The role of climate in sugar maple health: Historical relationships and future projections 1,2Jennifer Pontius, 3Evan Oswald, 4Sandy Wilmot, 3Lesley-Ann Dupigney-Giroux and 3Shelly Rayback 1 UVM, Rubenstein School of Environment and Natural Resources 2USFS Northern Research Station 3UVM Department of Geography 4 VT Forests Parks and Recreation

The Sugar Maple Decline Complex Primary Decline Drivers: Soil nutrient status, calcium, aluminum acid deposition, defoliation, herbivory   Sugar maple (Acer saccharum Marsh) is among the most ecologically, economically and culturally important trees in North America, but has experienced a decline disease across much of its range. We investigated the climatic and edaphic factors associated with A. saccharum growth in the Adirondack Mountains (USA) using a well-replicated tree-ring network incorporating a range of soil fertility (base cation availability). We found that nearly 3 in 4 A. saccharum trees exhibited declining growth rates during the last several decades, regardless of tree age or size. Although diameter growth was consistently higher on base-rich soils, the negative trends in growth were largely consistent across the soil chemistry gradient. Sensitivity of sugar maple growth to climatic variability was overall weaker than expected, but were also non-stationary during the 20th century. We observed increasingly positive responses to late-winter precipitation, increasingly negative responses to growing season temperatures, and strong positive responses to moisture availability during the 1960s drought that became much weaker during the recent pluvial. Further study is needed of these factors and their interactions as potential mechanisms for sugar maple growth decline.

The Sugar Maple Decline Complex Field Studies Exploring Sugar Maple Climate relationships: Likely limited by coarse resolution (spatial, temporal and metric detail) Sugar maple mortality Primarily driven by interaction between base cation status and defoliation Drought and cold winter temperatures associated with higher mortality Sugar maple growth (Basal Area Increment) Nutrition driven with weaker relationship to climate than expected Miller Ontario’s hardwood forests are currently subjected to high levels of air pollution, but critical levels at which point adverse effects may occur are poorly known. In this study, we sampled 35 hardwood plots dominated by sugar maple (Acer saccharum Marsh.) located along a contrasting climate, soil acidity, and air pollution gradient in southern Ontario to explore relationships between these potential ecosystem stressors and ecosystem responses. Foliar sulfur (S) and nitrogen (N) contents were positively correlated with modeled deposition, and foliose lichen species richness was negatively correlated with modeled air pollution levels (S deposition, N deposition, and atmospheric ozone AOT40), whereas foliar calcium, magnesium, and manganese contents were correlated with A-horizon soil acidity. Forest floor S and N contents and C/N ratios were related to soil pH, with high S and N contents and low C/N ratios occurring on the more acidic soil in the northern part of the region, which receives the lowest modeled loadings of S and N deposition and experience colder and wetter climate. Forest health as determined by canopy condition was not related to indices of air pollution, climate, or soil acidity, and no relationship was found among air pollution, soil acidity, and ground vegetation species richness or diversity. Cleavit The regeneration ecology of sugar maple (Acer saccharum Marsh.) has been impacted by acid rain leaching of base cations from the soils throughout much of its range. We tracked the survival and causes of death for a natural cohort of sugar maple seedlings across 22 sites in the Hubbard Brook Valley in New Hampshire, USA, where soil acidification has been documented. Survival over 7 years averaged 3.4%; however, significant differences in survival were observed among sites, which were classified into three main groups based on the shape of their survival curves. These site groups differed in position on the landscape, seedling nutrition and leaf size, and the prevalence of damage agents, but not in soil Ca. First-season mortality was high (71%), and the main damage agents were fungal infection (Rhizoctonia spp.) and caterpillar herbivory (Geometridae). Other principal causes of mortality in order of importance were winter injury, mechanical damage, and rodent (Myodes gapperi Vigors, 1830) tunneling, and all damage agents varied significantly in severity between years. This study highlights the importance of landscape-level variation in biotic factors for predicting sugar maple regeneration success. Predictions of sugar maple regeneration will require a better understanding of controls on initial seedling growth and the suite of biotic agents that damages seedlings. Pitel Sugar maple (Acer saccharum Marsh.), a keystone species of northern hardwood forests, is susceptible to decline, especially on sites low in the soil base cations calcium (Ca) and magnesium (Mg). A common stressor of sugar maple is forest tent caterpillar (FTC;Malacosoma disstria Hübner), an indigenous defoliator. The recent outbreak of FTC (2002–2007) affected 600,000 ha of forest in the northeastern United States and Canada. We assessed the condition of sugar maple trees in 47 North American Maple Project stands in Massachusetts (2006–2007) and Vermont and New York (2007–2008) just after the peak of the FTC outbreak. Mortality was highest in stands with the most crown dieback the previous year (R2 = 0.62, P < 0.001). In addition to drought, cold winter temperatures, and concave microrelief, mortality reflected an interaction of defoliation with soil base cation availability (P= 0.02), with stands defoliated in 2005 that also had low Mg saturation in the A horizon being most likely to suffer high mortality. Sites with above-average annual sugar maple mortality (>3 or 4%) occurred on soils with low concentrations of Ca (0.31–0.46 cmolc kg−1 in the upper B horizon), Mg (0.06–0.10 cmolc kg−1), and K (0.03–0.05 cmolc kg−1). This work extends the thresholds for these base cations determined by previous research on the Allegheny Plateau to a larger geographic area. Bishop Sugar maple (Acer saccharum Marsh) has experienced poor vigor, regeneration failure, and elevated mortality across much of its range, but there has been relatively little attention to its growth rates. Based on a well-replicated dendrochronological network of range-centered populations in the Adirondack Mountains (USA), which encompassed a wide gradient of soil fertility, we observed that the majority of sugar maple trees exhibited negative growth trends in the last several decades, regardless of age, diameter, or soil fertility. Such growth patterns were unexpected, given recent warming and increased moisture availability, as well as reduced acidic deposition, which should have favored growth. Mean basal area increment was greater on base-rich soils, but these stands also experienced sharp reductions in growth. Growth sensitivity of sugar maple to temperature and precipitation was non-stationary during the last century, with overall weaker relationships than expected. Given the favorable competitive status and age structure of the Adirondack sugar maple populations sampled, evidence of widespread growth reductions raises concern over this ecologically and economically important tree. Further study will be needed to establish whether growth declines of sugar maple are occurring more widely across its range. Read More: http://www.esajournals.org/doi/abs/10.1890/ES15-00260.1 Sugar maple canopy condition No relationships with climate indices Sugar Maple Seedling Survival Mortality driven by herbivory, fungal infection and winter injury symptoms (nutrient status held constant)

US Forest Service Climate Change Tree Atlas GIS Approach: relative importance of species …. linked to soil, site and climate characteristics …… to model regional habitat suitability under current and future climate scenarios.

US Forest Service Climate Change Tree Atlas GIS Approach: relative importance of species …. linked to soil, site and climate characteristics …… to model regional habitat suitability under current and future climate scenarios.

Isolating the Relationship between Climate and Sugar Maple Decline Project Objective: Develop a set of downscaled, ecologically relevant climate indices Develop downscaled climate maps for historical and projected climate scenarios for the state of Vermont Why Climate data used in conjunction with ecological observations commonly originate from local meteorological stations or gridded observational products, which are generally more accurate and meaningful when the spatial scales better match the target. In order to obtain observational climate data products with fine resolutions, daily climate time series were extracted from an 800m gridded climate data product based on station observations for each of the 30 NAMP plots used in this study. These observations were further downscaled via the Abridged Spatial Disaggregation Method (Oswald and Dupigny-Giroux, in review) using 4km PRISM AN81d dataset of daily maximum temperature, daily minimum temperature, and daily precipitation totals (Daly et al. 2008, http://www.prism.oregonstate.edu). This downscaling method utilizes the Norm81m mean values of the daily meteorological variables for the 1981-2010 time frame (Daly et al. 2008, http://www.prism.oregonstate.edu) to downscale the station observations to the 800m resolution. From the daily time series extracted from each NAMP plot grid cell, 141 individual climate indices were calculated for each year over the available period of record (1981-2012). These climate indices included several common climate metrics (e.g., length of the growing season, minimum winter temperature, etc.), but also included what we identified as novel and potentially ecologically relevant metrics (e.g., winter thaw events, early frost events, number of extreme hot or cold days, etc.) (Table 1). Evan Oswald, Ph.D. PACE Fellow (Postdoc Applying Climate Expertise) Professor Lesley-Ann Dupigny-Giroux, Ph.D. UVM Department of Geography, Char and

Isolating the Relationship between Climate and Sugar Maple Decline Project Objective: Link climate indices to long-term sugar maple health assessments Sandy Wilmot, Forest Health Specialist Vermont Department of Forest Parks and Recreation Field data were collected from the Vermont subset of the North American Maple Project (NAMP) regional network of long-term sugar maple monitoring plots (Cooke et al. 1992). As a part of this project, sugar maple-dominated forests at 30 locations across the state (Figure 1) were visited annually from 1988-2012, to evaluate tree health and symptoms of current or recent stress impacts following published NAMP protocols (Millers et al. 1991). Measurements included crown dieback (recent twig mortality) and foliage transparency (a measure of foliage density), defoliation and weather-related tree damage. While these metrics were recorded for individual trees, plot level averages were required to match the resolution of downscaled climate data. In addition to mean dieback and transparency, the proportion of trees with high dieback (>15%dieback) and high foliar transparency (>25% transparent) was calculated for each year. 30 plots across a range of elevation and bioregions measured annually between 1988 and 2012 including a suite of canopy condition metrics

Forest Stress Index (FSI) Isolating the Relationship between Climate and Sugar Maple Decline Project Objective: Remove the influence of common disturbance agents to isolate relationships with climate indices Summarize the various canopy condition metrics into one summary value Plot-Level % of trees with High Dieback and Transparency Mean Canopy Dieback Mean Canopy Transparency The creation of a statistical model for estimating FSI values based on climate variables, while accounting for disturbance events was accomplished using an "iterative estimation of partition regression models" (Fiebig, 1995). This technique allows for the simultaneous assessment of both climate and disturbance models to predict FSI while also allowing for: a) a predictor-variable selection model to be incorporated into the process and b) control over the Y-intercept. In this study, a Y-intercept was included for the climate term of the model, but not for the disturbance term. The iterative estimation method (Figure 2) was run on the pooled yearly data (in total, 718 plot-year observations) beginning with a multiple linear regression between disturbance predictors and FSI values. The resulting disturbance adjusted residual values for the 718 observations were then used in a multiple linear regression between climate predictors and FSI values. Climate predictors were selected via a forward stepwise regression predictor selection process at the 99.9% confidence level. Climate adjusted residuals from the resulting climate-based regression model were subsequently used to fit a new disturbance model. This process of using iteratively refined residuals continued until the coefficients for both models converged, such that the selected predictors and their corresponding regression coefficients did not vary by more than 0.00001 from one iteration to the next. The effect of considering the disturbance impact on the observed FSI values (Figure 3a) was to reduce the FSI values proportionally with increasing disturbance values (Figure 3b). The differences between Figure 3a and Figure 3c demonstrate this impact of this disturbance adjustment on FSI values. No adjustments to FSI values were made when a zero disturbance was recorded, which was the case for the majority of plot-year observations (Figure 3b). Accounting for the influence of disturbance was important in allowing us to examine specifically the climate contribution to sugar maple condition, which is captured in the Disturbance Adjusted FSI (Figure 3c). Across all plots and years, this adjustment shifted the mean FSI from 0.00 to -0.17. Adjustments for disturbance (Figure 3b) highlight high disturbance years including: 1988 (pear thrips injury), 2005 and 2006 (forest tent caterpillar defoliation) and 1998 (ice storm, which affected nearly 20% of Vermont’s forested area and exactly 20% of our plots). of downscaled climate data. In addition to mean dieback and transparency, the proportion of trees with high dieback (>15%dieback) and high foliar transparency (>25% transparent) was calculated for each year Forest Stress Index (FSI) Mean of all Normalized Metrics Normalize to Historical Plot Distribution Pontius, J., & Hallett, R. (2014). Comprehensive methods for earlier detection and monitoring of forest decline. Forest Science, 60(2).

Isolating the Relationship between Climate and Sugar Maple Decline Project Objective: Identify key climate indices linked to sugar maple condition and model FSI under various climate scenarios Climate Only 5-terms r2 = 0.185 p < 0.001 RMSE = 0.541 PRESS RMSE = 0.546 Disturbance Adjusted FSI model included five climate predictors (Table 2) accounting for approximately 19% of the total variation in sugar maple FSI (R2 = 0.185, p < 0.001, RMSE = 0.541, PRESS RMSE=0.546, MAD = 0.32). For comparison, the full regression model, including both disturbance and climate terms, explained 31% of the variability in the observed FSI values (R2=0.309, p<0.001, RMSE=0.541, PRESS RMSE= 0.546, MAD=0.317). This indicates that while disturbance may be the have the strongest single impact on yearly sugar maple condition, combined climate variables account for a larger portion of the long-term variability in sugar maple condition. Predicted FSI Climate Plus Disturbance 5-terms r2 = 0.309 p < 0.001 RMSE = 0.541 PRESS RMSE = 0.546 Actual FSI

Isolating the Relationship between Climate and Sugar Maple Decline Project Objective: Examine region wide historical variability in climate impacts on sugar maple health Higher Decline Typical Condition Healthier than Average In order to better understand the historical climate impacts on FSI beyond the NAMP plot locations, spatially continuous climate indices on 800m raster grids were created for the final key climate predictor terms for each year during the 1981-2012 period using the same downscaling technique described above. The assumption is that these plot-based models capture the general relationship between sugar maple and climate across the state. Because climate conditions vary from year-to-year and location-to-location, the resulting predicted FSI climate impacts were unique each year. The high spatial resolution nature of the climate data allows for distinguishing relationship with geographical features.

Isolating the Relationship between Climate and Sugar Maple Decline Project Objective: Project potential impacts to FSI under future climate scenarios 2021 – 2050 Low Emissions (B1) High Emissions (A2) 2041 – 2070 Low Emissions (B1) High Emissions (A2) Change in stress condition 0.344 0.675 Higher Decline Typical Condition Healthier than Norm Gridded spatial projections of the key climate indices were used to explore the ways in which the condition of sugar maple may respond to ongoing and future climate change. In this study, we used the daily downscaled climate model projections provided by the third National Climate Assessment (NCA, Kunkel et al. 2013) Climate Model Intercomparison Project (CMIP3, http://www.ipcc.ch) to model each of the 141 climate indices included in this study. Statistical downscaling of these NCA data to roughly 13km x 9km grid cells by Stoner et al. (2013) yielded 171 individual grid cells over Vermont, representing climate conditions at four time frames (1981-2000; 2021-2050; 2041-2070 and; 2070-2099) under two emissions scenarios ("A2" high-emissions and "B1" low-emissions). We consider the historical 1988-2012 normals for the 141 climate indices included in this study to represent a current conditions “baseline” (Table 2). Gridded projections of the key climate indices were used in conjunction with the final climate regression model coefficients to model a spatially explicit projection of future sugar maple FSI at various time periods under high and low emissions scenarios. Uncertainty in climate projections was quantified as the magnitude of absolute difference between FSI values estimated using (PRISM) observational climate data and those estimated using NCA climate model output for the historical period (1981-2010). This uncertainty was used to identify thresholds for likely impact in the spatial projections. Change in stress condition 0.162 0.201

Low Emissions (B1) High Emissions (A2) Isolating the Relationship between Climate and Sugar Maple Decline Project Objective: Project potential impacts to FSI under future climate scenarios 2070 – 2099 Low Emissions (B1) High Emissions (A2) Change in stress condition Low Emissions FSI 0.678 High Emissions Scenario FSI 1.557 Higher Decline Typical Condition

Based on Historical “Norms” Isolating the Relationship between Climate and Sugar Maple Decline Implications FSI Distribution Based on Historical “Norms” Very Healthy Healthy Average Moderate Decline Severe Decline 2021-2050 2041-2070 2070-2099 Low Emissions Scenario Under the Low Emissions Scenario by 2070-2099 Sugar Maple will be in Moderate to Severe Decline 50% of the time.

Based on Historical “Norms” Isolating the Relationship between Climate and Sugar Maple Decline Implications FSI Distribution Based on Historical “Norms” Very Healthy Healthy Average Moderate Decline Severe Decline 2021-2050 2041-2070 2070-2099 High Emissions Scenario Under the High Emissions Scenario by 2070-2099 Sugar Maple will be in Moderate to Severe Decline 80% of the time.

Isolating the Relationship between Climate and Sugar Maple Decline Implications Target management where sugar maple is most likely to tolerate changing climate Minimize secondary stress agents Adaptive Management to prepare for the loss of sugar maple in high risk locations

Isolating the Relationship between Climate and Sugar Maple Decline Utilizing this Information Climate Change Forest Health Research Group RSENR McIntire Stennis Program Online Decision Support Tool To incorporate sugar maple niche mapping as well as many other stress drivers, ecosystem responses and management objectives in a spatial mapping interface.

Isolating the Relationship between Climate and Sugar Maple Decline University Cooperative for Atmospheric Research Postdocs Applying Climate Expertise