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Aim Species diversity is distributed heterogeneously through space, for reasons that are poorly understood. We tested three hypotheses to account for spatial variation in coniferous tree species diversity in a temperate island archipelago. The theory of island biogeography (ToIB) predicts that island area affects species diversity both directly (by increasing habitat diversity) and indirectly (by increasing abundances, which in turn reduce extinction rates). The ToIB also predicts that island isolation directly affects species diversity by reducing immigration rates. The passive sampling hypothesis predicts that island area and isolation both affect species diversity indirectly, by increasing and decreasing abundances, respectively. Community assembly rules (i.e. even partitioning of conifer abundances among islands) might also reduce tree species diversity beyond the core predictions of ToIB and the passive sampling hypothesis.Location Barkley Sound, British Columbia, Canada.Methods The abundances of eight coniferous tree species were quantified on 34 islands and two (1 ha) mainland plots. The predictions of the ToIB and the passive sampling hypothesis were tested using path analysis, and null models were used to test for abundance-based assembly rules and to further test the passive sampling hypothesis.Results Path analysis showed that island area and isolation did not have direct, statistical effects on tree species diversity. Instead, both geographic variables had direct statistical effects on total tree abundances, which in turn predicted tree diversity. Results from several passive sampling null models were correlated with observed patterns in species diversity, but they consistently overestimated the number of tree species inhabiting most islands. A different suite of null models showed support for community assembly rules, or that tree species often reached higher abundances on islands that housed fewer heterospecific trees.Main conclusions Results were inconsistent with the ToIB. Instead, patterns in tree diversity were best explained by a combination of stochastic (passive sampling) and deterministic (assembly rules) processes. Stochastic and deterministic processes are commonly considered to be exclusive explanations for island community structure, but results from this study suggest that they can work synergistically to structure island tree communities.

In an experimental greenhouse, growing a tomato crop, it was investigated if a reduction in spray pressure could improve the spray result, while, simultaneously, emission to the ground could be reduced. Spray deposition on the leaves and the emission to the ground was evaluated at different spray pressures (2.5, 5, 10 and 15 bar). An Empas vertical spray mast with 6x2 Teejet XR8002VK flat fan nozzles was used to spray the tomato crop in three stages of crop growth, respectively 0.75, 2.25 and 2.80 m height, spraying 500-1500 l ha-1 (stage 1) and 1000-3000 l ha-1 (stage 2 and 3) depending on the spray pressure. Flow rate ranged from 0.74 to 1.80 l min-1 at an increasing spray pressure from 2.5 to 15 bar. The VMD (Volume Median Diameter) decreased in the same pressure range from 207 to 124 µm. The emission of spray liquid to the ground was measured in the spraying path and beneath the plants between the rows closest to the spray mast. The highest emission to the ground appeared closest to the spray mast, and increased at higher spray pressures. In crop growth stage 1 and 2 about 35% of the spray volume emitted to the ground, in stage 3 only 15%. The direction of the nozzles (upwards directed with an angle of at least 40 0) appeared to be of great importance. The deposition of spray liquid on the leaves was measured at two rows (A: closest to the sprayer, B: the next row behind it) at one, two or three heights depending the stage of the crop. Highest spray deposition could be found in row A, at the upper side of the leaf and at a higher working pressure. Differences were smaller in the next row and at greater height in the plant. Finally it could be concluded that a decrease in spray pressure to 5 bar gave an adequate deposition on the leaves in µl cm-2 , and a decrease in emission to the ground.

Whitebark pine (Pinus albicaulis Engelm.) is a widely distributed high-elevation species in western North America that is threatened primarily by an introduced disease and other disturbances. In British Columbia, this tree is a component of harvested forests, yet knowledge of post-harvest survivorship and factors that promote successful retention is lacking. Our objectives are to describe the temporal attrition of retained mature whitebark pine trees and to identify factors that likely influence survivorship during the critical initial post-harvest period. We assessed five separate harvest units in southeastern British Columbia. Dendrochronological investigation revealed that retained trees experienced high annual mortality rates (3–16%) across harvest sites during the initial five-year post-harvest period. By eight years post-harvest, retention survivorship ranged from 17–80%. After eight years post-harvest, mortality rates drastically declined. The preponderance of fallen stems oriented towards the northeast suggests that storm system events arriving from the Pacific Ocean are the most significant drivers of blowdown. We estimate that survivorship is positively associated with shorter tree heights and longer crown lengths, a lack of disease cankers, a greater presence of rodent wounding, and higher numbers of surrounding retained trees. We found little effect based on slope and aspect. As these trees are an endangered species, harvest operations should be practiced cautiously in associated forests. We recommend carefully selecting retention trees, ensuring an adequate number of neighbor trees, and orienting retention patches to avoid predominant storm wind directions.

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