Climate change is particularly apparent in many mountainous regions, with warming
rates of more than twice the global average being reported for the European Alps. As
a result, the probability of climate extremes has increased and is expected to rise further.
In an earlier study, we looked into immediate impacts of experimentally imposed heat
waves in alpine grassland, and found that these systems were able to cope with heat
as long as enough water was available. However, concomitant drought led to increased
stress, and reduced aboveground biomass production and green plant cover. Here, we
studied the legacy effects (lag-effects) of the imposed climate extreme to see whether
delayed responses occurred and how fast the alpine grassland could rebound from
the initial changes. Green cover continued to be suppressed the two following years in
communities that had been exposed to themost intense hot drought, while aboveground
biomass production had returned to control levels by year 2. The initial lower resistance
of the forb fraction in the communities was not compensated by faster recovery later
on. This resulted in alpine communities that became (and remained) relatively enriched
with graminoids, which resisted the original extreme better. The responses of alpine
grassland to heat extremes with or without drought observed in this study resemble those
typically found in lowland grassland in the short term. However, alpine grassland exhibited
longer legacy effects from an annual perspective, with delayed recovery of aboveground
production and persistent changes in community composition. This suggests that once
initial resistance thresholds are exceeded, impacts may be longer-lasting in alpine
grassland, where recovery is constrained by both the short growing season and difficult
seedling establishment.