Landscape metrics indicate differences in patterns and dominant controls of ribbon forests in the Rocky Mountains, USA

Question: Do landscape metrics reflect differences in dominant factors controlling ribbon forest patterns among sites? Location: West Flattop Mountain, Glacier National Park, Montana ( Flattop); Medicine Bow Mountains, Wyoming ( Medicine Bow); Park Range, Colorado ( Park Range). Methods: High-resolution aerial photography was used to delineate ribbon forest patches, and to calculate landscape metrics to distinguish between long, narrow, regular patterns expected from strong microtopographic control, and smaller, more compact, and variable patterns expected from wind-snowdrift interactions. Results: All but two metrics were significantly different (P<0.05) among the three sites. The rank and magnitude of differences indicated that ribbons at Flattop and Park Range are more similar to each other than to those at Medicine Bow. Flattop ribbons were also more elongated, narrower and less variable than those at Park Range, suggesting differences in the type and strength of structural control. Previous research showed that Flattop ribbons occupy regular lithologic ridges, while our observations of ribbons and analysis of geologic maps suggests weaker and less consistent microtopographic control at Park Range, and dominant wind-snowdrift interactions with little to no microtopographic influence at Medicine Bow. Conclusions: Landscape metrics indicate differences in pattern among sites that reflect differences in dominant factors influencing ribbon forest development and maintenance. Explanations of ribbon forest dynamics are site-specific and are more complex than is currently recognized. The sites vary in the level of endogenous versus exogenous control of ribbon patterns, and consequently in the sensitivity of this phenomenon to climate.