Native Trees for a Changing Environment

The loblolly pine is native to Maryland (this one is at Assateague), but is not a common tree statewide. Climate change may change that. (Image: Some rights reserved by Rev. Xanatos Satanicos Bombasticos (ClintJCL))

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.

Acer rubrum (red maple) is a dominant tree in Maryland today. It will be less dominant as temperatures rise and precipiation decreases. (Image: Some rights reserved by KimManleyOrt)

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“.

Pinus taeda is a minor tree species in Maryland today, but will become more important with global climate change. This map shows the relative change in importance (green = more important. (Source: USDA)

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.

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Comments

  1. Sue Sweeney says

    Vince – great subject! One of the things that I’ve been pondering: some tree species are found all along the Atlantic Coast – Zones 4 to 8. However, that doesn’t mean the tree in front of me in what used to be Zone 6a is a Zone 8-rated tree.

    If I plant a seed from the Zone 6a tree, will it as an adult in 25 or 50 years be able to withstand a Zone 7 or 8 climate (e.g.no real freeze in winter, very hot, very long summers)? If I plant, on the other hand, a Zone 7 or 8 rated genotype, will it be able to take our (sometimes, may be) our still cold winters? Most importantly, will our native bugs recognize it?

    Meanwhile, what about the Zone 7 insects being forced north? Do they need their Zone 7 trees?

    Some scientists tell me the best thing is to make space for Nature to adapt by growing many young local saplings, and selecting the most heat-resistant (Nature may be able to do this latter step better than humans – if we’re going to help it would mean planting a lot of the tree and seeing which live).

    What are your thoughts?

    • says

      Sue,

      These are great questions, and I’m not entirely sure the evidence is clear about what the best strategy will be. Managed relocation (aka assisted migration) is a relatively new topic of study for scientists, and I don’t anyone can say what the optimal approach will be.

      If local populations have a lot of genetic variability, for example, a strategy of selecting local saplings might work. But for some species (like oaks) there doesn’t tend to be be much local genetic diversity: you’d need to range anywhere from 10 to 25 miles to collect enough acorns to produce a heterogeneous trial plot.

      As is often the case, wildlife gardeners will be leading the charge ahead of scientists themselves. So an “all of the above” strategy is probably not a bad bet: plant some trees that are adapted now, some that are adapted to the anticipated conditions 100 years from now, and some (most) in between. Give “nature” this large library of genetic material, and hope she can work it out.

      I will say that what makes trees such a challenge relative to, say, insects or herbaceous plants is the generation interva: wildflowers or insects may produce one or more generations per year, while trees may produce a new generation only every 20 to 50 years. Evolution only works as fast as reproduction, so trees may need more help than other kinds of plants.

      VV
      Vincent Vizachero recently posted..Native Plant Cultivars – Good, Bad, and Ugly

  2. says

    Excellent article. And we have to assume city trees, already in heat islands, will be stressed even more. One of our heat-sturdiest trees, the American elm, is mostly gone from the urban landscape, but may be starting a comeback.
    I have seen the devastation from the emerald ash borer in Windsor, Ont. Here in the GTA (Greater Toronto Area) it is estimated that about a third of the tree canopy is ash trees. Our (US and Canada) lack of appropriate import restrictions from China amounts to a tree holoucaust. When will we learn?

  3. Denise meehan says

    Very interesting topic. I am having trouble decoding the graph. Maybe because it is late for me, or maybe I missed the key, but I really wish there was a For Dummies version of this.
    Any hints ? Thanks

  4. says

    Fascinating and frightening. As I look out on the Western Massachusetts landscape just beginning to turn green again, I do wonder what things will look like without our sugar maples and birch. When we should be rushing towards green energy we are stalled in the muck that is causing the warming trends. I suppose I should be looking towards Maryland’s landscape to see what mine may look like in the future.
    Carol Duke recently posted..Spring Spreads Swaths of Sweetness in Petals and Song

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