Here we discuss the specific interplay between climate change and choices that humans make about what plants to plant where - whether in explicitly designed plant assemblages, or in restoration and natural areas.  Ornamental and Urban Planting addresses range shifts within explicitly designed plant assemblages, and Assisted Migration addresses efforts by humans to effect species changes within natural plant communities. 

In attempting to understand future climate conditions, people have looked to climate analogues to describe what a place will be like in the future. This is a somewhat useful but also imperfect way to understand changing climate conditions. Check out this Nature article Contemporary Climate Analogues for 540 North American urban areas in the late 21st century for an in-depth look at the pros and cons of this approach.

Ornamental and Urban Planting

Many designers would like to know how they can respond to and anticipate future climate conditions in their plant selections, and how to continue to support wildlife with native plantings even as baseline conditions are changing.

Growing Conditions, expect the following:

• Summers will become hotter and longer, leading to more drought stress on plants

• Winter wet will continue, and may increase in some locations

• Winters may be milder on average, but extreme cold snaps may also happen more frequently

• Weather will become more erratic, stressing plants with sudden change

• For more detail see related section Climate Change in Oregon (link), and USDA Hardiness Zones (link) 

Many locally native plants are already adapted to a broad range of conditions, and are likely still suited to future climate scenarios.  For example, Philadelphus lewisii grows in wet west-side forests and in dry east-side locations, as well as north into British Columbia and south into California.

Notice whether a plant or plant community is at the edge of its range, and how that range will be affected by future climate. For example, Garry oak grows in Portland, but is also capable of growing in much dryer hotter conditions, such as the Rogue Valley. On the other hand, bigleaf maple also grows in Portland, but most of its range is more coastal or more northern, so is less of a good bet for the future.

Don’t just look south, look inland.  Discussion of climate change has until recently mostly focused on warming, leading plant lovers to look south for examples of which plants will thrive in their area in the future, and for sources of heat adapted genotypes of shared plant species. However, plants from further south may not be adequately adapted to winter conditions. For the PNW, looking inland may be an alternative way to find landscapes and plant communities that may have broad overlap with your own, while being adapted to a bit harsher conditions in both summer and winter. 

Respect Soils and geology. Even as climate shifts, underlying soil types remain the same, and designers must consider how a plant’s native soil compares with soil where it will be planted. This is especially relevant for attempts to cultivate garden-worthy native plants outside of their historic range. For example, some Northern California plant communities are associated with serpentine soil, which is not found further north. 

Use the USDA Web Soil Survey  tool to define an area of interest, and download soil names and soil descriptions for your site

Assisted Migration

Assisted migration refers to the practice of humans helping plants to migrate faster than they could naturally, with the hope that this will help ecosystems and species to better weather climate change. 

Assisted migration is controversial among ecologists, as humans have a history of getting it wrong when we try to modify the natural environment. 

For a deep dive on what is being done in the PNW, read the Columbia Insight article What is ‘assisted migration’ and what are the risks?, along with this related article, from OPB. Also check out this Assisted Migration Primer from the Bonneville Environmental Foundation.

Assisted species migration refers to moving a discrete species from one location to another. The purpose of assisted species migration may be for the sake of preserving a species whose historic range is becoming less suited to its needs - for example, moving giant sequoia north in anticipation of its no longer being able to grow in California. In other cases, assisted migration is undertaken to benefit a receiving ecosystem that is deemed to need new species or new genetic subtypes for its continued resilience - for example, planting incense cedars in the North Willamette Valley, to replace Western redcedar which are becoming marginally suitable in parts of their historic range. 

Assisted species migration carries risk because new species may not support wildlife native to a region, and because new species may problematically outcompete native species in a region. 

Assisted population migration refers to moving genes within a population, but not moving species. An example is taking seeds of Douglas-fir from a harsher/dryer part of their range, and planting them in a part of their range that is expected to become dryer in the future. This approach has been widely adapted by the US Forest Service through their Experimental Network for Assisted Migration and Establishment Silviculture (ENAMES) project, and is preferred by ecologists as it does not alter the basic plant species composition of an area. 

Tools to inform assisted population migration: 

The Seedlot Selection Tool (SST) is a GIS mapping program designed to help forest managers match seedlots with planting sites based on climatic information. The climates of the planting sites can be chosen to represent current climates, or future climates based on selected climate change scenarios. 

The Species Potential Habitat Tool (SPHT) is designed to help forest managers identify species or vegetation types that are suitable for specific sites given various climate change scenarios. With this information, forest managers can promote the transition of forests to species compositions that are better adapted to future climates.

Important Note: Transporting actual live plants from one ecosystem to another may spread pests and disease (see Pests and Diseases (link).) Transporting seeds is a safer method.

Some Naysayers

Field trials involving assisted population migration are relatively new, and there has not been time to gather definitive results on the success of this approach. 

Bucharova et al, 2016, describes a study in Germany, in which researchers compared the performance of multiple ecotypes of 6 grassland species, grown in a common garden, during a natural heat wave. The researchers found that contrary to expectation, the ecotypes from warmer climates did NOT outperform the local ecotypes during this heat wave.