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.