In the USA, there have been few scientific assessments of grassland response to burning in seasons other than late spring (the traditional time for burns as this favours warm-season perennial grasses which provide forage for livestock). This study recorded changes in vegetation cover, species richness, diversity and aboveground biomass production in upland and lowland ungrazed tallgrass prairie burned annually for 8 years in autumn (November), winter (February) or spring (April).
The study was undertaken at Konza Prairie Biological Station, Kansas (39°05' N, 96°35' W). Vegetation (typical of native tallgrass prairie) is dominated by warm-season perennial grasses (primarily big bluestem Andropogon gerardii, indiangrass Sorghastrum nutans and little bluestem Schizachyrium scoparium), with high forb diversity.
Burning: Six watersheds (11-39 ha) ungrazed by cattle for over 30 years and spring-burned every 3 or 4 years since 1972, were selected. For this experiment, burning began in November 1993 (two watersheds burned; autumn treatment). Subsequent burns were two watersheds in February 1994 and two in April 1994. The same two watersheds were burned in the same season for 8 years. Average burn dates were 26 November, 17 February and 24 April.
Sampling: Commencing 1994, vegetation composition was assessed in four, 50-m long transects (each with 5 plots), at upland and lowland sites in each watershed. Species cover was estimated in a 10-m² circular area around each plot, and frequency of occurrence (i.e. proportion of plots where a species occurred) recorded. Plots were surveyed each year in June and August.
Aboveground biomass production was measured at the end of each growing season by clipping samples adjacent to each transect. These were divided into graminoid, forb, and woody components, oven-dried and weighed.
A total of 148 plant species were recorded. Site (upland or lowland) affected responses of some species, primarily influencing rate of change. Average grass and forb biomass did not differ among burn seasons in upland or lowland sites.
Autumn and winter burning produced similar trends over time for most species. Big bluestem cover increased with all burn regimes, indiangrass increased only with spring burning. Perennial forb cover increased after several years of autumn or winter burning; largest increases were of three composite species and legumes. Species richness increased through time and was similar among all burn treatments at the end of the study period.
These results are at odds with many views of how tallgrass prairie vegetation responds to season of burning and questions whether burning should only occur in late spring.
If using or referring to this published study, please read and quote the original paper, this can be viewed at: https://www.uair.arizona.edu/holdings/journal/issue?r=http://jrm.library.arizona.edu/Volume56/Number2/