It’s that time of year. From mid-November when the oak leaves have fallen until snow covers the ground it’s prescribed burn season at Timberhill.  We have found that annual dormant season burns have the least impact  and best meet our goal to control woody undergrowth and stimulate fresh new growth of forbs and graminoids.  But getting it done each year is easier said than done.  First of all the volunteers who help us burn work full time during the week and can only help on weekends.  So the weather has to cooperate.   Then we have to find four people to help.  Our regular crew consists of three people so we’re always looking for a fourth.  Given the criticism we have had of our burn regimen it would be easy to find excuses not to burn every year.

Although one may vary the timing with occasional late summer or fall burns, prevailing opinion supports a regimen of  spring burns where one third of a site is burned each year on a three year rotation.   The primary criticism of our burn regimen, therefore, is one of timing. Instead of spring we always burn during the dormant season (November 15-April 1) when fire does the least damage.   We ignite each burn unit along the firebreaks and do not reignite what doesn’t  burn inside the unit. This results in a patchy burn. Because of the low fuel load annual fire scuds over the surface and does not heat the soil preserving the underground fungi and microbes.   A study by Dr. Sandra Rideout-Hanzak (Texas A &M University-Kingsville) recorded ground temperature on thermocouples placed in the ground prior to and after a dormant season burn .  The thermocouples did not record any temperature change one inch below ground.

After burn photo showing unburned wildflower stalks and leaf litter

Plants and animals are least vulnerable to fire during this time of year.  They are not reproducing, and the reptiles and small mammals are hibernating.   Insects are in diapause and fire adapted species have burrowed into the ground.  Late fall and winter burns leave many partially burned and unburned patches that retain habitat  for leaf litter dwelling insects often the most affected by prescribed burns. Their populations will decline after a burn, but recolonize quickly  on the abundance of lush plants stimulated  by fire.

The studies that suggest  insects are being extirpated from fire managed sites and that fire exclusion will result in greater species richness and populations has been disproved by Ron Panzer and Mark Schwartz. Their paper “Effects of management burning on prairie insect species richness within a system of small, highly fragmented reserves” compared the population density and species richness of remnant dependent insects in Chicago area burned and unburned prairie remnants.  In sites burned as frequently as every two years they found that,  ”Prevailing rotational, cool season burning practices have generally been compatible with the conservation of insect biodiversity within the highly fragmented prairie reserve system in the Chicago region.”

Of the 27 butterfly species studied, four were found exclusively on fire managed sites. This was also true of the 67 leafhoppers studied:  19 occurred exclusively on fire-managed sites.  Even fire-sensitive species “occurred in significantly greater numbers within fire-managed sites.” This paper concludes that “In contradiction to the predictions of these observers [fire attrition advocates], the data presented here suggest that rotational burning has contributed to the protection of several species that would otherwise have been lost.”  In other words fire managed sites create habitat for conservative species not found in unburned sites.

Regal fritillary at Timberhill

This is certainly true at Timberhill.  In only two days here last summer. Biologist Laura Rericha was able to collect  29 species of native bees.   Two were very conservative species. A study she made of Timberhill ants identified 57 species, two of which were Iowa records. The Timberhill butterfly list includes 14 skipper species and  continues to grow each year.   Even regal fritillaries are observed nectaring on butterfly milkweed each summer.     So whenever I am tempted to give in to prevailing opinion and change our burn regimen I  recall the adage, “Don’t fix what isn’t broken.”