By Christopher Marciello:
Quite simply, they grew here. They have adapted to the environment that we are choosing to live in. Plants, like everything else, die. Any time one is transplanted (or just plain old planted), there is a possibility of its dying. That’s just how it is and those of us who relish our kinship with the children of green algae know this to be true. Now, when you put any plant into a foreign environment, one for which it has not developed survival skills over centuries, the likelihood of its expiring increases exponentially.
To provide exotic plants with a suitable living environment, often times we have to go through some extremes to accommodate them. Of course there are exceptions, most notably plants that are Mediterranean or South African in origin. They love it here. An example is rosemary, Rosmarinus Officianalis. This member of the mint family thrives here. It has made Southern California its second home. It’s used in borders, as a form of erosion control, and it will take over. Another is red-flowered ice plant, Malephora Crocea. This South African visitor is often used for erosion control and has become ubiquitous in low water, low maintenance areas. This plant, while slightly less invasive than some other varieties of “ice plant,” is invasive. If its seeds spread, it will take over — and it’s vigorous.
But I digress slightly. These are some examples of plants that do well here; many others require us to use very finite resources to provide them a home. The biggest example of this would be turf grass. There are quite a few varieties and, to keep it simple, I will ask this: Where in San Diego County do you find any place that is not in an oak grove or some type of similarly shaded spot that looks like a lawn or golf course? Now, I’ve hiked all over SD County and in my experience I can honestly say it doesn’t exist. Know why? The grasses that are used for turf grass don’t grow here. It’s that simple. Turf grass is thirsty and SD county gets between 9 and 13 inches of rainfall on average. That is a substantial amount if you have invested your energy in a rainwater harvesting system. If you haven’t, then the water is coming out of the massive aqueduct moving it across miles of desert and urban areas.
The article I’ve linked to talks about this water usage. “California’s cities and suburbs used approximately 8.9 million acre-feet of water in 2000, or about 232 gallons per person per day..” www.ppic.org/content/pubs/cep/ep_706ehep.pdf . That report is now almost 7 years old. There are quite a few more of us here now and a lot of us want lawns. In addition, a fair portion (80%) of the water we are using is from an out-of-state source, some having traveled to us for over 400 miles.
There are alternatives to the common turf grasses. They are not going to look like a turf lawn, however. What they do create is a gorgeous meadow, and — as opposed to having a personal putting green in front of your house — you can create an ecosystem that, once established, will thrive, using only the most essential of resources.
Secondly, non-native species can show a type of behavior known as allelopathy, a biological phenomenon in which a plant excretes chemicals into the soil to prevent competition from other plants. This characteristic is greatly reduced in plants that have co-evolved, but for natives this can be quite damaging.
Which leads us to another cause for transitioning to a native plantscape: Less work.
On average you’ll have to babysit your plantings for the first year, a little longer for some. By then, the system has begun to work and for the most part it will take care of itself. Keep in mind that often plants are sold as drought tolerant, and this is mostly true for the correct varieties. What drought tolerant does not mean is that you will necessarily find them aesthetically attractive during said drought. This can be mitigated with water conserving additions such as earth works, the creation of earthen barriers woven into the landscape that slows the movement of water off the property and encourages absorption on site, and rainwater harvesting. Natives tend to respond well to both of these water harvesting techniques. Grasses for certain will appreciate your efforts.
In addition — and this goes back to the original point — for all intents and purposes, many of the exotics that are used are weeds. They choke out natives, deplete the soil layers, and thus create environmental pollutants that end up in our drinking water (which we then filter with other chemicals to make it drinkable) and ultimately in our oceans. The ocean and beaches, I believe, are two of the main reasons we live here.
Exotics can displace the nutrient balance within the soil. While some plants draw nutrients from deep within the soil, others remove them from the top layers. When a non-native begins to disrupt the soil structure, it prevents native plants from access to vital nutrients. This eventually interrupts the ecosystem that has built itself in the area. Also, non-native species can be allelopathic, as previously discussed, thus preventing competition from other plants. This can be quite damaging. Plants require three main nutrients, in addition to 10 others: nitrogen (N), phosphorus (P), potassium (K). When placed onto or into the soil and at levels which cannot be absorbed by the plants, they become toxic to the environment.
How do exotics help create environmental pollutants? This is how:
Since they have no natural defenses against the “pests” within the region where they’re being inserted, exotics often require some type of pest control or significant soil amendments, nitrogen being a major example. The algae blooms which follow rainstorms often are the result of excess nitrogen making its way to the ocean from agricultural and yard run off. Excess nitrogen in drinking water becomes nitrite, which is linked by the US EPA to birth defects and cancer. In addition, it is implicated as a complicating factor in insulin-dependent diabetes, hyperthyroidism and central nervous system malformations ( Environmental Health Perspectives, Feb, 2007). This is a significant risk for young children and pregnant women. Here is an excellent, short article about the effects of excess nitrogen: www.vision.org.