The São Francisco Farm Arboretum celebrated in an upcoming book

The centenary São Francisco Farm arboretum, in Aveiro, will be celebrated in a new book to be published in 2023. And to get to know these magnificent trees, there is mapping and georeferencing work ongoing since the start of 2023, with the help of a drone and a LiDAR (Light Detection And Ranging) sensor.

There are more than 400 large trees and shrubs worth knowing and preserving at São Francisco Farm. In addition to their large size, they stand out for their beauty and old age – some of them were planted more than a century ago. “Furthermore, these are unique species in the country and a fair deal are also unique in the whole of Europe”, João Ezequiel proudly states, curator of São Francisco Farm and leader of the team engaged in mapping them and which shall result in a book under the name The Monumental Arboretum of São Francisco Farm.

The team relies on two further members: researcher André Duarte and forest engineer Luis Muñoz, both from RAIZ – Forest and Paper Research Institute, the research and development (R&D) structure of The Navigator Company, based on this Farm in Eixo, near the city of Aveiro.

The wealth of this particular heritage is undeniable: in the São Francisco Farm arboretum there are more than one hundred species of Eucalyptus and Corymbia (a botanical species that includes the so-called garden eucalypts) forming together one of the largest eucalyptus arboretums outside Australia.

These trees are part of around 450 species of flora identified on this farm, some of them protected, such as the butcher’s-broom (Ruscus aculeatus), others endemic, such as Rubus vigoi that only grows naturally in the Iberian region, thus turning this 14-hectare area a biodiversity hotspot that should be further studied, documented and preserved.

Did you know that in the São Francisco Farm arboretum, there are…

• Some of the largest Portuguese specimens of the species Corymbia calophylla (33.1 m high and 3.6 m from P.A.P.), Eucalyptus botryoides (48.6 m high and 4.3 m from P.A.P.), Eucalyptus smithii (47.9 m high and 4.3 m from P.A.P.) and Eucalyptus ovata (40.6 m high and 3.6 m from P.A.P.) and Eucalyptus eugenioides (39.4 m high and 3.8 m from P.A.P.). “We believe that these last two specimens may be the largest specimens of their kind in Portugal and among the largest worldwide”, says João Ezequiel;
• This work further shows that the biggest trees on São Francisco Farm are now a Eucalyptus grandis, about 52 m high and only 39 years old. As for their size, the largest trees are both centenarian, e.g. a eucalyptus (Eucalyptus globulus), which, together with a Monterey cypress (Cupressus macrocarpa), are 5.6 m wide and at breast height;
• Trees of exceptional size of assorted species, including eucalyptus (Eucalyptus pulchella, Eucalyptus obliqua, Eucalyptus viminalis, Eucalyptus muelleriana, Eucalyptus microcorys), cypresses (Cupressus lusitanica and Cupressus macrocarpa), sequoias (Sequoia sempervirens), tulip trees (Liriodendron tulipiffera) and even stone pines and oak trees (Pinus pinea and Quercus robur), all mentioned in Ernesto Goes’ book Monumental Trees of Portugal (1984);
• Several unique species of eucalyptus in Portugal, such as Eucalyptus risdonii, Eucalyptus tenuirramis and Eucalyptus obtusiflora.

Technology supports the preservation of the São Francisco Farm arboretum

And when traditional measurement techniques fail to help us obtain the desired detail, new technologies come into play, “which we already use to know our forest areas, for georeferencing and to obtain all dendrometric parameters from trees,” explains João Ezequiel to Biodiversidade.

That’s the case of LiDAR technology, whose sensor was previously attached to aeroplanes and helicopters and is currently used in drones. This sensor provides information of great biometric precision, such as the height, size and volume of vegetation and increasing productivity on site, providing helpful information for a better managemet of the forest. The result is a 3D model of the area under analysis, with millions of points and so precise that we can see the vegetation in close detail from the canopy to the ground.

As to the use of new technologies by Navigator, Luis Muñoz clarifies that “we used them in a very comprehensive manner: for example, satellite images used to map both conservation and production areas, and also to assess the strength and health status of the forest, and to make volume estimates.”
The case of the São Francisco Farm arboretum “is quite complex, because it has large and small trees side by side, with large shading from canopies and trees standing very close to each other”, thus making it difficult to measure them from the soil. “In addition, we have the asymmetry of the terrain itself in an embedded valley,” adds João Ezequiel. In light of these characteristics as regards both relief and density of vegetation, the best technological option available to make such mapping and characterization is the use of the LiDAR sensor attached to a drone.

André Duarte clarifies that these measurements using drones “are very important to obtain some details in forests, such as the incidence of pests and diseases, invasive species or even spontaneous vegetation”.

The complementarity between tools on the ground and in the air – satellite, aeroplane and drone images – combined with work on site allow us to obtain an increasingly detailed map of the forest cover and existing biodiversity: “we can reduce costs, both material and human, and in addition we can achieve greater precision as regards the results obtained”, explains Luis Muñoz, not least because an increase in precision of some centimetres enables us to manage the forest stands more effectively. “It’s a qualitative leap in knowing where [species] are and how to act” to protect and preserve them.