Data from: Effects of altitude, land use and microsites on the early-life performance of a high mountain tree: insights from an in situ sowing experiment.

Aim. Understanding the forces that drive range shifts in forest landscapes
is imperative for predicting species distributions under anthropogenic
climate and land use change. However, empirical studies exploring how
these components jointly influence critical early-life stages of mountain
tree species across environmental gradients are scarce. We used the
high-mountain tree Polylepis australis as model species to investigate the
relative importance of altitude and associated climatic conditions, land
use for livestock and microsite characteristics on early-life performance.
Location. Córdoba Sierras, central Argentina. Methods. We set up an
extensive in situ sowing experiment with a robust split-plot design that
integrated spatial scales ranging from 0.4 m2 subplots at the microsite
level (associated with vegetative and micro-topographic structures), to
livestock exclosure and enclosure plots of several hectares, to an
altitudinal gradient of 1000 m. Components of early-life performance were
monitored across two subsequent growing seasons. Results. Microsite
characteristics played a fundamental role in P. australis establishment,
whereby interactions with altitude and/or land use suggested alternate
mechanisms: facilitation (likely reduced desiccation) dominated at low
altitude while at high altitude abiotic stress (likely intensive frost and
radiation) overruled any microsite effects. At mid altitude benefits of
competition release prevailed over facilitation and microsite effects
gained importance under livestock presence. Inconsistencies between pre-
and post- emergence responses illustrated potential tradeoffs between
beneficial and detrimental effects of microsite conditions upon
performance throughout early life: a favorable location for seeds may
abruptly turn adverse for seedlings. Main conclusions. We unravel how
changes in altitude, anthropogenic disturbances and microsite
characteristics jointly modulate P. australis performance across stages of
early establishment. Such information is fundamental when categorizing
specific microhabitats as “safe sites” for tree regeneration especially in
mountain environments with high spatiotemporal heterogeneity.