The effects of droplet size and numerical deposit density on herbicide efficacy differed among investigations that relied on commercial nozzles to produce droplets strictly within small, medium, or large sizes. A droplet generator capable of producing uniform and homogeneous droplets was therefore used in a greenhouse experiment. Four droplet size classes (150, 350, 450, and 650 μm) using glyphosate, hexazinone, and triclopyr on red alder, aspen, and white birch were studied. Herbicides applied in small (150 to 450-μm) droplets were more phytotoxic than large (660-μm) ones because of their greater numerical coverage and translocation. Leaf age, weed species, herbicide type, and mixture of droplet sizes were not critical in modifying the effects of droplet behavior; however, the concentrations of herbicide used had a positive effect. When the herbicides were applied at high concentrations, the influence of droplet size was nullified. These findings may help reduce the cost of application and the chemical burden in a forest environment.

Given the difficulty of separating the three Picea species—P. glauca, P. mariana, and P. rubens (white, black, and red spruce)—in the pollen record, little is known about their unique histories in eastern North America following deglaciation. Here we report the first use of a classification tree analysis (CART) to distinguish pollen grains of these species. It was successfully applied to fossil pollen from eight sites in Maine and one in Massachusetts. We focused on the late glacial/early Holocene (14,000 to 8000 cal yr B.P.) and the late Holocene (1400 cal yr B.P. to present)—the two key periods since deglaciation when Picea has been abundant in the region. The result shows a shift from a Picea forest of P. glauca and P. mariana in the late glacial to a forest of P. rubens and P. mariana in the late Holocene. The small number of P. rubens grains identified from the late glacial/early Holocene samples (<5%) suggests that that species was either absent or rare at most of the sites. The occurrence and distribution of the three species do not reveal any geographic or temporal trend during late glacial time, but the data suggest that they were distributed in local patches on the landscape. The results of this study indicate that the recent population expansion of Picea (1000 to 500 cal yr B.P.) was likely the first time since deglaciation that P. rubens was abundant in the region.

Picea is an important taxon in late-glacial pollen records from eastern North America, but little is known about which species of Picea were present. We apply a recently developed palynological method for discriminating the three Picea species in eastern North America to three records from New England. Picea glauca was dominant at ∼ 14,500–14,000 cal yr BP, followed by a transition to Picea mariana between ∼ 14,000 and 13,500 cal yr BP. Comparison of the pollen data with hydrogen isotope data shows clearly that this transition began before the beginning of the Younger Dryas Chronozone. The ecological changes of the late-glacial interval were not a simple oscillation in the position of a single species' range, but rather major changes in vegetation structure and composition occurring during an interval of variations in several environmental factors, including climate, edaphic conditions, and atmospheric CO2 levels.

The germination of intact, moist-chilled white spruce (Picea glauca [Moench.] Voss.) seeds and liquid–nitrogen–decoated (LN2), unchilled seeds is significantly more than of intact, unchilled seeds and intact, unchilled seeds exposed to LN2. The testa is largely responsible for imposition of dormancy in these seeds, although the megagametophyte and/or nucellus also play a role. One or both of these tissues undergoes significant weakening during moist chilling. Excised embryos from dormant and nondormant white spruce seeds elongate when placed on solid Murashige and Skoog minimal organics medium supplemented with a carbon source (sucrose, glucose or galactose), but elongate very little on medium without sugar. They are not killed by rapid imbibition on unsupplemented media. Thus, embryos of white spruce do not exhibit innate dormancy, but are dependent on a carbon source for elongation, and have dormancy imposed on them by their surrounding structures.