Eighteen years of ecological monitoring reveals multiple lines of evidence for tundra vegetation change

Abstract

The Arctic tundra is warming rapidly, yet the exact mechanisms linking warming and observed ecological changes are often unclear. Understanding mechanisms of change requires long‐term monitoring of multiple ecological parameters. Here, we present the findings of a collaboration between government scientists, local people, park rangers, and academic researchers that provide insights into changes in plant composition, phenology, and growth over 18 yr on Qikiqtaruk‐Herschel Island, Canada. Qikiqtaruk is an important focal research site located at the latitudinal tall shrub line in the western Arctic. This unique ecological monitoring program indicates the following findings: (1) nine days per decade advance of spring phenology, (2) a doubling of average plant canopy height per decade, but no directional change in shrub radial growth, and (3) a doubling of shrub and graminoid abundance and a decrease by one‐half in bare ground cover per decade. Ecological changes are concurrent with satellite‐observed greening and, when integrated, suggest that indirect warming from increased growing season length and active layer depths, rather than warming summer air temperatures alone, could be important drivers of the observed tundra vegetation change. Our results highlight the vital role that long‐term and multi‐parameter ecological monitoring plays in both the detection and attribution of global change.

Extensive land cover change across Arctic–Boreal Northwestern North America from disturbance and climate forcing

“…Consistent with these field observations, our results show that Qikiqtaruk‐Herschel Island experienced an increase in shrub cover of 9.67 km 2 (+59.5% relative to 1984) and reductions in sparse vegetation and barren land of 4.69 km 2 (−36.6% relative to 1984). These changes coincide with a 2.5–4°C increase in air temperature, earlier snow melt, and decreased frost frequency over the island (Myers‐Smith et al, ), suggesting that climate warming is the key driver behind shrub expansion. The spatial pattern of shrub expansion appears to follow the patterns of rivers or other hydrological channel, suggesting a role of changing hydrology in the proliferation of Arctic shrubs.…”

“…However, the shrub expansion we map here is borne out by in situ observations. For example, Figure shows land cover changes that we map on Qikiqtaruk‐Herschel Island, Yukon Territory, a small (136 km 2 ) island off the northern coast of Canada, along with a pair of photos collected across a 27 year time span (1987 and 2014) on the island (Myers‐Smith et al, ). These photos confirm pronounced increases in the height and cover of Salix richardsonii shrubs in locations that were previously dominated by herbaceous vegetation.…”

“…A detailed example of the impact of climate change on shrub cover in the high tundra at Qikiqtaruk‐Herschel Island, Yukon, Canada. (a) Land cover in 1984; (b) land cover in 2014, following substantial shrub growth; (c) the net change in land cover; (d) a field photo taken in 1987 showing primarily grass tundra; and (e) a field photo taken in 2014 showing substantial in situ increases in both height and coverage of Salix richardsonii shrubs (Myers‐Smith et al, ). Photographs provided by Myers‐Smith et al Inset indicates approximate area within the ABoVE Core Study Domain…”

Author responses to refaree feedback

“…Coastal erosion mobilises large amounts of sediment, organic matter, and nutrients from permafrost Overduin et al, 2014;Retamal et al, 2008;Wegner et al, 2015), which are released into the nearshore waters and affect marine ecosystems (Bell et al, 2016;Dunton et al, 2006;Fritz et al, 2017). Several studies have reported signs of accelerating coastal erosion rates at locations around the Arctic, including the western Arctic (Barnhart et al, 2014;Jones et al, 2008Jones et al, , 2009bMars and Houseknecht, 2007;Radosavljevic et al, 2016) and Siberia Kritsuk et al, 2014;Novikova et al, 2018;Ogorodov et al, 2016). However, the spatiotemporal resolution of circum-Arctic studies limits inferences of widespread changes in coastal erosion rates (Fritz et al, 2017).…”

“…The use of remote sensing to measure changes in permafrost landscapes is increasingly common (Novikova et al, 2018). However, optical image coverage in high-latitude regions has historically been widely limited to relatively coarse temporal and spatial resolutions, due to frequent cloud cover and logistical challenges that limit both satellite observations and aerial surveys .…”