For a few years, questions about the impacts of climate change were hypothetical. Supposing the predictions are true, what then?
After a while, the nature of the questions shifted: What can be done now to mitigate the effects of climate change when it comes?
This year, at the annual Hawai`i Conservation Conference, held last month in Honolulu, the questions are not hypothetical. They’re not phrased in the future tense. They are immediate: How do we deal with the impacts of climate change that are beginning to be seen already in Hawai`i’s ecosystems?
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Silverswords at the Limit
Paul Kruschylnecki, of the University of Hawai`i’s College of Tropical Agriculture and Human Resources, has been counting silverswords on Haleakala for years, following on regular censuses of selected areas taken since the 1980s. “In most respects,” he said in his conference talk, “this is thought to be a conservation success story.” From a point in the 1920s where only a few plants remained, he noted, there was “dramatic recovery, mostly through management actions,” with the number of plants growing as the number of browsing animals shrank. “It was a great story,” he said.
But it may have been fiction. Starting in the 1980s, researchers began to look more closely at the status of silverswords in plots established by Lloyd Loope and, later by Don Drake. “The trend is all downhill,” Kruschylnecki said. “Healthy plants shrink and die without flowering.”
“Then we began looking at the climate: the mean annual temperature, annual rainfall, et cetera,” he continued. “Right now, the most important thing correlating with growth rates is the amount of rain in the dry, summer season.” Work by University of Hawai`i geography professor Tom Giambelluca predicts “a slight increase in the number of zero-rain days” over the course of the year as a likely consequence of climate shift, Kruschylnecki said, with most of those days occurring in summer months.
“But a large part of the silversword range wasn’t represented” in the established plots, he continued. “We wanted to find out how representative the trends are, so last year, we censused additional ranges, measuring the ratio of live to dead plants, the population size and structure, the degree of shrinkage in the plants. Ultimately, we hoped to see if there were patterns with either elevation or precipitation.”
The percent of the live population correlated well with elevation: the lower the elevation, the lower the percentage of live silverswords. “It was a dramatic difference,” he said, although there were a few outliers.
“So we tried to explain the outliers. In the process of collecting more data, it became obvious that there were differences in the outlier populations, very specific differences.” In some cases, the lower-elevation plants that were doing well were in an area where there was a lot of other vegetation, even moss, suggesting the presence of a seep at the bottom of a cinder cone. Elsewhere, the healthier plants were growing at the base of a rock outcrop that was capturing the moisture in fog and making it available to the plants. “Probably these are the reasons these particular populations are doing better than others at the same elevation,” Kruschylnecki said.
Overall, the pattern indicates that most populations, across the silversword’s entire range, have been declining over the last seven to 14 years, with the decline greater at lower elevations, he said.
“If the trend continues, silversword distribution is moving upslope, exactly what you would expect. It’s not really a surprise, but it still had us scratching our heads as to why this was occurring,” he said. “We don’t know yet, but we have a couple of working ideas.”
First, he said, “higher temperatures exacerbate water stress” at lower elevations. Also, it’s possible that drought tolerance might increase with elevation; “we don’t think this is the main thing, but it could contribute. It’s something we’re investigating,” he said.
“So, is climate change impacting silverswords? Yes, we think so, but we would like more information: better data on wide population trends, understanding why plants are dying, patterns in mortality, and what will happen with the trade wind inversion,” he said.
“We’re talking about silverswords, but that’s not the only life form in this area. There are endemic herbivores, predators, and pollinators. And while it seems in some areas that silverswords are the only plants, a lot of other plants make up alpine and subalpine vegetation. These other plants might be suffering the same effects, but we just don’t have the data yet.”
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Birds Are Losing Sanctuaries
Eben Paxton of the U.S. Geological Service’s Pacific Islands Ecological Research Center (PIERC), presented the results of work that he and numerous colleagues from half a dozen other agencies and institutions have been doing on the effects of climate change on Hawai`i’s forest birds.
Paxton noted that avian malaria has resulted in forest birds being restricted to high-elevation forest refuges, away from the mosquitos that carry the disease. “In areas of high-elevation forest,” he noted, “we have a full complement of forest birds. In mid-elevation forests, disease is episodic. We have some birds, but not the full complement. At low elevations, there’s rampant disease, little native forest, and few forest birds.
“Conservation efforts have focused on protecting high-elevation refuges. Unfortunately, global warming threatens these refuges and facilitates mosquitoes moving up in elevation.”
The result? “Birds will be squeezed into an increasingly narrow band of forest, and fifty to 200 years from now, disease will be in all forest refuges.”
The loss of disease-free sanctuaries challenges status quo management, he said, posing a problem “with no apparent solution. … Issues are complex, our knowledge is incomplete, and the scale of the problem is daunting. But actions are needed now to keep one step ahead of the threat.”
PIERC’s Andrew McClung discussed the prospect of establishing new populations of the Laysan duck and Laysan finch. Until recently, the home range of these birds amounted to little more than one and a half square miles of low-lying land, prone to inundation by storms, tsunamis, and eventual sea-level rise.
Beginning in 1967, individuals from both species were translocated to Pearl and Hermes atoll; three of four populations there have been lost, however – most recently during the March tsunami. In 2004 and 2005, Laysan ducks were shipped to Midway. There, the 40 initial founders have grown to 400 birds, where “they seem to be doing well,” Paxton said, “but are vulnerable to disease risk, storms, and tsunamis.” He also noted that the mean elevation of these translocation targets is lower than that of Laysan itself, making inundation of their habitat even more likely.
To maximize the species’ chances of survival over the next century, management options might include such things as “floating islands” (anchored decommissioned ships, for example) or construction of seawalls. However, long-term, “both species will eventually require higher elevation refugia with a low predation risk,” Paxton said.
Black-footed albatross are larger and longer-lived than either the Laysan duck or the Laysan finch, but they face similar problems, as Beth Flint, of the Fish and Wildlife Service, and Crystal Krause, of PIERC, pointed out in their talk. “The entire world population of black-footed albatross is found only on 28 square kilometers,” Flint noted, and 95 percent of the breeding population nests in the Northwestern Hawaiian Islands. There is a small population of black-footed albatross in Japan, she said,
but 95 percent of the population nests on the low islands in the Hawaiian archipelago. In addition to sea-level rise and habitat loss, the birds “face a lot of other threats,” Flint said, including interaction with fishing gear, invasive vegetation, and land-based contaminants.
This year alone, two-thirds of the black-footed albatross chicks were lost in the two severe winter storms and the March tsunami. “Not only do nests get washed away,” Flint said, “but the actual topography of the land is changed. Land is cut away, and large areas of habitat are erased.”
Apart from the direct effects of storms, changes in ocean chemistry resulting from global warming may also pose threats to the species, Flint said. Ocean acidification and increased average temperatures on the coral and algae reefs that create the islands where these animals nest “are difficult to predict and quantify,” Flint said, but will still have an effect. “We anticipate we’re going to be losing habitat for the black-footed albatross,” she said.
Krause described a range of actions that emerged from a workshop on management strategies to protect the birds. While management of existing colonies, including the removal of vegetation interfering with nesting, should continue, other approaches might be more difficult. Translocation to higher islands may be difficult, she said. Albatross are philopatric – they return to the same nest site year after year. Also, the presence of possible predators of ground-nesting birds on higher islands would need to be addressed.
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FFS Seabird Sites All But Vanish
With A Two-Meter Sea Level Rise
From the mountains to the sea, Hawai`i’s native birds will suffer as a result of climate change. A warmer climate will shrink the disease-free zone for native forest birds, pushing them to higher elevations. And according to a conference poster by scientists with the U.S. Geological Survey and the U.S. Fish and Wildlife Service, it will also force the 17 seabird species that nest in the low-lying Northwestern Hawaiian Islands at French Frigate Shoals (FFS) to crowd onto ever smaller spits of sand.
The authors — Crystal Krause, Jeff Hatfield, Michelle Reynolds, and Karen Courtot — note that erosion has already significantly reduced nesting habitat at FFS. For example, at Tern Island, nearly two hectares have been lost to erosion since 1942.
But with a rise in sea level as a result of climate change, some of the smaller islands at FFS will all but disappear by 2100. Research suggests that sea level may rise up to two meters by the end of the century, leaving little room at Tern, which has a maximum elevation of 3.37 meters, and none or next to none at Disappearing, Shark, East and Gin islets, which are roughly two meters high.
With a two-meter rise, not including wave run-up, Shark islet (0.31 hectares) disappears completely, East and Gin islets shrink to 0.03 ha, Disappearing (0.37 ha) shrinks to 0.01 ha. Tern, which has about 13.57 ha of seabird habitat, would have 11.67 ha left.
Even a one-meter sea-level rise (SLR) would cut the land at Disappearing islet to less than a tenth of a hectare and would reduce the dry land at Gin by about 50 percent.
“Seabird nesting habitat in FFS is vulnerable to even modest levels of SLR,” the poster states. “The seawall at Tern Island may prevent massive inundation from sea-level rise before 2100, however, portions of nesting habitat left unprotected by the sea wall are vulnerable to SLR. If wave run-up were included, more extensive inundation could occur.”
(This was illustrated in another poster, by Paul Berkowitz of UH-Hilo and Curt Storlazzi and Reynolds of the USGS. They demonstrated that at Laysan Island, inundation areas increase exponentially when wave run-up is incorporated into sea-level rise calculations. For example, the inundation area at Laysan with a two-meter rise in sea level goes from 15.5 ha to 58 ha when run-up is included.)
The potential result of sea-level rise may be an “atoll-wide shortage of nesting habitat for seabirds utilizing all habitat types,’ the authors write. “FFS shrub habitat occurs almost exclusively at Tern Island [and] continued shoreline erosion threatens scarce shrub habitat for the black noddy, great frigatebird, red-footed booby, and white tern.”
They suggest that resource managers can use inundation projections to anticipate vulnerable areas. Continuing efforts to increase nesting habitat (i.e., planting vegetation, adding artificial nesting structures, maintaining the seawall at Tern) is critical as shoreline habitat is lost, they write.
A related poster by Reynolds, Hatfield, Krause, Paula Hartzell, and Elizabeth Flint notes that for the great frigatebird, the red-tailed tropicbird, and the gray-backed tern, populations have already reached Tern Island’s carrying capacity.
“A shortage of nest sites may either simply prevent some pairs from breeding, or in some cases, actually reduce the reproductive success of birds that do breed. Species that are already at carrying capacity or exhibit strong density dependence are likely to be the first to respond negatively to small changes in habitat loss due to sea-level rise caused by climate change,” they write.
Patricia Tummons and Teresa Dawson
Volume 22, Number 3 — September 2011