Effects of cryptogams on the microenvironment of vascular plants at the subalpine/alpine ecotone in the North Cascades, Washington

Background/Question/Methods

Recent global evidence of facilitation as a critical organizing force in alpine plant communities highlighted the need for a more comprehensive assessment of species interactions in these systems. Cryptogams (lichens and mosses) comprise a considerable portion of the alpine vegetative cover worldwide. Here we describe the potential for cryptogams to affect the physical and chemical setting of co-occurring vascular plants. We performed a series of cryptogam removal/addition experiments in the North Cascades as part of an effort to discern the effects of cryptogams on the growth of co-occurring plants. In removal and addition plots we monitored soil temperatures at the surface and 5 cm depth, soil moisture using time-domain reflectometry, plant-available nitrogen using ion-exchange resin probes, and leaf temperatures using fine-wire thermocouples. Results/Conclusions The treatments had considerable impacts on the near-surface soil temperature and moisture regime. The removal of two different lichen growth forms led to more pronounced diurnal temperature swings at the soil surface along with reduced soil moisture in the crustose lichen removal. Mean daily maximums were approximately 5 degrees Celsius higher in both lichen removals than controls. The addition of the crustose lichen dampened diurnal variability in surface soil temperatures, whereas the addition of moss had the opposite effect, primarily due to warmer daily maxima. Interestingly, in both the lichen and moss additions, leaf temperatures of focal individuals of Carex scirpoidea increased. Season-long N supply rates were unaffected one year post-treatment. Our results demonstrate the capacity for cryptogams to alter their associated microenvironment and hint at their potential for affecting co-occurring vascular plants.