Structure of cliff vegetation on exposed cliffs and the effect of rock climbing

Abstract

Vegetational structure of exposed dolomitic cliffs in the driftless region of northwest Illinois was quantified from 186 quadrats on five cliffs. All cliffs were sparsely vegetated, with a total of 41 species (14 lichen and 27 vascular) recorded in the upper 6 m. On all cliffs, cover averaged 16.03%, with lichen contributing 10.23% cover and vascular vegetation 5.80% cover. Seventy percent of all vegetation grew within 3 m of the cliff top. Linear regression indicated that both cover and density of vascular, but not lichen, flora increased with increased fracturing and decreased with distance from the cliff top. TWINSPAN arranged the quadrats into five groups that differed in lichen and vascular cover and a sixth group that consisted of bare rock. Spatial distribution of the community groups occurred at a small scale, influenced by small scale differences in rock fracturing, slope, weathering, and likely moisture availability. Climbing significantly reduced lichen cover and lichen species density by 50%, from 13.7% cover and 2.4 species/0.25 m2 on unclimbed cliffs, to 6.7% cover and 1.2 species/0.25 m2 on climbed cliffs. Climbing did not have an apparent effect on vascular vegetation, which ranged from 2.74 to 10.62% cover on individual cliffs. Total plant cover averaged 19.7% on three unclimbed cliffs and 12.3% on two climbed cliffs, because of the impact on lichen cover. Although climbed cliffs had lower lichen cover, distribution of TWINSPAN-defined community groups was similar on both climbed and unclimbed cliffs, indicating that environmental and physical variables were the primary determinants of cliff flora on these vertical exposed cliffs. Keywords: cliff, vegetation, lichen, rock climbing, rock fractures.