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Environmental information systems
Using indicators can help determine the status of forest health and is essential to knowing the best management practices for encouraging forest resilience. Indicators are a basic tool used in forest monitoring, for sustainable forest management. Forest Europe has set a list of ‘Forest Ecosystem Health and Vitality’ indicators including deposition and concentration of air pollutants, soil condition and defoliation.
Deposition and concentration of air pollutants
The atmosphere contains many substances of natural and anthropogenic origin. A large part of them can settle, be adsorbed, or be included in rain and snow and finally reach land surface as wet and dry deposition. Human activities have led to a dramatic increase in the deposition of nitrogen and sulphur compounds.
Although nitrogen is an essential nutrient for plants and may stimulate tree growth, especially in areas with naturally low soil nitrogen availability, prolonged periods of high nitrogen deposition can have harmful effects on forest ecosystems. Excess nitrogen in forests can lead to reduced biodiversity, soil acidification, nutrient imbalances, altered species composition and increased susceptibility to environmental stressors.
Negative effects on forests are noticeable when the total deposition of inorganic nitrogen (i.e. the sum of nitrate and ammonium) exceeds a specific threshold that generally ranges between 5 and 20 kg per hectare per year for forests, a limit known as the critical load.
Most of Europe’s forests have a low level of inorganic Nitrogen deposition (ICP-Forest reporting).
Soil condition
Soil condition can be used as an indicator of forest health by assessing key factors such as nutrient levels, pH balance, organic matter content, soil structure and microbial diversity. Healthy forests typically have nutrient-rich, well-structured soils with slightly acidic to neutral pH, good organic matter content, and well-drained but moisture-retentive soil that supports diverse plant and microbial communities. For more details on forest soils see the soils section.
Defoliation
Defoliation refers to the loss of leaves from a tree and the defoliation rate is the percentage of leaves that have been lost or damaged, compared to a fully healthy tree of the same species. A defoliation rate of more than 25% signifies a moderately to severely defoliated tree. Defoliation can occur due to various factors, including pests, diseases, pollution, drought, and other environmental stressors.
Mean defoliation is increasing both in broadleaved and coniferous trees in Europe.
Broadleaved species
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Coniferous species
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Foliar nutrient content
Foliar nutrient content is the concentration of different nutrients, such as nitrogen and phosphorus, in tree foliage. The foliar nutrient contents depend on the availability of nutrients in the soil and on the uptake ability of trees. The nutrient concentrations and ratios relate to resilience and susceptibility of trees to pests, diseases and to growth levels.
For Pinus sylvestris, Picea abies and Fagus sylvatica, the proportion of monitoring sites with a foliar nitrogen-to-phosphorus (N:P) ratio exceeding the critical threshold increased from 1995- 2017, while for Quercus species this proportion declined. This shows that different species respond differently to atmospheric condition changes. Monitoring the indicators of forest health (like those mentioned above) gives us the tools to manage forests for optimal resilience.
The percentage of plots with a foliar N:P ratio above the critical limit increased for Pinus sylvestris, Picea abies and Fagus sylvatica. For Quercus spp. it decreased.
Resilience
According to the International Panel on Climate Change (IPCC) resilience is the ability of a system and its component parts to anticipate, absorb, accommodate, or recover from the effects of a potentially hazardous event in a timely and efficient manner (Climate Change: New Dimensions in Disaster Risk, Exposure, Vulnerability, and Resilience).
Forest resilience has several vital components, e.g., biodiversity, adaptive capacity and connectivity. These components play an essential role in making forests more resilient to disturbances.
Forest management with resilience in mind implies using diverse practices and governance tools that are particular to each forest. Such adaptive management strategies favour open options and coping with uncertainty.
Components of forest resilience
