Insects and Pathogens in a Pollution-Stressed Forest

Pronos, J.; Merrill, Laura D.; Dahlsten, Donald L.

doi:10.1007/978-1-4612-1436-6_15

Cited by 13 publications

(4 citation statements)

References 18 publications

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“…Mortality was attributed to drought, bark beetle infestation, and air pollution. In the San Bernardino Mountains, stand‐thickening has led to increasing densities of snags related to infestations of bark beetles and pathogens ( Pronos et al , 1999 ). High subcanopy tree mortality in this range was ascribed to competition for light and soil moisture ( Mcbride & Laven, 1999).…”

Section: Discussionmentioning

confidence: 99%

Californian mixed‐conifer forests under unmanaged fire regimes in the Sierra San Pedro Mártir, Baja California, Mexico

Minnich

Barbour

Burk

et al. 2000

Journal of Biogeography

126

162

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Aim This study appraises historical fire regimes for Californian mixed‐conifer forests of the Sierra San Pedro Mártir (SSPM). The SSPM represents the last remaining mixed‐conifer forest along the Pacific coast still subject to uncontrolled, periodic ground fire. Location The SSPM is a north–south trending fault bound range, centred on 31°N latitude, 100 km SE of Ensenada, Baja California. Methods We surveyed forests for composition, population structure, and historical dynamics both spatially and temporally over the past 65 years using repeat aerial photographs and ground sampling. Fire perimeter history was reconstructed based on time‐series aerial photographs dating from 1942 to 1991 and interpretable back to 1925. A total of 256 1‐ha sites randomly selected from aerial photographs were examined along a chronosequence for density and cover of canopy trees, density of snags and downed logs, and cover of non‐conifer trees and shrubs. Twenty‐four stands were sampled on‐the‐ground by a point‐centred quarter method which yielded data on tree density, basal area, frequency, importance value, and shrub and herb cover. Results Forests experience moderately intense understory fires that range in size to 6400 ha, as well as numerous smaller, low intensity burns with low cumulative spatial extent. SSPM forests average 25–45% cover and 65–145 trees per ha. Sapling densities were two to three times that of overstory trees. Size‐age distributions of trees ≥ 4 cm dbh indicate multi‐age stands with steady‐state dynamics. Stands are similar to Californian mixed conifer forests prior to the imposition of fire suppression policy. Livestock grazing does not appear to be suppressing conifer regeneration. Main conclusions Our spatially‐based reconstruction shows the open forest structure in SSPM to be a product of infrequent, intense surface fires with fire rotation periods of 52 years, rather than frequent, low intensity fires at intervals of 4–20 years proposed from California fire‐scar dendrochronology (FSD) studies. Ground fires in SSPM were intense enough to kill pole‐size trees and a significant number of overstory trees. We attribute long fire intervals to the gradual build‐up of subcontinuous shrub cover, conifer recruitment and litter accumulation. Differences from photo interpretation and FSD estimates are due to assumptions made with respect to site‐based (point) sampling of fire, and nonfractal fire intensities along fire size frequency distributions. Fire return intervals determined by FSD give undue importance to local burns which collectively use up little fuel, cover little area, and have little demographic impact on forests.

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Section: Discussionmentioning

confidence: 99%

Californian mixed‐conifer forests under unmanaged fire regimes in the Sierra San Pedro Mártir, Baja California, Mexico

Minnich

Barbour

Burk

et al. 2000

Journal of Biogeography

126

162

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“…Also, several attributes associated with tree defence against beetle attack were compromised by oxidant exposure, including sapwood, phloem moisture content and phloem thickness (Pronos et al . ).…”

Section: Organismal Effects Cascade To Community and Ecological Procementioning

confidence: 97%

“…), shifting species dominance in the understorey (Temple ) and influencing insect and disease incidence (Pronos et al . ). Confounding factors such as drought and fire suppression add to the complexity of the San Bernardino Mountain story (Minnich et al .…”

Section: Case Studiesmentioning

confidence: 99%

Ozone effects on plants in natural ecosystems

2019

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Tropospheric ozone (O 3 ) is an important stressor in natural ecosystems, with welldocumented impacts on soils, biota and ecological processes. The effects of O 3 on individual plants and processes scale up through the ecosystem through effects on carbon, nutrient and hydrologic dynamics. Ozone effects on individual species and their associated microflora and fauna cascade through the ecosystem to the landscape level. Systematic injury surveys demonstrate that foliar injury occurs on sensitive species throughout the globe. However, deleterious impacts on plant carbon, water and nutrient balance can also occur without visible injury. Because sensitivity to O 3 may follow coarse physiognomic plant classes (in general, herbaceous crops are more sensitive than deciduous woody plants, grasses and conifers), the task still remains to use stomatal O 3 uptake to assess class and species' sensitivity. Investigations of the radial growth of mature trees, in combination with data from many controlled studies with seedlings, suggest that ambient O 3 reduces growth of mature trees in some locations. Models based on tree physiology and forest stand dynamics suggest that modest effects of O 3 on growth may accumulate over time, other stresses (prolonged drought, excess nitrogen deposition) may exacerbate the direct effects of O 3 on tree growth, and competitive interactions among species may be altered. Ozone exposure over decades may be altering the species composition of forests currently, and as fossil fuel combustion products generate more O 3 than deteriorates in the atmosphere, into the future as well.

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“…For example, Grulke and colleagues (1998) found that across an ozone-pollution and nitrogendeposition gradient, root biomass in trees at the least polluted sites were up to fourteen times greater than those at the most polluted sites. These changes can lead to substantial loss of vigor, which can increase a tree's susceptibility to other stresses, such as drought and insect infestations (e.g., bark beetle [Dendroctonus brevicomis]), cause abnormally high rates of tree mortality, and initiate changes in forest structure and function (Miller, Taylor, and Wilhour 1982;McLaughlin and Percy 1999;Pronos, Merrill, and Dahlsten 1999). Pollution stress can also reduce the genetic variability within populations by removing sensitive individuals; sensitive trees will ultimately become unable to compete with the less sensitive trees (Binkley, Droessler, and Miller 1992;Bytnerowicz and Grulke 1992).…”

Section: Indirect Effects Of Ozone-induced Damagementioning

confidence: 99%

Potential Impact of Ozone on Coniferous Forests of the Interior Southwestern United States

Diem

2003

Annals of the Association of American Geographers

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Despite the well-documented negative impacts of ozone on the health of coniferous forests in southern California and the significant growth experienced by southwestern cities over the past several decades, the ozone/forest dynamic in the interior portion of the southwestern United States has been largely ignored. Primarily through a review of literature pertaining to most aspects of ozone and its impact on forest health, this article provides insights on the ozone/forest dynamic within coniferous forests of the interior Southwest. It is suggested that ozone absorption in southwestern coniferous forests may equal that in southern California, owing to the long-distance transport of atmospheric pollutants into the interior Southwest and the presence of the North American monsoon. Nevertheless, research gaps identified in this article suggest a need for future research on ozone exposure levels and the ozone sensitivities of conifer species and varieties in southwestern coniferous forests.

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Insects and Pathogens in a Pollution-Stressed Forest

Cited by 13 publications

References 18 publications

Californian mixed‐conifer forests under unmanaged fire regimes in the Sierra San Pedro Mártir, Baja California, Mexico

Californian mixed‐conifer forests under unmanaged fire regimes in the Sierra San Pedro Mártir, Baja California, Mexico

Ozone effects on plants in natural ecosystems

Potential Impact of Ozone on Coniferous Forests of the Interior Southwestern United States

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