The question “What is Native?” is one I have been asked many times during my years growing California native plants. The answer I have given in the past usually went something like this: Any plant that was brought here by humans is exotic, and any plant that occurred here without human intervention is native. One of the problems with such an answer, however, is that it puts humans smack dab in the middle of the picture, and it sets a rather arbitrary time frame by which to decide what is or is not native. Although human beings have indeed had an incredible impact on the planet, it is the relationships between other organisms that lie at the heart of this question. Therefore, I think a better answer would be this: In order for a plant or animal to be considered “native” it must have evolved with the other organisms in the geographic region where it is found. By looking at things on an evolutionary and geological time scale we can begin to make sense of the question of what is native.
Sixty-five million years ago this state was a fairly flat, warm, and wet place. It was inhabited by plants and animals adapted to a tropical climate. Over the course of several geological epochs, California underwent radical changes, becoming cooler and drier and considerably steeper. During this time, plants and animals that relied on warmth and moisture retreated southward, and organisms that thrived in a Mediterranean climate moved in, or evolved from existing populations. During the course of millennia they established relationships and interdependencies that formed the basis for one of the most diverse arrays of life on the planet. One often hears about the incredible diversity of the rainforests, but California is no slouch in that regard; it is home to an astonishing number of plants and animals.
Most of California is bordered by either oceans, deserts, or mountain ranges, all of which present formidable barriers to the movement of plants and most animals. It also possesses both the highest and lowest points in the contiguous forty-eight states, and spans more than a thousand miles of latitude. These factors have combined to produce a vast array of different habitats, each providing its own specific constraints under which evolution may proceed.
None of the many species that make their home in California, however, live in isolation. Each is mixed up in a dance of baffling intricacy and mind-boggling scope. There are, I have been told, over 400 species of gall wasps that rely on the roughly 20 species of oaks found here. These wasps each use a particular part of a particular oak in which to lay their eggs – some choose the young twigs of the valley oak (Quercus lobata), others the leaves of the blue (Quercus douglasii), or coast live oak (Quercus agrifolia). Without the oaks these wasps could not complete their life cycle and would rapidly become extinct. These native wasps and native oaks also have connections to hundreds, if not thousands, of other insects, birds, amphibians, mushrooms, plants, and mammals. Each organism is a strand in the web of interdependencies. A native plant or animal, then, is one that is enmeshed in this miraculous web, this dance of life. Not only is it a participant but, by long association with its neighbors, it is one of the architects of the place in which it lives.
In contrast, a plant or animal that evolved somewhere else, and has recently been introduced to a new habitat, has none of these connections with the local community. Not unlike a person who moves to a new town, the plant or animal will develop relationships with the locals, but these do not have the depth and complexity of those that have evolved over the life of the community, be it hundreds or millions of years. The anise swallowtail butterfly and sweet fennel (Foeniculum vulgare), a plant brought here by European immigrants, have developed that sort of “shallow” relationship. This butterfly once fed primarily on a native plant in the carrot family called yampah (Perideridia spp.), common in grasslands all over the state. Because yampah goes dormant in late spring, the butterfly had only one or two broods each year. With the introduction of sweet fennel, however, which actively grows all summer, the swallowtail now produces multiple broods. But what has been a boon to one species of butterfly is the bane of many coastal grasslands as a whole. In its native habitat sweet fennel is a well-behaved member of a complex community that both supports its existence and restricts its spread. In coastal California it is free from the biotic constraints of its homeland and is spreading rapidly, displacing native species that are more restricted in their ecological associations.
On Santa Cruz Island, off the coast of southern California, sweet fennel covers a huge portion of what were once grasslands, forming such dense stands that it has effectively eliminated all other species of plants from the areas where it grows. This is just one example in a laundry list of species that are threatening our wildlands. Here on the central coast along with sweet fennel are English ivy (Hedera helix), French broom (Genista monspessulana), Cape or German ivy (Delairea odorata), Tasmanian blue gum (Eucalyptus globulus), ice plant (Carpobrotus edulis), pampas grass (Cortaderia jubata), and periwinkle (Vinca major), to name a few.
So what does it matter if the members of our many unique communities are displaced by a few well-adapted individuals from other parts of the world – if western bluebirds and purple martins are replaced by European starlings, and the willow thickets that line our streams are covered in blankets of Cape ivy? The arguments for the preservation of ecosystems seem to break down into two groups: those that see such systems as being necessary for the survival of human beings, and those that advocate such actions in the belief of the intrinsic value of all life.
Perhaps the simplest and, to my mind, the most eloquent statement made in defense of biodiversity from the first perspective was written by Aldo Leopold, one of the founders of the environmental movement. He wrote, that the first rule of intelligent tinkering is to never throw anything away. I picture myself working on my car which, no matter how many times I do it, remains a mystery to me. I can see myself in the middle of a driveway surrounded by oddly shaped bits of metal, some of whose functions I understand and others I can only guess at. There have been times when I put everything back together and, wiping the grease from my hands, I look down and see some seemingly insignificant part lying on top of the engine. Sometimes the car runs fine without it, sometimes it won’t make it out of the driveway. I always save those pieces, whether it seems like I need them or not. Species extinction is occurring worldwide at an unprecedented pace; bits and pieces of the mechanisms of ecosystems are being scattered, or removed willy nilly. We don’t yet know how these plants and animals fit into that complex dance – those mechanisms, that are life on this planet – and we are still finding out how heavily we may rely on them.
The second argument for ecosystem preservation is harder to articulate. My sister teaches third grade, and she was bemoaning the fact that she had the hardest time getting her students to pick up trash in the classroom. They would say: “It’s not my trash, I didn’t put it there.” My sister would then explain that it wasn’t hers either, but that it was everybody’s room, and they were all in this together. We are all in this together, and we have responsibilities extending beyond ourselves, beyond our children, beyond our own society and species, and into the larger community in which we live.
[Reprinted from The Cypress Cone, CNPS Santa Cruz County Chapter, August 1996]