Forests for People

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Forest protection

and climate change

Gillian Allard, Susan Braatz and Beverly Moore, Food and Agriculture Organization

hanges in the patterns of disturbance in forests are

expected under a changing climate as a result of warmer

temperatures, changes in precipitation and increased

drought frequency. This will play a major role in shaping the

world’s forests and the forest sector.

Disturbances are a natural and integral part of forest ecosystems and

have major impacts, positive and negative. They influence forest

structure, composition and functioning and can be important for

maintaining biological diversity and facilitating regeneration. When

disturbances exceed their normal range of variation, however, the

impacts on forests can be extreme, affecting entire landscapes,

causing large-scale tree mortality, destroying undergrowth and

degrading soils. Global climate change and variability are exacerbat-

ing many of these impacts by making forests more prone to damage

by altering the frequency, intensity and timing of insect and disease

outbreaks and extreme weather events such as cyclones, storms,

heat waves and drought and increasing the risk of landslides and

large-scale fires.

Large wildfires, or mega-fires, have been noted in all regions of

the world. The frequency of their occurrence is likely to increase as

droughts intensify, fuels accumulate and landscapes become more

homogeneous. They are not always single wildfires but often occur

as groups of multiple fires across a large geographic area. Mega-fires

are often extraordinary for their size, but they are more accurately

defined by their complex, deep and long-lasting social,

economic and environmental impacts such as adversely

altering energy, water, nutrient and carbon cycles,

causing a decline in biodiversity and increasing carbon

emissions and weed invasion.

In places where climate

change increases the risk of wildfire, measures should be

taken to reduce this risk by putting in place effective fire

management measures, including prevention, detection,

control and rehabilitation.

Changes in precipitation can increase the risk of

erosion, landslides and floods. Reducing the risks

might entail maintaining or increasing vegetative cover

and minimizing disruption on erodible slopes, increas-

ing protection of riparian strips to protect river water

quality, and taking protective measures in drylands that

are at risk of drought and increased wind erosion.

A changing climate will alter the disturbance dynam-

ics of native forest insect pests and pathogens, as well

as facilitate the establishment and spread of non-indige-

nous species. Such changes in disturbance dynamics, in

addition to the direct impacts of climate change on trees

and forest ecosystems, can have devastating impacts

because of the complex relationships among climate,

disturbance agents and forests.

Climate, and in particular temperature and precipita-

tion, has a very strong influence on the development,

reproduction and survival of insect pests and patho-

gens. It is highly likely that these organisms will be

affected by any changes in climate. Because they are

cold-blooded organisms, forest insects and pathogens

can respond rapidly to their climatic environment. With

their short generation times, high mobility and high

reproductive rates, it is likely that they will respond

more quickly to climate change than long-lived organ-

isms, such as higher-order plants and mammals, and

thereby may be the first predictors of climate change.

Increases in summer temperature will generally

accelerate the rate of development in insects and

increase their reproductive capacity, while warmer

winter temperatures may increase overwinter survival.

Warmer winter temperatures, however, can decrease

snow depth. Decreased snow depth may lower the

winter survival rates of many forest insects that over-

winter in the forest litter where they are protected

by snow cover from potentially lethal low tempera-

tures.

The magnitude of the impacts of temperature

on forest pests will differ among species depending on

Outbreaks of the mountain pine beetle (

Dendroctonus ponderosae

) in western

Canada and the United States have been exacerbated by changes in climate

Image: Ronald F. Billings