Ferns exhibit a widespread distribution, with their highest diversity found in tropical regions and their lowest in Arctic areas. Tropical rainforests, in particular, are home to the greatest concentration of fern species. New Zealand, a country where the fern holds symbolic significance, boasts approximately 230 species, dispersed across its diverse landscapes. Ferns are also a common sight in European woodlands.
Key Insights
- The biogeographical distribution patterns of ferns and angiosperms are shaped by a combination of vicariance and long-distance dispersal. However, due to their more efficient spore dispersal, ferns are more commonly subject to the latter. As a result, fern species often have broader geographical ranges, and the relative diversity of ferns compared to seed plants is particularly pronounced on remote, mountainous tropical islands, such as Hawaii and the Mascarenes. Furthermore, fern communities across continents tend to exhibit greater compositional similarity than those of seed plants.
- Despite their capacity for long-range spore dispersal, many fern species exhibit localized distributions. This is due to the infrequent success of long-distance dispersal, habitat specialization, geographical isolation, and competitive interactions among species.
- Fern species richness follows a distinct latitudinal gradient, peaking in the tropics, where ferns thrive in abundance, particularly in moist habitats with moderate temperatures at elevations between 1000–2500 meters. Species in tropical mountain ranges generally exhibit elevational amplitudes of approximately 1000 meters. Notably, the peak of endemic species is found at higher altitudes than the peak of species richness.
Ferns occupy a wide array of habitats, ranging from remote mountain summits to arid desert rock faces, bodies of water, and open meadows. In general, ferns tend to be specialists in marginal environments, often flourishing in locations where environmental conditions limit the success of flowering plants. Some fern species, such as bracken fern in the Scottish Highlands or mosquito fern (Azolla) in tropical lakes, are notorious for their aggressive, widespread colonization. Ferns can be found in four primary habitat types: moist, shaded forests; crevices in rock faces, particularly those shielded from direct sunlight; acidic wetlands such as bogs and swamps; and tropical trees, where a significant portion of species are epiphytes (approximately a quarter to a third of all fern species).
Epiphytic ferns, in particular, host an astonishing variety of invertebrates. It is estimated that bird’s-nest ferns alone may harbor up to half of the invertebrate biomass within a hectare of rainforest canopy.
Many ferns rely on symbiotic relationships with mycorrhizal fungi. Additionally, some ferns are highly selective in their habitat requirements, thriving only within specific pH ranges. For instance, the climbing fern (Lygodium palmatum) of eastern North America prefers intensely acidic, moist soils, whereas the bulblet bladder fern (Cystopteris bulbifera) is restricted to limestone-rich environments.
Ferns’ spores are rich in lipids, proteins, and calories, making them a food source for various vertebrates. The European woodmouse (Apodemus sylvaticus) has been observed consuming the spores of Culcita macrocarpa, while both the bullfinch (Pyrrhula murina) and the New Zealand lesser short-tailed bat (Mystacina tuberculata) also feed on fern spores.
