STRESSORS

an average of 11 indicator datasets

Latest weighted average score:

3.7/5

Score is trending flat over time
Weighted average score of Stressors Indicators

Stressors are environmental conditions that can hurt forest ecosystems if they occur outside of the ideal or normal conditions. All biological life needs favorable temperatures and sufficient water to survive, but long-lived trees have evolved and adapted to current conditions. As our climate changes and new stressors emerge, we may see that the conditions go beyond the conditions that trees have grown to tolerate in our region.

-- Expert interpretation for Stressors is not avaialable --

Stressors provide information on the future productivity of a forest, whether the stressor is beneficial, damaging, or has no impact. While forests are able to adapt and build resistance to environmental stressors over time, the combination of many stressors or wide departures from historical conditions may lead to irreversible change. This could in turn affect forest structure, condition, and productivity.

Because of climate change, monitoring stressors is of high importance. Climate change itself is a large stressor because it is leading to conditions that are out of the historical norm, leaving some tree species unable to adapt. However, there are a number of stressors that have seen improvement recently, and tracking is equally important to protect the gains we have made.

To assess stressors, the Forest Indicators Dashboard uses data on stressors that occur naturally, including pollution, climatic variables and invasive pests.

Indicator Weight
Precipitation Acidity 10%
Growing Season Length 15%
Ozone Exposure 3%
Mercury Deposition 2%
Minimum Temperature 10%
Maximum Temperature 10%
Precipitation 10%
Snow Cover 10%
Climate Extremes 10%
Drought 10%
Damage by Invasive Pests 10%

Precipitation Acidity

Precipitation with high acidity (a lower pH) is harmful to trees as it damages leaves and leaches important nutrients from soils. Unpolluted rain has a pH of around 5.6. A high score means that measured precipitation pH is at or near this number.

Precipitation Acidity contributes to 10% of the overall Stressors category score.

Growing Season Length

While an extended growing season may benefit some plant species, others may not be as equipped to deal with an earlier spring or later fall and could face stresses like frost damage or higher energy needs. Ideally, a healthy forest would have a growing season that remains relatively consistent. A high score means that the growing season length is not shorter or longer than the long-term average.

Growing Season Length contributes to 15% of the overall Stressors category score.

Ozone Exposure

High levels of ozone exposure can cause leaf damage, which can reduce the efficiency of processes such as photosynthesis. A high score means that ozone levels are below the threshold for causing damage to trees.

Ozone Exposure contributes to 3% of the overall Stressors category score.

Mercury Deposition

Mercury is a toxin that can be found in water, air, and soil. Mercury gets absorbed by plants and then gets passed through various food webs. High concentrations of mercury can lead to a reduction in growth and productivity in plants and higher wildlife mortality. A high score means that there is a low level of mercury deposition.

Mercury Deposition contributes to 2% of the overall Stressors category score.

Minimum Temperature

With climate change, minimum temperatures are projected to increase. These higher minimum temperatures stress the native forest species by moving conditions away from what they are adapted to handle. A high score means that the minimum temperature is close to the long-term mean.

Minimum Temperature contributes to 10% of the overall Stressors category score.

Maximum Temperature

With climate change, maximum temperatures are projected to continue to increase. Higher maximum temperatures can reduce species diversity and introduce extended periods of drought. A high score means that the maximum temperature is close to the long-term mean.

Maximum Temperature contributes to 10% of the overall Stressors category score.

Precipitation

Water is essential to a healthy forested ecosystem, but excess water can lead to flooding and disease outbreaks, while a lack will lead to drought. Fluctuations in rainfall above or below the long-term mean will lead to stressful conditions for some forest species while creating ideal conditions for other species. Ideally, a healthy forest ecosystem has water availability that remains consistent. A high score means that precipitation levels are near the long-term mean.

Precipitation contributes to 10% of the overall Stressors category score.

Snow Cover

Snow cover is projected to decrease in depth, duration, and extent under climate change. Lack of sufficient snow cover can make tree roots vulnerable to freezing damage and cause nutrients to be leached from the soil. Snow cover fluctuations above or below the mean may result in undesirable conditions for native forest species. A high score means snow cover is near the long-term mean.

Snow Cover contributes to 10% of the overall Stressors category score.

Climate Extremes

Changes in the proportion, extent, and severity of extreme weather events are an indication of a volatile and changing climate. Not only are extreme events stressful to forests, but they can cause significant problems for our infrastructure and health as well. A high score means that the there is a high number of extreme events in a given year.

Climate Extremes contributes to 10% of the overall Stressors category score.

Drought

Lack of water, particularly during the growing season, can result in short-term changes in our forests, for example, a tree will halt photosynthesis and growth until there is sufficient water. But droughts can also result in more serious consequences to forests, like lack of a viable seed crop or large die offs of vulnerable species, locations, or age classes. A higher score means drought severity is not deviating from historical patterns.

Drought contributes to 10% of the overall Stressors category score.

Damage by Invasive Pests

An invasive pest is an insect or disease that is not native to our region’s forests and can cause extensive damage where it is introduced. An example is emerald ash borer. When an invasive pest is introduced to an area, native trees can succumb to serious damage because they have not evolved to develop chemical and physical defenses against them. A high score means that there is a low amount of damage to trees from invasive insects and diseases.

Damage by Invasive Pests contributes to 10% of the overall Stressors category score.

STRESSORS INDICATORS