DOI: 10.5061/dryad.906ft
title: Data from: Spatiotemporal fire dynamics in mixed-conifer and aspen forests in the San Juan Mountains of southwestern Colorado, USA

description: Mixed-severity fire regimes may be the most extensive yet poorly
 understood fire regimes of western North America. Understanding their
 long-term spatiotemporal dynamics is central to debates regarding altered
 fire regimes and the need for restoration in the context of changing
 climate and nearly a century of active fire suppression. However, the
 complexity of fire patterns and forest stand and landscape structures
 characteristic of mixed-severity regimes poses a substantial challenge to
 understanding their long-term dynamics. In this study, we develop analysis
 methods aimed at understanding the fire-driven forest dynamics of
 mixed-severity systems and apply them in the San Juan Mountains of
 southwestern Colorado. We sampled fire scars, stand structure, and
 &gt;4,300 tree ages across two 1,340-ha landscapes (Williams Creek and
 Squaretop Mountain) that span the environmental gradient of montane
 mixed-conifer and aspen forests. New approaches were applied to identify
 pulses of tree recruitment, evaluate climate and fire as potential drivers
 of synchronous recruitment pulses, and combine fire scar and recruitment
 data to reconstruct fires. The reconstructions provided detailed fire
 history for each stand, which in turn was used to develop a fire-severity
 metric, compare fire frequency and severity by forest type, and develop a
 simulation procedure to evaluate the degree to which tree regeneration
 depended on fire by species within each forest type. Twenty fires were
 reconstructed since 1685 at Williams Creek and 13 fires since 1748 at
 Squaretop Mountain. Patterns of fire severity varied within each fire and
 over successive events, including high-severity patches of 100s of ha in
 both study areas. Dry mixed-conifer forests experienced relatively short
 fire intervals (mean 21 years) and low fire severity, and regeneration of
 the main conifer species was largely dependent on open conditions
 sustained over successive fires. Moist mixed-conifer forests experienced
 longer fire intervals (mean 32 years) and a broader range of severities,
 and fire-caused canopy openings were important for initiating pulses of
 tree recruitment. Most (83%) aspen stands included two or more post-fire
 cohorts. The methods presented here can be adapted to other mixed-severity
 systems to better understand their long-term spatial and temporal dynamics
 and develop restoration priorities.
description: Tepley&Veblen2015_transect_dataForest stand- and age-structure-data were collected across two ca. 1,340-ha study areas (Squaretop Mountain and Williams Creek) located within the San Juan National Forest of southwestern Colorado as part of a study to evaluate historical fire regimes and fire-driven forest dynamics across the moisture gradient of mixed-conifer and aspen forest. Within the data file, a separate sheet is provided for each of the following datasets: (1) transect locations, (2) overstory (&gt; 15 cm dbh) species composition and size structure, (3) ages of overstory trees, (4) sapling (1.5–15.0 cm dbh) density, (5) the forest type for each transect, and (6) codes for species used in the other datasheets.