There is no single measure of forest biodiversity. Species counts can give us an indication, but biodiversity also includes genetic variation, the structure of forests and the ecological processes taking place within them. A measure that captures one part of that picture may tell us relatively little about another.
That makes measuring change more demanding than simply choosing an indicator and tracking whether it rises or falls. We first need to be clear about what aspect of biodiversity we want to understand, then use monitoring that can capture it at the right scale and over a long enough period.
On 16 September 2026, Teaming Up 4 Forests will publish the Productive and Biodiverse synthesis study, examining how Europe’s forests can remain productive while maintaining or improving biodiversity. One part of the study looks specifically at how forest biodiversity can be defined and measured in ways that remain scientifically credible, practical to monitor and clear enough to communicate.
What is forest biodiversity?
The Convention on Biological Diversity defines biodiversity as variation within species, between species and among ecosystems. In forests, that complexity can be understood through three dimensions: composition, structure and function.
Composition describes what is present, from genetic variation within populations to different species and forest types. Structure concerns how those elements are physically organised, including features such as age classes, deadwood, habitat trees and canopy layers. Function covers the ecological processes taking place within the forest, such as regeneration, nutrient cycling, decomposition and species interactions.
These dimensions overlap, but they are not interchangeable. A forest might show little change in the number of species present while its age structure, deadwood or ecological processes are changing. Species richness is therefore useful, but it cannot stand in for biodiversity as a whole.
How is forest biodiversity monitored?
Across Europe, forest biodiversity is monitored through a range of sources.
National Forest Inventories provide information across large areas and recurrent intervals, and are particularly valuable for identifying long-term trends. They increasingly record biodiversity-related features such as deadwood, tree microhabitats and age structure. Their broad coverage, however, means they are less suited to detecting some rare species or other fine-scale ecological features.
Specialist biodiversity networks and long-term field plots can provide much greater ecological detail, including information on particular species groups and processes. Their coverage is usually narrower. Remote sensing adds another perspective: satellite imagery and other technologies can monitor forest cover, canopy structure, fragmentation and connectivity consistently over large areas, but these are often indirect measures of biodiversity and still need to be interpreted alongside observations on the ground.
The strength therefore comes from combining sources. Each answers different questions, at different scales and with different levels of detail.
Time is equally important and the response to management or disturbance may take years to become detectable. Short-term monitoring can therefore confuse temporary variation with a longer-term trend. Consistent observation over time is essential if we want to understand whether biodiversity is genuinely changing and capture the regeneration of forests and species over time.
Good biodiversity indicators simplify without distorting
Monitoring produces large amounts of complex information. Indicators make some of that information easier to compare, report and use in decisions.
But simplification comes with a responsibility. An indicator has to be practical enough for forest managers and policymakers to use while remaining faithful to the ecological change it is intended to represent. A technically precise measure that cannot be interpreted outside a specialist field has limited value; an apparently simple measure that hides important changes in the forest can be actively misleading. The study therefore stresses the need to balance scientific rigour with practical use and clear communication.
So the answer to the title is not a single indicator or monitoring system. Measuring change in forest biodiversity requires us to be precise about what is changing, combine evidence that captures different dimensions of biodiversity, and observe those changes at appropriate magnitude and time scales.
Productive and Biodiverse will be published on 16 September 2026. Join the Teaming Up 4 Forests launch webinar that day to hear the researchers introduce the study and explore how it approaches questions of biodiversity, measurement and forest management.
Register to the webinar here: https://tinyurl.com/TU4F-16-September
