Vegetation responses to 26 years of warming at Latnjajaure Field Station, northern Sweden

Abstract

Climate change is rapidly warming high latitude and high elevation regions influencing plant community composition. Changes in vegetation composition have motivated the coordination of ecological monitoring networks across the Arctic, including the International Tundra Experiment (ITEX). We have established a long-term passive warming experiment using open-top chambers, which includes five distinct plant communities (Dry Heath; Tussock Tundra; and Dry, Mesic, and Wet Meadow). We have measured changes in plant community composition based on relative abundance differences over 26 years. In addition, relative abundance changes in response to fertilization and warming treatments were analysed based on a 7-year Community-Level Interaction Program (CLIP) experiment. The communities had distinct soil moisture conditions, leading to community specific responses of the plant growth forms (deciduous shrubs, evergreen shrubs, forbs and graminoids). Warming significantly affected growth forms, but the direction of the response was not consistent across the communities. Evidence of shrub expansion was found in nearly all communities, with soil moisture determining whether it was driven by deciduous or evergreen shrubs. Graminoids increased in relative abundance in the Dry Meadow due to warming. Growth form responses to warming are likely mediated by edaphic characteristics of the communities and their interactions with climate.

Nitrogen restricts future sub-arctic treeline advance in an individual-based dynamic vegetation model

“…Higher summer soil moisture in the wetter climate scenarios shifted the ratio of summergreen to evergreen shrubs in favour of the summergreen shrubs, in line with observations (Elmendorf et al, 2012). Conversely, drier scenarios yielded an increased abundance of evergreen shrubs, similar to what has been observed in drier parts of the tundra heath in the Abisko region (Scharn et al, 2021). Within RCP8.5, the warmest (MIROC-ESM-CHEM-RCP8.5) and coldest (GFDL-ESM2M-RCP8.5) scenarios gave rise to very similar treeline positions at the end of the projection period (2090-2100).…”

Nitrogen restricts future treeline advance in the sub-arctic

“…Higher summer soil moisture in the more precipitation rich climate scenarios shifted the ratio of summergreen to evergreen shrubs in favour of the summergreen shrubs, in line with observations (Elmendorf et al, 2012). Conversely, drier scenarios yielded an increased abundance of evergreen shrubs, similar to what has been observed in drier parts of the tundra heath in the Abisko region (Scharn et al, 2021). Within RCP8.5, the warmest (MIROC-ESM-CHEM-RCP8.5) and coldest (GFDL-ESM2M-RCP8.5) scenario gave rise to very similar treeline positions at the end of the projection period (2090-2100).…”

Limited decadal growth of mountain birch saplings has minor impact on surrounding tundra vegetation

“…The limited birch sapling growth we observe was restricted to growth in stem width but not height. Air temperatures have increased in the Abisko area over the last century (Callaghan et al, 2013 ), but in Latnjajaure, the increase has not been as strong during the last decade as during the 1990s and early 2000s (Björk et al, 2007 ; Scharn, Brachmann, et al, 2021 ). Furthermore, the wind is causing local variation in physiognomy seen in the world's treelines (Richardson & Friedland, 2009 ).…”

“…The mean annual temperature at Latnjajaure Field Station ranges from −2.9°C to −0.5°C (1993–2016) and has increased at a rate of 0.4°C [CI = 0.2–0.7°C] per decade from 1993 to 2016 (Scharn, Brachmann, et al, 2021 ). The mean annual precipitation is 847 mm, with a range of 605 and 1091 mm (1990–2015; Scharn, Brachmann, et al, 2021 ). There is no in‐site climate data for the forest, but at the nearby Abisko meteorological station (385 m a.s.l.…”