Climate change impacts and vulnerability in Europe 2016

Climate change impacts on environmental systems
4.4.7 Forest pests and diseases
Key messages
• The incidence of forest insect pests, which represent a serious threat to forests, has increased across Europe.
• Climate change will have a major influence on the spatial and temporal distribution of forest insect pests in Europe, with
increased risks projected in most regions.
Relevance
Forest insect and pathogen species are currently
expanding their geographical ranges, in many cases
owing to introductions facilitated by international
trade. Several invasive alien species have damaging
impacts on agricultural, forest and natural resources.
Populations of forest insect pests can be influenced by
climate change, as it leads to a longer growing season,
variations in precipitation patterns, modifications
in food availability, and qualitative and quantitative
changes in their predator and parasite populations
(Netherer and Schopf, 2010). There is evidence that
these changes affect the distribution and relative
abundance of pest species in forest ecosystems, thus
changing the frequency of pest outbreaks (Marini
et al., 2012; Spathelf et al., 2014; Barredo et al., 2015).
In Europe, higher temperatures are likely to promote
distributional shifts of forest insect pests towards
northern latitudes and higher elevations.
In the southern Mediterranean region and in some
continental zones, warmer temperatures and the
increased frequency of droughts are likely to affect
heat-sensitive insects, resulting in a northwards and
upwards shift of their geographic range. Heat‐tolerant
species, on the other hand, such as the pine
processionary moth (Thaumetopoea pityocampa) or the
oak processionary moth (Thaumetopoea processionea),
will probably benefit from warmer conditions and
hence expand their geographical range beyond the
Mediterranean region and expand into previously
unaffected areas. However, temperature increase
and drought could shrink the southern range of these
species, resulting in some cases in range contraction
(Netherer and Schopf, 2010; Battisti et al., 2014).
Past trends
Disturbances such as drought, windthrow, fires, and
attacks by insect pests and pathogens of trees are
naturally occurring in forests. Nevertheless, despite
many uncertainties, there is consensus on an increased
incidence of pests and diseases in European forests
(Marcais and Desprez-Loustau, 2007; Moore and Allard,
2008) and on shifts in the spatial and temporal range
of insects as a result of climatic change (Netherer and
Schopf, 2010; Bebber et al., 2014; Seidl et al., 2014).
In addition, some species of fungi and pests benefit
from milder winter temperatures in temperate forests,
facilitating the spread of pests formerly controlled by
frost sensitivity (Settele et al., 2014), while other species
spread during drought periods to northern latitudes
(Drenkhan et al., 2006; Hanso and Drenkhan, 2007).
A review study concluded that several changes have
already been observed in the occurrence of forest pests
in Europe (Netherer and Schopf, 2010). The European
spruce bark beetle (Ips typographus) has been reacting
to warmer and drier spring and summer periods in
recent decades by having a shorter development
period, which enables multiple generations (Baier et al.,
2007). The spread of insect outbreak zones has been
observed in those regions with the greatest warming in
boreal forests (Malmström and Raffa, 2000; Volney and
Fleming, 2000). In temperate continental forests, tree
defoliation by the gypsy moth (Lymantria dispar dispar)
and the incidence of other insect pests are among the
factors responsible for oak decline in central Europe
(Balci and Halmschlager, 2003). In addition, altitudinal
shifts of the moth have been observed in Slovakia
(Hlásny and Turčáni, 2009). In the Mediterranean
region, altitudinal range expansion of the pine
processionary moth (Thaumetopoea pityocampa) has
also been observed in mountain regions of the Sierra
Nevada in the United States and the Sierra de Baza in
Spain (Hódar et al., 2003) and in mountainous regions
of Italy (Battisti, 2008; Petrucco-Toffolo and Battisti,
2008). In Britain, Dothistroma needle blight has spread
rapidly since about 1995 (Forestry Commission, 2012).
Climate change has driven range shifts in tree species
and increased drought effects resulting in forest
dieback (Allen et al., 2010). In addition, forests are
increasingly coping with human-related stressors
that affect forest condition, either directly through
logging and clearing or indirectly through air pollution
and introduction of invasive species (Trumbore et al.,
180 Climate change, impacts and vulnerability in Europe 2016 | An indicator-based report