title: Contrasting spatial patterns in active-fire and fire-suppressed Mediterranean climate old-growth mixed conifer forests.
abstract: 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.
authors.affiliation: Department of Environmental Science, Policy, and Management, University of California, Berkeley, California, United States of America.
authors.forename: Danny L
authors.initials: DL
authors.lastname: Fry
authors.affiliation: Department of Environmental Science, Policy, and Management, University of California, Berkeley, California, United States of America.
authors.forename: Scott L
authors.initials: SL
authors.lastname: Stephens
authors.affiliation: USDA Forest Service, Pacific Southwest Research Station, Davis, California, United States of America ; University of California Center for Fire Research and Outreach, College of Natural Resources, Berkeley, California, United States of America.
authors.forename: Brandon M
authors.initials: BM
authors.lastname: Collins
authors.affiliation: USDA Forest Service, Pacific Southwest Research Station, Davis, California, United States of America.
authors.forename: Malcolm P
authors.initials: MP
authors.lastname: North
authors.affiliation: Departamento de Biología de la Conservación, Centro de Investigación Científica y de Educación Superior de Ensenada, Ensenada, Baja California, México.
authors.forename: Ernesto
authors.initials: E
authors.lastname: Franco-Vizcaíno
authors.affiliation: Natural Resources Management and Bioresource and Agricultural Engineering Departments, California Polytechnic State University, San Luis Obispo, California, United States of America.
authors.forename: Samantha J
authors.initials: SJ
authors.lastname: Gill
mesh_terms: D002140:California; D002980:Climate; D003710:Demography; D005390:Fires; D016468:Forestry / Q000379:methods*; D065928:Forests; D008800:Mexico; D011156:Population Density; D013045:Species Specificity; D064028:Tracheophyta / Q000254:growth & development*