Redwood (Sequoia sempervirens) forests span six degrees of latitude in a narrow strip along California’s coast. From north to south, decreasing storm frequency and intensity as well as increasing fire return intervals promote a range of moisture availability, tree architectural complexity, and stand ages that translate into variation in habitat from an epiphyte’s perspective. In a previous study in the north, high lichen richness was associated with complex tree architecture, but redwood trees in the south were not considered even though they greatly extend one end of this gradient in habitat variation. Using climbing techniques to access the crowns of large redwoods, we surveyed epiphyte richness and abundance in the southern range of redwood. The primary objective was to understand how and why epiphyte communities change with latitude and with differences in tree architectural complexity. We expected that a southward decline in moisture availability combined with simpler tree architecture would drive a concomitant decline in epiphyte species richness.
Results/Conclusions
Compared to the north where epiphytic vascular plants and bryophytes comprised a substantial proportion of the species richness, communities in the south were dominated by lichens. Surprisingly however, lichen richness in the south exceeded richness in the north. This result suggests that habitat variation is less important for epiphytic lichen richness than climatic factors. The drier conditions in the south appear to favor lichens over bryophytes and vascular plants. Such a shift in community composition may represent a release in competition wherein climatic suppression of the larger vascular plants and bryophytes opens space for rich communities of smaller lichens that can tolerate relatively arid conditions. In addition, lichen species richness may be boosted along the California central coast by a convergence of northern and southern floras that together create relatively high species richness.