Rockrose thickets are shrub formations that occupy a considerable area of the Iberian landscape, extending over approximately 3 million hectares. In Spain, these plant formations, dominated mainly by species such as the sticky rockrose (Cistus ladanifer) and the steppe rockrose (Cistus laurifolius), can become an interesting source of bioeconomy, although currently only 1% of the surface is being used.
LUIS SAÚL ESTEBAN, researcher at CEDER-Ciemat, and PEDRO PABLO PELLÍN, manager of the company El Jarpil, which provides a mobile still, explain the objectives and present some results of the ESjara project from the Moncalvillo pastureland, in the province of Burgos.
Esteban emphasizes that ESjara is a project of a supra-regional nature that allows for collection trials in rockrose thickets of different species and analysis of the composition of the different essential oils obtained in regions of Extremadura, Andalusia, Castilla y León and Castilla-La Mancha.
Essential oil and hydrosol markets
The sticky rockrose is the most widely used and known species for its production of labdanum, an aromatic resin used mainly in perfumery. The global production of essential oil from this species of rockrose is concentrated mainly in Spain, Portugal and northern Morocco and in a small area of southern France, although with completely different compositions, explains Pellín.
The typical yield from a wild rockrose thicket is around 1 per 1,000, meaning approximately one kilogram of essential oil is obtained for every 1,000 kilograms of freshly processed plant material. Under optimal conditions, production can reach up to 1.5 kilograms of oil per hectare, says Pellín.
Prices for essential oil of rockrose range from 850 to 1,000 euros per kilo, depending on the composition and quality, which in turn vary according to the geographical area, the harvest time and the Market demand. Other species, such as the steppe, do not yet have a market; understanding the composition and potential uses of their oil is one of ESjara's objectives.
In addition to its traditional distribution in the global market for perfumery, the essential oil of rockrose is increasingly used for applications in cosmetics and agriculture, especially to obtain fungicides and anti-germination agents.
Part of the hydrosol, the abundant liquid byproduct or co-product generated during the distillation process, is being used in the cosmetics industry, for example, in shaving lotions, shampoos, toothpaste, etc. It can also be used to replace the aqueous phase in other cosmetic products, thus harnessing its beneficial properties. According to Pellín, the market offers prices of around €2 per liter when produced in large volumes, and although he considers it difficult to valorize all the hydrosols generated, he believes it is possible to find new uses for them within the framework of a circular economy.
Mechanization and distillation in situ
Another aspect that ESjara is testing is the mechanization of the harvest using a shredder-collector designed by CEDER-Ciemat and the machinery manufacturer López Garrido.
Rockrose is traditionally harvested by hand from wild plants, with yields of between 600 and 800 kilograms per harvester. Mechanization reduces costs by quadrupling productivity and standardizes product quality.
However, Pellín points out that mechanization requires immediate distillation to avoid losses in essential oil yield, as the machinery fragments the leaves where the oil is concentrated more intensely than when harvested manually. Thanks to the mobile still, which allows for the distillation of the rockrose in situ, they can to evaluate the yields of essential oils and hydrosols obtained with mechanized harvesting.
The harvesting device is equipped with a horizontal shaft of movable hammers and an auger that directs the shredded material towards a side fan, which propels it into the hopper, where up to 1200 kg can be accumulated. Harvesting is carried out with the tractor in reverse, ensuring that the wheels follow the harvester to avoid crushing the vegetation.
The robust design of the implement is key, as the components must withstand constant abrasion, especially the rotor and hammers, the auger, and the fan. To prevent blockages and ensure efficient and continuous operation, a specific range of angular speeds has also been established for these parts.
The equipment allows the collection of rockrose biomass and other shrubs, and has even been successfully tested with forest debris, Esteban assures.
In some well-managed areas, yields of up to 6,000 kilograms per hectare of green plant have been achieved, with a yield of 3 hours per hectare, he says.
Regarding the productivity of green material from rockrose thickets, according to calculations carried out by Agresta, a partner in the project, a rockrose thicket that is harvested every 5 years can produce around one ton or one and a half tonnes of biomass per hectare per year, which is equivalent to 5 or 6 tons per hectare at harvest time.
Other benefits of managing rockrose thickets
In addition to the production of essential oils, rockrose offers other opportunities in the field of bioeconomy, such as generating renewable energy. The residual biomass obtained after distillation, once dry, can be used in a boiler, taking advantage of its calorific value, which is comparable to that of pine chips, according to Luis Esteban.
Although its quality varies depending on harvesting conditions, the ash content ranges from 21% to 31% ash. Esteban emphasizes that this biomass is competitive in the energy market, especially compared to other lower-quality or more problematic materials such as straw. An approximate price, delivered to the power plant, would be between €35 and €40 per ton.
The management of rockrose thickets also has positive effects on the preservation of the traditional landscape and associated biodiversity.
In the Moncalvillo pastureland, the clearing of rockrose thickets to obtain essential oil, carried out every five years, will facilitate the better growth of the oak trees that make up the original pastureland and will help prevent fires.
The pasture is A traditional ecosystem and cultural landscape that combines spaced trees, mainly holm oaks, cork oaks, or oaks, with pastures and scrubland, where different activities such as agriculture, livestock farming, and forestry coexist in a balanced way. These are formations rich in biodiversity, in which the Areas of scrubland located in areas such as valleys serve as a refuge for wildlife.
The gradual abandonment of livestock farming over the years has allowed scrubland to invade pastures. In the specific case of Moncalvillo, after the clearing work carried out with subsidies from the Regional Government of Castile and León, the scrubland, thanks to its pioneering nature, is able to recolonize the dehesa (pastureland) and form dense stands in just a few years.
The sustainable use of these vegetation formations can contribute to rural development, generate employment, and add another piece to the much-discussed circular economy. It will be necessary to have programs driven by public administration that allow for intervention in the rockrose thickets and continue research to develop new applications for the products and improve technologies for their valorization.
More information
Article published in BIOMASS NEWS 10 – Autumn 2024