Annual Vitousek Gathering in Hilo: Like ‘Drinking from a Fire Hose’

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The lecture hall at the University of Hawai`i at Hilo was packed to the rafters for two days in June. Under the direction of Stanford University’s Peter Vitousek, one of the foremost figures in the study of Hawaiian ecosystems, around 200 researchers, scientists, and students had come together, as they have for more than 20 years, to hear short synopses of some of the cutting-edge research being conducted on the land, under the sea, and in the air enveloping the Hawaiian archipelago.
And short means very short. No one was allotted more than 10 minutes, with most having just five in which to describe their work. Vitousek himself was the timekeeper, making sure that the ambitious schedule of 73 talks would stay on track in a process he likened to “drinking from a fire hose.”

The presentations covered a wide variety of disciplines. As Vitousek explained: “The most important way we can honor the extraordinary place we are working, the extraordinary interaction of people and land … is to do work … across the broadest range of understanding we have.”

“Push yourself to understand talks that don’t come easily,” he exhorted those present. “Push yourself to express the things you’re interested in… Push yourself to connect.”

We present here summaries of just a few of the presentations.

* * *
Marine Subsidies
For Montane Soils

For millennia, seabirds nesting high in the mountains of Hawai`i fertilized the forests with their nitrogen-rich guano. With seabird populations now diminished to a fraction of past levels, do they still contribute in any measurable way to soil fertility?

Julia Rowe, a Ph.D. student in the Department of Natural Resources and Environmental Management at the University of Hawai`i, is seeking to answer just that question. Over the last year, she has been studying levels of nutrients in soil at upper Limahuli and Hono o Napali, on the north shore of Kaua`i.

Rowe set up plots five meters in diameter in areas where Newell’s shearwaters and Hawaiian petrels were present and in comparable areas where there were no birds. By tracing isotopes of nitrogen, Rowe is able to determine what percent of nitrogen-based nutrients are in the soils and available to plants.

“To be frank,” she said at the Vitousek gathering, “I was surprised to see any differences between seabird and non-seabird areas.” Later, she told Environment Hawai`i, she had thought that with seabird numbers so low and rain so high in the areas studied, most of the nitrogen and other nutrients brought in by the birds would leach from the soil before being taken up by plants.

Yet, despite her low expectations, she did find a difference. Most nutrients (total nitrogen, nitrate, and ammonium) were higher in the seabird plots, she reported, although only ammonium was present at a higher level that was statistically significant.

Looking at the isotopic ratios in soil and leaves, she found `ohi`a leaves to have significantly higher concentrations of marine-sourced nitrogen. At the seabird sites, 29 percent of the nitrogen in `ohi`a was traceable to marine sources. In uluhe, the contribution was much lower – only 14 percent. Rowe offered a tentative explanation: “The uluhe samples and the soil cores I took would be accessing N from a shallow area, whereas the `ohi`a roots will be deeper. The nitrogen that makes it down this far may be accessible to the plant, whereas the nitrogen towards the surface may get washed away faster, though I can’t say for sure.” She also noted that ferns have low nutrient needs in general, which could help explain why they do not draw up that much nitrogen in the first place.

As to why seabirds preferred some areas over others, Rowe said she had not yet finished analyzing the vegetation community in the plots. “All the areas were at similar elevations and had generally the same vegetation, same precipitation. Everything I can measure looks pretty much the same at all the plots,” she said.

Most likely, “there are simply not enough birds to be able to take advantage of all the suitable habitat,” she said. “Birds are still getting wiped out by cats, rats, and other predators. Other seabird folks I have talked to say the density of seabirds could be a lot higher.”

“The reason I do this project,” Rowe volunteered, “is that over the last 10 years or so that I have been living on the islands, I’ve been hearing people talk about the forests, abandoned terrace gardens of the native Hawaiians, and other ecosystems. People wonder how these systems thrived when there are so few inputs of nutrients and the nutrient levels are so low…. But seabirds used to be much more cosmopolitan. They would have been delivering N and P across all of the islands and in almost every ecosystem.”

* * *
Dryland Agriculture Area
Found at Kaupo

The dryland agriculture systems of Kohala and Kahikinui that fed so many thousands of native Hawaiians are well documented. Recently, however, yet another such area has been discovered near Kaupo, on the southern flank of Haleakala.

Oliver Chadwick, a professor in the Department of Geography and Environmental Studies Program at the University of California, Santa Barbara, described just how the discovery was made.

“Patrick Kirch was fooling around with Google Earth,” Chadwick reported. “There was a whole field system he had never seen before in Kaupo, on leeward Maui.” Kirch, an archaeologist at UC Berkeley, is one of the foremost experts in the Polynesian settlement of the Hawai`i islands. Kirch, Chadwick, and Vitousek have collaborated closely in the study of the dryland agricultural systems of the Hawaiians before western contact.

Although in most people’s minds wetland taro cultivation is closely associated with Hawaiian agriculture, dryland systems may have been just as important, if not more so. “It may well be that the maximum production, the increase in production that allowed Hawaiian culture to flourish, came from these dryland systems,” Chadwick said.

Kaupo is on a relatively young “outflow feature” of Haleakala, he noted, with an age range from less than 5,000 years old to about 140,000 years old. “That matters,” he continued, “because … if we get ages as great as what is in the surrounding area – from 350,000 to 400,000 years old – then we get into nutrient limitations because of the length of time leaching was occurring.”

Kirch stated in a follow-up email that the Kaupo field system seems to have been more intensive than that in Kahikinui. “Early missionary census data indicate a considerably higher (denser) population in Kaupo than Kahikinui,” he wrote. “In addition, we know from Hawaiian oral traditions that Kaupo was the ‘royal seat’ of King Kekaulike in the 1700s, which also speaks to its importance.”

The area “joins Kahikinui, Kohala, and Kona as one of the substantial dryland agricultural areas on Maui and Hawai`i islands capable of producing considerable surplus per agricultural worker in support of the larger Hawaiian culture,” Chadwick concluded.

* * *
Wekiu Bug Update

For more than a decade, concerns that telescope development near the summit of Mauna Kea would have a damaging impact on the global population of wekiu bugs have been voiced by opponents of further telescope construction. The bug is found only at high elevations on the mountain; at one point its population was thought to be so reduced that it was proposed as a candidate endangered species.

But Jessica Kirkpatrick, resource management assistant at the Office of Mauna Kea Management, has put to rest notions that the wekiu bug and telescopes are incompatible. Kirkpatrick and colleagues Fritz Klasner and Jesse Eiben have been monitoring for invasive species of arthropods on Mauna Kea for the last couple of years as part of an ongoing cooperative program of the OMKM, Bishop Museum, UH-Manoa, and UH-Hilo to identify possible threats to the wekiu bug.

Last year, she, Klasner, and Eiben found, was a banner year for the bugs, “with the highest capture rates and concentrations ever documented.” Some of the highest capture rates, they report, “were immediately outside of [telescope] facilities, areas that have been previously disturbed.”

While most of their work was focused on censusing wekiu bugs and looking for threats to them, recently their work has shifted to arthropod monitoring more generally, looking especially for potentially invasive species.

The work is paying off. In 2013, inspections discovered two species of ants (including the big-headed ant) in shipments of equipment. (The deliveries were rejected.) Sticky traps caught one wasp, suspected to be a species introduced in 1939 for biocontrol of brown- and black-widow spiders.

* * *
Post Mortem on Koa Looper Outbreak

On January 8, 2013, Natural Area Reserve System staff first noticed a huge swath of defoliated koa trees on the Hamakua Coast of the Big Island. A helicopter survey a few weeks later confirmed that more than 20,000 acres of koa had lost foliage due to an outbreak of the koa looper moth – the first such outbreak on the island since 1953.

For the next few months, said Robert Peck of the Hawai`i Cooperative Studies Unit, the moth continued to chew its way up the mountain and across the island. “By mid-May,” Peck said, “it was safe to say that most large tracts of koa had been, if not entirely defoliated, at least partly so.”

The moth is endemic to Hawai`i and at least 14 outbreaks had been observed since 1890. But none of them had been well studied. Peck and several of his colleagues determined to do just that, taking a close look at the koa moth outbreak at Hakalau Forest National Wildlife Refuge, on the windward slope of Mauna Kea. “We wanted to describe the dynamics of the koa moth outbreak – determine patterns of defoliation and tree survival, quantify the nutrient pulse and its effect on understory plants, and identify its impact on the food web,” Peck said.

At the time their study began, in March, no defoliation had occurred yet at Hakalau. By April, they were noticing a few caterpillars on the koa trees. “In mid-May, we got a pulse, and over the course of the next six weeks, the numbers built up, then tailed off by the end of July,” Peck said.

When the outbreak was at its peak, he continued, “at times, caterpillars were dripping off the trees.” The caterpillars declined only when there was no more koa foliage to consume, Peck said. “That’s when they began to spill over to other plants – things they wouldn’t normally eat.”

Stephanie Yelenik of the U.S. Geological Survey studied the effect of frass from all those caterpillars on understory plants and soil. “A lot of koa were greatly defoliated,” she reported. “Caterpillars were eating up koa leaves and phyllodes and it was coming out as frass,” a polite term for feces.

With koa being a nitrogen-fixing tree, soil under koa trees already have high levels of nitrogen, so, Yelenik continued, “if you have a lot of frass falling on a system that has a lot of nitrogen, are we going to see a pulse – and does it even matter?”

There were “a lot of caterpillars, and a lot of frass,” Yelenik said. “You could even hear it falling.” “Frass fall” for the duration of the outbreak was estimated to range from 2,000 to 6,000 kilograms per hectare. That translates into around 192 kilograms per hectare of nitrogen – “equivalent to nitrogen fertilization for food crops,” Yelenik said.

At Hakalau, some koa stands consist of trees that were planted over what were once fields of pasture grasses. With the flush of nitrogen, one obvious question was what would happen to the non-native grasses. “There was a concern that these pasture grasses that remain in the restored areas might experience a spurt of regrowth,” Yelenik noted.

She and her colleagues then looked at whether nitrogen from the frass fall was making its way into several different plant species, including exotic grasses and native plants. “We took samples of grass and natives over time, in both open areas and under koa,” she said. “In general, we’re picking up more N in koa stands.”

Paul Banko of the USGS studied the way in which birds at Hakalau responded to the koa moth outbreak. “There was very heavy defoliation throughout the study area,” he said, “but still a lot of variation.” In the stands of planted koa, among trees with a diameter larger than 8 centimeters at breast height (dbh), “a tremendous amount of biomass was consumed,” Banko reported. “In other stands, the biomass consumed was less – but the koa is also less dense in those areas.”

After 25 weeks, the trees were producing new foliage, with larger trees producing more than smaller trees and seedlings, he said. The type of foliage regenerated also varied. “Larger trees produced fewer true leaves and more phyllodes than younger trees,” he said. “Is that due to the larger trees having greater nutrient reserves? Or is it more expensive for the tree to produce true leaves than phyllodes?” An answer awaits another day.

Bird activity predictably decreased as the defoliation increased. However, Banko said, “during the outbreak, caterpillar ingestion went way up.”

– Patricia Tummons

 

Volume 25, Number 2 August 2014

 

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