High Arctic ecosystem states: Conceptual models of vegetation change to guide long-term monitoring and research

Abstract

Vegetation change has consequences for terrestrial ecosystem structure and functioning and may involve climate feedbacks. Hence, when monitoring ecosystem states and changes thereof, the vegetation is often a primary monitoring target. Here, we summarize current understanding of vegetation change in the High Arctic-the World's most rapidly warming region-in the context of ecosystem monitoring. To foster development of deployable monitoring strategies, we categorize different kinds of drivers (disturbances or stresses) of vegetation change either as pulse (i.e. drivers that occur as sudden and short events, though their effects may be long lasting) or press (i.e. drivers where change in conditions remains in place for a prolonged period, or slowly increases in pressure). To account for the great heterogeneity in vegetation responses to climate change and other drivers, we stress the need for increased use of ecosystem-specific conceptual models to guide monitoring and ecological studies in the Arctic. We discuss a conceptual model with three hypothesized alternative vegetation states characterized by mosses, herbaceous plants, and bare ground patches, respectively. We use moss-graminoid tundra of Svalbard as a case study to discuss the documented and potential impacts of different drivers on the possible transitions between those states. Our current understanding points to likely additive effects of herbivores and a warming climate, driving this ecosystem from a moss-dominated state with cool soils, shallow active layer and slow nutrient cycling to an ecosystem with warmer soil, deeper permafrost thaw, and faster nutrient cycling. Herbaceous-dominated vegetation and (patchy) bare ground would present two states in response to those drivers. Conceptual models are an operational tool to focus monitoring efforts towards management needs and identify the most pressing scientific questions. We promote greater use of conceptual models in conjunction with a state-andtransition framework in monitoring to ensure fit for purpose approaches. Defined expectations of the focal systems' responses to different drivers also facilitate linking local and regional monitoring efforts to international initiatives, such as the Circumpolar Biodiversity Monitoring Program.

The neglected season: Warmer autumns counteract harsher winters and promote population growth in Arctic reindeer

“…In addition to the short‐term gain of higher plant productivity, we anticipate two other positive warming effects. First, vegetation communities are predicted to change from moss‐dominated, to graminoid‐dominated swards, where the reduction in moss layer reinforces soil warming and mineralization, to further increase productivity (Ravolainen et al, 2020). This process is driven partly by positive feedback mechanisms from the greater density of reindeer (Van der Wal & Brooker, 2004).…”

Survey of the vascular plants of Alert (Ellesmere Island, Canada), a polar desert at the northern tip of the Americas

“…For example, from south to north, 85 species were found at Alexandra Fiord (Muc et al 1989), 40 in the central part of Ellesmere Island (Lévesque 1997), 75 at Sverdrup Pass (Bergeron andSvoboda 1989), 151 at Quttinirpaaq National Park (Parks Canada 1994), and 36 at Ward Hunt Island (Vincent et al 2011). Part of the variation among surveys likely reflects the size of the surveyed area, as well as environmental conditions and landscape heterogeneity (e.g., topography, hydrology, substrate, and microclimate; Ravolainen et al 2020;Taylor et al 2020).…”

“…These ecosystems are expected to be the most impacted by the ongoing climate change due to Arctic amplification, which refers to the greater climatic changes occurring near the North pole compared to the rest of the globe (Smith et al 2019). With the steep climate warming occurring over the last decades (Meehl et al 2007), Arctic regions have already experienced changes in vegetation composition, biomass, and diversity (Elmendorf et al 2012a(Elmendorf et al , 2012bRavolainen et al 2020). Therefore, establishing ecological baselines and updating past inventories are critical scientific endeavors to monitor, predict, and manage current and future impacts of climate change (Mihoub et al 2017).…”

Arctic terrestrial biodiversity status and trends: A synopsis of science supporting the CBMP State of Arctic Terrestrial Biodiversity Report

“…These include species diversity and composition, phenology, spatial structure, demographics, temporal cycles, health, and productivity and other ecosystem functions and processes. Presented within this issue are complementary approaches to vegetation monitoring, ranging from plotbased measures (Bjorkman et al 2020) to literature and database analyses (Wasowicz et al 2020), conceptual discussions (Ravolainen et al 2020), and pan-Arctic remote sensing derived data analyses (Jenkins et al 2020). Monitoring attributes describing productivity and phenology is Fig.…”