Don’t Fix What Isn’t Broken

Posted on December 5, 2011 by SBrown

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.”

Learning from Nature

Posted on November 17, 2011 by SBrown

Each summer when I see Turkey vultures ride into the sky on thermal updrafts and soar overhead it takes me back to my childhood and learning from nature with my father, aircraft designer Alexander M. Lippisch. Best known for the ME163 rocket fighter, Lippisch was inspired by nature for most of his unconventional aircraft designs. The swept wing tailless ME163 rocket fighter, for example, was based on the delta shaped seed pod of the Javan cucumber, Zanonia macrocarpa, that an uncle had given him.

While Lippisch was working for the Office of Naval Research (leave it to the government to assign an expert in supersonic flight to design boat hulls) he met aerophysicist Dr. August Raspet. A highly skilled sailplane pilot, Raspet spent many hours in gliders. But no matter how skillfully he was able to glide his way among the air currents it was never as well as the ever present turkey vultures. Their ability to soar and maneuver through the air far surpassed his sailplane’s performance. Lippisch had also observed these birds and was fascinated by how they used air currents, floating lazily, banking and turning at will with never a wing flap. Both men were interested in studying bird flight to determine if application of its principles could be applied to the design of conventional aircraft.

“Your observation on the Turkey Buzzard (vulture) is very interesting. Had I completed the performance measurements of the Buzzard which I tried several years ago we could have analyzed the data to determine the effective aspect ratio.” (Raspet to Lippisch letter, 10 March, 1948.)

This shared interest resulted in a productive collaboration.

Turkey vulture in flight

Raspet began his measurements of Turkey vulture flight performance in 1949, after being appointed director of the Department of Aerospace engineering at Mississippi State University . He followed the birds in his sailplane comparing their performance in spirals, relative climb rates, as well as cross-country straight flights. In order to make actual measurements of the difference in performance between the sailplane and bird, a camera in the nose of his sailplane filmed bird flight and a ground observer filmed the sailplane. The soaring speeds of the birds during spiraling flight could be measured against that of the glider by evaluating the films.

“On my Kite [Kirby-Kite sailplane] I get the real soaring effect by flying right at stall and letting the ship wallow in and out of lifting zones. Recently I followed a buzzard at 800′ all over the area in this manner.”(Raspet letter to Lippisch, 2 April, 1949.)

After analyzing measurements of the wild bird’s flying skills Raspet wondered whether ”feathers are necessary on a sailplane.”

Correspondence between Raspet and Lippisch discussed how the analysis of Turkey vulture flight could be applied to tackle two of the major problems of conventional aircraft design: how to maintain a smooth (laminar) airflow over the wing surface and how to reduce the major drag induced by the whirling mass of air flow (vortices) over the wing tips. From Raspet’s measurements and observations they learned that vultures change the shape of their wings to maintain a smooth (laminar) flow of air over the wing surface. This increases lift and reduces drag. Regarding the wing tip vortices Raspet wrote,

“In fact, it can happen that the tip feathers actually reduce the tip losses to a point where the complete planform of the wing is aerodynamically active.” (Sailplane Project of Mississippi State College”, p. 3)

Turkey vulture using slotted wing tips increase lift and reduce drag

Based on these observations Lippisch proposed use of small wings or wing slots to recover the energy lost at the wing tips of conventional aircraft. He received a patent for this design in 1956.

(From Henry V. Borst, The Aerodynamics of the Unconventional Air Vehicles of A. Lippisch. 1980 )

Raspet ‘s research resulted in his receiving a long term federally-funded program to study how laminar flow could be achieved in low-speed aircraft and the application of composite materials in aircraft design. Tragically, he died in the crash of a Piper Cub demonstrating boundary layer modifications on April 27th, 1960.

Buckeye Butterflies Breeding at Timberhill

Posted on November 6, 2011 by SBrown

Common Buckeye

One of the most common butterflies at Timberhill is the Buckeye (Junonia coenia), a medium sized brown peacock butterfly. Distinguished by the bold pattern of eyespots, white bars and orange cell bars on its wings this species is found throughout the United States (except the northwest) but is most common in the southern states. Buckeyes do not overwinter in Iowa and specimens seen here are ones that have migrated north from the south in late spring. It is presumed that they migrate south in the fall. The description in Butterflies of Iowa poses the question do they breed in Iowa? They do at Timberhill.

In order for butterflies to breed a site must have the plants the larvae feed on. Of those preferred by Buckeyes Bastard toadflax, wild petunia, and slender false foxglove are all abundant at Timberhill. In late August and September the longitudinally striped caterpillars with their pattern of branching spines were easy to spot feeding on slender false foxgloves, Agalinis tenuifolia. These annuals are stimulated by fire and are particularly abundant in the old corn field in our West Creek unit. Large clumps bloom throughout the field in late summer.

Buckeye larva on slender false foxglove

Below is a photo of the hard outer shell of a Buckeye chrysalid from which an imago, the perfectly formed butterfly, emerged in September, 2011. Buckeyes have 2-3 broods between May and October. The chrysalid stage lasts only two weeks in the fall. Presumably that gives the adult stage plenty of time to head south. However, we were still seeing occasional adult specimens as late as November 4. Shouldn’t they have headed south by then?

Buckeye chrysalis

Late Summer Camouflage: Goldenrod Crab Spider & Goldenrod Stowaway

Posted on October 17, 2011 by SBrown

You have to look closely to spot either of these two species, the Goldenrod crab spider and the Goldenrod stowaway moth. Both fend off predators by camouflaging themselves in the inflorescences of yellow flowering plants such as goldenrod.

On a sunny afternoon last month I was in the Hidden Prairie looking for native pollinators on goldenrod when I saw a honeybee hanging at an odd angle from a goldenrod inflorescence. It wasn’t until I looked closely that I could see that the bee had been caught in a Goldenrod crab spider’s fangs. This spider does not spin a web. It sits in wait on goldenrod and ambushes its prey. The spider’s venomous bite paralyzes the prey, then it liquefies the body contents and sucks it dry.

Goldenrod crab spider and honeybee prey

Camouflage is the Goldenrod crab spider’s, Misumina vatia, primary defense. In this photo you can see how well this Misumina blended into the goldenrod blossom before it ambushed the honeybee. Misumina prefers to hunt from goldenrod since this species attracts so many pollinators. However, it can change color (yellow or white) over a period of several days to blend into other flowers.

Goldenrod stowaway moth

Later that day we saw this goldenrod stowaway moth, Cirrophanus triangulifer, spending the day in a Bur marigold, Bidens polylepis, along the driveway. Bright golden yellow with deeper gold-ochraceous markings it blends in perfectly with yellow inflorescences. On wing in August and September its larvae feed on Bidens species.

Bur Marigold, Bidens polylepis

LASIOGLOSSUM VERSATUM: DIVORCE BEE STYLE

Posted on October 2, 2011 by SBrown

On a recent sunny day Bill and I had the unexpected pleasure of following naturalist Laura Rericha on walk through our restoration. Laura and Dr. Gerould Wilhelm were co-authors of the 2007 Timberhill Savanna: Assessment of Landscape Management. It was by watching and listening to them in the field that I gained a true understanding of savanna restoration.

Laura and Jerry’s first visit to Timberhill was in 2003, ten years after Bill and I had begun restoring Timberhill. Although we were having excellent results from our management, others were highly critical of our methods. We were told that we should be planting savanna indicator species, and that we were burning too frequently at the wrong time of year. In any case it didn’t matter since everyone knew there were no oak savanna remnants worth saving in Decatur County, Iowa.

Thanks to Jerry and Laura that has all changed. On his first visit in June, 2003, Jerry noted 206 native vascular plants. (Finding 180 species in a single survey usually indicates a high quality remnant.) When Laura surveyed the ants for the Timberhill study she identified fifty two species, two of which were new to the Iowa list. (The Iowa lists contains 100 species.) Laura and Jerry’s work gave Timberhill legitimacy.

On her own initiative Laura has mastered ornithology, botany, and myrmecology. Her current research is surveying the native bees of the Midwest. Wild native bees such bumblebees and sweat bees evolved with the plants they pollinate. They are seriously threatened by loss of natural habitat. Currently four dozen native wild bees are listed on the Xerces Society’s red list.

L. versatum worker bee looking for a home

Thanks to Laura, Bill and I were able to observe the behavior of Lasioglossum versatum a greenish black sweat bee that nests in the soil. She pointed out swarms of Lasioglossum versatum workers circling over and around small holes in the soil. The holes were entrances to an aggregation of L. versatum nests that spread over the trail and into the adjacent woodland.

From a small entrance (3-5 mm.) in the soil the nests extend underground through tunnels with branch burrows and individual cells for eggs and larvae. Several fertilized queens hibernate in each nest during the winter and will produce the next generation the following spring. (They do not tunnel new nests each year.) As winter approaches the queens must prepare for propagation of their species.

When they sense cold weather approaching the queens drive the worker bees out of the nests. After hard frost there will be no more flowering plants to supply the bees’ pollen. To survive diapause with enough food for the larvae the queens must drive the workers out of the nests. Fascinated we watched the worker bees frustration as they swarmed over and around the nest aggregation. Whenever a worker came close to nest entrance a queen’s head moved into the opening, blocking the hole. The queens will continue to guard the nests until there is no longer any threat of the workers returning.

L. versaturm queen blocking nest entrance

Were we to follow the protocol of burning every three years we would probably not have been able to observe this drama. The ground would have been covered with leaf duff, obscuring the nest entrances. Would Lasioglossum versatum even be nesting here if the ground was covered with dead leaves?

Reference: Charles D. Michener. “The Bionomics of a Primitively Social Bee, Lasioglossum versatum (Hymenoptera: Halictidae). Journal of the Kansas Entomological Society. Vol. 39, No. 2 (Apr., 1966), pp, 193-217.