Economics of Cogongrass Control in Slash Pine Forests

Journal of Agricultural and Applied Economics, Oct 2007 by Alavalapati, Janaki R R, Jose, Shibu, Stainback, George A, Matta, Jagannadha R, Carter, Douglas R

Cogongrass (Imperata cylindrica), an invasive weed, is a threat to slash pine forests. Using a dynamic optimization model, we estimated the impact of cogongrass on the profitability of slash pine forestry under four scenarios: no threat of cogongrass infestation; infestation is uncertain, and no control measures are taken; infestation is uncertain, but control measures are undertaken by one landowner but not the neighbors; and infestation is uncertain, and control measures are undertaken by everyone. Results indicate that annual net returns per acre under each scenario, respectively, are $25.30, $16.97, $13.89, and $17.38. Results suggest fostering a cooperative behavior among landowners is desirable.

Key Words: cogongrass, infestation, invasive species, productivity, profitability

JEL Classifications: Q0, Q2

Cogongrass (Imperata cylindrica), a perennial grass native to Southeast Asia, has been identified as the seventh worst weed species in the world (Dozier et al.; Holm et al.). This nonnative weed is spreading across forests in the southeastern United States at an alarming rate. Although nine Imperata species have been reported worldwide, only two closely related species, I. cylindrica and I. brasiliensis (Brazilian satintail), are seen in the United States. An ornamental variety of cogongrass, known as "Japanese Blood Grass," is sold for landscaping in the United States. Although this reddish grass is not an aggressive invader, it has the potential to revert to the green, invasive form (Greenlee).

Understanding the habitat of cogongrass will help to realize the potential threat this species poses to managed and unmanaged forest ecosystems of the Southeast (Jose et al.). This weed usually grows in warm areas. However, it has been widely distributed between 45� latitudes in the northern and southern hemispheres at altitudes ranging from sea level to 2,700 m (Holm et al.; Hubbard et al.). It can grow on a wide range of soils from nutrient-poor, coarse sands to nutrient-rich, sandy loam soils. Cogongrass grows in full sun and in deep shade (down to 2% of full sun) and tolerates extreme drought as well as water logging. It thrives in disturbed areas, such as cutover sites, minimum tillage cropping systems, reclaimed mined areas, and roadsides, as well as in less disturbed areas, such as pine and hardwood forests, grasslands, and recreational areas (King and Grace; Willard, Gaffney, and Shilling; Willard et al.). Thus, cogongrass can potentially invade any piece of land and turn into an "alien nightmare" for the landowner (Jose et al.).

History

Literature suggests that cogongrass was introduced accidentally as packing material in Alabama in 1912 from Japan (Jose et al.). In the 1920's, cogongrass was intentionally brought to the United States as a potential forage crop. Forage trials were carried out at university experiment stations in Texas, Mississippi, Alabama, and Florida. Anxious cattle ranchers planted cogongrass to improve pastureland and thus helped spread the species throughout the Southeast. Although it has a short-term forage value while leaves are young and tender, mature leaves are unpalatable because of high silica content (Dozier et al.). As a result, cogongrass lost its appeal as a forage crop very quickly. However, its use for soil reclamation by the Soil Conservation Service and for soil stabilization along roadways by state departments of transportation continued until recently. Further spread throughout the Southeast occurred when soil contaminated with cogongrass rhizomes was used for highway and railroad construction and maintenance work. Most recently, natural and planted forests in the South have become the greener pastures for cogongrass invasions (Ramsey et al.)- Today, cogongrass is sparsely spread throughout the southeastern United States from Texas to Virginia, threatening the ecological and economic integrity of our natural and planted forestlands (Figure 1).

Spread and its Impacts

The spread of an exotic invasive species depends partially upon its ability to multiply and establish rapidly in new habitats. Cogongrass can reproduce by both sexual and asexual means. Cogongrass is a prolific seed producer, with as many as 3,000 seeds per plant. Wind dispersal of seeds as far as 15 mi. is possible (Hubbard et al.). However, low seed germination rates (Shilling et al.) and low viability (Dozier et al.) have been reported as limitations to cogongrass sexual reproduction. Once a plant is established from a seed, its local spread is facilitated mainly through rhizomes. Rhizomes can give rise to shoots at every node (0.5-1.5 in. apart), and each node can produce as many as 350 shoots in 6 weeks covering an area of 43 ft2 in 11 weeks (Eussen). Rhizomes give cogongrass its competitive edge as an aggressive invader. In general, burning, mowing, or even some herbicide applications will not control cogongrass. It can regrow and spread aggressively from the buried rhizomes.

Recent studies in a Florida sandhill savanna have shown that cogongrass can displace most of the sandhill vegetation, except for large trees (Lippincott). Preliminary studies conducted at a northwest Florida longleaf pine forest revealed similar trends (Collins et al.; Jose et al.). Cogongrass can alter the soil chemistry, nutrient cycling, hydrology, and disturbance regimes of the infested site.1 As a result, natural and artificial regeneration of forest stands infested with cogongrass is very problematic. Cogongrass can also create a severe fire hazard in pine plantations and natural habitats. Biomass accumulation of cogongrass can be higher than that of native ground vegetation, and this invader burns hotter because of high silica content. Temperatures as high as 450�C at heights ranging from 0 to 5 ft (Lippincott), if persistent for more than a few seconds, can kill not only tree seedlings, but also juvenile trees in plantations and natural areas (Jose et al.). In sum, the impact of cogongrass on timber and nontimber productivity can be severe (Daneshgar et al.).