This page has short articles about scientific topics related to the research of MyGardenOfTrees intended to a broad audience from scientist from different fields, foresters, and intererested citizens

June 2022

Assisted migration or assisted gene flow?

Humans have been moving around species for centuries

Assisted migration (AM) is the human-aided movement of individuals to a new location. Foresters and gardeners have even been translocating plants since centuries, and some of these introductions have led to continental scale spread of non-native species. For example, black locust (Robinia pseudoacacia L.) was introduced to Europe principally for soil stabilization, honey making and quality hard wood. While it still delivers these important ecosystem services, it presents risks of invasiveness in high biodiversity native grasslands. The risks and benefits balance of these translocations is often unclear, AM is increasingly proposed as an “active” conservation and climate change adaptation strategy for forest trees.

Assisted migration (AM): what is behind the word?

AM could imply various types of human intervention (Fig. 1, Scenarios) that entail very different benefits and risks. The “ingredients” of AM are a Host and a Donor population that can have different biological characteristics (Fig. 1). The host population is a collection of individuals of a species of a given region that reproduce with one another that is under some real or perceived threat of environmental change. The donor population is also a collection of individuals of a species (either the same as the host or different) at a different geographic location that is considered, based on some direct or (mostly) indirect evidence, good candidate to replace or be mixed with the host population.

In the case of black locust, since there are no native relatives of the species in Europe, its introduction may be referred to as Assisted Colonization. Here, the benefits were principally economic: honey production, soil stabilization and wood production. Concerning the risks, black locust can become a threat to a whole ecosystem, such as in the case of the high diversity grasslands, accompanied with a high risk of invasiveness.

Fig. 1. Characteristics of different types of assisted migration and their risks and benefits.

Assisted gene flow: the risks and benefits are inherently genetic

When the host and donor populations are genetically similar (or related) to each another, we are talking about assisted gene flow (AGF). The name refers to its aim, which is “moving genes” of the donor population so they integrate to the host population after some generations of inter-breeding (called introgression). The risks and benefits are principally related to the hybridization between two populations. Under AGF, the often controversial economic benefits of AM are not relevant: the translocation is motivated by preserving the ecosystem in a state as close as possible to its current state, thus with all its biodiversity and its functions. We hope to achieve this by manipulating the foundation species of the ecosystem only. Further, under AGF, the risks of invasiveness or importing diseases and pests or even collapse of a whole ecosystem, are minimal. In contrast, the major benefit of AGF are outbreeding depression and hybrid incompatibility. The understanding of these risks often requires long term experimental research and understanding of evolution and genetics, which can make knowledge transfer difficult. Very briefly, when populations that had an independent evolutionary history for a long period of time, their genetic material could develop in a direction that when member of these populations interbreed, their survival and growth is low, lower than that of the parental populations.

May 2022

Provenance trial and micro-gardens: What is the difference?

Provenance trials

  • Provenance trials are used to compare growth traits of different provenances thus established for up to 50 years or more.

  • Seeds collected in the autumn are dried and stored until the following spring or for a later year

  • Seeds are stratified artificially to break the seed dormancy.

  • Seeds are grown to seedlings in an ideal and controlled environment of a nursery (1).

  • The long-term planting sites are prepared to receive the young seedlings (2) after extensive soil preparation (3).

  • Given the extensive work and space requirements, provenance trials are established at limited number of locations (4).


  • Micro-gardens are used to compare the growth and regeneration capacity of different provenances and families across many different environments

  • Seeds are collected in the autumn and sent to forester participants.

  • Seeds are placed in the forest without soil preparation (1 & 2).

  • The untreated seeds are directly planted into the soil (Fig 2).

  • The seeds/seedlings are left undisturbed. The only treatment provided is protection from mice/birds predation (Fig 3).

  • MyGardenOfTrees trials are established in forests at multiple locations within and beyond the natural range of the species.