Treesearch

Future anthropogenic-induced changes to the earth’s climate will likely include increases in temperature and changes in precipitation that will increase the frequency and severity of droughts. Insects and fungal diseases are important disturbances in forests, yet understanding of the role of drought in outbreaks of these agents is limited. Current knowledge concerning the effects of drought on herbivorous insect and pathogen outbreaks in U.S. forests is reviewed, and compared between the relatively mesic and structurally diverse forests of the eastern U.S. and the more xeric forests of the...

Questions: How do stand-level biomass and percentage of deadmaterial in chaparral vary as a function of stand age? How do the landscape properties of aggregation index and patch size vary in each of the dominant species groups as a function of stand age? Location: Stands of 7-, 28-and 68-yr-old chaparral, San Diego County, CA, US. Methods: We sampled and estimated above-ground biomass in 8 m 9 8m field plots. Each stand was classified into species groups using high-resolution imagery. After establishing coefficients for the average biomass per area for each species group and stand age...

Chronic nitrogen deposition has measureable impacts on soil and plant health.We investigate burning emissions from biomass grown in areas of high and low NOx deposition. Gas and aerosolphase emissions were measured as a function of photochemical aging in an environmental chamber at UC-Riverside. Though aerosol chemical speciation was not available, results indicate a systemic compositional difference between biomass grown in high and low deposition areas. Aerosol emissions from biomass grown in areas of high NOx deposition exhibit a lower volatility than biomass grown in a low deposition...

Fire behaviour data from 240 laboratory fires in high-density live chaparral fuel beds were compared with model predictions. Logistic regression was used to develop a model to predict fire spread success in the fuel beds and linear regression was used to predict rate of spread. Predictions from the Rothermel equation and three proposed changes as well as two physically based models were compared with observed spread rates of spread. Flame length–fireline intensity relationships were compared with flame length data. Wind was the most important variable related to spread success. Air...

Anticipating the response of small mammals to climate change requires knowledge of thermal conditions of their habitat during times of the day and year when individuals use them. We measured diurnal and seasonal temperatures of free air and of six habitat components for American pikas (Ochotona princeps) over five years at 37 sites in seven mountain ranges in the western Great Basin, United States. Talus matrices (subsurfaces) had low daily variances and, in the warm season, remained cool during the hottest times of the day relative to surfaces and free air. During winter, matrices were...

This report synthesizes information to help promote the distinctive ecological and cultural benefits provided by California black oak. Production of abundant, high-quality acorns desired by Native Americans in California, as well as other valued services, requires the presence of mature, broad-crowned trees with low fuel levels and low pest levels. Although black oaks are vulnerable to intense fires, they depend on low-intensity, more frequent fires to reduce competition from conifers, pest loads, and build-up of fuels that promote intense fires. Traditional burning by Native Americans...

In the western United States, forests are experiencing novel environmental conditions related to a changing climate and a suppression of the historical fire regime. Mixed-conifer forests, considered resilient to disturbance due to their heterogeneity in structure and composition, appear to be shifting to a more homogeneous state, but the timescale of these shifts is not well understood. Our objective was to assess the effects of climate and fire suppression on stand dynamics and demographic rates of an old-growth mixed-conifer forest in the Sierra Nevada. We used a Bayesian hierarchical...

For many, citizen science is exciting because of the possibility for more diverse, equitable partnerships in scientific research with outcomes considered meaningful and useful by all, including public participants. This was the focus of a symposium we organized at the 2015 conference of the Citizen Science Association. Here we synthesize points made by symposium participants and our own reflections. Professional science has a participation problem that is part of a larger equity problem in society. Inequity in science has negative consequences including a failure to address the needs and...

This study compiled recent inventory data from 929,823 street trees in 50 cities to determine trends in tree number and density, identify priority investments and create baseline data against which the efficacy of future practices can be evaluated. The number of street trees increased from 5.9 million in 1988 to 9.1 million in 2014, about one for every four residents. Street tree density declined from 65.6 to 46.6 trees per km, nearly a 30% drop. City streets are at 36.3% of full stocking. State-wide, only London planetree (Platanus χ hispanica) comprises over 10% of the total, suggesting...

Accurately measuring the biophysical dimensions of urban trees, such as crown diameter, stem diameter, height, and biomass, is essential for quantifying their collective benefits as an urban forest. However, the cost of directly measuring thousands or millions of individual trees through field surveys can be prohibitive. Supplementing field surveys with remotely sensed data can reduce costs if measurements derived from remotely sensed data are accurate. This study identifies and measures the errors incurred in estimating key tree dimensions from two types of remotely sensed data: high-resol...