Endangered Meadow Violet Gets New Home in Bulgaria

The meadow violet, Viola pumila Chaix, is one of the most endangered plants in Europe, and in Bulgaria it survives in only a handful of small populations. Now, researchers report the first successful relocation of an endangered plant species in the country, moving an entire population out of the path of a motorway and establishing a new locality where the violets have flowered, dispersed seed and produced juvenile plants over two years of monitoring. The study, published in the journal BioRisk, offers a detailed protocol that could guide conservation translocations of other rare plants facing similar infrastructure threats.

Viola pumila is a stenobiontic species, meaning it depends on very narrow habitat conditions. It is a hemicryptophyte, with regenerative buds located below the soil surface, and a representative of the spring ephemeroids: it begins growth in early spring, develops rapidly under favorable soil moisture and scant competition for light, and completes its aboveground life by October, when the plant dries out and prepares for overwintering. According to Eckstein and colleagues, whose morphological description remains the most complete, the species has a peculiar life cycle and reproduction. Pollination most likely takes place through self-pollination, a cleistogamic mechanism characteristic of members of the Violaceae family. The violet is also myrmecochorous: ants partially disperse its seeds, which carry elaiosomes. When the seed boxes crack, they shoot seeds up to 1.19 meters away, and the scattered seeds rest in the top five centimeters of soil, where they undergo stratification before beginning their active life cycle.

The species has a Eurasian-continental distribution in the temperate climate zone, with populations registered in Western, Central and Eastern Europe. It is included in the red lists of Switzerland, the Czech Republic, Italy and Bulgaria. In Bulgaria, the meadow violet was considered extinct for a prolonged period until its rediscovery in the 1990s. Six localities were known, but two have disappeared in recent years. The remaining populations, found at altitudes between 500 and 1000 meters above sea level, consist of several tens to several hundreds of specimens, with the largest around the villages of Kokalyane and Tsraklevtsi and in the vicinity of Aldomirovsko and the Dragoman marshes. The species suffers from limited reproductive abilities and weak competitiveness, and faces anthropogenic threats including ploughing, conversion of mesophilic meadows into arable land, changes in the water regime, expansion of highly competitive tufted cereal grasses and infrastructure construction.

The population at the center of the new study was threatened with direct annihilation by a large linear infrastructure project: the enlargement and restructuring of an existing road section between Sofia and Kalotina into the Europe Motorway. In the late spring of 2019, the team conducted an on-site field survey along the road between kilometer 21 and kilometer 22, using the transect method repeated three times over three days by three qualified experts. They identified a total of 50 individuals of Viola pumila forming eight tufts, growing alongside species such as Alopecurus pratensis, Deschampsia cespitosa, Lysimachia vulgaris, Molinia caerulea and Potentilla reptans. The situation demanded fast and precise action: localization of a possible new habitat, selection of relocation tactics, procedures for transporting and planting the violets, and a plan for sustaining the new local population.

To identify the most suitable relocation sites, the researchers processed digital data with the standard tools of ArcGIS 10, intersecting the layer of natural habitat distribution within the Natura 2000 site SCI BG0000322 Dragoman with the boundaries of the national protected area Aldomirovsko Blato and the layer of municipal property within it. Four municipal land properties in the territory of the village of Aldomirovtsi emerged as candidates, all within the protected area, which was declared to preserve the natural habitats of protected and rare waterfowl and 40 species of higher plants. A fifth property harboring one of the country’s most numerous violet populations was rejected because it is private land outside the protected area. After geodetic and ecological field surveys, the team selected property 00223.257.68 as the most suitable terrain, meeting the meadow violet’s requirements for soil, vegetation and water regime: floodplain meadows moist enough that water was retained above the soil surface in local depressions, with soil of the meadow-swamp type covered by hydrophilic, mesophilic and xeromesophilic grass communities. Part of the terrain belongs to natural habitat 3150, Natural eutrophic lakes with Magnopotamion or Hydrocharition, and another part to habitat 6510, Lowland hay meadows. The other three candidate properties were flooded almost all year round and occupied only by habitat 3150, making them less suitable. Because the species is extremely rare and the population numbered only 50 specimens, the researchers decided not to divide the individuals into experimental treatments, instead planting all specimens together at the single most optimal location.

The relocation technology was carefully timed and executed. The violets were manipulated in the morning or late afternoon, when sunshine intensity is low and temperatures are cooler. Using suitable tools, the plants were dug up along with the adjacent soil around their rhizomes, within a radius of 25 centimeters from the rhizome center, and immediately placed in vegetation containers 30 centimeters deep with water added. The specimens were covered with transparent foil to preserve soil moisture and plant freshness during transport. At the new locality, the violets were planted in pre-prepared and moistened pits, three holes sized to the rhizomes in a row at 10-meter distances to ensure enough space for the root system. The rhizomes were carefully positioned and the soil compacted to reduce soil air, then each plant received 60 centiliters of water to prevent water stress and speed adaptation. Critically, the relocation was accomplished before the end of the vegetation period, before the full rupture of the seed boxes, so that seed dispersal would occur on the spot of the new location, improving the chance of successful seed generation, an approach consistent with Volis’s framework for plant reintroductions.

After planting, the team provided in situ care until full adaptation, a period of three to six months, followed by two years of monitoring. Watering was carried out every three days during the first month after relocation in June, then every seven days during July and August. Mowing was performed on an area of four square meters around each of the three micro-localities in the middle of July, with mowing around the localities repeated at three-month intervals thereafter. Monitoring included observation of seed dispersal, flowering during the next vegetation cycle, and surveillance for pressures such as fire, pollution and ploughing. All activities were coordinated with the competent authorities, and because the new habitat was on municipal property managed by the municipality of Slivnitsa, regular grooming of the terrain and monitoring of the plants were possible.

The two-year follow-up monitoring showed success in preserving the relocated specimens and their successful reproduction. Applying Volis’s two-stage model of reintroduction success, the first stage, flowering of mature relocated plants, was completed when the team detected flowering in mature adults in the year after reintroduction. The second stage, establishment of entirely new reproductive individuals at the site, began in the year of relocation with the scattering of seeds from the cracked seed boxes of the transferred adults. In early July 2021, the second year after relocation, the team identified new juvenile specimens between 2 and 7 centimeters tall, in the vegetation phase between the first and third pair of true leaves, all sprouted after the relocation. Seven young specimens were found at relocation point 2 and two at point 3, located outside the main tuft. With the discovery of juvenile plants at the site, the researchers consider the second, concluding phase of Volis’s model successfully completed.

A dramatic test came in October 2019, when a large-area fire was detected within the Natura 2000 site SCI BG0000322 Dragoman and reached the territory of the new locality. Using two Sentinel-2A L2A satellite images, one from September 21, 2019, before the fire, and one from October 26, 2019, immediately after its end, the team mapped the burned boundaries with ArcGIS 10 tools. None of the three plots with relocated plants was affected by the fire, although all vegetation in the vicinity burned out. The researchers attribute this to the special algorithm of cultivation of the relocated plants and especially the mowing measures: the cleaning of the area and mowing around the nests with the reintroduced plants during the first year reduced the dry biomass available to the flames. As Allen noted in a 2000 Australian bulletin on fire impacts on wetland flora, plants can survive fires by regenerating dormant buds from stems or roots, and fire can trigger germination of soil-stored seeds, but a fire during an inappropriate growing season would result in the loss of seed stocks or mature plants. The strength and intensity of fire depends on the season of occurrence, which shapes the plant communities of wetlands, where fires may destroy significant dry biomass above the water level and nearby mesophilic vegetation.

The study also sounds an alarm about the condition of the violet’s habitat at the biogeographical level. According to Bulgaria’s second report under the Habitats Directive for the period 2013-2018, the conservation status of habitat 6510, Lowland hay meadows, in the Continental Biogeographic Region was assessed as Unfavourable-Bad, with poor future perspectives. Identified threats include abandonment of haymaking, overgrazing, ploughing for arable land and changes in water regimes; mowing delays or sporadic mowing rapidly change species composition, and drying of marshy soils leads to fast mineralization, carbon dioxide and nitrogen release, encroachment of nitrophilous plants and disappearance of the peat layer. The researchers propose a set of nine conservation measures: regulation of the haymaking regime, regulation of grazing, conversion of abandoned arable land into meadows, restoration of disturbed water regimes, creation of incentives and compensatory mechanisms for private landowners, fire prevention, surveillance of meadow status and data collection, updating of the Standard Data Forms of Natura 2000 sites, and raising stakeholder awareness through regular information campaigns. The successful relocation demonstrates that saving rare plants from infrastructure projects is achievable by adhering to a defined algorithm of actions, from site selection through planting to long-term management, and that reliable up-to-date information on the distribution and condition of Viola pumila and its habitats is crucial for proper conservation policy.

Subject of Research: Conservation biology

Article Title: Relocation and formation of new local population of Viola pumila Chaix – an endangered species in Europe and identification of measures for improvement of its habitat

Article References: Kaschieva, M. Z., & Nedyalkov, N. P. (2022). Relocation and formation of new local population of Viola pumila Chaix – an endangered species in Europe and identification of measures for improvement of its habitat. BioRisk, 18, 1-16. https://doi.org/10.3897/biorisk.18.76114

Image Credits: AI Generated

DOI: 10.3897/biorisk.18.76114

Keywords: Viola pumila, plant conservation, species relocation, Bulgaria, Natura 2000, endangered species, lowland hay meadows, BioRisk, Relocation, formation, local, population