Faune et flore exotiques envahissantes et à fort développement

• On average, 86% of wetland sites evaluated for this issue (140 in mainland France and 25 overseas) faced invasive exotic species between 2010 and 2020. During the previous 2000-2010 campaign, this proportion was higher on mainland sites (97% of covered sites versus 88% in 2020). Conversely, overseas sites seem to experience growing pressure as only 52% of overseas sites were affected by this issue in 2010 compared to 80% in 2020. • While peatland massif sites appear to have been spared (only 42% of sites affected) over 2010-2020, inland plain sites (100%) and alluvial valley sites (96%) were particularly subject to this issue. • On average, 9 invasive exotic animal species and 6 invasive exotic plant species are present on mainland sites (5 overseas) evaluated for this issue. Alluvial valley sites and Atlantic coastal, English Channel, and North Sea sites concentrate the most invasive animal and plant species (10 animal species and respectively 8 and 7 plant species on average). A slight upward trend can be observed since the previous campaign as 8 animal species and 5 plant species were recorded.

• On mainland France, of the 140 sites evaluated on this theme, Brière marsh, the Somme (upstream of Amiens), and Île d'Oléron are the sites hosting the largest number of invasive exotic animal species (40 species). Sites along the Loire from Orléans to Beuvron (32 species), Brouage (31 species), and Belledonne and Grandes Rousses (27 species) concentrate the largest number of invasive exotic plant species. Although minority, 18 sites harbor no invasive exotic species. • Their presence level on the site was assessed through spatial extent. A species may be found sporadically with limited footprint on the site (localized) or encountered diffusely across the entire site (very widespread). • The coypu, a species introduced for its fur in 19th-century Europe and listed as a plant pest organism whose control can be made mandatory, is present on 98 mainland sites. This most frequently cited species is, in 52% of cases, very widespread on sites, in 26% of cases widespread, and only in 16% of cases found locally. Other species, such as the American crayfish (69 sites) which appears on the EU list of invasive species of concern, are present mainly across the entire site (36% very widespread and 26% widespread). The muskrat (66 sites) is conversely a species found more homogeneously (30% very widespread, 27% widespread, and 33% localized). • Asked about their perception of proliferation of these animal species between 2010 and 2020, referents estimate that the majority of animal species declined on evaluated wetland sites. A proliferation of all these animal species was observed between 2000 and 2010. This trend appears to result from control policies against invasive exotic species pursued in recent decades. Only the American mink and Egyptian goose increased over ten years. Other species like catfish, sunfish, brown rat, or largemouth bass stabilized. • Japanese knotweed, an invasive plant species classified among the world's most harmful, is encountered on numerous sites (75), mostly locally (49% of sites). Water primrose, an aquatic plant from South America, is present more diffusely (39% localized, 31% very widespread, and 27% widespread) on 62 sites. Other plant species, such as black locust (58 sites), butterfly bush (44 sites), or box elder (41 sites), are frequently present and exert pressure on ecosystems at mainland evaluation sites. • While invasive exotic plant species had also all expanded between 2000 and 2010, an inflection of this trend can be observed over 2010-2020. Thus, certain species, such as black locust or butterfly bush, are less present in 2020 than they were in 2010. Eradication efforts must continue on other species like goldenrod and waterweed which continue their proliferation. Japanese knotweed, an emblematic invasive exotic species of wetland habitats, appears to have been contained over the past ten years on evaluation sites, according to referents.

• Overseas, of the 25 sites evaluated on this theme, the lakes of the far south (23 species), the bays of Carénage and Prony (14 species), the 14 ponds of Saint Martin and Saint Paul pond (13 species) group the most animal species likely to threaten the site. Saint-Vincent bay (34 species), Gouaro-Déva (32 species), or the bays of Carénage and Prony (24 sites) harbor the most plant species. Only five sites have no invasive exotic species: mudflat of Badamiers and Boueni Bay (Mayotte), Lower Mana (French Guiana), Saint Paul pond, and altitude wetlands of Montagne Pelée caldera (Martinique). • Arriving accidentally by ship during early expeditions, the black rat is the most cited species on overseas wetland sites (14 sites). This species is present locally in 50% of cases, and very widespread or widespread in 25% of cases. Considered one of the 100 most invasive species worldwide, it is involved in the extinction and decline of many island species including birds, small mammals, reptiles, invertebrates, and plants. Other species, like the house mouse and brown rat, frequently cited (9 sites), are found locally (respectively 56% and 78% of cases). • Brown aster, an invasive plant species of Réunion wetlands, is most frequently cited (5 sites). This species is found locally in 40% of cases; in 20% of cases, it is widespread on the site. Like this species, silk tree, water hyacinth, and Japanese tulip tree are the other most mentioned plant species. In over 60% of cases, these three species are present locally on the site.

• Between 2010 and 2020, 57% of evaluation sites faced at least one native species with strong development. Mainland sites were particularly affected by this issue (63% of them versus 17% of overseas sites). • On average 2 native animal species and 1 native plant species are counted on mainland sites (3 animal species and 1 plant species between 2000 and 2010). Inland plain sites are those presenting the most species while peatland massif or overseas sites appear less affected by this issue.

• Of the 125 mainland sites evaluated on this issue, 77 faced at least one species during 2010-2020. Certain sites are particularly affected: the Seine from Troyes to Aube (11 species), the Loire from Orléans to Beuvron (11 species), Dombes (10 species), and Lake Der and its surrounding areas (10 species). 48 sites reported no native species with strong development. • The wild boar, a native species whose populations continuously grow (809,992 harvests in the 2019-2020 season, a 8.4% increase) is by far the most present animal species on evaluation sites (66 sites). Other species, such as the great cormorant with nearly 10,000 breeding pairs recorded in 2018 or the mute swan, are frequently found (respectively 47 and 32 sites). Referents commented on the presence of these species in 2010 and 2020. Of the 7 main animal species cited, all except the mute swan slightly declined on evaluation sites over 10 years. • Algae are the most mentioned plant group (26 sites) ahead of other hydrophytes (15 sites) and duckweed (14 sites). Unlike animal species, among the main plant species reported, only duckweed declined.

Of the 18 overseas sites evaluated on this issue, only three faced at least one native species over the past decade: Crique and Pripri creeks of Yiyi (2 species), Badamiers mudflat (2 species), bays of Carénage and Prony (1 species). Very little data was provided on this theme for overseas territories in questionnaires. No trend can be drawn for this past decade.

• Asked for the first time about common and high-priority species present on emblematic wetland sites, referents commented on their general status (good to poor). Although other factors can influence the status of these species (anthropogenic causes, hydrological issues, climate change effects), this information was cross-referenced with the presence of so-called problematic mainland species (insufficient data for overseas). • Note: To highlight a correlation between the presence of so-called problematic species (invasive exotic species and native species with strong development), the choice was made to retain only two classes (good status integrating very good and good status, and poor status integrating very poor and poor status). The 'do not know' option was extracted from the analysis.

A general trend emerges: the higher the number of invasive exotic and native species with strong development present on a territory, the more the share of sites where common and high-priority species status is good tends to decrease. Indeed, when fewer than two problematic animal species are present, 74% of sites have common and high-priority animal species in good status whereas only 47% do when 13 or more problematic species are present. This situation is also observed for plant species: 67% of sites have common and high-priority species in good status when fewer than two problematic plant species are encountered versus only 43% when 11 or more problematic species are hosted by the wetland.

In France, between 2010 and 2020, 57% of evaluated sites intervened on invasive exotic and native species with strong development, these species having entered competition with native species. Direct ecosystem disruption and habitat closure constituted the second and third intervention reasons (respectively 50% and 45% of sites). According to referents, other factors remained marginal during this past decade (vehicle collisions, health problems). While only 15% of mainland sites intervened to limit the impact of these species on recreation activities, this reason represents the third source of intervention on overseas sites.

Within the National Strategy on invasive exotic species (objective 5 - Master widely distributed invasive exotic species), national control plans detail various actions to implement on territories to achieve management or eradication objectives for invasive populations. Native species with strong development are also subject to control plans against overpopulation through adapted hunting management (case of wild boar and great cormorant populations, for example).

Management and limitation of problematic animal and plant species on emblematic wetland sites over this past decade focused on three main approaches: pulling, mowing, and burning (67% of cases), trapping and control shooting (59% of cases), or administrative hunts and hunting (45% of cases).