How Gleditsia triacanthos invades across biomes

A plant can invade territory when it's adapted to it, but how can a plant be adapted to multiple biomes. A new paper examines how Honey Locust seedlings use plasticity to tackle new locations.

Gleditsia triacanthos, or Honey Locust, is a plant native to North America, but it has become a successful invasive species elsewhere. What is the secret of its success? Often plants succeed because they’re adapted to the local environment. Other times they spread as they’re plastic, able to change form. This means they can become suited to where they find themselves.

Seed pods of the Honey Locust

Pedro Tognetti and colleagues have been investigating G. triacanthos in Argentina where it has been an issue, and Tognetti explained: “G. triacanthos is a problem in different natural and managed ecosystems around the globe. In Argentina, this species invades quite different biomes, from montane forest, woodlands, grasslands and agricultural systems. Interestingly, this implies an area of around 1500km (N-S) by 700km (E-W) in the central East part of Argentina, an area similar to that in G. triacanthos‘ native range in USA.”

The tree is particularly good at moving in to territory when changes in land use make disturbances in the soil.

One of the surprising findings is that the seedling survival falls when vegatation is removed. Noemí Mazia believes this is due to how the tree establishes itself. “The establishment and survival of this invasive tree is higher in wet years and very low patch cover exposes seedlings to desiccation and tree attack by diggers and browsers like armadillos. In relation to community structure, establishment and survival is higher for early successional stages dominated by forbs with respect to mature grasslands.” This would be supported by her previous work on movement of G. triacanthos into Pampean grasslands

Measuring a seedling

Gonzalo Ibáñez noted that it is important to understand how this tree establishes itself, as when it arrives it makes a place very different. “Natural biomes drastically change with the invasion of G. triacanthos. The establishment of this woody plant alters water and carbon cycles, reduces plant and animal biodiversity, and generates opportunities for new invaders like Ligustrum lucidum (a kind of privet).”

“Productive and anthropogenic areas are also altered with the invasion of G. triacanthos. Dust roadsides are closed by the canopy of these trees. Pastures and foraging paddocks reduce their productivity and carrying capacity, also working personnel and animals are frequently injured with the thorns of the trees. In these systems, the use of machinery and chemicals for the control of G. triacanthos also increase, augmenting contamination risk and use of energy.”

The team have plans to build on the findings in this paper. Tognetti is interested in the approach of plant population genetics. “According to our results both mechanisms account to allow this tree to invade quite different ecosystems in structure and functioning. From invasion ecology, we want to explore the genetic structure of the Argentinean populations. In particular, we are starting a long-term experiment to understand growth and reproductive trait variation, comparing a set of US native populations and those tested in our paper.”

Invasion ecology is another topic, that the paper addresses as Ibáñez highlighted. “Knowing the high invasion capacity across natural biomes, we want to explore the land uses and anthropogenic activities that are more prone to and enhance G. triacanthos invasion. In particular, we are working on understanding the role of herbivores, mainly cattle in extensive pastoralism, and agricultural activities, crops and their technology, in promoting or limiting the expansion of this noxious plant.”

However, while G. triacanthos is a problem, it doesn’t have it all its own way. Matzia noted that there is biotic resistance to the invasion. Rodents have developed a taste for G. triacanthos seeds.” This is part of a wider interaction that the paper studies. “Our paper proposes scenarios for G. triacanthos invasion in different biomes, with different current and historical use. Managers and conservationists may be interested in limiting or controlling invasion.”

It looks like this work will be a useful reference for ongoing research on G. triacanthos and plant invasion for a years. As climate changes, the honey locust will become more of a problem because, as the authors conclude: “…high levels of phenotypic plasticity should allow G. triacanthos populations to respond to sudden changing environmental conditions better than locally adapted genotypes.”