CGR02 Sweep sampling of Grasshoppers on Konza Prairie LTER watersheds


Sweep samples were taken for grasshoppers (Acrididae) at two sites for each of 14 Konza Prairie LTER watersheds. Samples are taken in late July to early August. At each site on each occasion, 10 sets of 20 sweeps (200 sweeps total) are taken. Stored data include for each site on each occasion: total number of each species (all instars combined) collected and total number for each instar for each species (200 sweeps combined).

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Long-term monitoring of dynamics of species composition and abundances in grasshopper assemblages associated with varying frequency of fire.


Location of Sampling Stations:Two replicate sites per treatment. All sites are on upland (Florence) soils. In order from east to west:

Ungrazed: 002D A:grid V-26, B:U-24; 001D A:T-24, B:R-27; 0SuB A: R-27, B:Q-28; 004F A:Q-28, B:P-28; 020B A:O-28, B:N-28; 002C A:L-29, B:L-31; 0SpB A:K-29, B:J-28; 004B A:H-28,B:F-27.

Grazed: N20B A:S-24, B:P-2; N01B A:S-25, B:P-23; N04D A:L-28, B:K-28; N04A A:G-25, B:F-26; N01A A:G-19, B:G-21; N20A A:G-20, B:E-19

Frequency of Sampling: All sites are sampled twice (approximately 1 week apart) in late July to early August.

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

Methods: Sampling is done by sweeping with canvas beating nets 38 cm in diameter. A sample of 200 sweeps (ten sets of 20 sweeps each) is taken at each site on each occasion. A sweep is taken at each step by traversing an arc of 180o with the net through the top layer of vegetation. After 20 such sweeps, the contents of the net are emptied into plastic bags. Air is squeezed out and samples are kept on ice until they can be frozen. Samples will be sorted and identified to species and instar. At this time, all 'other' insects are also kept.

All samples are taken between 1000 and 1500 hours on clear, calm warm days: cloud cover should be less than 50%, winds less than 24km/hr (15 mph), and ambient air temperature should be 25-40oC.

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 does provide 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.

Weather measurements are taken at each watershed before sweeps are completed. These measurements are recorded as CGR021. Time is recorded on a 24-hour scale, along with five wind speeds taken at 30 second intervals 5 feet above the ground. *Cloud coverage that is directly overhead is estimated by eye and recorded. Wind speed and temperature are collected in miles per hour and Fahrenheit using a WindMate 200 (occasionally temperature is taken from truck's thermometer). These numbers are then converted to metric units in excel when the data is being entered. For wind speed all five measurements are entered, then averaged, and finally converted to kilometers per hour. Temperatures is entered as Fahrenheit and converted to Celsius. All conversions are computed in excel using the existing formulas. The previous machine used to measure wind speed had a limit of detection of 5 mph. If the wind was blowing but could not register on the machine, then it was recorded as less than 5. However, in order to compute an average these measurements were entered as 2.5 mph. Also cloud coverage is sometimes recorded as less than 5% or as a range of percentages but when the data is entered the largest recorded number is used. (Ex. Recorded as less than 5%, Entered as 5; Recorded as 10-15%, Entered as 15)

*For the years 1983 - 2011 wind speeds were not always collected in this manner, instead measurements were taken at 5 second intervals or only one speed was recorded. However, the purpose of the weather information is to determine whether or not samples could be collected within the weather parameters as described above. Once collection has begun, and due to variable conditions on the prairie, the judgment of the research tech is employed to determine adequate collection conditions. (Maps of all grasshopper sites available in Appendix M, contact site IM if needed).

Summary of All Changes:

1982-1987: Sites were sampled at various earlier dates in addition to the late July-early August.

1985: Sweeping was restricted to all sites being sampled (twice, on different dates) in late July and early August. Additional watersheds (002D, 004D (now 0SpB), 004F AND 010D (now 0SuB) were added to the sampling regime for early August to provide more long-term data on the influence of fire frequency on grasshoppers. Sampling on watersheds to be grazed (N01B, N04D, and N20B) was discontinued.

1986: Watershed 004G (now 00WB) was temporarily added. Sampling in June and early July was reduced to watersheds 001D, 004D, 010D and 020B only; too few grasshoppers are collected by sweeping in the first half of the summer for all watersheds to merit sampling.

1987: Sampling in June and early July was restricted to sites 001D, 002C, 004B and 004F.

1994: Fire regime changed for 004D (became 0SpB) and 010D (became 0SuB). In the years when 0SuB is burned the sweeps are done 2 weeks earlier than normal. The summer burn is conducted on the first water appropriate day in late July to early August.

1996: Wildfire in February, burned 004F, 0SuB, 001D and 002D.

1998: 0SuB done earlier than other sites (mid-July) under the mistaken idea that the summer burns were to occur this year.

2002: Grazed (bison) transects were added in N01A, N01B, N04A, N04D, N20A and N02B. An older version of the methods manual indicates that 3 lowland (Tully) sites were once done. Locations were: 001D A: T-28; 004B A: G-28; B: S-28; B: F-28; 020B A: N-29; B: N-29

2011: WindMate 200 replaced previous machine used for checking wind speeds. The previous machine had limit of detection of 5mph. WindMate 200 specifications: Temperature -20 oC to 158 oF accuracy +1.8 oC to 89 mph accuracy +3%.

2013: Beginning with this year, Oecanthinae spp., Gryllidae spp., Tettigoniidae spp., are being added to our list. These are not new species to Konza. We are adding them to the official listing because they are related and ecologically similar.

2016: In years when SuB is burned, pre-burn and post-burn sweeps will be done. Timing for pre-burn will be mid-July and timing for post-burn will be mid-September.

2018: March 14. 004B – A was burned in a wildfire. A third sweep, “C”, will be done in the vicinity of pab011 FC until 2021 when 004b is scheduled to burn per “normal” schedule.

For additional metadata information see: http://lter.konza.ksu.edu/sites/default/files/DC.pdf

For additional methods information see: http://lter.konza.ksu.edu/sites/default/files/MM.pdf

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