patch-burn grazing

PBG07 Grasshopper species abundances in the Patch-Burn Grazing experiment at Konza Prairie


‘PBG’ datasets are associated with a long-term, large-scale study that is addressing the effects of fire-grazing interactions in the context of a Patch-Burn Grazing management system designed to promote grassland heterogeneity. Effects of patch-burn grazing management on plant and animal diversity and the nature and variety of wildlife habitat are being assessed in two replicate management units, each consisting of three pastures (watersheds) designated C03A/C03B/C03C and C3SA/C3SB/C3SC. In each patch-burn grazing unit, one watershed is burned and two that are left unburned in a given year. The burning treatments are rotated annually so that each pasture is burned every third year. Each patch-burn grazing unit is paired with an annually-burned pasture for comparison with traditional grazing systems (C01A and C1SB). All grazing units are stocked with cow/calf pairs from approximately 1 May until 1 Oct at a stocking density equal to 3.2 ha per cow/calf. To examine the impact of patch burning and grazing in all 8 units, we monitor changes in plant species composition, residual biomass, grassland bird populations, insect populations, small mammal populations, soil nutrients, and stream water quality1(1C3SA/C3SB/C3SC unit only). The KSU Department of Animal Science monitors cattle performance, including weight gain and body condition to assess the economic feasibility of using patch-burn management on a widespread basis.

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To estimate grasshopper densities in the patch-burn grazing experiment. Model response to grazing.


Location of Sampling Stations: Grasshopper density is determined on upland topographic locations. C3A, C3B, C3C, C1A, C3SA, C3SB, C3SC, C1B. 4 sits per watershed, 4 transects per site.

Frequency of Sampling: Grasshopper abundances are sampled once in late summer (August-September), with each site sample twice in a season a week apart.

Variable Measured: Number of individuals (categorized by instar) for individual grasshopper species.

Methods: Three watershed units (C3A, C3B, C3C) constitute 'patches' that are alternately burned in a 3-year rotation within a single, fenced pasture (i.e., patch-burn grazing). Two additional watersheds are serving as controls: a grazed, annually/uniformly-burned watershed (C1A) and an ungrazed, annually/uniformly-burned watershed (1D).

Grasshopper sampling is done by standardized sweeping with canvas beating nets 38 cm in diameter. A sample of 250 sweeps (ten sets of 25 sweeps each) is taken at each site (4 independent sites per watershed) on each occasion. A sweep is taken at each step by traversing an arc of 1805 with the net through the top layer of vegetation. After 25 such sweeps, the contents of the net are emptied into individual plastic bags. Air is squeezed out and samples are kept on ice until they can be later frozen that same day. Samples are sorted and identified to species and instar at a later date. Samples are taken between 1000 and 1500 hours on clear, calm warm days: cloud cover is less than 50%, wind speed less than 24km per hr (15 mph), and ambient air temperature should be 25-40oC.

Sampling is replicated at each site a week apart. Sweep sampling methods follow those used for grasshopper sampling in the bison grazed watersheds. Sweeping effectiveness varies with site and season on Konza Prairie (e.g. sweeping is less effective on unburned prairie than on burned prairie). However, sweeping provides good estimates of relative abundances of individual species present at any one place and time on both burned and unburned prairie. For more information, consult: Evans, E.W., R. A. Rogers, and D.J. Opfermann.1983. Sampling grasshoppers (Orthoptera: Acrididae) on burned and unburned tall grass prairie: night trapping vs. sweeping. Environmental Entomology 12:1449-1454. Rarefaction calibrations determined that the cumulative species abundance curve reached an asymptote between 175-250 sweeps.

Note: in 2012, data missing for watershed C3B, Repsite A.

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