Among Extinctions, Invasions, Disease, Some Hopeful Signs for Hawaiian Plants

“You can’t pay too much attention to invasives.” That was the message Michael Soulé, professor emeritus of environmental studies at the University of California at Santa Cruz, brought to the 2007 Hawai`i Conservation Conference, held in Honolulu July 25-27.

Soulé was the keynote speaker at the conference, and he gave his audience some tough love. Among the obstacles to restoration he cited was the lack of “a sense of urgency – the oomph factor.”

“Time is of the essence,” he said, and then provided a quick, if controversial, to-do list: “Extirpate all mammals on islets within five years… Neuter all cats… Re-wild offshore islets with native species. Restore areas with conservation easements. Fence all reserves – the idea of multiple use is a sacred cow, but it doesn’t work.”

People involved in this work tended to engage in what he called a “Nietzschean fallacy,” preferring genetic purity even at the cost of extinction. “They say, ‘don’t mess with Mother Nature.’ But we’ve already messed with her…

“For some reason, biologists harbor a fear of mixing things up,” he said, “even though a certain amount of outbreeding is healthy.”

To many in the audience, Soulé’s message was anathema. To others, especially those involved with inter-situ restoration efforts, he was preaching to the choir.

You might think an endangered plant growing on land owned and maintained by the state of Hawai`i’s Department of Land and Natural Resources would have it made in the shade. The DLNR, after all, is the agency within the state that is chiefly responsible for protecting endangered species.

Think again.

Specifically, think of Delissea rhytidosperma, a shrub once abundant in Kaua`i’s Hanakapiai Valley, now part of Na Pali Coast State Park. Since 2003, says David Bender of the National Tropical Botanical Garden, it has been all but extinct in the wild, eaten or trampled to death by the goats that the Department of Land and Natural Resources does little to control.

Or think of ohai (Sesbania tomentosa), which once graced the vast dunes of Polihale State Park, on Kaua`i’s western shore. While it may be found elsewhere, Bender says the Polihale population is gone, thanks to the off-roaders and all-terrain-vehicle enthusiasts whose pastime is, apparently, more valued by the state than is the plant’s very existence.

For several years, though, these and other Kaua`i plants have been grown at the National Tropical Botanical Garden in an effort to develop something its conservation director, David Burney, calls “inter-situ” plant conservation. Neither in-situ (in the plants’ recognized range) nor ex-situ (in a garden or greenhouse), inter-situ conservation has been developed by the garden as a means of growing sizable numbers of native plants in almost a farm-like setting. There, with minimal human support (initial irrigation for seedlings, some weeding and mulching), they can flourish and be used later for outplantings in the species’ home range when – if – the time comes when that original home range is protected.

“In-situ conservation is the heart and soul, the very best, the only way to preserve ecosystems,” Bender said in a talk at the Hawai`i Conservation Conference. “But for a subset of critically endangered plants, it’s not enough. It’s too little, too late for a lot of these guys.”

The problem, Bender said, was, “the political will – to fence, to remove ungulates – is lacking.” And although “we need to work on this front,” he said, in the meantime, inter-situ conservation has an important role to play.

Bender listed the many advantages of inter-situ over ex-situ conservation. It can protect and establish new plant populations; can allow for maintenance of a given plant’s “evolutionary context” better than ex-situ conservation; provides accessibility for management, monitoring, and research; and does not jeopardize populations that remain in the wild. In some cases, as with the Kaua`i D. rhytidosperma and ohai, “inter-situ populations become the only populations left,” he said.

The NTBG collected seeds of D. rhytidosperma and a closely related species, Delissea kauaiensis, and is now growing them “in semi-natural, inter-situ” conditions at Limahuli Valley and Lawa`i, two of the garden’s properties on Kaua`i.

While purists might criticize the practice, which involves placing plants outside their historic ranges, Bender noted that often, what is known about a plant’s home range is the result of surveys taken in modern times, when the range may have already been substantially reduced by centuries of human-induced alterations. “Lots of recorded ranges are less than a hundred years old,” he said, and don’t necessarily match up with suitable “potential” ranges,” to say nothing of what recent developments in the field of paleo-ecology disclose.

The garden has done much the same thing with ohai. “The only population at Polihale was in decline for 10 years because of motocross riders and ORVs,” Bender said. “There was no signage, no fences, no management.” Without vegetation, “the whole dune habitat could be destabilized.”

The NTBG collected seeds from Polihale and established a population at Lawai.

“In the future, we’ll come to value these inter-situ sites, since they’ll be the only ones left” where some of Hawai`i’s rarest plants can continue to be found, he said.

While the idea of moving species outside their documented range is generally frowned on, he said, “we need to get beyond this.”

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From Cane to Conservation: Makauwahi Cave Reserve

And Lida Pigott Burney is working to do just that. At Makauwahi Cave, near Maha`ulepu, she and her husband, David, discovered evidence that before the arrival of humans, lowland, coastal vegetation included many of the plants now found only in high mountain areas. As a result of their cave excavations, begun in the early 1990s, the Burneys decided to attempt to grow many of these plants in the prehistoric ranges.

The Burneys obtained a license from Grove Farm, owner of the cave and surrounding land, to use 17 acres of overgrown, fallow cane land for their experiment to see if traditional farm methods and farm machinery could be used in restoration projects.

The Burneys began by disking 5 acres in 2004 and then letting the land lie fallow a year. The next year, they installed an above-ground irrigation system, and planted about 1,000 trees, 83 percent of which survived.

Encouraged by their success, they have since established six management units, with each plant inventoried and mapped to allow for close monitoring and easy retrieval, in the event it is needed for outplanting, landscaping, or other use.

As the plants mature, the Burneys use mulch made from native grasses. This, they hope, will not only keep down weeds, but allow the grasses to grow in. The larger trees are also used to provide cover for shade-tolerant understory plants. After just a couple of years, the straight, regimented rows of plantings are softened.

“One thing about using old farm land,” David Burney said, “is the convenience aspect. Plants laid out in rows can be moved; they become portable plant communities.” To those who might criticize it as unnatural, he has a quick comeback: “Nothing is more unnatural than human-caused extinctions.”

Line them up end to end, and it’d take three erythrina gall wasps to match up with a mosquito. Despite their tiny size, however, the wasps spread across the Hawaiian Islands like a firestorm in 2005. First detected in the spring on O`ahu, by August, the wasps had landed on Maui. As Art Medeiros of the U.S.G.S. Pacific Island Ecosystems Research Center on Maui explained, it took just 22 days for biologists on Maui to admit defeat and give up on eradication efforts. By fall, the gall-forming wasp Quadrastichus erythrinae was on every populated island in the chain, devastating not only native wiliwili (Erythrina sandwicensis) but the closely related coral trees, widely used in landscaping. Daniel Rubinoff, a researcher with the University of Hawai`i who is analyzing the DNA of a variety of erythrina gall wasps, noted that in its quick dispersal, the wasp “was behaving more like a pathogen than an insect.” The rapid invasion of the emerald ash borer or the Asian longhorn beetle on the continental United States “looks like molasses in the freezer” by comparison.

As Medeiros explained, the wiliwili is a keystone species in low-elevation native dry forests. Until the arrival of a seed beetle in 2003, native wiliwili were thought to be one of the most resilient native tree species, Medeiros said, “thriving even adjacent to human habitations.”

But however bad the damage caused by the seed beetle (Specularius impressithorax), it was a walk in the park compared to the train wreck caused by the gall wasp. Every tree was infested, and many trees died. The wasps cause leaves to transform into what Rubinoff described as deformed tubers. “No trees flowered in 2006,” Medeiros said, although “some are flowering this year.”

The state’s response to the invasion was almost as quick as the invasion itself. The Department of Agriculture’s exploratory entomologist, Mohsen Ramadan, was dispatched to Tanzania in January 2006 to search for parasites on gall wasps. Tanzania was selected as the starting point for his work because of the high number of Erythrina species found in that country, Ramadan said in his presentation at the conservation conference.

Ramadan believes that in the remote Tanzanian province of Ngorongoro he found a match for the gall-forming wasp in Hawai`i. The Tanzanian wasp mates with individuals from Hawai`i, he said, and apart from a slight color variation in the hind legs, the two wasps are virtually identical.

A year later, Ramadan was in Tanzania again, this time searching for parasites of the gall wasp that might be used for biocontrol. Again, he reported success, finding three ectoparisitoids – even tinier wasps – that feed on the larvae and pupae of the gall wasp, keeping the gall wasp populations under control.

The Hawai`i gall wasps have no parasitoids, Ramadan said – a fact that could account for the devastation wrought when they infest Erythrina trees in the islands. Ramadan described the Erythrina trees in Tanzania as “very healthy,” with very few galls, even though on the same tree, even on the same leaf, “you see more than one gall-forming species.”

Ramadan shipped some of the infested leaves to Hawai`i, where the parasitoid wasps emerged and were studied as possible biocontrol agents. “We’re confident the parasitoids are host-specific,” he said. His office has now completed studies on one of the parasitoids and is seeking permission to release them into the field.

Rubinoff, however, is not so sure that the gall-forming wasp in Hawai`i is the same as the one Ramadan discovered in Tanzania. Rubinoff and his colleagues sequenced DNA from 169 wasps from all over Africa, and found no match for the single haplotype that has invaded the Indian and Pacific oceans. The invader “is 10 percent diverged from East African species,” he reported, “and may be a new genus, since 2 to 3 percent divergence is typical for species” within the same genus.

Rubinoff and colleague Mark Wright, also at the University of Hawai`i, told Environment Hawai`i that they did not receive for testing any of the specific wasps that Ramadan used in his crossing experiments. “Therefore,” said Wright, “we cannot say with absolute certainty that they are or are not the same as Q. erythrinae, but all the Ngorongoro samples we have sequenced were very different from the invasive species of Quadrastichus.”

Wright went on to say that Ramadan’s technique was “not convincing: he did not actually get the wasps to reproduce; they mated and transferred sperm, but this is not conclusive evidence of them being the same species. Should they have produced progeny, we would have been more supportive of his results, but even that would remain questionable. Bear in mind that lions and tigers (certainly different species) can reproduce with each other in captivity, and indeed do produce viable offspring. But nobody would suggest they are the same species… In light of this, we are hesitant to accept Mohsen’s results as being in any way conclusive, and maintain that we have yet to find the exact origin of Q. erythrinae.”

Still, on one point Rubinoff, Wright, and Ramadan are in agreement – and that is the likely effectiveness of the parasitoid wasp. “The natural enemies being considered for biological control of Q. erythrinae may indeed be very effective,” Wright said in an email to Environment Hawai`i. “There is a school of thought in the field of biological control that ‘new associations’ among species of pests and parasites may be more effective than ‘old associations’ (which often coevolve to the point where their populations exist in equilibrium). In theory, because the new association has not had a long history of coevolution, they do not reach equilibrium, and the parasites are able to suppress the pest with great effectiveness.”

Flint Hughes sees a cautionary tale in the zeal of the foresters a century ago to revegetate Hawai`i’s denuded hills with introduced species. “Of the alien woody plants now considered the greatest threats in Hawai`i,” he said, “more than half were part of systemic plantings in Hawai`i forest reserves.”

And things can only get worse with the predicted rise in temperature associated with climate change. “With a 2-degree Centigrade increase, the plant ranges will move to higher elevations. In many cases, the non-natives are already right along the lower edge of the natives’ range, knocking at the door.”

Hughes used albizia (Falcataria moluccana) as an example of good intentions run amok. The fast-growing albizia was intended to prevent erosion and enrich soil through its nitrogen-fixing capacity. But, as illustrated in a photograph of the albizia-invaded walls of Hanalei Valley that Hughes displayed, the albizia can actually foster erosion. The tree grows quickly and is soon unable to support its own heavy limbs. On steep slopes, its shallow roots give way, exposing bare soil and causing small landslides. Far from deflecting runoff, albizia trees can contribute to it. As Dieter Mueller-Dombois has explained, “albizia trees act as funnels for rain water because of their generally upward angled branch system. Because of this, they have a high rate of stem run-off, which is further accelerated due to their smooth bark.”

In fact, Hughes suggested that albizia may have had a starring role in the catastrophic floods in Manoa Valley in 2004. High in Manoa Valley, the trees were planted a century ago by forester Harold Lyon, of Lyon Arboretum fame. While no definitive study was done of the limbs that blocked the Woodlawn bridge, causing so much of the damage to laboratories and libraries at the University of Hawai`i, Hughes speculated that the high winds and heavy rains associated with the flood could easily have caused albizia higher in the valley to shed limbs, contributing to the debris that clogged the bridge. In a plenary talk, Mueller-Dombois noted that the widely publicized crisis that occurred at Lyon Arboretum that same year “was due mainly to albizia, which were breaking and posing a hazard” not just to the visiting public, but to workers as well.

Nor is the trees’ nitrogen-fixing quality a good thing, especially in native forests. Hughes’ own work shows that in the wake of albizia incursions, strawberry guava (Psiddium cattleianum) is hard on its heels, taking advantage of the nitrogen-enriched soil. Once albizia invades a forest dominated by `ohi`a (Metrosideros polymorpha), it is only a matter of time before the `ohi`a dies out. Hughes has observed `ohi`a deaths at nearly 100 percent after albizia invasions.

The same week as the conservation conference occurred, the front pages of Honolulu dailies showed another aspect to albizia, which were being cut down along a major highway in O`ahu. While the white trunks and graceful arching branches make the tree attractive, its beauty is only skin deep. The O`ahu trees were targeted, according to Scott Ishikawa, spokesman for the state Department of Transportation, because their weak branches made them unsuitable for highway landscaping. Many of the cut trees exhibited hollow cores, the result of disease or termite damage.

The Outdoor Circle immediately protested. In response, the DOT backed off and agreed to hold off on further albizia removals along H-2, pending the outcome of talks with the Outdoor Circle and other interested parties.

Bob Loy, director of environmental programs for the Outdoor Circle, was asked why his organization would object to the removal of albizia.

“It’s not all that simple,” he said. “Here’s the way we look at it. The spot removal of 75 albizia trees in midst of a forest of thousands of the same trees in the exact same area will do nothing to control the problem of their invasiveness.

“Second, regarding safety: we certainly do not oppose the removal of any tree, albizia or any other kind, that poses a threat to human safety. But the fact that albizia trees drop limbs doesn’t mean they’re necessarily a threat to safety. Many of these trees are far enough away from road that under no circumstances, even if the entire tree failed, would any wood reach the roadway.”

The DOT had not shown that the trees posed such a risk, Loy said, and, in light of the DOT’s past actions, he was skeptical of their promise to replant the albizia with native species. “What trees are they going to use? Where will they come from? How big will they be?” Loy asked.

“The DOT isn’t always consistent in how it manages roadside landscaping,” Loy continued. “Albizia, for all their negatives, in their current location, where they don’t pose a hazard, do have some community value, in the absence of anything else. They do beautify the road, and it’s an important road to make sure there’s some scenic beauty.”

There was, finally, a protocol issue. “Had the DOT followed a kind of protocol that made this an open process, where what was being done was shown to be necessary, and had they shared that info with community and organizations like ours, … this could have been met with a much different level of acceptance.”

The arrival to Hawai`i in 2005 of a rust, Puccinia psidii, that infests trees in the myrtle family sent shivers down the spines of many Hawai`i botanists. While the rust was known as eucalyptus or guava rust, local botanists worried it could infest `ohi`a as well, the dominant species in Hawai`i forests.

Lloyd Loope, with the USGS Pacific Islands Ecosystem Research Center in Makawao, was among those who feared the worst. The state Department of Agriculture, Loope noted, renamed the fungus `ohi`a rust.

“That name served to dramatize the true threat of this species of rust to Hawai`i’s dominant native forest species,” Loope said. In hindsight, though, it may have caused some to misgauge the threat, “which,” he said, “in retrospect seems not to lie in the billions of spores blowing around these islands but in new strains of the rust” that may hitch a ride to the islands on imports of myrtle family host plants to Hawai`i. So far, “only a small percentage of `ohi`a have been affected” by the rust, Loope said.

In response to that threat, the state Department of Agriculture “is willing to move forward with an interim rule,” barring imports of plants belonging to the myrtle family, Loope said. A risk assessment was submitted to the DOA in April; Loope said he expects the interim rule to be submitted to the Board of Agriculture within weeks.

While the `ohi`a may have dodged a bullet, not so the unfortunate rose apple (Szygium jambos). Loope displayed images from East Maui that showed entire valleys where the foliage of rose apple trees had turned to gray, devastated by rust.

The strain of rust found in Hawai`i differs from those found elsewhere, he said. For example, the rust has been in south Florida for 30 years, where it damages allspice trees, but leaves rose apple untouched. The strain here, so damaging to the rose apple, has no impact on allspice.

— Patricia Tummons

Volume 18, Number 3 September 2007