United States Department of Agriculture
Whiteville, North Carolina
In 1974, a US law was passed that commanded that we keep out exotic weeds; Randy Westbrooks believes we should actually do it. While he believes that we can and should control exotics, he points out that our nation is "hooked" on them. For example, at dinner last night we had 14 exotic species and just two native ones.
The idea of harmful exotics is not new but attitudes on the subject have changed in the past 20 years. There used to be no such thing as a weed; not anymore. Some 99% of this country has been used up for the benefit of one species - Homo Sapiens. Humans have cut down 32 million acres of long leaf pine forest in North Carolina alone. It is essential to at least maintain the last 1% of this country that is left in parks.
Biological pollution is a global issue. For the US, the Animal and Plant Health Inspection Service (APHIS) is the keeper of the gate. They can do more and we can do things too. We can't stop all invasions but we can minimize them. Weed science, biology, and plant quarantine are three fields concerned with non-indigenous invasive species.
The issue of species movement began with Pangea, the huge supercontinent that existed 250 million year ago when species could move around freely. When the continents began to split up about 180 million years ago, complex, balanced, distinct ecosystems developed; this would have continued if people hadn't come along. Differing climates and soils, the physical separateness of the continents, and other factors maintained these distinct ecosystems. There are four times as many species on Earth as would be predicted given the land area. One reason for this is that the separate continents have acted as species pumps.
But when humans started migrating around the globe, in the last couple of thousand years, biological invasion really became a problem. Some 4,500 exotic species have been established in the US, and 650 of these are known to be harmful. They cause both ecological and economic harm, reducing biodiversity in ecosystems and adversely effect agriculture and other human activities. The modern era on Earth might be referred to as "The Homogocene" - the time in which the worlds flora and fauna are being homogenized by humans.
Non-indigenous invasive species are biological pollutants that pose a threat to pristine and disturbed ecosystems. Some examples are feral burrows, insects, the HIV virus, and fire ants. We are just trying to control fire ants now, because we know we cannot eliminate them. They came into the US with a load of lumber in 1905 and spread like wildfire throughout the Southern US.
Another invader is Kudzu, a plant introduced in 1876 by Japanese immigrants in Philadelphia. It was also introduced in the 1890s in Florida as cattle forage, and in the 1930s as a roadside erosion controller in Alabama. Kudzu is a pea-like legume that has become an enormous problem in many several US regions. Currently, Kudzu in the US does not produce many seeds because we don't have the pollinating insect that spreads it in Japan. If this insect ever does enter the US, we will really be in trouble. It wasn't until 1963, that we began to realize we had made a huge mistake by introducing Kudzu into the US.
Crab grass is an invasive plant brought into the US at the request of Polish immigrants in 1849. The Gypsy Moth was brought into Massachusetts in 1869 to spin silk and was released during a storm, resulting in widespread infestation. The Asian gypsy moth is now a problem invader in many states, including North Carolina.
The melalueca tree was brought to Florida from Australia to dry out swamp land and make it suitable for agriculture. It is very difficult to predict whether a species will become a harmful invader since we don't know how species will react to new conditions. The melalueca tree seemed relatively harmless for 50 years before its population began exploding in the Florida Everglades. In another Florida example, the state spends $12-14 million a year to keep hydrilla clear of boat ways. Often, people driven by profit motive cause these invasions.
Environmental Effects of Biological Pollutants:
Though very concerned about the effects of chemical pollution and the bioaccumulation of pesticides and other chemicals in ecosystems, Westbrooks believes that biological invasions are an even more significant problem than chemicals in the environment because they are longer lasting.
USDA APHIS is the keeper of the national gate, with agents stationed at all ports of entry. But this is where the invaders come from. The long term goal for APHIS is to protect agricultural and natural ecosystems from invaders before they become biological pollutants.
About 75% of row crop weeds in the US come from other countries. So most of the chemicals we use and most of the money we spend on controlling pests and weeds are due to exotics. Westbrooks thinks it makes sense to use pesticides to control large infestations rather that trying to use biological controls which may not be successful and could allow invasions to spread.
Experience has taught that certain commodities from certain countries are likely to be contaminated with exotic pests. The 1974 Noxious Weed Act provides authority to control 75 species of weeds which come into the US on ships, planes, in water and dry ballast, and in agricultural commodities. APHIS tools for excluding noxious weeds include an inspection guide, an identification guide, and seed collection. However, there is a major problem with the listing system for noxious weeds Ð it takes too long to get dangerous invaders listed for exclusion.
Witchweed is a root parasite on corn and sorghum from Africa. It reduces corn yield 50-75% in ear size, and kills some plants. Tropical soda apple (native to Brazil), is a new exotic weed in Florida that is being spread to the US West in cattle that are moved to range land there. It is also spread by raccoon, deer, and infested sod.
If such invasions continue, the Earth will become simpler and poorer biologically Ð instead of six bioregions, there will be one. Biological pollution is the single most underestimated threat to sustainability. We generally wait until things get out of hand before we do anything about them. Prevention is always better and cheaper than a cure. Can we change our reactive stance to one that is more proactive?
We need to use caution in the movement to free trade. The North American Free Trade Agreement (NAFTA) and the Global Agreement on Tariffs and Trade (GATT) have potentially frightening implications for the movement of species around the planet. If we become a true global village, the final chapter of biological invasion may come to pass. People who want to bring in nonnative species for profit should have to prove that the species has never been a problem as a weed or invader elsewhere. That is not enough though, because there are some species that don't seem to a problem right away but then become a problem later. What can we do? We can work harder to determine the vectors of unintentional introductions, and exercise more control over intentional introductions.
We need research that leads to action - not either one in isolation. Some states have noxious weed laws and can list species independently of federal law, but some do not. The interstate control question is a real morass - very little has existed until very recently. Laws are very different from state to state and conflicting jurisdictions are problematic. APHIS also introduces species for biological control, which may seem like a conflict with what their main purpose is. Education of the public and school children is a critical component in making the APHIS system work.