Hawaiʻi is extremely special because of our geographic isolation and unique biodiversity. A combination of dispersibility, random chance and fitness allowed a small subset of plants and animals to make the 2,400-mile journey and evolve into our diverse native species. The severe isolation of the Hawaiʻian Islands contributed to the evolution of endemic species which are found nowhere else on Earth. 90% of our native plants are endemic, the last 10% are indigenous. On average, over a period of 70 million years, 1 plant successfully colonized every 10,000 years.
Throughout the ages Hawaiʻi’s native plants and animals cooperated, complementing each other’s roles and filling niches. The long process of evolution, in the absence of predators and humans, rendered the native flora and fauna almost defenseless. They lost their thorns, spines, poisons, and bad tastes because they were simply not needed. Why spend energy on an expensive security system when you have the world’s biggest moat, the Pacific Ocean?
Polynesian introductions – 0 to 50 nonnative species (400 AD to 1777)
The isolation of Hawaiʻi was interrupted with the arrival of the Polynesians and their 50 nonnative species. The Polynesian plants lived in relative balance with the native plant species. No plant was crowed out or displaced due to the newly arrived plant species. Eventually, almost all of the Polynesian introduced species naturalized. On average, over a period of 1,400 years, 3 plants naturalized every 100 years. A human footprint was made, small in comparison to the onslaught that would come as the world discovered the “Crossroads of the Pacific.”
The crossroads of the pacific – 50 to 250 nonnative plants (1778 to 1950)
More and more plants along with ungulates were introduced to Hawaiʻi as whalers, missionaries, voyagers and plantation workers made the arduous journey across the ocean. The hillsides once clothed in an abundance of native vegetation were eaten to nothing, destroyed in favor of ranching, agriculture and development. The native plants had no defenses against the onslaught of hooved animals, who roamed freely across the landscape for over 100 years while voraciously consuming any available vegetation and compacting soil, preventing new plant growth. Humans added to the problem by overharvesting wood; trees were cut faster than they could be replenished. As forests were cleared for pasture and development, the impact on our natural resources became alarmingly apparent. Muddy rivers carried away precious soil during heavy rains, and sheets of brown water runoff dumped sediment on coral reefs. In many places, so much soil washed away that only bedrock was left. The agricultural industry felt the effects of this soil loss and lack of water replenishment. Many forestry trees were imported to prevent more soil runoff and for experimental plantings: Albizia, Cinnamomum verum, Macaranga mappa, Psidium cattleianum and Schefflera actinophylla. These species naturalized within unprecedented lag times, 14 years on average. This is an extremely fast lag time when compared to European tree plantings where lag time averaged 170 years.
Modern times – 250 to 12,000 nonnative plants (1951 to present day)
In modern times horticultural plants are being imported to Hawaiʻi and dispersed by humans at an accelerated rate due to the advent of the internet age and fast shipping. We live in a global economy where anything we want is just a click away and a few days wait for your package to arrive. It is legal to import > 99 % of plants to Hawaiʻi, even plants listed as invasive or weedy.
There are an estimated that 12,000 intentional introductions being cultivated in Hawaiʻi, with more being imported and planted every day. A small percentage of these plants are likely to escape cultivation to invade our landscape and negatively affect our natural resources. Recently Hawaiʻi has been called “The endangered species capital of the world”, this is after a less than 300 years of exotic introductions since Cook’s arrival. One study suggested alien plants are the main cause of biodiversity loss in Hawaiʻi, while the US Mainland lists habitat destruction as their main cause for biodiversity loss. We can get ahead of the problem by planting pono, using plants that won’t over power and displace the native species.