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LAND-USE AND CLIMATE CHANGE IN THE UK: THE NEED FOR A STRATEGIC ECOLOGICAL OVERVIEW updated 5 Jan 2020 In the topical discussion on the issue of climate change and land management there generally seems to be a lack of any strategic ecological overview. Below are my thoughts on some of the issues about which I think there needs to be a lot more discussion: Loss of the biodiversity of open ground habitats 1) A large proportion of British biodiversity occurs in grazing-dependent grasslands and heaths (e.g. chalk grasslands, limestone grasslands, unimproved grasslands generally, grasslands managed for the large blue butterfly, marshes, lowland heath.) 2) However, on farmland the area most likely to be planted with trees is that least likely to be of value to the farmer. Hence trees are often planted on the remaining semi-natural open habitats, to the detriment of the species found there (to the detriment of biodiversity). Tree planting does not always mitigate climate change 3) It has been known for many years (e.g. a 1994 report from the then ITE) that trees planted on deep peat can dry out the soil, releasing the oxidised soil carbon back into the atmosphere at rate of about 8 tonnes/hectare/ year. Most terrestrial carbon in the UK occurs in the soil and even an organic layer 10-15 cm thick contains more carbon than any high forest on the same piece of land (see the calculations at https://www.fenton.scot/ecology/02. CarbonStoreComparisonPeat&Forests - J Fenton.pdf). On organic soils (podsols, peaty gleys, shallow peats, peats) trees can oxidise this carbon, and in the long term may release more carbon than that fixed by the trees: and upland areas with such soils are where much tree planting is likely to be targeted. Planting on more mineral-rich, low carbon soils will not have this effect, although it should be noted that ancient grasslands can contain a lot of stored carbon in the soil. 4) Current forestry policy is not to plant on peat >50cm deep, which accepts that trees can oxidise the peat; this is also the reasons there is felling of plantations on deep peat. But deep peat does not arrive from nowhere: it starts off shallow. Hence the land with the most long-term carbon storage potential is that over soils with shallow organic layers which over millennia can go on to form peat. Hence, if climate change mitigation is to be taken seriously, then all stratified soils with an organic surface layer should be left unplanted. 5) Trees significantly reduce the albedo of the land compared to open ground, and, at higher latitudes, the extra heat absorbed by a three-dimensional forest is perhaps a more important driver of climate warming than the stored carbon (as noted in the IPCC Fourth Assessment Report: Climate Change 2007). 6) In the last couple of years, in Scotland at least, there has been a return to forestry ploughing: taking a plough over the whole landscape to prepare it for tree planting. This will dry out the soil (its aim, after all, is to benefit sapling establishment) and so result in release of carbon through oxidation of organic soil carbon, as well as increasing flood-risk through faster water run-off. 7) At the other end of a forest’s life, felling and timber extraction uses large machinery, often churning up large tracts of soil, again leading to carbon release. The vegetation colonising clear-fell sites is that characteristic of dry soils, indicating loss of moisture content and increased oxidation of soil organic matter. Tree planting can reduce biodiversity and not help the climate 8) Hence planting trees can reduce the biodiversity of the UK (if planted on valuable natural habitat) and help warm the climate through soil oxidation and albedo reduction. The debate to date has been far too simplistic – all tree planting good! (but I suppose most people like simple messages). 9) Additionally, over large tracts of the uplands (particularly in Scotland north of the Central Belt, and possibly also some of the English uplands?) there is no evidence that trees would still be the climax vegetation (see my latest paper at https://www.fenton.scot/woodland history and ecology.htm). Hence tree planting will both reduce biodiversity (see 1 above), if biodiversity is defined as the natural vegetation and associated animals of a given locality, and reduce the overall naturalness of the landscape. 10) If open upland landscapes are a feature of at least some of the UK uplands (a characteristic of our oceanic climate) then changing them to woodland contributes to the loss of unique upland landscapes at a European scale; after all, a large proportion of our open upland habitats are seen as being of international importance, being on Annex 1 of the EU Habitats Directive. Their loss contributes to the global homogenisation of landscapes, a concern of the European Landscape Convention. Do we really want to dramatically change our cherished upland landscapes? Peat bog processes not always beneficial to climate change mitigation 11) Upland blanket peat cannot go on getting thicker for ever and eventually erodes naturally (although human action can also instigate it). Upland peat goes through long-term natural cycles of growth and erosion. The natural erosive phase liberates the stored carbon into the atmosphere. Peat bogs can also release methane (a short life-cycle greenhouse gas) but perhaps more important is their role as a long-term carbon sink/store. 12) Lowland raised bogs are still having their peat extracted for horticultural purposes (including for growing mushrooms); for example there is permission to extract 100,000 cubic metres annually until 2042 from Auchencorth Moss south of Edinburgh. This will release significant amounts of stored carbon and help cause climate change. It seems to me to be a higher priority to stop this kind of activity than to attempt large-scale revegetation of naturally-eroding blanket peat in the uplands (although some peat erosion, particularly in the Peak District and Southern Pennines, is probably anthropogenic so revegetation here is more easily justified). Values of nature conservation can conflict with those of climate change mitigation 13) Where peat is eroding naturally (as it is over large parts of the Scottish uplands), then revegetating it to minimise carbon emissions is going against natural processes, going against letting nature be wild (the principle of rewilding). Sometimes the values of nature conservation conflict with the values of climate mitigation: an issue never discussed. But in a given location, a decision sometimes has to be made as to which value system should take precedence. Another example of this is planting trees in locations where there would not naturally be trees. 14) If we want to keep some parts of the UK wild, then we will have to zone for this, while admitting that in these areas climate change mitigation is a lower priority than biodiversity conservation. Scotland’s Wild Land Areas are perhaps examples of large- scale locations suitable for this approach. Eating less meat: role of livestock in climate change 15) A distinction needs to be made between the addition of new carbon to the atmosphere from fossil fuel extraction and the cycling of existing carbon in the atmosphere. Global warming is caused primarily by the former, whereas carbon release to the air by terrestrial ecosystems is merely the cycling of existing carbon through photosynthesis and respiration. Having said that, agriculture can add new carbon to the atmosphere through the use of fossil fuels in farming practice such as the use machinery and the creation of fertilisers. 16) The role of livestock in contributing to climate change also needs strategic ecological thinking. Much of lowland Britain was wetland before agricultural drainage over the centuries. Hence soil methane output has probably been reduced by human activity; additionally most native ungulates have become extinct, or reduced to very low levels, so that methane output from indigenous herbivores will have been reduced. Therefore any increase in methane output from modern livestock has to be set against the reduction in methane output from the loss of natural wetlands and indigenous herbivores. Has modern farming actually increased methane output compared to the original natural level? In any event, livestock grazing has a role to play in being an analogue for the missing native herbivores: a role to play in maintaining natural, grazing-dependent ecosystems (see 1 above). 17) Unlike carbon dioxide, methane breaks down in the atmosphere having a lifetime of ca. 9 years. A comparison with whisky manufacturing is useful: if you set up a new distillery and manufacture whisky at a constant rate, because the whisky cannot be sold for three years, whisky stocks will build up over three years. Thereafter, if you sell all you manufacture, the stock of whisky will remain constant. Similarly with methane from livestock: if livestock numbers remain constant, then stocks of methane in the air will remain constant (they cannot cause an increase). The methane they release will have a warming effect, but this will not be increasing over time. 18) In the UK, much biodiversity depends on grazing (see 1 above), and grazing plays an important role in maintaining ecosystem productivity through the role of herbivores in nutrient cycling (think ‘manure’!): this will be lost if livestock numbers are reduced (for climate reasons), and such grazed habitats are replaced by arable land to grow food, or by trees. In the uplands, a change from grazing to trees has the impacts discussed in 3-10 above. Even if reducing livestock numbers did help mitigate climate change, there needs to be a discussion about whether, in a given locality, the relative importance of climate mitigation and conservation values as discussed in 13-14 above. 19) In a warming world there is in increased risk of damaging wildfires. Grazed systems are less fire-prone than ungrazed ones because excess vegetation is grazed instead of remaining in situ. Grazed ecosystems, therefore, have a role in mitigating fire risk. 20) Hence there may not a strong case for a reduction in meat production from traditional, grass-/native vegetation-fed systems. Indeed, such reduction will damage the UK biodiversity and its valued landscapes – and could result in increased climate warming (see 3-7 above). This is not the same as saying that intensive animal-rearing systems are similarly beneficial: their grassland monocultures and their heavy use of NPK causing eutrophication and nitrous oxide release are good neither for biodiversity or the climate. However it is possible that livestock that can thrive on native vegetation release less methane than those which are intensively reared. 21) In all terrestrial ecosystems there is a complex cycling of carbon between the soil, live plants, animals and the atmosphere. In any comparison of the global warming impact of livestock systems and purely arable systems, like must be compared with like: for example, a grass-based livestock system may store more carbon in the soil than an arable one. Certainly fertilisers with a fossil carbon footprint are used on many pastures, but more might be needed on any arable fields which replaced them – so that fertiliser use could increase, and therefore also the fossil carbon footprint. Additionally, arable agriculture can use more machinery (ploughing, harrowing, sowing, fertilising, etc.) than livestock farming. Perhaps the only sure way to significantly reduce the fossil carbon footprint of arable land, in particular the reduced use of fertilisers, is by the return of crop rotation. This generally necessitates mixed farming, i.e. both arable and livestock (again, think manure!). 22) A current concern is the proliferation of plastic particles across the globe. Hence in future there could be trend back to natural, non-polluting fibres which are not fossil-fuel dependent – such as wool. The UK, with a climate suitable for grass growth, is ideally placed for wool production so that it would be short-sighted to cover suitable habitat with trees. 23) Ultimately long-term global warming is caused primarily by the release of ancient fossil carbon, not the cycling of atmospheric carbon from land management. Hence land-based mitigation measures need to be viewed with caution and, long-term, can only play a small part in the climate change problem. For example, trees cannot go on sequestering carbon for ever: once a new plantation has reached a steady, climax state, then the rate of trees dying will be the same as the rate of new growth and the carbon store becomes constant; if felled, the amount stored will equate to half the standing crop averaged over the life of the forest, although this is complicated if the felled timbers remains a store, e.g. used structurally for buildings. Summary 24) Planting trees can only ever be a temporary measure and, for reasons discussed above, its role in climate mitigation at our high latitude can be overplayed (or even be negative). On land, only peat-forming terrestrial systems can result in long-term carbon storage: as stated above, shallow peat/organic soil has the best potential, but there is currently no policy to protect this from, amongst other things, tree planting. Deep peats can naturally erode and begin releasing their stored carbon. 25) In the UK, particularly in the west with a climate suitable for grass, livestock grazing brings many benefits: these include the utilisation for food of land otherwise unsuitable for agriculture, maintaining the biodiversity of open habitats, maintaining soil fertility (including a role in crop rotation), maintaining cherished landscapes, producing non-fossil fuel fibres and leather, and aiding fire control. 26) Both climate change and habitat loss are issues of concern. But sometimes, preventing one can damage the other. Ultimately climate change is brought about by the release of stored (fossil) carbon rather than by the cycling of terrestrial carbon. The only sure way to stop climate change is to stop using fossil fuels. We must avoid ‘quick fix’ land management solutions which, perhaps unintentionally, also result in habitat loss. A lot more debate to be had…

A View from Argyll James Fenton’s perspective on current conservation issues Click here for previous blogs