Temporal factors affecting sap sugar content (SSC) were assessed in a 65-yr-old plantation of sugar maple (Acer saccharum Marsh.) located in Québec. A total of 694 maples were measured and the variation in SSC was assessed between 2 sampling years, among 3 days within each sugar season, and among hours within each sampling day. Average individual tree variation in SSC was extensive, ranging from 1.3 to 5.5% for spring 1994, and from 1.4 to 4.8% for spring 1995. The correlation between DBH and SSC was weak for both sampling years. SSC did not vary extensively between sampling hours within days, while it varied significantly among sampling days for both years analysed. However, the largest source of variation in SSC was between the 2 sampling years. Tree relative performances in SSC were moderately conserved among days within years and to a lesser degree, between sampling years. The relative magnitude of the differences between statistical treatments and the stability analysis of tree relative performances indicated that, for adequate estimation of an individual tree's SSC, sampling over years appears superior to sampling over several days within a single sugar season. Also, sampling towards the end of the sugar season or during days with lower SSC appears less reliable for mass selection.

The use of methylcyclopentadienyl manganese tricarbonyl (MMT) in unleaded gasoline has become a source of manganese (Mn) contamination to which urban ecosystems are exposed. The potential of coniferous trees as spatial and chronological indicators of Mn pollutation was investigated. Manganese concentrations in xylem from blue spruce (Picea pungens) growing near (high-exposure site) and far (low-exposure site) from a road were measured as a function of the year of wood formation. Exchangeable Mn content, which is the soil fraction most readily available for uptake by trees, was also measured in the soils of both sectors. The results of the soil analysis show that exchangeable Mn concentrations are about 10 times higher in soils exposed to contamination (p < 0.0005), in comparison with the concentrations found in soils weakly exposed. However, the Mn concentrations in the trees near the road were not significantly different from those in the reference trees (p > 0.05). Therefore, it appears that blue spruce is not sensitive to soil Mn contamination arising from the use of MMT in gasoline.

Methylcyclopentadienyl manganese tricarbonyl (MMT) is an organic derivative of manganese used as an additive in unleaded gasoline in Canada since 1977. Moreover, Canada is the only country in the world to have authorized the replacement of lead alkyls by MMT in gasoline. The purpose of the present study is to assess the importance of air contamination by Mn in relation to other air pollutants (gaseous and particulates), meteorological variables and traffic density. The concentration of both the gaseous (O3, CO, NO, NO2, SO2) and the particulate pollutants (Mn, Pb, NO−3, SO−−4, TSP) had been measured by the Montreal Urban Community in 1990 at seven sampling stations located in high traffic and low traffic density areas. Data on the meteorological conditions during that same period were also used. Non-parametric correlation, ANOVA and discriminant analyses were used to compare gaseous and particulate pollutants found between both levels of traffic density. In almost 50% of the daily air samples measured in 1990, the Mn concentrations are higher than the urban background level estimated at 0.04 μg m−3 and the variations of Mn concentrations are significantly correlated in time with traffic density. Moreover, Mn and TSP discriminate the best high and low traffic density areas. No significant differences have been observed between Pb, O3 and SO2 concentrations in both areas. These results should not be interpreted in terms of potential health effects since it is presently impossible to determine the fate of the Mn in the environment and its importance in terms of human exposure.