Oak woodland regeneration - I'm confused!

[Deb London]

A local wood in North London is predominantly oak. All the oak trees seem to be very large, possibly hundred(s) of years old.

Beneath the oak canopy there are a variety of smaller trees. Cherry, ash, elm (I think, will wait and see), thorn bushes. Even in clearings there seem to be no smaller oak trees, no saplings, nothing at all.

I'm left wondering how the oak trees originally got there. Since I can't see any small oak trees, I'm beginning to think the wood was planted. And now when I see oak woodland I really do wonder if any of it is natural?

How does oak woodland regenerate itself, left to its own devices?

[Cotham Marble]

Originally Posted by Deb London

Beneath the oak canopy there are a variety of smaller trees. Cherry, ash, elm (I think, will wait and see), thorn bushes. Even in clearings there seem to be no smaller oak trees, no saplings, nothing at all. I'm left wondering how the oak trees originally got there. Since I can't see any small oak trees, I'm beginning to think the wood was planted. And now when I see oak woodland I really do wonder if any of it is natural? How does oak woodland regenerate itself, left to its own devices?

There are some complicated issues behind these questions. I don't have any definitive answers but perhaps these observations are of help:

Oak reproductive strategy involves a considerable investmentment in both seed number and seed size - compare an acorn with an ash key - yet in open competition ash will out run oak in both successful germination and seedling growth. I'm not sure what the implications are for oak forest self regeneration but the adaptive functions of the acorn would seem to play a key role.

A more tractable issue, though complex in effect, is the role of life cycle. My guess is that the wood you refer to is well managed with few dead trees in it. In 'pristine' forest there would be a huge number of damaged and decaying trees and these would be a reservoir of available nutrients in which saplings could quickly become established. Perhaps this is the environment for which acorns are particularly suited ?

CM

[Bobbobthebob]

It could be an example of what Oliver Rackham (in his book ,Woodlands) calls the "oak change". Basically it appears that, as of ~100 yrs ago, few oak saplings are thriving in already established woodland and Rackham suggests the blame lies with an introduced American mildew that increases an oak sapling's light requirements.

I'm admittedly pulling this from memory and I'm sure I got the time period wrong; I'll see if I can find the relevant info when I'm back home from work.

[Deb London]

Thanks both. Very interesting, if a little complicated and/or pessimistic.

[Besnard Lake]

Deb,

Oak trees rely on animals to disperse their acorns. Jays are the oaks best friend, carrying acorns for miles around. When wild boar were ubiquitous, they would churn up the woodland floor looking for acorns and those that were not eaten would be pushed from beneath the canopy of teh tree and those that were eaten would be deposited from the other end of the boar in another location. The acorn is less prolific than any tree with winged seeds for the reason that acorns drop pretty much vertically to the ground. They therefore grow under the canopy of the parent tree, competing for light, water and nutrients. This is not a clever way for a long-lived tree to spend it's years. Ash trees disperse thousands of seeds safe in the knowledge that they will grow well away from the parent tree.

Regards

Bes

[Bobbobthebob]

I found the section on the oak change:

Originally Posted by Oliver Rackham

Hitherto oaks had grown more or less readily from seed within existing woods. With few exceptions, this ceased in the twentieth century. Oak now grows freely from the acorn almost anywhere - heathland, farmland, railway land - except within existing woods.

...

The most plausible reason is the introduction from America of oak mildew (Microsphaera alphitoides), a fungus disease first noticed in 1908 that rapidly spread to every deciduous oak in Europe. It has little effect on oaks growing in the open - but it may be death to an oakling in a wood struggling against shade. In effect, it seems to make oak a more light-demanding tree.

^^ It's a very good book. I'm still part way through it but it's well worth the read.

[Littlesparrow]

I sometimes have a pocket full of acorns or conkers when I'm out walking he dog. then if I see a suitable space (not next to someones house) I drop a few acorns. It works I've seen several little trees come up.

[Dorts]

Originally Posted by Littlesparrow

I sometimes have a pocket full of acorns or conkers when I'm out walking he dog. then if I see a suitable space (not next to someones house) I drop a few acorns. It works I've seen several little trees come up.

That is exactly the way our ancestors kept their woodlands going strong, by regularly spreading acorns and beech 'mast' on the woodland floor.
Dorts.

[Deb London]

A fungus that reduces the competitive advantage of oak seedlings and that has been introduced a century ago makes a lot of sense to me. And if animals (including our ancestors) played an important role in acorn dispersal, and if this influence has also changed, then I can see why oak regeneration might be reduced these days. These types of changes would explain why the oak woodlands that I know were given the chance to form in the past, but why regeneration might have diminished considerably. So thanks for all the ideas.

I've just remembered a wood of young oak that I haven't visited for around 10 years, although it's not far away. I'm enthused to go and try and identify the species of oak there soon. I think the trees were all approximately the same age, suggesting that this wood was planted, and not natural. Since it seems that our ancestors had a significant effect on the success of oak woodlands in the past, this new woodland now seems more in keeping with the way things used to be than I thought when I first found it.

[pobjoy7]

Oak trees have an intimate association with Jays, which distribute (bury) the acorns. Their preferred position for these acorns is well outside the wood, or at the woodland edge. Oaks need plenty of light to grow and any acorns dropping within a wood that does not have any clearings, will not survive.

Our woodlands are shadier now than at any previous time, perhaps since the Neolithic. It is hardly suprising that young Oaks aren't seen in a shady Oakwood, despite the problems with American mildew (worse on Pedunculate oaks).

If Oak regeneration is wanted, manage the wood so that standard oaks are well spaced; even one and a half times the mature height apart isn't too far. Pollard the smaller ones inbetween so that light levels can be managed; then keep the deer and sheep out. Plenty of young oaks will then appear.