Trends in Developed Land Cover Adjacent to Habitat for Threatened Salmon in Puget Sound, Washington, U.S.A.

For widely distributed species at risk, such as Pacific salmon (Oncorhynchus spp.), habitat monitoring is both essential and challenging. Only recently have widespread monitoring programs been implemented for salmon habitat in the Pacific Northwest. Remote sensing data, such as Landsat images, are therefore a useful way to evaluate trends prior to the advent of species-specific habitat monitoring programs. We used annual (1986-2008) land cover maps created from Landsat images via automated algorithms (LandTrendr) to evaluate trends in developed (50-100% impervious) land cover in areas adjacent to five types of habitat utilized by Chinook salmon (O. tshawytscha) in the Puget Sound region of Washington State, U.S.A. For the region as a whole, we found significant increases in developed land cover adjacent to each of the habitat types evaluated (nearshore, estuary, mainstem channel, tributary channel, and floodplain), but the increases were small (<1% total increase from 1986 to 2008). For each habitat type, the increasing trend changed during the time series. In nearshore, mainstem, and floodplain areas, the rate of increase in developed land cover slowed in the latter portion of the time series, while the opposite occurred in estuary and tributary areas. Watersheds that were already highly developed in 1986 tended to have higher rates of development than initially less developed watersheds. Overall, our results suggest that developed land cover in areas adjacent to Puget Sound salmon habitat has increased only slightly since 1986 and that the rate of change has slowed near some key habitat types, although this has occurred within the context of a degraded baseline condition

Akaike’s Information Criterion for Simple and Segmented Regression Analyses: Puget Sound Scale.

<p>Akaike’s Information Criterion corrected for small sample sizes (AICc), calculated for two regression models (simple and segmented) in six habitat areas, at the Puget Sound scale. The difference in AICc (where Δ AICc = simple AICc—segmented AICc) is also provided.</p><p>^a Δ AICc >4 indicates support for the segmented regression model.</p><p>Akaike’s Information Criterion for Simple and Segmented Regression Analyses: Puget Sound Scale.</p

Segmented Regression Analysis Results: Puget Sound Scale.

<p>Model coefficients (a_<i>1</i>, <i>b</i>_<i>1</i>, and <i>b</i>_<i>2</i>), standard errors (SE), breakpoints, and <i>R</i>² values resulting from fitting segmented regression models to time series of developed land cover in six habitat areas, at the Puget Sound scale.</p><p>^a<i>b</i>_<i>1</i> represents the slope for the first part of the time series (1986-breakpoint year) in ha/year.</p><p>^b<i>b</i>_<i>2</i> represents the slope for the second part of the time series (breakpoint year-2008) in ha/year.</p><p>Segmented Regression Analysis Results: Puget Sound Scale.</p

Trends in Developed Land Cover: Puget Sound Scale.

<p>Change over time in developed land cover, summarized at the Puget Sound scale for six habitat areas. Developed cover is depicted in ha (left axis) and % (right axis), and two types of regression models are fit to the data: simple (gray line) and segmented (black line). For the segmented model, the breakpoint estimate and standard error are also shown (dotted white line and gray rectangle, respectively).</p

Changing Trends in Developed Land Cover: Watershed Scale.

<p>Heat map illustrating trends in developed land cover (regression slopes), summarized at the watershed scale for six habitat areas. Warmer colors indicate increasingly positive slopes; cooler colors increasingly negative slopes. A change in cell color between the first and second cell within a habitat-by-watershed combination indicates a substantially better fit of the segmented regression, compared to the simple regression (i.e., Δ AICc >4), hence <i>b</i>_<i>1</i> and <i>b</i>_<i>2</i> are shown. If Δ AICc was <4, both cells depict <i>b</i>_<i>0</i> for the simple regression, unless the <i>b</i>_<i>0</i><i>p</i>-value exceeded 0.05, in which case both cells were assigned <i>b</i>_<i>0</i> = 0. Note that the North Central sub-region has no corresponding watershed and, therefore, was omitted (but see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124415#pone.0124415.s002" target="_blank">S2 File</a>).</p

Trends in Developed Land Cover Adjacent to Habitat for Threatened Salmon in Puget Sound, Washington, U.S.A.

<div><p>For widely distributed species at risk, such as Pacific salmon (<i>Oncorhynchus</i> spp.), habitat monitoring is both essential and challenging. Only recently have widespread monitoring programs been implemented for salmon habitat in the Pacific Northwest. Remote sensing data, such as Landsat images, are therefore a useful way to evaluate trends prior to the advent of species-specific habitat monitoring programs. We used annual (1986-2008) land cover maps created from Landsat images via automated algorithms (LandTrendr) to evaluate trends in developed (50-100% impervious) land cover in areas adjacent to five types of habitat utilized by Chinook salmon (<i>O</i>. <i>tshawytscha</i>) in the Puget Sound region of Washington State, U.S.A. For the region as a whole, we found significant increases in developed land cover adjacent to each of the habitat types evaluated (nearshore, estuary, mainstem channel, tributary channel, and floodplain), but the increases were small (<1% total increase from 1986 to 2008). For each habitat type, the increasing trend changed during the time series. In nearshore, mainstem, and floodplain areas, the rate of increase in developed land cover slowed in the latter portion of the time series, while the opposite occurred in estuary and tributary areas. Watersheds that were already highly developed in 1986 tended to have higher rates of development than initially less developed watersheds. Overall, our results suggest that developed land cover in areas adjacent to Puget Sound salmon habitat has increased only slightly since 1986 and that the rate of change has slowed near some key habitat types, although this has occurred within the context of a degraded baseline condition.</p></div

Percentage of Developed Land Cover in 1986: Watershed Scale.

<p>Percentage of developed land cover at the start of the time series in 1986, summarized at the watershed scale for six habitat areas. Format is identical to that in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124415#pone.0124415.g003" target="_blank">Fig 3</a>.</p

Percentage of Developed Cover in 1986 vs. Annual Change in Developed Land Cover (<i>b</i>_<i>2</i><i>– b</i>_<i>1</i>): Watershed Scale.

<p>The relationship between the percentage of developed land cover in 1986 and the difference in the annual rate of change in the percentage of developed cover before and after the breakpoint (<i>b</i>_<i>2</i><i>– b</i>_<i>1</i> in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124415#pone.0124415.e002" target="_blank">Eq 2</a>), for each of six habitat areas. Positive values on the <i>y</i>-axis indicate that the slope of the right-hand segment (latter part of the time series) exceeds the slope of the left-hand segment (earlier part of the time series); negative values indicate the opposite.</p

Developed Land Cover in 1986 and 2008: Puget Sound Scale.

<p>Developed land cover (as hectares or percent of total area) in 1986 and 2008, summarized at the Puget Sound scale for six habitat areas.</p><p>^a Calculated as the difference in developed cover (in ha) between 2008 and 1986, divided by the developed cover in 1986, and expressed as a percentage.</p><p>^b Calculated as the difference in developed cover (%) between 1986 and 2008.</p><p>Developed Land Cover in 1986 and 2008: Puget Sound Scale.</p