Meet the Natives

In an earlier post (Floral Inflation), I described how Midway Atoll went from having just a dozen or so species of plants to over 200 over the course of about 100 years (the botanical equivalent to the acceleration of a Lamborghini). And although I included the names and photos of a few native plant species, I didn’t really do them justice. I thought I should revisit to topic and introduce you to some of the beautiful and interesting native plants we have out here and so I began the task of researching the plants and taking some photos. Little did I know that I would be pulled, in an ironically-metaphorical sense, “into the weeds”. What once seemed like a neatly circumscribed topic became muddied with complications. What is native to this place? And how do we know?  What to do about the fact that the very physical environment of Midway has changed so radically over the decades? It has taken me some time to extract myself from the thicket but I hope that you will find what I have to share with you worth the wait.

Every ecologist is well-versed in concepts of “native” versus “exotic” and uses this as a way to separate the “good species” from the troublesome. Back in New Mexico and Oregon it was a pretty straightforward task to take the list of plants found at a site and split them into these two categories. Generally speaking, if a plant existed in the area prior to the arrival of white people it was considered native and if it wasn’t it was exotic (the exact word used changed over time as folks struggled to find something politically acceptable and included “non-native”, “alien”, and “invasive”). It wasn’t that the indigenous peoples of North America didn’t move plants around (for example, bringing corn from Mexico to the Mississippi basin), but the changes that ensued after Columbus’ “discovery” were so profound in comparison that dividing things into “pre-“ and “post-Columbus” has typically proven very useful (check out this book by Charles C. Mann for more on that topic). Ecosystems that still retained their native species were judged to be more pristine while those dominated by exotics were thought of as degraded.

So my original plan was to do a little research into the dozen or so plants I had been told were native to Midway and write about them. Early on I had noticed a few things that seemed really cool. Even though there weren’t many native species, they seemed diverse in terms of their growth forms – which included bunchgrasses, sedges, sprawling vines with showy flowers, big shrubs that enable the formation of dunes, and delicate wildflowers – as well as in their life histories – a mix of opportunistic short-lived plants that produced a lot of seed and long-lived plants with more complicated ecological relationships. One thing most of them had in common was the ability to grow from cuttings or to produce large, durable, seeds worthy of sea voyages – traits essential for establishing themselves remote islands far from their source populations.

As I was putting together that post though I also took on the task – as part of my work responsibilities – of compiling a list of plant species for the atoll. In doing so I relied heavily on the work of Forest and Kim Starr, botanists based out of Maui who have for decades catalogued and researched Midway’s flora. They listed not a dozen but 39 native species encountered here over the years. Digging deeper, I found that while the term native could be applied to species discovered here during the very first botanical surveys, it might also include those found on nearby islands or even on one of the main Hawaiian islands (Oahu, the Big Island, Maui, etc.) but encountered here at a later date. And what about species that might have been missed on those earlier surveys or those that were native to the region but only showed up once the island had extensively modified during “military occupation” or where purposefully introduced? What did it really mean to be a native plant species on Midway? This was a question without a simple answer and required that I examine each species individually using whatever evidence I could acquire which included research into published journal articles and unpublished works (the “gray literature”) as well as herbarium records and online databases.

In the end I reckoned 22 of the 39 species to be truly native to Midway atoll, meaning, they were had a very good chance of being here before the Pacific Commercial Cable Company set up operations here in 1903.  The remaining 17 species were those that were native to somewhere in Hawaiian archipelago but probably had made it to Midway with the help of people – either by them acting as their couriers or by the changes wrought by them as a consequence of their presence here. My research also revealed what had been lost. Of the 22 native species, about half had their entire populations eliminated from Midway as a consequence of the environmental perturbations that resulted from the island’s occupation (one of these was subsequently reintroduced and still struggles to survive). Three are now extinct – that is, vanished entirely from the planet.  The 12 survivors are clearly a hardy bunch and play important roles in the US Fish and Wildlife Service’s efforts to restore the islands ecosystems.

The first botanical surveys of Midway Atoll were conducted by ornithologist William A. Bryan who visited these remote islands for just a few hours in 1902 (a side trip taken while en route from Marcus Island back to Honolulu). Until that time, Midway had been visited primarily by bird hunters and a few unfortunates who found themselves shipwrecked here.  Little had been done to modify the environment at the time and Bryan described Sand Island as a “barren, blinding, heap of sand” noting also that nearby Eastern Island was much greener, covered in low shrubs, and more hospitable despite its smaller size and simpler topography. In his very short time at Midway, Bryan recorded a mere 13 species of plants consisting of three shrubs, four wildflowers, four grasses, and two vines but admitted that that he would likely have encountered more species if he’d been there longer. Eight of these plants are still present on the atoll and are critical players in restoration efforts here, including alena (Boerhavia repens), emaloa (Eragrostis variabilis), koali awa (Ipomoea indica), and popolo (Solanum nelsonii). Unlike some of the northwestern Hawaiian Islands, there are no plant species endemic to Midway (that is species that occur here but nowhere else in the world). Of the 13 true natives, five no longer occur on Midway and of these, two are extinct. One of these is the grass Kamanomano (Cenchrus agrimonioides var. laysanensis) which was once abundant on several of the Northwestern Hawaiian Islands but was last seen in 1961 on nearby Kure Island.  The other, ʻahinahina (Achyranthes atollensis) was a shrub in the amaranth family with hairy leaves that grew up to four feet high on sand mounds and was never seen again on Midway after 1902!

Undisputed natives. Boerhavia repens (top) and Lepturus repens (bottom) were
noted during the very first botanical explorations of Midway. Both of these species have widespread distributions across the tropics and subtropics.

Erling Christophersen and Edward Caum, travelling with the Tanager Expedition in 1923-4, were the next to document the flora of Midway and turned up four additional native plant species. These included the beautiful morning-glory vine Pohuehue (Ipomoea pes-caprae ssp. brasiliensis), and the spectacular yellow-flowered ilima (Sida fallax). Ilima, which also occurs on the main Hawaiian Islands has great cultural significance and is the most desired flower when creating the traditional lei or flower wreath. Two of the four species are, however, now gone from Midway. Phyllostegia variabilis, appears to have disappeared from the planet so quickly that there is no common name for it and virtually no information about it (try finding anything about this species using Google and you will surely be disappointed!). Moa (Psilotum nudum), is a rootless fernlike plant that no longer occurs on the atoll but persists across a wide swath of sub-tropical and tropical areas of the globe and was used by native Hawaiian people to prevent chafing incurred in the wearing of loincloths!

Botanists travelling with the Tanager Expedition (1923-4) were able to make a more complete list of Midway's flora adding Sida fallax (top)  and Ipomoea pes-caprae ssp. brasiliensis (bottom) to the list of native species.

The 1930s and ‘40s were periods of profound change at Midway as the islands became a tourist destination with the establishment of a Pan American Airways Clipper station (which included a hotel and restaurant) and then, shortly after, drew the attention of the US military as global tensions rose and the atoll was recognized as a place of strategic significance. Buildings were erected, roads constructed, and runways paved. Occasional visits by botanists documented the effects that these changes had on Midway’s flora. Johnson Neff and Philip Du Mont spent a month on the atoll in 1954 to “study bird problems” but also found time to document the plant life as it existed at that time. Two native species, mau'u 'aki'aki (Fimbristylis cymosa) and ena'ena (Pseudognaphalium sandwicensium var. sandwicensium) were recorded for the first time. These are species that, though native to the Hawaiian islands, had never before had a place to grow on Midway but were now found to be growing along paved surfaces. Ena’ena, interestingly, mostly finds its home on lava flows on the Big Island but was thriving in this novel ecosystem. In 1980 Derryl Herbst added kaʻa, puʻukaʻa (Cyperus polystachyos) to the list of sort-of-native Midway plants. This widespread and hardy sedge found a niche at the end of a runway where water pooled during the wet-season and decades later became a foundational species in creating wetland habitat for the endangered Laysan duck. The discovery of the succulent akulikuli (Sesuvium portulacastrum) in 1995 by Marie Bruegmann is a bit of a mystery as habitat for this plant – areas close to the beach that receive salt spray and are occasionally washed over by storm-driven waves – would seem to have been some of the least disturbed areas on the atoll.

Extensive modification of Midway's environment created suitable habitat for "new native species"
such as Fimbristylis cymosa (top) which grows in cracks in the runways; Although it is likely that the hardy,
salt-tolerant mat-forming Sesuvium portulacastrum (bottom) existed on Midway for many centuries it was not discovered until the 1990s.

When management of Midway was turned over to the US Fish and Wildlife Service in 1996 (see Trading Guns for Goonies) restoration of native plants became a priority. Ten species of plants native to the Hawaiian islands were either introduced or just showed up in the years that followed. These included species that were in trouble elsewhere and needed new homes. Aweoweo (Chenopodium oahuense), a robust shrub in the goosefoot family, and and Bryan’s flatsedge (Cyperus pennatiformis var. bryanii) were brought to Midway from Laysan Island, the former becoming an important species used for restoration while the latter failed to establish. Efforts to secure the critically endangered loulu lelo (Pritchardia remota) compelled Fish and Wildlife Service staff to collect several hundred seeds from their source population on Nihoa island and grow them out in the nursery on Midway. Today, five of these plants survive adding a some security to the original population.

Though not native to Midway, the Nihoa fan palm (Pritchardia remota), originall found only on the
island of Nihoa in the Northwestern Hawaiian Islands is currently being grown on the atoll as
part of efforts to secure its global population.

Efforts to re-establish the native plants of Midway Atoll and to provide habitat for endangered plants native to other parts of the Hawaiian archipelago are more concerted now than ever. The US Fish and Wildlife Service has stepped up its efforts to restore degraded habitat on Midway atoll which now includes a native seed library, a greenhouse, and a brand-new, 6,600 sq ft shadehouse. Through its native plant propagation program Midway has become an important site for conservation of the popolo at a time when populations elsewhere continue to decline. Exact definitions of what is native or not no longer seem so important in a world of changing climate and rising seas. What seems imperative now is to do the most we can with this 2 square miles of sand and coral out here in the Pacific Ocean with respect to both the wildlife and the plant life. This will require boldness, creativity, but also humility. Of the 22 “original” native species, half had their entire populations eliminated from Midway as a consequence of the environmental changes wrought upon the island during the early part of the 20^th century and only one of these, akiaki (Sporobolus virginicus) has been successfully reestablished. We need to do better than that in the future and doing so will require utilizing sound science in guiding future actions. That and maybe a little luck!

Currently, 20 species of "native" plants are being propagated by the
US Fish and Wildlife Service at Midway Atoll.

Floral Inflation

Why Midway violates ecological laws and what it means for conservation in the long-term

E.O. Wilson, the avuncular, silver-haired ant biologist, conservationist, and ambassador for biodiversity is probably the most famous ecologist the world has ever known, which maybe isn’t saying much. But if you are or were a student of biology you might remember what put him on the ecology top hits charts back in the 1960s: a manuscript titled The Theory of Island Biogeography in which he and Robert MacArthur argued that that the number of species found on any given island was the result of two simple things: the rate if colonization (new species arriving on the island) and extinction (the rate at which species wink out due to random population fluctuations, disease, etc.). The closer an island is to the mainland, the higher the rate of colonization. The bigger the island, the larger the populations and therefore the lower the extinction rates. So large islands close to continents should have way more species than small islands far from continents. It all makes sense and the empirical evidence support the theory pretty well. For example, Cuba, a large island (over 100,000 square kilometers or 42,000 square miles) is a just 160 km (100 miles) or so from the shores of North America and has a whopping 8,000 species of flowering plants while the much smaller St. John, Virgin Islands (50 square kilometers or 19 square miles) sitting far out in the Caribbean far from any continent has just 1,000 species.

So what does this have to do with Midway?

The three islands of Midway Atoll total just under 6 square km (about 2.25 square miles) and are at least 3,500 km (2,800 miles) from either Asia or North America and over 1,900 km (1200 miles) from Honolulu. These are some of the smallest and most isolated islands in the world and according MacArthur and Wilson's theory, one would expect that the number of plant species found here would be very small. And indeed, this is what ornithologist William Alanson Bryan found when he arrived on Midway Atoll in 1902. Bryan reported finding just eight species of plants on Sand Island and ten on nearby Eastern Island. Today, a visitor to Midway could expect to find nearly 200 species of plants! What happened?

Native plants of Midway Atoll. Clockwise from upper left: Nohu (Tribulus cistoides), Emoloa (Eragrostis variabilis), Naupaka (Scaevola taccada), Ilima (Sida fallax).

It all started around the turn of the 20^th century when the Commecial Pacific Cable Company decided that Midway was a critical link in their efforts to establish a telegraph line across the Pacific Ocean. Once the decision was made to route the cable through this remote atoll, a station had to to be established and along with it a small settlement to accommodate the personnel needed to maintain it. Prior to this the only visitors to Midway were native Polynesians who occasionally traveled through, shipwrecked sailors, and feather hunters. Never before had people actually intentionally settled the islands of Midway Atoll!

When the cable company began construction of their outpost, Sand Island was “an uninhabited shimmering white pile of sand” but it didn’t take long for the newly arrived inhabitants to begin to reshape the island to meet their expectations. The ships that the cable station with food and other provisions also brought with them soil and plants to establish vegetation more to the inhabitant's liking. In October 1903 the ship Whalen brought 400 tons of soil to Midway from Honolulu as well as plants and grass seeds. Plants included coconut, milo, banana, passion fruit, and banana. Ironwood trees (Casuarina equisetifolia) were also imported with the intention of providing the new residents shade from the sub-tropical sun as well as species such as beach morning glory (Pohuehue or Ipomea pes-caprae ssp. brasiliensis) which were hoped would stabilize the shifting sands.

Top: Establishment of the Commercial Pacific Cable Station resulted in the introduction of many introduced species including ironwood (Casuarina equisetifolia) and Cook Pines (Araucaria columnaris); Bottom: Exotic grasses such as Bermuda grass (Cynodon dactylon) were introduced to hold down the sandy soils of Midway Atoll and continue to dominate in many areas.

Over the years, many tons of soil and hundreds of plants were intentionally transported to Midway, including an assortment of vegetables and fruits grown to enhance the diets of the residents. In addition to desirable plants, some weedy species were brought in inadvertently, some of which proved to be a real nuisance later on. Midway’s rich history as cable station, air transport stopover, military outpost, and cold war surveillance outpost, also made it a hotspot for non-native plant introduction as each new cohort of occupants brought with them plant species they found interesting or useful. This has included turfgrasses for golf courses, palm trees for tropical ambiance, food plants such as papaya, and ornamental flowers for their beauty.

Exotic plants have satisfied appetites, both aesthetic and culinary for residents of Midway Atoll in the past and present.  Upper left: Spider lily (Crinum asiaticum) though unattended continue to thrive outside the "Midway Mall". Lower right: Well-tended papaya trees (Carica papaya) at the Aree House provide for an occasional Thai green papaya salad.

By importing so many species of plants to Midway over the past 100 years, residents have “short-circuited” MacArthur and Wilson’s Theory of Island Biogeograhy. Despite the fact that Midway is about as far from any continent as it could be, immigration rates (i.e., the rate at which new species arrive) have been relatively high. The end result is that Midway Atoll has much higher plant species diversity than would be expected based on purely “natural” factors. Today, Midway has about ten times the number of plant species as there were a little more than 100 years ago when the first inhabitants arrived.

The inflated plant species richness of Midway Atoll has its pros and cons. Many of the plant species that have been introduced here have proved to be invasive. That is, they do so well as to dominate areas to the point of causing problems for native species. A good example of this is golden crownbeard (Verbesina encelioides), a sunflower-like plant which grew so well here that it covered 70% of the islands soils and degraded habitat for both Laysan’s and Black-footed albatross. The US Fish and Wildlife Service worked hard to reduce the amount of this weed and now it covers less than 1% of the islands. Ironwood has also proven to be problematic as it dominates areas so completely that nothing can grow in its shade.

Some introduced species such as ironwood (Casuarina equisetifolia; upper left) prove to be invasive requiring management while others, for example, sea grape (Coccoloba uvifera; lower right))  appear to be benign or even beneficial.

Prior to the habitat restoration efforts undertaken by the US Fish and Wildlife Service, vegetation on Midway was nearly exclusively non-native and provided sub-optimal conditions for seabirds and other wildlife. Over the past 15 years much progress has been made in bring back the natives. Restoring native plant species is important not only for wildlife but for the plant species themselves, as many have seen their populations drastically reduced on other islands through the introduction of non-native animals such as rabbits and goats. In this new era, Midway Atoll, despite the fact that it has been intensively utilized for a variety of uses for over 100 years, has the potential to contribute significantly not only in the conservation of seabirds but also for native plants of the Northwestern Hawaiian Islands. The work to be done here at Midway does not fit neatly into what might be regarded as “restoration” as the islands have been modified so extensively over the past century that going back to what once was is simply not possible. Instead, we are challenged to managing these islands to their highest purpose, something that requires a solid understanding of the past, an acute awareness of the current needs of both plants and wildlife, and a creative vision for the future.

Acknowledgements: Thanks to William Alanson Bryan for having the forethought to visit and document Midway Atoll way back in the early 1900s. Much appreciation to Forest and Kim Starr who have returned to Midway three times in the past two decades to document the vascular flora of Sand, Eastern, and Spit Islands. Meticulous documentation of the plant species growing on Midway is certainly not an easy or glamorous job but were essential in the writing this blog post. Thank you all!