A Mid-Elevation Woodland and Succession on the 1974 Flow


This site is organized by dividing it on three web pages.

The 1974 Flow

After walking about 150 yards through the forest, the trail ends as it encounters the 1974 flow.  You won't have a trail for the rest of your walk.  This should not be a problem if you observe a bit of basic orientation.

Start by turning left and generally following the margin of the intact forest staying about 100 feet out on the pahoehoe lava.  After walking about 200 feet you'll be well out on the 1974 flow and will be near some prominent tree molds.  Wander in this area to get a sense of the vegetation patterns and then make your way back to the highway back down the middle of the flow (turn left -- you'll be heading north).

The general layout of the flow can be seen in the panoramic photo below.

There is an extensive lava flow that is punctuated by "tree molds."  Scattered Metrosideros polymorpha (Hawaiian: `ohi`a) trees are common on the flow, ranging from tiny individuals in the cracks to individuals up to about 10 ft tall.  There are other shrubs and ferns, as well as lichens, on this flow.

Even though the woodland on this site was destroyed more than 20 years ago, evidence of the former large trees remains as slowly decomposing logs scattered about the lava flow.

Panoramic view of the tree-molds on the 1974 lava flow

The "tree molds" stand from a few feet to over 8 feet high.  They are the result of pahoehoe flowing through the forest and cooling when it wrapped around a tree trunk.  As the flow subsided and the level of the lava dropped, the lava around the trees was cool enough to remain standing.

The upper portion of the tree were killed although it is now thought that some of the roots may have survived.

The picture below shows a rare piece of charcoal resulting from the combustion of a tree trunk.  Generally, however, the molds are hollow with the tree having been completely burned or the charcoal simply having disappeared from the surrounding lava enclosure.  Such a hole make a fine refuge for new growth such as the swordfern (Nephrolepis sp.) shown in the picture below on the right.

tree mold
tree mold with charcoal trunk tree mold with fern
The smooth, hard surface of the pahoehoe makes a harsh environment for plant growth.  Where there are cracks, however, small plants may find a good place to grow.  Temperatures are more moderate in the shade, moisture may accumulate by running off the adjacent surfaces and organic matter is less likely to blow away.  If a plant can establish, it will contribute to the process of environmental change by further aiding in the collection of moisture, shading the substrate and contributing organic matter.

The plant growth will add to the process of substrate breakdown by the mechanical cracking of the lava as the plant roots grow outward.

Metrosideros polymorpha (Hawaiian: `ohi`a) are well adapted to this environment and are a common plant, even in the early stages of colonization.

Ferns are also common.  The fern below on the right is Sadleria spp. (Hawaiian: `ama`u).

Metrosideros polymorpha
fern Sadleria spp.
Dubautia scabra (Hawaiian: na`ena`e) is a common shrub on this recent lava flow.

The larger plants have rounded, mound-like shape.  The leaves are very shiny, appearing as though they are covered with wax.

You can see the tiny flowers in the picture below.  These develop into tiny seed-like dry fruits (below right). The tuft of bristly hairs on the fruit allows them to be carried considerable distances by the wind.

This plant contributes a lot of biomass to the litter.

Dubautia ciliolata
Dubautia ciliolata (flowers) Dubautia scabra
Litter breakdown is associated the common lichen, Stereocaulon volcani.

Although Stereocaulon can be found growing directly on lava, it is also found on leaf litter or large pieces of wood.  The two pictures below (the right one is a close-up view) show the slow process of decay of a tree branch that was killed at the time of the eruption.  Most of the large pieces of wood on this flow have Stereocaulon growing somewhere on them.

Stereocaulon volcani (on leaf litter)
Stereocaulon volcani (on dead branch) Stereocaulon volcani (on dead branch)
There are some invasive alien plants that are growing on this lava flow.  Two species of Rubus are found here, with the blackberry (Rubus argutus; Hawaiian: `ohelo `ele`ele) the most common (below left).  The yellow Himalayan raspberry (Rubus ellipticus) is found in one deep crack (below right).

Rubus argutus

Rubus ellipticus
The paintbrush plant (Castilleja arvensis) is a likely hemiparasite since it is always found on this flow growing alongside the native Dubautia scabra.

Castilleja is easily recognized by its bright pink terminal leaves.

Castilleja arvensis
Buddleia asiatica (Hawaiian: huelo `ilio) is common on this flow. The common name, dog tail, is very descriptive and is the translation of the Hawaiian name for this plant. Buddleia asiatica

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Last Updated: 07/31/02

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