Imperata cylindrica (Cogon grass) Research

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Daneshgar, P., S. Jose, A. Collins, and C. Ramsey. 2008. Cogongrass (Imperata cylindrica), an alien invasive grass, reduces survival and productivity of an establishing pine forest. Forest Science 54:579-587.

A 27-month-long study was conducted to compare the impacts of Imperata cylindrica (L.) (Beauv.) and native vegetation competition on the productivity of Pinus taeda (L.) seedlings. In March 2003, 1-year-old pine seedlings were planted in the following treatments: vegetation free (VF), native competition (NC), and I. cylindrica (IC) competition. At the end of the study, only 26% of the IC seedlings survived, half of what was observed in the NC treatment. The IC seedlings had significantly smaller root collar diameter than the NC seedlings (P < 0.0001) after the first growing season and by the end of the third growing season the height and stem volume index were significantly less as well (P < 0.0001). After one full growing season, the NC and IC pine seedlings had 21 and 11.5% of the total biomass of the VF seedlings, respectively. After three growing seasons, the IC pine seedling total biomass was 2.4% of that of the VF seedlings and 18% of that of the NC seedlings (P < 0.0001). The greatest difference was in the pine needle biomass with the IC pine needle biomass being only 11% of that of the NC. During the first growing season, the IC pine seedlings maintained the lowest levels of light-saturated net photosynthesis and stomatal conductance. These results may be explained by reduced amounts of foliar nitrogen and water stress that result from I. cylindrica competition. The pines in the IC treatment had the lowest total foliar surface area and the lowest specific leaf area, which may explain the reduced productivity. Evidence from this study suggests that I. cylindrica competition significantly reduces the productivity and growth of P. taeda seedlings compared with that from native vegetation.

Daneshgar, P. and Jose, S. 2009. Imperata cylindrica, an invasive alien grass, maintains control over nitrogen availability in an establishing pine forest. Plant Soil 320:209–218

In a field experiment in Florida, USA, 15N-labeled Ammonium Sulfate was used to compare how Pinus taeda seedlings take up and use N in the presence of I. cylindrica and native vegetation using three treatments: 1) vegetation free 2) native competition, and 3) I. cylindrica competition. Imperata cylindrica competition led to smaller pine seedlings with significantly less N content in the pine foliage and roots than those in the native treatment. Competition from I. cylindrica for N contributed to the pine seedlings taking up a greater percentage of the applied fertilizer than the seedlings competing with native vegetation; however, because of their reduced growth they were less efficient in utilizing the fertilizer N. The belowground biomass of I. cylindrica on average was seven times higher than the native species. Despite its lower N concentration in foliage and roots, it retained significantly more N per hectare compared to the native vegetation. While the native species retained more N aboveground, I. cylindrica held significantly more belowground, thus invasion by this grass would lead to a shift of N pools from above to belowground. The fact that we were able to account for 81.5% of the applied fertilizer in the I. cylindrica treatment compared to 62.2% in the native treatment suggests that I. cylindrica tightly retains most of the available N on site making it a particularly good invader.

Hagan, D. L., Jose, S., and Lin, C. 2013. Allelopathic exudates of cogongrass (Imperata cylindrica): implications for the performance of native pine savanna plant species in the southeastern US. J. Chem. Ecol. 39:312–322

We conducted a greenhouse study to assess the effects of cogongrass (Imperata cylindrica) rhizochemicals on a suite of plants native to southeastern US pine savanna ecosystems. Our results indicated a possible allelopathic effect, although it varied by species. A ruderal grass (Andropogon arctatus) and ericaceous shrub (Lyonia ferruginea) were unaffected by irrigation with cogongrass soil "leachate" (relative to leachate from mixed native species), while a mid-successional grass (Aristida stricta Michx. var. beyrichiana) and tree (Pinus elliottii) were negatively affected. For A. stricta, we observed a 35.7 % reduction in aboveground biomass, a 21.9 % reduction in total root length, a 24.6 % reduction in specific root length and a 23.5 % reduction in total mycorrhizal root length, relative to the native leachate treatment. For P. elliottii, there was a 19.5 % reduction in percent mycorrhizal colonization and a 20.1 % reduction in total mycorrhizal root length. Comparisons with a DI water control in year two support the possibility that the treatment effects were due to the negative effects of cogongrass leachate, rather than a facilitative effect from the mixed natives. Chemical analyses identified 12 putative allelopathic compounds (mostly phenolics) in cogongrass leachate. The concentrations of most compounds were significantly lower, if they were present at all, in the native leachate. One compound was an alkaloid with a speculated structure of hexadecahydro-1-azachrysen-8-yl ester (C23H33NO4). This compound was not found in the native leachate. We hypothesize that the observed treatment effects may be attributable, at least partially, to these qualitative and quantitative differences in leachate chemistry.

Willard, T. R. and D. G. Shilling. 1990. The influence of growth stage and mowing on competition between Paspalum notatum and Imperata cylindrica. Trop. Grasslands 24:81-86.

In greenhouse experiments, cogongrass was more competitive than seedling bahiagrass but much less competitive than established bahiagrass. Mowing slightly increased the relative competitiveness of established bahiagrass. When grown in pure stand, 2 mowings caused an 8 percent and 21 percent decrease in the foliage weight of cogongrass and established bahiagrass, respectively. However, when the 2 species were grown in a 50:50 mixture, 2 mowings caused a 45 percent and 13 percent decrease in the foliage weight of cogongrass and bahiagrass, respectively. These data indicate that under conditions of no nutrient or water stress cogongrass effectively competed with seedling bahiagrass but not with established bahiagrass.

Summaries and Reviews

D. P. Garrity, M. Soekardi, M. van Noordwijk, R. de la Cruz, P. S. Pathak, H. P. M. Gunasena, N. van So, G. Huijun & N. M. Majid (1996). The Imperata grasslands of tropical Asia: area, distribution, and typology. Agroforestry Systems volume 36, pages3–29

The rehabilitation or intensified use of Imperata grasslands will require a much better understanding of their area, distribution, and characteristics. We generated estimates of the area of Imperata grasslands in tropical Asia, and suggested a typology of Imperata grasslands that may be useful to define the pathways toward appropriate land use intensification. We conclude that the area of Imperata grasslands in Asia is about 35 million ha. This about 4% of the total land area. The countries with the largest area of Imperata grasslands are Indonesia (8.5 million ha) and India (8.0 million ha). Those with the largest proportion of their surface area covered with Imperata are Sri Lanka (23%), the Philippines (17%), and Vietnam (9%). Laos, Thailand, Myanmar, and Bangladesh evidently all have similar proportions of their land area infested with Imperata (about 3 to 4%). Malaysia (< 1%), Cambodia (1%), and the southern part of China (2%) have but a minor proportion of their total land area in Imperata. The species was found widely distributed on the full range of soil orders. It occupied both fertile (e.g. some of the Inceptisols and Andisols) and infertile soils (Ultisols and Oxisols) across a wide range of climates and elevations. Imperata lands fall into four mapping scale-related categories: Mega-grasslands, itmacro-grasslands, meso-grasslands, and micro-grasslands. The mega-grasslands are often referred to as ‘sheet Imperata’. They are the large contiguous areas of Imperata that would appear on small-scale maps of say 1:1,000,000. We propose that this basic typology be supplemented with a number of additional components that have a key influence on intensification pathways: land quality, market access, and the source of power for tillage. The typology was applied in a case study of Indonesian villages in the vicinity of Imperata grasslands. We propose an international initiative to map and derive a more complete and uniform picture of the area of the Imperata grasslands. This should include selected studies to understand conditions at the local level. These are critical to build the appreciation of change agents for the indigenous systems of resource exploitation, and how they relate to local needs, values and constraints.

MacDonald, G.E. (2004) Cogongrass (Imperata cylindrica): Biology, Ecology, and Management. Critical Reviews in Plant Science, 23, 367-380.

Cogongrass is considered to be one of the ten most troublesome and problematic weedy species in the world. This species is found throughout tropical and subtropical regions, generally in areas disturbed by human activities. Over 100 common names have been associated with cogongrass, including japgrass, speargrass, alang-alang, and bladygrass. Although this species has several commercial uses, the problems associated with its weediness far outweigh most positive benefits. Cogongrass is a major impediment to reforestation efforts in southeast Asia, the number one weed in agronomic and vegetable production in many parts of Africa, and is responsible for thousands of hectares of lost native habitat in the southeastern U.S. Biologically, cogongrass possesses several features that foster its spread and persistence. Management efforts for cogongrass consist of an integrated approach with several control strategies. In agronomic production, the use of cover crops is widely successful, but incorporation into the overall production scheme is challenging. Success has been achieved with continuous deep tillage or chemical applications, but long-term eradication/suppression must employ sustainable revegetation strategies.

Penulis: A. Sunjian