“Look at those giant birds nests up in the trees!”
The first time we walked through one of New Zealand’s native forests, we noticed what looked like giant birds nests high up in the branches of some of the massive trees. Some of these masses of dirt and foliage were truly immense, measuring five or six feet in diameter and resting on branches more than a hundred feet high off the ground.
Were they birds nests? Or part of the tree? Or something growing on the tree?
One of the initial things you notice if you look closely at trees in a New Zealand subtropical native forest is that the larger trees are covered with countless other plants. No man is an island, and no tree apparently grows by itself. Or at least not for long. Mosses, fungi, lichens and tiny ferns cover the bark of the trees. Various creepers, large and small, cling to the trees sides and wind their way up the trunks or dangle from the branches. Plants and vines balance and gyrate upward from the forest floor trying to catch a purchase on a branch and hitch a ride up towards the sunlight.
In fact, it has been found that more than fifty different varieties of plants can live in and on some of the giant New Zealand native trees. Indeed, so many other things are growing on some trees that it is often hard to identify the tree’s true leaves.
What we were actually seeing when we saw those masses of earth and foliage was another plant living on the branches of the tree, specifically, the perching tree lily, a tall clumping plant with arching flax-like leaves that forms large colonies in forest tree branches.
Two species of perching tree lily, both of which are similar in appearance, occur in New Zealand. Their scientific names are Astelia solandri and Collospermum hastatum; they are called kowharawhara and kahakaha respectively by the Maori.
The perching tree lily is what is called a nest epiphyte. Nest refers to the nest-like appearance of these plants—so we weren’t too far off, although they have nothing to do with birds. An epiphyte is a plant that grows non-parasitically on another plant, as opposed to a parasitic plant that takes something or derives some of its nutrients from the host plant. The perching tree lily is the largest of the so-called nest epiphytes.
With no vines or root system to connect it to the ground, this plant lives its life truly perched on the branches of trees.
The survival strategy of all plant life consists of compromises. By being positioned high above the shaded forest floor, the perching tree lily receives plenty of sunlight; however, the drawback of being perched on a tree branch is that the plant doesn’t have soil with nutrients to grow in, at least not at first, and has no direct source of water and is prone to desiccation. But the perching tree lily has modifications that allow it to live under these conditions. It derives water from the rain and nutrients from the air and the debris that accumulates around it.
The seeds of the plant are spread by birds, which often drop the seeds into crevices in the branch network of the host tree. Often there is moss in the crevice and if enough rainwater collects, the seed germinates. The leaves of the plant form a v-shaped funnel which direct any rainwater down into the base of the plant where a reservoir stores the water for drier times. As the plant’s leaves break down, they are held in place by the plant and thus the plant creates its own compost, which holds moisture and nutrients eventually building up a spongy matte around the base of the plant. Insects also live and die amidst the plant adding to the nutrients in the soil.
A side effect of growing so immense in size and weight is that some of these plants actually succumb to gravity and fall to the ground particularly on windy stormy days, or they grow heavy enough to break off the branch they are perched on. The perching tree lily earned the name “widow-maker” by early New Zealand bushmen for exactly this reason, its propensity to come crashing down when the trees were disturbed.
Do plants like the perching tree lily actually know that they are living on the branches of other plants? Do they plan it that way, and work out the strategy of how to survive under those conditions?
Some biology and ecology books sometimes make it sound as if plants have strategies. A strategy implies something being thought out prior to an action being taken. Does a plant say, “Hey, I think a good strategy would be to send tendrils upward and try to snag onto a branch of a big tree.” Does the perching tree lily say, “I think I’ll live on the branches of this big tree and get plenty of sunlight but I’ll have to work out of system to get nutrients.”
No, nothing is thought out in advance. Everything in nature just does things, and some things work and some things don’t work. Those things that work tend to perpetuate themselves, that is, they lead to survival, reproduction and relative continuance. Looking at such so-called strategies retrospectively—we only see the successes—we tend to think we are seeing something with planning involved.
Do plants have any idea that their so-called strategies work now or will continue to work in the future? Nope. In fact, in a very real sense, nothing in a forest has any sense of what anything else is doing. It’s like a chess game with constantly changing rules. No one knows the rules or what the other side is going to do. Just as no individual species has any idea what it is doing, it also has no idea what it might do in the future. In fact, to be more accurate, none of the plants in a forest even know they are in a competitive environment.
Obviously, for that matter, nothing in a forest has any sense that we, as humans, exist at all. Many of the plants in the New Zealand bush are relatively unchanged from Jurassic times, but we are the only ones that make the distinction between Jurassic times and now.
All of this is in part what makes life so potent. Nothing in nature has any idea what it or anything else is doing. Just as the perching tree lily has no idea or conscious concern what it is doing, neither does Ebola or the millions of other life forms on this earth, which certainly should give us pause when wantonly dealing with them.