Structure Condition Services Stressors
Trees die for a variety of reasons, from windstorms and lightning strikes, to fungal or insect infestations. The trunks may persist for decades as standing dead trees providing habitat for birds and animals, or as logs slowly rotting on the forest floor and gradually returning nutrients to living plants. However, changes to the baseline tree mortality rate may signify that environmental conditions are changing and hastening the death of trees. Here, tree mortality is computed as the ratio of the annual volume of trees that dies to the volume of all live trees ≥5 inches recorded in forested Forest Inventory and Analysis plots1. A high score means that tree mortality is remaining stable over time.
The score is calculated using a target value and the historical range of the the entire long-term dataset. The higher the score, the closer this year's value is to the target.
Once the score is computed for each year, the trend in scores over time is calculated. If the trend is significantly positive or negative, the long-term trend is marked as increasing or decreasing respectively.
Distance between target and maximum (scored 1-5)
|Directionality of scores||
No change from the long-term mean is better
|Minimum value used in scoring||
Data minimum - 10% of the range
|Maximum value used in scoring||
Data maximum + 10% of the range
Data on annual tree mortality were extracted from the USFS Forest Inventory and Analysis Program EVALIDator1. We used FIA-established queries to retrieve volume estimates for tree mortality (“0213 Average annual mortality of sound bole volume of trees (at least 5 inches d.b.h./d.r.c.), in cubic feet, on forest land”) and live trees (“0024 Sound bole volume of live trees (at least 5 inches d.b.h./d.r.c.), in cubic feet, on forest land”) filtered by trees ≥5 inch DBH (“and tree.DIA>=5”). We computed tree mortality as the ratio of the annual mortality tree volume relative to the volume of all live trees ≥5 inch DBH on sampled plots. Annual data began in 2008 with a more complete inventory in 2010. We relied on FIA’s statistical models for computing this value over time. We set the target for this dataset as the long-term mean. The current year is scored for where it falls between the target and the upper scoring bounds (maximum value in the dataset plus 10% of the range) or the lower scoring bounds (minimum value in the dataset minus 10% of the range), scaled to be between 1 and 5.
The average crown dieback of trees in Vermont's forest provides us information on overall forest health.
Damages to forests occur from insects, diseases, weather events, animals, and human impacts.
Forest growth provides information on how much biomass Vermont's trees add annually.
Higher values of canopy density indicate a more lush, green, and productive forest.
Mapped forest mortality is an assessment of the total area of current-year tree mortality across the landscape.
The proportion of trees with damage and decay provides information on the condition and the potential timber quality of Vermont's trees.
Individual tree mortality is a natural and common event, but changes to the baseline rate can signify worsening environmental conditions for trees.