The effects of a half century of warming and fire exclusion on montane forests of the Klamath Mountains, California, USA

These files are the raw data used in the manuscript "Effects of a
half century of warming and fire exclusion on montane forests of the
Klamath Mountains, California, USA" Manuscript authors: Erik S.
Jules, Melissa H. DeSiervo, Matthew J. Reilly, Drew S. Bost, and Ramona J.
Butz Climate warming and altered disturbance regimes are changing forest
composition and structure worldwide. Given that species often exhibit
individualistic responses to change, making predictions about the
cumulative effects of multiple stressors across environmental gradients is
challenging, especially in diverse communities. For example, warming
temperatures are predicted to drive species upslope, while fire
exclusion promotes expansion of species at lower elevations where fire was
historically frequent. We resampled 148 vegetation plots to assess
46-years (1969 to 2015) of species and community-level response to warming
and fire exclusion in a topographically complex landscape in the Klamath
Mountains, California (USA), a diverse region that served as a climate
refugia throughout the Holocene. We compared cover and assessed change in
the elevational distributions of 12 conifer species at different life
stages (i.e., seedlings, saplings, canopy). We observed consistent but
non-significant shifts upward in elevation for eight species, and a
significant shift upward for one species, all of which were far less than
expectations based on recent warming. Six species declined in total cover
and another five declined in at least one life stage, while the drought-
and fire-intolerant Abies concolor increased by 30.7%. The largest
declines were at lower elevations in drought-tolerant, early seral species
(Pinus lambertiana and Pinus ponderosa) and at higher elevations for the
shade-tolerant Abies magnifica var. shastensis and the regionally rare
Abies lasiocarpa. Regionally rare (Picea engelmannii) and endemic (Picea
breweriana) species had reductions in early life stages, portending future
declines. Multivariate analyses revealed a high degree of inertia with a
minor but significant shift in composition and a slight decrease in
species turnover along the elevation gradient driven by expansion of A.
concolor. Our results indicate that most species are declining, especially
at lower- and mid-elevations where fire exclusion increased cover of
shade-tolerant species and reduced recruitment for fire-adapted species.
Collectively, declines in most species, insufficient upward movement to
track warming, reductions in drought- and fire-tolerant early seral
species, and an increase in a single, shade-tolerant species will leave
these communities maladapted to projected climate scenarios and questions
the potential for future climate refugia in this region.