Data from: Elevation and shade interact to affect survival and growth of native tree seedlings in an Andean forest restoration field experiment

Andean tropical montane forests are increasingly threatened by human
activities and global environmental change. Restoration efforts are
limited by insufficient understanding of the factors that influence native
seedling establishment during the early stages of restoring degraded
exotic pasturelands. Although elevation, light incidence, and competition
with exotic grasses have been pointed out as barriers to forest recovery
in tropical montane regions, the performance of native tree species in
grasslands—and their response to variation in these environmental
factors—varies greatly. Here, we conducted a field experiment to evaluate
the effects of shade cover and mowing on the initial survival and growth
of native tree species with contrasting elevational distributions across
the Andean region. We planted seedlings of five species in three degraded
pasture sites dominated by exotic grasses along a 900-m elevational
gradient, using a full-factorial design with shade cover and mowing
treatments replicated in eight blocks per site. Over 17 months, we
observed marked variation in survival and growth rates among species along
the elevational gradient. The effect of elevation on seedling survival was
closely linked to species’ elevational preferences: species with
low-elevation affinities experienced significant declines in survival at
higher elevations, whereas high-elevation species performed better at
higher sites. Increasing elevation also had a consistent negative effect
on growth rates across all species. These elevational patterns were driven
by underlying differences in temperature and solar radiation, two key
factors shaping seedling performance. Furthermore, survival depended on
the interaction between shade cover and elevation, with all species
exhibiting higher survival under shade at the highest elevations. In
contrast, responses to mowing and any interactions with elevation and
shade were species-specific and transient. Our experimental study
showed that restoration efforts should consider species-specific
elevational preferences, with shade substantially enhancing seedling
survival at high-elevation sites. In contrast, the widely adopted practice
of mowing to control non-native grass species in restoring Andean forests
may be beneficial only to certain species. Given the generally low
survival and slow growth rates observed at the highest elevations,
conservation efforts should prioritize adaptive protection of remnant
forests in these areas to complement restoration strategies.