Tom's Blog

Friday, October 24, 2014

Legacy effects in prairie restoration

In the past dozen or so years ecologists have begun to realize that the future of a prairie remnant is strongly influenced by its past history, and these “legacy effects” are important in restoration work.

I stumbled on these concepts of historical ecology while working on the restoration of Black Earth Rettenmund Prairie, a State Natural Area. Before it became a Prairie Enthusiasts’ site, this outstanding natural area was owned by the Nature Conservancy (TNC), and TNC had extensive files on its history. Also, there is an extensive sequence of air photos to follow the changes through the years.

In 1937, when the first air photo was taken by the U.S. Soil Conservation Service, the prairie was almost completely devoid of woody vegetation. During the four decades between the early period and 1980 there was a gradual increase in wooded area, and the rate accelerated between 1980 and 1987 (see graph below). The early shrub/tree development took place in the south part of the prairie, which is adjacent to a fairly extensive undisturbed woodlot. By 1949, the woody patches had increased, and some of the trees in the South unit were now quite large. (The stumps from some of these trees still remain today.)

Although only approximate, the rate of increase in woody vegetation has some resemblance to a growth curve. There is an extended lag phase in the early years, but beginning in the mid 1970s there seems to be a “tipping point” after which the site seems to “explode” with woody vegetation. (The terms “tipping point” and “explode” were first suggested to me by Randy Hoffman. According to him, left unchecked other prairie remnants in Wisconsin show this same phenomenon. The graph shows that at the peak, almost half of the site was wooded.

Upon acquisition in 1986, this preserve became a major project of the DNR and TNC. Tree and shrub removal and frequent prescribed burns by the DNR and TNC were used in attempts to restore the prairie.

Although these efforts led to substantial success, the legacy of the woody vegetation remains, considerably complicating restoration efforts. New shoots still appeared in former aspen areas. Sumac and gray dogwood were particularly troublesome, but brambles and grape were also a problem. One former wooded area had been invaded by willow and hazel, which have proved difficult to eradicate.

I gave a presentation on my work at the North American Prairie Conference in Winnipeg, Manitoba, in 2012.  My paper has now been published and can be downloaded as a PDF using this URLThis Blog Post is a brief summary.

A view looking SW from Fesenfeld Road, showing the extensive clone of aspen on the top and sides of the north unit. Note also the large clone of sumac on the lower slope (above the cropped field). 1986 photo from TNC archives taken by a real estate assessor.
A view of the “Saddle” area of Black Earth Rettenmund Prairie, probably taken in the late 1970s. In addition to the substantial brush, the edge of a large aspen clone can be seen in the lower right corner. Photo kindly provided by Cliff Germain, retired head of the Bureau of Endangered Resources, Wisconsin Department of Natural Resources.

Woody vegetation for different years as measured on air photos by GIS. (a) Thumbnails for 1937, 1987, and 2010. (b) Change in woody areas with time over the 73-year period.

The present work suggests some principles of importance for restoration ecology.

·       You can’t let things get out of hand. During the early stages, shrub establishment may seem benign and not worth worrying about. This is obviously wrong. At first, shrubs and trees are easy to remove. However, once the explosive phase of growth has set in, not only is the biomass needed to be removed much larger, but the whole population is growing at a vastly increased (quasi exponential) rate.
·       The importance of frequent fires. Fire is now a widely accepted component of prairie and savanna management systems. However, there is a tendency to assume that fire on a three- to four-year cycle may be sufficient. This is a mistake. Beginning at the time of TNC acquisition, burns have been conducted on the various units on the average every second year. Despite this frequency, shrub growth remains a problem. Sumac, prairie willow, brambles (Rubus spp.), and gray dogwood in particular continued to thrive. Aspen shoots continue to appear in former aspen areas. In those areas where the legacy of shrub growth remains, annual fire should be considered. The historical GIS data will help locate the areas where annual fires should be carried out.
·       However, burns alone are not enough. At Black Earth Rettenmund Prairie, with its biennial burn cycle, sumac, gray dogwood, prairie willow, etc. have remained or have developed into problems. There are strong reasons to believe that all clonal shrubs, even if they are native, should be eradicated by a multi-year program of herbicide use. If the prairie is burned in alternate years in the spring, then the shrubs should be treated with herbicide in the late fall of the second year after the burn (that is, before the upcoming spring burn).
·       Eradication of clonal shrubs is essential, even if native, because annual stewardship cannot be guaranteed to continue into the indefinite future.
·       Legacy effects must be taken into consideration when planning management strategies. Areas that were woody in 1986, when restoration began, continue to inhibit the established of true prairie species, especially graminoids. These areas not only need tree and brush removal, but planting with seed collected elsewhere on the site.
·       Significance of herbicide use. The prejudices against use of herbicides remain. The first seven years of restoration work at Black Earth Rettenmund Prairie were wasted by trying to control shrubs without the use of herbicides. (The State Natural Area Board had refused permission to use herbicides.) Although trees can often be controlled without herbicide (by girdling), shrubs, with their paramount ability to resprout, cannot be controlled without herbicide.
·       Seed collecting and overseeding are essential. A site that has been wooded for an extended period of time almost certainly has lost most or all of its warm season grasses, as well as some of the more light-demanding forbs. The seed bank for such a site is uncertain, and probably highly variable. Without overseeding, restoration of such a site may take years. Even if there is a good seed source near by, spontaneous overseeding will be random and, depending on the quality of the seed, the success will be highly variable. Even 25 years after the initial restoration work, formerly wooded areas at Black Earth Rettenmund Prairie still remained impoverished, even though they have been reseeded with native grasses and forbs. Although each restoration project must be analyzed individually, if the site was wooded it can safely be assumed that overseeding is advisable. In fact, why not plant? Unless this is a research site, it seems better to plant than to wait and see what happens. Overseeding is easy and relatively inexpensive, and the sooner it is begun the better. The only reason not to overseed may be if a local seed source is not available.

For some reason, Black Earth Rettenmund Prairie did not become infested with red cedar, as have all the other hillsides in the area. This was fortunate, because the shade imparted by red cedar is much worse than that of aspen or shrubs. Cedar-infested sites quickly lose all of their species diversity. In one study at Konza Prairie, herbaceous cover decreased over 99%. (See Briggs, John M., Knapp, Alan K. and Brock, Brent L. 2002. Expansion of woody plants in tallgrass prairie: a fifteen-year study of fire and fire-grazing interactions. American Midland Naturalist 147: 287-294.)

(I am grateful to Wayne and Sharon Gaskill, stewards for TNC, for sharing with me their detailed stewardship files.)

Friday, October 17, 2014

Oaks: Great fall color!

Earlier in the fall I thought the fall color was going to be a bust, but there has been a marvelous transformation over the last week. The color this year is now fantastic. Not only the maples, which are usually the most prized, but the oaks, which are the dominant species in our area. Yesterday I took at least a 100 photos (bless the unlimited capacity of a digital camera!).

The Hill's oaks are generally the most colorful oaks in our area (they are related to the scarlet oak of Illinois), and this year turns out to be no exception. The two bright red trees in this photo are Hill's, although some other Hill's are reddish orange, red, or even yellow orange.
Mixed oak area at the north side of Toby's Prairie. The red trees are Hill's oaks.

The stand of oaks in the photo below is interesting, because they are all white oaks, and all about the same age. This is a stand at the east end of the Conservancy (those on the right are part of the East Basin savanna). The color range is really wide, varying from yellow, through orange, to rather red.

These trees are all white oaks (Quercus alba), mostly about the same age (around 50 years). Striking variation in color!
The physiology and biochemistry of fall color is fairly well understood.

The shorter daylength in fall triggers a physiological process that results in the decomposition of the green chlorophyll pigment of the leaves. Remaining behind are carotenoids, pigments which are responsible for the yellow, orange, or brown colors.

The red colors come from anthocyanins which the plant produces from sugars in the leaves. Leaf sugar increases when the temperature drops and anthocyanin production begins. The amount of anthocyanin that can be produced depends, among other things, upon the sugar concentration in the leaves. This process is highly variable from year to year, depending on weather, which affects the physiological state of each tree. Another factor is genetics, which determines which enzymes are present to carry out a particular biochemical pathway.

Considering all these factors, it is understandable that leaf color can vary greatly, depending on the amount of chlorophyll remaining, the amount and character of the carotenoids, and the amount and character of the anthocyanins. There is species to species variation, as well as year to year variation. A wide variety of colors are possible, and an individual tree can vary from one year to another.

Further, some species, such as hickories, birches, and aspens, lack the enzymes for making anthocyanins, so their fall colors are exclusively yellow or orange. 

Thus, it is not surprising that the stand of white oaks shown in the photo should vary so much from tree to tree.

Friday, October 10, 2014

The Mystery of Masting in Oaks

This is the time of year when acorns are dropping and you can hear them crunch under your feet as you walk through the woods. However, only a few oak trees are dropping acorns. This year at Pleasant Valley Conservancy only one oak species seems to be producing acorns: northern red oak.

Acorns from an oak in Unit 11B at the edge of the gravel road. Listen for the crunch as you walk by!

Mast is a term used to describe the hard fruit of various trees such as beech or oak. Oaks as a group produce lots of acorns only every three or four years, and a high production year is called a good mast year. I discussed the masting phenomenon in 2011 when bur and white oak were heavy acorn producers. 

This year, so far, the only trees I have found dropping acorns are red oaks (Quercus rubra). Other oak species in the red-oak group such as Hill's and black oaks do not (so far) seem to be dropping acorns. The last good mast year for the whole red-oak group was in 2010.

It is not unusual for masting to occur only in a single species, such as we seem to be having this year, although the mechanism by which the trees bring this process about is a mystery. There are lots of papers discussing this mystery, but no concrete data. Look for the work of Walter D. Koenig, although his research has focussed on California oaks.

I was surprised to find that other oaks of the red-oak group were not producing acorns. At the east end of Toby's Prairie there is a large grove of Hill's oak (also in the red-oak group), none of which were dropping acorns. And right at the edge of that grove was a single red oak dropping acorns. (The ground was covered, just under this tree.)

How do they synchronize acorn production? Not by chemical signalling, apparently.

Wednesday, October 8, 2014

Savanna understory: factors influencing

This is a nice time for an overview of the understory vegetation in our bur oak savannas. The canopy cover varies quite a bit from one area to another, and this greatly affects the understory vegetation.

The best way to see the savannas right now is to take a stroll through the mowed trail that goes from the west end of Toby's Prairie to the Saddle Road at the west end of Unit 11A. The first part of the walk is through a savanna that is mostly closed (Unit 11B). About half way along you come out into a quite open savanna (Unit 11A). The transition is very easy to discern, because of the distinct difference in the understory vegetation. Unit 11A; open savanna: tallgrass. Unit 11B; closed savanna: sedges, milkweeds, purple Joe Pye, boneset, other forbs.

The two photos (11B; above) here show the difference.

The air photo/map below shows the approximate locations of the camera and the photo directions. The air photo, taken leaf-on by NAIP in the summer of 2013, clearly shows the locations of the oaks. The map was done by ArcGIS. The location of the gravel service road is shown by the orange dashed line.

Several items of management are relevant. The savannas were cleared of undesirable vegetation in 2000-2003 and were planted several times with open or closed savanna seed mixes. (The open savanna mix contained little bluestem, big bluestem, and Indian grass. The closed savanna mix did not have the prairie grasses.) The savannas have been burned annually since 2003 (11 years). It took about three growing seasons for the prairie grasses to get started in Unit 11A. Indian grass is the predominant prairie grass. Note that what we are seeing here is the late summer/early fall vegetation. The prairie grasses only become significant in late summer. During most of the summer a wide variety of forbs are present, including compass plant, pale purple coneflower, Canada milkvetch, etc.

Since the soil, topography, and weather are similar in both units, the most significant factor controlling the understory vegetation is light. Where the canopy is very open, prairie grasses dominate. In the more closed canopy, prairie grasses are only scattered.

Another matter of interest. Unit 11A had remnants of a prairie vegetation when we started restoration. Lead plant and New Jersey tea were present and have increased once the invasive woody plants were removed.

Friday, October 3, 2014

Filling spray bottles with herbicide

We use 16 or 32 ounce spray bottles for a lot of our herbicide applications. They are ideal for basal bark applications of small brush. They also work well for small-volume leaf applications (what I call the "herbicide spritz"). Although there is a lot of "stoop" labor in using them, the herbicide can be applied precisely and without any loss to the soil. Backpack sprayers such as the Solo are fine for large-sized shrubs or trees, but they waste too much herbicide when used for the small shrubs we mostly deal with.

The photo here shows the technique I use for filling such bottles. I do it on the tailgate of the Kawasaki Mule, which avoids the necessity to stoop. The whole procedure is done over a children's sled, so that accidental spillage is controlled. The blue bottle contains the herbicide reservoir, generally enough for a whole day's work. This bottle originally contained laundry detergent and pouring from the lip is easy to control. The box of industrial-strength tissue is a required item. When the spray apparatus is removed from the sprayer its lower tube always contains a few drops of herbicide so it is laid on a sheet of tissue. The small funnel is also laid on this tissue after it is used. When the operation is completed, any drops on the funnel, sled, or elsewhere are wiped up, the tissue folded and discarded into a trash container. The herbicide mixture being used here is 20% Garlon 4 in Bark Oil NT with an oil-soluble red dye added.

The choice of spray bottle is critical. Some work well and others are disasters. From lengthy experience, we have found that the cheap spray bottles sold at Ace or True-Value Hardware are fine, and are cheap enough so that they can be tossed as soon as they start leaking. (All spray bottles will inevitably leak.)

My rule is that as soon as a spray bottle shows the slightest sign of leakage it is tossed. At our hourly rate, the time it takes to fix and/or clean a bottle is not worth it. In addition to the time it takes to fix a spray bottle, you have the time wasted in the field with a leaking sprayer.

I prefer the 32 ounce spray bottle, which holds enough herbicide for a couple of hours work.

The ideal method for basal bark application to sumac, buckthorn, gray dogwood, black walnut, etc. is to grab a stem and pull it toward you, so that the far side of the stem base is exposed. Lean over and give a single "spritz" to the base of the stem. This is all that is needed. For small stems, only one side needs to be treated. Some of my earlier posts have details.

Monday, September 29, 2014

Fall color: good time to find sumac invaders

Those following these posts know that sumac has been one of our serious threats and that we have worked out methods for its eradication. One of the secrets is early detection followed by immediate control. Because of its intense red color in the fall, this is an ideal time for making sumac surveys.

Large clones are of course easy to find. However, a prairie restorationist may be unaware, during the summer when the sumac leaves are green, of how serious a clone has become. (See the photo below, which is not from either of our sites.)

High quality prairie remnant being invaded by three sumac clones.
Left unchecked, these clones might eventually take over the whole site.
For the two sites that we manage, we have worked hard to eradicate sumac. Our goal is to have no sumac on the site, not even single plants. We wait patiently for sumac's intense red color to develop and then do a thorough canvas. We pick a good day when the sky is clear and the sun is shining. Yesterday was perfect and Kathie and I spent most of the day looking for sumac plants. A good pair of binoculars is very useful, as single patches of red on a hillside can be due to various species, most of which are lots less harmful than sumac.

These include woodbine (Parthenocissus quinquefolia; intense red), hazel (Corylis americana; deep maroon), and gray dogwood (Cornus racemosa; dark red). Only sumac has compound leaves, which are usually easy to discern at a distance. The photo below shows how easy it is to spot a single sumac plant.


At Pleasant Valley Conservancy we found 10 single plants scattered over about 50 acres of oak savanna. None of these were on prairies, either planted or remnant. Only two patches were clones, but each of these was small (ca. 5 feet in diameter). When found, clones or single plants can be immediately treated by basal bark with Garlon 4 in oil. It is important to even treat single plants, because each plant has the potential for forming a clone. It was indeed satisfying that we saw so very little red!

At Black Earth Rettenmund Prairie we found only one clone of any size, and this was on the neighbor's pasture. There were 8 plants scattered over this 16 acre remnant prairie.
So little sumac? How could we be so lucky? Hard work and persistence.

Although we started to work on sumac in 2008, it was not until 2011 that we got serious. Using GPS (and GIS) we had mapped all the sumac clones on each site. The details of how we eliminated sumac are given in several posts, which are summarized in this link.

I should emphasize that we can't relax just because we have essentially eradicated sumac from these sites. Sumac is a prolific seed producer, and birds move these seeds around very effectively. If we drop our guard, we may soon find new clones. Also, single plants that we have missed have the potential for starting new clones. 

Restoration work is never finished.

Wednesday, September 24, 2014

Classic open-grown savanna oak

I couldn't resist posting this fine image of the signature bur oak at Pleasant Valley Conservancy. The weather has been very fine in late September this year, and with clear skies the vegetation really shines.

Although the bur oaks never show much color, the other oak species are starting to turn. The Hill's oaks usually have especially nice color, especially in the borders around Toby's Prairie.

Come out and see them!