Attracted by higher crude protein, grasshopper abundance and offtake increase after prescribed fire
Nicholas Gregory Heimbuch \(\cdot\) Devan Allen McGranahan \(\cdot\) Carissa L. Wonkka \(\cdot\) Lance Vermeire \(\cdot\) David Branson
2023-10-04
Standing crop removal
Standing crop was statistically-significantly lower outside of grasshopper exclosures in both fall and spring burns (\(t =\) -7.4, \(P\) < 0.001 and \(t =\) -5.8, \(P\) < 0.01, respectively). There was no difference in offtake among spring and fall burns (\(P\) > 0.05), with grasshoppers removing approximately 1.0 (± 0.2) kg ha-1 d-1 in each . Standing crop was not different between grasshopper exclosures and areas accessible to grasshoppers in unburned plots (\(t =\) -0.16, \(P\) > 0.05). Offtake was significantly lower in unburned plots than plots burned in both the previous fall and spring (\(P\) < 0.01 and \(P\) = 0.02, respectively).
| Treatment | Total biomass removal |
|---|---|
| Fall | 64.3 +/- 3.9 |
| Spring | 55.3 +/- 9 |
| Unburned | 0.6 +/- 8.3 |
| Treatment | Daily biomass removal rate |
|---|---|
| Fall | 3.9 +/- 0.5 |
| Spring | 2.4 +/- 1.3 |
| Unburned | -0.4 +/- 1.9 |
Crude protein content
Crude protein content varied among the fire treatments (\(t =\) 57, \(P\) < 0.001. Crude protein content in fall and spring burns averaged 6.4% ± 0.2 s.e. and did not differ among each other (\(P\) > 0.05). But crude protein content in unburned plots was lower than in both fall and spring burns plots (-2.7, \(P\) < 0.001 and -3.1, \(P\) < 0.001, respectively).
Across all samples, crude protein content did not vary among leaves and stems (\(t =\) 2.7, \(P\) > 0.05). Despite a trend towards higher crude protein in leaf tissue in unburned plots , the pattern was not influential enough to create a significant fire treatment \(\times\) organ interaction (\(t =\) 2.1, \(P\) > 0.05).
Grasshopper abundance
Grasshopper density was similar across plots at the beginning of the study period (early July) but increased significantly over the next month in fall and spring burn plots (\(\tau =\) 0.29, \(P\) < 0.01 and \(\tau =\) 0.62, \(P\) < 0.001). Grasshopper abundance remained constant over the study period in unburned plots (\(\tau =\) 0.039, \(P\) > 0.05). While grasshopper abundance increased in both burn treatments, the rate of increase was approximately three times greater in plots that had been most recently burned in the spring than those that had been burned in the previous fall , which represented more than a five-fold increase in density from approximately 10 to 55 grasshoppers m-2.