According to an acceptation forged during the latter half of the 20th century, the French term génie végétal covers any technique that uses living plants for various land-management purposes, especially stabilizing embankments, bunds and riverbanks, and depolluting soil, water, and air. So far untranslatable into English except by the unused expression vegetation engineering, it is a bit broader than the notion of soil bioengineering. Issues like maintaining biodiversity and fighting global warming, as well as concerns about landscape, have turned this traditional knowledge into a key element in contemporary environmental management. In this day and age, “soil bioengineering” is often opposed to “civil engineering” which is associated with more mineral-based approaches. This appreciation for plant-based engineering, which is closer to nature, is rooted in the practices and debates of the Enlightenment. It raises the question of how techniques circulate between traditional expertise and academic , or legitimate, knowledge, as well as exploring feedback from experiences in different territories.
“Grassroots” Soil Bioengineering: Rural People’s Knowledge and Managing Nature
Domesticating the dynamics of nature is a critical issue for pre-industrial agrarian societies, for whom uncultivated plants (saltus) constituted an essential resource. In Brittany, heath gorse provided precious fertilizers when mixed with manure from barnyards and stables. In the lower Languedoc, in the Lodévois garrigues, Spanish broom plant was pruned and sown at the end of the early modern period, because in addition to fertilizer, it provided textile fibers that could substitute for wool. So plants were carefully tended everywhere, because they constituted essential resources for farming (ager), rural crafts and the domestic economy. Planted along the banks of waterways, hedges and riparian forests were indissociable from those everyday practices employing plants in preindustrial societies.
Along waterways and coastlines, certain plants were used as tools for micro land-management practices. With its tadpole shape, willow is the most iconic variety in grassroots soil bioengineering. When its cuttings were planted in valleys, it supplied kindling and material for basketry and wickerwork. In addition, the trees’ extensive root networks stabilized embankments and prevented flooding. In 1758, a “Mémoire sur la culture de l’osier” (“Memoir on Growing Willow Trees”) published in the Journal Œconomique pointed out that “landowners near rivers often plant willow on [their] property in order to preserve their legacy, because willow withstands floods better than anything else,” and adding that “the silt the water leaves behind when it ebbs only makes the willows spread even more easily”. Along coastlines, where salt limits the flora, halophiles like marram grass (i.e. European beachgrass), maritime pine and tamarisk were similarly used to prevent sediment shift while also providing fuel and even lumber. These types of “local ecological knowledge” (LEK) to use an expression coined by anthropologists, are set in singular environmental settings, constituting an empirical way of practicing soil bioengineering.
Engineers and Botanical Knowledge during the Enlightenment
Since the Renaissance, engineers have been intermediaries connecting a rationalized vision of a space or area with ever-more reproducible kinds of technical know-how. Traditionally, their ingenium has been associated more with stone, clay or even water than with living things. Nevertheless, at the end of the modern era, the rise of civil engineering, which had been put in charge, most notably, of creating riparian and coastal infrastructure, led to growing technical interest in plants. On the scale of the Kingdom of France, engineers’ curiosity about the uses of plants was originally aroused by public authorities’ investment in inland navigation, at the instigation of the Comptroller-General, Philibert Orry (1730-1745). That curiosity was stoked once again in the 1770s, when responsibility for commercial ports was placed under the aegis of the civil-engineering council, i.e. the administration of Ponts et Chaussées. Before turning to botanists for their academic knowledge, those engineers were inspired by traditional knowledge. In their book Recherches sur la construction la plus avantageuse des digues (Research into the Most Advantageous Dam-Building Methods, 1764), Guillaume Viallet, Chief Engineer of the Generality of Caen, and Abbot Charles Bossut, professor at the Royal Engineering School in Mézières, referred to “the simplest methods commonly used to prevent rivers and streams from ruining their banks.” They explained that the “most common method is to plant dwarf willows & dogwood all along the waterway, & especially at the foot of banks that one wishes to preserve.”
The hybridization between botanical knowledge and engineering practices took place more systematically in places for the diffusion of knowledge, such as academic institutions. In April, 1777, under the leadership of Chief Engineer Armand Bernardin Lefebvre, the Royal Academy of Belles-Lettres of Caen established a prize for “trees, shrubs & plants that grow along the shoreline of the sea without needing to be bathed at every tide, that could be employed for the construction of dams & groynes.” The winner of the competition, Gabriel Aimé Noël, a geographer-engineer involved in the early stages of creating Cherbourg Harbor, provided lengthy discussions about coastal soil bioengineering in his treatise (ill.1). Around the same time, naturalists and polymaths of all sorts – who were interested in both arts and sciences – turned their attention to those soil bioengineering techniques. In the mid-1770s, in the context of a competition organized by the Academy of Marseille, the former First Consul of Arles, Jean-François de Lalauzière, calculated that, “to give the Rhone a stable and unchanging mouth that could ensure prompt navigation,” one would need to reign in the estuary with dams reinforced by planting willow trees (ill.2).
Coastal Soil Bioengineering’s Apogee at the End of the Early Modern Period
At the end of the early modern period, at the same time that the ideal of greener, more plant-filled cities was gradually gaining hold for health, aesthetic and recreative reasons, the coastlines of the Kingdom of France became a major open-air laboratory for integrating botanical knowledge into land-management practices. In the lower Languedoc, building a network of canals in the lagoons and turning estuaries into channels required stabilizing dunes and dams by planting tamarisks, which were protected by specific policies (ill.3). In Gascony, the earliest plantings along the sandy coastline under the rule of the Captal de Buch, in the southern part of the Arcachon basin and near the Gironde estuary were followed by larger-scale undertakings. In the 1780s, for instance, Nicolas Brémontier, Chief Engineer of the Generality of Bordeaux, obtained funding from the central government that enabled the systematic planting and sowing of pine trees and broom plants. Begun on the eve of the French Revolution, that initiative slowed in the 1790s, but picked up again during the Directory and the First Empire thanks to the creation of a departmental Dunes Commission.
In the 1800s, the chief engineer faced tremendous controversy from academics aiming to establish whether his work was based on “new discoveries” or whether it was simply an “imitation of what had been done elsewhere.” Those quarrels bear witness to the ambiguity of such engineering innovations, since they are founded on the systematization and improvement of technical solutions that have withstood the test of time and that are essentially the brainchildren of age-old empiricism. Thanks to an undeniable knack for self-promotion and the unprecedented scale of planting supported by the centralized administration, Brémontier’s action made a huge impression and constituted a key event in the rise of soil bioengineering on a European, and even Atlantic, scale: throughout the 19th century, a great many engineers saw his project as foundational and thought of their own work as stemming from it.
