The vegetation and ecological gradients of calcareous mires in the South Park valley, Colorado

Abstract

The vegetation, environment, and ecological gradients present on three calcareous mires in the South Park valley, Park County, Colorado, were investigated. Vegetation was classified into four habitat classes, nine subclasses, and twelve species associations using two-way species indicator analysis (TWINSPAN). Detrended correspondence analysis (DCA) was used to ordinate vegetation samples along two axes representing the three predominant ecological gradients: water table height, miremargin to expanse, and region. Canonical correspondence analysis (CCA) was used to directly relate local environmental conditions to vegetation. Water table depth, microtopographical development, soil and water pH and nutrient level, soil organic matter, and hydraulic head were significantly correlated with vegetation gradients. The mire soils consist of intermixed areas of organic and mineral soils. Mire soils and water are highly alkaline and nutrient-rich. Mean pore water calcium concentration on these mires is 115 mg/L, electrical conductivity averages 575 µS, and mean pH is 7.4. Owing to these conditions, the fen floras include a number of highly minerophilic species. Based on water chemistry and species criteria, each site was classified as rich to extremely rich fen, with the two fen types mixing in complex patterns according to local environmental conditions. The species Trichophorum pumilum, Salix candida, Salix myrtillifolia, Carex microglochin, Carex viridula, Carex scirpoidea, Eriophorum gracile, Triglochin maritimum, Triglochin palustris, Kobresia myosuroides, Kobresia simpliciuscula, Thalictrum alpinum, Scorpidium scorpioides, Scorpidium turgescens, and Calliergon trifarium were determined to be indicative of extremely rich fen conditions in the southern Rocky Mountains.Key words: Colorado, canonical correspondence analysis, detrended correspondence analysis, extremely rich fen, gradient analysis, mire.