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.
Juergen Kluge, University of Marburg (Germany)
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.
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.