First leaf

First leaf fully open, and recognisably the shape, if not the full size of the adult leaf

• For compound leaves like ash the leaf must be erect but the pinnate leaflets don’t yet need to be
   
• For larch first leaf is the start of needle forming. At the base the needles are still joined in the bud cover but the tops of the needles have separated.
   
• Use mature trees (30 years old or more), as young trees show different responses
   
• Even trees of the same species, close to each other can behave very differently
   
• If in doubt, wait until first leaf happens on 3 trees of the same species