The nature of high altitude precipitation and its effect on scots pine und sitka spruce : Air Pollution and Forest Decline. 14th International Meeting for Specialists in Air Pollution Effects on Forest Ecosystems

1989

9 Abb., 1 Tab., 15 Lit. Ang., En, Zfsg. En

Unselbständiges Werk

9091

200034649

The high leels of acidity in cloudwater require the dynamics of cloud droplet/needle/environment interactions to be studied closely. Experiments were set up to investigate the interaction between needles and deposited cloudwater, the enhancement of acidity due to evaporation and the nature of snow melt. Both Scots pine and particulary Sitka spruce decrease cloudwater pH when in contact with needles despite cation leaching. Acidity enhancement due to evaporation was proportional to the evaporative driving force but the different effects of wind were noted. Measurements in situ showed rapid increases in the acidity of cloud had lifted. Meltwater from snow on shoots contained higher concentrations of ions than that from ground snow. In controlled experiments Scots pine and Sitka spruce were resistant to typical cloudwater pH levels. When needle browning occurred the cuticle appeared to remain undamaged. Frozen-hydrated, feezefractured SEM revealed international tissue necrosis corresponding to browing progression and the development of an apparent defence mechanism.