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Wednesday, February 13, 2019

When, How, and Why to Plant Woodland Seed

A healthy bur or white oak woodland on good soil seems to be as rare as a fine prairie or savanna. Lack of fire has killed most species.

Even if an apparently thriving April and May flora survives, the June flora is weak, and the July through September floras are nearly or entirely gone. Thus, gone too are the animals - especially the invertebrates - that depend on those missing floras. Thus, such neglected woodlands have lost or are losing the vast majority of their species.

At Somme we rush to save the patient. We gather seed every year of more than 200 mostly rare plants. Decades ago, we found the now-rare species hanging on along the edges of railroads, power lines, highways, and mowed paths - where their diminishing, unnatural populations had enough light to hold on for a while. These days, most of those populations are gone, but we gather from their descendants that bloom and set seed in the growing "under restoration" areas.

We probably gather $100,000 dollars worth of rare seed every summer through fall (if we were to buy it - but then we would not be saving the local ecotype - and most species aren't even commercially available). And we probably put work that's worth that much into cutting brush from planting areas every winter. We don't want to waste our seed or work.

We plant woodland seeds after a fall burn if possible. But there were no good days for a woodland burn in fall 2018. The burn will have to wait until spring 2019, and we'll somewhat reluctantly plant most seed in burned areas then. But some species don't do well unless their seeds have lain in the cold, wet, alternately frozen/unfrozen ground all winter long. (Would seeds filter down through those leaves and do well after a spring burn? For most areas, we doubt it, but that's an important question we haven't tested.) So we'll keep much of our woodland seed cold over the winter and get those precious embryos into the cold wet ground as early as possible after the spring burn.

Soon after the burn we broadcast many mixes of roughly prepped seed. Shown here
are bags of WMC (wet-mesic closed) and the emotionally named WOW (wet open woods) mixes. 

After thinning brush and pole trees, to complete recovery of the shaded-out ecosystem, we broadcast diverse seed mixes that include many rare, conservative species. 

We have found that, in our oak woods, the unburned leaves are often so thick that very few seedlings come up through them, without a burn (see tests, below). So, if we don’t get a fall burn, we plant some of our seeds (in newly thinned woods) in spots where we rake leaves away, so the seeded species can establish without being smothered. They then will begin to spread their own seed year after year. Orders of magnitude more seed will then be produced annually and in time be everywhere, finding every niche. 
  
On slopes, we rake narrow (two or three feet wide) lines along contours. Any other approach could result in unacceptable amounts of erosion. If a rich spring flora survives on a south-facing slope without a turf, many bulbs and corms can "frost heave" out of the ground and die after a fall burn or raking. So we try to leave some such areas unraked and unburned.   

Prairie planting is different. We plant most of that seed in the fall. Prairie leaves don't mat as thickly or completely as woodland leaves.

Most species we plant by seed - rather than plugs. Seeds produce results slower, but those results, for most species, are much better – because we can spread seeds so much more diversely over so much larger an area. Diverse seeds become established in their best niches.

Since it's difficult to get wetter areas burned, in fall we often find we have to rake leaves there to get the best results. It's not our most fun work, but subsequent years' thriving ecosystems inspire us. 
Our initial scientific tests of raking vs. not-raking took place in December 2013; see diagram below for one example:


We raked the leaves off ten similar patches and spread seed in them. For the five patches north of a line marked by two white oaks, we then raked the leaves back on top
In August 2014, the circular patches (which show up green, above) that had little leaf litter show success for many species. The patches smothered by leaves were still just bare ground (leaves much rotted away by this late-summer photo) and dead leaves. (You can see the two white oaks that marked the line behind the red oak in the foreground.)
The difference between the leaf-covered and leaf-uncovered patches was night and day. We checked again in 2015, following a burn, to see in the seeds might just have remained dormant, waiting for better conditions. But the leaf-covered patches (marked by circles of dead sticks) were still mostly dry leaves and bare dirt.

More variations on this kind of experiment would help us make better plans. But for now, we plant in burned or raked areas whenever we can, especially when restoring mesic woods with a dense mat of oak leaves.

A good comment on May 19, 2019 (see below) pointed out that the need for raking or burning may apply only to oak leaves. Maple leaves rot so quickly that they seemed not to impede seedling establishment.

What has our success at Somme looked like?
Two photos of restored, replanted woods below:

Wild geranium, golden Alexanders, and wild hyacinth blooming in early summer.

By mid summer, great blue lobelia, cardinal flower, and sweet black-eyed Susan (above) have over-topped the May and June flora (which yet needs the open-woods light to set seed, down below). This is a young restoration, which we expect to become more diverse in time. 

12 comments:

  1. From Kirk Garanflo:

    What was the depth of the leaves in the leaf-covered patches? Less than 1/2 inch? For all practical purposes the FPDCC had no fall burn season. A spring burn season may be a washout too, so leaf litter will certainly be present in the woodlands; it will be interesting to see how the woodland spring ephemerals respond at Poplar Creek and elsewhere.

    At Bluff Spring Fen late winter-sown seeds are often just scattered onto the layer of snow in the open areas with the expectation that they will work their way to the surface as the snow melts.

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    1. Oak leaves don't mat down so much, so in the fall they were perhaps two inches deep, and less in spring, but more matted then. We don't need to worry about perennial spring ephemerals; they have enough stored up energy to force themselves up through the duff. It's the seeds, especially the smaller ones, that fail.

      Yes, we too throw seeds into snow or on leaves in some places. Maple leaves decay rapidly and are less of a barrier. In some places leaves blow into piles, so the blown-clear patches are especially good for planting. If there's already existing vegetation, often leaves will get caught at odd angles, so there are openings for seedlings to peek through. If even one percent of the seeds find success, that may be enough to work over the long run. But for restoration we hope to improve the odds.

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  2. I too have had issues getting a good burn to plant seeds in woodlands.
    The leaf litter is usually light that with uncooperative weather makes it hard. I am concerned with not having a decent (hot) fire to kill all the tree/brush seedlings.

    So the best I could do was plant into burn circles from brush clearing. I have done approx 40-50 spots like such. After burning and the ashes are cool and safe I blow them out of the area and rake approx 3-4 ft around the burnt circle. Into this I planted my seed last fall. I will find out this spring if I am successful.

    I am hopeful as I have planted into the same situation for prairie seed. Interesting that area had zero weeds in it, nothing but native plants.

    Would be interested in your thoughts on getting seeds going in a woodlot without having a decent fire. Have you tried prepping using a large propane torch and passing it over the ground to clean off light leaf litter and hopefully kill off tree/brush seedlings?

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  3. Since we're in an urban context with many burn restrictions we treasure and choose to save our burn days to support and progress sites that have already gone through some of the restoration process rather than to prep the site. We find that sites primarily comprised of maple leaves we're able to lay the seed on top of the leaves just before a snow. By the time spring rolls around the maple leaves are decomposed enough to allow the seeds soil contact (would love to one day actually be able to test if this is true for all species or if the earlier species don't respond as well). Where oaks are the primary component we have to remove the leaves with either raking or blowing to get germination. We did a couple trial plots, both sites getting the same seed mix laid the morning of a snow, but only some plots getting blown or raked out. It was night and day. For slopes we often do lines perpendicular to the slope also to hold soil. The issue with raking or blowing vs burning seems to be that we get more"weed" plants germinating also,most likely from disturbing the ground and seed bank at a greater level.

    Right now we're trying to figure out a way to get a more thorough burn for new restoration areas that have little ground veg due to lack of sunlight. If we are going to use one of our burn days to prep a site in conjunction with thinning then we need it to be more thorough than the extremely patchy leaf burns. If anyone has
    tried something successfully I'd love to know. Right now our thoughts are on finding a fast growing grass, perhaps even a cover crop, that isn't persistent and can handle shade.

    ReplyDelete
    Replies
    1. To Anonymous/May 19, 2019: Thanks for helpful comments and observations. Yes, maple leaves rot quickly, as do many other non-oak species. We and others should repeat your experiment and report on results. Thanks again. Please keep reporting.

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  4. Any update on this? I've been wondering if I should clear the forest floor of all debris before seeding.

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  5. Andy, thanks for asking. Our preferred method of planting most seeds in woodlands is after a fall burn. If we don't manage to get an area burned and it needs seeds, our approach depends on what the area looks like.

    If there's a dense mat of leaves (or leaves and twigs), our experience is that most seeds will not do well. So we rake most leaves off areas before we plant, sometimes in patches, often in strips along contours (so that we don't encourage erosion). Once we get quality plants established in an area, the unplanted patches will fill in over time, as the established plants shed seeds annually.

    If there are areas where the leaves have blown off, we plant there. If there are areas where existing dormant vegetation has prevented the formation of a thick mat of leaves (had thus we can still see the soil here and there), we sow seeds in fall in those areas.

    ReplyDelete
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    1. Thank you for the reply!

      I recently collected all the debris in my woods using a lawnmower with a hopper attachment, then dumped the debris for mulching.

      Here's the area, it is 1000 sq ft https://i.imgur.com/a9bdNyM.jpeg

      My plan is to collect all the leaf debris once all the leaves have fallen, and then seed late this Autumn. I cannot burn for various reasons, otherwise I would. I'm thinking the next best thing would be to clear the area in the woods to bare soil, and then immediately seed. I would probably do this right before the first big snowfall.

      Does this sound like a good strategy to you?

      -----

      This Wisconsin woods is comprised of oak, maple, box elder, and crabapple. There is not much invasive pressure (in fact it is thriving with jewelweed). It is near the bottom of a valley and has 6" of sandy loam followed by clay. I am using "Prairie Moon Shady Woodland Mix - 1000 sq. ft" for seed.

      Please let me know your thoughts, thanks!!

      Delete
  6. The comment above (beginning "Andy, thanks...") is by the person theoretically in charge of this blog, Stephen Packard. I have to admit that I'm much better at ecology than at the Internet. My efforts sometimes fail to label my comments properly, and the system won't let me correct the mistakes (so far as I have time to figure out). Sorry.

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    1. Not a problem Stephen thank you for the reply!

      I recently collected all the debris in my woods using a lawnmower with a hopper attachment, then dumped the debris for mulching.

      Here's the area, it is 1000 sq ft https://i.imgur.com/a9bdNyM.jpeg

      I decided to do this before the leaves fall just in case it's better to have leaves present for seeding. But then thankfully I came across your work here, indicating a full clearance is best. So my plan is to collect all the leaf debris once it has fallen and then seed late this Autumn. I cannot burn for various reasons, otherwise I would. I'm thinking the next best thing would be to clear the area in the woods to bare soil, and then immediately seed. I would probably do this right before the first big snowfall.

      Does this sound like a good strategy to you?

      -----

      This Wisconsin woods is comprised of oak, maple, box elder, and crabapple. There is not much invasive pressure (in fact it is thriving with jewelweed). It is near the bottom of a valley and has 6" of sandy loam followed by clay. I am using "Prairie Moon Shag Woodland Mix - 1000 sq. ft" for seed.

      Please let me know your thoughts, thanks!!

      Delete
    2. Typo: Prairie Moon *Shady Woodland Mix

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    3. Andy, thanks for good comments and questions.

      What you suggest seems fine to me. I should say that the words "I cannot burn for various reasons" translate to "It's difficult to burn for various reasons" - but that's okay. In my own yard I have large "wild-ish" woodland patches which I manage for seed of rare plants for restoration to the real wild (for example the Somme preserves). I don't burn them. I would be a lot of work to get proper approvals and would make some neighbors nervous. It seems not worth it. Like you, I remove last year's dead vegetation and compost it.

      Sometimes I put the composted material back onto those beds. I worry that just removing it is a form of mining some materials out of the soil. On the other hand, burning also mines some material out of the soil, as some components blow away. Long ago, when the whole landscape burned, such vaporized and particulate matter from other fire upwind would fall back on that soil. These days, there's typically little nearby burning to result into replenishing a patch of what's been raked or burned away. It's probably a small problem.

      Yes, I seed shortly before snow or a heavy rain if practical.

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