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Study of the Ecology of Pioneer Lichens, Mosses, and Algae on Recent Hawaiian Lava Flows

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Title:Study of the Ecology of Pioneer Lichens, Mosses, and Algae on Recent Hawaiian Lava Flows
Authors:Jackson, Togwell A.
Date Issued:Jan 1971
Publisher:University of Hawai'i Press
Citation:Jackson TA. 1971. A study of the ecology of pioneer lichens, mosses, and algae on recent Hawaiian lava flows. Pac Sci 25(1): 22-32.
Abstract:The ecology of pioneer lichens, mosses, and blue-green algae on some
recent Hawaiian lava flows was investigated quantitatively. Up to an elevation of at
least 3,000 feet, the major variables of the physical environment are rainfall, rock
texture, and sea breezes.
The lichen Stereocaslon vulcani, the most abundant and widespread pioneer
organism, shows a marked preference for regions of higher rainfall, but all species
of Parmelia and Cladonia, together with an unidentified crustose lichen, were found
only in areas of lower rainfall. The mosses and blue-green algae prefer relatively
humid regions, but Campylopus densifolius is able to grow in some areas that are
too dry to permit growth of Rhacomitrium lanuginosum,
Rough aa lava provides a more favorable substrate for Stereocaulon vulcani than
does the smoother pahoehoe, but this effect becomes less pronounced with increasing
rainfall. Thus, aa creates a more moist environment than does pahoehoe, probably
because its highly irregular, pitted surface is better able to trap and retain rainwater.
A possible contributing factor is the greater susceptibility of aa to chemical weathering.
On some lavas, lichens and mosses preferentially colonize seaward-facing rock
surfaces. This is ascribed to water vapor conveyed inland by sea breezes. Nutrients
in wind-borne ocean salts may play a secondary role.
The net effect of rainfall , rock texture, and, in some cases, sea breezes determines
the abundance and gross vegetative morphology of Stereocaulon vulcani, its ability
to gain a foothold , and the level of maturity which it can attain. The successfulness
of S. vulcani in colonizing lava can be ascribed to its ability to invade vesicles and
narrow recesses in the rock, its ability (or that of its associated microflora, or both)
to accelerate the chemical weathering of the rock, and its rapid rates of dispersal,
establishment, and growth. Under optimal conditions, S. vulcani spreads rapidly
over a fresh rock surface, and dominates the pioneer community, probably by
preempting space which might otherwise be occupied by slower-growing species.
In one particularly damp area, mosses and blue-green algae increase at the expense
of S. vulcani, In one exceptionally dry area, Stereocaulon is initially the most
abundant lichen on the aa flows, but it never attains maturity, and its numerical
importance is gradually superseded by that of Parmelia and Cladonia, which are
better adapted to dry conditions.
No evidence of "mat" formation was found. Vascular plants spring up in crevices,
while lichens, mosses, and algae occupy the intervening rock surfaces.
Appears in Collections: Pacific Science Volume 25, Number 1, 1971

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