CHESNEYA NUBIGENA ON A HIMALAYAN GLACIAL MORAINE: A CASE OF FACILITATION IN PRIMARY SUCCESSION?

Facilitation during plant succession is predicted to be an important mechanism in extreme environments whereby facilitating species moderate the micro-habitat and allow colonization by secondary species. This paper proposes two criteria for exploring facilitation. (1) Does the proposed facilitator modify the physical environment? (2) Does this modification enable colonization by later species? Failure to demonstrate either of these criteria is sufficient reason to reject the facilitation hypothesis. Criterion 1 can be addressed in a brief field season, and determines whether the more detailed physiologic and fitness studies of criterion 2 are warranted. These criteria can be used to allocate effort in extreme environments where research is difficult, and we apply them to evaluate possible facilitation by Chesneya nubigena on a glacial moraine in the Nepal Himalaya. This study demonstrates that Chesneya moderates the physical environment (criterion 1) by forming soil, increasing organic composition, and by raising soil temperatures, perhaps providing a micro-habitat suitable for colonization by grasses and forbs. Physiological and fitness benefits conferred on the secondary species (criterion 2) remain to be demonstrated.