If you want to protect endangered species at a botanic garden, you might want to check if their non-endangered neighbours can survive at their new home. A study published in Biological Conservation by Georgia Thomas and colleagues finds that the actual location you source plants from and not their overall climatic distribution is the best guide to predicting how plants will grow in a protected garden.
The research will help botanic gardens identify which endangered species they are best suited to rehome outdoors and which will require more careful hosting. Ex situ conservation can provide workers in the field with more time to tackle conservation challenges at problem locations and provide a source of material for reintroduction if necessary. This kind of conservation is essential for those species that cannot be conserved in seed banks. While some botanic gardens may seem ornamental, with a selection of exotic trees from around the world, those individuals growing could be providing a vital lifeline to a species, much like a pair of pandas at a zoo.
However, Thomas and colleagues say there seems to be little work predicting the survival of plants grown from wild-collected propagules in outdoor landscapes at botanic gardens. They set out to determine what can predict a plant’s survival using mixed effects Cox models. The authors write: “We relied on data gathered by horticulturalists during the last 20 years, detailing the survival of 1184 plantings of 410 species sourced from 530 localities across the world. Using the models with highest empirical support, we predicted survival of plants grown at MBG [Missouri Botanical Garden] from wild-collected propagules based on provenance.”
The prime factor in whether or not a plant survived in its new location was the climate at the place where the propagule was sourced, and this factor was more important than the overall range a plant could occupy. The authors say that this result suggests that local adaptation to climate matters and that this is common in many plants.
Another factor was whether or not the plant was woody. The botanists used the woody / non-woody difference as a proxy for generation time. Plants tend to trade-off between survival and reproduction. Plants primed to live fast and die young won’t invest so much in survival. They conclude that woody plants should be easier to conserve in botanic gardens than herbaceous plants because the woody plants take so long before they think about reproduction.
Most of the plants in this study were not threatened. The team found that the models with the highest empirical support show that not threatened species tend to survive better than threatened species in Missouri Botanical Garden’s outdoor plots. They suggest that a correction could be made for this over-estimation of survival. However, they also cite another study in Switzerland that found geographic range size alone had no significant effect on survival.
Another problem to be aware of is invasiveness. Thomas and colleagues write: “Growing species from around the world in outdoor landscapes of a botanic garden entails the risk of introducing invasive species… This risk may be higher when plants are sourced from sites that are climatically similar to the botanic garden.”
“All plants should be evaluated for their invasive potential before being added to a garden landscape and closely observed afterwards. This is particularly important when models based on climatic provenance, like the ones developed here, predict that a plant has high probability of survival in a botanic garden far beyond its native geographic range.”
The model is not just for exotic plants. The team concludes that the model can also help ex situ conservation of plants from nearby regions.
Thomas, G., Sucher, R., Wyatt, A., Jiménez, I., 2022. Ex situ species conservation: Predicting plant survival in botanic gardens based on climatic provenance. Biological Conservation. https://doi.org/10.1016/j.biocon.2021.109410