During the second week of our mid-trimester break, while my friends were off exploring the other half of the South Island, I was back in Wellington because my New Zealand Flora and Fauna class had a week of mandatory field work. We went out to a native bush area called Otari-Wilton’s Bush and an eco-sanctuary called Zealandia, and spent our time studying some of New Zealand’s native plants and birds out in the wild. Even though I wasn’t technically on vacation anymore, it was a really nice break for me to be outside doing hands-on study instead of being stuck in a classroom. I learned a lot over the five long days of coursework, and now I can go out into the bush pretty much anywhere in the country and show off my super nerdy tree and bird knowledge by pointing out some of the most common species as we pass them. I learned around 8 birds and 20 plant species, and I know at least a few will be burned into my brain forever after the amount of time I spent studying them (I’m looking at you, Pseudopanax crassifolius).
But beyond memorizing leaf appearances and bird calls, I learned a lot about the irregularity of the plants and animals in this country compared with mainland species. Life behaves very differently in an isolated environment, and New Zealand’s lengthy separation from the rest of the world has given rise to some really interesting evolutionary patterns and adaptations. For example, a significant number of plant species demonstrate heteroblasty. Heteroblasty is any measurable change in appearance or function of a plant over its lifetime. The two most important heteroblastic characteristics to examine in New Zealand plants are leaf morphology and branching patterns.
New Zealand doesn’t have any native land mammals, and especially not mammalian herbivores, so most of the plant-eating animals in the country are birds. Because of this, plants need to have special adaptations to avoid being predated by toothless, beaked animals. One of the ways they do this is through their branching patterns. Much of New Zealand’s fauna exhibits something called divaricate branching. Divaricate branching is a science-y way of saying plants have branches that come off at wide angles. Think obtuse angles, almost horizontal. This gives plants a distinct matted, scrubby look, and makes it a lot harder for them to get eaten. Imagine trying to swallow two branches in the shape of a V that is wider than your mouth, with no teeth or lips to help you out. If you’re a bird and have the option of eating that plant or another species with normal branches, you will probably learn to avoid the divaricately branched plants for easier targets that offer a bigger energy return for less work.
The other most visible sign of heteroblasty in New Zealand plants is leaf morphology. Many native plants exhibit striking changes in leaf appearance in different stages of their life. Seedling, juvenile, and adult plants take on very distinct characteristics, to the point that many tree species were classified as multiple species in the past based on morphological differences. While adult plants in New Zealand look relatively normal, the leaves on seedlings and juveniles look wildly different. They are generally either very small with coloration meant to camouflage them, long and thin, or hard with sharp serrations to deter herbivorous predators and minimize the payoff animals get by eating them. Then, once they become adults, plants generally have normal, leaf-shaped leaves that are soft and green and of a normal size with relation to the tree. In New Zealand, this transition usually occurs at a plant height of approximately 3 meters across the board, regardless of species. Researchers have explained this using what has been termed (by one of my professors) the moa hypothesis. The moa hypothesis, in succinct terms, says that plants evolved certain characters to defend against flightless browsing herbivores (like the moa, a large extinct bird in the ostrich family), and the largest recorded moa was around 3 meters tall. Thus, plants have these evolved defense systems until, based on historical predator-prey interactions, they “outgrow” the need for them.
Evolutionary adaptations are really amazing. Taking New Zealand Flora and Fauna has opened my eyes to some of the ways plants defend themselves and change to thrive in a specialized environment with specific predators and cohabitants. Even though I don’t see myself becoming a botanist, I still really enjoyed spending time in the field identifying trees and shrubs and it was kind of fun to be able to point out cool plants to my friends on hikes and be an endless source of leaf and bird facts. This class has just been one of the many unique opportunities I’ve had here that makes me so glad I chose Wellington, and I’m so grateful to be here that the long 8 hour days in the field (while I was sick with a cold/flu/sinus infection, no less) were tolerable… I might even say they were fun if you ask me on a good day