A digital forest and four innovative technologies to monitor tree water in the Mediterranean

In the heart of the Collserola Natural Park, the forest hides much more than it seems. Between the trees and the undergrowth, CREAF researchers have set up a real outdoor laboratory : dendrometers that 'listen' to the heartbeat of the trees; antennas that pick up satellite signals thousands of kilometres away; sensors that record temperature, humidity and photosynthesis in almost real time, and equipment that scans the trees as if taking an X-ray of their interior.

All of this is to understand how Mediterranean forests respond to drought and improve prediction models . This information is also key to knowing the risk of fire in an area, because the drier the vegetation, the more likely it is that fire will spread.

Collserola became an ideal laboratory because it is a clear example of a Mediterranean forest, with species such as Scots pine, holm oak and oak. CREAF's research is carried out in several plots around the Can Balasc estate, where four types of cutting-edge technologies are used to monitor the amount of water in a forest at different scales: from the interior of the trees - for example, sap flow - to the scale of the plot or forest.

One of the key initiatives being developed at Can Balasc is FUNBOSC , a project that is building a monitoring network for the forests of Catalonia . “The aim is to create a system that helps monitor the amount of water in the forests and whether there is any drought impact,” explains Rafael Poyatos, CREAF researcher and leader of this research.

The first station capable of measuring multiple physiological variables in trees has been installed on the project plots. Sensors include sap flow meters, which indicate how much water is circulating within the tree; trunk water content sensors, which show how much water is stored; and dendrometers, which record microscopic variations in trunk diameter.

This microcycle of contraction and expansion is related to water availability, “when the tree is stressed by drought, this pattern changes. For example, a few years ago we discovered that heat waves turn off the heartbeat of Central European trees ,” adds the researcher.

The data is automatically sent to a server and can be viewed in the form of graphs. Although the installation is recent - it has been operating in Can Balasc since last year - the idea is to expand this network with new stations: one already installed in Prades, a future one in Montseny and another in the Pyrenees in Scots pine forests . “The objective with this sensor network is to help better manage forests and the risk of fires”, explains Poyatos.

Meanwhile, the DRASTIC project studies trees with another innovative approach: the creation of digital twins - a virtual copy of a real object. It does this using terrestrial scanners that shoot lasers to generate highly detailed three-dimensional images of trees. These images allow us to reconstruct their architecture and calculate the volume and surface area of the tree, which is related to the amount of water.

“It’s like studying a forest from a distance,” explains Laura Wynne Stewart. This type of digital twin is relatively common in agriculture, but it is still very uncommon in forest ecology , “which makes this project groundbreaking,” adds the researcher.

So far , 36 trees of three Mediterranean species have been scanned: Scots pine, holm oak and pedunculate oak . In addition, 18 of these trees have sensors installed that allow physiological data to be related to their three-dimensional structure. “The aim is to improve forest models and better understand factors such as the risk of tree mortality,” explains ICREA researcher at CREAF Maurizio Menccucini, who coordinates the project.

GPS is not only used to find streets or guide us by car; it also has a surprising use: monitoring the state of forests. This technology is used by the MOIST project, which studies the water status of vegetation at both the plot and forest scale. To do this, Can Balasc has installed two antennas that capture microwave signals from GPS satellites: one on a tower, above the treetops, and another under the vegetation cover. In the coming months, they will also be installed in Prades and Montseny.

How does it work? The upper antenna receives the signal without interference, while the lower one receives it after it passes through vegetation.

This methodology has been used very little to study forests and, in Catalonia and Spain, it is the first time that it has been applied combined with so much field data. “The data will also serve to validate the drought estimates in the forest made by some satellites,” adds Chaparro.

In parallel, the team is also testing a complementary approach through the PROTEOS project, where researcher Oliver Blinks and research technician Laura Bartra, both from CREAF, are installing sensors capable of both emitting and receiving microwave signals. The idea is that these devices will be connected to each other in the forest and allow them to measure how the attenuation of the signal varies between different points. This would allow them to detect, for example, more attenuation on rainy days or in areas with denser vegetation, and less in drier conditions. All this opens the door to obtaining an even more precise picture of the water status of the forest.

Another team is working through the MICROCLIM project on IoT (Internet of Things) technology, which allows the installation of wirelessly connected sensors. These sensors collect a wide variety of variables, such as soil moisture, sap flow, photosynthesis or microscopic variations in tree volume in real time.

Although scientific results have not yet been published, researchers have already been able to validate some indicators that combine field and satellite data.

The teams working at Can Balasc also share data to validate and refine their estimates. “This allows us to check whether the drought data at the individual scale - of a single tree - coincides with those we obtain at the forest scale from satellites. In this sense, Can Balasc has become a true digital forest for CREAF research,” concludes the team.