A hypothesis to explain lichen-Rangifer dynamic relationships

Eldar Gaare

doi:10.7557/2.17.1.377

Abstract

A small group of fruticous lichen species, viz. Cetraria nivalis, Cladonia mitis, C. stellaris, and Stereocaulon paschale forms extensive mats in the most winter habitats of Rangifer tarandus populations in Norway. The plant communities accessible for grazing are often found on easily drained, moraine ridges. These lichen species are perennial, lying on the ground while growing slowly at the top. As they decompose they add humus to the top of the soil profile. The lichen mats catch all water from small showers, thus preventing vascular plants from obtaining a more regular water supply. Grazing removs whole plants and gradually makes larger and larger holes in the lichen mats. Wind and water erode the humus, with only coarse gravel remaining. This diminishes the soil water storage capacity. Without grazing, lichens will gradually build a humus layer, which would improve the soil water storage capacity. In time vascular plants then would take the place of the lichens. I propose the hypothesis that by (over-)grazing Rangifer improve their winter pastures by making conditions more favourable for lichens than for vascular plants.The fact that lichens are more scarce on habitats with more and regular precipitation, 1) in more oceanic climates, 2) on soils with more silt, and 3) on bird perches with thick peat due to regular fertilising, support this hypothesis.

Highlights

I n today'smanagementof Rangifer populations, semi-domestic and w i l d, the carrying capacity is often linked to the lichen resources (e.g. Gaare & Skogland, 1980) The objective is to balance the population's yearly intake of lichens and damage from trampling of the lichen mat to its annual regrowth
There most of the winter pastures seem to day to be severely overgrazed
The reindeer may survivewithoutlichens, as onSvalbard (Ekern & Kildemo, 1978; Brattbakk, 1985), but commonly lichens dominate on winter range

Summary

Introduction

I n today'smanagementof Rangifer populations , semi-domestic and w i l d , the carrying capacity is often linked to the lichen resources (e.g. Gaare & Skogland, 1980) The objective is to balance the population's yearly intake of lichens and damage from trampling of the lichen mat to its annual regrowth. I n today'smanagementof Rangifer populations , semi-domestic and w i l d , the carrying capacity is often linked to the lichen resources Gaare & Skogland, 1980) The objective is to balance the population's yearly intake of lichens and damage from trampling of the lichen mat to its annual regrowth. O n e year ofgrazingshould be followed b y 2-3 years of lichen regrowth This conservative management practice has not been the rule i n the Fennoscandian semi-domestic reindeer ranges. The reindeer may survivewithoutlichens , as onSvalbard (Ekern & Kildemo, 1978; Brattbakk, 1985), but commonly lichens dominate on winter range Throughout theirdistribution , Rangifer populations benefit from the species unique ability to digest lichens well

The Snøhetta case

Succession in reindeer winter pasture

Findings

Long term considerations