4. The Distribution of Epiphyllous Lichens in Kitchener Park.
Epiphyllous lichens have been observed on the following species: Hymenophyllum demissum, H. scabrum, Dicksonia fibrosa, Cyathea dealbata, Polystichum vestitum, P. Richardi, Dryopteris decomposita, D. pennigera, Asplenium adiantoides, A. lucidum, A. bulbiferum, A. flaccidum, Blechnum procerum, Pellaea rotundifolia, Histiopteris incisa, Pteridium esculentum, Polypodium pustulatum, P. diversifolium, Cyclophorus serpens, Podocarpus totara, P. spicatus, P. dacrydioides, Astelia nervosa var. sylvestris, A. Solandri, Earina mucronata, Dendrobium. Cunninghamii, Loranthus micranthus, Beilschmeidia tawa, Melicope simplex (uncommon), Alectryon excelsum, Melicytus micranthus, Metrosideros Cobensoi, M. perforata, M. hypericifolia, Myrtus bullata, Nothopanax anomalum, Pseudopanax crassifolium, var. unifoliolatum, Olea Cunninghamii. A number of species, e.g., Rhipogonsum scandens, Myrtus obcordata, and various ferns, have been observed with Phycopeltis tropica, but with-
out lichens. Thus, of the 140 species found in the forest 38 are found to bear lichens. The following species usually bear them in abundance: Podocarpus totara, P. spicatus, P. dacrydioides, Earina mucronata, Beilschmiedia tawa, Alectryon excelsum, Metrosideros Colensoi, Myrtus bullata, and to these especial attention was directed, though many of the others, were often well covered. Theloschistes flavicans occasionally occurs on the leaves of Alectryon excelsum, Podocarpus spicatus and other species, but is not a typical epiphyllous lichen, and is not here further dealt with.
The following data concerning the species attacked are of interest—
(1) Habitat:—14 plants of the forest-floor are attacked, 21 of the shrub-layer, 15 of the tree-layer.
(2) Growth-form:—There are 17 ferns (5 small, 6 medium, 6 large); 2 tree-ferns; 14 shrubs; 2 semi-woody plants; 3 lianes; 7 trees (which may also be attacked in the shrub-stage).
(3) Leaf-size:—22 bear small leaves or leaflets, 11 medium, 5 moderately large.
(4) Leaf-texture:—2 are very thin, 13 thin, 18 rather thick, 5 thick.
(5) Upper leaf-surface:—26 are smooth, of which 5 are more or less glossy; 12 are very slightly rough. All are glabrous, or practically so, when mature.
(6) Leaf-apex:—None possess distinct “drip-tips.” In plants not affected only 1 can be said to possess a true “drip-tip.”
(7) Frequency of attack:—5 are rather rarely attacked, 14 occasionally, 9 frequently, 10 commonly. The most common species of lichen is Lopadium subcaerulescens, attacking 31 species. L. Allanii may be more abundant than is at present known. Not only are many species attacked, but many leaves may be almost completely covered by the lichen, especially in Beilschmiedia tawa and Alectryon excelsum. Strigula africana appears to be confined to B. tawa and A. excelsum, but on both may be very plentiful. Bacidia spp. appear to be confined to the podocarps, and Phylloporina spp. to the Myrtaceae.
The following tentative conclusions seem worthy of record as providing working hypotheses and a basis for further record:—
(1) The habitatal requirements of epiphyllous lichens must be considered in two groups— (a) the conditions offered by the leaves themselves, including their life-history, physical, anatomical and constitutional features: (b) the outer environmental factors, especially intensity of light, wind and humidity.
(2) The species of supporting plant is not purely accidental, though certain lichens have a wider range of hosts than others. This may not apply to Fitting's third group. The incidence of the species Physcia at Kitchener Park appears to depend on a moderate degree of humidity, moderate shade, and relatively persistent leaves on the host plant. But species otherwise favourable to lichen development may be free owing to an unfavourable outer environment, e.g., Myrtus bullata is free if the insolation is too strong. Certain genera with apparently suitable leaves do not appear to develop lichens, e.g., Hoheria, Griselinia, Pittosporum, Coprosma, Rhipogonum. The reason may lie in their constitutional characters.
(3) Leaves of relatively short-life may be attacked, but for full development of epiphylls a certain persistence is required. Leaves of Alectryon excelsum and Beilschmiedia tawa often show light attack by Strigula africana towards the end of the first growing season, this being as true of seedlings as of adult plants. The leaves are more and more covered till at leaf-fall, which does not appear to be hastened, the surface may be completely covered. The lichen may fructificate on dead, fallen leaves where the ground is dry. A considerable degree of humidity favours the early establishment of lichens. This is aparently especially important in filmy ferns, lichen-attacked leaves being first more or less covered with bryophytes.
(4) The lichens appear to inflict little real damage, as seedlings survive and older trees appear to be as vigorous as those free from attack.
(5) Great wettability of surface does not appear to be required, nor is a ready run-off of water of any moment.
(6) A certain optimum of light-intensity is required for full lichen-development. Leaf-lichens are very rare in the deepest shade, and in the fullest sun, with marked development in moderate shade. This is seen well in plants of the forest floor, and in leaves of the shrub-layer. As the tree is ascended the lichen development decreases to the vanishing point. Juvenile Nothapanax crassifolium is generally strongly attacked, while the adult is rarely so. There is in general a distinct belt of major attack.
(7) Considerable humidity favours attack. Margins of pools in the forest-interior show a more or less marked lichen girdle. Shade and humidity tend to be associated, but humidity cannot prevail over the effect of deep shade.
(8) Strong wind is apparently prejudicial to lichen attack, but its effect is not always easy to disentangle from that of insolation. As a result of both factors, marginal plants are less attacked than those more protected.
(9) The epiphyllous lichens form more or less distinct communities, this being aided apparently by the different environmental requirements of the lichens. Humidity favours Lopadium, and shade with less humidity Strigula. Leaves subject to much drip from above will be covered with Lopadium. Bacidia appears on juvenile leaves of podocarps in the shrub-layer, associated with Lopadium. L. sub-caerulescens is the most frequent lichen on Beilschmiedia tawa, and may form pure communities. Strigula africana may also form pure communities on B. tawa, but where the two lichens occur together S. africana is dominated and suppressed. On Alectryon excelsum Strigula africana is much the more common lichen, but here too it may be suppressed by L. subcaerulescens.
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