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Altitudinal Gradient Distribution of Pteridophytes on Mt. Banahaw de Lucban, Luzon Island, Philippines
Abstract:
An altitudinal transect study of pteridophytes was conducted at the northeastern slope of Mt. Banahaw de Lucban. Ninety-three species representing 47 genera and 24 families were found in the study area, 15 percent of which were Philippine endemics. The most represented families were Polypodiaceae (11 spp.), Hymenophyllaceae (11 spp.), and Aspleniaceae (9 spp.) while the most represented genera were Asplenium (9 spp.), Lycopodium (5 spp.), and Selaginella (5 spp.). The pterido-flora of the mountain exhibited a strong Malesian floristic affinity.
Five altitudinal pteridophyte zones were proposed based on the results of cluster analysis and principal component analysis: (a) Zone 1: Cyathea contaminans – Dicranopteris – Nephrolepis – Diplazium patches from 700-800 masl; (b) Zone 2: Sphaerostephanos hirsutus var. hirsutus – Selaginella delicatula patches from 750- 900 masl; (c) Zone 3: C. philippinensis – Selaginella patches from 900-1,200 masl; (d) Zone 4: C. philippinensis – C. callosa – Asplenium cymbifolium – S. cumingiana patches from 1,200-1,550 masl; and (e) Zone 5 which was further divided into Subzone 5A (C. callosa – C. loheri – Hymenophyllaceae patches from 1,550-1,800 masl, and Sub-zone 5B (C. loheri – Cephalomanes apiifolia patches from 1,800-1,875 masl. These pteridophyte zones coincided with the woody species zones and differed significantly with the altitudinal fern zones of Mt. Makiling.
Species diversity gradually increased with elevation, reaching a maximum at 814-886 masl. On the other hand, species cover did not show any direct relationship with altitude. Majority of the fern patches sheltered all the pteridophyte height classes designated in the study. At least 85 percent of the pteridophyte species were preferential.
Stepwise multiple regression revealed that altitude and soil pH exhibit a linear relationship with pteridophyte species distribution. Altitude and soil pH influenced 65 percent of the variation in principal component 1 [PC1 = 0.0839 + 0.0010 (altitude) - 0.2072 (soil pH); r = 0.8058) and explained 27 percent of the variation in principal component 2 [PC2 = 2.0453 – 0.0005 (altitude) - 0.2560 (soil pH); r = 0.5206]. On the other hand, slope was found to be linearly related to species diversity, explaining 16 percent of the variation in H’ [H’ = 1.4928 + 0.0092 (slope); r + 0.3995]. The strong linear relationship expressed by pteridophyte distribution with elevation justified the designation of altitudinal pteridophyte zones.
Thirty-three species were restricted to one zone. The preference of many pteridophyte species to microenvironments that can be found along the altitudinal gradient qualified them as effective zone markers.