Projected avifaunal responses to climate change across the U.S. National Park System

<div><p>Birds in U.S. national parks find strong protection from many longstanding and pervasive threats, but remain highly exposed to effects of ongoing climate change. To understand how climate change is likely to alter bird communities in parks, we used species distribution models relating North American Breeding Bird Survey (summer) and Audubon Christmas Bird Count (winter) observations to climate data from the early 2000s and projected to 2041–2070 (hereafter, mid-century) under high and low greenhouse gas concentration trajectories, RCP8.5 and RCP2.6. We analyzed climate suitability projections over time for 513 species across 274 national parks, classifying them as improving, worsening, stable, potential colonization, and potential extirpation. U.S. national parks are projected to become increasingly important for birds in the coming decades as potential colonizations exceed extirpations in 62–100% of parks, with an average ratio of potential colonizations to extirpations of 4.1 in winter and 1.4 in summer under RCP8.5. Average species turnover is 23% in both summer and winter under RCP8.5. Species turnover (Bray-Curtis) and potential colonization and extirpation rates are positively correlated with latitude in the contiguous 48 states. Parks in the Midwest and Northeast are expected to see particularly high rates of change. All patterns are more extreme under RCP8.5 than under RCP2.6. Based on the ratio of potential colonization and extirpation, parks were classified into overall trend groups associated with specific climate-informed conservation strategies. Substantial change to bird and ecological communities is anticipated in coming decades, and current thinking suggests managing towards a forward-looking concept of ecological integrity that accepts change and novel ecological conditions, rather than focusing management goals exclusively on maintaining or restoring a static set of historical conditions.</p></div

Example of projected bird assemblage changes by mid-century at Golden Gate National Recreation Area.

<p>Under RCP8.5 in summer, climate suitability is projected to improve for the Great Egret (<i>Ardea alba</i>), remain stable for the Nuttall’s Woodpecker (<i>Picoides nuttallii</i>), and worsen for the Wilson’s Warbler (<i>Cardellina pusilla</i>). Climate suitability is at risk of disappearing for the American Robin (<i>Turdus migratorius</i>), potentially resulting in extirpation from the park. Although the Blue Grosbeak (<i>Passerina caerulea</i>) is not currently found in the park, climate is projected to become suitable for this species, potentially resulting in local colonization. Bird illustrations by Kenn Kaufman.</p

Classification of 274 U.S. national parks into trend groups based on the proportion of potential colonizations and extirpations.

<p>Each circle represents a park. The median proportion of colonizations and extirpations across parks under RCP8.5 in summer (represented by solid vertical and horizontal lines in the plot) were used to classify parks into all trend groups except intermediate change. The upper and lower quartiles of each axis (represented by the diamond in the center of the plot) mark the boundaries of the intermediate change group. Alaska is shown in the inset on the left and the National Capital region is shown in the inset on the right.</p

Relationships of the proportion of potential colonizations, extirpations, and turnover rate to latitude.

<p>Rates/proportions between the present and mid-century under RCP8.5 in summer and winter. Significance of the regression fit is denoted by “***” where <i>p</i> < 0.001, and <i>r</i>^<i>2</i> values are shown next to each curve where significant.</p

Projected species composition changes from the early 2000s to mid-century across 274 U.S. national parks.

<p>Potential (A) colonizations and (B) extirpations in summer and winter under RCP8.5 are shown as a proportion of the current total number of species. Circle sizes represent proportions in summer, and colors represent proportions in winter. Breaks in classes are based on quartiles. Alaska is shown in the inset on the left and the National Capital region is shown in the inset on the right.</p

Protected Area Tourism in a Changing Climate: Will Visitation at US National Parks Warm Up or Overheat?

<div><p>Climate change will affect not only natural and cultural resources within protected areas but also tourism and visitation patterns. The U.S. National Park Service systematically collects data regarding its 270+ million annual recreation visits, and therefore provides an opportunity to examine how human visitation may respond to climate change from the tropics to the polar regions. To assess the relationship between climate and park visitation, we evaluated historical monthly mean air temperature and visitation data (1979–2013) at 340 parks and projected potential future visitation (2041–2060) based on two warming-climate scenarios and two visitation-growth scenarios. For the entire park system a third-order polynomial temperature model explained 69% of the variation in historical visitation trends. Visitation generally increased with increasing average monthly temperature, but decreased strongly with temperatures > 25°C. Linear to polynomial monthly temperature models also explained historical visitation at individual parks (R² 0.12-0.99, mean = 0.79, median = 0.87). Future visitation at almost all parks (95%) may change based on historical temperature, historical visitation, and future temperature projections. Warming-mediated increases in potential visitation are projected for most months in most parks (67–77% of months; range across future scenarios), resulting in future increases in total annual visits across the park system (8–23%) and expansion of the visitation season at individual parks (13–31 days). Although very warm months at some parks may see decreases in future visitation, this potential change represents a relatively small proportion of visitation across the national park system. A changing climate is likely to have cascading and complex effects on protected area visitation, management, and local economies. Results suggest that protected areas and neighboring communities that develop adaptation strategies for these changes may be able to both capitalize on opportunities and minimize detriment related to changing visitation.</p></div

Potential changes in bird assemblages by mid-century, by emissions pathway and season, as measured by (1) average ± SE of Bray-Curtis dissimilarity index across parks, average ± SE of (2) the proportion of potential extirpations and (3) potential colonizations across parks, (4) count and percent of parks with more than 25% extirpations, (5) count and percent of parks with more than 25% colonizations, and (6) count and percent of parks where the number of potential colonizations exceeds potential extirpations.

<p>Potential changes in bird assemblages by mid-century, by emissions pathway and season, as measured by (1) average ± SE of Bray-Curtis dissimilarity index across parks, average ± SE of (2) the proportion of potential extirpations and (3) potential colonizations across parks, (4) count and percent of parks with more than 25% extirpations, (5) count and percent of parks with more than 25% colonizations, and (6) count and percent of parks where the number of potential colonizations exceeds potential extirpations.</p

Historical (1979–2013) and potential future visitation (2041–2060) patterns in example parks.

<p>a) Acadia National Park, Maine; b) Grand Teton National Park, Wyoming; c) Blue Ridge Parkway, North Carolina and Virginia; d) Arches National Park, Utah; e) Big Cypress National Preserve, Florida; and f) Pu‘uhonua o Hōnaunau NHP (National Historical Park, Hawai‘i; where a visitation-temperature relationship was not supported and historical mean monthly temperature [gray triangles and dashed line] is shown). Historical (black) error bars are +/- one standard error and future projection error bars show +/- one standard error of the prediction estimates. Solid red lines are for RCP 8.5 and solid orange lines are for RCP 4.5 low maximum growth projections, dotted lines of the same color and thickness show high maximum growth projections when different from low maximum growth.</p

Potential future total annual visitation (2041–2060) expressed as a percentage of historical values (1979–2013).

<p>Future visitation for each park is based on modeled monthly visitation relationship to temperature. Future projections, a) RCP 4.5 low growth and b) RCP 8.5 high growth, were limited to parks with temperature as an explanatory variable in the best-fit model and an adjusted R² ≥ 0.5 (<i>n</i> = 282).</p

Potential future change in length (days) of the overall visitation season at parks (2041–2060 – 1979–2013).

<p>Overall visitation season length was defined as beginning on the date when 10% of historical cumulative visitation was achieved and ending on the date when 10% of historical cumulative visitation remained for the year. Projections did not vary between low- and high-maximum growth models for each RCP. Boxplots: thick vertical black line indicates median, the boxes are the interquartile range (IQR), and the whiskers extend 1.5 x IQR.</p