Zone Matcher: A climate-based web application for deployment and assisted migration of forest trees

Populations of forest trees are generally adapted to the climates they
inhabit. The farther trees are moved from their local climates, the more
long-term growth and survival tend to decrease. Current tree deployment
and assisted migration rely on ‘climate distance thresholds’ (CDTs), which
are climatic distances beyond which tree performance is considered
unacceptable. Fixed zone systems, which have been used to guide deployment
of native or orchard seedlots for more than 50 years, usually consist of
contiguous geographic areas (zone units) divided into elevational bands
(zones). In contrast, focal zone systems allow seed transfer among fixed
zones that have similar climates. By using recent historical climates and
future climate projections, focal zones can be used for current tree
deployment or assisted migration. We developed a focal-zone system for the
Pacific Northwest region of North America. First, we worked with
stakeholders to select the base zones for the system. These consisted of
geographic zone sets from Washington, Oregon, California, and
Idaho/western Montana, and ecological zone sets from the U.S. and British
Columbia. Second, by analyzing climate variation across the region, we
developed a normalized Euclidean climate distance function consisting of
nine climate variables from ClimateNA. Third, we inferred CDTs from
analyses of climate variation within the base zones and from provenance
tests. Fourth, we compared seed deployment areas using the fixed zone
versus focal zone system, with and without assisted migration. Finally, we
developed the Zone Matcher web application which implements our focal zone
system. Across the region, we identified climate matches among 4,393
partially overlapping zones covering approximately 252 M ha. The unique
area covered by these zones was about 167 M ha. Compared to fixed zones,
our focal zone system increased the deployment area about 19- to 39-fold
for the ecological zones and 72- to 342-fold for the geographic zones.
This expands seed deployment options, allows more seedlots to be
considered for a planting site, facilitates assisted migration, and
simplifies sharing of seedlots among organizations. In addition to
climate, seed transfer should also consider factors such as plantation
soils, microtopography, and projections of competing vegetation, insects,
diseases, and fire.