Growth Increment Patterns in the Roots of Two Alpine Forbs Growing in the Center and at the Periphery of a Snowbank

Abstract

Snowbanks are characteristic for many alpine areas and add considerably to the great variability of growth conditions in high mountain systems. We studied the long-term (5- to 9-yr) growth response of two alpine forbs, Pedicularis recutita and Cirsium spinosissimum, to the environmental conditions in the center and at the periphery of a snowbank in the Swiss Alps. For that we analyzed the growth increments (annual rings) in the roots or rhizomes of the plants. While for both species there were no considerable size differences (number of shoots) between individuals growing in the center of the snowbank and those at the periphery, the growth patterns differed depending on species, temporal variations in growth conditions, and growth position. There were synchronous fluctuations in the width of the annual growth increments that were more pronounced in C. spinosissimum than in P. recutita and were restricted to plants growing in the center of the snowbank. These were apparently related to interannual variations in climatic conditions. In addition, C. spinosissimum plants growing at the periphery of the snowbank showed initially wide but strongly declining growth increments whereas plants growing in the center of the snowbank showed initially narrower but relatively stable growth increments. These patterns were only weakly reflected in P. recutita. Our results suggest that effects of climatic fluctuations on plant growth can be amplified in snowbanks and that there may be favorable growth conditions initially at the periphery of the snowbank that are compensated for in the center of the snowbank, in the long run, by continuously low-competition growth conditions.