Dynamic disequilibrium: Recent widespread increases in vegetation cover on subarctic floodplains of Interior Alaska

• Published in: Ecosphere
• Main Authors: Frost, Gerald V., Roland, Carl A., Schmidt, Joshua H.
• Other Authors: National Park Service
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2023
• Subjects: Subarctic; Tundra; Alaska
• Online Access: http://dx.doi.org/10.1002/ecs2.4344; https://onlinelibrary.wiley.com/doi/pdf/10.1002/ecs2.4344; https://onlinelibrary.wiley.com/doi/full-xml/10.1002/ecs2.4344; https://esajournals.onlinelibrary.wiley.com/doi/pdf/10.1002/ecs2.4344

Abstract Boreal forest and tundra ecosystems are undergoing rapid climatic and environmental changes with consequences for ecosystem structure, function, and services. Although riparian zones occupy a small footprint within subarctic landscapes, they have disproportionately high value as foci of hydrological processes, biogeochemical cycling, ecological disturbance, biodiversity, and wildlife activity. Recent observations of increased winter discharge, reduced peak flows, and increased connectivity between catchments, streams, and groundwater in subarctic riparian zones have prompted predictions of altered riverine disturbance regimes, increased channelization, and a decline in the extent of active floodplains. However, few observational data exist concerning the spatiotemporal dynamics of subarctic floodplain vegetation, which can serve as a bioindicator to corroborate such predictions. We analyzed the distribution and extent of riparian ecotypes across a network of streams in 12 Interior Alaska watersheds using high‐resolution image pairs from circa 1981–2010. All stream reaches encompassed pronounced elevational gradients and included elevational forest–tundra ecotones. We classified riparian ecotypes using an image‐based point‐intercept sampling approach, calculated the probability of ecotype transitions, and evaluated relationships between ecotype transitions and environmental covariates. Our results reveal widespread increases in the stature, density, and extent of riparian vegetation spanning gradients of elevation, floodplain morphology, and climate. Ecotype transitions occurred at >20% of sample points, and there was a strong imbalance toward forward successional transitions (16.5%) versus backward transitions (4.0%). That is, we observed a strong tendency toward increasing cover, stature, and density of vegetation communities across our extensive sampling domain across our approximately 30‐year sample period. This relatively rapid riparian “greening” signal tended to be most pronounced in our ...