Studies on lichen-dominated systems. I. The water relations of Cladonia alpestris in spruce–lichen woodland in northern Ontario

Abstract

The water relations of Cladonia alpestris in spruce–lichen woodland in northern Ontario is described. The rate of drying of the lichen canopy was measured by resistance grids inserted into the canopy and monitored during the drying cycle. The effects of dew were measured in a similar fashion and shown to form an insignificant proportion of the total annual metabolism of the lichen. The lichen mat showed a very high stratified resistance to water loss and the effective mulching properties produce a high level of water availability under the lichen mat. This was confirmed using neutron attenuation techniques and the significance of this discussed in relation to the development of lichen woodland. The physiological response of the lichen to conditions of varying levels of saturation is also discussed.

ECOLOGICALLY‐LINKED VARIATION IN MORPHOLOGY, ACETYLENE REDUCTION, AND WATER RELATIONS IN PSEUDOCYPHELLARIA DISSIMILIS

“…Thus the water relations of lichens were said to be purely physical and to resemble those of a gel. This view was so widely accepted that artificial models designed to simulate the water relations of lichens were simply portions of filter paper (Kershaw and Rouse, 1971;Harris, 1972). More recent work has demonstrated an intraspecific variation in morphology and water relations for Alectoria ochroleuca and Cladina alpestris (Larson and Kershaw, 1976), whilst Larson (1979) has shown interspecific differences in water relations of Umbilicaria species.…”

Remise en production des pessières à lichens de la forêt boréale commerciale :

“…Certains auteurs suggèrent que les lichens terricoles, espèces également envahissantes suite à l'ouverture du milieu, influenceraient la croissance de certains conifères soit par la libération de composés phenoliques, la compétition pour les nutriments ou par des limitations physiques (Kershaw et Rouse, 1971;Kuuluvainen et al, 1993). Compte tenu de leur albédo élevé, les lichens contribueraient à maintenir des conditions de sol frais et humide (Kershaw et Rouse, 1971).…”

“…Compte tenu de leur albédo élevé, les lichens contribueraient à maintenir des conditions de sol frais et humide (Kershaw et Rouse, 1971). Ces conditions édaphiques défavorables se répercuteraient ainsi la croissance des autres plantes (Kershaw et Rouse, 1971;Grossnickle, 2000).…”

“…Les sols sous d'épaisses couches de lichens peuvent conserver une humidité supérieure à des sols sans lichens, l'évaporation de l'eau dans la couche de lichens durant les jours chauds de l'été n'étant que partielle (Kershaw et Rouse, 1971). Le nombre de degrés-jours nécessaires pour débuter la saison de croissance serait aussi atteint plus tard dans la saison.…”

EFFECTS OF A SIMULATED ACID RAIN EPISODE ON PHOTOSYNTHESIS AND RECOVERY IN THE CARIBOU‐FORAGE LICHENS, CLADINA STELLARIS (OPIZ.) BRODO AND CLADINA RANGIFERINA (L.) WIGG.

“…Field data are often difficult to interpret because long-term experiments integrate many abiotic and biotic factors in addition to a specific pollution treatment. Changes in shade, nutrient levels and soil moisture may result in shifts in the abundance of dominant lichens (Kershaw & Rouse, 1971;Yarranton, 1975;Foster, 1985). The dominant species of interest in this study, Cladina stellaris and Cladina rangiferina regularly co-occur but have different micro-habitat pref-erences (Lechowicz & Adams, 1974 a, b) and successional patterns (Kershaw, 1977;Foster, 1985), These two species are widely distributed throughout the boreal region of North America, the eastern part of which is regularly subjected to acidic deposition, with the pH of ambient rain 45 or less.…”