Gradient analysis of reversed treelines and grasslands of the Valles Caldera, New Mexico
Abstract:Objective: Treeless meadows and parks are widespread but poorly understood features of the montane vegetation of the western USA. These communities frequently form reversed treelines where grassy valleys occur below forested slopes above. Our purpose was to assess the environmental correlates of such treelines, as well as patterns in the composition and diversity of grasslands and forest margins in the Valles Caldera National Preserve.
Location: Valles Caldera National Preserve (35°50′-36°00′ N, 106°24′-106°37′ W, 2175-3150 m), Jemez Mountains, New Mexico, USA.
Methods: We conducted a gradient analysis based on 200 nested quadrats on transects crossing reversed treelines and spanning the compositional heterogeneity of grasslands. We used cluster analysis and non-metric multidimensional scaling to assess relationships between compositional variation and environmental variables.
Results: We found strong, highly significant relationships of the vegetation to gradients in slope inclination, soil texture, moisture, nutrient availability, and nighttime minimum temperatures. Reversed treelines are most strongly associated with shifts in the thermal regime, exhibit weaker relationships with soil texture and nutrient content, and show no relationship with gravimetric soil moisture. Gradients in aspect, soil moisture, and annual mean temperature are associated with compositional variation within grasslands and forest margins.
Conclusions: Lower nightly minimum temperatures and fewer consecutive frost-free days resulting from cold-air drainage may prevent tree seedling establishment in valley bottoms via photo-inhibition, tissue damage, or frost heaving. Fine-textured soils may also impede tree seedling establishment in valley bottoms. These findings lay the groundwork for experimental and physiological tests of these potential causes of these reversed treelines.
Document Type: Research Article
Publication date: 2007-02-01
More about this publication?
- The Journal of Vegetation Science publishes original articles, short notes and review articles in the field of vegetation science, both methodological and theoretical studies, and descriptive and experimental studies of plant communities and plant populations. The Journal is the Official Organ of the International Association for Vegetation Science (IAVS).
- Editorial Board
- Information for Authors
- Submit a Paper
- Subscribe to this Title
- Membership Information
- Terms & Conditions
- Ingenta Connect is not responsible for the content or availability of external websites