A century of sulfur dioxide fumigation, copper and nickel particulate deposition, fire, soil erosion and enhanced frost action resulting from mining and smeltering has created 17, 00 ha of barren land and 72 000 ha of stunted, open birch-maple (Betula/Acer) woodland in the Sudbury area of Ontario, Canada. The primary factor limiting plant colonization is the acidic, aluminium-, copper- and nickel-toxic properties of the soils, although certain plant species have developed genetically based metal tolerance. In the revegetation programme, manual surface application of ground limestone, with or without an accompanying fertilizer and/or grass-legume seed application, leads to immediate colonization by woody species including birch (Betula spp.), aspen (Populus tremuloides) and willows (Salix spp.), and more than 3000 ha have been treated in this way by the Regional Municipality of Sudbury since 1978. Native coniferous species (Pinus spp.) have also been planted in groups to form a seed source for future colonization.

The commonly observed negative relationship between stomatal density (SD) and atmospheric CO2 has led to SD being proposed as an indicator of atmospheric CO2 concentration. The use of SD as a proxy for CO2, however, has been hampered by an insufficient understanding of the intraspecific variation of this trait. We hypothesized that SD in Pinus sylvestris, a widely distributed conifer, varies geographically and that this variation is determined by major climatic variables. By sampling needles from naturally growing trees along a latitudinal range of 32.25°, equivalent to 13.7°C gradient of mean annual temperature (MAT) across Europe, we found that SD decreased from the warmest southern sites to the coldest sites in the north at a rate of 4 stomata per mm2 for each 1°C, with MAT explaining 44% of the variation. Additionally, samples from a provenance trial exhibited a positive relationship between SD and the MAT of the original localities, suggesting that high SD is an adaptation to warm temperature. Our study revealed one of the strongest intraspecific relationships between SD and climate in any woody species, supporting the utility of SD as a temperature, rather than direct CO2, proxy. In addition, our results predict the response of SD to climate warming.

Activity of soil dehydrogenase (DHA) was measured in the mineral soil in a forest stand of 15 to 16-year-old Scots pine (Pinus sylvestris L.) from geographically diverse populations, as an indicator of biological activity of soil microorganisms, in a provenance experiment in Poland. The pine populations originated from six European countries (Sweden, Russia, Latvia, Poland, Germany, France) and differed widely in aboveground biomass and productivity. Soil DHA during two growing seasons showed pronounced seasonal variability, which was significantly related to the fine root concentration of nonstructural carbohydrates. Higher DHA was found in soil under canopies of the central and southern European populations than in those from more northern parts of the Scots pine range. Significant positive correlation between soil DHA and aboveground tree biomass suggest that these patterns most likely resulted from differences in carbon dynamics and productivity among populations.