Appendix A. Summary of topographic variables, derived canopy cover, and large tree density distributions.

Summary of topographic variables, derived canopy cover, and large tree density distributions

Stand characteristics.

<p>(a) Distribution of trees (> 5 cm DBH) in 5 cm diameter classes in the prescribed fire (FIRE), control (CTRL), mechanical thinning (THN) and mechanical thinning followed by prescribed fire (THN+FIRE) treatments at Blodgett Forest (3 replicates per treatment). Tree diameter distribution was measured the year before the treatment (PRE) in 2001, the first post-treatment year in 2003 (POST_1), and seven years post-treatment in 2009 (POST_7). Each class is labeled with the lower interval limit. (b) Difference in number of trees between 2001 and 2003 (POST_1) and 2003 and 2009 (POST_7) by diameter class.</p

Effects of treatments on soil CO₂ efflux and soil environmental conditions.

<p>Comparison of (a) soil CO₂ efflux, (b) soil temperature, and (c) soil water content (SWC) between fire (FIRE_Fs) and harvest (HARV) treatment sites and the control site (CTRL_Fs). Each symbol represents the average of the 20–29 plots measured in 2012 using the chamber technique. The harvest data is the average of values from units with and without soil ripping. Slope and r² of the linear regression are also shown.</p

CO₂ concentration.

<p>Concentration of CO₂ measured at 2, 8, 16 and 24 cm depths at the control (CTRL_Fs), prescribed fire (FIRE_Fs), and harvest (HARV) treatment sites in 2012.</p

Soil carbon pools.

<p>Soil carbon pools.</p

Seasonal trends of soil CO2 efflux, soil temperature and soil water content.

<p>(a) Soil CO₂ efflux, (b) soil temperature (10 cm depth), and (c) soil water content (8 cm depth) recorded during 2011–2012 from profiles installed at the control (CTRL_Fs), prescribed fire (FIRE_Fs), and tree harvest with (HARV_RIP) and without soil ripping (HARV_{NO_RIP}) sites. (d) Comparisons of soil CO₂ efflux at the control site (CTRL_Fs), and soil CO₂ efflux at the fire (FIRE_Fs) and harvest (HARV) sites modeled using climate data recorded at the control site.</p

Tree biomass carbon stocks, growth and productivity.

<p>Tree biomass carbon stocks, growth and productivity.</p

Study layout.

<p>Map of the Blodgett Forest. The control, mechanical thinning, prescribed fire, thinning followed by prescribed fire treatments each had three replicates. Soil CO₂ flux and soil carbon pools were measured in the clear-cut harvest treatment area and one of the replicates of the control and prescribed fire treatments. Timing of treatments (treat.) and measurements (meas.) during a period of 17 years, from 1995 to 2012, is also shown.</p

Soil tortuosity and diffusion.

<p>(a) Comparison of the empirically determined soil tortuosity factor at the control (CTRL_Fs), fire (FIRE_Fs), and tree harvest with (HARV_RIP) and without soil ripping (HARV_{NO_RIP}) treatment sites. Values predicted from the exponential Moldrup curve are included for comparison [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0150256#pone.0150256.ref035" target="_blank">35</a>]. (b) Seasonal trend of the diffusion coefficient at the treatment sites calculated from the specific relationship between tortuosity factor and soil water content ξ = 0.007e^4.094*^(1-swc) and the CO₂ diffusivity in free air, which was affected by soil temperature, atmospheric pressure, and soil water content monitored at each site.</p

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