The response of boreal peatland community composition and NDVI to hydrologic change, warming, and elevated carbon dioxide

Abstract

Widespread changes in arctic and boreal Normalized Difference Vegetation Index (NDVI) values captured by satellite platforms indicate that northern ecosystems are experiencing rapid ecological change in response to climate warming. Increasing temperatures and altered hydrology are driving shifts in ecosystem biophysical properties that, observed by satellites, manifest as long‐term changes in regional NDVI. In an effort to examine the underlying ecological drivers of these changes, we used field‐scale remote sensing of NDVI to track peatland vegetation in experiments that manipulated hydrology, temperature, and carbon dioxide (CO2) levels. In addition to NDVI, we measured percent cover by species and leaf area index (LAI). We monitored two peatland types broadly representative of the boreal region. One site was a rich fen located near Fairbanks, Alaska, at the Alaska Peatland Experiment (APEX), and the second site was a nutrient‐poor bog located in Northern Minnesota within the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment. We found that NDVI decreased with long‐term reductions in soil moisture at the APEX site, coincident with a decrease in photosynthetic leaf area and the relative abundance of sedges. We observed increasing NDVI with elevated temperature at the SPRUCE site, associated with an increase in the relative abundance of shrubs and a decrease in forb cover. Warming treatments at the SPRUCE site also led to increases in the LAI of the shrub layer. We found no strong effects of elevated CO2 on community composition. Our findings support recent studies suggesting that changes in NDVI observed from satellite platforms may be the result of changes in community composition and ecosystem structure in response to climate warming.

Effects of climate warming on Sphagnum photosynthesis in peatlands depend on peat moisture and species‐specific anatomical traits

“…It rather corroborates the most recent model simulation and experiment of the peatland C sink with warming (Gallego-Sala et al, 2018;Laine et al, 2019). While our results are reassuring in showing that the natural peatland C sink may remain in future, none of the potential changes in vascular plant performance have been taken into account (Gavazov et al, 2018;McPartland et al, 2019;Rastogi et al, 2019). Vascular plants may differ from Sphagnum mosses in their sensitivity to rising temperatures and soil moisture Dieleman, Branfireun, McLaughlin, & Lindo, 2015;Mäkiranta et al, 2018;Rastogi et al, 2019), and exert powerful braking effects on potential benefits of climate warming on Sphagnum photosynthesis (Bragazza et al, 2016;Gavazov et al, 2018;Jassey et al, 2018).…”

Rapid loss of an ecosystem engineer: Sphagnum decline in an experimentally warmed bog

“…S. magellanicum in particular has a narrow niche breadth with respect to shade (Vitt & Slack, ). Measurements of leaf area index and normalized difference vegetation index (NDVI) documented increased shrub cover in warmer enclosures and effects of elevated CO 2 on NDVI only in the warmest enclosures (McPartland et al, ). Negative effects of elevated CO 2 on Sphagnum growth also were reported in a greenhouse study with peat monoliths (Heijmans, Klees, de Visser, & Berendse, ).…”

“…). Measurements of leaf area index and normalized difference vegetation index (NDVI) documented increased shrub cover in warmer enclosures and effects of elevated CO 2 on NDVI only in the warmest enclosures(McPartland et al, 2019). Negative effects of elevated CO 2…”

Decreased carbon accumulation feedback driven by climate‐induced drying of two southern boreal bogs over recent centuries

“…Yet, here we evidenced consistent climate-driven water level variations, dry shifts and subsequent changes in biological assemblages in two adjacent bogs under warmer conditions in the past. With prolonged warming and consequent peat surface drying, Sphagna communities may be even gradually replaced by shrubs (McPartland et al, 2019;Munir, Xu, Perkins, & Strack, 2014), which would have more profound impacts on peatland carbon uptake capacity (Loisel et al, 2014;Munir et al, 2014).…”

“…Peatlands play a key role in global biogeochemical cycling by fixing atmospheric CO 2 through plant photosynthesis and releasing CO 2 and CH 4 through decomposition. Peatland biological communities (plants and microbes) are strongly controlled by temperature and hydrology, which affect peatland carbon (C) sequestration and sink potential (Jassey et al, 2015;Laine et al, 2019;McPartland et al, 2019;Riutta et al, 2007). Bog plant communities dominated by Sphagna are sensitive to environmental change, especially during the growing season (Loisel, Gallego-Sala, & Yu, 2012), and plant functional type successions may even occur under climate change, which could impact peatland carbon sink capacity (Loisel et al, 2014).…”