Onto the top-3 then in Dove Stone's wildlife countdown to Saturday's BioBlitz. So far in the top-10 we've taken a closer look at butterflies, birds, sedges, moss, fungi, bumblebees & bats. It's time to talk trees, and in particular to take a look at one of our native deciduous species, Downy Birch (Betula pubescens) also known as White Birch or Hairy Birch. This is a widespread tree, distributed across Europe and North Asia. It's always interesting to know how old trees are and generally the life span for a Downy Birch will be between 60 and 90 years old, althought there are some instances of Downy Birches which have lived well beyond this.
Downy Birch is closely related to Silver Birch (Betula pendula), of course, so how to tell the two apart ? With regards to the general impression of these two birches, Silver Birch has an overall drooping, pendulous shape to its branches, hence the name Betula pendula whilst Downy Birch tends to be more upright in its growth and Silver Birch tends to be taller than Downy Birch. There are intermediate forms between these two species with various combinations of these characteristics which keeps identification interesting ! Obviously leaves are a major help when it comes to identification. Downy Birch has rounder leaves and a single row of teeth on the leaf margin whilst Silver Birch leaves have a longer point and have a double row of teeth.
Downy Birch is appropriately named as its twigs are covered in small hairs or 'down'. Silver Birch twigs in comparison will have small white warts on them. Take a look at these trees' barks and you'll see that Downy Birch is a greyish white with horizontal grooves compared to Silver Birch, which really is much whiter with conspicuous dark patches. Young trees will have bark that's reddish-brown in colour.
Birches are monoecious; each individual tree has both male and female flowers / catkins. Downy Birches will flower from, very approximately, about five years onwards. Each catkin can contain hundreds of seeds and a large tree can produce up to 1 million seeds a year ! The seeds actually have two transparent wings which helps their dispersal. Whilst they can be dispersed large distances, most seedling trees become established within a short distance of the parent tree.
So why have a native, deciduous tree in the Dove Stone top-10 of wlldife ? BioBlitzes are all about biodiversity and birches support a large number of invertebrates; there are over 300 species that are known to feed on them ! These in turn provide food for birds, as does the birch itself through its seeds. Earlier in the week we took a look at fungi with Amethyst Deceiver, which is commonly found with Beech. Birches are also associated with particular fungi, probably the best known of these is the classic fairy toadstool, the Fly Agaric (Amanita muscaria). Other fungi to look out for around Birches are Orange Birch Bolete ( Leccinum versipelle ) and Brown Birch Bolete ( Leccinum scabrum ) to name just two. Fungi themselves of course play an important part in biodiversity through breaking down dead wood and other organic matter which in turn release nutrients that benefit other organisms.
And just a brief mention to of woodland understorey. Common flowers to birch woods include early spring flowers such as Primroses (Primula vulgaris) and Violets (Viola riviniana) and slightly later in spring and summer shade-loving flowers such as Bluebell (Hyacinthoides non-scripta), Wood Anemone (Anemone nemorosa) and Wood Sorrel (Oxalis acetosella).
And that's it. The Downy Birch. What a top-tree, and definitely one to record at Saturday's BioBlitz ! Tomorrow we're onto the top 2...