Treesearch

Much has been made of the need for cities to become more sustainable, particularly since for the first time in human history over half of the world's population are urban dwellers. Cities concentrate human activities in an exceptionally powerful manner, and this includes resource use and the generation of pollution. Attention has turned towards cities for their capacity to enhance and use nature's services – ecological sustainability – to remediate some of their own environmental impacts. Insufficient attention has been paid to the challenges of implementation of this new approach to...

Urban forests are increasingly being seen as an important infrastructure that can help cities remediate their environmental impacts. This work reports on the first steps in implementing a million tree program in Los Angeles and the ways such a biogenic—living—infrastructure has been approached. Numbers of studies have been done to quantify the benefits of urban forests, but little has been written on the process of implementing urban tree planting programs. The investigative methods were primarily qualitative, involving interviews, attending meetings and conducting literature reviews....

The Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins, was detected in 2001 in northern Minnesota outside its natural range and the range of its native hosts, Douglas-fir, Pseudotsuga menziesii (Mirbel) Franco, and western larch, Larix occidentalis Nutt. Consecutive years of detection indicated that D. pseudotsugae may have been established in a new environment and provided a possible example of an indigenous exotic species in North America. Pheromone-baited logs of P. menziesii and tamarack, Larix laricina (Du Roi) K. Koch. were placed at four sites in northern Minnesota in an attempt...

When an herbivorous insect enters a new geographic area, it will select host plants based on short and long distance cues. A conifer-feeding bark beetle that has been recently introduced to North America, the Mediterranean pine engraver, Orthotomicus erosus (Wollaston), has a potentially wide host range, especially among members of the Pinaceae. The long-distance response of the beetles to tree odors may be a key feature of the mechanism of host recognition and selection. We used a laboratory olfactometer to study the walking response of 1,440 O. erosus to odor cues from the bark and...

The goldspotted oak borer, Agrilus coxalis auroguttatus Schaeffer (Coleoptera: Buprestidae), is a new threat to several native oak species in California (CA) (Coleman & Seybold 2008a, b). The beetle larvae feed in and damage the outer xylem, cambium, and phloem of coast live oak, Quercus agrifolia Née (Fagaceae), California black oak, Q. kelloggii Newb., and canyon live oak, Q. chrysolepis Liebm., killing these trees after several years of repeated injury. Infested trees can be identified by crown thinning and dieback, D-shaped adult emergence holes primarily on the main stem, and dark...

Landowners and managers have been seeking ways to protect susceptible oak (Quercus) species and tanoak (Lithocarpus densiflorus) from sudden oak death (SOD) caused by Phytophthora ramorum. Because disease epidemiology differs between tanoaks and susceptible oaks, we are testing different control strategies appropriate for different forest types. The disease management studies described here test whether various management techniques will be effective when applied in the field at the stand scale.

Permanent plots were established in 2000 to examine how tree and site factors affect risk of Phytophthora ramorum stem canker (sudden oak death [SOD]) and determine how affected stands change over time due to disease. P. ramorum canker was prevalent in the sampled coast live oak (Quercus agrifolia) or tanoak (Lithocarpus densiflorus) stands in 2000. In September of each year from 2000 through 2008, we collected data on P. ramorum symptoms, tree condition, tree failures, regeneration, and various other factors in 150 circular plots (8 m radius) at 12 locations in Marin, Sonoma, and Napa...

Colonization of N. densiflorus tissues by P. ramorum is not well understood. The pathogen is able to colonize nearly all tissues of this host but it is unclear how a tree is ultimately killed. Because this is such a destructive invasive pathogen, it is important to investigate its pathogenic strategy. Microscopic investigation of xylem colonization has been conducted, but colonization of bark tissues, which has always been regarded as an important part of infection, has not been investigated previously. In this research, P. ramorum infected N. densiflorus bark tissues were examined using...

Processes operating across different spatial scales (for example, individual, community, landscape) influence disease dynamics. Understanding these processes and their interactions can yield general insights into disease control, disease dynamics within communities, and community response to disease. For Phytophthora ramorum, pathogen establishment and disease intensity are key drivers of deleterious impacts on ecosystems such as changes in fuel loads, tree mortality, and transformation of native plant communities. We studied infection rates of P. ramorum for major overstory species...

Fuel management techniques are commonly used in shrublands to reduce wildfire risk. However, more information about the ecological effects of these treatments is needed by managers and ecologists. In an effort to address this need, we performed a replicated (4 replicates per treatment) 48-ha experiment in northern California chaparral dominated by Adenostoma fasciculatum to determine the effects of two fuel reduction types (prescribed fire and mastication) and three different seasons of treatment (fall, winter, and spring) on shrub cover, height, and seedling density. Exclosures (2.5 m2...