “Precipitation” is the total precipitation in a year in inches. Total precipitation appears to increase in the North and East but declines in the Southwest. There was no historic data for total precipitation. “Dry days” is the number of days in a year when precipitation is less than .01 inches. Changes in this number indicate trends towards drier or wetter conditions. The dry days data indicates that in regions like the Northwest, while total precipitation may not change or may increase, there will be an increase in dry days throughout the year. Under climate change, there is the potential for not only shifts in the amount of precipitation, but also shifts in the amount of precipitation received at any given time or the form of the precipitation (i.e. snowfall, ice, or liquid rain). The Northeast, Midwest, and Southeast are particularly likely to be affected by these extreme rainfall events. These heavy rainfall events lead to an increased risk of flooding [23, 24]. https://doi.org/10.1371/journal.pclm.0000225.g001 Species are also expected to shift their distributions in response to rising temperatures, with about half moving 50–1600 km towards higher latitudes or up to 400 meters higher in elevation [25]. Species are not only shifting geographically, but also in their timing, or phenology. Many species are already shifting to earlier spring breeding, migration, or in the case of many plants, blooming [25]. These changes in timing and geography may lead to cascading impacts across entire ecosystems, disrupting ecosystem functions and relationships between species. This may impact keystone species, or species whose presence is crucial to maintaining an ecological community [26, 27] or multi-species interactions such as food webs, pollination and seed dispersal interactions [28, 29]. These shifts in phenology can have greater impacts on the larger ecosystem, disrupting trophic interactions and leading to trophic mismatches and community instability [14, 30–32]. Mismatches between the life cycles of plants and their pollinators have been of particular concern due to changes in emergence and flowering time [33, 34]. In the case of plants, the extirpation of a keystone plant could lead to cascading effects on dependent animals, particularly pollinators and seed dispersers [27]. While this study examines climate change on a species-by-species basis, climate change will impact not only an individual species, but their network of relationships in ways that can be unpredictable and lead to cascading effects in the entirety of the ecosystem.

ESA protections and climate change In the United States, the Endangered Species Act is the primary law that protects rare species at risk of, or threatened by, extinction. The ESA initially only protected wildlife, with the first plants added in 1977 [25]. In 1982, an amendment was added to prohibit the removal of endangered plants from federal land [35]. With this addition, the number of plant species with ESA listings grew, and, since 1994, plants have made up a majority of the species listed [25]. However, despite their listing, critics of the ESA note that recovery efforts tend to focus on charismatic wildlife, leaving plants with fewer resources than other species [25, 36]. Additionally, a core feature of the ESA is the prohibition against “taking” an endangered animal. In this case “taking” would mean to harass or harm the species in addition to selling the species or their parts. This prohibition does not apply to plants. Under the ESA, plants are protected from removal on federal land or destruction in knowing violation of state law. However, on private property, there is no prohibition against “taking” endangered plants and lichen [25, 35]. So, while the ESA is often held up as a powerful conservation tool, it is less protective for plants and lichen than it is for animal species. Rare species are assessed for listing on the ESA as either “threatened” or “endangered” by the secretaries of the Interior and Commerce- using five factors: Habitat destruction and degradation Overutilization Disease or predation Inadequacy of existing protections Other factors If this assessment find that listing is warranted, and is not precluded by other higher priorities, a species may be listed as either “threatened” or “endangered” at which point the agencies that oversee the implementation of the Endangered Species Act- in the case of plants the US FWS prepare plans and implementation for the species recovery. The primary document created in this process is the recovery plan. While agencies are not required under the ESA to implement all actions outlined in the recovery plan, the goal of recovery plans is to provide “a feasible and effective pathway to recovery” of a species [37]. From there, the ESA mandates that species periodically are reviewed. These reviews are conducted through a systematic procedure, the 5-year review. If a species has an up-to-date recovery plan, then a 5-year review will evaluate if that plan is being followed and how the species status may have changed since the previous 5-year review. If a species does not yet have a recovery plan, or the recovery plan is out of date, then a 5-year review may become a more intensive analysis of the recovery of the species. In general- a 5-year review will have the most up-to-date information on an ESA listed species [38]. Despite the growing threat of climate change for rare species, climate change is not included as one of the five evaluation factors when listing a species and creating a recovery plan. This is partially due to the timeline of legislation surrounding the ESA. The last major amendment to the ESA was in 1988 [39]. The first ESA listed animal to evaluate climate change as a primary threat for their listing was the polar bear (Ursus maritimus) in 2008, followed by many more species that same year [40]. Since this 2008 listing, there has not been an amendment to the ESA, so climate change continues to be generally considered either as a contributor to “Habitat destruction” or as one of the “Other factors” in a species assessment. The US Fish and Wildlife Service (US FWS), the primary agency that oversees the implementation of the ESA for listed plants, has acknowledged climate change as a challenge to conserving wildlife and has stated that they develop conservation programs with climate change in mind [41–44]. In some cases, climate change may fall neatly under “Habitat destruction” such as rising sea levels encroaching on a narrow strip of beach habitat. However, this is not always the case. Climate change will impact species in a variety of ways that are not tied directly to habitat, such as: an increase in fungal diseases and other pathogens, phenological mismatches, a loss of obligate species, changes in disturbance regimes, and the loss of crucial climate envelopes [25, 44]. This means that while climate change may be integrated into other factors and objectives, it is not required to be considered in a holistic way while assessing species for listing and recovery under the ESA. While the immediate problem might be addressed, if the underlying cause is linked to climate change, the species may need a different approach to promote its recovery. The threat assessment of climate change towards ESA listed organisms has been carried out previously a handful of times. In 2010, Povilitis et al. evaluated all species with recovery plans, both plants and animals. This initial analysis showed that more recent recovery plans (starting in 2004 and ending in 2010 when the study was published) were more likely to list climate change as a threat [45]. However, at the time, only 26 recovery plans listed climate change as a threat for animals, and no plant recovery plans listed climate change as a threat [25]. In 2019, Delach et al. assessed the sensitivity of 459 endangered animals to climate change, if climate change was listed as a threat, and if any actions were implemented to mitigate climate change. They found that almost all animal species are sensitive to climate change, but only 64% listed climate change as a threat and even fewer (18%) had management actions in place [40]. This more recent evaluation has not been carried out for plants. Finally, it is important to note that endangered species are not evenly distributed across US FWS regions. In particular, imperiled vascular plants tend to cluster in the central valley of California (FWS Region 8: Pacific Southwest), southern Appalachia (FWS Region: 4 Southeast), and the Southeast (FWS Region: 4 Southeast), these distributions and how climatic conditions may change in the future seen in Fig 1 [46–48]. Some of these trends reflect biodiversity and endemism hot spots and correspond to the three recognized biodiversity hot spots within the United States (including islands and territories): Polynesia Micronesia (FWS Region 1: Pacific), the Caribbean (FWS Region: 4 Southeast), and the California Floristic Province (FWS Region 8: Pacific Southwest) [49]. However, using the ESA as a metric for rare plants and lichens underestimates the true total number of rare and endemic plants across the United States [50–52]. Rare plants and lichens can, and do, exist across the United States but are not listed under the ESA and outstrip the capacity of the ESA. NatureServe, which evaluates the rarity of plants, has over 2800 plants ranked as G1 (critically imperiled) or G2 (imperiled) in the United States, while there were only 771 plants and lichens listed within the ESA during this evaluation [53]. Therefore, this study should be used as a conservative examination of the impact of climate change on rare plants and lichen, but also can serve as a proxy for the impact of climate change on rare plants, since ESA listed species have been evaluated for a variety of external threats.

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[1] Url: https://journals.plos.org/climate/article?id=10.1371/journal.pclm.0000225

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