Complex Interactions in Oak Savanna Restorations

Observations Requested for U.S. Fish and Wildlife Service Synthesis

Do you restore oak savanna in the Midwest? If you've noted complex interactions occurring as a result, Pauline Drobney, Prairie and Savanna Zone Biologist with the US Fish and Wildlife Serve, is interested in hearing your observations. Drobney and fellow wildlife biologist Rebecca Esser are working on a handbook for identifying and restoring oak savannas.  "The best indicators of condition and ecological health are those involving multiple taxa and abiotic conditions," notes Drobney. "They indicate processes are working. I'd like to find ways for savanna managers to be able to look for discrete signs of increasing health or degradation."

One example was recently shared on the Iowa Native Plants list serve by Sibylla Brown, who has noted Edwards' hairstreak butterflies in frequently burned oak dominated systems in southern Iowa:

According to Cech & Tudor’s Butterflies of the East Coast, '"Edwards' hairstreaks are confined to low-growth scrub oak habitats with nearby ant colonies (principally, if not exclusively Formica integra)." The ants tend and protect Edwards’s larvae in exchange for sweet secretions.  The ant colonies are located not just where Edwards’s occur, but also where they can obtain an uninterrupted supply of ‘honeydew’-both during and after the Edwards’s brief larval period. The presence of tenant larval treehoppers and scale insects-which ants also attend-is thus important.  Attendant ants construct conical, ant hill-like shelters at the base of host trees, where older Edwards’ caterpillars rest during the day  At night, the caterpillars emerge to feed, escorted by protector ants.

If you have an observation to share, feel free to add a comment below, or contact Pauline Drobney.

Why We Burn: the Message From Timberhill

 Eastern bluebird utilizing cavities created by red-headed woodpeckers. Photo by Sibylla Brown.

Editor's note: Thanks to the author Sibylla Brown for permission to share her writing and photograph with the TPOS audience. Founded by William & Sibylla Brown in 1993, Timberhill Oak Savanna comprises 200 acres of woodlands, prairie openings and wetlands in Decatur County, Iowa. Sibylla documents the restoration journey with insightful posts at their website, where this excerpt orginally appeared - Timberhill Oak Savanna.

Running fire through our 200 acres each year takes a lot of effort. Our crew all have weekday jobs so the only days we can schedule a burn is on Saturday or Sunday.  And if it rains or is too windy we have to reschedule.  Our land is divided into four burn units. We need a crew for three of them. That’s three scheduled burns.  It would be easy to skip a year or burn just one unit a year.  But then I remember why we burn:  that prescribed fire is the best way to maintain habitat for a diversity of wildlife.

At Timberhill, fire has created a structural complexity that includes prairie openings and woodlands with healthy live trees, snags, down wood, and understory flora of grasses, sedges, and forbs.  The snags and standing dead trees are essential habitat for red headed woodpeckers. Red-heads build a new nest each year.  Their abandoned nests provide nesting for other species after the first year. For indigo buntings, field sparrows and prairie warblers there are prairie scrub and woodland interface. Several pairs of summer tanagers raise broods in the more heavily timbered tracts.  There is even colony of Henslow’s sparrows in our West Creek prairie.

Ours is a sharply dissected landscape with ridgetop prairie openings, steeply timbered slopes, and ravines. Before we began restoration a hard edge separated the prairies from the woodlands.  Fire has eliminated this barrier and to the birds Timberhill is now one continuous tract.  Even birds sensitive to forest fragmentation such as the wood thrush and yellow-throated vireo make this their summer home.

Without any seeding the number of vascular plants has increased almost 500%.  Not only has fire increased soil fertility by releasing nutrients into the soil, but is has stimulated plants from the seed bank. These plants harbor an abundant insect population for breeding and brood rearing. Fire has also lowered soil acidity by stimulating legumes such as cream wild indigo, leadplant, white prairie clover, tick trefoil, and  bush clovers. These plants provide high quality protein for quail, wild turkey, and other birds.

The increased diversity and abundance of butterfly nectar sources has been remarkable, especially in our West Creek unit. In 2005 when we began restoration there I could find only 2 butterfly milkweed plants.  Last summer I counted 40.  Later in the season numerous swamp milkweeds and rough blazing stars continue to provide nectar into fall. From first bloom to fall frost various hairstreaks, fritillaries, skippers, and other butterfly genera are abundant on these nectar plants. (Our annual dormant season fires have the least impact on the invertebrates.  We have documented many fire sensitive species at Timberhill.)