Saturday, 6 December 2014

Ivy on trees

People often wonder if ivy is bad for trees.  It doesn't strangle young trees like honeysuckle, or weigh down the tops like old-man's-beard. 
Here it is on our two sentinel ash trees at the main entrance to Filnore Woods.  The trees are thriving because the ivy is confined to the inner parts, and the twigs and branches still get plenty of light to grow.
Because of their feathery leaves, ash trees produce a dappled shade which allows the ivy to get enough light to grow even in summer.  For this reason ash trees often carry a load of ivy.  
Why does that matter?  Well three reasons really:
  1. It adds to the weight and wind resistance of the tree and its branches, so winter winds are more likely to break the branches.  That's why broad-leaved trees reduce their wind resistance by dropping their leaves before the winter storms
  2. New shoots to replace old branches need light to reach the bark where the emergency buds (adventitious buds) are waiting. If ivy covers the bark the tree has no chance of sending out new shoots.
  3. An ivy clad tree is harder to inspect for defects which might cause damage.
HOWEVER . . . .  there are several good things about ivy:
  1. It provides excellent shelter for roosting or nesting birds
  2. In its autumn-blooming flowers it produces nectar when most other trees are producing seed
  3. In spring it has berries for birds and others to eat when most other trees are flowering
  4. It is a really good habitat for scores of little creatures - spiders, insects and little mice.
So how do you decide?
Well on the whole ivy is OK until it starts creeping out along the branches.  At that stage it is beginning to get the upper leaf over the tree.

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