FRAM FORUM 2015
IN BRIEF
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Browning in a crowberry heath in Storfjord, Troms County. Photo: Jarle W. Bjerke
the worst affected areas, which were under multiple stressors. Every season during the 2011–2012 hydrological cycle (starting in October 2011) included at least one extreme weather event. Autumn was unusually warm and this slowed down cold hardening in plants. The turn from autumn to winter was associated with the storm “Dagmar”, one of the strongest storms Norway has seen in the last 30 years. Midwinter was extreme in the unusual combination of shallow snow depths and extreme fluctuations in temperature, from record low to unusually warm over short time periods, preceded and followed by numerous freeze-thaw cycles. The shallow snow depth led to exposure of many plants that under normal snow conditions would be covered by snow and thus sheltered from ambient temperature extremes and solar radiation (February–April). May to July was anomalously cool, delaying snowmelt and spring leafing. At summer solstice, the snow cover was more than double the norm. In mid-summer, some extreme minimum temperatures were measured related to five frost events. The lowest temperature recorded was −8.5°C in late June (extracted from MODIS LST satellite data). The summer also had periods of extreme rainfall causing flooding, and heavy storms causing
salt spray on coastal vegetation. Snowfall and low temperatures in the high mountains during the entire growing season decreased the productivity there. Furthermore, during the peak growing season, outbreaks of leaf-attacking insects caused major defoliation of trees and shrubs, and rust fungi caused premature autumn yellowing of willow trees. All these events and outbreaks led to decreased plant vitality, as measured in the field, and reduced vegetation greenness, as measured by satellites. The various events affected different plant types. While evergreen plants like crowberry and juniper are most vulnerable to winter desiccation, frost events in summer mostly damage thin-leaved herbs and forbs. This effect was most striking in dense stands of tall ferns. Pest outbreaks mostly damage deciduous trees such as birch and various species of willow, but in the areas with the highest densities of moth caterpillars, forest floor vegetation also becomes defoliated. Re-surveys of sites with damaged evergreen plants in 2014 show that damage is still visible as non-vegetated areas with lots of dead, greyish plant remains.