Treesearch

Pine cone beetles (Conophthorus spp.) feed and kill immature cones of Pinus species, thereby reducing seed production and seriously impairing reforestation of forest ecosystems. Population variation of Conophthorus reproductive behavior has hampered the development of semiochemical control of these pests. This diYculty is compounded by a lack of taxonomic knowledge and species diagnostic characters. Researchers and managers rely, in part, on host associations and geographic locality for species identiWcations and these have arguable taxonomic utility. However, host use and/or geographic...

Invasive species pose major threats to the integrity and functioning of ecosystems. When such species alter ecosystem processes, they have the potential to change the environmental context in which other species survive and reproduce and may also facilitate the invasion of additional species. We describe impacts of an invasive N2-fixing tree, Falcataria moluccana, on some of the last intact remnants of native wet lowland forest undergoing primary succession on 48-, 213-, and 300-yr-old lava flows of Kilauea Volcano on the island of Hawai‘i. We measured litterfall, soil nitrogen (N) and...

Climate change predictions derived from coupled carbon-climate models are highly dependent on assumptions about feedbacks between the biosphere and atmosphere. One critical feedback occurs if C uptake by the biosphere increases in response to the fossil-fuel driven increase in atmospheric [CO2] ("CO2 fertilization"), thereby slowing the rate of increase in atmospheric [CO2]. Carbon exchanges between the terrestrial biosphere and atmosphere are often first represented in models as net primary productivity (NPP). However, the contribution of CO2 fertilization to the future global C cycle has...

The endemic tree Acacia koa is used to reforest abandoned agricuItural lands in Hawaii. Growth may be constrained by soil infertility and toxic concentrations of aluminum (AI) and manganese (Mn) in acidic Oxisols and Ultisols, The effects of phosphorus (P) fertilization at time of planting, soil type, and seed source on koa growth were studied for three years. Phosphorus, applied as triple superphosphate and at rates of at least 300 kg P ha-1, significantly increased height, basal stem diameter, crown volume, and aboveground wood biomass of trees from the local (Oahu) seed source, but not...

Stocking relationships are an important tool for foresters because they provide a means for evaluating how effectively the trees in a stand use available growing space. While stocking guidelines are not available for many tropical tree species, readily obtained measurements of stem and crown diameters can be used to develop preliminary stocking guidelines for most tree species. We demonstrate this approach for the endemic Hawaiian hardwood, Acacia koa, a species of major ecological and economic value in Hawaii. Using data from repeated censuses of multiple sites, we evaluated the influence...

Successful fire exclusion in the 20th century has created severe fire problems across the West. Not every forest is at risk of uncharacteristically severe wildfire, but drier forests are in need of active management to mitigate fire hazard. We summarize a set of simple principles important to address in fuel reduction treatments: reduction of surface fuels, increasing the height to live crown, decreasing crown density, and retaining large trees of fire-resistant species. Thinning and prescribed fire can be useful tools to achieve these objectives. Low thinning will be more effective than...

A series of laboratory fire spread experiments were completed to analyze the effect of terrain slope on marginal burning behavior of live chaparral shrub fuels that grow in the mountains of southern California. We attempted to burn single species fuel beds of four common chaparral plants under various fuel bed configurations and ambient conditions. Seventy-three (or 42%) of the 173 fires successfully propagated the 2.0 m length of the elevated fuel bed for slope percent ranging from –70% to 70%. There exists a critical slope above which fire spread is successful, and below which fire...

Current fire models are designed to model the spread of a linear fire front in dead, small-diameter fuels. Fires in predominantly living vegetation account for a large proportion of annual burned area nationally. Prescribed burning is used to manage living fuels; however, prescribed burning is currently conducted under conditions that result in marginal burning. We do not quantitatively understand the relative importance of the fuel and environmental variables that determine spread in live vegetation. Laboratory fires have been burned to determine the effects of wind, slope, moisture...

Based on energy conservation and detailed heat transfer mechanisms, a simple physical model for fire spread is presented for the limit of one-dimensional steady-state contiguous spread of a line fire in a thermally-thin uniform porous fuel bed. The solution for the fire spread rate is found as an eigenvalue from this model with appropriate boundary conditions through a fourth order Runge-Kutta method. Three experiments on fire spread are compared to the model simulations and good agreement is demonstrated. The comparisons with wind tunnel experiments on white birch fuel beds show that the...

We investigated a simultaneous temporally and spatially resolved 2-D velocity field above a burning circular pan of alcohol using particle image velocimetry (PIV). The results obtained from PIV were used to assess a thermal particle image velocimetry (TPIV) algorithm previously developed to approximate the velocity field using the temperature field, simultaneously captured by an infrared (IR) thermal camera. By tracing “thermal particles,” which were assumed to be virtual particles that corresponded to pixels of temperature values in successive IR images, the TPIV algorithm estimated a...