Vegetation mosaics, patch dynamics and alternate stable states in an arctic intertidal marsh.

Soil degradation occurs following loss of vegetative cover at both the landscape and individual patch scale at La Pérouse Bay, Manitoba. At the landscape scale, soils from vegetated patches had a higher infiltration rate, and higher moisture, organic content and nitrogen content, but lower salinity and bulk density, than comparable values for exposed mineral soils. These differences in soil properties resulted in higher establishment success of the forage grass, Puccinellia phryganodes, in vegetated than in mineral soils. At the patch scale, similar to the landscape scale, soil conditions because more adverse for plant growth with increasing patch size (2.5 to 40 cm diameter) following experimental grubbing, resulting in a decrease in the re-colonization potential of Puccinellia. Localized vegetation removal by geese limits plant-soil interactions resulting in areas of intact intertidal salt marsh changing to an alternate state of exposed mud flats, where soil conditions offer little possibility of re-vegetation.