The use of native plants in residential landscapes is critical to the protection of our wildlife. Among native plants, some of the most valuable are our trees. Native trees provide fruit, nuts, and seeds in addition to acting as host plants to a huge number of butterflies and moths.
History is often our guide when we chose which native trees to plant: native plant advocates often recommend planting trees that were present in a geography before the influence of humans. Yet this focus on the geographic component of “nativeness” is not always well placed. In cases where a particular location has been significantly altered by people, the plant community that once existed in that location may not longer be sustainable. That doesn’t mean we shouldn’t use native plants, but rather that we sometimes need to think more holistically about WHICH native plant communities to favor in our disturbed environments.
Without a doubt, one of the most widespread and pervasive disturbances we face is that of climate change. This is a global phenomenon, with different impacts in different places.
Here in Maryland, for example, the average annual temperature has already risen by two degrees Fahrenheit since 1900 and is expected to rise by an additional 4 to 8 degrees by 2100. Our state will receive more precipitation as well (approximately 20% more) but the change will be uneven throughout the seasons with more in the winter and less in the spring.
I mention this because many of the young trees we plant today will still be – or could be – alive in 2100 with proper care. Many of the large trees in my urban yard – not the most friends environment, mind you – are pushing 100 years old today.
Yet the trees we plant today will face a very different environment in their maturity than they do now. It seems prudent that we take this into account, as much as possible, when selecting which species of tree to plant.
My general advice is to choose trees which are native here now but which are also more likely to benefit from climate change rather than suffer from it. But how to decide this?
Here in Maryland we are lucky enough to have been included in the Climate Change Tree Atlas constructed by the USDA Forest Service’s Northern Research Station. Covering 134 common tree species of the Northeast, the Climate Change Tree Atlas is a spatial database that includes information about the relative importance of these species now and also in several models of climate change.
The atlas is a tremendous online resource detail, with an array of of tables and maps too expansive to cover in detail here. One component that I find most useful is a section called “Species Winners and Losers by State“.
This section includes data on the importance value – a measure of frequency and dominance – for the tree species and the impact of climate change for each species in each state.
For example, one of the most important tree species today is Acer rubrum, or red maple. Yet this is also likely to be one of the Maryland tree species most severely impacted by climate change. Two other tree species, Pinus taeda (loblolly pine) and Quercus stellata (post oak) are much less common here now but are particularly well suited to the predicted Maryland climate in coming decades.
Does this mean we should stop planting Acer rubrum? Of course not. It is and will remain a valuable tree, and today’s wildlife surely depend on it. On the other hand, would it be wise to plant Acer rubrum less often than we commonly do? Probably so.
I encourage you to begin investigating the impact of climate change on YOUR area, and to consider ways that the information you uncover might affect your tree planting plans. If you live in an area not covered by the Climate Change Tree Atlas, you may want to talk with local biologists or ecologists to see if there are similar resources. If you, like Maryland, are anticipating warming temperatures then I’d favor planting species for which your location is NOT at the current southern edge of their natural range.
To some this advice might seem like unnecessary meddling with nature, but I tend to view it as a logical extension of the old maxim “right plant, right place“. With perennials and shrubs, which have shorter lifespans than most trees, focusing on the current state of the place may be perfectly fine. With trees, thinking about the future state of the current place might be a wise move.