Treesearch

Boreal forests and woodlands comprise about 29 percent of the world's forest cover. About 70 percent of this forest is in Eurasia, mostly in the Russian Federation. Boreal forests contain about 45 percent of the world's growing stock and are an increasingly important part of global timber production. Fire impacts large areas of boreal forest annually in Russia, and in excess of 60 percent of these fires are believed to be caused by human activity. Because of the large extent of boreal forest, the large amount of fire activity, and the expected sensitivity of carbon cycling in these systems...

Ozone measurements are presented from the Bulgarian Govedartsi ecosystem study site, Ovnarsko No. 3. The site is located on the south slope of the Govedartsi Valley in the northwestern part of the Rila Mountain area. The Rila is the highest mountain in the Balkan peninsula and is representative of rural conditions in that part of Europe. The experimental site, Ovnarsko, is situated at 1,600 m above sea level and about 10 km west of the village of Govedartsi. There are no anthropogenic sources for ozone precursors for at least 30 km in all directions. Ozone concentrations within the...

Indicators of ecosystem nitrogen (N) status are needed for monitoring and for identifying ecosystems that are at risk of becoming N saturated. The N chemistry of a number of plant, soil and hydrologic components were analyzed to assess the N status of mixed conifer forests across an N deposition gradient in the San Bernardino Mountains east of Los Angeles, California. All of the measured parameters at Camp Paivika on the western high-deposition end of the gradient indicated that the forest is N saturated, while forest stands on the eastern end of the gradient are N-limited. On the basis of...

Preliminary results of studies on nutrient fluxes in forests of the eastern Sierra Nevada were compared to those from more humid and polluted ecosystems. Snowmelt, soil solution, soil, and streamwater were collected from Jeffrey and lodgepole pine (Pinus jeffreyii [Grev. and Balf.] and Pinus contorta Dougl.) stands in Little Valley, Nevada, and from California red fir (Abies magnifica A. murr.) and Jeffrey pine/white fir (Pinus jeffreyii/Abies concolor [Gord and Glend.] Lindl.) stands at Sagehen, California. Snowmelt, soil solutions, and streamwaters from both sites were circumneutral and...

A variety of vascular plant species exhibit typical foliar injury symptoms when exposed to ambient ozone, making them useful as bioindicators of relative air quality for a particular location or region. They are quite useful in areas where mechanical ozone monitors are not available. Bioindicators are often introduced plant species known as sentinels. They are known to be sensitive to ozone and will respond rapidly if they are given special care to ensure ozone uptake and injury. Sentinels are usually genetically-uniform, rapid growing herbaceous annuals. Their rapid and well-characterized...

Mountains occupy only 3 percent of Poland. They are the northern part of the European arc of the Carpathian and Sudety Mountains, extending about 700 km along the southern Polish border. They are of medium height (about 1,500 m., maximum 2,600 m. a.s.l.), and diversified in terms of climate, geology, soils, vegetation, and anthropogenic impacts. The forest vegetation of the Sudety and Carpathian Mountains forms three elevational zones. Forests occur in the foothills (as high as 600 m. a.s.l.), the lower mountain forest zone (as high as 1,250 m. a.s.l.) and the upper montane forest zone (as...

Ozone injury was monitored on foliage of ponderosa (Pinus ponderosa Dougl. ex Laws.) and Jeffrey (Pinus jeffreyi Grev. & Balf.) pines at 11 locations in the Sierra Nevada and 1 site in the San Bernardino Mountains of southern California. Ozone injury on all age cohorts of needles on about 1,600 trees was surveyed annually from 1991 to 1994. A new method for describing ozone injury to whole tree crowns, the ozone injury index (OII), was field tested and improved. The OII ranged from 0 (no injury) to 100 (the maximum possible injury). The OII multi-year average was only 5 at Lassen Volcanic...

Plants react biochemically to ozone in three phases: with constitutive chemicals in the apoplastic fluid and cell membranes; by forming messenger molecules by the affected constitutive materials (ethylene); and by responding to the messenger molecules with pathogenic RNAs and proteins. For instance, plant reactions with ozone result in constitutive molecules such as the ozonolysis of ethylene in the gas spaces of the leaf, and the reaction with ascorbic acid in the apoplastic fluid. Formation of messenger molecules include the stimulation of ethylene production. Responses to the messenger...

The coastal sage scrub (CSS) vegetation of southern California has been declining in land area and in shrub density over the past 60 years or more, and is being replaced by Mediterranean annual grasses in many areas. Although much of this loss is attributable to agriculture, grazing, urbanization and frequent fire, even protected areas have experienced a loss in native shrub cover. Nitrogen (N) deposition has not previously been examined as a contributor to CSS decline, but up to 45 kg/ha/yr are deposited in the Los Angeles Air Basin. Several mechanisms were examined by which atmospheric N...

Urban air basin produced oxidants, notably ozone, induce a decline in productivity in plants. This loss of productivity is manifested by slower growth, hindered development, lower reproduction rates, impaired ability to resist disease, and other stresses. While many metabolic events have been linked to oxidant exposure, three major shifts have been well-studied: increased production and more rapid turnover of antioxidant systems; production of symptoms similar to a mechanical wounding of the tissue, especially ethylene production; and decline in photosynthesis. Although these processes may...