Treesearch

Information about the sensitivity of lodgepole pine to climate will allow forest managers to maximize growth, better understand how carbon sequestration changes over time, and better model and predict future ecosystem responses to climate change. We examined the effects of climatic variability during the 20th century on the growth of lodgepole pine along an elevation gradient in the North Cascades National Park, Washington. Multivariate analysis and correlation analysis were used to simplify growth patterns and identify climate-growth relations. Mid-elevation chronologies correlated...

Effects of canopy ozone (O3) exposure and signatures of genetic structure using isozyme markers associated with O3 tolerance were analyzed in ~20-, ~80-, and >200-yr-old ponderosa (Pinus ponderosa Dougl. ex Laws.) and Jeffrey pine (Pinus jeffreyi Grev. & Balf.) in Sequoia National Park, California. For both species, the number of alleles and genotypes per loci was higher in parental trees relative to saplings. In ponderosa pine, the heterozygosity value increased, and the fixation index indicated reduction of homozygosity with increasing tree age class. The opposite tendencies were...

The level II approach of the critical loads concept adopted by the UNECE aims at a flux based evaluation and takes into account environmental factors governing stomatal conductance. These factors will probably be affected by global change. The flux concept predicts that a decrease in stomatal conductance would protect trees from air pollution effects by decreasing uptake. However, experimental evidence is inconclusive. Numerous results suggest that pollutants and factors subject to global change (drought, CO2) may interact and even exacerbate effects, probably because antioxidative defense...

We tested the effect of daytime chronic moderate ozone (O3) exposure, short-term acute exposure, and both chronic and acute O3 exposure combined on nocturnal transpiration in California black oak and blue oak seedlings. Chronic O3 exposure (70 ppb for 8 h/day) was implemented in open-top chambers for either 1 month (California black oak) or 2 months (blue oak). Acute O3 exposure (~1 h in duration during the day, 120–220 ppb) was implemented in a novel gas exchange system that supplied and maintained known O3 concentrations to a leaf cuvette. When exposed to chronic daytime O3 exposure,...

We designed a new gas exchange system that concurrently measures foliar H2O, O3, and CO2 flux (HOC flux system) while delivering known O3 concentrations. Stomatal responses of three species were tested: snapbean, and seedlings of California black oak (deciduous broadleaf) and blue oak (evergreen broadleaf). Acute O3 exposure (120-250 ppb over an hour) was applied under moderate light and low vapor pressure deficits during near steady state conditions. The rate of stomatal closure was measured when the whole plant was placed in the dark. An adjacent leaf on each plant was also concurrently...

Fire is a part of the forest ecosystem, and its effects have been well documented in the scientific literature. But controversy remains about the effects of management options in a burned forest, and the scientific basis for decisionmaking about postfire management is uncertain and has not been effectively articulated. Management concerns after a fire include minimizing erosion and its effects on aquatic systems, retaining adequate forest structure for fire-associated wildlife, capturing the economic value of the wood through postfire timber harvests, minimizing the likelihood of an insect...

Climates are expected to warm considerably over the next century, resulting in expectations that plant populations will not be adapted to future climates.We estimated the risk of maladaptation of current populations of coastal Douglas-fir (Pseudotsuga menziesii var. menziesii) to future climates as the proportion of nonoverlap between two normal distributions where the means and genetic variances of current and future populations are determined from genecological models derived from seedling common garden studies. The risk of maladaptation was large for most traits when compared with the...

Soil thickness can be an important factor influencing vegetation, yet few spatially explicit studies have examined soil horizon thickness and vegetation composition in summer drought forests. We compared seismic and soil penetration measurements of combined A + C and Cr horizon thickness, soil moisture and temperature, and stand variables in a contiguous 4-ha mixed-conifer stand of the Sierra Nevada. Thickness of A + C and Cr horizons were highly variable but were not correlated to each other. Total basal area and canopy cover were positively related with A + C horizon thickness, and shrub...

Communities across the U.S. have been taking action to adapt to the wildfire risk they face. In a series of case studies conducted in 15 communities, researchers identified and described four elements that form the foundation for community wildfire preparedness: landscape, government, citizens, and community.

We simulated long-term forest management activities on 16,000-ha wildland-urban interface in the Blue Mountains near La Grande, Oregon. The study area is targeted for thinning and fuels treatments on both private and Federally managed lands to address forest health and sustainability concerns and reduce the risk of severe wildfire. We modeled number of benchmark management scenarios through time, and examined potential wildfire behavior, stand structure, species composition, and other forest characteristics over the study area. The simulation models indicated that substantial area would...