An ecological paradox: high species diversity and low position of the upper forest line in the Andean Depression

Abstract

Systematic investigations of the upper forest line (UFL) primarily concentrate on mid and high latitudes of the Northern Hemisphere, whereas studies of Neotropical UFLs are still fragmentary. This article outlines the extraordinary high tree diversity at the UFL within the Andean Depression and unravels the links between the comparatively low position of the local UFL, high tree-species diversity, and climate. On the basis of Gentry′s rapid inventory methodology for the tropics, vegetation sampling was conducted at 12 UFL sites, and local climate (temperature, wind, precipitation, and soil moisture) was investigated at six sites. Monotypic forests dominated by Polylepis were only found at the higher located margins of the Andean Depression while the lower situated core areas were characterized by a species-rich forest, which lacked the elsewhere dominant tree-species Polylepis. In total, a remarkably high tree-species number of 255 tree species of 40 different plant families was found. Beta-diversity was also high with more than two complete species turnovers. A non-linear relationship between the floristic similarity of the investigated study sites and elevation was detected. Temperatures at the investigated study sites clearly exceeded 5.5°C, the postulated threshold value for the upper tree growth limit in the tropics. Instead, quasi-permanent trade winds, high precipitation amounts, and high soil water contents affect the local position of the UFL in a negative way. Interestingly, most of the above-mentioned factors are also contributing to the high species richness. The result is a combination of a clearly marked upper forest line depression combined with an extraordinary forest line complexity, which was an almost unknown paradox.

RQGIS: Integrating R with QGIS for Statistical Geocomputing

“…This is most helpful in the presence of temporal and spatial autocorrelation (e.g, Iturritxa et al, 2015). Sometimes mixed-effect models may also account for autocorrelation since random intercepts allow for correlation within a group (e.g., Peters et al, 2014). Another way of dealing with spatial autocorrelation is e.g., to include auto-regressive correlation structures in a GLM or GAM within a Bayesian modeling approach (Zuur and Ieno, 2017).…”

Phylogenetic niche conservatism does not explain elevational patterns of species richness, phylodiversity and family age of tree assemblages in Andean rainforest

“…One likely driver is e.g. the high habitat heterogeneity along the studied gradient caused by a combination of complex topography and related climate and soil conditions (Homeier et al 2010;PeTers et al 2014; werner and Homeier 2015). At this time, we do not have the amount and type of data needed for a deeper understanding of species richness along the studied elevational gradient.…”

Soil Temperature and Soil Moisture Patterns in a Himalayan Alpine Treeline Ecotone

“…To date, only a few studies have investigated soil moisture (SM) and its effect on tree growth at high altitudes in more detail (Leuschner and Schulte, 1991;Gieger and Leuschner, 2004;Köhler et al, 2006;Liu and Luo, 2011;Öberg and Kullman, 2012;McNown and Sullivan, 2013;Paulsen and Körner, 2014;Peters et al, 2014). Thus, spatiotemporal distribution patterns of SM conditions in alpine treeline ecotones are insufficiently documented in literature (Müller et al, 2016).…”