Summary Hypotheses of forest decline are summarized. Stressed trees may be a more suitable food source for invertebrate herbivores than unstressed trees because stress causes an increase in the tissue content of soluble nitrogenous compounds. There is reasonable correlative evidence that air pollutants influence the outbreak patterns of forest insect species. In some cases, formerly innocuous insects may become pests. The occurrence of specific insect pests with specific air contaminants is reviewed. Emphasis is placed on the decline of Fraser fir (Abies fruseri (Pursh) Poir.) in the southern Appalachians and the occurrence of the balsam woolly adelgid. Variable mortality patterns of Fraser fir may be caused by locally distributed air pollutants acting in combination with other types of stress including that caused by the adelgid.

Interactions of insects, trees and air pollutants

Measurement of Photosynthesis and Transpiration in Spruce Trees with Various Degrees of Damage

CO2/H2O gas exchange parameters of one- and two-year-old needles of spruce and fir.

Osmotic cell sap potentials of diseased and healthy spruce, fir and beech leaves, fine roots and cortes were determined with the aid of capillary cryoscopy. With one exception (fir needles) the diseased trees showed no reduction in osmotic potential compared to healthy trees.

Osmotic potential of spruce, fir and beech as a contribution to water budget in connection with forest decline (“Waldsterben”)

Recently, symptoms of decline have been widely observed in Yezo spruce (Picea jezoensis) and Todo fir (Abies sachalinensis) in Hokkaido. In order to clarify the mechanism of decline, the water status of Yezo spruce and Todo fir trees in the Tokyo University Forest in Hokkaido were investigated. The decline is observed mainly in stands damaged by Typhoon XV of 1981 (D-stands), but is not observed in undamaged stands (C-stands). Sampled trees in both types of stands were selected, the severity of their decline estimated, diurnal water potentials measured and water relation parameters such as water potential at turgor-loss point (\(\Psi _{w(tlp)} \)) and osmotic potential at full saturation (\(\Psi _{s(sat)} \)) were estimated by pressure-volume analysis. The diurnal trends of leaf water potential and midday water potential (\(\Psi _{w(min)} \)) of the sample trees were clearly different between the D-stands and the C-stand. Water stress in trees was much more severe in the D-stands than in the C-stand.\(\Psi _{w(tlp)} \) and\(\Psi _{s(sat)} \) of the declining trees were lower in the D-stands than in the C-stand. However,\(\Psi _{w(tlp)} \) and\(\Psi _{s(sat)} \) were not significantly different between declining trees and healthy-looking trees in D-stands. It was concluded that stand-level water stress, induced by the destruction of the canopy by the typhoon, was associated with the decline symptoms. The measurement of water relation parameters proved to be useful for diagnosis and prediction of decline at a stand level in this area.

Water Relations of Yezo spruce and Todo fir in Declined Stands of Boreal Forest in Hokkaido, Japan

The present study comprises comparative investigations of transpiration, photosynthesis and osmotic potential of various twigs of a healthy and a diseased fir. Possible causes for the registered differences are discussed.

K. Lautenschlager

Papers

Osmotic potential and gas exchange in healthy and diseased silver firs (Abies alba Mill.)