Birds Carried Plants to the Massif de la Hotte From Cuba

The Massif de la Hotte in southern Hispaniola is so thickly blanketed in vegetation that the mountain seems like a puzzle nobody intended to be solved in this fashion. Its terrain is steep, rugged and crowded with plant life.

For decades, researchers questioned why this one mountain range contains more plant species than nearly anywhere else in the Caribbean. The explanation emerged not from analyses of soil or layers of rock, but from the air.

The investigation started with a seemingly simple question about plants. Birds received little initial attention, and seed dispersal appeared to be a minor factor. Yet the evidence would not remain confined to that assumption.

A substantial proportion of the plants on the mountain did not originate elsewhere on Hispaniola. Instead, they arrived from eastern Cuba.

For millions of years, something had repeatedly transported seeds over open sea.

Unexpected journeys over water

Located on the Tiburon Peninsula at Hispaniola’s south-western tip, the Massif de la Hotte appears to have received many of its plants by air, according to the study.

Scientists considered alternative explanations, but birds were the most convincing. They consume fruit, cover long distances and do not invariably destroy seeds during digestion.

One journey was particularly notable. Around 1.6 million years ago, a bird flew non-stop for more than 160 kilometres from southern Cuba to the peninsula. Before it departed, it had eaten the sweet fruit of a Miconia plant.

The seed endured the trip, arrived undamaged and germinated. That one plant subsequently gave rise to 18 species, most of which remain exclusive to the Massif de la Hotte.

Such plants are not exceptional in the region. Roughly 34% of Hispaniola’s plant species are endemic, with many restricted to this single mountain range.

“It’s a biodiversity hotspot within a biodiversity hotspot,” said study lead author Andre Naranjo, who conducted the research while working as a postdoctoral associate at the Florida Museum of Natural History.

Vanishing forests in a protected landscape

The Caribbean Islands rank among the world’s 36 biodiversity hotspots. Each of these areas supports at least 1,500 endemic plant species and has lost a large share of its original habitat.

Although the Massif de la Hotte falls within Pic Macaya National Park, approximately 75% of its forest has disappeared.

“Within the last 35 years, whole habitats have been clear cut by people in the surrounding villages for firewood to literally just survive because the economic situation in Haiti is so dire,” said Naranjo.

That destruction has made historic plant collections invaluable. Fieldwork in southern Haiti has been suspended because of civil unrest.

Consequently, every pressed leaf and identified stem collected before 2014 is now more significant than ever.

A long history of plant collectors

Contemporary Massif de la Hotte research is founded on over a century of earlier work.

Swedish botanist Erick Ekman reached Haiti in 1917, following malaria, financial disagreements and a stop at a Cuban sugar plantation. He travelled with little equipment, worked by himself and endured austere conditions.

“A stalk of bamboo, properly plugged, served as his canteen and his food supply was limited to a few biscuits and tea. He depended on the hospitality of the inhabitants of any area he visited,” wrote botanist Richard Howard.

“He was willing to accept even the poorest accommodations.” Whenever his water ran out, Ekman drank from bromeliad leaf clusters.

“This water may look bad, at times, and may be the natural habitat of many strange animals, but one ceases to be finicky when one’s lips burn from thirst.” If that source failed as well, he covered his “burning lips in mosses and moist soil.”

Ekman gathered 16,000 plant specimens in Hispaniola and another 19,000 in Cuba. His collections assisted in identifying 2,000 new species.

Mountains raised relatively recently

Scientists revisited these southern mountains during the 1980s. Although the Massif de la Hotte has an ancient appearance, it is comparatively young.

The peninsula began as a shallow marine plateau, where limestone accumulated from dead plankton. Tectonic activity later folded and elevated it by more than 975 metres.

Available evidence indicates that the mountain has stood above sea level for roughly six million years. Its slopes rise to around 2,350 metres.

The lower terrain once supported Rak Bwa, or rock forest: a severe environment of jagged limestone and concealed sinkholes. By the 1980s, about 90% had vanished.

At higher altitudes are rainforests, fern thickets, bamboo tangles, cloud forests and pine savannahs. The pine, Pinus occidentalis, requires fire.

As Ekman once wrote, “thousands of pine seeds germinate simultaneously, and thus a whole mountainside may be covered by a lustily growing pine forest.”

Fieldwork in these mountains could be dangerous. “A number of times, we’d be in our tents, and we’d hear the rumble,” said Roger Portell. “Some of the boulders were four feet high.”

DNA evidence from Massif de la Hotte plants

The recent study examined melastomes, shrubby plants that include Miconia. Hispaniola has nearly 200 melastome species, 64 of them found in the Massif de la Hotte alone.

“There are almost 200 species of melastomes on the island of Hispaniola, and they can be a dominant component of the understory and even the canopy,” said study senior author Lucas Majure.

The team sequenced DNA from 102 endemic melastomes. Using fossil dates, they calculated when species emerged and traced their origins. Their findings revealed birds travelling in all directions throughout the Caribbean.

However, one route appeared repeatedly: eastern Cuba to the Massif de la Hotte, spanning from six million years ago to less than one million years ago.

Soils, pressure and survival

Part of the explanation may be beneath the plants. Eastern Cuba contains extensive serpentine soils, which are metal-rich and toxic.

“What’s interesting about eastern Cuba, geologically speaking, is there are a lot of serpentine soils in the area,” Naranjo said.

Plants able to persist in these soils often encounter limited competition. Across time, they develop unusual adaptations. Those characteristics may also have enabled melastomes to establish themselves on the limestone soils of southern Hispaniola.

“There’s clear evidence that some of these melastome groups originated on serpentine soils and then moved to other soil types. It seems to be a recurring pattern,” Majure said.

Their prospects nevertheless appear constrained. Many endemic melastomes occur above 1,000 metres. As temperatures increase, they have no higher ground to reach.

“They can’t go anywhere else, so you can imagine minor changes in climate will have a major effect on things that have this really narrow ecological niche,” Majure said.

The complete study appeared in the journal Botanical Journal of the Linnean Society.