A Tale of Two Tracts: Success Stories of Restoration on Slopes of Haleakala

posted in: Forests, Invasives, March 2014 | 0
The Nature Conservancy’s Waikamoi Preserve in east Maui has been mostly free of feral pigs and goats for the last two decades. But what has that meant for the native vegetation on the high slopes of Haleakala?
In 2008, four researchers – Guy Hughes and Eric Brown, with the National Park Service’s Kalaupapa National Historical Park, and Alison Cohan and Mark White, with TNC – set out to determine how conditions on the ground had changed since 1994, roughly when the ungulates were removed, by retracing transects that were established then as a kind of “before” baseline.

On the opposite, leeward side of the mountain, over roughly the same period, hundreds of volunteers led by the indefatigable Art Medeiros worked to restore native vegetation on a small, four-hectare tract of what had once been a species-rich dry forest, reduced to mostly non-native grass cover by more than a century of grazing.

In 2012, Medeiros, with the USGS’ Pacific Island Ecosystems Research Center on Maui, and Erica von Allmen and Charles Chimera, with the Pacific Cooperative Studies Unit of the University of Hawai`i, compared vegetation on the area where the restoration activities occurred to that on a control area, which was nearly identical in vegetation at the time the restoration work began in 1997.

The results of the two research efforts were published in the January issue of Pacific Science. And, at a time when news from the frontlines of environmental management is generally pretty grim, the two articles are a welcome beacon of hope.

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At Waikamoi, Removing Pigs,
Goats Makes All the Difference

High on the windward slopes of Haleakala, an area of 428 hectares has been transformed. At the lower elevations, the landscape is characterized by a rainforest, but as the elevation increases, rainfall declines. At the higher elevations, at the time the baseline transects were established, the vegetation was characterized as subalpine shrubline shifting to a grassland, dominated by non-native species, in the highest regions.

There was no effort to replant species or manage the area in any way other than through the removal of the feral animals. Yet the landscape changes were dramatic. As the authors write, “we observed a consistent pattern of change on two parallel transects established within a fairly homogeneous subalpine habitat during a relatively short time scale, suggesting that the vegetation community was shifting to an assemblage with a higher abundance of native flora.”

They suggest three reasons for the shift: first, the release of native species, mosses, and woody species “from severe feral animal disturbance;” second, “the replacement of grass vegetation groups with native shrub, native fern, and lichen groups;” and, third, “relatively drier subalpine conditions” in 2008 than existed in 1994. The first and second reasons are directly related to the absence of the ungulates.

As to the third, they write: “Under increasingly dry conditions, one might have predicted a reduction in lichens and bryophytes rather than increases. However, we documented an increase in lichens and bryophytes by more than 300 percent… suggesting that the changes are likely attributable to ungulate removal.”

As the lichens and mosses moved into higher elevations, the non-native grasses declined, with grass cover being halved during the study period while “native ferns increased significantly, and native shrub cover tripled.” In the lower-elevation forested habitat, the authors found, mosses increased in both the understory and upper layers of the forest.

Their conclusion? “Feral animal removal was effective in promoting native habitat recovery and is recommended as a recovery program strategy that should be prioritized in the largely native areas with a limited presence of invasive alien plant species.”

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Intensive Management
Pays Off at Auwahi

At Waikamoi, managers had a lot to work with. Although the native landscape had been altered by goats and pigs, the most severely degraded areas were adjacent to a relatively intact native ecosystem, which allowed them to be repopulated with native plants naturally.

At Auwahi, on the other hand, the study site was nowhere near anything that resembled a native forest – and had been that way for decades. By the 1960s, the authors note, 95 percent of the Auwahi dry forest had been destroyed. Auwahi had become “a museum forest (i.e., a high-diversity forest lacking recruitment).”

Private landowner Haleakala Ranch attempted to protect the remaining forest by fencing out ungulates – “which unfortunately accelerated kikuyu grass growth and increased tree mortality… and minimal conservation benefit was realized.”

In 1997, Medeiros and his volunteers and colleagues began what is described as “a multiphased restoration effort” – removal of ungulates, suppression of kikuyu grass with herbicides, and the mass planting of `a`ali`i (Dodonea viscosa) on four hectares. The `a`ali`i was to function as a nurse plant: hardy, easy to propagate, and quick to grow, it could provide a sheltering habitat for later plantings of rarer species.

Fifteen years and countless volunteer days later, the difference between the managed tract and the control area was dramatic. In the managed tract, ground cover from non-native grasses was reduced 73 percent. Cover from native species had increased by nearly 58 percent. Vegetation in the control area, meanwhile, was unchanged.

What’s more, some of the rarest dry forest species had begun to reproduce on their own in the restoration site. Among those was `aiea (Nothocestrum latifolium Gray). In 2012, the authors note, “two wild Nothocestrum latifolium seedlings were discovered … distant from mature Nothocestrum individuals, apparently the result of seed dispersal by birds, likely the non-native Zosterops japonicus (Japanese white-eye). Though modest, this recruitment represents the only currently known natural regeneration of the species,” which is the sole native host plant for caterpillars of the endangered Blackburn’s spinx moth (Manduca blackburni).

Unfortunately, one non-native tree seems to have taken advantage of the same conditions that favor the natives: the tree poppy,Bocconia frutescens. “Although most non-native species declined dramatically,” the authors write, the tree poppy recruitment was higher than it was in 1997 and also in the control area. “As such, weed control in the restoration area … is currently devoted predominantly to Bocconia…. These results demonstrate the vulnerability of even relatively restored ecosystems to non-native woody species such as Bocconia with the ability to recruit seedlings in shaded or semishaded sites.”

Along with the need to control weeds is the ongoing requirement to keep out the pigs. The authors relate an incident in 2010 that illustrates the pigs’ predilection for the most endangered plants: that year, “two juvenile feral pigs entered the restoration site, their smaller size allowing entry through perimeter fence mesh (since repaired). Before their removal, the pigs apparently searched for and destroyed the entire outplanted population of approximately 100 established Vigna [Vigna o-wahuensis] while minimally impacting other plant species. The pigs excavated the plants, consuming all parts including roots.” Still, two years later, “24 newly emerged Vigna seedlings were recorded in count plots (all near original plantings).”

The Hawaiian dry forest is one of the most imperiled ecosystems and, “without development and implementation of appropriate management strategies,” the authors write, “remaining Hawaiian dry forest will likely disappear within the next century.” But the multiphased approach to restoration of degraded areas “offers one strategy to conserve and restore tracts of dry forests in Hawai`i and perhaps elsewhere,” they conclude.

For Further Reading

See the articles in the January 2014 issue of Pacific Science (Volume 68, Number 1):

“Subalpine Vegetation Change 14 years after Feral Animal Removal on Windward East Maui, Hawai`i,” by Hughes et al.

“Dry Forest Restoration and Unassisted Native Tree Seedling Recruitment at Auwahi, Maui,” by Medeiros et al.

 

 

Volume 24, Number 9 March 2014

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