Environmental and Biotic Determinants of Growth and Height of Arctic Willow Shrubs along a Latitudinal Gradient

Ecological factors determining the growth of arctic shrubs remain poorly understood, thereby obscuring the current predictions about climate change effects. I conducted a study on the Yamal Peninsula, West Siberia, to find out which factors determine the growth and height of upright willows (Sali.-V glauca and S. lanata). I sampled willow thickets at different slope positions at 13 sites along a 300-km-long north-south transect. The measurements included the height of willow shrubs and the length and diameter of shoots. The length and diameter of willow shoots increased southwards and with increasing distance from the sea. At the top of the slope and in areas with shallow thaw, the height and growth of willow were low compared to other slope positions and to areas with deep thaw. An increasing level of reindeer (Rangifer tarandus) grazing intensity was associated with decreased height and growth of willow and also associated with reduced foraging activity of willow grouse (Lagopus lagopus). The results show that even though increasing summer warmth is likely to enhance willow growth, there are other factors such as distance from the sea that also affect the growth and height of willow. The results suggest that reindeer grazing may locally counteract the effects of climate change.