Albizia

In the late 1800s, the once impenetrable native forests were almost totally destroyed by grazing animals like cattle, goats, and deer. The mountainsides of most of the main islands were stripped of vegetation. Native plants were eaten to the ground, and the roots were trampled. The ground was left bare hard dirt and rocks, unable to absorb water. Rain caused catastrophic erosion that washed away topsoil and smothered coastal reefs in muddy silt. The Hawaiian Islands were quickly becoming uninhabitable.

In 1917, Joseph Rock imported the albizia tree (Falcataria moluccana) from Indonesia, in an attempt to quickly restore the watershed. The albizia grows extremely quickly in Hawai‘i, up to 15 feet per year—faster than in other places like Florida and Australia.  It can reach a height of up to 150 feet (50 m). The albizia quickly restored a watershed forest to be able to capture water again.

After 100 years, the albizia has changed the landscape of Hawai‘i. It quickly spread to dominate the landscape. The albizia increases soil nitrogen which makes the ground around the trees more suitable for invasive species over native species. The result is that most of the forests with albizia are full of other introduced plants.

When one or only a few plant types dominate, they are vulnerable to suddenly collapsing. Introduced plants do not have a strong relationship with each other or the environment. Furthermore, alien species can compete with each other to weaken the ecosystem.

Restoring the native forests requires careful planning. Carelessly removing invasive trees will recreate the problem they were introduced to solve. It’s important to rebuild the native populations while managing the spread of invasive plants.