Written by: Sina Bohm; Reviewed by: Olga Kildisheva
The Netherlands is a densely populated country. Anthropogenic impacts impose challenges for many wild species. Wild plant populations can experience many challenges: pollution, nitrogen deposition, genetic erosion, scarce pollinator presence, fragmented landscapes, and more. For many species, it is impossible to cope with these pressures by themselves. Often, human intervention is needed to ensure their local survival.
As an ecologist, my work focuses on identifying the limitations that populations of threatened plant species face. The more I study these wild plant populations, the more I realize the complexity of the challenges they face and the interdependence of their relationships. Plants are connected to and rely on their surroundings in countless ways: bacteria and fungi shape soil function and make nutrients and water available; co-existing plant species affect each other's light conditions; animals forage on plants and disperse seeds; and pollinators promote gene flow. External pressures, often human-induced, can influence these intricate relationships and create cascading effects throughout entire ecosystems.
Ultimately, by identifying these challenges, I aim to find ways to improve the health and resilience of plant populations. In a fragmented landscape like the Netherlands, the natural recovery of many rare plants is difficult because of changes in land use. For example, traditional grazing practices with roaming sheep, which historically helped with seed dispersal, are now much less common.
For plant species that have lost their dispersal vectors, targeted reintroductions can help them colonize new, suitable habitats. The ultimate goal is to re-establish a healthy plant metapopulation with enough connectivity and restored dispersal methods to ensure its long-term self-sufficiency and resilience. Therefore, plant reintroductions can be an effective conservation tool, but only when they are part of a larger plan for ecosystem and process restoration.
I consider myself fortunate to collaborate with a dedicated team of researchers and practitioners who share the goal of protecting and restoring viable plant populations and ecosystems in the Netherlands. At the heart of this collaboration is the "The Living Archive Foundation” (Het Levend Archief). This organization manages the National Seed Bank of the native Dutch flora, which serves as both a safeguard for wild plants and a source of seeds for reintroductions. The foundation also facilitates communication among a diverse group of stakeholders from different institutions: nature managers who care for plant populations in the field, botanists and volunteers who collect seeds, and researchers like me who investigate the best practices for plant reintroductions.
In a recent study that I performed as part of my PhD research, I investigated the role of native microorganisms in reintroduction success of three rare plant species, Hypericum pulchrum, Solidago virgaurea, and Primula elatior. To do so, I grew plants from seeds from wild populations in a greenhouse – in total about 400 individual plants per species. Half of the plant containers were amended with a small amount of soil that I collected from the same wild populations, with the idea that the soil fungi and bacteria might affect seedling growth. The other half, I left untreated as a control. After growing the plants for a couple of weeks in the greenhouse, I transferred them to a suitable reintroduction site. I found that two species, Solidago virgaurea and Hypericum pulchrum, responded positively to microbial inoculation. However, for Primula elatior, microbial inoculation negatively affected plant survival and growth.
Whether a species benefits from microbial inoculation likely depends on both its specific plant traits and the soil conditions. For example, Primula elatior grows under relatively nutrient-rich and moist conditions and can likely acquire most of the essential nutrients and water on its own, without the additional help of beneficial mycorrhizal fungi or bacteria. In contrast, Solidago virgaurea and Hypericum pulchrum, grow on poorer soils and appear to benefit from the presence of native microorganisms, which likely help with nutrient acquisition. The negative response of Primula elatior to microbial inoculation could have been pathogen-borne, as inoculation using soil from native plant population can transfer not only beneficial but also harmful microorganisms, though additional research is needed.
For conservation reintroductions, it would be very useful for practitioners to know which plant species are most likely to benefit from microbial inoculation and which are not. To answer this question, more experimental reintroductions are needed on a broad range of different plant species. My colleagues and I are working on this!