Imperata cylindrica (cogongrass) is a rhizomatous perennial grass native to Southeast Asia that forms expansive monocultures which deteriorate habitat quality for native biota. Currently listed as invasive/noxious by state and federal agencies in the United States, it is also noted as a pest in 73 countries on 6 continents. Studies involving cogongrass have traditionally focused on control efforts, revealing that long-term control depends on rhizome elimination. Moreover, basing control evaluations on foliar responses alone often overestimate long-term treatment efficacy due to considerable root mass that has re-growth potential. Currently, a basic understanding of above and below ground biomass, their relative abundances and contributions to growth and survival remains lacking. A study performed in Uganda found that intense grazing suppresses vegetative spread rates and permits co-existence of a number of species within a cogongrass stand. A reclaimed phosphate mine located in Mulberry, FL, offers a unique opportunity to analyze above ground (cover) and below ground (rhizomatous) biomass contributions to growth of variably sized patches (36 sq. m – 1200 sq. m) in the presence of intense seasonal grazing by cattle. This study tests the following hypotheses:  1.) rhizome penetration precedes foliage, indicating stand expansion depends on below ground biomass. 2.) stored energy in rhizomatous material is utilized for re-growth after herbivory, indicating that recovery after disturbance depends on below ground biomass. 3.) light availability directly affects rhizome growth (i.e. growth rate, internodal length) and subsequent above ground biomass growth. Data collection and analysis includes calibrated visual cover estimation and soil core sampling at a 2 sq. m resolution along the perimeter and at the interior of each stand of 4 treatments: grazed, ungrazed, shaded and unshaded (n=4 for each). Additionally, new biomass produced by removed rhizomes is quantified. Patch boundary analysis utilizes GIS to perform Squared Euclidean Distance split-moving window to illustrate sharpness and shape.

Results/Conclusions

Preliminary results indicate a directional relationship between cover and rhizome density, such that the presence of cover indicates the presence of rhizomes, but not vice versa. To date, variability in rhizome density has been highest in areas with little to no cover, immediately adjacent to areas of high cover, supporting the hypothesis that rhizome presence precedes above ground biomass, indicating stand expansion is dependent on below ground biomass. Additional findings indicate that foliar re-growth on removed rhizomes begins immediately (within 24 hrs) after removal in the absence of light and additional moisture.