May 2020 - 26

VINEYARD MANAGEMENT
Mapping winegrape suitability in Michigan
By Erin L. Bunting
Michigan State University
Over a two-year period, beginning in
2018, Remote Sensing and GIS Research
and Outreach Services (RS&GIS), within
the Michigan State University (MSU)
Department of Geography, Environment
and Spatial Sciences, along with partners
in the MSU Departments of Horticulture
and Geography-Climate, worked to map
land suitability for winegrape (Vitis
vinifera) cultivation in Michigan using
newly-available data and advanced spatial
analysis.
The goal of the project, which
was funded by the Michigan State
Horticultural Society (MSHS), was to
assist the grower community with their
goal to expand the industry across the
state by precisely mapping areas suitable
for cultivation. The study paired known
growth requirements for wine grapes
with long-term climate information and
physical landscape characteristics, such as
slope, aspect, soils composition and land
cover, to quantify suitability.
This work resulted in suitability maps
Figure 1. Locations of counties across the state of Michigan used in the study
(17). Traditional counties where vinifera are grown are highlighted in dark green.
Other project counties have little or no current vinifera cultivation (light green).
for red and white varietals in 17 Michigan
counties (Figure 1). Several growers
and vineyard managers shared local
knowledge through surveys conducted
at both the Northwest Michigan Orchard
and Vineyard Show and Southwest
Michigan Horticulture Days. Grower
input helped to calibrate the models used
to define suitability. The results of this
research project were recently published
in the scientific journal, Atmosphere
(Wanyama et al. 2020; www.mdpi.
com/2073-4433/11/4/339).
Processing and results
The study brought together data from
various sources. The models combined
data such as slope, aspect, temperature,
precipitation, soil drainage and more
to define suitability for red and white
varietals of vinifera. One of the primary
datasets was newly released highresolution
topographic data. These data
allowed us to generate precise slope and
aspect measurements across the state.
Data processing details can be found
in Section 2.2 in the recently published
article. The choice of these variables was
based on review of scientific literature and
expert knowledge specific to Michigan
viticulture and climatology.
As with most suitability models, a
threefold methodological approach was
used; (1) reclassifying variables based on
their viticultural suitability, (2) weighting
the variables depending on relative
importance and, finally (3) combining
them to generate final suitability maps.
Based on expert knowledge and a review
of the literature, climate variables,
specifically temperature and precipitation,
were highly weighted because of the
large influence they have on grape vine
survival, production and fruit quality.
During the spring, freeze events,
particularly those following a period of
warm temperatures, negatively impact
bud survival.
During the growing season,
temperatures above 35˚ C can inhibit
growth, also negatively impacting
production. In winter, very cold
temperatures can be devastating, as vines
are likely to be damaged at temperatures
colder than -20˚ C. Precipitation is also
important, particularly its amount and
timing. While a high amount of rainfall
is required for vegetative growth, it can
increase risk of diseases during berry
development and maturation.
Soil variables, such as drainage, pH
and rooting depth, are important to
vinifera growth, but to a lesser degree
than climate. The effect of topography on
growth is directly related to climate. Slope
indicates how well cold air and water
drains from the site. Aspect determines
the amount of sun and wind exposure,
Figure 2. The final scoring for the three main categories of the model input
data including: climate, soil, and topography / land cover variables. The upper
portion of the map highlights the climate scoring difference between red, left,
and white, right, vinifera.
26 | FruitGrowersNews.com
Figure 3. Distribution of total area (in hectares) of potentially suitable land for red vinifera
varietals by class. Note that medium-low suitability class is not visible because of the small
proportion of land in this class. Note: G. Traverse is Grand Traverse.

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May 2020

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