Fire Regime Proposal

“Managers must not be so concerned with the short-term effects that they lose sight of the future needs of species. A fire-damaged tree will continue to provide habitat for countless species until and even after it dies.”

A pre-burn briefing should be conducted before every prescribed burn.

This portion of the Fire Management Manual will be devoted to the spatial and temporal details of prescribed fire at the Preserve – where and when fire treatments will occur. The benefits of prescribed fire for native plants are discussed in the Justification portion of this manual. Covered here will be how fire treatments can be planned to benefit other conservation targets such as birds, mammals, amphibians, reptiles and invertebrates.

Weather Conditions for Prescribed Burning

Of all the variables involved in predicting suitable weather for prescribed burns, none is more important than Relative Humidity (Rh) and it’s interaction with air temperature. The ideal relative humidity for a burn will be between 25% and 60%. Below 25% is considered too hazardous to burn and at humidity levels above 70% grass burns poorly, if at all.

In predicting the change in relative humidity, as it is affected by air temperature through the day, a good rule of thumb is that Rh will drop to ½ of its previous value as air temperature increases by 20º F. and Rh will double as air temperature falls 20º F. If the early morning air temperature is 40º with an Rh of 84% and the high temperature for the day is expected to be 80º, it would not be a safe day to burn. As the air temperature warms to 60º the Rh will fall to 42% and at 80º the Rh will plummet to 21% - too dry to burn. It is also considered hazardous to burn when air temperatures are above 80º as fire behavior becomes erratic at these temperatures.

Ideal atmospheric burn conditions are slightly unstable to promote good smoke dispersion. At Asylum Lake Preserve, a steady breeze of 3-12 miles-per-hour, from the south or southwest, are optimum conditions in which to burn because the fire will be carried in a predictable direction. It is not recommended to burn on an extremely calm day as wind gusts can carry the fire in unanticipated directions.

It is difficult to predict good burn weather more than a few hours ahead of time, but weather conditions at the Preserve should be monitored for several days in advance of a possible “window” of opportunity. Meteorologists should be consulted to make sure frontal systems will not be moving through the area on the day of the anticipated burn. The site should be walked on the day of the burn to check wind direction, wind speed and relative humidity. A test fire should always be conducted to double check conditions.

Fire Effects on Wildlife Foods

In addition to their aesthetic and ecological value, the plants which comprise the restoration also serve as sources, or attract sources, of food for a diverse number of animals and insects. Prescribed fire has a number of positive affects on these plants as outlined below.

Fire Effects on Birds

Of all the North American grasslands, tall and mid-grass prairies have been among the most severely altered by human activities. Over the past 25 years, data from the USGS North American Breeding Bird Survey indicate that almost 70% of the 29 grassland birds surveyed showed evidence of declining populations.

Henslow’s Sparrow (Ammodramus henslowii), a species found in tallgrass prairies, savannas and grasslands is now on the Audubon Watchlist. Breeding Bird Survey data indicate that populations of this small sparrow have declined more than 80% since 1966. The reason for the decline is loss of habitat to agriculture and sprawl and the succession of grasslands and savanna to shrub and forest environments. The species has evolved to occupy a small niche made possible by the ephemeral nature of grassland habitat. Preferring denser habitat in which to nest, Henslow’s Sparrow finds grasslands that are 2-3 years post-burn to be ideal. However, as vegetation gets denser the birds will abandon the site unless it is burned again. Another species that will avoid burned sites for 2-3 years is the Eastern Meadowlark which prefers ample ground vegetation.

Eastern Meadowlark (Sturnella neglecta) prefers to nest

in denser vegetation, 2-3 years after it has been burned

Habitat for Henslow’s Sparrow has declined more than 80% since 1966.

Like the Eastern Meadowlark, Henslow’s Sparrow prefers to nest in ample vegetation

Grassland birds that prefer to nest in the open such as Horned Larks, Lark Sparrows, Upland Sandpipers and Western Meadowlarks will inhabit burned areas almost immediately. Since ground nesting bird populations can be affected by fires of any severity, the season of burning is important. Fall burns promoted better nesting success for Upland Sandpipers and Northern Harriers. If burning in the spring, the earliest dates of nesting for birds found in our area should be checked. Other raptors respond favorably to burns in any season since prey populations are more exposed.

Horned Larks prefer nesting in the open, such as on recently burned areas

Northern Harriers benefit from fall burns. Bare ground makes their prey easier to find.

Management Recommendations for Birds

The 70 or so acres that comprise the restoration at the Preserve are now (2003) very weedy with alien plants such as Bull Thistles, Canada Thistles, Wild Carrot and Goldenrods dominating the landscape. During the first three years of establishment, the Best Management Plan is to burn yearly to control invasive weeds and grasses and allow the seeded natives to establish. The chart on the next page shows how the property has been divided into 6 ‘Burn Units’ in anticipation of a spring 2003 burn. The Burn Plan for Units 1 through 4 recommends a slow backing fire (pg.6) in order to protect the Bur Oaks planted there. This will allow the fire crew time to extinguish fires at the base of the trees before damage is done. Burn Units 5 and 6 will require a backfire followed by strip head fires (pg. 7) which will burn the areas quickly.

It is anticipated that the above burn plan will be carried out ONLY in the years 2003, 2004 and possibly 2005. After the prairie/savanna has become established, the Best Management Plan will be to rotate burns and mowing through the 6 burn units. For instance, Unit 1 may receive a fall burn in 2005 while the other Units remain unburned. Then, in spring 2006, Unit 5 may receive a spring burn with no burning in other units. The decision to burn and the season in which the burn is conducted will depend upon weed competition and will be an ongoing management issue. The combination of mowed, burned and unburned areas will create habitat for a wider range of species. The most important things to remember are 1) burn the best habitat as infrequently as possible 2) don’t burn the same Unit in the same season each time and 3) don’t burn more than ¼ of the acreage in any given year.

Backfire, into the wind, is to be used in Burn Units

Backfires burn more slowly into the wind and create less smoke than headfires. However, lacking the updraft created by a swiftly moving headfire, smoke remains closer to the ground.

Fire Effects on Mammals

During spring burns, mammal species that are most vulnerable to fire are those small mammals with young. However, these species are also those that have high reproduction rates and populations recover rapidly.

The White-Footed Mouse is a beneficial prairie inhabitant. They eat

harmful insects and help spread spores of mycorrhizal fungi – necessary for the survival of many plants.

Populations of ground squirrels, pocket gophers and deer mice were more abundant even 1-2 years after fire in a tallgrass prairie. Carnivores and omnivores tend to thrive in areas where their preferred prey or forage is available.

Fire Effects on Amphibians and Reptiles

Due to the low densities, nocturnal habits and underground nature of these animals, an intensive multi-season effort is necessary to detect and monitor amphibians and reptiles. However, most seem to be either unaffected or positively affected and seem to adapt to rotational burning on larger plots. It will be important to avoid predictable rotations. Too much predictability may favor one set of plants and animals over others. “The best way to manage for reptiles and amphibians is simply to restore, on a large scale, elements of the pre-settlement landscape.”

The same type of management plan recommended for birds, rotationally burning the 6 burn units, seems to be the best long-term plan for reptiles and amphibians as well. “Future research should address microsite conditions, patchiness within burns and seasonality of fire effects for specific ecosystems. Studying the interactions between burn seasons and life cycles of animal species, especially insects and herptiles, is vital.”

Fire Effects on Insects

Animals represent 75-80% of life on earth; insects represent 75-89% of all animal life. Insects serve as herbivores, predators, scavengers, parasites, parasite hosts and agents of seed dispersal. In contrast to the way prairie plants can hold their own in hospitable locations, the situation with prairie insects is more precarious. Healthy thriving sites may contain few prairie insect species.

- Remnant Reliance

Insects which rely on conservative plants in prairie remnants are known as “remnant reliant” species. Many insects are remnant reliant because they depend on conservative native plants for food while wide-ranging species feed on abundant food plants in woodlands and agricultural fields. Insects such as grouse locusts, carrion beetles, stink bugs and tree hoppers are “remnant independent” and can be found in almost any degraded site.

Over time, some insects have modified their behavior to changing conditions. Black Swallowtail butterflies (Papilio polyxenes) have adapted to feeding on Queen Ann’s Lace and the Eastern Tailed Blue (Everes comyntus) and Spotted Skipper (Erynnis baptisiae) have adapted to feeding on non-native legumes. The Baptisia Dusky Wing Skipper has gone from remnant reliant to a wide-ranging species because it has adapted to eating Crown Vetch.

Management Recommendations for Insects

Management implications for insects suggest that we manage the Preserve for those Remnant Reliant species that are missing from our reconstruction – the rest are either there already or will soon come. However, managing for Remnant Reliant species will not be an easy task. New prairies are unlikely to be populated by migrating conservative insects because both the prairie and the insect populations are so isolated.

To make the prairie reconstruction more biologically authentic and to increase habitat for rare insects, translocations or “stocking” the site is the best option. Literature reveals that new prairie reconstructions are more likely to support conservative insect species if they are located near high-quality prairie remnants. If our existing 70-acre reconstruction were stocked with appropriate conservative insect populations it could serve as a high-quality, albeit artificial, source of remnant reliant species for what are now “old fields.”

Translocating insect populations to new sites is an emerging field. Sod transplants from threatened sites have been performed and are best for eggs, pupae and larvae. If a donor site has a large supply of adult insects, transferring them to our Preserve is also a possibility. Sweep nets are used to capture the adults who are then chilled in ice chests for the move to Asylum Lake Preserve. The donor site MUST have an abundant supply as it is possible to wipe out entire populations using this method. Transferring captively-reared larvae and adults is also being attempted with the Regal Fritillary at University of Massachusetts and the University of Connecticut.

Monarch butterfly larvae feeding on Common Milkweed

Insects that require nectar and pollen are much less specific about the source than those who consume plants. Plants that are good nectar sources and are easy to establish include Prairie Coreopsis, Pale Purple Coneflower, Lead Plant, Blazing Stars and Goldenrod. Lead Plant and Blazing Stars are also good food plants for many remnant reliant species.