# Volcano Watch — Native ohia lehua tree closes its pores to volcanic pollution

March 31, 2005

The past week marked the celebration of the 42nd annual Merrie Monarch Festival on the island of Hawaii. Throughout the seven-day cultural event, participants and spectators can be observed wearing beautiful lei, many created with native Hawaiʻian plants.

Particularly notable are lei incorporating the striking yellow, orange or red lehua blossoms of the ohia lehua tree, and its reddish colored young leaves, or liko lehua. Another often-used plant, the aalii, produces colorful seed capsules that enhance the fullness of a braided or wrapped lei (lei haku or lei wili).

An interesting scientific discovery was made regarding these two species of plants during the early years of the festival. In 1979, during Kīlauea's brief (40-hour) upper east rift zone eruption at Pauahi Crater, researchers examined the effects of volcanic fume on the adjacent forest stand. They found that the ohia lehua (Metrosideros polymorpha) and the aalii (Dodonaea viscosa) varied greatly in their susceptibility to sulfur dioxide. This is the primary noxious gas in the Kīlauea plume and the main contributor to volcanic pollution, known locally as vog. While sulfur dioxide gas is known to injure foliage, the researchers found that the ohia lehua has developed a clever adaptation to minimize injury.

In contrast to the delicious Hawaiʻian plate lunches that are available to festival-goers, plants use water, carbon dioxide, and light energy to make carbohydrates through photosynthesis for their nourishment. Carbon dioxide enters the plant's leaves through pores in the leaves' waxy outer surface. These pores are aptly named stomata, after the Greek word for "mouth." When the stomata are open, gases diffuse into and out of the leaf, while closed stomata inhibit gas exchange.

In examining plant communities downwind of the eruptive vent, researchers found that visible injury diminished with increasing distances. SO<SUB>2</SUB> concentration also decreased downwind as the plume dispersed and was diluted. The pattern of injury for aalii was typical of about 20 other species abundant in the area. Most of the plants were severely injured or dead 50 yards from the eruptive vent, while approximately 1 mile downwind, there was no sign of dead or even yellowing leaves.

In contrast, mature leaves of the ohia lehua exhibited no symptoms of damage, even close to the vent. The leaves showed more stomatal closure when exposed to higher concentrations of noxious sulfur dioxide gas. Young ohia leaves, however, were severely injured close to the eruptive vent, with the few survivors showing only partial stomatal closure.

The stomata in the aalii leaves did not close at all in response to sulfur dioxide, and the plants were severely injured by exposure to high concentrations of the pollutant. However, new leaves of this tenacious plant resprouted quickly after the damage, enabling recovery.

SO<SUB>2</SUB> concentrations between 0.1 and 1 ppm are known to cause rapid changes in the stomatal opening for a wide range of plant species. This is an important adaptation, since many plants are exposed to man-made sulfur dioxide pollution. The exposures for the ohia and aalii studied in the natural volcanic environment of Hawaii, ranged from less than 1 ppm to greater than 100 ppm SO<SUB>2</SUB>.

Recently, increases in the gas emission rate from Kīlauea, in combination with a lack of trade winds, has caused high concentrations of SO<SUB>2</SUB> in areas of East Hawaii. Last Saturday, during a particularly notable event, SO<SUB>2</SUB> concentrations reached nearly 3 ppm at Hawaii Volcanoes National Park Visitor Center.

While some residents reported discomfort, and certain exotic plants showed signs of stress and burned leaves, this brief event caused little impact to native forest plants. Evolving in a volcanic environment has engendered creativity in endemic plant adaptations, at the same time it allows us all to enjoy the beauty of these plants, especially during Merrie Monarch week.

### Volcano Activity Update

Eruptive activity at Puu Oo continues. The Puu Oo crater camera is offline for repair.

The PKK flow continues to produce substantial breakouts from atop Pulama pali to the coastal plain. Open lava channels have been visible intermittently on Pulama pali and on the west and east branches of the PKK flow. Lava is currently entering the ocean at four areas. Highcastle, East Laeapuki, Kamoamoa, and Kailiili entries are about 3.7 km (2.3 miles), 4.9 km (3 miles), 5.3 (3.3 miles) and 7.5 km (4.7 miles), respectively, from the ranger shed on Chain of Craters Road. Expect a 1.5- to 2-hour walk each way to the nearest entry at Highcastle. Stay well back from the sea cliff, regardless of whether there is an active ocean entry or not. Heed the National Park warning signs.

During the week ending March 31, three earthquakes were felt on Hawaii Island. A magnitude-2.4 quake occurred 15 km (9 miles) northeast of Waikii at a depth of 15 km (9 miles) at 9:44 p.m. on Monday, March 28; it was felt at Kamuela. A magnitude-2.7 earthquake occurred 12 km east of Holualoa (Hualālai) at a depth of 29 km (18 miles) at 10:11 a.m., also on Monday; it was felt at Kalaoa. Another magnitude-2.4 quake occurred 5 km (3 miles) southeast of Kīlauea summit at a depth of 25 km (15 miles) at 7:19 a.m. on Wednesday, March 30; it was felt in Volcano village.

Mauna Loa is not erupting. During the week ending March 30, seven earthquakes were recorded beneath the summit area, only one of which was deep and long-period in nature. Inflation also continues beneath the summit.