Multi-year data from satellite- and ground-based sensors show details and scale matter in assessing climate’s effects on wetland surface water, amphibians, and landscape conditions

Abstract

Long-term, interdisciplinary studies of relations between climate and ecological conditions on wetland-upland landscapes have been lacking, especially studies integrated across scales meaningful for adaptive resource management. We collected data in situ at individual wetlands, and via satellite for surrounding 4-km2 landscape blocks, to assess relations between annual weather dynamics, snow duration, phenology, wetland surface-water availability, amphibian presence and calling activity, greenness, and evapotranspiration in four U.S. conservation areas from 2008 to 2012. Amid recent decades of relatively warm growing seasons, 2012 and 2010 were the first and second warmest seasons, respectively, dating back to 1895. Accordingly, we observed the earliest starts of springtime biological activity during those two years. In all years, early-season amphibians first called soon after daily mean air temperatures were ≥ 0°C and snow had mostly melted. Similarly, satellite-based indicators suggested seasonal leaf-out happened soon after snowmelt and temperature thresholds for plant growth had occurred. Daily fluctuations in weather and water levels were related to amphibian calling activity, including decoupling the timing of the onset of calling at the start of season from the onset of calling events later in the season. Within-season variation in temperature and precipitation also was related to vegetation greenness and evapotranspiration, but more at monthly and seasonal scales. Wetland water levels were moderately to strongly associated with precipitation and early or intermittent wetland drying likely reduced amphibian reproduction success in some years, even though Pseudacris crucifer occupied sites at consistently high levels. Notably, satellite-based indicators of landscape water availability did not suggest such consequential, intra-seasonal variability in wetland surface-water availability. Our cross-disciplinary data show how temperature and precipitation interacted to affect key ecological relations and outcomes on our study landscapes. These results demonstrate the value of multi-year studies and the importance of scale for understanding actual climate-related effects in these areas.

Challenges in Complementing Data from Ground-Based Sensors with Satellite-Derived Products to Measure Ecological Changes in Relation to Climate—Lessons from Temperate Wetland-Upland Landscapes

“…Yet, these data are necessary for resource managers and other stakeholders to understand the nature of real changes, not those simply predicted by risk models [ 21 ], and to manage resources effectively and adaptively in the face of climate change. This lack of critical information motivated us to design and implement a study integrated across scales, sensors, and disciplines to assess recent relations among temperature, precipitation, wetland and upland water availability, and the statuses of amphibian populations in our study areas [ 27 ]. Our analysis of the first five years of data collection provided an opportunity to further evaluate our approach for executing the remote sensing component of the assessment.…”

“…Bottcher et al [ 114 ] found close correspondence between the beginning of photosynthetic activity (from in-situ CO 2 fluxes) and the timing of snowmelt as the ground in coniferous forest began to be exposed. Results by Sadinski et al [ 27 ] suggest it is difficult to ignore snow/snowmelt in studying land-surface phenology, as they found green-up to be closely aligned with the timing of snowmelt in years when snow melted later, but not in years when snow melted earlier. Ultimately, we need an improved method for addressing the influence of snow on our ability to detect the onset of green-up, as a good estimate for SOST is critical not only for studying changes in weather/climate conditions in relation to biological responses at the start of the growing season, but also because SOST is used in calculating additional phenological metrics, such as time-integrated NDVI and the length of the season [ 25 ].…”

“…Wetland sites were selected by positioning a rectangular grid of 25 ha cells across each study area, randomly selecting cells (10 from Tam, SC, and NTL and five from UMR), then surveying the selected cells from the ground to locate the first wetland in each cell that we confirmed was, or that appeared to be, an amphibian breeding site [ 27 ]. We deployed field sensors at individual wetlands beginning in 2008 (details provided in [ 27 ]). Acoustic recorders were installed as soon as thawing permitted and prior to when amphibians began calling to record amphibian calling hourly throughout each breeding season.…”

“…As described in Section 2.1 , we analyzed satellite-based variables at the scale of landscape blocks to assess their temporal relations with ground-based measurements of GDU and precipitation [ 27 ]. We chose 2 km × 2 km as the block size because it accommodated the approximate averages of published home ranges and maximum distances traveled for amphibian species that live in our study areas [ 43 , 44 , 45 , 46 ].…”

“…NDVI also has been linked with biodiversity in studies of trophic interactions [ 3 ]. We brought all these measurements into an integrated analysis of inter- and intraseasonal processes and characteristics across the study areas for the first five years of data collection, from 2008 to 2012 [ 27 ].…”