Wednesday, 11 April 2018

First Leaves of Greater Butterfly Orchids at a Chilterns site.

I spent the day in the Chilterns yesterday taking a look at the Greater Butterfly orchid population that a landowner and I are monitoring there.

Leaves are appearing.   

We have two enclosures, North and South, separated by a track and fenced to keep out muntjac.  The Southern section is divided roughly in half, with one half designated as a study area.  There we counted  how many plants from last year were showing leaves.  Of the 56 plants from last year, I overlooked 8, leaving 48 of which 40 had leaves, rather higher than I expected.  4 plants had double leaves (which is a puzzle as they do not spread vegetatively) and there were 8 new plants, again fewer than I had expected. The population seems to be at an equilibrium, which is not surprising as it has been there for some years and has not been subjected to serious change. 

 Habitat management consists of bramble removal, but not every year.  We are though experimenting, and this year we removed bramble from the study section in January, but not the other half of the South enclosure.  There were only 5 new plants in that section compared to 101 plants last year, whereas in the North enclosure, where bramble was removed in January there were 30 compared to 186 plants last year.   On the face of it, bramble removal does seem beneficial, but it is probably simply a matter of being able to find plants more easily.   

The next visit will be in early May when buds should start appearing, but we don't expect flowers until early June, 7 weeks from now.   Then we will do a full survey of flowering and non-flowering plants, from which we can draw proper conclusions about population dynamics.

The orchids  seem to take longer to flower, shaded in the Chilterns, compared to those out in the open on Skye.   Buds around 24 v 18 days from first leaves, flowers 45  v 30 days from first leaves.  The landowner also noted that a few plants he has in a meadow always flower earlier than those in the woodland which we are studying.  

Yesterday light levels in the orchid enclosures were the same as in the open, but when the plants flower light levels are maybe 60% of those in the open, as leaf cover (mainly beech) intensifies. 

No comments:

Post a Comment