Vegetation zonation along the slopes of a mountain, from low to high altitude, is a well-known pattern in landscape ecology. A similar picture is also described in the field of freshwater ecology. Rivers and streams show different types of habitats between upland and downland site locations. We studied both segmentations of altitudinal gradient in a subtropical hotspot of biodiversity, namely the mountainous rainforest of Yungas from Northwestern Argentina. We assessed the agreement between vegetation stratification (fog grasslands, cloud montane forest and low montane rainforest) and the tripartition of assemblages of mayflies (an ancient group of aquatic insects). The products we offer here accompany the paper of Biotropica entitled The inter-forest line could be the master key to track biocoenotic effects of climate change in a subtropical forest.

We established a pair of altitudinal cutoffs in each of the watersheds from Argentinean Yungas. They correspond to the upper and lower limits of the middle layer, and they were obtained through an optimization task. The objective function was to maximize the overlap between the extent of such a middle layer and the area classified as cloud montane forest. The upper limit approaches to the treeline, whereas the lower limit is expected to fit the inter-forest line. Interestingly enough, assemblages of aquatic insects can be ordinated along altitudinal transects, but the main distinction occurs at either side of the hypothetical inter-forest line rather than the treeline. This finding is consistent throughout the study area. Map of the three altitudinal floors, as well as the different watersheds, are available as raster files.       

A) Raster of layers (altitudinal tripartition) in the mountain cloud forests from Northwestern Argentina (Yungas). Map generated using the Compliance and Commonality index (C&C index).  The different strata are delimited by specific elevation lines at each hydrographic basin. They embrace to the largest possible extent the next vegetation formations, from highlands to lowlands: fog grasslands, montane forest and low montane rainforest. The treeline matches broadly the upper limit of the intermediate stratum, while the lower limit of such a stratum is tied to the inter-forest line.

B) Watersheds. Fundamental watersheds from Northwestern Argentina (Yungas). They were delimited using a high-resolution DEM of the study area, and fulfill the next eligibility criteria: C&C higher than 0.5, extent area larger than 5.36 km2 (i.e. > 100 raster cells), maximum altitude above the 1,500 m a.s.l. and with raster cells classified in either one of three vegetation formations of concern. On average, all fundamental watersheds are robust since the mean C&C index is 0.81 (more than 80% of the middle layer is occupied by montane forest and more than 80% of the montane forest falls within the middle layer).