Sunday, February 11, 2007

Not all invasive species are exotics

We often think of invasive or noxious species as exotic species that have come to a new area from some far off place-examples include the starling, fire ants, zebra and quabba mussels, or kudzu. Indeed here in Eastern Kansas its difficult to find a habitat that doesn't have it's complement of these sorts of invasive species. Yet some native species have characteristics of invasive species. A good example in Kansas is the red cedar.

Red cedar is not a true cedar but is a juniper (Juniperis virginiana). I've always had mixed feelings about this tree. On the one hand it is great for many species of wild birds since it both provides shelter and food in the form of these berries from a USDA website:

When relatively scarce it can provide a nice contrast in the land scape. On the other hand it is very invasive. For instance I don't have any red cedars in my yard but have to constantly fight the seedlings in my garden. It seems they just happen to germinate in those areas of the garden where I have my prized butterfly weed growing-an invasive species battle on the small scale. Red Cedar's native range is throughout much of the Eastern United States and west through Central Kansas. Indeed, the Red cedar is Kansas' only native conifer. A good range map is here from the United States Geological Survey's website.

So if it is a native species-why is it classed as an invasive species? First of all it is an exotic invasive species in certain parts of the United States, in both Oregon and Hawaii. Next within its and around its native range, the Red Cedar is spreading into grassland systems where it allegedly reduces the productivity of range land by altering the microclimate around the trees which encourages the growth of less desirable non native cool season grasses, according to the Nebraska Extension Service.

The Red Cedar may also be allelopathic, that is produce chemicals that inhibit the growth of other plants, Stipe, Dan J and Thomas Bragg(1989). Allelopathy may be an important reason for the success of many exotic plant species. This idea is termed the "Novel weapons hypothesis", Calloway R and W. Ridenour (2004. By the way red cedar is the source of cedar for hope chests and pet beddings and the 'cedar oil' because of it's repellent effect on insects, Schmidt, T and Wardle T (2002).

The Nebraska Extension Service has some interesting tidbits on control. Complete eradication is not feasible and probably not desirable. Fire seems to be the most effective control where feasible especially when the trees are small. The extension service also says that goats have been used as control, and recommends 10 goats per acre in lands that can be fenced and expect to let the goats graze for several years or else the trees will recover.

This image shows my own little cedar problem. These seedlings appear to have germinated from mulch I obtained from the City of Lawrence's mulch program or from a local garden store.

So what we have in red cedar is a species, that has at least some of the characteristics of more traditional invasive species: adaptability to many habitats, suitability as an early successional species, rapid dispersal, ability to crowd out other species by direct competition for resources by altering microclimate and indirectly by allelopathy. Further the spread of this species into new habitats appears to be related to human interference with these habitats. In the case of red cedar and the prairie ecosystems its spread appears to be facilitated by suppression of the fires that maintain the open prairie combined with loss of large grazing herbivores especially the bison, an issue discussed by Collins et al(1998).

Whether red cedar is called an invasive species or just a noxious species really hides the more important issue, that the ecosystems of this planet are being altered by human activity at an increasingly rapid rate, bringing about unpredictable changes in the ecosystems of this planet. This is true even in the absence of the current focus on global warming. Like it or not we are creating a global flora and fauna, consisting of those relatively few species who just happen to have a mix of characteristics that enables them to survive the effect of human disturbance.

My own belief is that we are long passed the point where most of the planet's ecosystems, at least terrestrial and freshwater aquatic systems, are robust enough to survive the rapid changes we as a species are making without management. We can talk about creating reserves to preserve some remnant of biodiversity as E.O. Wilson has, but unless we have a global consensus that we need to manage the affects of human disturbance, the long term prospects for maintaining some significant fragment of biodiversity at all levels of scale are not good.

By the way if you are interested in keeping up with the latest on invasive species, Dr. Jennifer Orth has a wonderful blog called appropriately the Endangered Species Weblog. (oops update! Poor Dave points out it's Invasive Species Weblog....)

Other links:

Calloway R and W. Ridenour (2004) "Novel weapons: invasive success and the evolution of increased competitive ability" Frontiers in Ecology and the Environment: Vol. 2, No. 8, pp. 436–443.

Collins S L, Alan K. Knapp, John M. Briggs, John M. Blair, Ernest M. Steinauer (1998) "Modulation of Diversity by Grazing and Mowing in Native Tallgrass Prairie"
Science. Vol 280 pp 745-747.

Schmidt, T and Wardle T (2002) "Impact of Pruning Eastern Redcedar
(Juniperus virginiana) " Western Journal of Applied Forestry, Vol. 17, No. 4,pp 189-193.

Stipe, Dan J and Thomas Bragg(1989). "Effect of eastern red cedar on seedling establishment of prairie plants" in Prairie pioneers : ecology, history and culture : proceedings of the Eleventh North American Prairie Conference pp. 101-102).

Technorati Tags:

Post a Comment