USFS Pacific Southwest Research Station

Davis, CA, United States

USFS Pacific Southwest Research Station

Davis, CA, United States
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Bigelow S.W.,USFS Pacific Southwest Research Station | Bigelow S.W.,Forest Adaptation Research | Papaik M.J.,USFS Pacific Southwest Research Station | Caum C.,São Paulo State University | And 2 more authors.
Climatic Change | Year: 2014

Large trees (>76 cm breast-height diameter) are vital components of Sierra Nevada/Cascades mixed-conifer ecosystems because of their fire resistance, ability to sequester large amounts of carbon, and role as preferred habitat for sensitive species such as the California spotted owl. To investigate the likely performance of large trees in a rapidly changing climate, we analyzed growth rings of five conifer species against 20th century climate trends from local weather stations. Over the local station period of record, there were no temporal trends in precipitation, but maximum temperatures increased by 0.10 to 0.13 °C/decade (summer and autumn), and minimum temperatures increased by 0.11 to 0.19 °C/decade in all seasons. All species responded positively to precipitation, but more variation was explained by a significant positive response to minimum winter temperatures. High maximum summer temperature adversely affected growth of two species, and maximum spring temperatures in the year prior to ring formation were negatively associated with growth of one species. The strong coherent response to increasing minimum temperatures bodes well for growth of large trees in Sierra/Cascades region mixed conifer forest under continued climatic warming, but these trees will still be under threat by the increased fire intensity that is a indirect effect of warming. © 2014 Springer Science+Business Media Dordrecht (outside the USA).

Van de Water K.,University of California at Davis | North M.,University of California at Davis | North M.,USFS Pacific Southwest Research Station
Forest Ecology and Management | Year: 2011

Fire plays an important role in shaping many Sierran coniferous forests, but longer fire return intervals and reductions in area burned have altered forest conditions. Productive, mesic riparian forests can accumulate high stem densities and fuel loads, making them susceptible to high-severity fire. Fuels treatments applied to upland forests, however, are often excluded from riparian areas due to concerns about degrading streamside and aquatic habitat and water quality. Objectives of this study were to compare stand structure, fuel loads, and potential fire behavior between adjacent riparian and upland forests under current and reconstructed active-fire regime conditions. Current fuel loads, tree diameters, heights, and height to live crown were measured in 36 paired riparian and upland plots. Historic estimates of these metrics were reconstructed using equations derived from fuel accumulation rates, current tree data, and increment cores. Fire behavior variables were modeled using Forest Vegetation Simulator Fire/Fuels Extension.Riparian forests were significantly more fire prone under current than reconstructed conditions, with greater basal area (BA) (means are 87 vs. 29m2/ha), stand density (635 vs. 208stems/ha), snag volume (37 vs. 2m3/ha), duff loads (69 vs. 3Mg/ha), total fuel loads (93 vs. 28Mg/ha), canopy bulk density (CBD) (0.12 vs. 0.04kg/m3), surface flame length (0.6 vs. 0.4m), crown flame length (0.9 vs. 0.4m), probability of torching (0.45 vs. 0.03), predicted mortality (31% vs. 17% BA), and lower torching (20 vs. 176km/h) and crowning indices (28 vs. 62km/h). Upland forests were also significantly more fire prone under current than reconstructed conditions, yet changes in fuels and potential fire behavior were not as large. Under current conditions, riparian forests were significantly more fire prone than upland forests, with greater stand density (635 vs. 401stems/ha), probability of torching (0.45 vs. 0.22), predicted mortality (31% vs. 16% BA), and lower quadratic mean diameter (46 vs. 55cm), canopy base height (6.7 vs. 9.4m), and frequency of fire tolerant species (13% vs. 36% BA). Reconstructed riparian and upland forests were not significantly different. Our reconstruction results suggest that historic fuels and forest structure may not have differed significantly between many riparian and upland forests, consistent with earlier research suggesting similar historic fire return intervals. Under current conditions, however, modeled severity is much greater in riparian forests, suggesting forest habitat and ecosystem function may be more severely impacted by wildfire than in upland forests. © 2011.

Earles J.M.,University of California at Davis | North M.P.,University of California at Davis | North M.P.,USFS Pacific Southwest Research Station | Hurteau M.D.,Pennsylvania State University
Ecological Applications | Year: 2014

Widespread fire suppression and thinning have altered the structure and composition of many forests in the western United States, making them more susceptible to the synergy of large-scale drought and fire events. We examine how these changes affect carbon storage and stability compared to historic fire-adapted conditions. We modeled carbon dynamics under possible drought and fire conditions over a 300-year simulation period in two mixed-conifer conditions common in the western United States: (1) pine-dominated with an active fire regime and (2) fir-dominated, fire suppressed forests. Fir-dominated stands, with higher live- and dead-wood density, had much lower carbon stability as drought and fire frequency increased compared to pine-dominated forest. Carbon instability resulted from species (i.e., fir's greater susceptibility to drought and fire) and stand (i.e., high density of smaller trees) conditions that develop in the absence of active management. Our modeling suggests restoring historic species composition and active fire regimes can significantly increase carbon stability in fire-suppressed, mixed-conifer forests. Long-term management of forest carbon should consider the relative resilience of stand structure and composition to possible increases in disturbance frequency and intensity under changing climate. © 2014 by the Ecological Society of America.

Timmer M.,San Jose State University | Timmer M.,USFS Pacific Southwest Research Station | Suddjian D.L.,801 Monterey Avenue | Lambrecht S.,San Jose State University | Bros-Seemann S.,San Jose State University
Western Birds | Year: 2011

Widespread decline of Yellow Warbler populations in California has led to increased interest in their conservation and management. However, because the species is now rare throughout much of its historic range in the state, there is relatively little demographic information about it. Predation and Brown-headed Cowbird parasitism are cited as causing declines, but their effects are poorly quantified. To address this information need, in 2008 we investigated the reproductive biology of the Yellow Warbler along the Pajaro River in Santa Cruz and Monterey counties, California, where the species is still relatively abundant. We examined predation and parasitism pressures by monitoring nests and recording reproductive success. In this heavily disturbed area, the Yellow Warblers nest success was very low (10%), revealing that one of the larger populations of this species remaining in the region may be threatened.

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