The role of plant functional traits in shrub distribution around alpine frost hollows

Introduction/Aims Functional traits aid understanding of species distribution and community composition along environmental gradients. However, studies that detail trait measurements along fine-scale environmental gradients are lacking for many vulnerable ecosystems. In this paper, we quantify how plant traits might explain the composition of shrubs in one such vulnerable system – frost hollows. Location Bogong High Plains, Victoria, Australia. Methods We measured species composition and a suite of traits (shrub height, stem specific density, leaf area and SLA, xylem vessel area and density, and leaf bud traits) for shrub species in three, 10 m × 10 m quadrats located across transition from hilltops down into frost hollows. We used ordinal regression to model vegetation transitions by relating the changes in shrub species occurrence along frost hollow gradients to each trait, and across multiple traits. We also assessed intraspecific trait variations along gradients. Results Several traits explained the position of species along a gradient of cold air accumulation (slopes leading into frost hollows). The most important traits were maximum shrub height, leaf area and xylem traits, which were clearly related to species location on the slopes in single trait models. More complex relationships were revealed with multi-trait models, which indicated that shorter species, those with smaller leaves and larger buds for their leaf size, and those with lower vessel density were more likely to be found toward the bottom of the slope. Within species, taller individuals and those with denser stems were also more common up-slope. Conclusion Our results suggest a shift in ecological strategies in frost hollows: the advantages of being taller and having large leaves may be diminished in these stressful environments. Shrubs that are shorter and have smaller leaves may also be better at avoiding the risk of frost damage. Our study shows how the fine-scale turnover of shrub species composition around frost hollows relates to plant functional traits, and captures the allocation trade-offs between coping with environmental stress and being competitive within these plant communities.