I sometimes get asked: “why don’t you just leave the common alone, why do we even need to manage it, surely it can look after itself?”
Well, let’s imagine some awful virus spreads across Barnes and we can’t get onto the Common for decades to carry out any conservation work. The Common is left in peace and to evolve as it wishes.
We have a pretty good idea of what may happen, and it’s based around natural succession. If we leave an area of open ground or grassland without intervention (from both human and grazing animal), it will eventually go through several stages of succession and ultimately end in high forest.
You may also see this final stage described as climax vegetation or woodland. However, this term is misleading as it suggests that the final stage is in fact richer or greater than prior stages.
We only need to look at the Common over the last 70 years to see this in action and luckily, we can. Below is an aerial picture from 1950. For you to get your bearings I’ve added the compass as well as two red dots, one on Mill Hill and the other on Barnes Station. As you can see the Common is predominantly open, with very little tree cover. The only trees being those planted on avenues and roads during the 19th Century, mainly common lime (tilia x europaea), horse chestnut (aesculus hippocastanum) and London plane (platanus x hispanica). If you were to look at the OS maps of 1870 you would see that the Common is almost treeless, as it was grazed which kept it open.
Comparing the 1950 image to the current day you can immediately see how the treescape has changed, with the development of a large amount of high forest. Those woods you may have thought had been on the Common for time eternity really haven’t! Woodland is now the Common’s largest habitat with over 70 acres out of ~120. As a habitat, it’s incredibly important and we are lucky to have it. Some of our richest terrestrial wildlife sites in the UK include woodland. In an urban setting they help provide immediate escapism from the built environment around us.
So, we now know that if we were to leave the Common alone it would revert to closed canopy woodland. What’s the problem with that? I love a tree probably a lot more than the next person, but in order to support a wide array of flora and fauna we need a mosaic of different habitats across the Common. The fancy scientific term for this week is habitat heterogeneity. Essentially, this means that species richness can be positively associated with having a greater variety of habitats across an area. Simple (ish)!
If we just had woodland across the Common, then we would only support species associated with woodlands and we would lose all the other habitats that develop in order to get to the woodland stage. The starting phase of succession for some of the Common would be bare gravel and the associated acid grassland. This is a nationally important habitat, which subsequently supports an array of rare invertebrates3.
Amongst these grasslands we have areas of scrub, which may take the form of gorse (look out for the green hairstreak spotted recently, below) or blackthorn; aptly named the mother of the oak! Scrub is an incredibly important habitat, in particular for songbirds. The creation of scrubland at Knepp Rewilding Project has highlighted it’s importance. You don’t have to look far before you see examples of saplings popping up through the scrub, quite often silver or downy birch (betula pendula/pubescens) and pedunculate oak (quercus robur). Combining all these different habitat structures creates more niches for different species i.e. there is more chance that the specific environment for a certain species can be found4,5.
A prime example of this mosaic habitat can be seen surrounding Van Burens meadow, the picture below taken from meadow corner here. The meadow is a mix of different types of grassland, both those found on neutral soils and in some areas, those found on acidic soils. To the right of the picture you would find closed canopy woodland, in its dark phase, with a dense understory of holly and some bramble (Rubus fruticosus) and to the left there is a brilliant example of scrub and acid grassland mosaic.
Unfortunately, we cannot stock suitable grazing animals (at very low densities as high densities can be detrimental) to maintain this mosaic habitat and so in certain situations we need to intervene to maintain the habitat diversity and structure. We need to look at the site as a whole and how everything interacts. The fact that the site looks natural and wild usually means we’re doing a good job! We try not to be too prescriptive and allow dynamic processes, where possible, to take place. However, where we can see opportunities to be of benefit to flora and fauna, we intervene.
However, creating and maintaining habitat for wildlife doesn’t stop at the boundaries of a nature reserve. In fact, many of our nature reserves have become habitat islands amongst a desert. We need to make sure that our green spaces are connected as isolation can limit species dispersal and its chances of survival as well as affect an areas overall species richness. It’s all good having suitable habitat in one area but if wildlife can’t get there in the first place it will struggle to colonise. Likewise, a population cannot expand if it is limited to a single site. This can even bring in issues with inbreeding and loss of genetics diversity.
As well as connecting up our public green spaces your gardens can act as brilliant interconnected networks for wildlife. No matter how big or small, they can act as steppingstones between larger areas of habitat. As the pivotal Lawton Report on making space for nature states; we need bigger, better, more joined… up ecological networks, so If you’re curious about what you can do to help wildlife in your garden feel free to get in touch.
I hope this helps answer the question that we started with as to why we don’t just leave the Common alone. Ensuring that this hidden gem is protected and enhanced for both wildlife and people for both current and future generations is our main aim!
György, K., Zoltán, B., Bence, K. and Csaba, N. (2018) Habitat heterogeneity as a key to high conservation value in forest-grassland mosaics. Biological Conservation. 226 pp. 72–80.
Holt, R.D. (2009) Bringing the Hutchinsonian niche into the 21st century : Ecological and evolutionary perspectives. Proceedings of the National Academy of Sciences. 106 pp. 19659–19665.
Peterken, G. and Mountford, E. (2017) Woodland development: a long-term study of Lady Park Wood. CABI.
Richmond Biodiversity Partnership (2019) London Borough of Richmond Upon Thames Biodiversity Action Plan.
Wichmann, M.C., Schwager, M. and Jeltsch, F. (2004) Animal species diversity driven by habitat heterogeneity / diversity : the importance of keystone structures. Journal of Biogeography. 31 pp. 79–92.
Yang, Z., Liu, X., Zhou, M., Ai, D., Wang, G., Wang, Y., Chu, C. and Lundholm, J.T. (2015) The effect of environmental heterogeneity on species richness depends on community position along the environmental gradient. Scientific Reports. , pp. 1–7.