Thermal effect of the Middle Ural copper smelter (Russia) and growth of birch leaves.

Toxic effects of industrial emissions on vegetation have been extensively studied, and at the same time indirect effects of pollution are less known. In 2011 and 2015, we studied temperature regime and leaf growth for Betula pubescens and B. pendula in deciduous forests near the Middle Ural copper smelter (MUCS). At two polluted sites (1 and 2 km from the smelter) and two unpolluted sites (16 and 27 km), we logged continuously air temperatures during the growing season (May-August) and measured leaves until completion of growth (May-June). Near MUCS, daily mean air temperatures were 0.7-1.0 °C higher with daily temperature range 2.2-2.7 °C greater than at distant sites. Daily air temperature range decreased from spring to midsummer, suggesting that the ability of vegetation to mitigate temperature variations increases with plant biomass, which peaks in midsummer. Growth of birch leaves near MUCS began 4-10 days earlier and completed 3-7 days earlier than far away. Thermal sum over the leaf growth period did not differ between areas in 2011, and in 2015 was lower in the polluted than in the unpolluted area. The earlier leaf growth completion near MUCS can be attributed to higher air temperatures and more rapid accumulation of required thermal sums.