Tom's Blog

Monday, December 15, 2014

Corylus americana: an invasive shrub?

Hazel is a native shrub that is widespread in Eastern U.S. It is found in every county in Wisconsin, and was occasionally reported by the surveyors in the original public land survey as part of the plant understory. Although not considered an invasive plant in Wisconsin, it is a serious problem in the red or jack pine forests of Minnesota.  It is also considered a problem in other areas, as the following quote from the Flora of North America attests: “Corylus americana is a weedy species, sometimes considered a pest in carefully managed forests.” 

During our early savanna restoration work, based on the prevailing sentiment in southern Wisconsin, we either ignored hazel or allowed it to grow, in some cases even encouraged it. Now we realize that this may have been a mistake.

Although it grows rhizomatously, its rhizomes only grow a short way before they send up new shoots. Thus, in contrast to sumac, gray dogwood, and prickly ash, hazel often grows as tight, compact bushes. A single bush like this may remain compact for a number of years, although its duration in this well-behaved capacity is unpredictable.

Under some conditions a single hazel bush may turn into what is called a “hazel thicket”.
In his pioneering paper on the relationship between forests and fire, Gleason noted that the margin between prairie and forest consisted chiefly of hazel, “a shrub which is not seriously affected by repeated burning…. There is one record known to the writer of a large hazel thicket, covering several acres at the western edge of an upland forest, and several such records of scattered thickets of hazel in the middle of the prairie.” (Gleason, Henry A. 1913. The relation of forest distribution and prairie fires in the Middle West. Torreya 13: 173-181.)

A survey of the literature reveals a number of mentions of “hazel thickets” associated with either prairies or savannas. Thus, hazel “can” become a problem, although the conditions leading to this situation are not clear. At any rate, it seems obvious to me that it would be foolhardy to allow hazel to “run amok”.

At Pleasant Valley Conservancy I have been seen several sites where hazel seems to be getting out of hand. At the south side of Toby’s Prairie, in a former aspen zone, hazel has been spreading even in the face of annual fire. It has also spread extensively in some areas of the White Oak Savanna (Unit 12A), also burned annually. Both of these areas seem to have the potential of becoming bad, so we are killing them this winter by Garlon basal bark.

On the other hand, there are several hazel bushes along the margin between the Ridge Prairie and the East Basin that seem to be well behaved. They were left ten years ago when we cleared all the honeysuckles away, and although they have bulked up they have not spread.

These are savannas. How about prairies? Here I think it depends upon the history of the site, what I call the “legacy”. At Black Earth Rettenmund Prairie, where hazel was present before restoration work began, there is a large hazel clone on the Saddle that has survived dozens of prescribed burns. Also, on the knoll at the top of the North Unit, where the woodies formerly consisted of prairie willow and sand cherry, both relatively benign, in 2012 many clones of hazel appeared. Even more disturbing, they were not only spreading rhizomatously, but were sending up suckers (see photo). In this clone I counted over 350 shoots.

Given these conditions, it seems reasonable to control the hazel, and this is what we are doing.

New shoots of a hazel clone spreading away from the main shrub.

Friday, December 12, 2014

Effect of savanna restoration on wildlife

We have known intuitively almost since we started our savanna restoration work that we were benefiting wildlife, especially songbirds. Now there is some quantitative research that confirms this.

The work was done by wildlife biologists Frank Thompson and Sybill Amelon and their students at the University of Missouri-Columbia and summarized in the U.S. Forest Service Northern Research Station website.

The approach used was to contrast the use by birds and bats of actively restored savannas with unrestored sites that were now closed canopy forests. The work was done in sites in Missouri, Arkansas, and Tennessee. The results showed that blue-winged warbler, Eastern towhee, Eastern wood pewee, field sparrow, prairie warbler, and summer tanager were more abundant in the restored sites, whereas Acadian flycatcher and worm-eating warbler were more abundant in the non-managed sites. The conclusion was: "Savannas and woodlands provide habitat for a diverse mix of grassland-shrub and canopy nesting birds that are of high conservation concern."

Parallel work was done on bats in the Missouri Ozarks by Clarissa Starbuck, a student of Thompson. See concluded that: "Habitat conditions created by savanna and woodland restoration and management resulted in greater occupancy of the big brown bat, eastern red bat, evening bat, and tri-colored bat than was observed in mature, non-managed forest. The northern long-eared bat, however, had greater occupancy in highly forested landscapes and closed canopy forest or woodlands with open understories."

Our work at Pleasant Valley Conservancy has shown that plant species diversity is also higher in the savanna than in either the prairie or woodland habitats. A scan through our detailed species list will confirm thisThe complete list of savanna species can be found in this link.

Here is a quote from our oak savanna web site: "Because the open canopy means that light can get to the forest floor, the oak savanna has a wide diversity of grasses and other flowering plants. Because the habitat is so variable, there is more diversity in savanna than there is in prairie. In 2004, 184 species of flowering plants were identified in the oak savanna areas of Pleasant Valley Conservancy. The list to the right, an aggregate of years 2002 to 2007, has 275 species. However, not all species were present in all savanna areas."

With this great vegetation diversity, it seems reasonable that wildlife of all kinds of species would benefit from a restored savanna.

Tuesday, December 9, 2014

Winter work

So far this year things seem favorable for winter work. No significant snow and not too cold.

Most of the seeds are planted but Kathie still has some special species to get on the ground. Today she's planting yellow pimpernel, a fine savanna species that is not too common. We have a couple of native populations but fairly small, so we are trying to enhance the population. She is kicking the seeds in at the west end of Unit 10.

She also has purple milkweed seeds to plant, and these will probably go into the bur oak savanna. I'm trying to avoid areas where large populations of woodland sunflower might invade, as this species grows in such tight clones that nothing else can become established.

Another one she's planting is wood betony, a hemiparasite that plays an important role as a keystone species. Originally we just had it in a few spots, but through judicious planting we now have it in quite a lot of areas.

The main program for now is brush control. As long as snow is scarce we cut and treat or basal bark shrubs.

One important target are the numerous oak grubs, which we find not only in the savannas but also in those prairies in which there is a woody legacy. This is a good time to spot them as they still have their leaves. Basal bark with Garlon 4 in oil is the most efficient way to deal with them.

Monday, December 1, 2014

Prairie restoration: winter overseeding

Winter came early this year, but fortunately the snow was light enough so our crew could get out and plant. Since most of our habitats are already fairly well established, our work consists mostly of "overseeding", adding new species to existing prairies.

Here Kathie is planting the Ridge Prairie and East Basin with lupine and a few other species that like the sandy habitat we have at this end of our Conservancy.

We often get queries about the best time to plant. Some folks think you should only plant after a burn, when the ground is bare. However, it depends on the habitat. Prairies are different than savannas.

Early winter is an ideal time to plant species that need cold moist stratification. When you look at this  planting site you might wonder if the seeds will reach the bare ground. However, discussions with some of the most experienced prairie restorationists have convinced us that this site is fine for planting without a burn. Why?

This site is burned annually, which means that there is no residual prairie thatch (see my recent post on this topic). Thus, the ground is mostly bare, so the seeds can get to the surface. The winter's snows, and lots of freeze and thaw, should work them into the soil.

The same situation doesn't exist for oak savannas. The leaves come down in the fall so the ground is now covered with leaves. For overseeding we plant the oak savannas in the early spring, just after our spring burns.

However, back in 2002-2005, when we were planting the oak savannas for the first time, we burned in the fall and then planted, as the photo below shows.

Monday, November 24, 2014

The role of fire in a tallgrass prairie

It’s not too early to think about next spring’s controlled burns. One point that arises is burn frequency.

Restoration should be guided by the goals of the project. Thus, if the focus is tallgrass prairie, a fire-dependent ecosystem, then annual burns are essential, especially if it is a prairie remnant. (Prairies planted on former ag fields are a different topic.)

My recent post which analyzed the extensive research by the Konza Prairie group showed that for brush control in tallgrass prairies annual or biennial burns are essential.

Brush control is only one of the important reasons for burning a prairie or savanna remnant. The other major reason is because the forbs and warm-season grasses demand it. There is a vast amount of research that shows that without fire the species that we most want will have difficulty thriving. One of fire's main accomplishments is to remove the thick prairie thatch so that the delicate new prairie plants can reach the light.

The thickness of the prairie thatch varies from year to year depending on the summer rainfall. Sometimes it is so thick that delicate plant seedlings can not find their way through it.

A thick prairie thatch from a single year's growth. This is the prairie grass from the previous season, being mowed to widen a fire break before burning. Last year’s growing conditions were very good, so the grasses are lush. Also, snow was light so that the plants remain upright, guaranteeing a hot fire. 
Concerning the prairie thatch, pioneering papers by Weaver in Nebraska and Rice in Oklahoma are well worth consulting. Rice in particular showed that one role of fire was to remove last year’s thatch so that sun could reach the soil and encourage the growth of warm-season plants. The graph below makes this case very well.

Rice, E.L. and Parenti, R.L. 1978. Amer. Jour. Botany 65: 1091-1097. Rice’s burns were done in the spring dormant season.

In our own simplified work we divided a well established prairie into two halves, burning one and leaving the other unburned. The result with Toby’s Prairie is shown in the photo below. We obtained a similar result with the Pocket Prairie.

Toby’s Prairie divided into two blocks. The block to the right was burned and the block to the left was unburned. The difference in growth of the prairie grasses (Indian grass and little bluestem) is striking. The burn was done on 5 April 2006. The photo was taken on 15 Feb 2007.

How does fire act on a prairie? The photo below shows fire backburning through a prairie consisting of Indian grass and little bluestem. After the ashes are blown away, bare soil will be exposed. In this photo, because of the heavy snows the previous winter, the grasses lay flat, thus ensuring that the flame heights are low.

The action of fire on dormant prairie grasses. In such a thick mat, delicate prairie plants have a hard time finding the light.
Suppose you don't burn? The prairie plants will eventually find their way through the thatch, probably two weeks later. Eventually a new, somewhat impoverished, prairie will form which will form a new layer of thatch. Some of last season's thatch will decompose but not all, so the thatch gets thicker, and in the next year even thicker. Eventually the prairie will reach a point at which most prairie plants cannot survive. But the woody plants can, and eventually the prairie will become some sort of wood lot.

Tuesday, November 18, 2014

White-tailed Deer: Another reason to do an oak woods burn!

A neighbor scouting for deer in the North-facing oak woods that we had recently burned spotted nine female deer with their heads down, feeding. Eating on what? Acorns, of course. Everyone knows that acorns (hard mast in hunter terminology) are a favorite deer food: “the ecological equivalent of manna from heaven”. But you don’t usually see that many in a woods all together.

What is unusual here?
  • As I posted last month, this is a big mast year for red oaks, at least at Pleasant Valley Conservancy. 
  • The North Woods at Pleasant Valley consists primarily of red oaks, so right now the forest floor is full of acorns.
  • Two weeks ago we burned the whole North Woods.
  • Burning does two things for the acorns
    • It gets rid of the leaves so the ground is bare and the acorns are visible
    • The heat roasts the acorns and makes them more palatable.
  • Deer love acorns

Acorns in the red oak group taste bitter because of their high tannin content. One way to get rid of the tannins apparently is by roasting. “Acorns roasting on the open fire”?

My neighbor also managed to attract two fawns to him by a few of the right type of “clucks”. Pretty tame!

There is a question about the effect of fire on acorn viability. According to some U.S. Forest Service work, temperatures where oak leaves are burning can range from <79 to="">371 C. Viability tests on acorns collected after a prescribed burn showed that “patchy, low-intensity dormant season burns in oak forests reduced the viability of red oak acorns located on the leaf litter surface, but did not generally affect acorns in the duff or mineral soil.” Greenberg et al. Acorn viability following prescribed fire in upland hardwood forests. Forest Ecology and Management 275 (2012) 79-86.

In a good mast year lots more acorns are on the ground than needed for oak reproduction. The benefits of fire for oak growth must far outweigh any harmful effects.

It may still be possible to see a forest floor full of acorns. Unit 11B, the savanna just south of the upper road, has mostly red oaks, and a few weeks ago the ground was full of acorns. You should hear the ground crunch under your feet as you walk through these woods. Unless the squirrels have already packed them all away!

Sunday, November 16, 2014

Native invasive plants

Can a "native" species be called an invader? Whether an invader is native or not is irrelevant. If it spreads into an area, forms monocultures, and results in a marked decrease in diversity, it is undesirable and should be controlled.

Here are a few native invaders that under some conditions meet these criteria.

Latin name
Common name

Shrubs and trees

Celastrus scandens
American bittersweet
Twining; forms berries
Cornus racemosa
Gray dogwood
Prairies and open savannas
Cornus stolonifera
Red-osier dogwood
Wet areas
Corylus Americana
Under some conditions
Definitely invasive in Minnesota; probably in Wisconsin
Juniperus communis
Common juniper
Fire-sensitive; forms berries
Populus grandidentata
Big-toothed aspen
Root suckers
Populus tremuloides
Quacking aspen
Root suckers
Rhus glabra
Smooth sumac
Probably allelopathic; prefers sunny areas; root suckers; can dominate a site
Rhus hirta
Staghorn sumac
Probably allelopathic; prefers sunny areas; root suckers; can dominate a site
Rubus allegheniensis
Forms patches
Rubus flagellaris
Spreads close to ground
Rubus idaeus
Red raspberry
Forms very dense clones;
Rubus occidentalis
Black-cap, black raspberry
Tip roots
Salix exigua
Sandbar willow
Wetlands; root suckers; forms very dense clones; can dominate a site
Salix humilis
Prairie willow
Only rarely invasive
Vitis spp.
Zanthoxylum americanum
Prickly ash
Prairies and open savannas

Herbaceous plants

Arnoglossum atriplicifolia
Pale Indian plantain
Root suckers
Helianthus divaricatus
Woodland sunflower

H. grosseserratus
Sawtooth sunflower

H. tuberosa
Jersualem artichoke

Solidago canadense
Canada goldenrod

Woodland Sunflower can easily destroy the habitat for dozens of native species. So can sumac.

Here is a recent review with many examples: Carey, Michael P. et al. 2012. Native invaders--challenges for science, management, policy, and society. Frontiers in Ecology and the Environment. Volume 10(7): 373-381, doi:10.1890/11060 (published online 15 June 2012).