Differences in growth, leaf senescence and injury, and stomatal density in birch (Betula pendula Roth.) in relation to ambient levels of ozone in Finland

agentes nocivos air pollution arbre forestier avejentamiento betula pendula chloroplaste chloroplasts clone clones cloroplasto crecimiento croissance damage densidad density estoma facteur nuisible feuille finland finlande finlandia foliage forest trees growth hojas injurious factors leaves ozone ozono senescence stomata stomate symptome symptoms