Archive
CLIMATE CHANGE 1
27/09/2019
I have mentioned it in various items in recent years, but as Climate Change (with its sister connected subject the Species Extinction Crisis) is at last and quite rightly top of the mainstream news media, I offer my thoughts in a series of short articles on it.
A few ignorant political science-deniers here and in the USA notwithstanding, and we all know who they are, anthropogenic Climate Change has the weight of solid science and long meticulous recording behind it. What’s more, we can see its frightening effects in melting glaciers and ice sheets, extreme weather expressed as droughts, floods and unusually strong storms, the movement of cold-intolerant species northwards, etc. It is heartening to see the awareness led by Sir David Attenborough, the “Greta phenomenon” and others now spreading worldwide amongst our youngsters, increasingly supported by the not-so-young – but depressing to observe the deplorable environmental vitiation that would ensue from our leaving the EU.
Enough of the general. For this first short item, let’s consider the plants of our greenspaces and how they might react to longer periods of drought in a warmer world. We have seen hints of problems, for example in the increased failure rate of new tree plantings from lack of water, in the Midlands anyway. The land around my house is surrounded by a network of ditches, many constructed centuries ago and that were, for the three decades or so that I have known them, always wet and flowing in winter, but these last few years they have remained completely dry. Ponds shrink or disappear, streams become a trickle and lakes retract. A few years is not enough to be statistically significant of course, and association is not causation, but still.
Vascular plants (i.e. tracheophytes, which excludes bryophytes, algae, lichens & fungi) have developed many mechanisms to protect themselves from desiccation: densely hairy leaves, thick epidermal or waxy coatings, dormancy by ceasing to support epigean (above ground) biomass and by storage of moisture in hypogean (below ground) bulbs, roots and tubers, the ability to close stomata and slow/cease transpiration, etc. Only those tracheophytes known as “resurrection plants” can recover when the relative water content of their tissue falls below 40%. (Note, though, that many mosses and lichens cope superbly with extreme desiccation.)
Cacti & succulents are drought resisters par excellence. This is a photo of part of my personal collection.
Extreme water conservation is found in cacti and succulents and, although we have no native cacti in Britain (even if a few will grow outside – I have a couple in an exterior dry sunny trough that are never protected), we do have native succulents. Some of these, such as biting stonecrop Sedum acre, are common in dry places and open grassland. We may see several of them increasing in frequency. Other succulent candidates may include roseroot Rhodiola rosea, navelwort Umbilicus rupestris, white and English stonecrops Sedum album and S. anglicum, orpine Hylotelephium telephium and rock stonecrop Petrosedum forsteranum. There are also well-established/naturalised exotics such as Caucasian-stonecrop Phedimus spurius, reflexed stonecrop Petrosedum rupestre, some other crassulaceous species, house-leek Sempervivum tectorum, etc. Many of these are already used on green roofs and walls where xerocolous vegetation is essential; increasing the vegetation to cover such substrata is good for absorbing CO2 and pollutants, cooling/insulating the structures, and for providing food, shelter and breeding places for invertebrates and larger fauna – a boon to biodiversity as well as combatting climate change.
Three drought resistant hardy succulents naturalised in parts of Britain (left to right: Petrosedum rupestre, Phedimus spurius and a variety of house-leek Sempervivum tectorum. Photos by the author.
The National Vegetation Classification notes several dry grassland plant community types, usually on poor, calcareous xeric soils (chalk and limestone as one might expect) and generally falling into the Festuco–Brometalia (Natura 2000 type 6210). Many species in these swards are not obligate calcicoles so may become more widespread as they become selected by climate change primarily for their drought tolerance as much as their ability to grow in limy soils. It will be interesting, if potentially worrying, to see what phytosociological trends occur in coming years. Some such species we may see as increasing components of drier grassland may be:
There are many others – some are noted in our leaflet on Green Roofs & Walls – please ask if you would like a copy.
Woody native species resistant to drought include Scot’s pine Pinus sylvestris, silver birch Betula pendula, holly Ilex aquifolium, hazel Corylus avellana, hawthorn Crataegus monogyna, Midland hawthorn Crataegus laevigata, common whitebeam Sorbus aria, sessile oak, Quercus petraea and wayfaring-tree Viburnum lantana. There are also sweet chestnut Castanea sativa, and holm oak Quercus ilex which are naturalised in parts of Britain. Remember that planting trees is an important weapon in our armoury to fight climate change (see news item www.bettsecology.co.uk/latest-news/treemendous-potential).
But climate change is happening quickly. Everyone’s help will be needed to keep grasslands, woodlands and other habitats that are at risk well-vegetated. Once soil erosion sets in, it is very difficult to reverse, even impossible in human timescales. Very dry vegetation is at risk from fire but botanical resistance to that is another topic. Sparsely vegetated land is subject not only to wind erosion but to that from flash floods because there is no or little protective vegetation buffer.
Betts Ecology are keenly aware of climate change and the urgent challenges it poses for our greenspace. We encourage robust vegetation, tree and shrub planting and we try to get developers to design green roofs and walls into their plans, so far with little success, but we are keeping up the pressure.
© Betts Ecology
