Modelling the impacts of climate change on tree growth - future species suitability

 

A knowledge of how climate change will affect the growth potential and ecological suitability of individual tree species is essential for developing climate change adaptation strategies. As part of this process, the ESC decision support system has been developed to account for the effects of predicted climate change.

The Ecological Site Classification Decision Support System

Ecological Site Classification Decision Support System (ESC-DSS) was initially developed as a site-based decision support system to provide guidance on species choice and native woodland suitability in Britain. For a given site, the suitability of individual species for timber production is predicted on the basis of four climatic (accumulated temperature, exposure, moisture deficit and continentality) and two edaphic factors (soil wetness and soil fertility). Potential yield of a given species is modelled as a function of accumulated temperature, which is then reduced by limitations imposed by the next most limiting factor. The underlying climate data represent the 1961-90 average climate at a spatial resolution of 10 km. The data have been modified by incorporating the UKCIP02 climate change scenarios to provide predictions of the effects of climate change on species’ suitability for timber production. The suitability of a given site for native woodland restoration can also be modelled. Changes to species’ suitability are assessed for the full range of climate change scenarios (Low and High emissions), but only for the 2050s because the climate data fall outside the parameter range of the knowledge-based models beyond this timeframe.

In the case of commercial suitability, accumulated temperature (AT) is assumed to be the principle determinant of yield, with the product of AT and the next most limiting factor providing a site level assessment of suitability. A slightly different approach is used for native woodland, in which the suitability of a woodland community is derived from soil quality estimates based on plant indicator species within the field layer, and the climatic suitability for the main tree species.

The suitability models for individual species are based on productivity data for Britain, together with expert judgement. A number of assumptions have been made, that should be considered when interpreting the suitability maps and climate change. In particular, the following have not been considered:

• The direct effects of rising atmospheric CO2 concentrations on growth and evapo-transpiration
• The effects of a possible change in the frequency of severe pathogen or insect pest outbreaks
• Changes to the frequency of extreme climatic events
• The predicted increase in winter windspeed rather than mean annual windspeed
• Changing soil moisture quality index as well as the moisture deficit.

Suitability maps

The maps show predictions of the most suitable broadleaf and conifer species that are cummonly planted at present. These are predictions are for the 2050s, under both the Low and High emissions scenarios.

The effect of climate change on potential broadleaf suitability as predicted by Ecological Site Classification for the UKCIP02 2050s High and Low emission scenarios – broadleaf species most suited.

Effects of climate change on the identity of the most productive conifer species as predicted by Ecological Site Classification for the UKCIP02 2050s High and Low emission scenarios.

Under the Low emissions scenario, ash replaces beech as the most suitable broadleaf species across much of southern England; in turn, ash is replaced by pedunculate oak under the High emissions scenario. The range of sessile oak is predicted to contract significantly to the north and west.

Of the conifers, Corsican pine is predicted to benefit most from predicted climate change, and expand its range to the north and west. The area where Sitka spruce is predicted to be the most suitable species contracts to the north and west, and is replaced by Douglas fir and Corsican pine. For both broadleaf and conifer species, these changes in species suitability generally refect moisture limitation where ranges contract to the north and west. Although, particularly for broadleaves, the effects of climate change on species suitability appear serious, productivity of the most suitable broadleaf or conifer species is not affected greatly. However, these predictions are only for the 2050s, and beyond this timeframe, the implications for tree growth are far more significant.

The effect of climate change on the potential broadleaf suitability as predicted by Ecological Site Classification for the UKCIP02 2050s High and Low emission scenarios - productivity class (GYC: m3/ha/yr).

The effect of climate change on the potential conifer productivity as predicted by Ecological Site Classification for the UKCIP02 2050s High and Low emission scenarios - productivity class (GYC: m3/ha/yr).

Maps of predicted yield under the 2050s Low and High scenarios are also provided for the following individual species:

In these suitability maps, the 'marginal' classification indicates that the broad woodland type will be viable, but that changes are likely to the make-up of the ground vegetation community structure. This is further explored in a poster entitled Modelling the effects of climate change on oak woodland in Britain ^(PDF-1550K) presented to a conference on 'Global Climate Change and Biodiversity' in April 2003.

Future developments

• The effects of rising atmospheric carbon dioxide concentrations will be incorporated
• The yield predictions of ESC yield will be tested against detailed productivity data
• French productivity data, together with native woodland distribution (EUNIS classification) will be added to the ESC knowledge base
• Site level and GIS DSS versions of ESC which include climate change predictions will be made available to aid decision making
• A combination of ESC and MONARCH may be used to identify the potential make-up of the new ground vegetation sub-communities following climate change
• The UK NVC system within ESC could be converted to the EUNIS system to enable the DSS to be applied outside the UK.