Hawaii is a hotspot for scientific research. My first encounter with research on the islands was a seminar on the diversity of endemic Hawaiian violets at Ohio University, and since then I've encountered people working on a wide variety of projects from leaf mining moths to the relationship between food web complexity and forest patch size. Naturally, I was excited to finally see the islands for myself. Between the native plants and animals, the petrogylphs, the clear night sky on Mauna Kea, and the eruptions on Kilauea I didn’t expect much opportunity for paleobotany, but plant fossils abound on the lava flows.
Hawaii is full of endemic species that evolved here over time. The Big Island is less than a million years old, Kauai is about 5 million years old, and the oldest seamount in the Hawaiian-Emperor chain is Meiji, about 82 million years old. As the islands formed and eroded, they were colonized by plants and animals from older islands and from the surrounding continents. Before people arrived, the diversity of plants and animals was determined by the balance between dispersal, successful establishment upon arrival, and in-situ diversification.
Chain of Craters Road at Volcanoes National Park crisscrosses the old lava flows as it winds down the mountain to the southern coast. At Lua Manu Crater, I photographed some of the different plants that have colonized the 1974 lava flow. We encountered only a subset of the plants that can tolerate the full sun and virtual absence of soil.
A casual glance at the surrounding forest serves to drive home the importance of establishment, rather than dispersal, as the limiting factor for building a new plant community on the lava flows. Seeds and spores easily reach the lava flows. Competition with other plants is hardly an important factor for the early arrivals, but the ability to tolerate the harsh abiotic conditions is paramount.
Right away we noticed the Stereocaulon lichens growing on the rocks. These are composite organisms made up of cyanobacteria, fungi, and a recently discovered yeast relative. The cyanobacteria component enables the lichen to photosynthesize and fix nitrogen from the air, while the fungus provides protection and helps obtain nutrients from the rock substrate. The role of the yeast will no doubt be revealed soon. Lichens are important on the lava because they promote weathering and soil formation on the lava flows; in fact, we found some mosses taking advantage of the incipient soils.
Several species of ferns peak out of the cracks and crevasses, including Nephrolepis exaltata (common sword fern), Sadleria cyatheoides (‘Ama’u), Pityogramma austroamericana (Gold fern), and Polypodium pellucidum (folded fern). The ferns start out as gametophytes which are small, heart-shaped thalloid plants only a few cell layers thick. Although they lack cuticle, many are desiccation-tolerant. The ability to survive drying out almost completely allows them to persist on the basalt between rains until the larger and more familiar fern sporophyte can become established.
Finally, there are the flowering plants. The largest and oldest individuals are Metrosideros polymorpha, a Hawaiian endemic tree in the same family as Eucalyptus and cloves. Dubautia ciliolate was also common and a fun one to see, as it is part of the silver sword alliance. The silver sword alliance is a group of about 50 species in the sunflower family that have diversified on the islands of Hawaii.
We also came across a few monocots, including the introduced grass Andropogon virginicus and this plant, which I haven’t identified yet.
As the lava flowed through the forest in 1974, it burned and buried nearly everything in its path, but when it encountered moist tree trunks, the lava cooled and insulated the trunks. The rest of the tree burned away in the extreme heat, and the resulting molds preserve the diameter and texture of the trees. Tree-holes now dot the landscape, and in some areas molds of palm fronds and various fruits are preserved.
As we continued to walk and take in the plants and rock features the clouds rolled in and it began to rain. So we continued down the road to the coast. With the low angle light of the late afternoon we took in the Pu'u Loa petroglyphs. Until next time!