RESTORING THE DRY FOREST ECOSYSTEM OF BONAIRE

Nicholas Verhey, Echo Foundation, Kralendijk, Bonaire, Caribbean Netherlands

The dry forest ecosystem of Bonaire has been decimated over the last 500 years by human intervention. Uncontrolled deforestation by early European colonizers and the introduction and spread of invasive herbivores have created myriad problems for the native flora and fauna on the island. Animals such as the Yellow-shouldered Amazon Parrot (IUCN status: vulnerable) have lost critical habitat for nesting, roosting, and feeding, and native trees such as Guaiacum officinale and G. sanctum (IUCN status: endangered) have been unable to re-establish because of the invasive herbivores, principally goats and donkeys. The Echo Foundation was established in 2010 to protect Yellow-shouldered Amazons on Bonaire by addressing the biological and social factors that underpin the island’s environmental situation. Echo is currently implementing a project that involves fencing ten one-hectare plots around the island and growing and planting 20,000 native trees in these plots.   These areas are being fenced to exclude the goats and donkeys, providing a sanctuary for native trees to grow and spread as well as to supply natural habitat for parrots and other animals. Additionally, the trails through these areas will allow easy access to natural spaces and offer educational opportunities to residents and visitors on the island, thereby raising awareness of the environmental problems and increasing the cultural value of the forest.  This project was mandated and funded by the local island government, openbaar licham Bonaire.

Echo’s native plant nursery currently contains about 8,000 trees of more than 30 different species. With such a large quantity of trees to be grown, efficiency is key. Attention must be paid to each step of the plant propagation process to ensure that time, space, and energy are not being wasted. Each species of tree being grown requires specific knowledge of the most successful and efficient method of propagation. Seed germination, cuttings, and seedling collection are all used depending on the specific characteristics of each tree species.  

Luckily, most native trees can be grown from seed. This method offers an efficient way to grow a large quantity of genetically diverse trees. For some species such as Cynophalla hastata, ripe seedpods can be picked directly from the tree and the seeds can be cleaned and planted immediately. C. hastata will germinate in one to two weeks with a success rate of about 75%. For other species such as Guiacum sanctum, germination may be low and require up to two months.  For some slow-germinating species such as Manihot carthagenensis, filing the hard seed coat can increase the germination percentage and speed. 

Some tree species for which different seed treatments such as soaking, drying, filing, and cracking do not yield satisfactory results, may be grown from cuttings. Unlike propagation from seeds, cuttings yield trees that are mature enough to plant out in about three months, whereas seedlings require about six months. Bontia daphnoides and Bursera karsteniana provide good examples of trees that have low and slow seed germination, but grow very well from cuttings. Sections of branches approximately one to four centimeters in diameter and about 40 centimeters in length are cut from healthy trees with a sharp blade and planted in small pots until rooting and leaf growth are present. Echo’s nursery has a covered mist house that keeps the soil damp and the branches moist to give the cutting the highest chance of rooting and growing.

Cuttings, germinating seeds, and collected seedlings can all benefit from the constant moisture of the mist house.

Cuttings, germinating seeds, and collected seedlings can all benefit from the constant moisture of the mist house.

The final method of propagation used by Echo is the collection of seedlings found growing in nature. This method is not as widely used, as it has the potential to hinder natural regrowth of trees. However, in areas with a high density of invasive goats, donkeys, or native iguanas, seedlings growing out in the open do not last for more than a week. Moving the seedling to the care and protection of the nursery and then planting it in a protected area gives it the highest chance of survival. This method of propagation also provides the most efficient means for growing some trees. Up to 30 seedlings may be collected from beneath a single tree and no time or space is wasted waiting for non-viable seeds to germinate or unhealthy cuttings to root. 

All propagation methods require transplanting the tree into a larger pot to allow it to reach a point of maturity sufficient for planting out into a reforestation site. Standard round pots filled with nutrient rich soil will yield a large, healthy tree, but will also take up far too much space in the nursery. To ensure that a sufficient number of trees can be grown, we use 10 cm by 10 cm square pots with a depth of 25 cm, allowing for deep taproot growth without an unnecessary amount of space being used. Cones 5 cm in diameter and 25 cm deep are used for smaller species. All pots are raised above ground level on re-used crates to prevent roots from growing into the nursery soil. This is called air pruning because as soon as the roots exit the bottom of the pot, they reach air and do not grow longer. With daily watering and plenty of nutrients and room to grow, most native trees of Bonaire require about six months to be mature enough to plant into a reforestation site.

Square pots on reused crates. This allows for a large number of healthy trees to be grown in a small amount of space.

Square pots on reused crates. This allows for a large number of healthy trees to be grown in a small amount of space.

Echo’s herbivore exclusion areas will control invasive herbivory while also educating people about the forest of Bonaire. The problems associated with overgrazing and a lack of biodiversity will be displayed by the juxtaposition of the current forest and the forest as it could be. Additionally, these areas will create pockets of biodiversity allowing all native plants, animals, and invertebrates to thrive. Should the invasive herbivores be removed, these pockets will become centers from which native plants can spread, restoring Bonaire’s forest to a healthy state.