Stand structure and vegetation dynamics of a subalpine wooded fen in Rocky Mountain National Park, Colorado

Abstract

Abstract. The tree population size structure and relationship between tree diameter and age were examined in a subalpine fen and surrounding Picea‐Abies forest in northern Colorado. The fen grades from a sedge fen, through an ecotone, to a treed fen. Tree growth rate varies across the vegetational gradient, with the sedge fen having the slowest growth, and the upland forest having the fastest growth. Differences in growth rate are related to the average size of peat hummocks, with areas containing tall hummocks exhibiting the highest tree growth rates. Size structures display the characteristic reverse‐J distribution generally indicative of stable populations, but forest vegetation is expanding into the open regions of the fen, and within the treed fen an increase in Abies lasiocarpa is occurring. These changes are primarily attributed to a positive feedback situation wherein the fen's surface is built up by peat accumulation. Distinct hummocks form first on the open fen but then coalesce to form raised peat islands in the treed fen. This new substrate provides habitat with a comparatively low water table and allows the growth of mesophytic forest vegetation. A pathway for this vegetational development is proposed.

Relationships between vegetation type, peat hydraulic conductivity, and water table dynamics in mountain fens

“…The abundance of each plant species is listed in Table as dominant, subdominant, or occasional based on canopy cover. Detailed data and regional characteristics of the fens are published in Cooper (), Johnson (), and Chimner and Cooper (). Plant species nomenclature follows Weber and Wittmann ().…”

Influence of Bedrock Geology on Water Chemistry of Slope Wetlands and Headwater Streams in the Southern Rocky Mountains

“…Nutt.) (<50% overstory canopy cover) typical of Rocky Mountain forested wetlands (Johnson 1996(Johnson , 1997Lemly 2007).…”

Historical range of variation assessment for wetland and riparian ecosystems, U.S. Forest Service Rocky Mountain Region

“…In contrast to boreal regions, ericaceous shrubs are often a minor component of vegetation in Region 2 peatlands. Forested fens ("treed fens") are also widely distributed in subalpine environments, although these appear to be less common than in boreal regions (Johnson 1996(Johnson , 1997. The most common overstory dominants in treed fens are Picea engelmannii, P. glauca and Pinus contorta, which have genotypes that can tolerate the saturated conditions found in fens.…”

“…Vegetation patterns in fens often exhibit distinct zonation patterns. Complex gradients broadly structure vegetation patterns in relation to the morphology and hydrology of the wetland (Cooper 1996;Cooper and Andrus 1994;Johnson 1997). The patterns of vegetation structure, as well as the relative importance of environmental processes on vegetation, vary depending on the scale evaluated (Hajkova and others 2004).…”