Cabrillo to be “Weed” Free . . . even the pretty ones

Many volunteers have heard the park proclaim that Cabrillo will be weed free. We established the Weed Warrior program to help us reach our goal. Our primary targets the past couple of years have been Iceplant and grass species. Visitors often stop and questions about why we would want to destroy something that looks nice and, after all, is just trying to make its own way in the world. Isn’t the National Park Service an agency of preservation?

The answers to these questions immediately raise several more. What is a “weed” anyway? Why are some plants weeds and others not? Who makes that decision? If they grow here aren’t they adapted to this environment? And why does it really matter? Welcome to the rest of this article.

Figure 1: The flowers and succulent leaves of these Iceplants may be pretty, but at Cabrillo, theses invasive species prevents other native plants from growing.

From a scientist’s viewpoint, these questions start to delve into some really interesting issues in conservation biology. First, the word “weed” is subjective and we use the term somewhat loosely, which is something, we are taught in high school, scientists are loathe to do. In general a weed is a plant that grows very quickly, often in a disturbed area, and is undesirable for one reason or another. Because of that last part, undesirable for some reason, the term is very subjective. One person’s weed may be another person’s bird of paradise. In biology we often use the term “weedy” to refer to an organism that grows very fast and thrives on disturbance, natural or otherwise. In that sense, animals can be weedy too. An example might be rabbits. In the absence of predators and enough food they will multiply very quickly (this actually happened in New Zealand where rabbits were introduced). Or plants that fill in bare space after a fire. Many grasses fall into this category. In the Cabrillo tidepools Ulva spp. (a.k.a. sea lettuce) is considered weedy (but it’s native). But the term as used in biology can apply to any organism, wanted or unwanted, native or non-native. However, when we start talking about invasive species (a.k.a. non-native, introduced, exotic, alien) the negative connotation of the unwanted creeps back into the meaning. We definitely find invasive species undesirable. It just so happens that many of them also share those characteristics of being fast growing and quick to take over after a disturbance. Thus we often describe them as “weeds”. Not scientific, but we use it out of habit and convenience.

So, if an invasive plant adapts to an environment and thrives, is it a weed? Like beauty, it depends on the eyes of the beholder.

Is Iceplant with its’ beautiful flowers and succulent growth adapted to the sage scrub at Cabrillo? Not really. It is adapted to a similar environment somewhere else. It is adapted to a Mediterranean-like environment in South Africa where it originated. But of course, southern California, another Mediterranean-like environment, is very similar and therefore Iceplant thrives here too. It also thrives in Australia for the same reason. (If you are wondering where the Mediterranean regions outside of Italy and Greece are, think of all the places good wine comes from. Those places not coincidentally are all Mediterranean-like in climate.) What it means to be adapted to a particular environment is something you could spend a whole semester on in a college level seminar. One way to think of it, though, is that other organisms at Cabrillo have not adapted to Iceplant. Predators that might eat it, diseases that might infect it, and other plants that might compete with it are probably not found here. They are all in South Africa, where they all had time to adapt to each other. It grows very well in the absence of those things. So it’s the lack of adaptation that may be the key to its success. That’s one hypothesis, anyway. In truth, what makes one species a successful invader is a topic of great debate among scientists.

Why is Iceplant bad? Again, it is bad for Cabrillo for a subjective reason. The goals of conservation biology are always subjective; we simply strive to use objective science to obtain them. We wish to maintain a natural environment. More specifically, the National Park Service has policies (approved by Congress) that specifically state we will not tolerate invasive species (NPS Management Policies 2006, Section 4.4.4). One reason for such a policy is that this agency is charged with maintaining places within its borders in as natural a condition as possible (or in a certain historical condition, such as a battlefield, which obviously is not natural. Certain parks have very specific legislation that may be different from others.) Iceplant got to southern California because humans helped it, either accidentally or on purpose. Ergo, not natural. In addition, invasive species as a group have a tendency to cause a lot of damage, several billion dollars a year in some cases. But there are many intrinsic damages that are not accounted for monetarily. Only 1% of the coastal sage scrub environment which was once found in southern California is remaining. Development has been the main culprit for the loss of coastal sage scrub. Cabrillo is a portion of the 1%. But regardless, when you kill off 99% of something it’s safe to say the rest is highly threatened. All the species that inhabit it are too. We have already lost several species of reptile (e.g. coastal horned lizard) at Cabrillo and there are some plants that are threatened or endangered as well (e.g. sea dahlia, with its lovely yellow flower). The “weedy” nature of many invasive species can take over an area and threaten the native species further. In some cases the invasive species can be toxic in some way to other organisms, out-compete other organisms, or simply be unpalatable to native consumers which in turn have trouble finding food.

A curious aspect of this problem in conservation biology is that it’s all relative. If we were standing in South Africa, there might be some species from southern California that is threatening Iceplant and the other plants it lives with there.

The National Park Service, along with most conservation biologists, finds value in preserving the native environment because it benefits humans in some way. The fact that Iceplant is pretty doesn’t really matter to us. The fact that this point of view is harmful to Iceplant also doesn’t   matter to us. It is subjective to a human standard and we are perfectly willing to kill one thing in preservation of another (the philosophy of that behavior is the subject of another college seminar). If our goal was to make the sage scrub as beautiful as possible, or to make it as yellow as possible, we might try to do something different, and perhaps promote Iceplant as much as we could. But those are not our goals. Preserving (or restoring) the native organisms growing at Cabrillo for the education, inspiration and enjoyment of this and future generations is our goal.

Keith Lombardo pulling Ice Plant

Figure 2: Biologist Keith Lombardo removes invasive ice plant, allowing the threatened, native Sea Dahlia (yellow flowers) to grow.

An astute reader might ask how we decide whether a species has been here long enough to no longer be considered non-native (or invasive). After all, if we went back 10,000 years we would find many species we consider to be native today completely absent. Native Americans moved species around for their own benefit. Early European explorers moved species around for their benefit and accidently. Modern humans move things around on purpose and accidently all the time, and have been doing it for a couple centuries now. Where do we draw the line? Again, it’s subjective. But we need to do it somehow. The National Park Service considers any species that was present before the arrival of Juan Rodriquez Cabrillo in 1542 to be native, and any species that got here with the help of people after JRC to be non-native. If a species is capable of moving here on its own, with no help from people whatsoever, then we generally welcome it to the neighborhood and watch with a curious and scientific eye whether it survives or not. If these policies are debatable, they are also practical.

So . . . death to all weeds! That is our subjective goal, and it seems obtainable. Fortunately Cabrillo is in relatively good shape. Most of the park is dominated by native plants. We have our targets set primarily on a handful of species (e.g. Iceplant, Tocalote, Stinknet, some grasses . . .) with the goal of eliminating them completely over the next few years. A lot of the effort is simple good old fashioned elbow grease and persistent determination. We pull weeds for a few hours every week and have good natured debates on our scientific objectivity at the same time. And if you are eager or willing to help (or even just want to debate our definition of weeds), we definitely like volunteers to join us. If you are so inclined please contact either biologist Keith Lombardo (619-557-5450 x4582, or Volunteer Coordinator Debbie Sherman (619-557-5450 x4590,


Last revised 25-Jun-17