Data from: Lagged climate-driven range shifts at species’ leading, but not trailing, range edges revealed by multispecies seed addition experiment

Climate change is causing many species' ranges to shift upslope to
higher elevations as species track their climatic requirements. However,
many species have not shifted in pace with recent warming (i.e., ‘range
stasis’), possibly due to demographic lags or microclimatic buffering. The
‘lagged-response hypothesis’ posits that range stasis disguises an
underlying climatic sensitivity if range shifts lag the velocity of
climate change due to slow colonization (i.e., colonization credits) or
mortality (i.e., extinction debt). Alternatively, the ‘microclimatic
buffering hypothesis’ proposes that small-scale variation within the
landscape, such as canopy cover, creates patches of suitable habitat
within otherwise unsuitable macroclimates that create climate refugia and
buffer range contractions. We simultaneously test both hypotheses by
combining a large seed addition experiment of 25 plant species across
macro- and micro-scale climate gradients with herbaria records to compare
patterns of seedling recruitment relative to adult ranges and microclimate
in the North Cascades, USA. Despite high species-to- species variability
in recruitment, community-level patterns monitored for five years
supported the lagged response hypothesis, with a mismatch between where
seedlings recruit vs. adults occur. On average, the seedling recruitment
optimum shifted from the adult climatic range centre to historically
cooler, wetter regions and many species recruited beyond their cold (e.g.,
leading) range edge. Meanwhile, successful recruitment occurred at warm
and dry edges, despite recent climate change, suggesting that
macroclimatic effects on recruitment do not drive trailing range dynamics.
We did not detect evidence of microclimatic buffering due to canopy cover
in recruitment patterns. Combined, our results suggest apparent range
stasis in our system is a lagged response to climate change at the cool
ends of species ranges, with range expansions likely to occur slowly or in
a punctuated fashion.