Treesearch

Responses of forest trees to defoliation by insects such as gypsy moth vary greatly from site to site and from individual to individual. To determine whether some of this variation could be explained by variation in other stress factors, red oak (Quercus rubra L.) seedlings were exposed to low and high light, water, mineral nutrient, and defoliation treatments, in a complete factorial design in a greenhouse. Significant interactions were observed among factors for photosynthesis, growth, and mortality, indicating that the response to defoliation was influenced by other stresses. Defoliation...

The requirement for polyamines in the proliferation of cells was first demonstrated in bacteria (3). While significant progress has been made in this field using animal cell cultures, only preliminary studies have been reported with plant tissues. Serafini-Fracassini et al. (9) showed a marked increase in polyamine synthesis early during the G 1 phase, concomitant with the synthesis of RNA, following the break of dormancy in Helianthus tuberosus tuber tissue. A second phase of polyamine accumulation began during the progression of S phase. Torrigiani et al. (10) and Phillips et al. (7)...

Carrot cell cultures provide a model experimental system for the analysis of biochemical and molecular events associated with morphogenesis in plants (3, 4, 5, 14). Among the biochemical changes accompanying somatic embryogenesis in this tissue is an increased biosynthesis ofpolyamines (1, 2, 7, 10, 11, 13). A variety of inhibitors of polyamine biosynthetic enzymes have been used to analyze the role of polyamines in somatic embryogenesis. A summary of our work on the effects of DFMO, DFMA, MGBG and CHAP on somatic embryogenesis, cellular polyamine levels, and activities of ADC, ODC, AdoMet...

Development of Pb pollution histories using tree ring analyses has been troubled by possible mobility of Pb within stem xylem. In a 2-yr study, we exposed red spruce (Picea rubens Sarg.) seedlings to Pb during one growing season, with Pb excluded in either the previous or following growing season. Lead levels within xylem rings and bark were subsequently determined using atomic absorption analyses. Lead concentrations in tissues from exposed seedlings were significantly higher than controls, and significant Pb concentrations were found in xylem formed during periods of Pb exclusion. Routes...

There is little available knowledge of the absolute or relative effects of trees and buildings on wind at or below building height in residential neighborhoods. In this study, mean wind speed was measured at a height of 6.6 ft (2 m) in neighborhoods of single-family houses. BuIlding densities ranged between 6% and 12% of the land ares, and tree-cover densities were between 0 and 77%. Measurements were made with cup anemometers at points either 1/2 or 1 building height from 15 sample houses.

Calli of American elm susceptible and resistant to Dutch elm disease were exposed to a culture filtrate of a pathogenic isolate of Ceratocystis ulmi. Cells from untreated tissue exhibited typical internal composition associated with healthy, actively growing cells. All cells exposed to culture filtrate showed appreciable ultrastructural changes. Cells from susceptible American elm displayed mitochondrial and cytoplasmic disruption. Damage to membranes was evident by the appearance of incomplete cell walls and distinctive plasmolysis. Cells of the resistant American elm differed dramatically...

An elm germplasm improvement program was established using three distinct approaches: (1) development of protoplast regeneration protocols with the goal of attempting somatic hybridization between Ulmus americana and disease resistant hybrids; (2) evaluation of the extent of somaclonal variation in plants regenerated from protoplasts; and (3) selection in vitro of variants from Ulmus americana callus lines exposed to toxin and culture filtrates of Ceratocystis ulmi. Plants were regenerated from protoplasts of the Dutch elm disease resistant hybrid Ulmus x 'Pioneer', but repeated attempts...

Oak sawlog and pulpwood losses in stands defoliated by gypsy moths have become a critical problem for some forest landowners. The salvage of gypsy moth-killed hardwoods can become an important source of pulpwood and sawlogs. This study documents a methodology and provides guidelines to determine defoliated oak stands that are economically salvageable. Stand data from 574 defoliated oak stands were integrated with stump-to-mill logging costs and wood values. Cable and ground-based logging costs were integrated with three levels of sawlog and pulpwood-fuelwood prices to determine if salvage...

The Norway maple, Acer platanoldes, was introduced into the United States about 1756 after being cultivated in England since 1683. This species remained in relative obscurity in the U.S. until the mid- to late-1800's, but is now one of the most popular urban trees. In certain regions of the United States, Norway maples dominate street tree populations and commonly escape to compete with native species. The extensive use of this species in North America has led to various problems across its new range. Some of these problems may be overcome by future introductions from its native range in...

Street tree pruning and removal needs were examined for 11 species from inventory data collected in 11 cities in the North Central and Northeastern United States. The needs ranged from predominantly no pruning and routine pruning of small trees to safety pruning and removal of large trees. Species were ranked in terms of overall pruning and removal urgency, with London planetree and honeylocust having the least urgent pruning and removal needs and American elm and boxelder the most urgent needs.