For thousands of years, the moa, the large now-extinct, flightless bird endemic to New Zealand (see previous post) was a predominant large herbivore throughout New Zealand.
Plants and animals carry out a continual arms race. Animals, in this case the moa, want to eat the plants expeditiously and the plants want to keep from being eaten.
You might think that all a plant can do is sit there. But over time, selection pressure occurs. Those plants that have any tiny variation that makes them more likely to survive (not to be eaten) pass on those traits, and those that don’t—well, they often get eaten. This all occurs over hundreds and thousands of years. And those traits along with others that promote survival are passed on. When we see a present-day plant, we are seeing the sum total of all the traits that allowed it to survive and fill its particular niche in the forest.
Young plants are particularly vulnerable. For example, if I’m a big tree and a moa eats a few of my leaves, it’s no big deal. But if I am a tiny shoot coming out of the ground or a small sapling and a moa eats me, I’m completely gone. That’s all she wrote.
Some plants protect themselves by camouflaging themselves at young ages so they are less likely to be seen by browsing herbivores. Again, plants don’t camouflage themselves but rather those plants whose color blends in with the ground are less likely to be eaten and thus more likely to survive.
Many New Zealand plants also exhibit a very tangled growth phase when young or in a juvenile form. This is known as divarication and means having branches at a variety of wide intertangled angles. The tiny growing part of the plant is often inside this relative bundle of foliage and thus is hard to get to. In a sense, a plant turns itself inside out, putting its leaves on the inside, and the harder, bark-like, hard-to-munch-on stuff on the outside as a protection. Indeed, in New Zealand some bulwark of defenses similar to this protects most of the growing parts of native plants. And at least one study shows that large birds such as ostriches and emus have significantly more trouble accessing the leaves of divaricating plants.
Lancewood (Pseudopanax crassifolius) has one of the most unique life cycles of New Zealand plants.
When it first sprouts the lancewood’s leaves are brown and mottled and appears like a relatively non-descript plant on the forest floor. Both of these traits cut down on the amount of photosynthesis that can be performed but are perhaps an acceptable trade-off for being able to not be noticed. But as the plant grows taller, lancewood becomes weaponized. Its small leaves develop into meter-long rigid barbed spears slanting downward toward the forest floor. And if that weren’t enough, there are also bright warning spots next to each spike.
Large birds, such as the moa, eat by approaching leaves end-on and sticking them down their throats. The lancewood’s spikes serve to deter any predators lest they risk poking out an eye or being stuck elsewhere by the sharp barbed leaves. The bright spots warn of this. Indeed, detailed study of the lancewood by a team from Victoria University in Wellington in 2009 felt that the purpose of these characteristics was to protect the plant from the moa.
After the juvenile lancewood becomes about 3 meters high, which can take 10-15 years, it changes shape again.
The dagger-like leaves begin to point upward to form the top of the tree and a tall straight trunk develops until its appearance is like that of most other trees in a forest growing up to 20 meters high. All the previous changes are now gone. The difference between the juvenile plant and the adult plant are so striking that early botanists initially mistook them as two different species.
Supposedly the lancewood has reached a height and size where it is out of reach of the moa, and so can “relax” its defenses.
The flora and fauna of New Zealand developed in relative isolation similar to Madagascar and the Galapagos, in a sense allowing all sorts of seemingly-bizarre experiments to occur. Walking in the native forests here, you can see the lancewood tree in both forms. It is details like the story of the moa and the lancewood that make the natural history of New Zealand so fascinating.