Treesearch

Since wildland fires occur in living vegetation, the fuel moisture content must be considered in order to correctly predict the behavior of the fire. One facet of combustion of pyrolysis gases that has not been considered in previous research is the effect of moisture on the combustion process. This effect is investigated by using CHEMKIN software to study an opposed diffusion flame model for three pyrolysis fuels relevant to wildfires. The effect of moisture on flame structure is investigated by varying the mole fraction of water vapor in the fuels, with air as oxidizer. In all cases, the...

Elevated concentrations of atmospheric CO2 and tropospheric O3 will profoundly influence future forest productivity, but our understanding of these influences over the long-term is poor. Leaves are key indicators of productivity and we measured the mass, area, and nitrogen concentration of leaves collected in litter traps from 2002 to 2008 in three young northern temperate forest communities exposed to elevated CO2 and/or elevated O3 since 1998. On average, the overall effect of elevated CO2 (+CO2 and +CO2+O3 versus ambient and +O3) was to increase leaf mass by 36% whereas the overall...

Recent findings, policy, regulation, and management relating to tree disease caused by Phytophthora species in wildlands and nurseries of North and South America are reviewed. These include the isolation of Phytophthora alni uniformis Brasier & S.A.Kirk in Alaska, and detection of population shifts in NA1, NA2 and EU1 clonal lineages of Phytophthora ramorum Werres, de Cock, & In’t Veld. The dissemination of Phytophthora ramorum from infested nurseries in water run-off presents a challenge for forest and plantation management. In the United States, forest Phytophthoras are viewed as a...

To evaluate the number of stream sample sites needed to effectively survey a given stream network for species of Phytophthora, two stream networks, Davidson River and Cathey's Creek, in western North Carolina (USA) were studied. One-litre water samples were collected from the terminal drainage points and most of the tributaries in each stream network and filtered through polycarbonate membrane filters with 3-µm pores. Ten taxa of Phytophthora were detected in the two stream networks: six species—P. cinnamomi, P. citricola, P. citrophthora, P. gonapodyides, P. heveae, and P. pseudosyringae—a...

Umbellularia californica is one of the key infectious hosts of the exotic Phytophthora ramorum, which causes sudden oak death (SOD) in California and Oregon forests. This study provides a comprehensive analysis of the epidemiologically relevant parameters for SOD in California and southern Oregon, including potential differences between the two states. Experimental infection of U. californica leaves was optimal when leaves were wet for 6–12 h, temperature was approximately 19°C and pathogen concentration was approximately 2+74 zoospores mL-1. Seasonal variation in host susceptibility and...

We measured the dynamics of both biomass and nutrient pools on 7-, 17-, 31- and 51-year-old Pinus massoniana plantations in southern China. Using a chronosequence approach, we found that biomass of each component increased with aging while its proportion decreased except stem-wood. Nutrient pools varied with biomass pools except for foliage. For all harvest intensities (stem only, stem and branches, and aboveground), increasing the rotation length from 31 yrs to 51 yrs increased the biomass collection by ≥7.1% and reduced the nutrient export for K, Ca and Mg by ≤6.3% during 155 years,...

We compared the distribution and frequency of American marten (Martes americana) detections during historic surveys and a recent survey on the Sagehen Experimental Forest (SEF) in the Sierra Nevada Mountains, California. This area has been the location of 9 previous marten surveys during 1980–1993, each involving a systematic detection/non-detection survey on the same grid. These data are a time series of information on the occupancy of martens that can be related to habitat change in the study area. Our objectives were to 1) resurvey martens in SEF using methodology similar to previous...

Novel genotypes often arise during biological invasions, but their role in invasion success has rarely been elucidated. Here we examined the population genetics and behavior of the fungus, Leptographium procerum, vectored by a highly invasive bark beetle, Dendroctonus valens, to determine whether genetic changes in the fungus contributed to the invasive success of the beetle–fungal complex in China. The fungus was introduced by the beetle from the United States to China, where we identified several novel genotypes using microsatellite markers. These novel genotypes were more pathogenic to...

Using data from a water-balance instrument cluster with spatially distributed sensors we determined the magnitude and within-catchment variability of components of the catchment-scale water balance, focusing on the relationship of seasonal evapotranspiration to changes in snowpack and soil moisture storage. Co-located, continuous snow depth and soil moisture measurements were deployed in a rain–snow transition catchment in the mixed-conifer forest in the Southern Sierra Nevada. At each elevation sensors were placed in the open, under the canopy, and at the drip edge on both north- and...

Many aspects of forest hydrology have been based on accurate but not necessarily spatially representative measurements, reflecting the measurement capabilities that were traditionally available. Two developments are bringing about fundamental changes in sampling strategies in forest hydrology and biogeochemistry: (a) technical advances in measurement capability, as is evident in embedded sensor networks and remotely sensed measurements and (b) parallel advances in cyberinfrastructure and numerical modeling that can help turn these new data into knowledge. Although these developments will...