Sugar Maple in Wisconsin

i
Potential Range Shift of Sugar Maple (Acer Saccharum)
in Wisconsin and Proposed Adaptive Strategies
Elizabeth Phillippi Ryan Thompson
UW-Madison UW-Madison
Department of Botany Nelson Institute for Environmental Studies
12/9/2015
Abstract: Sugar maple (Acer saccharum) is a keystone species in northern hardwood forests. It is
economically important as a source of timber and maple syrup for Wisconsin. It ranges across the
northeastern United States and is found in high abundance in northern Wisconsin. This tree is
threatened by climate change and its suitable habitat will slowly shift north as the state warms and
precipitation in the summer and winter become inappropriate for the persistence of sugar maple.
Several conservation meansures, including educational programs for landowners, manual planting and
deer population control are discussed herein.

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Table of Contents
ECOLOGICAL SIGNIFICANCE................................................................................................................1
SENSITIVITY .......................................................................................................................................3
HABITAT ......................................................................................................................................................3
PHYSIOLOGY .................................................................................................................................................4
EXPOSURE .........................................................................................................................................5
TEMPERATURE ..............................................................................................................................................5
PRECIPITATION..............................................................................................................................................7
OTHER THREATS............................................................................................................................................9
ADAPTATION OBJECTIVES ..................................................................................................................9
ADAPTIVE STRATEGIES..................................................................................................................................10
MONITORING PLAN .........................................................................................................................13
INFORMATION NEEDS AND ASSOCIATED INDICATORS.........................................................................................13
MONITORING APPROACH .............................................................................................................................13
SUMMARY.......................................................................................................................................14
APPENDIX A.....................................................................................................................................15
CONCEPTUAL MODEL...................................................................................................................................15
APPENDIX B.....................................................................................................................................16
SUPPLEMENTAL IMAGES ...............................................................................................................................16
APPENDIX C .....................................................................................................................................18
MONITORING PLAN INDICATORS....................................................................................................................18
WORKS CONSULTED.........................................................................................................................21

1
Ecological Significance
Sugar maple (Acer saccharum) is a major component of the forests of Wisconsin. Early survey records
show it to be common in many forest cover types (Figure SI-1). Sugar maple has persisted as a dominant
tree in northern hardwood forests (Figure 1), even through heavy logging and burning in the mid-1800’s,
referred to in the literature as The Cutover. Recovery from The Cutover has seen sugar maple make up
nearly eleven percent of Wisconsin’s growing stock volume mostly as a component of Maple-Beech-
Birch forests, which account for twenty-seven percent of the forest land in Wisconsin, though its
recovery is hindered by habitat fragmentation (WDNR, 2010).
Sugar maple is a keystone species of many northern hardwood stands and provides habitat for many
birds, including cavity-nesters and screech owls (Tirmenstein, 1991). A. saccharum is of particular
importance to the leaf flycatchers. Decline of sugar maple in their range has led to thermal stress among
the nestlings, owing to loss of canopy cover (Minorsky, 2003).
The buds and leaves of the sugar maple are prime browsing for insects like the gypsy moth and the
linden looper, as well as larger mammals like snowshoe hares, porcupine and whitetail deer, with the
heaviest browsing by whitetails over the winter. The seeds, which can occur in vast numbers, are often
harvested by squirrels and other small rodents.
Humans utilize the sugar maple as a resource as well. Many of the stands around Wisconsin are
periodically harvested for sawtimber. Wisconsin exports much of its hardwood harvest, with about 10%
of the GDP traceable back to furniture and other fixtures (Bowe, 2012). Maple is well-suited to
woodworking, going into products like instruments, gunstocks, and bowling pins. This periodic thinning
can release suppressed maple seedlings and regenerate age classes if the stand is unevenly-aged. This is
impossible in even-aged stands because the trees are all the same age.
Sugar maple is also the source of maple syrup. Its sweet sap flows during the first spring thaw events,
pulled up through the roots and circulating in the trees’ vascular tissue. The sap can be collected and
boiled down to produce the world’s most popular pancake topping, at around 34 liters of sap per liter of
syrup. Syrup is a multi-million-dollar industry worldwide, with Federation of Quebec Maple Syrup
Producers, Canada’s maple syrup cartel, controlling 71% of the world’s supply (Cecco, 2015).

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In 2014 Wisconsin was the fourth largest producer of maple syrup in the United States, accounting for
6% of the total 3.1 million gallons produced (Whetstone, 2015). The production of syrup is tied up with
the flow of sap, which is in turn influenced by the weather. Sugar maples are sensitive to a number of
climatic factors, including the length of winter and how cold it is. A long, colder winter that keeps the
ground frozen can delay bud break in the trees, creating a larger window for sap harvest. Sap quality is
also affected by the preceding summer. If the summer is warm and mostly sunny, more starch will be
produced, increasing the concentration of sugar in the sap flowing in the spring (Bergeron, 1999).
Figure 1: Volume of sugar maple in Wisconsin

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Sensitivity
Areas of Potential Vulnerability Habitat Physiology Phenology Biotic Interactions
Relative Vulnerability 3.57 2.5 -0.42 1.00
Qualitative Assessment Vulnerable Vulnerable Resilient Slightly Vulnerable
Table 1: Abbreviated results from the System for Assessing the Vulnerability of Species (SAVS) for Acer Saccharum in
Wisconsin. Quantitative vulnerabilities are relative to each of the potential vulnerability categories. The qualitative
assessment relates to the severity of the vulnerability in general.
Habitat
Precipitation and Temperature
Sugar maples are incredibly sensitive to soil moisture content. They show a preference for well-drained,
uncompacted, mesic soils (Tirmenstein, 1991). Flooding quickly kills the root system, injuring the tree
with the possibility of death if the flooding is prolonged (Iles, 1993). Xeric environments are also hard on
sugar maples. During periods of drought the root pulls air into its xylem instead of water, resulting in an
embolism. Cavitation (breaking the water column in the xylem) damages the vascular tissue. If
prolonged, it can cause dieback or
kill the tree (Sperry and Tyree, 1988).
Fire
Drier conditions, especially in the
autumn when dry leaves cover the
forest floor, favor forest fires that
have been recently suppressed by
humans in the northeastern forests.
Sugar maple does not recover well
from crown or ground fires (USFS,
2010). Their thin bark and papery
samaras do not possess the
resistance to ground fires that
thicker-barked trees and harder seeds, like acorns, do (Greenburt et al., 2012).
Figure 2: Climate envelope for maple in its full range across the US and Canada (grey)
and just in Wisconsin (red). This makes up the climate space sugar maples currently
persist in. (Based on data from Landscape Change Research Group. 2014. Climate
change atlas. Northern Research Station, U.S. Forest Service, Delaware, OH.
http://www.nrs.fs.fed.us/atlas. And Climate Reanalyzer)

4
CASE STUDY
Sugar maples are sensitive to
damage by winds and ice
storms. When maples were hit
with a glaze storm in NY, 1942,
there was little tendency
towards repair and continued
sprouting (WDNR, 2012).
Physiology
Temperature and Snow Effects
Sugar maple germinates at low temperatures, often beneath the spring snow cover, when the soil is no
warmer than 10° C for 35-90 days (Yawney and Carl, 1968). Above 10° C, germination tends to fail.
(Godman et al., 1990). Indeed, nearly 87% of germination of sugar maples occurs at 1° C (Godman and
Mattson, 1992). Like the seeds, the roots need to be tucked in over the winter. Without the subnivium
to winter under, maple roots are prone to root freeze when frost creeps deep into the soil in during
absent or sparse snow cover. Root freeze results in lower sugar content and reduced sap flow in the
affected trees and can cause dieback (Robitaille et al., 1995). When followed by periods of drought, root
freeze can be particularly devastating, leading to permanent cavitation and impairing the movement of
water through sapwood (Houston, 1999). Warm temperatures during the day, followed by rapid night
freezes can cause cells in the bole to rupture, a process known as winter sun scald, and the shrink-swell
of the trunk can cause cracks that are vulnerable to fungal assailants (WDNR, 2012).
Biotic Interactions
Sugar maple is a common target for North American browsers. Squirrels eat the seeds and deer and
porcupine eat the bark and buds of saplings and older trees. In most cases, winter browsing by larger
herbivores, especially deer, does not detrimentally affect the growth of older trees in the long run
(Jacobs, 1969). Insect activity can defoliate sugar maples to an extent that acutely stresses the tree.
Warmer winters are making it more difficult to achieve die-off of insect populations and can lead to
increased browsing as more bugs reproduce and survive.
Whether by insects, wind or hail (WDNR, 2006), defoliation
makes it easier for secondary organisms, like the fungi
Armillaria, to infect the roots of young, defoliated trees. These
infections often precede dieback. Logging injuries that open the
trees’ interior to the surrounding environment can have the
same effect (Houston, 1999). Repeated partial cutting,
especially in uneven-aged stands, can lead to persistent damage
and defect (Nyland, 1997).

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Surprisingly, humans offer much less disturbance to sugar maples than many other animals. While
harvest of sawtimber can damage stands if carried out carelessly, the resultant thinning can promote
growth of even-aged stands by clearing basal area for new seedlings to sprout (Nyland, 1999). Humans’
interest in the sap of sugar maples, as well as their appreciation for their brilliant fall foliage, has
provided incentive to protect and maintain local populations, though their low resistance to soil
compaction and pollution has reduced their popularity as street trees.
Exposure
There have been increasing observations of sugar maple dieback
since the 1950’s. This has been attributed to a number of causes,
many of them regionally specific. It has been noted universally that
older trees are more susceptible to the stresses associated with
dieback (Houston, 1999). This could be devastating for elderly, and
therefore stress-susceptible, even-age stands where the narrow age
distribution of the constituent trees could stunt regeneration,
delaying the recovery of the stand.
Temperature
This is of particular concern when examining the effects of
temperature on stand health. The peaks and valleys in the global
mean annual temperature (Figure 2) correlate to sugar maple dieback events as well as recoveries
(Mickler et al., 2000). Cooler annual means correlate to recovery of the observed maples, and peaks
with dieback events in eastern North America and central Europe. As the average temperature
continues to rise, there is a greater probability of diebacks from which there will be no recovery. Where
that threshold lies has yet to be seen.
Figure 2: Climate change correlated to
sugar maple dieback. As mean
temperatures peak, dieback events begin
(↑). When the temperatures dip, recovery
is observed (↓) in North America and
central Europe (Houston, 1999).

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In Wisconsin, over the next one hundred years, the annual average temperature is predicted to rise at a
rate of .05 ℃ per year, settling around 14℃ by 2100 (Figure SI-2). Climate models presented by WICCI,
which are specific to Wisconsin, predict an increase in extreme summer temperatures across the state,
with frequency of very hot days (exceeding 32℃) likely to double the current frequency. While the
models project that summer temperature shifts will be less than other seasons, these increases are
projected to be highest in northern Wisconsin, around
3℃, where sugar maple populations are greatest
(Figure 3).
Increased summer temperatures can stress the
maples and exacerbate dieback. High temperatures
don’t pose a direct risk to these trees, which can
persist with average temperatures as high as 19℃ (at
lower densities than observed in WI) with appropriate
precipitation (Figure SI-3). However, Wisconsin is not
projected to have annual precipitation increase
consistent with the preferred climate space
associated with the new average temperatures, which
will rapidly be approaching the current boundary of
the bioclimatic envelope by 2100.
The higher temperatures, combined with a projected decrease in summer precipitation, can quickly dry
out a forest, increasing the risk of drought and forest fires (USFS, 2010).
In Wisconsin, the trees are also exposed to extremes of winter temperature. Early thaw followed by a
rapid return to freezing conditions, is associated with decline or dieback events of sugar maples
(Houston, 1998), in some cases from the development of an embolism in the sapwood. Research
indicates that these events of thaw-freeze are strongly correlated with a high El Nino-low Southern
Oscillation (ENSO) Index (Auclair, 1998), suggesting that climate change at the global level has potential
consequences for maple at the local level.
Figure 3: Modern range and relative abundance of
sugar maple in North America, based on current FIA.
[Image via Forest Service’s Tree Atlas, Iverson, L. et al.
2008]

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CASE STUDY
Despite the large seed crop of 1977,
recruitment of maple seedlings failed almost
entirely in the spring of 1978. Unusually
rapid warming of the soil surface in
Northern Wisconsin and loss of the
subnivium led to nearly complete failure of
seedling recruitment that year. The only
seedlings to actually sprout came from the
snowbanks left over from plowing the roads
(Godman and Mattson, 1980).
Precipitation
As winter precipitation plays a
large role in the survival of Acer
seedlings, any changes in snow
cover or snow depth have
implications for increased risk of
seedling death. During the last five
decades of the 20th century,
Wisconsin witnessed an increase
of precipitation of 13 mm both in
the winter and spring. This trend is
projected to continue into the
middle of the 21st century with expected increases of 25% in the winter, although with a greater
likelihood that precipitation will fall as rain rather than snow in both winter and spring, which indicates
likely decreases in snow cover and snow depth (WICCI, 2011).
Sugar maple roots rely on snow cover to help preserve them against the ground-penetrating cold and
resulting root freeze, while their seeds rely on the spring snow cover for germination purposes.
Research by Notaro, et al. has created downscaled models for the Great Lakes Region and found that
there will be fewer snowfall events in Wisconsin, with
as many as twenty snow accumulation days lost by the
end of the century (Figure 4). In Wisconsin, the spring
snow cover (MAM) is projected to drop off sharply near
the middle of this century and disappears entirely by
2070 (Figure SI-4). Lack of snow cover is a factor that
increases the chances of root freeze, and ensuing
dieback of maples (Houston, 1998). No doubt this
contributes to the retreat of suitable sugar maple
habitat predicted by the US Forest Service.
Sugar maples do not reach sexual maturity and bear
seeds until 22 - 40 years of age. While older trees can
Figure 4: Scaled-down climate models predict a loss of 10 to 20 days per year that
have snowfall events totaling at least one cm when the data from 1980-99 is
compared to the projections for 2080-99 (Notaro, 2015).

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Figure 4: Current (green) and predicted mean center of
distribution for sugar maple by 2100 for RCP+8.5 emission
scenario (red). [Image via Forest Service’s Tree Atlas,
Iverson, L. et al. 2008. Estimating potential habitat for 134
eastern US tree species under six climate scenarios. Forest
Ecology and Management 254:390-406.
http://www.treesearch.fs.fed.us/pubs/13412]
produce higher volumes of seeds, Wisconsin’s forests are relatively young. Most stands are between
twenty and forty and nearly ten percent are less than twenty years old (WDNR, 2010)
Recruitment of seedlings, when considered with climatic factors, is potentially complicated by the
inconsistency of seed crops from year to year. Sugar maples mast every 2-5 years, the seeds are wind-
dispersed and can get as far afield as 100 m from their parent (Godman and Mattson, 1992). Samaras
rarely make it more than 15 m from the forest edge (WI-DNR, 2012), which could limit the trees’ ability
to colonize newly formed niches. This, combined with many stands only recently achieving, or still
working toward, seed-bearing age could make it difficult to match the northward shift of the ideal sugar
maple climate space (Figure 5).

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Other Threats
Another consideration for survival of maple populations is the presence and abundance of herbivores
that browse maple seedlings and saplings, as repeated browsing can significantly decrease the chances
of regeneration (Nyland, 1998). Wisconsin hosts a large population of white-tailed deer which can favor
sugar maple over other, less palatable, tree species, and have been shown to nearly eradicate maple
populations (Matonis, 2011). Decrease in snow cover and increase in rainfall during winter produce
favorable conditions for increases in deer populations, as they will have greater foraging access,
although this may also be at least partially offset by decreases in deer populations due to mortality from
disease outbreaks (LeDee et al., 2013).
Another risk is the spread of invasive species, which can be augmented by altered site conditions due to
climate change (Walther et al., 2002). Gypsy moth has long been a nuisance in Wisconsin and can
defoliate maple trees on a massive scale if its preferred hosts are not abundant.
Adaptation Objectives
We applied principles of adaptive management from the Conservation Measures Partnership (CMP) and
used the Miradi software application to clarify goals, create a conceptual model (see Appendix A), devise
strategies to reduce threats, and create objectives for conserving sugar maple populations in Wisconsin.
Based on the predictions of temperature and precipitation in the next century, some losses in maple
populations are inevitable. However, with some strategic actions, future generations of trees can be
protected (and our grandkids can continue to enjoy locally produced maple syrup!).
Conservation Goal: By 2050, maintain at least 60% of current population levels of sugar maple in
Wisconsin, with a minimum of X trees1
above 30 years of age per hectare within each distribution.
In order to achieve this goal, some general objectives should be pursued:
 Reduce pressure and threats to reproductive success of sugar maples in Wisconsin
 Reduce or eliminate threats to survival of adult trees, such as insects and fire regime
 Protect existing sugar maple habitat or identify new locations with favorable habitat conditions
1
Further research needed to clarify number of adult trees required to sustain healthy populations

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We consider the following strategies to be potentially effective means of reducing some of the threats
associated with climate change.
Adaptive Strategies
1) Conduct manual seeding or planting of seedlings/saplings by conservation
teams and farmers
To ensure resistance to environmental changes that detrimentally affect the reproductive success of
sugar maple populations, seedling density should be approximately 300,000 per hectare, which leads to
a survival rate of several hundred adult trees (RVCA-LRC, 1995). Conservation teams led by the DNR and
including citizen scientists, volunteers, or landowners can monitor seedling abundance by taking
samples in microplots mapped within public or private plots of land (USDA, 1999), and then plant
seedlings within each plot as necessary to reach density goals. It may be important to harvest samaras
and bank maple seeds to continue cultivating seedlings in greenhouses.
2) Increase deer hunting
licenses
This strategy is designed to increase
resilience of sugar maple
populations by reducing the threat
of overbrowsing by herbivores
(Figure 5), specifically deer, whose
populations tend to increase with
increasing temperatures, as noted
previously. The Wisconsin DNR
wildlife managers monitor
populations and assess whether the
levels are above predetermined
population goals (WDNR, 1998). When populations exceed those goals, the DNR raises the harvest
quota, allowing hunters to harvest greater numbers of antlerless deer.
Figure 5: Simplified conceptual model with direct threat of Overbrowsing by
Herbivores (especially deer), climate change drivers, stresses on
reproductive success, and strategies to mitigate threat.

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3) Organize management of parasites, native problematic species, and invasive
species by conservation teams and farmers
Another resilience strategy is managing
problematic species (Figure 6). Considering
the variety of potential threats from native
problematic species and invasive species, it
will be vital to conduct regular monitoring
of presence of these species, including
forest tent caterpillar, linden looper, and
the invasive gypsy moth. To control forest
tent caterpillar and linden looper,
insecticide sprays are typically used (US
Forest Service, n.d.). For gypsy moth, a
national campaign called Slow the Spread
(STS) led by the USDA Forest Service
presents a plan for deploying pheromone-baited traps that detect presence of newly established
populations, which then allows for aggressive eradication (Tobin & Blackburn, 2007).
4) Coordinate landowner education on maintaining maple populations
A multifaceted strategy of landowner education can improve both the resilience of maple populations
and promote resistance to environmental threats. Through a collaboration between experts on sugar
maple and landowners experienced in their management, a campaign can be designed, produced, and
distributed to landowners. Some of the strategic actions might include when and how to plant seedlings,
pruning of competitors, logging best practices to limit injuries to trees, and identification of invasive
species. An example of this type of educational campaign was produced in Ontario, Canada by the
Rideau Valley Landowner Resource Center, presenting these and other practices (RVCA-LRC, 1995).
5) Conduct prescribed burns
Prescribed burns are a common resilience strategy with numerous objectives and benefits, such as
reducing fuel availability and thus reducing wildfire, site preparation for seeding or replanting forests,
and as part of an invasive species management plan. The Wisconsin DNR publication “Wisconsin Forest
Figure 6: Simplified conceptual model portraying threat of
Problematic Species, with climate change drivers, ecological stresses
to survival, and strategies to mitigate the threat

12
Management Guidelines” contains a chapter on fire management, which presents specific actions to
plan, prepare, and conduct prescribed burns (WDNR, 2011). To begin, conservation teams and
landowners identify maple forest areas to be managed with burn regime. The next vital objective is to
establish a written burn plan to detail limits and control line of burn area, safety issues and potential
hazards, acceptable weather conditions, fuel types, fuel load, and vertical arrangement of fuels.
6) Protect unfragmented forest lands through conservation easements and
other policy tools
Another strategy to encourage resilience of maple populations is to prevent fragmentation of their
habitats through human development, infrastructure, and roads, all of which has the potential to limit
reproductive success, impair other vital ecosystem functions, and introduce invasive species (EOEEA,
2011). A number of policy tools exist for this purpose, one of the most common being conservation
easements, which will prohibit specific forms of development from taking place on a plot of land. In
order to implement an easement, it is necessary to identify land trusts or other organizations with
funding and interest in protecting land, and landowners with interest in selling or donating an easement
on their lands.
7) Assisted Migration: Identify new locations of suitable habitat and plant
seedlings in new locations
A final strategy of assisted migration involves a realignment of management objectives, recognizing that
it may not be possible to protect existing distributions, but rather is necessary to relocate to suitable
locations. This strategy is likely best considered as a last-ditch effort to protect trees in the case that
temperature and precipitation conditions become largely untenable for maple populations in their
current range. To implement this strategy, the first objective would be to identify public or private lands
with appropriate soil, temperature, precipitation, and biotic conditions for sugar maple to thrive. Then
seedlings could be planted following criteria laid out in Strategy 1 above. Ultimately, this strategy may
also require shifting Wisconsin’s borders northward, quite naturally presenting somewhat of a political
challenge in facing resistance from Michigan, Minnesota, and Ontario, Canada.

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Monitoring Plan
The monitoring plan in this report is intended for use by the Wisconsin DNR and private landowners
whose properties currently or may one day contain sugar maple populations. The monitoring data may
also be of interest to conservation organizations, donors to conservation projects, and also citizen
scientists who may participate in maple conservation programs. This monitoring plan was developed
following principles outlined by the CMP Open Standards for the Practice of Conservation.
Information Needs and Associated Indicators
The focus of monitoring over the coming decades should include the ecological status of current sugar
maple populations, environmental conditions and changes, and the effectiveness of conservation
actions. For each of these, a number of specific indicators have been identified that can help to assess
overall health and ongoing vulnerability of maples in Wisconsin. See Table 1, 2, and 3 in Appendix C for a
more detailed view of monitoring methods and logistics of data collection for each indicator. The
logistics include the method, such as surveys or use of quadratic frame, as well as who conducts the
monitoring, when it takes place, and how often. A brief justification for the relevance of monitoring each
indicator is provided.
Monitoring Approach
For all of the indicators listed in Appendix X, the time series monitoring approach is likely ideal, as these
management steps will need to continue for decades to come. The time series approach entails taking
several baseline measurements taken at regular time intervals (weeks, months, or years) prior to a
conservation intervention, followed by ongoing measurements after the actions have been taken. In the
case of sugar maples, due to the long lifetimes of the trees and the time to maturity, monitoring actions
would likely be conducted once a year at the most frequent, or perhaps every five years or so.

14
Summary
At present, sugar maple in Wisconsin is not significantly threatened. However, with increases in
temperatures as well as precipitation variability in both winter and summer, threats to maples will likely
increase. Changes in habitat conditions represent the most significant threat to the trees. Lack of snow
cover inhibits germination, and thus affects reproductive success. As Wisconsin’s precipitation levels lie
towards the lower end of sugar maple’s climate envelope, any decrease in annual precipitation has the
potential to push it out of its comfort zone. Maples are also highly sensitive to soil moisture, preferring
to remain in the Goldilocks zone; soil that’s too dry can cause embolisms, while flooded soils can kill the
root systems of trees. With increasingly warmer and drier conditions wildfires tend to increase, which
presents a major threat, as maples have thin bark and their papery samaras can ignite easily.
Biotic interactions also pose a considerable risk, including problematic insect species and overbrowsing
by herbivores. Cold winters typically thin the ranks of both insects and deer, so as winter temperatures
increase, the risk of defoliation by insects and overbrowsing of seedlings by deer also becomes more
likely. The spread of the invasive gypsy moth can also be exacerbated by changing climate.
Of the recommended strategies listed above, perhaps the most feasible and easily implemented include
organizing a landowner education campaign to share tips and resources for protecting sugar maple on
private lands, increasing deer hunting licenses, participating the Slow the Spread invasive management
program, and conducting prescribed burns. Ongoing monitoring over the coming decades will be
essential, with some baseline assessments of current populations and habitat conditions, and regular
assessment following strategic actions.
To help protect this valuable species in Wisconsin, it’s recommended that steps are taken sooner rather
than later to ensure that sugar maple continues to have suitable habitat in the state. Our state tree, with
its gorgeous fall foliage, beautiful hardwood, and last but not least, the glorious maple syrup it produces,
deserves our protection!

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Appendix A
Conceptual Model

16
Appendix B
Supplemental Images
y = 0.0535x - 98.262
R² = 0.9549
5
7
9
11
13
15
17
1990 2010 2030 2050 2070 2090 2110
AnnualAverageTemperature(⁰C)
Year (C.E.)
Average Temperature in WI
SI-2: Data for Region (42N-47N;268E-273E) using satellite data, the CCSM4 global circulation models, and
RCP+8.5 emission scenario (Data obtained using Climate Reanalyzer (http://cci-reanalyzer.org), Climate
Change Institute, University of Maine, USA).
SI-1: Pre-settlement forest types in which sugar maple was a major component.
Data from land survey records (Finley,1976).

17
SI-4: Past and projected snow accumulation in Wisconsin using satellite data for Region (42N-47N;268E-273E), the
CCSM4 global circulation models, and RCP+8.5 emission scenario (Data obtained using Climate Reanalyzer (http://cci-
reanalyzer.org), Climate Change Institute, University of Maine, USA).
SI-3: Niche model for the Eastern US habitat of sugar maple (Landscape Change
Research Group. 2014. Climate change atlas. Northern Research Station, U.S. Forest
Service, Delaware, OH. http://www.nrs.fs.fed.us/atlas.)

18
Appendix C
Monitoring Plan Indicators
Table 1: Monitoring plan for status of current sugar maple populations
Status of current sugar maple populations
Indicator Description Method and Logistics
Species
abundance
and age
distribution
In order to sustain healthy populations, a
significant proportion of adult trees should
be present, as maples don’t begin producing
seeds until roughly 30 years of age.
 Annual forest surveys
 US Forest Service, landowners,
citizen scientists
Seedling and
sapling
abundance
Abundance of seedlings and saplings is an
indicator of reproductive success. Low levels
determine whether seedling planting is
required.
citizen scientists
Trunk and
root integrity
Logging injuries, problematic insect species,
and fungal infections can cause death to
individual trees, as well as indicate threats to
the population.
citizen scientists
 Predetermined microplots within
existing populations
Crown cover Defoliation by insects can put considerable
stress on individual trees, so monitoring
crown cover can inform whether intervention
is necessary.
 Spherical densiometer
 Once every one to three years
 Landowners, citizen scientists
 Predetermined microplots within
existing populations

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Table 2: Monitoring plan for environmental conditions and changes
Environmental conditions and changes
Temperatures
in winter and
summer
Since temperature plays a key role in survival
of maple, continued monitoring of
temperature changes is vital.
 Weather station data
 NOAA, national weather service
Precipitation in
winter and
summer
Too much or too little precipitation
jeopardizes existing populations as well as
reproductive success.
Snow cover Maples require snow cover to germinate, so
persistent lack of snow cover threatens
reproductive success.
Soil moisture Closely related to precipitation levels, if the
soil is too dry or too wet, maples will suffer.
 Soil moisture sensor, remote
sensing
 US Forest Service
Table 3: Monitoring plan for effectiveness of conservation actions
Effectiveness of Conservation Actions
# of seedlings
surviving to
adulthood
The proportion of trees that survive to
adulthood after planting, along with climate
and other environmental conditions, can
indicate the suitability of particular areas for
maintaining maple populations.
 Landowner planting: app or
website for participants to
upload planting data
 Landowners
 Predetermined plots
Presence of
invasive and
problematic
species
Monitoring problematic native or invasive
species is an obvious and prevalent need for
the health of most ecosystems. Specific
species indicated above in sections on
Sensitivity and Exposure.
 Surveys, quadratic frame,
volunteer monitoring
 Landowners
 Predetermined plots

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Deer density
per hectare
As deer populations grow with milder
winters, this can represent a threat to
seedling survival rate. Taking census of deer
can ensure the DNR is able to issue and
appropriate number of hunting licenses.
 Hahn, Spotlight, or Mobile Line
deer census techniques
 Annually before hunting season
 Landowners, citizen scientists,
DNR
 Private and public plots of land
Species
presence and
richness
following
prescribed
burns
Some of the goals of prescribed burns are to
control certain invasive species and to
create suitable conditions for maple to
thrive by clearing out competitors.
 Quadratic frame
 After prescribed burns
 Landowners, citizen scientists,
DNR
 Private and public plots of land
# of wildfires
following
prescribed
burns
Another goal is to prevent wildfire by
intentionally limiting the amount of fuel
available to wildfire, and thus to avert
potential wildfires in a given area.
 Interview fire department for
fire data
# of
landowners
that have
participated in
education
campaign
In order to ensure success of sugar maple
landowner education programs, a sufficient
number of landowners in targeted areas
must participate in training and contribute
to strategic actions and monitoring.
 Survey
 Every one to three years after
education campaign launch
 DNR
 Private land plots

21
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