From April 25th to
30th, I visited the Moveclim monitoring plots on the island of La Palma,
Canaries, Spain. The collecting on the bryophytes has already mostly been done
a couple of weeks before, and so I joined the research team of Juana, Raquel
and Julio while installing data loggers and sampling the bryophytes at two
remaining sites.
Vanderporten et al. (2007) list 53 of fern species
for the Canary islands, of which about 35 may be found on La Palma. Within the
plots of the project, I found in total 13 species, of which Asplenium onopteris and Dryopteris oligodonta have been the most
frequent species and found in almost the half of the plots.
Figure 1 Photographs of selected plots from each elevation. Plot number and elevation is given.
Species richness trend
with elevation is as expected: at shady sites with Laurus canariensis, Ocotea foetens and other laurel species (monteverde) species richness is highest, creating the well known
hump around 800 m (see photos of
plots 400-1000 m in Fig. 1). This is also favoured by the fact that plots are
situated in a deep erosion gully (barranco)
with almost perennial running water. Towards lower and higher elevations, fern
richness, as well as number of individuals per plot is reduced
for similar reasons: drought. Below, at the hot and dry sites of the succulent
vegetation and at the transition to monteverde-forest
(photo from 50 m in
Fig. 1) with numerous Euphorbia-species
and Opuntia, and at the transition to
monteverde-forest (photo from 200 m in
Fig. 1) only drought resisting species like Adiantum
reniforme, Cheilanthes pulchella,
and Davallia canariensis could be
found sheltered between rocks in deeper shade. Above monteverde-forests, in Pinus-forests
(photos from 1400 m
and 1600 m in Fig. 1), increasingly thick carpets of pine needles up to 20 cm and
reduced ambient humidity prevent raise of most fern species, here as well
restricted to sheltered situations between rocks (Asplenium adiantum-nigrum, Cystopteris
diaphana) or as indicator after burning with subterranean rhizomes, Pteridium aquilinum susp. aquilinum (photo from 1400 m, with ca. 10-years-burned Pinus and Myrica faya). Asplenium adiantum-nigrum and Cystopteris diaphana are the only two
species found at and above treeline in open habitats, again only between rocks
in shrub-vegetation dominated by Adenocarpus
viscosus. Photos of most species
may be found in Fig. 3.
Figure
2 Photographs
of selected species from study plots. First row: Cheilanthes pulchella,
Adiantum reniforme, Davallia canariensis, Asplenium hemionitis,
Cystopteris diaphana; mid row: Dryopteris
oligodonta, Diplazium caudatum, Woodwardia radicans; bottom row: Asplenium onopteris, Polystichum setiferum,
Pteridium aquilinum.
References
Vanderpoorten, A., Rumsey, F.J., Carine, M.A. 2007.
Does Macaronesia exist? Conflicting signal in the bryophyte and pteridophyte
floras. Am J Bot 94:625-639.
