Linear forest patterns in subalpine environments

Studies of feedback between ecological pattern and process can benefit from the analysis of visually striking patterns, as they may reveal underlying processes and clarify the relative role of exogenous versus endogenous factors in driving vegetation change. Roughly linear forest patches are common in subalpine environments, including `hedges', `ribbon forest', and `Shimagare' or `wave regenerated forests' (waves). The influence of wind is common among these patterns, but the role of positive feedback, the most important component of self-organization in biological systems, varies. Hedges are orientated parallel to prevailing winds in several mid-latitude mountain ranges worldwide. Desiccation and ice-particle abrasion kills windward foliage while the vegetation shelters leeward seedlings and growth, so that the patches migrate slowly across the slope. Ribbon forest consists of strips orientated perpendicular to prevailing winds. They have been examined only in the US Rocky Mountains and are the least studied and understood of these phenomena. There are at least three distinct types of ribbon forest, which appear to develop in different ways. Waves are migrating strips of mortality and regeneration orientated perpendicular to prevailing winds in the USA, Japan and Argentina, and dominant controls vary by site. Hedges and waves can develop endogenously with a constant wind, and so can be considered self-organizing in the sense that feedback at the scale of individual trees creates a pattern across the scale of many trees without exogenous forcing. Most ribbon forests seem to be dominated by exogenous forces, but more work is needed to fully characterize the different types.