Native to the tropical and subtropical regions of the Americas, the genus Psidium or guava belongs to the vast eucalyptus family, and comprises at least 100 species. Bishop Museum’s A Tropical Garden Flora (2005) lists six species for Hawai‘i in its index. That’s plenty, though. Pretty plants with smooth, copper-colored bark, evergreen leaves and delicate, white blossoms, small shrubs or 25 feet high alike, guavas are a problem. True, they produce an abundance of great fruit, but they also act as gregarious weeds.
On your Kohala Zipline adventure, you’ll see:
Common guava – Kuawa – Psidium guajava
In the supermarket, you can easily find Hawaiian guava jam, jellies and juices. In the pastures surrounding Kohala Zipline, you’ll as easily see thickets of leafy, strong-branched shrubs bearing yellow-skinned ovoid fruits, which, when fragrant and ripe, yield those delicious foods. Common guava’s first arrival in Hawai‘i may have occurred in 1825 via the HMS Blonde from England, or perhaps as early as in the mid-1550s by way of Spanish ships. For sure, the shrub has been at home in the islands since early western-contact days and has long provided wood, fruit, and astringent medicine. Its pink pulp continues to nurture brisk commercial enterprise, but in recent years production has plummeted due to foreign markets.
Unfortunately, when not managed and contained, common guava overruns fields and roadsides, outcompeting native plants and slower-growing grasses. It especially overruns pasture lands, where it diminishes livestock feed. Mowing results only in stronger regrowth with multiple stems.
Strawberry guava – Waiawi – Psidium cattleianum
Perfumed and pretty, small, red-skinned strawberry guavas taste seductively sweet and tart. They can be white or purple-fleshed, and chances are you’ll find a few on your Kohala Zipline adventure.
But strawberry guava, a native to southeastern Brazil marked by dark-green glossy leaves, belongs to the most invasive tree species in Hawaii. And that’s serious stuff. In Hawaii, invasive species have managed to erase millions of years of natural history. Happily growing anywhere between sea level and 4,000 feet in elevation, strawberry guava alone directly threatens about a quarter of the State’s endangered plants. Spread by feral pigs and birds, without natural enemies to control it, it needs little to thrive. Its foliage shades out native plants, which are part of complex native ecosystems, providing habitat for native fauna and contributing to the replenishment of fresh water in the watershed. In some regions of Hawaii, invasive plants such as strawberry guava have already reduced estimated groundwater recharge by 85 million gallons a day.
Strawberry guava is hard to control manually. In 2008, after years of research, the Hawaii Department of Agriculture issued the first permits for the release of one of the plants native, natural enemies, the scale insect Tectococcus ovatus. This insect will reduce the vigor of strawberry guava without killing it. That means, you can come back and enjoy more strawberry guava, but native forest areas will perhaps be healthier.