Unexpected mechanisms sustain the stress gradient hypothesis in a tropical alpine environment
Article first published online: 9 AUG 2011
© 2011 International Association for Vegetation Science
Journal of Vegetation Science
Volume 23, Issue 1, pages 62–72, February 2012
How to Cite
Anthelme, F., Buendia, B., Mazoyer, C., Dangles, O. (2012), Unexpected mechanisms sustain the stress gradient hypothesis in a tropical alpine environment. Journal of Vegetation Science, 23: 62–72. doi: 10.1111/j.1654-1103.2011.01333.x
- Issue published online: 9 JAN 2012
- Article first published online: 9 AUG 2011
- Manuscript Accepted: 15 JUL 2011
- Manuscript Received: 1 FEB 2011
- Azorella aretioides;
- Biogenic habitat;
- Species-specific effects.
Does facilitation among plants increase with elevation in a humid tropical alpine system in which climatic and ecological conditions differ from other alpine environments? What mechanisms are involved in the interactions?
Volcano Antisana, Eastern Cordillera of the Ecuadorian Andes (00°28′S, 78°09′W).
We selected the cushion-forming Azorella aretioides as a potential nurse plant along an altitudinal gradient (4400, 4550 and 4700 m) in the high tropical Andes. We quantified its effects on other plants at species and community levels by comparing the product vegetation cover × number of individuals of every vascular species found inside and outside 265 cushions, using the relative interaction index. We inferred potential mechanisms behind the interactions through analysis of microclimate, soil moisture and soil nutrient measurements inside and outside cushions.
Predictions of the stress gradient hypothesis (SGH) were corroborated at community level, with transition from competitive or neutral effects of A. aretioides at 4400 and 4550 m to facilitative effects at 4700 m. Strong species-specific effects were observed along the altitudinal gradient, with a substantial effect of local habitat disturbance on the outcome of plant–plant interactions. Surprisingly, cushions lowered air and soil temperatures and air humidity, which reduced at higher elevations. Facilitation appeared to be caused by higher soil moisture and nutrient content beneath cushions.
Our data extend the framework of the SGH by corroborating it for the first time in a tropical alpine system. However, the mechanisms underlying plant–plant interactions differed from those generally reported from alpine environments, with facilitation varying according to resource-mediated stress (nutrients). It remains to be tested whether this is specific to tropical alpine systems.