Grass growth near treelines – questions, questions….

A post from Andrew:

Our two fields (which are managed as meadows) are adjacent but separated by a treeline.  The treeline comprises 6 large oaks and some hawthorn, willow, blackthorn, holly and hazel with bramble undergrowth.  The canopy of the oaks is just about continuous.  The treeline runs approximately north to south.

East of the treeline.  RH half of picture – Anthoxanthum in full flower.  LH half – grass not in flower.

West of treeline – LH half of picture Anthoxanthum flowering, RH half, no grass flowers

The grass at the edges of each field by the treelines, is noticeably fuller and lusher than that near the middle of the fields. There are several possible reasons for this:

  1. We cut round the edges of the field with a topper to knock back the blackthorn suckers and bramble from the hedgerows from spreading out into the fields. So, there is a strip all around the edges of each field where the cuttings stay on the ground, and fertilise it.  But this doesn’t fully explain the lush grass, because on the edges bound only by a fence or a low hedge, the grass is much less lush than it is under the trees.
  2. The leaf fall from the trees every autumn is making the soil under the trees much more fertile.  I don’t find this very convincing either, because the leaves don’t stay where they fall. They tend to get blown eastwards, so they tend to collect on the opposite side of the more easterly field.
  3. There is much less yellow rattle in the sward under the trees.  But why?  The hay gets flung about all over the place when it’s being turned and dried, so there must be as much seed landing there as out in the middle of the fields.  Is it because the yellow rattle plants don’t like shade?  Both sides of the treeline are shaded for part of the day, the west side in the mornings and the east side in the afternoons.
  4. Do different species of grass dominate under the trees and out in the open? And if so, is it because of soil nutrients, shade, or other reasons?  I’ll be more competent to answer this after attending a grass ID course (see another recent post).  At present, the sweet vernal grass Anthoxanthum odoratum is in full flower over most of the field.  The grass at the edge of the field is mostly not in flower. But the few grass plants there that are in flower also appear to be Anthoxanthum.
  5. Is it connected with what’s going on underground, such as associations between the tree roots and soil fungi?  Is this affecting nutrient levels?

Or is it a combination of two or more of these factors? Any suggestions and thoughts on this welcome. If you have your own examples please get in touch – and we can create a further blog post.

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