sugar maple in wisconsin

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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

3

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)

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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]

7

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

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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.

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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

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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

An

nu

al A

vera

ge T

em

pe

ratu

re (

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

19

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

20

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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