Insecticidal activity of some tenuazonic acid analogues

A series of analogues of the larvicide tenuazonic acid [3-acetyl-5-(l-methylpropyl)-pyrrolidine-2,4-dione] was prepared in an attempt to increase its activity and breadth of spectrum. Substitution brought about some changes in specificity, the greatest improvement being obtained with chlorophenyl substituents.     

Forest responses to climate change in the northwestern United States: Ecophysiological foundations for adaptive management

Climate change resulting from increased concentrations of atmospheric carbon dioxide ([CO₂]) is expected to result in warmer temperatures and changed precipitation regimes during this century. In the northwestern U.S., these changes will likely decrease snowpack, cause earlier snowmelt, increase summer evapotranspiration, and increase the frequency and severity of droughts. Elevated [CO₂] and warmer temperatures may have positive effects on growth and productivity where there is adequate moisture or growth is currently limited by cold. However, the effects of climate change are generally expected to reduce growth and survival, predispose forests to disturbance by wildfire, insects, and disease; and ultimately change forest structure and composition at the landscape scale. Substantial warming will likely decrease winter chilling resulting in delayed bud burst, and adversely affect flowering and seed germination for some species. The extent of these effects will depend on the magnitude of climate change, the abilities of individual trees to acclimate, and for tree populations to adapt in situ, or to migrate to suitable habitats. These coping mechanisms may be insufficient to maintain optimal fitness of tree populations to rapidly changing climate. Physiological responses to climatic stresses are relatively well-understood at the organ or whole-plant scale but not at the stand or landscape scale. In particular, the interactive effects of multiple stressors is not well known. Genetic and silvicultural approaches to increase adaptive capacities and to decrease climate-related vulnerabilities of forests can be based on ecophysiological knowledge. Effective approaches to climate adaptation will likely include assisted migration of species and populations, and density management. Use of these approaches to increase forest resistance and resilience at the landscape scale requires a better understanding of species adaptations, within-species genetic variation, and the mitigating effects of silvicultural treatments.     

Hormonal control of second flushing in Douglas-fir shoots

Spring-flushing, over-wintered buds of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) produce new buds that may follow various developmental pathways. These include second flushing in early summer or dormancy before flushing during the following spring. Second flushing usually entails an initial release of apical dominance as some of the current-season upper lateral buds grow out. Four hypotheses concerning control of current bud outgrowth in spring-flushing shoots were tested: (1) apically derived auxin in the terminal spring-flushing shoot suppresses lateral bud outgrowth (second flushing); (2) cytokinin (0.5 mM benzyladenine) spray treatments given midway through the spring flush period induce bud formation; (3) similar cytokinin spray treatments induce the outgrowth of existing current lateral buds; and (4) defoliation of the terminal spring-flushing shoot promotes second flushing. Hypothesis 1 was supported by data demonstrating that decapitation-released apical dominance was completely restored by treatment with exogenous auxin (22.5 or 45 mM naphthalene acetic acid) (Thimann-Skoog test). Hypothesis 2 was marginally supported by a small, but significant increase in bud number; and Hypothesis 3 was strongly supported by a large increase in the number of outgrowing buds following cytokinin applications. Defoliation produced similar results to cytokinin application. We conclude that auxin and cytokinin play important repressive and promotive roles, respectively, in the control of second flushing in the terminal spring-flushing Douglas-fir shoot.     

Growth indices and stomatal control of transpiration in Acacia koa stands planted at different densities

We examined the influences of selected environmental variables on stomatal behavior and regulation of transpiration in 26-month-old Acacia koa Gray (koa) stands planted at spacings of 1 x 1 m or 2.5 x 2.5 m and grown without irrigation. Field measurements were made during recovery from an extended 60-day dry period with only 38 mm of precipitation. Biomass and leaf area were also measured at 3-month intervals over the first 24 months after planting and again following completion of the transpiration (T) and stomatal conductance (g(s)) measurements at about 26 months after planting. Transpiration was measured as sap flow through intact branches by a heat balance method. After a 22-day period during which 130 mm of rain were recorded, average T was substantially higher in the 2.5 x 2.5 m stand on both a leaf area and ground area basis even though leaf area index was about 3.5 times higher in the 1 x 1 m stand. After an additional 25 mm of rain during an 8-day period, T was still slightly higher on a leaf area basis in the 2.5 x 2.5 m stand but was about 3 times higher on a ground area basis in the 1 x 1 m stand. A strong stomatal response to humidity limited the increase in T with increasing evaporative demand. Values of g(s) in koa phyllodes were comparable to those reported for leaves of other mesic tropical forest trees, but were several times higher than those reported for Acacia species native to arid and semi-arid regions. The 1 x 1 m planting yielded three times more biomass per unit ground area than the 2.5 x 2.5 m planting. However, greater stand density, which resulted in more rapid depletion of soil water between rainfall inputs, was associated with lower growth efficiency and lower radiation conversion efficiency.