Appendix A. A table depicting stand characteristics of modeled mixed-conifer conditions and a figure showing carbon carrying capacity for 24 scenarios examined.

A table depicting stand characteristics of modeled mixed-conifer conditions and a figure showing carbon carrying capacity for 24 scenarios examined

Contrasting Spatial Patterns in Active-Fire and Fire-Suppressed Mediterranean Climate Old-Growth Mixed Conifer Forests

<div><p>In Mediterranean environments in western North America, historic fire regimes in frequent-fire conifer forests are highly variable both temporally and spatially. This complexity influenced forest structure and spatial patterns, but some of this diversity has been lost due to anthropogenic disruption of ecosystem processes, including fire. Information from reference forest sites can help management efforts to restore forests conditions that may be more resilient to future changes in disturbance regimes and climate. In this study, we characterize tree spatial patterns using four-ha stem maps from four old-growth, Jeffrey pine-mixed conifer forests, two with active-fire regimes in northwestern Mexico and two that experienced fire exclusion in the southern Sierra Nevada. Most of the trees were in patches, averaging six to 11 trees per patch at 0.007 to 0.014 ha⁻¹, and occupied 27–46% of the study areas. Average canopy gap sizes (0.04 ha) covering 11–20% of the area were not significantly different among sites. The putative main effects of fire exclusion were higher densities of single trees in smaller size classes, larger proportion of trees (≥56%) in large patches (≥10 trees), and decreases in spatial complexity. While a homogenization of forest structure has been a typical result from fire exclusion, some similarities in patch, single tree, and gap attributes were maintained at these sites. These within-stand descriptions provide spatially relevant benchmarks from which to manage for structural heterogeneity in frequent-fire forest types.</p></div

Forest gap characteristics in old-growth Jeffrey pine-mixed conifer forests in California and northwestern Mexico, where summaries were calculated in two ways: all gaps within the four ha study area (with edge gaps), and excluding gaps where more than 10% of the gap area overlapped the 5 m perimeter buffer (without edge gaps).

<p>Forest gap characteristics in old-growth Jeffrey pine-mixed conifer forests in California and northwestern Mexico, where summaries were calculated in two ways: all gaps within the four ha study area (with edge gaps), and excluding gaps where more than 10% of the gap area overlapped the 5 m perimeter buffer (without edge gaps).</p

Study sites and live tree (diameters >5 cm) locations in old-growth Jeffrey pine-mixed conifer forests in the Sierra Nevada (upper shaded area), eastern California, and the southern Peninsular Range (lower shaded area), northwestern Mexico.

<p>Species identified as other include <i>Juniperus occidentalis</i>, <i>Abies magnifica</i>, <i>Populus tremuloides</i>, <i>Prunus emarginata</i>, <i>Quercus kelloggii</i>, and <i>Q. chrysolepis</i>.</p

Structural attributes of four old-growth Jeffrey pine-mixed conifer forests (patch values represent means (one standard error)).

<p>Within rows, means (one standard error) followed by same letters are not significantly different (<i>p</i>>0.05).</p

Mean (one standard deviation) fire return interval (FRI) summaries for old-growth Jeffrey pine-mixed-conifer forests in the Sierra Nevada, California, and northwestern Mexico.

<p>*Intervals calculated from fires that scarred three or more trees and at least 25% of the recording samples.</p

Proportion of 534 tree patches sorted by group number from four old-growth forest plots.

<p>A group represents a set of tree patches with similar forest characteristics interpreted using cluster analysis (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0088985#pone-0088985-g010" target="_blank">Figure 10</a>).</p

Proportion of trees within separate size classes in four old-growth Jeffrey pine-mixed conifer forest sites.

<p>Proportion of trees within separate size classes in four old-growth Jeffrey pine-mixed conifer forest sites.</p

Tree diameter distributions (10 cm size classes) by density for snags and live single (i.e., non-patch) trees in 4-ha stem mapped plots.

<p>Tree diameter distributions (10 cm size classes) by density for snags and live single (i.e., non-patch) trees in 4-ha stem mapped plots.</p

Forest patch and gap area distributions in four old-growth Jeffrey pine-mixed conifer forests.

<p>Areas were estimated from four ha stem maps. Not shown is the largest patch at Teakettle with an area of 2589 m².</p