By Eva Colberg, postdoctoral fellow at Cornell University. Nearly all of Mauritius’s contemporary conservation plights are rooted in or exacerbated by the effects of invasive, non-native species. To see what restoration can do for the island’s few remaining forests, Dr. Eva Colberg joined members of the Tropical Island Biodiversity, Ecology & Conservation research group to visit (and weed) one of the island’s forest restoration sites.
Red stems of strawberry guava (Psidium cattleyanum) form a wall dense enough to prevent walking through most of Mauritius’s remaining forests. Beyond impeding movement, the thick guava understory also reduces overstory tree fitness and disrupts native forest growth and succession. Originally from South America, strawberry guava is a classic case of a non-native, invasive species outcompeting and reducing habitat quality outside its native range (and islands are particularly vulnerable to invasion).
The ongoing onslaught of invasion means there’s no time to waste for restoration ecologists like F.B. Vincent Florens, Associate Professor at the University of Mauritius. “We have so many rare species on the brink of extinction [over 80% of the island’s endemic flowering plants are threatened], and have to work at the same time and learn as we go.” His life experience and ecological studies point to invasive species management as the island’s best hope for restoration and conservation, which he likens to healthcare. “First you save the person from dying and then you can treat the other issues.”
Despite decades’ worth of evidence pointing to the efficacy of invasive plant removal in Mauritius, it still isn’t widely implemented. Less than 5% of the island’s few remaining forests have been weeded of invasive plants, and even the best-protected forests are already dominated by invasive undergrowth. Frustratingly, some of the resources that could be used for invasive removal have instead hindered restoration via removal of native pioneer and nurse tree species. “We can do a lot of science, can come up with a lot of facts, but how do we get people to do what they don’t want to do?” Indeed, it’s far easier to uproot a small plant than to change someone’s mind, and Prof. Florens has an entire country to convince that saving their native forests is not only possible, but worth the effort.
Leighton Reid describes new research linking slow forest recovery to the ancient and protracted isolation that has made Madagascar a hotspot of global endemism – plus an example of working with local farmers to overcome these challenges and restore native rain forest.
Madagascar is a special place with a special history. Separated by ocean from Africa and India for the last 88 million years, this isolated tropical island has fostered the evolution of plants and animals found nowhere else on Earth. Lemurs, couas, and the plant family Sarcolaenaceae are all examples of organisms that evolved only in Madagascar. Collectively, such endemic species make up more than 80% of all plants and animals there.
Madagascar also has special problems. Almost half of the island’s forest has been cleared for agriculture since 1953, and remaining forests are at imminent risk. One recent study projected that if deforestation rates do not diminish soon, 93% of eastern Malagasy rain forest could be gone by 2070.
The combination of a large proportion of endemic species and a high degree of habitat loss makes Madagascar a biodiversity hotspot. Some people call Madagascar one of the hottest hotspots because its endemism and habitat loss are so extreme.
This week, a new study led by UC Berkeley PhD student Kat Culbertson identified another special problem in Madagascar: following disturbance, Malagasy forests recovery very slowly. Compared to other tropical forests around the world, Malagasy rain forests recover only about a quarter (26%) as much biomass in their first 20 years of recovery. Dry forests in Madagascar also recover more slowly, recovering just 35% as much biomass as American tropical dry forests over the same time period.
Why do Malagasy forests recover more slowly than forests in other regions? The answer may be related to Madagascar’s unusual evolutionary history. Culbertson and her co-authors developed four hypotheses and reviewed an array of scientific literature to evaluate support for each one.
Four ways that Madagascar’s unique history could lead to slow forest recovery
1. Native Malagasy forests lack resilience to shifting nutrient and fire regimes from current farming practices.Many rural people across Madagascar practice tavy, a farming method that involves clearing forest, burning it, and then growing rice – a staple crop. After one or a few years of growing rice, the land is allowed to recuperate for several years before it is cultivated again. In other tropical forest locations, such as southern Mexico where humans have farmed for thousands of years, similar practices can coexist with native forests, but Malagasy forests seem to have little resilience to tavy, as least at the intensity with which it is practiced today. For example, in eastern Madagascar, a 3-5 year tavy cycle can cause a native forest to transition to permanent herbaceous vegetation in just 20-40 years. The soil nutrient stocks in that fallow field may be as little as 1-6.5% of soil nutrients stocks in intact forest.
2. Madagascar is an island, and islands tend to have more problems with invasive species. Goats in the Galapagos, brown tree snakes in Guam, acacia in Hawaii, and rats everywhere – these are just some of the ways that island ecosystems have been overwhelmed and transformed by invasive species. Madagascar is no exception. Rain forest regeneration at Ranomafana is stalled by invasive guava, eucalyptus, and rose apple, while dry forest regeneration at Berenty is inhibited by a vine – Cissus quadrangularis. People in Madagascar have many more anecdotes about problems with invasive species like silver oak and Melaleuca quiquenervia, although the extent and impact of these invaders on forest recovery have not yet been studied.
3. Old, weathered soils have favored the evolution of slow-growing native plants. Madagascar is not only an island, it is a very old island, and as such its soils have been weathered and depleted of important nutrients like phosphorus. It’s hard to separate the effect of inherently low nutrient availability due to being an old island from the effect of human-induced nutrient scarcity through tavy, but one comparison of phosphorus content in rice stalks showed that phosphorus content was 10× lower in Madagascar compared to the rest of sub-Saharan Africa. If native trees have evolved to grow more slowly in Madagascar because of low nutrient availability, then on average exotic tree species should grow faster than native Malagasy ones in the same gardens. This has been shown in a few cases, but a more compelling analysis would need more species.
4. Finally, Malagasy forests have dysfunctional seed dispersal. One way in which Madagascar is different from other tropical areas is that by and large its trees have evolved to have their fruits dispersed by lemurs. Unfortunately, many of the lemurs that could disperse Malagasy tree fruits are either extinct or endangered – in many cases due to a combination of hunting and habitat loss. Moreover, the lemurs that remain are reluctant to venture outside of forest fragments (perhaps with good reason) and so they are unable to disperse seeds to regenerating farmlands that most need them.
In essence, the ancient and protracted isolation that has made Madagascar so unique has also made it uniquely vulnerable to contemporary changes like deforestation, fire, and agriculture. The result is an unfortunate combination: Madagascar not only has some of the highest deforestation rates, it is also one of the places least ecologically equipped to rebound from those disturbances.
The way forward – working with local people
Despite these challenges, Madagascar has committed to restoring four million hectares of lost habitat by 2030, an area nearly 7% the total national territory. This is a tall order in a country where technical difficulties are high and financial resources are often low, but it can be done, and the way forward, undoubtedly, is to work with local people.
One group that exemplifies bottom-up restoration is GreenAgain, a non-profit restoring native rain forest and supporting rural livelihoods in eastern Madagascar. GreenAgain is led and staffed by farmer-practitioners whose neighbors, family, and friends contract with GreenAgain to design, plant, and monitor diverse native forests on their lands. Last year, GreenAgain staff planted 20,000 trees across central eastern Madagascar, each one carried by hand, on foot, from one of eight regional tree nurseries. The rural farmers at GreenAgain collect rigorous data on tree survival and growth and collaborate with scientists to analyze and share the results of their tree planting experiments.
For example, one of the earliest experiments at GreenAgain was an assay of tree planting strategies intended to improve native tree seedling survival during plantings that occur in the dry season. Trees planted during the dry season typically have high mortality, sometimes in excess of 40%. One of the strategies that local farmers recommended to improve survival was to erect small teepees over each seedling using the leaves of a common fern, Dicranopteris linearis. These structures are temporary – they eventually dry out and blow away – but GreenAgain’s experiment showed that they reduced transplant shock (i.e., mortality in the first few weeks) by 75% compared to seedlings that were left to bake in the hot sun. In contrast, many of the other treatments had no discernable effect.
To analyze and publish these findings, GreenAgain partnered with an award-winning undergraduate researcher, Chris Logan, in my lab at Virginia Tech, who led a peer-reviewed paper that is now available at Restoration Ecology.
Could technological solutions like hydrogels or irrigation systems produce greater improvements in dry season tree survival? Yes – they probably could for a certain price, but homegrown solutions like fern leaf shade tents are free and easily accessible to any person doing restoration across eastern Madagascar. They are also more likely to be used because they were developed by local people.
This study also showed that some native tree species are much better at coping with dry season stress than other species, so another possible solution for dry season plantings could be to plant only the tough survivors. Once those trees survive and begin to produce shade, fern leaf tents may not even be needed anymore to help more sensitive native species survive and grow.
To read more about ongoing restoration and ecological research in Madagascar, read our new review of how Madagascar’s evolutionary history limits forest recovery and our new open-access paper about strategies for dry season plantings in eastern Madagascar.
If you are in a position to support the work of local farmers restoring rain forests in eastern Madagascar, consider donating to GreenAgain at their website, greenagainmadagascar.org.
By Thibaud Aronson and James Aronson. All photos by Thibaud Aronson.
The main island of Madeira is just 740.7 km2 (286 mi2), while the handful of others are rather barren, and mostly uninhabited. That means the entire Madeiran archipelago is about the size of a medium-sized National Park in the US, such as Crater Lake, in Oregon, for a total population of just over 250,000.
For garden and natural history/cultural history-oriented travellers, Madeira and its neighbors – the cooler Azores to the north, and the drier Canary Islands – are spectacular: these are three of the most appealing areas of the Atlantic for human habitation, gardening, farming, and hiking, with floras and faunas related to European, Mediterranean, and African biota, as well as some unifying Macaronesian elements shared among the three archipelagos. Agricultural crops are also quite spectacularly varied, with a strong presence of vineyards of very stunning appearance, and also subtropical bananas (about which, for some history, including the tale of the EU’s “bendy banana law”, see here).
Of particular interest on the island – of combined natural and cultural heritage value, are the laurel forests (laurisilva to botanists). Mostly dominated by evergreen trees and tall shrubs of medium stature – no more than 15-20 m high – these kinds of forests typically occur at subtropical latitudes, in areas with mild climate and high humidity. They can be seen – in unconnected fragments for the most part, and with varying botanical composition of course – in places such as the Himalayan foothills, central Chile, or the highlands of Ethiopia. In Europe, true laurel forests used to cover much of the Mediterranean basin during the Tertiary era, from which they receded and disappeared as the region’s climate got progressively drier. Apart from a few fragments left in the remote Anti-Atlas Mountains of Morocco, and one small patch in southern Spain, the only surviving Atlantic laurel forests are found in Macaronesia. The highlands of Madeira hold the largest and best-preserved stands, somewhat protected over the past six centuries by the island’s dramatic topography and, since 2009, thanks to recognition as a UNESCO World Heritage site covering 15,000 hectares.
Madeira’s laurisilva is draped in mist more often than not, and exuberant lichens and ferns cling to every tree branch, giving these forests a very primeval feeling, unlike anything else in Europe. The forest type is dominated by under a dozen evergreen tree species, most notably laurels (5 species in 4 different genera of Lauraceae) and tree heaths (Erica spp.), some of which get to be exceptionally tall for Ericas. But there are several dozen endemic shrubs and herbs in the undergrowth, such as various Geraniums and several giant daisy relatives. It has three endemic bird species as well.
The archipelago was uninhabited until Portuguese sailors claimed it for the Portuguese crown in 1417. The island’s appealing climate was not lost on them and they set about settling it. Much of what they did shaped the island that we know today and no doubt led to a massive amount of irreversible clearing, deforestation, and soil erosion, as we will discuss further on.
Madeira’s climate is very unbalanced. The northern slopes can receive nearly 3000 mm of rain in a year, while the southern part of the island is much, much drier. However, the south has gentler slopes, making it much more suitable for building and agriculture. Therefore, the Portuguese set about building levadas, irrigation canals to bring water from the north to the south. This enormous network, spanning thousands of kilometers, much of it dug from sheer cliff faces, with numerous long tunnels as well, was built over four centuries (with slave labor, many of whom lost their lives in the process); without it, large-scale settlement of Madeira would have been near impossible.
The island also achieved tremendous prosperity especially in the 17th, 18th and 19th centuries, thanks to its privileged position for maritime trade in the north Atlantic and, for a while, its role as one of the world’s largest sugar cane exporters. The richer inhabitants, taking advantage of the favorable weather, began a tradition of having extravagant gardens, with plants from all over the world. Indeed, a walk in the streets of any town on the island today will reveal gardens bursting with an incredible melting-pot of plants, with Hydrangeas (from east Asia), growing side by side with Agaves and Yuccas (from Mexico), Agapanthus (from South Africa), Brugmansias and Passionflowers (from the Andes), Bougainvillea from the South Pacific, and more marvels, all under the shade of massive Agathis and Eucalpyts (Australia) and Araucaria trees (Norfolk Island, and Chile)! There is perhaps no better illustration of this potpourri quality of the cultivated plants than the fact that Madeira’s official flower is the Bird of paradise, Strelitzia reginae, a native of… South Africa!
However, to anyone with naturalist’s eyes, a lot of what is seen outside of gardens is quite worrisome when one considers the island’s native flora, fauna, and varied ecosystems outside of the protected areas where the laurisilva occurs. There are massive areas of soil erosion, and as elsewhere throughout the Mediterranean region, abandoned lands and pastures that appear to have been cleared and then repeatedly burned over several centuries to maintain grazing lands for sheep and goats. Most of the extant revegetation has been done with Eucalyptus globulus, Mediterranean pines, and various other non-native conifers and Australian Acacias. Of these latter fast-growing, colonizing, bird-dispersed trees, at least 6 are invasive on Madeira and the Azores, the worst of the lot being Australian blackwood.
So what now, from a restoration ecology perspective? Madeira is subject to strict Portuguese laws regarding sale or import of known invasive plant species; this makes a lot of sense given that already 15% or more of the flora of Portugal, and probably more than that in the Azores and Madeira consists of non-native invasives. But a lot of work beyond protection against new invasions could be envisioned, starting with control or eradication efforts on such an island whose natural beauty and biodiversity are its greatest asset. Reintroduction and reinforcement of populations of endangered native species are also needed and initial experiments in ecosystem restoration could be undertaken on the main island and perhaps some of the smaller islands as well. Education and job training and greater funding for restoration work are all needed and would probably be of great, and lasting value to local communities and the Autonomous Region as a whole. Coordination with similar efforts in the Azores, and on the mainland territory of Portugal should all be encouraged.
One invader to be carefully monitored on Madeira is Kahili Wild Ginger (Hedychiumgardnerianum) a garden-escape that is known to do great ecological damage to native woodlands in Hawai’i, and elsewhere. The IUCN considers it to be one of the world’s 100 worst invasive species. Indeed, its 1.5 to 2 m tall stalks can form extensive stands, with dense mats of rhizomes, that can choke out native understory if left unchecked. Reportedly, control efforts are underway inside the Madeira Natural Park.
But what about all the areas infested with woody weeds outside the parks and UNESCO Heritage sites in the mountains? From our point of view, the extensive and multiplying stands of Acaciamelanoxylon and other invasive wattles (Australian acacias), of Gorse (Ulexeuropaeus) and a few other noxious woody weeds we saw plenty of, it seems clear that manual and mechanical controls, and perhaps some biocontrol would be worth testing.
And, what about everything that ecological restoration, sensu lato, could bring to Madeira? On one road, in the center of the country, we saw a rather large plantation of tree saplings that looked like Ocoteafoetens, one of the five native laurels of the laurisilva. That was encouraging to see, but the trees were planted grid-fashion and in monoculture, so that it was unclear what the intention was. As readers of this blog well know, reintroduction (or reinforcement of populations) of a single species of native plant or animal is not the same thing as ecological restoration: ‘restoration of Ocotea foetens’ is a non sequitur whereas reintroduction of this native tree, or its use in reforestation does make sense.
We also learned that studies are underway regarding the native olive tree, long considered a feral ecotype or, for some systematists, a subspecies of the widespread European olive, Olea europaea, but now generally accepted as an island endemic Olea madeirensis. Pride in such native species should be definitely encouraged, serving as a driver for more attention to what should be planted in the context of future ecological restoration programs in coastal areas and hills, and in environmental education programs, parks, and botanical gardens as well.
Next, let’s consider the spectacular Dracaena draco, or Dragon tree, that prospered on Madeira and also in the Canary Islands, Morocco, and Cape Verde, until Europeans in the 15th and 16th century began aggressive tapping of the sap from this stem succulent tree – the so-called Dragon’s blood – which was widely prized as a durable natural dye. By the end of the 16th century, Dragon tree was rendered nearly extinct in its natural distribution area thanks to a typical boom and bust pattern of exploitation, and today, the only wild populations of any importance occur on Tenerife, in the Canary Islands, with a few individuals in Morocco and Cape Verde.
This iconic tree is seen planted all over Madeira, and indeed in frost-free dryland gardens all over the world. But there probably isn’t a single wild dragon tree left on the island! So, what should attempts to restore an ecosystem with populations of Dragon tree look like, over and beyond reintroductions? What reference should be used and which provenances of what trees should be planted and what else is needed for the project to survive and be meaningful to Madeirans?
And now, for our last snapshot, let’s consider the Foxtail Agave, that is widely planted and clearly spreading on coastal cliffs and hills in Madeira. It is an absolutely stunning plant, and of great natural history interest but it starting to naturalize, following in the pattern of Agave americana and Opuntia stricta, that could already be considered serious weeds. Local people probably don’t consider that a problem, and we can certainly understand that, given the newcomer’s graceful beauty. But like the Kahili ginger, and the widely planted Aloe arborescens, the Foxtail Agave is a serious pest on O’ahu and other Hawai’ian islands, and this should give cause for concern to Madeirans.
But, then, who are we to say what attitude Madeirans and their authorities should adopt towards non-native invasives? Given the fact that tourism is now far and away the leading economic sector on the island, perhaps – like the Galapagos Islands, or Iceland, or Malta – greater sensitivity to the need for and the value of ecological restoration efforts will develop in the future.
One thing we could offer is a reminder that ecological restoration clearly includes restoration (or ecological and economic rehabilitation) of cultural or semi-cultural ecosystems, not to mention social-ecological systems and cultural landscapes. In the case of Madeira, this line of thinking would allow for reflection, and encourage investment in the restoration and rehabilitation of the working landscapes that thrived in lower latitudes on the southern half of the island with irrigation water being provided from the levada networks in the mountains. We can imagine remarkably interesting and inspiring landscape-scale restoration with ample opportunities for agritourism, and an expanded form of nature-based or ecotourism that would include cultural landscapes and heritage crops and traditional livelihoods, developed along corridors and valleys connecting levada canals all the way down to restored ‘working landscapes’ that certainly could have multiple benefits for local communities, for biodiversity, and for an emerging restoration economy linked to tourism. Worth considering, no?
On January 6-10, CCSD scientist Leighton Reid joined Bert Harris, Kelly Farrell, and David Wilcove on a search for what has become one of the rarest bird species in the western hemisphere.
Grand Bahama Island, only known home of the Bahama Nuthatch.
The Bahama Nuthatch (Sitta insularis) is or was a bird found nowhere except on Grand Bahama Island, a thin, 153-km long piece of weathered limestone lying 84 km east of Palm Beach, Florida.
The Bahama Nuthatch differs from a widespread southeastern US species, the Brown-headed Nuthatch (S. pusilla) in having a longer bill and a distinctive, high-pitched warbling call. It is a denizen of the Caribbean pine (Pinus caribaea) forests that cover about 60,000 ha of Grand Bahama Island. Perhaps always rare, the species was a lot more common in the 1960s than 30 years later in the early 1990s. Ten years ago, a nearly island-wide survey found only 14 individuals in a single tract of forest east of Freeport, the island’s largest settlement. A local nature guide, Erika Gates, regularly found one to three individuals of the species in this area through June 2016, but in early October 2016, Hurricane Matthew (Category 5) blew across the island, causing significant damage. The Bahama Nuthatch has not been detected since June 2016 despite Ms. Gates and others searching in its previous locations. It is considered “endangered” by the IUCN.
A postage stamp sheet commemorating the Bahama Nuthatch (Sitta insularis), an extremely rare species known only from a single island in the Bahamas.
Bert Harris plays the distinctive warbling call of the Bahama Nuthatch through a speaker into a very quiet Caribbean pine forest.
For six days in early January, four of us intensively searched the area around the two most recent sightings, the ones from May and June 2016. We focused on the core area at first and gradually expanded outwards as it became clear that we were finding no individuals at the former sites. We estimated that we searched an area of roughly 4600 hectares of pine forest over a period of 26 hours (88 person-hours). We travelled approximately 92 km of roads and trails, both driving and walking. Many of these were old logging roads, which crisscross the entire island. While driving, we stopped every 0.4 km (0.25 mi) and played a recording of the nuthatch’s distinctive call. While walking, we played the call more frequently.
We did not find any Bahama Nuthatches. We think that our group, the first to search for multiple days for this species since 2016, was also the first to fail to find it. Perhaps the species’ conservation status should be changed from endangered to critically endangered. Ideally, some Bahamian ornithologist will be able to survey again for the species during the coming breeding season, and if the species is rediscovered, its remaining habitat will be protected, restored, and expanded.
In addition to the Bahama Nuthatch, we noted that several birds which breed exclusively in the pine forests were also very rare or absent. Bahama Yellowthroats (Geothlypis rostrata), Bahama Warblers (Setophaga flavescens), and Olive-capped Warblers (S. pityophila) were relatively abundant during surveys in 1968 and 2007, but Bahama Yellowthroats were totally absent from our search, and we found only a handful of Bahama Warblers and Olive-capped Warblers, making them even rarer in our survey than the nuthatch was in 2007 (though we searched during some relatively cold weather and during the non-breeding season). We also failed to detect a single Bahama Swallow (Tachycineta cyaneoviridis). Looking through historical records on eBird we noted that the West Indian Woodpecker (Melanerpes superciliaris) was formerly abundant across the island but has not been recently seen.
The causes of decline for the Bahama Nuthatch and perhaps for other breeding birds of the pine forests are mysterious. Grand Bahama Island has been extensively logged, initially for large diameter timber (prior to 1900) and later (1940s-1970s) for pulpwood. The expansion of the city of Freeport and tree-killing inundation by seawater over large areas have both reduced the potential habitat area. Feral cats, introduced raccoons, and corn snakes introduced in the 1990s could be predating native birds. We saw at least nine raccoons during our short time on Grand Bahama. Altered fire frequency and the increased frequency of Atlantic hurricanes may also be impacting the species, possibly by removing snags that are required for nesting.
As recently as 2011, 65 Caribbean ornithologists were able to view the Bahama Nuthatch simultaneously and within three meters of a tour van. Photo by Erika Gates.
Restoration specialist, Mike Saxton, describes his observations on the distribution of invasive Japanese stiltgrass along a creek running through Shaw Nature Reserve.
Brush Creek (blue) runs eastward through Shaw Nature Reserve in Gray Summit, Missouri. Gray Summit Road is in the upper right.
July 28, 2017
Yesterday, Adam and I put in to Brush Creek at the Old Gray Summit Rd. bridge and headed upstream spraying Microstegium vimenium(Japanese stiltgrass). This was the second time through this area this year and I made this sweep solo 3 times last season. My first outing last season, I used 3 gallons of herbicide before I finished the first wetland cell…this year it’s been much, much lighter. Last year, with only 1 person spraying, I was hard pressed to leave the creek bed because there was so much to spray directly along the accessible banks. And in our first outing this season, Catherine and I stayed completely within in the creek, rarely going up on the banks.
However, yesterday Adam and I abandoned the creek bed and went crashing through the brushy banks, finding more Microstegium than I had anticipated. What was interesting was that pockets of stiltgrass followed a predictable pattern of distribution. In many areas, one creek bank will be severely down cut, perhaps 15 ft sheer banks, while the opposite bank is tapered with a more gradual slope. This is where you find the Microstegium. I posit that floodwaters do not over-top the high bank but rush over the lower bank depositing sediment and seed. Almost without fail, the lower bank, if totally brushy, would have scatted Microstegium. However, if the lower bank was open or had open pockets of sunlight, those pockets would be dense thickets of stiltgrass. We observed a nearly 1-to-1 correlation between bank height and stiltgrass presence/absence and open sunlit patches having dense patches of stiltgrass on the lower banks.
I was covering a roughly 20 ft swath out from the bank edge before it dropped into the creek bed. I did go further from the creek a number of times but wasn’t finding much (if any) the further I got from the creek.
Based on these observations, I believe that our current strategy of managing downstream from the “head waters” is prudent. Based on the diminished population this year and because the species has a 5-year seed viability, we should continue to see diminishing populations if we continue to be methodical and thorough with our management.
We repeatedly found dense patches of Microstegium in high light availability openings/tree fall gaps. This suggests to me that if we open up the brush creek corridor with forestry mowing/brush cutting, the increased light levels and soil disturbance might cause a spike in Microstegium populations. While the brush creek corridor isn’t priority #1, I know we’ll get there some day. Before we aggressively start clearing brush in this area, I’d like to have 3-5 years of aggressive Microstegium management under our belts. We have observed diminished populations in the wildflower garden, along Paw Paw Creek, and along Brush creek with just one year of management. Coupled this with a short seed viability…and we might have a winning strategy.
Large patch of Japanese stiltgrass (Microstegium vimenium) along Brush Creek at Shaw Nature Reserve.
Leighton Reid, a postdoctoral fellow in the Center for Conservation and Sustainable Development, reflects on tortoises, tree cacti, and ecological isolation.
The Galápagos is the world’s most pristine tropical archipelago, and it is utterly unique. Nearly the entire island group is a national park, and 200,000 visitors per year come to witness its ecological singularities ‒ things like penguins and iguanas swimming side-by-side through a mangrove lagoon. The archipelago consists of fourteen large, volcanic islands and over a hundred smaller rocks and islets. Most of the land surface is low and dry. The easternmost island is about 900 km from mainland Ecuador, which is a probable source for the organisms that first began to colonize Galápagos when its volcanic peaks surfaced above the Pacific five million years ago. Indeed, the islands’ ecology is characterized by their isolation. Each island contains a relatively low diversity of organisms, many of which are unafraid of large primates. The biotas’ ecological simplicity and naiveté have facilitated major scientific discoveries, such as that small, heritable variations can have life or death consequences for individuals and ultimately change populations.
One of the more bizarre life forms on Galápagos is the tree cactus. Prickly pear cacti (Opuntia species) are not particularly rare in the western hemisphere. In the United States, for instance, they occur in every state except Alaska. But over millions of years in Galápagos they have become quite varied. Some grow low to the ground, like the familiar continental forms, whereas others grow as trees, towering up to 15 m above the ground. The first botanist to speculate on this phenomenon was Alban Stewart (1911), a scientist-sailor with the California Academy of Science. He noted that erect, tree cacti tended to grow on islands that also housed another over-sized organism – the Galápagos tortoise (Chelonoidis nigra). Galápagos tortoises eat the fleshy cactus pads, which contain water – a limiting resource in arid environments. Stewart posited that the pressure from tortoises craning their long necks upward to munch cactus pads may have favored taller cacti.
Opuntia echios var. barringtonensis is one of the taller tree cacti, presumably made that way by pad depredation by giant tortoises over many generations.
A low-growing cactus (Opuntiaechios var. zacona) growing on Seymour Norte, an island that historically had no tortoises or iguanas. Herbivore pressure is visible here; an introduced land iguana (Conolophussubcristatus) has been taking bites from the lowest pads.
The relationship between tortoises and cacti was thrown into disarray after the Galápagos were discovered (accidentally) by Panamanian Bishop Tomás de Berlanga in 1535. By the late 19th Century, pirates and whalers removed thousands of tortoises from the islands, stowing the living animals in their holds as fresh meat for their long Pacific voyages. Eventually, overharvesting extirpated tortoises from several of the islands, with rippling effects on the rest of the ecosystem. Even where tortoises survived, they were often unable to reproduce because their offspring were eaten by introduced, European rats. Tree cacti were among the hardest hit; tortoise decimation stripped these plants of their main seed disperser.
Reintroduced giant tortoise in the littoral zone on Isabela Island.
In response to tortoise declines, the Charles Darwin Foundation and the Galápagos National Park Service began a captive breeding program on Santa Cruz Island. Since 1965 they have raised and repatriated thousands of tortoises to several islands, waiting to release them until the tortoises have gotten big enough to be “rat proof”. By and large the reintroductions have been successful. On Española Island, for example, tortoise populations had crashed to fifteen individuals in 1960, but by 2007 more than 1500 individuals had been repatriated, and the population appeared stable. Moreover, these reintroduced tortoises reinitiated seed dispersal for an endangered tree cactus (Opuntia megasperma var. megasperma), increasing the number of juvenile plants.
In addition to species reintroductions, ecological restoration in Galápagos has often entailed species eradications. Isolation historically shaped Galápagos ecology; nine hundred miles is a long way for a snake or a lizard to float on a vegetation raft. But Galápagos’s isolation was compromised by seafaring humans, who facilitated island colonization by domesticated animals and hundreds of plant species. Goats have been among the worst invaders. Until recently, goats overgrazed the islands’ vegetation, converting it into habitat unsuitable for native species. One of the most ambitious restoration projects in Galápagos has been eradicating goats from the archipelago. On the largest island, Isabela, more than 140,000 goats were killed in 2004-2005 using unconventional restoration tools, including helicopters, AR15 rifles, and Mata Hari goats – sterilized female goats induced into long-term estrus and fitted with radio telemetry collars to root out the last hold-outs. Goat eradication has resulted in spontaneous vegetation recovery. In addition to goats, the Charles Darwin Foundation and the Galápagos National Park Service have also eradicated eight exotic plant species. Other species will be harder to get rid of, like rats, guava, blackberry, and domestic cats.
Despite its one-of-a-kind nature, can the world’s most pristine tropical archipelago serve as a reference for other arid, tropical islands? That is, can we evaluate the success of other island restorations by comparing them to the relatively intact Galápagos’s ecosystem structure, function, and composition? Perhaps to some extent we can. Historical contingency leads to unique island assemblages (for example: giant tortoises in Galápagos, giant skinks in Cabo Verde, giant lizards in Komodo), but many islands may be characterized by their lack of functional redundancy. In other words, if you remove a species from an island, the ecosystem consequences may be greater than if you had removed a species from a more diverse mainland ecosystem. Additionally, plant restoration in the arid Galápagos suggests that when disturbances are removed, vegetation can recover rapidly. This may also be true of other oceanic archipelagos, whose plants and animals have already colonized difficult terrain from a long way away.
Land iguana and tree cacti (Opuntia echios var. echios) on Plaza Sur Island.
James and Thibaud Aronson are working on a book, with James’s longtime collaborator Edouard Le Floc’h, on “desert canopies” and ecological restoration in arid and semi-arid regions of the world. They report here on the first leg of their trip to Baja California, Mexico.
Isla Guadalupe is a large volcanic island (250 km²), 240 km west of northern Mexico, with fewer than 150 permanent inhabitants. Approximately one-fifth of the island’s 150 native plant species are endemic. Of particular interest are the remnant populations of trees in the foggy, northern highlands of the island, including an endemic variety of Monterey pine (Pinusradiata var. binata), and the endemic cypress.
Three additional tree species survive in small populations : an endemic oak (Quercustomentella), California juniper (Juniperus californica) and an endemic fan palm (Braheaedulis). At the southern end, there are remnants of both chapparal and matorral shrublands including taxa with Californian affinities and others from the Sonoran desert biome. The southern tip is very dry – with just 120 mm (5 in.) of mean annual rainfall. The northern half is mountainous with 250 mm (10 in.) of annual rain, and thick fogs that double or triple the effective precipitation.
People first came to the island in the early 19th century. By 1850, sailors had introduced goats to provide a meat reserve for passing ships. Not surprisingly, the goat population exploded, reaching an estimated 100,000 animals by 1870. Over-grazing led to the disappearance of entire plant communities and several dozen endemic species. One example is Hesperelaeapalmeri, an endemic member of the olive family. Particularly appreciated by goats, it was gone by 1870. Domestic cats got to the island somewhat later, probably introduced intentionally to control the mice. The cats went feral, and had an enormous impact on the extremely tame birds, both endemic land birds, and breeding seabirds.
By the early 20th century, 6 of the 9 endemic land birds had gone extinct, as well as an endemic seabird. Meanwhile, the Guadalupe fur seal and the northern elephant seal were hunted relentlessly, the former for its fur, the latter for its blubber. The hunting only stopped in 1894, when both species were thought to be extinct. Happily, both species did in fact survive, albeit in extremely small numbers; the entire fur seal population dropped to 15 individuals. In 1928, the island became a set-aside reserve and seal populations finally started to recover, and today, they number 20,000!
Fur seal (Arctocephalus townsendi) on Isla Guadalupe, March, 2015.
The northern elephant seals have done even better. They have recolonized much of the northern Pacific, and the total population is more than 150,000 individuals.
Elephant seal (Mirounga angustirostris) on Isla Guadalupe, March, 2015.
On land, however, things kept worsening. The goat numbers stabilized around 15,000. As a result of over-grazing, most of the island was stripped to bare soil and rocks; only a few hundred trees survived and goats ate every seedling they produced. Cats caused enormous mortality in breeding seabirds and one of the remaining three endemic land birds, the Guadalupe Junco (Juncoinsularis), was headed towards extinction, with only 50-100 individuals left.
That’s when the Group for Ecology and Island Conservation (GECI) got in gear, and it’s thanks to them that things are looking up. Since 1995, this NGO has eradicated 48 populations of invasive mammals – mostly sheep, goats, cats, and mice – on 30 Mexican islands. They got to Guadalupe in 2002 and started an intensive eradication campaign. By 2007, the goats were gone. Within a year, the trees had produced thousands of recruits, which today are several meters high, in the case of both the pine and the cypress. In fact, in 2008, a fire burned through a large portion of the remaining stand of cypress. A few years earlier, this would have been a catastrophe. But without goats to eat them, thousands of seedlings sprouted immediately all over the burnt area and are growing nicely, thanks not only to the absence of goats, but also to the heavy fogs, which provide favorable conditions for the seedlings. Besides, half a dozen native shrubs, including some endemic species, have reappeared in large numbers in many parts of the island. Several species which were though extinct have been rediscovered, and one new species has been discovered as well.
All is not well, however, in the invasives department, nor in soil conservation. Dozens of species of herbs and grasses from the Mediterranean Basin and Europe are prevalent in open areas, and there are dramatic signs of soil erosion. Former shrublands – matorral and chaparral – are deeply degraded everywhere on the island. Half a dozen species of native shrubs are re-colonizing certain areas and acting as very effective pioneer species. These are being watched and probably can be used in active restoration efforts in the future.
Feral cats and several kinds of mice are still present and continue to prey on birds. However, a fence now protects the southern tip of the island, which is home to a breeding colony of the Laysan albatross, one of few albatross populations in the world which is growing in numbers.
Laysan albatross (Phoebastria immutabilis) breeding and raising chicks on Isla Guadalupe.
To date, GECI has focused on eradicating invasive mammals, mainly to protect marine birds. The regeneration of the island’s vegetation was a happy by-product. However, they are now seeing the potential for taking a more active hand in restoring the islands’ plant communities. We suggested several approaches. One would be the establishment of plant nurseries to support both ex-situ conservation and reintroduction of plants within experimental plots set up to study what approaches are most effective for different plants, in different parts of the island. There are only 30 to 40 adult oak trees left on the island and less than 10 known Junipers. Unlike the endemic cypress, pine, and fan palm, neither the oak nor the juniper is recovering. Active intervention will be needed to reconstitute mixed conifer-oak woodlands and to bring the fan palm populations back to their former glory. Finally, some heavy work is needed in relation to water and soil management, and roughly 400 feral domestic cats still run free on the island. Total eradication will be extremely costly, but GECI hopes to achieve it by 2025. As is the case in Madagascar, and Sri Lanka, restorationists must learn how to cope with and manage fire.
With all this in mind, can our friends from GECI initiate a sustainable restoration process on the entire island, ideally within a coherent conservation, management, and restoration plan? Also, can the restoration work underway serve as a prototype for restoration on other islands, e.g., Mauritius and Madagascar where MBG scientists are already working?
Spontaneous Guadalupe cypress regeneration following the fire of 2008.