Battling back invasives with jackhammers

HAWAII—Pu`u Wa`awa`a State Forest Reserve, about 15 miles northeast of Kailua Kona on Hawaii, the Big Island, contains some of the best remaining dry and mixed mesic (an environment or habitat containing a moderate amount of moisture) forest left in the Hawaiian Islands, but these forests have been degraded in the past through over-grazing and neglect. In 2016, Hawaii successfully competed for a $300,000 Landscape Scale Restoration grant funded by the USDA Forest Service that will ultimately result in restoring 1,000 acres of forest in this important watershed.

Pu`u Wa`awa`a, translated as the many-furrowed hill, is in the North Kona district and encompasses over 35,000 acres of land on the leeward side of Hawaii Island. It spans eight miles from an elevation of 6,500 feet to sea level at Kiholo Bay. One unique aspect of the management plan for Pu`u Wa`awa`a, says Dr. Elliott Parsons, the forest reserve manager, is that it follows the ahupua`a system, a traditional division of land extending from the high mountains down to the ocean, and will preserve the entire watershed from the mist-shrouded uplands to the coast. An area with a deep history, diverse biological features, unique geological formations and amazing, natural beauty, this ahupua`a is managed as both a state forest reserve in the mauka, or mountain, and a state park in the Makai, or coastal lands. The project location falls within priority areas identified in Hawaii’s Forest Action Plan for groundwater recharge, wildfire management, and conservation of native biodiversity.

Pu`u Wa`awa`a Forest Reserve is an area of high strategic importance for protecting watersheds and native ecosystems, as the area is host to at least 16 endangered plant species, 12 plant species of concern, an endangered insect (the Blackburn’s sphinx moth) and a variety of locally rare species. Restored upper elevation areas will serve as a climate-change refuge for plants that have historically occurred at lower elevations.

Photo: A man stands along a path and fence that stretches out to a distant cinder cone in Hawaii.
Dr. Elliott Parsons, with the newly constructed Aiea unit fence behind him. Forest Service photo by Abby Frazier.
Photo: A huge field and grassland area spotted with low, gnarly trees and a cinder cone and snow-covered mountain in the background.
Looking at the Aiea unit—the area we are protecting with the aiea fence. There are koa trees and ohia trees in the foreground and in the background is snow-capped Mauna Kea. Photo courtesy Elliott Parsons.

“This project is not just a reforestation project, but also a rescue operation for numerous plants and animals at risk of extinction from wildfire, drought and invasive species,” said Parsons, who is overseeing the project. “The 1,000 acres that will be protected and restored from this project will provide habitat for six native forest birds, an endemic hawk and owl, numerous cave-adapted species in the extensive lava tubes in the area, some of which are new to science, and a refuge for at least 18 endangered plant taxa, including three critically endangered trees that are found only in this region—Hibiscadelphus hualalaiensis, Zanthoxylum dipetalum tomentosum and Delissea undulata.”

Restoration of forest land in the state of Hawaii is a complex undertaking that often requires a series of steps be taken prior to new plants being established:

  • Areas to be restored must be fenced and all invasive ungulates (e.g., wild pigs, goats, and sheep) removed to allow the native plants to re-establish, allow soil cover to improve and prevent the spread of invasive plants.
  • Non-native invasive plants are removed or at least reduced in number from inside these fenced areas.
  • Native plants can then be out-planted and maintained.
  • On the dry side of the Big Island, wildfire prevention is also needed; fuelbreaks have been created along the new fencelines and fire road access is maintained.

The restoration at Pu`u Wa`awa`a involves many partners, including Hawaii Division of Forestry and Wildlife, Three Mountain Alliance Watershed Partnership, Hawaii Island Natural Area Reserves System and federal agencies. This has allowed Forest Service funding to be leveraged by over 2 to 1.

As of the end of 2017, over two miles of enclosure fence has been completed under the grant while about 1.5 miles is in the process of being built. These fences will eventually enclose about 1,000 acres in two units, the Henahena and Aiea units. The construction of these fences is tough and slow work, as much of it is built over lava rock, which is where jackhammers come in—they are needed to set the fence posts and fencing anchors. Aerial surveys and motion-sensing camera traps have already been used to determine numbers, distribution and patterns of movement of non-native animals in the area.

Workers have also begun removing non-native invasive plants, including more than 125 silver oak trees, Grevillea robusta, from the Aiea unit. In addition, aerial surveys have been completed over both units to map other non-native plant species.

The Pu`u Wa`awa`a Forest Reserve has an on-site nursery where plant seedlings are grown from seed collected on the rserve and nearby. This nursery is being used to propagate both rare and endemic plants that will be planted into these two units. Rare plant surveys will be conducted within the units after the fence is completed to establish a baseline of existing rare plants. In the meantime, seeds are collected and plants are grown for outplanting elsewhere in the Reserve. By the end of 2017, 4,800 plants were propagated from 44 different native Hawaiian plant species for outplanting at Pu`u Wa`awa`a.

The restoration in progress is already an impressive change to see. Work is ongoing, but the ahupua`a system is alive and well in Hawaii!

Two men use a jackhammer to cut into lava rock. Two steel pipes already sticking out of two holes.
Crew installing pipe posts for braces for the Henahena Fence. Nāpu`u Conservation Project’s Jupiter Crosson and Justin Yeh using the rock drill to make holes for posts. Photo courtesy Kealaka`i Knoche, Pu`u Wa`awa`a field crew leader.
Photo: A fence divides two areas. One side has been restored, the other has not.
The fence contrasts an area on the left already undergoing restoration and the area on the right that will begin to be restored once the fence is in place. Forest Service photo by David Bakke.