The water in the top pond at Chishill just appears and with the exception of early 2012 the pond has always had water in it. This makes this one of those ‘wet holes’ which are good for wildlife. An indication of how wet it is can be seen in the willows which flourish around the edges. I always considered the willow as a weed until recently. If you break a piece off and push it into the ground it will grow, if you lay logs on the ground they will take root and grow and then you tend to be stuck with it. It was pointed out to me that the willow is a truly indigenous species to the UK and as a result it is popular with all manner of bacteria and fungi. Being a quick growing tree these bacteria and fungi break it down quickly making it a good friend to the resultant creepy crawlies and these being towards the bottom of the food chain are important to many other species. Hence the humble willow is not as bad as I originally thought.
Over recent years we have had the need to pollard the trees around the pond to reduce leaf fall into the water and shading. While dead leaves are not especially fertile the quantity that have fallen into the pond have increased nutrient levels in the water and moved the balance away from the original flora to allow firstly bitter cress and then algal blooms to dominate. Nature will always find something to use a space but this highlights how important it is to manage biodiversity features if you want to maintain their value in a particular area.