Human-induced climate change is a global issue that is starting to become apparent in many parts of the world. It is the primary environmental challenge of this century. Increasing levels of greenhouse gases such as carbon dioxide are enhancing the natural greenhouse effect and accelerating irreversible changes in the climate.
The impacts of climate change present very serious global risks and threaten the basic components of life, including health, access to water, food production and the use of land. As the earth gets warmer the damage from climate change will accelerate.
The changes in climate that Ireland will experience are still speculative but scientists have predicted that we will experience warmer drier summers in the south and east; while the country will experience wetter winters and more intense storms with higher wind speeds. The frequency of extreme climatic events will increase. For example drought frequency is predicted to increase to 3-4 droughts per decade over large parts of central and southern Ireland by 2050, increasing to more than 7 droughts per decade towards the end of the century. All of these effects are likely to have an impact on our forests and will create many challenges, but also, opportunities for Irish forestry.
LIKELY IMPACTS ON FORESTS
Given the rapid change in the predicted climate in Ireland over the next century and the relatively long periods between establishment and final harvest, (40 years for conifers and 80-120 years for broadleaves) it is likely that some species may not be suited to the future climate within one or two rotation cycles.
Species that originate from the cool temperate rain forests of Northwest America such as Sitka spruce, western hemlock, western red cedar are adapted to moist conditions. While these can be planted throughout the country at present, if droughts are to become a feature of our future climate then there may be a need to confine these species to the wetter regions. Similarly, broadleaves such as ash and beech are drought intolerant and planting would also need to be confined to suitable areas.
While the choice of alternative species is an option there are opportunities with some species to use different seed origins to those currently being planted. Many species e.g. Douglas fir, Norway spruce, Scots pine and lodgepole have wide natural ranges that cover many different climatic zones. Obtaining seed from the warmer, drier parts may provide genetic material that is better adapted to the new conditions.
Warmer drier periods during the summer season may provide better growing conditions for some of our current species, and also provide opportunities to grow new species. Broadleaves generally prefer warmer conditions than we experience in this country and a rise in summer temperature will benefit their growth and development e.g. oak, cherry, lime, Spanish chestnut, maples etc. Also, species such as Monterey pine from California and Eucalyptus from Australia which are currently marginally hardy in Ireland may become more widely planted.
Planning for a change in climate is difficult, particularly since the degree and rapidity of change is unknown. Trees have long life cycles and those that are being planted today may experience a different climate by the time they mature. Current research is developing a GIS decision support system for species selection and productivity based on the current climate, site attributes and soil types. These productivity models are being further developed to assess the sustainability of current forest species, and suggest the introduction of new species or management strategies, under future climate change scenarios.
Forest growth rates have been increasing since the middle of the 20th century. Some of this growth enhancement may be caused by the trend in land-use change and the increase in CO2 levels (carbon fertilization effect) but generally it is attributed to warmer climate conditions and extended growing season.
There are already signs that the growing season is lengthening in Ireland with trees starting to come into growth earlier than in previous years. Leaf unfolding has advanced by 3 weeks since 1970 for the common beech (Fagus sylvatica). This phenomenon is linked with increasing average spring temperatures.
Fires, insects, pathogens and extreme events
The frequency and intensity of forest fires, outbreaks of insects and pathogens, and extreme events such as high winds, may be more important than the direct impact of higher temperatures and elevated CO2.
Drier conditions will make forests more susceptible to fires and older plantations may become more vulnerable than heretofore. As ground fires become more frequent and intense there are greater chances of these spreading into tree crowns causing serious damage to forest crops and protected habitats.
Climate change can dramatically shift the current boundaries of insects and pathogens and modify tree physiology and tree defense mechanisms. Already the spread of pathogens such as Chalara fraxinea ash dieback disease and Phytophthora species across Europe is being attributed to climate change. Similarly invasive exotic alien species are finding favourable ecological conditions in areas that at one time would not have been suitable. This trend is likely to continue into the future.
Even without fires or insect damage, the change in frequency of extreme events, such as strong winds, winter storms, droughts, etc. can bring significant losses to commercial forestry. These effects of climate extremes include reduced access to forests, increased road and maintenance costs, direct damage to trees by wind, effects of wetter winters on harvesting schedules etc. High wind events can damage trees through branch breaking, crown loss, trunk breakage, or complete stand destruction.
While forest fires, insect outbreaks, wind damage, and other extreme events can result in substantial economic damage to the forest sector, other adverse effects include reductions in biodiversity and non-timber forest products and negative impacts on soil erosion and hydrology. In a changing climate, higher direct and indirect risks caused by more frequent extreme events will affect timber supplies, market prices, and cost of insurance although the costs are highly uncertain.
A significant portion (approx 40%) of Ireland’s forests has been established on peatland sites. Predicted rising temperatures, accompanied by a likely decrease in summer rainfall, will increase the moisture deficit of peatlands both in amount and in duration. This could initially be beneficial for the growth of trees as the water table would be lowered during the growing season allowing greater soil aeration resulting in increased rooting depth and perhaps wind stability. However, dryer conditions will increase the rate of oxidation of the peat leading to CO2 release, shrinkage, erosion, nutrient loss and maybe irreversible drying on certain sites. Increase fire risk is also a possibility not only for the trees but also for the peat soil. These factors threaten the sustainability of the forest soil and could, in time, lead to the eventual decline in forest productivity on these sites.
Long term monitoring studies, initiated in the 1980 to assess the impact of atmospheric pollution (acid rain) on European and Irish forests, are now being used to provide information on climate change. Data collected from a network of forest plots around the country (FutMon plots) will be used to monitor forest health, changes in soils, biodiversity, phenology, etc and will play a crucial role in understanding how forests will react to changes in climate.
Researchers in NUIMaynooth are undertaking a project called IMPACT modelling the effects of climate change on key pests to improve protection of biomass for carbon sequestration and bioenergy in the woodlands of Ireland and Wales. The team is also providing specific pest risk profiling and an assessment of those pests posing the greatest threats to tree growth.
Other studies include FORFLUX which is using the data from FutMon plots to gain an understanding of the complex interactions between the atmosphere, soils and surface waters while CARBIFOR attempts to characterize changes in biomass, decomposition, CO2 and non-CO2 greenhouse gas (GHG) flux associated with different soils and tree species, providing a more comprehensive assessment of the total greenhouse gas budget of Irish forest ecosystems.
Further information on the effects of climate change on forests can be accessed through the following links: