Health of Sugar Maple in Canada

Transcription

1

2 Health of Sugar Maple in Canada Results from the North American Maple Project, D. Lachance Quebec Region A. Hopkin Ontario Region B. Pendrel Maritimes Region J. Peter Hall Science and Sustainable Development Directorate, Ottawa Information Report ST-X-1 Published by Science and Sustainable Development Directorate Canadian Forest Service Natural Resources Canada Ottawa, 1995

3 Her Majesty the Queen in Right of Canada, 1995 Catalogue No. Fo29-33/ ISBN X ISSN X Copies of this publication may be obtained free of charge from: Natural Resources Canada Canadian Forest Service Ottawa, Ontario K1A 1G5 A microfiche edition of this publication may be purchased from: Micromedia Ltd. 24 Catherine Street, Suite 35 Ottawa, Ontario K2P 2G8 Editing and Production: Catherine Carmody Design and Layout: Danielle Monette Canadian Cataloguing in Publication Data Main entry under title: Health of sugar maple in Canada: results from the North American Maple Project, (Information report; ST-X-1) Text in English and French. Title on added t.p. inverted: La santé de l érable à sucre au Canada. Includes bibliographical references. ISBN X Cat. no. Fo29-33/ Maple Canada. 2. Tree declines Canada. 3. Maple sugar industry Canada. I. Canadian Forest Service. Science and Sustainable Development Directorate. II. Title: Results from the North American Maple Project, III. Title: La santé de l érable à sucre au Canada. IV. Series: Information report (Canadian Forest Service. Science and Sustainable Development Directorate); ST-X-1. SB68.M34H C E Printed on recycled paper PRINTED IN CANADA Printed on alkaline permanent paper

4 Contents Abstract Introduction Materials and Methods The Monitoring Network Data Analysis Data Quality Assurance Results and Discussion Stand Comparisons Dieback and Transparency Levels Between s Between Sugar Bush and Non-Sugar Bush Stands Between Regions Between Tree Diameter Classes Tree Mortality Dieback and Deposition Levels Changes in Crown Condition Fate of Trees Dieback and Taphole Closure Conclusions References

5

6 5 Abstract The North American Sugar Maple Project (NAMP) is a joint project of the Canadian Forest Service, Natural Resources Canada, and the United States Department of Agriculture Forest Service, initiated in 1988 with the goal of monitoring changes in crown condition of sugar maple (Acer saccharum Marsh.). The project includes 233 sites throughout the range of sugar maple in eastern North America. This report describes the condition of sugar maple for the 62 sites in Canada from 1988 to 1993; half of the trees were in sugar bushes (stands managed for sap production) and half in stands not managed as sugar bushes. In general, the condition of sugar maple crowns improved between 1988 and 1993, particularly in Quebec, which had the highest level of crown dieback in In Ontario, trees were affected by drought and defoliation by insects. Trees in New Brunswick and Nova Scotia remained in good condition. Differences in crown condition were small between stands managed for sap production and non-sugar bushes, and between sites with different levels of wet acidic sulfate and nitrate precipitation. Dieback and transparency levels increased with increasing tree diameter. Tree mortality was higher in the intermediate/suppressed crown classes than in the dominant/codominant classes, and was higher in the larger diameter classes. Mortality did not differ between sugar bush and non-sugar bush stands. Trees with high initial levels of dieback showed a greater tendency to decline further than those with low levels of damage. The rate of taphole closure was significantly reduced as dieback levels increased. Introduction Sugar maple (Acer saccharum Marsh.) is one of the most important hardwood species in eastern Canada. It is valued for wood and syrup production, for its aesthetic qualities and as a national symbol. Canada produces between 8% and 85% of the world s maple syrup; Vermont and New York are the largest producers in the United States. In 1991, the value of the maple syrup industry in Canada was $7.8 million, the largest proportion of this amount going to Quebec (Bureau de la Statistique du Québec 1992). The sugar maple also influences the life-style of many Canadians. The wood is prized for furniture. The maple syrup cottage industry makes headline news, with thousands of Canadians flocking to sugar bushes when the sap starts to run in the spring. The leaf colors draw people out to admire the spectacular autumn landscape. For these reasons any threat to the health of the sugar maple is of national concern. Governments are expected to know its state of health and to take remedial action if appropriate. The health of forests is particularly important today with the greater public awareness and interest in the value of the forest as a multiple-use resource. Perceived stressors such as climate change, air pollutants, and human impact on the forest pose questions about current and future forest health and sustainability. Data on the current health and condition of the forest are necessary to answer basic questions about the resource. We also need to be aware of the influences of growth-impacting stressors and be able to explain changes in tree condition. Monitoring networks such as the North American Maple Project (NAMP) provide the knowledge to respond to these issues. Episodes of deterioration of maple have been reported previously (McIlveen et al. 1986; Walker et al. 199; Millers et al. 1989). In response to concern over the fate of sugar maple, various regional studies have been undertaken to evaluate the situation and to determine the reasons for the decline (Lachance 1985; McLaughlin et al. 1985; Hendershot and Jones 1989; Gross 1991; Ouimet and Fortin 1992). In 1988, NAMP established a network of 166 monitoring sites in the northeastern United States and Canada covering most of the range of sugar maple. At that time, four Canadian provinces and seven states were participating in the project. Today, three more states have joined and additional monitoring sites have been established for a total of 233. NAMP is a joint project between the United States Department of Agriculture Forest Service and the Canadian Forest Service (CFS), Natural Resources Canada (Millers et al. 1991). The objectives of NAMP are to determine the rate of annual change in sugar maple condition; whether the rate of change in sugar maple condition differs with the level of sulfate and nitrate wet deposition, between a sugar bush and undisturbed forest, and for various levels of initial stand decline conditions; and the possible causes of sugar maple decline and the geographical relationships between potential causes and extent of decline.

7 6 Results of the program have been published intermittently (Millers et al. 1992, 1993, 1994; Allen et al. 1992). Regional information on the project is published annually in CFS forest health survey reports. This present report describes sugar maple condition based on results from the Canadian monitoring sites. Materials and Methods The Monitoring Network A NAMP monitoring site consists of a plot-cluster of five 2 m 2 m plots on which all trees 1 cm and more diameter at breast height (dbh) are identified. There are 62 monitoring sites in Canada: 24 in Ontario, 24 in Quebec, 12 in New Brunswick, and 2 in Nova Scotia (Fig. 1). As much as possible, sites were paired, one being established in a stand currently tapped for maple sap (sugar bush), the other in a nearby stand not having sustained tapping or other silvicultural treatments in the 5 years preceding plot establishment (non-sugar bush). Descriptions of plot establishment and monitoring are provided by Millers et al Stands were between 5 and 15 years, all with different levels of damage or dieback to the crown, and contained over 5% of sugar maple trees in the overstory. Attempts were made to distribute the plot system across the range of sugar maple in Canada. To ensure that human disturbances had not occurred in unmanaged plots and that sites were accessible for annual assessments, locations were not chosen randomly In addition, the presence of many sugar maple stands on private property further complicated site selection. Stand health condition varied, but those showing very severe decline symptoms were avoided since it might be impractical to perform long-term monitoring on these plots. At plot establishment, data on plot-cluster location, site description, stand description (age, dbh, species composition, disturbance, tapping, crown classes, etc.) were taken (Millers et al. 1991). Annual measurements included defoliation, tree vigor, new damage on boles, and an assessment of crown condition. Crown condition assessment was based on dieback and transparency. Dieback is defined as branch mortality that begins at the terminal portion of a branch and progresses downward and is assumed to be the result of stress. It is estimated as a proportion of the crown that shows this condition and is recorded in 1% classes, with % and 1% 5% classes included. Trees in the first three classes, % 15% dieback, are considered to be in good condition. 1 2 Sugar bush Undisturbed forest Kilometres Figure 1. Location of NAMP monitoring sites in Canada.

8 7 Transparency is defined as the amount of skylight visible through the foliated portion of the crown and thus is the opposite of foliage density. An estimate for transparency is averaged for the living crown as a whole and recorded in the same percent classes as dieback. A crown transparency up to 25% is considered normal for a healthy sugar maple. Drought, particular weather conditions at time of flushing, and insect defoliation significantly impact transparency, but generally good growth the following year will bring back thick foliation. However, if a stand as a whole is above 25% transparency, this may indicate significant stress with the possibility of dieback appearing the next year. Data Analysis Plots were measured annually by the CFS Forest Insect and Disease Survey (FIDS) (Millers et al. 1991). Data management, storage, and analysis were provided by the State University of New York, College of Environmental Science and Forestry, Syracuse, New York. Additional analyses were obtained from CFS collaborators. This report describes only data collected from live dominant and codominant trees, unless otherwise stated. Averages of crown dieback and transparency were based on individual plot cluster averages (Allen et al. 1992). A oneway analysis of variance (ANOVA) at a significance level of p =.5 was used to test differences between means. Scheffé s method was used for comparisons of means of dieback and transparency. Differences in dieback and transparency with respect to diameter classes were also evaluated and grouped according to the classes used in tapping recommendations for Ontario conditions (Coons 1987). Average cluster dieback and transparency between various air pollutant deposition zones were compared. Fiveyear mean values from 1986 to 199 for wet deposition for each plot location were obtained from Environment Canada, Downsview, Ontario. Plots were divided into zones of low ( 15 kg/ha), medium (16 25 kg/ha), or high (>25 kg/ha) sulfate deposition zones, and low (1 15 kg/ha), medium (16 2 kg/ha), and high (>2 kg/ha) nitrate deposition zones. Data Quality Assurance High quality and consistency of the data were a prerequisite for this project. A system of quality assurance was established to ensure comparability of data collected by a variety of people over time and space. People measuring trees attended a training and certification session immediately before the field season. These sessions were held by the project s national scientific coordinators. Quality control was further ensured by having two certified crown raters simultaneously rate dieback and transparency from opposite sides of a tree. Crown dieback and transparency were remeasured for at least 5% of the trees by another team within 2 3 weeks of the first visit. The data were then compared with the first series. Less than 1% error from the project limits of one class above or below the original measurement was accepted (Burkman et al. 199). Otherwise the data were rejected and the plots remeasured. Thus far the quality of data has been in the range of 95% acceptable measurements for dieback and 92% for transparency (Millers et al. 1993). Results and Discussion Stand Comparisons The plots contained 3172 dominant/codominant sugar maples, divided almost equally between sugar bush and non-sugar bush stands (Table 1). Sugar maple comprised 78.1% of the trees in the plots; the other species were monitored, but the data are not reported here. Overall, about 5% of the sugar maples in both sugar bush and non-sugar bush stands were between 1 and 24 cm dbh (Table 2). Smaller trees were more prevalent in the New Brunswick/Nova Scotia plots. However, in Quebec and Ontario, larger trees, cm dbh, formed as large or a larger percentage of the stands as the smaller trees. Ontario had the highest percentage of large trees (61+ cm dbh) in the network. In all provinces, smaller (1 24 cm dbh) trees were more prevalent in non-sugar bush plots. Dieback and Transparency Levels Between s Nationally, there was no significant difference in dieback on trees between years either in sugar bush (p =.4) or in non-sugar bush stands (p =.51). The percentage of dominant/codominant trees with % 15% dieback (i.e., in good condition) was more than 9% every year from 1988 to 1993 (Table 3). Sugar bush trees in Quebec showed an improvement in crown condition in 1989 and 199 as evidenced by the increase in the percentage of trees in low dieback levels and the decrease in the percentage of trees in higher levels (Table 3; Figs. 2-5). Periods of drought and defoliation by the forest tent caterpillar (Malacosoma disstria Hbn.) in Ontario during 1988 and 1989 prevented an improvement in tree condition in Ontario (Forestry Canada 1992). Trees in New Brunswick and Nova Scotia improved slightly, although their general condition was good at the beginning of the study.

9 8 The improvement in crown condition is supported by results of other surveys in Quebec (Gagnon and Roy 1992) and Ontario (Hopkin and Dumond 1994). Gagnon and Roy described an improvement in crown condition in 1989 followed by stable conditions. The degree of improvement varied throughout the province. Results from a network established in Ontario in 1987 show that the health of sugar maple is generally characterized as good and tree condition is improving from levels recorded in 1987 (Hopkin and Dumond 1994). Isolated areas of decline were observed, caused by drought and defoliation. Statistically significant differences in crown transparency occurred between years and between regions (Table 4). Higher transparency values occurred in all regions in 1989, and transparency was particularly high in Quebec in Table 1. Dominant and codominant tree species in the North American Maple Project (NAMP) in Canada. Number of trees (% of total) Tree species Canada Ontario Quebec N.B./N.S. Sugar maple (Acer saccharum Marsh.) 1 SB 1641 (83.) 456 (88.5) 64 (86.4) 545 (75.5) NSB 1531 (73.4) 472 (73.4) 66 (8.5) 399 (64.1) Total 3172 (78.1) 928 (8.1) 13 (83.3) 944 (7.2) American beech (Fagus grandifolia Ehrh.) 15 (3.7) 53 (4.6) 24 (1.5) 54 (4.) Red maple (Acer rubrum L.) 136 (3.3) 29 (2.5) 35 (2.2) 91 (6.8) Yellow birch (Betula alleghaniensis Britt.) 132 (3.2) 9 (.8) 58 (3.7) 65 (4.8) Ash (Fagus sp.) 83 (2.) 55 (4.7) 27 (1.7) 1 (.1) Basswood (Tilia americana L.) 5 (1.2) 3 (2.6) 2 (1.3) (.) Cherry (Prunus sp.) 42 (1.) 29 (2.5) 13 (.8) (.) Other species 2 15 (3.7) 53 (4.6) 24 (1.5) 54 (4.) 1 SB = sugar bush; NSB = non-sugar bush. Based on 1988 data at establishment. Table 2. Diameter at breast height (dbh) frequency for dominant and codominant sugar maple in sugar bush (SB) and non-sugar bush (NSB) plots in dbh Class Number of trees (% of total) (cm) Plot type Canada Ontario Quebec N.B./N.S SB 716 (43.6) 19 (23.9) 229 (35.8) 378 (69.4) NSB 763 (49.8) 157 (33.3) 291 (44.1) 315 (78.9) SB 528 (32.2) 148 (32.5) 248 (38.8) 132 (24.2) NSB 53 (34.6) 29 (44.3) 254 (38.5) 67 (16.8) SB 219 (13.3) 87 (19.1) 15 (16.4) 27 (5.) NSB 169 (11.) 78 (16.5) 75 (11.4) 16 (4.) SB 121 (7.4) 68 (14.9) 46 (7.2) 7 (1.3) NSB 52 (3.4) 22 (4.7) 29 (4.4) 1 (.3) >61 SB 57 (3.5) 44 (9.6) 12 (1.9) 1 (.2) NSB 17 (1.1) 6 (1.3) 11 (1.7) (.)

10 9 Fluctuations in transparency are particularly noticeable when the percentages of trees in different transparency classes are compared over time (Table 5). The original plot selection may explain some of the differences in transparency levels observed in 1988 and A good growing season, such as 1993 in Quebec and the Maritimes, may result in low transparency values (Figs. 4b, 5b). Conversely, the poor growing season during 1992 in Quebec, with dry conditions in May at the time of leaf flushing followed by a cold, wet summer, resulted in transparency levels higher than both the preceding and the following year. Transparency is a sensitive stress parameter requiring continual monitoring of factors affecting growth to be able to explain changes. Table 3. Frequency of dieback for dominant and codominant sugar maple. Dieback (% of trees at each dieback level) Region level (%) Canada > Ontario > Quebec > N.B./N.S > Table 4. Comparison of average annual cluster transparency of dominant and codominant sugar maple in sugar bush (SB) and non-sugar bush (NSB) stands between years. (average transparency ± standard error) Region Canada SB 17.4 ± 1.3 ab 21.3 ± 1.1 a 15.5 ±.8 bc 12.3 ±.4 c 14.8 ±.8 bc 11.5 ±.8 c NSB 15.7 ± 1.5 ab 19.8 ± 1. a 14.4 ±.7 b 11.8 ±.4 b 14.1 ±.7 b 12. ±.8 b Ontario SB 13.9 ± 1. ab 19.3 ± 2.2 a 15.2 ± 1.2 ab 11.7 ±.7 b 16.6 ±.9 ab 15.8 ±.9 ab NSB 11.7 ± 1.1 a 16.1 ± 1.8 a 14.4 ± 1.5 a 11.5 ±.8 a 15. ± 1.1 a 16.3 ±.8 a Quebec SB 24.1 ± 2. a 24.3 ± 1. a 16.6 ± 1.5 b 13.2 ±.4 bc 16.6 ±.8 b 8.6 ±.5 c NSB 21.7 ± 2.7 ad 23.3 ±.9 a 14.8 ±.8 bc 12.5 ±.4 bc 16. ±.8 bd 9.4 ± 1. c N.B./N.S. SB 12. ± 1. a 19.8 ± 2. b 14. ± 2. a 11.8 ± 1.2 a 8.7 ±.7 a 9.2 ±.9 a NSB 1.6 ±.6 a 2.3 ± 1.8 b 13.7 ±.7 a 11.3 ± 1.1 a 9.5 ±.9 a 9.1 ±.4 a Note: Means within a row followed by the same letter are not significantly different (p.5).

11 1 2 (a) Dieback 1 (b) Transparency % >35% Figure 2. Percent of trees, by year, with moderate and high levels of (a) dieback and (b) transparency for dominant and codominant sugar maple in Canada. 2 (a) Dieback 1 (b) Transparency % >35% Figure 3. Percent of trees, by year, with moderate and high levels of (a) dieback and (b) transparency for dominant and codominant sugar maple in Ontario.

12 11 2 (a) Dieback 1 (b) Transparency % >35% Figure 4. Percent of trees, by year, with moderate and high levels of (a) dieback and (b) transparency for dominant and codominant sugar maple in Quebec. 2 (a) Dieback 1 (b) Transparency % >35% Figure 5. Percent of trees, by year, with moderate and high levels of (a) dieback and (b) transparency for dominant and codominant sugar maple in New Brunswick and Nova Scotia.

13 12 Annual fluctuations in transparency levels are not necessarily correlated with dieback (Figs. 2b 5b). The relatively high levels of transparency during 1989 in Quebec and the Maritimes correspond to relatively low levels of dieback during the period, but transparency does not have adirect affect on the level of dieback and seems to be an independent stress parameter related to current growth conditions. The transparency of trees in Ontario is relatively stable with little year-to-year fluctuation unlike Quebec and New Brunswick/Nova Scotia, which show large fluctuations from 1989 to 1993 (Figs. 3b 5b). Between Sugar Bush and Non-Sugar Bush Stands Statistically significant differences were observed in levels of dieback between sugar bush and non-sugar bush stands (p =.1). However, this difference was confined to the period and was largely influenced by plots in Quebec (Table 6). In Quebec, the site selection procedures emphasized variations in dieback levels between sites and the need for easy accessibility. This resulted in higher initial levels of dieback in Quebec than elsewhere (Fig. 6). The consequent unequal pairing of sugar bush and non-sugar bush study sites may have exaggerated the differences. However, once severely affected trees began to recover, the difference between sugar bush and non-sugar bush stands diminished. In all three regions and in most years dieback was higher in sugar bush than in non-sugar bush stands, suggesting more stress in the former group. Human activity is more frequent in sugar bush than in non-sugar bush stands, which may stress the ecosystem more. Stress factors included soil compaction, modified drainage, and root or stump wounding, all of which result from human activities. Most sugar bushes have been managed for sap for several years, and differences are possibly due to the type and proportion of trees present in each stand type. Sugar bushes are likely to have fewer stems per hectare, more large-crowned and older trees, and fewer other species than non-sugar bushes. Thus, a sugar bush is a relatively pure and mature stand, situated on a modified site that may be more sensitive to incidental stress than undisturbed natural stands. Overall, however, these differences in dieback between sugar bush versus non-sugar bush are slight. Millers et al. (1992) on analyzing data from more than 7 trees reported that approximately 86% of the sugar maple trees with more than 5% dieback had major damage to boles and roots. This type of damage is also more likely to occur in a sugar bush than in natural stand. Our data also show higher levels of dieback on the more damaged trees (Table 7), but a larger sample of trees would be needed to confirm this. No significant difference in transparency was observed between sugar bush and non-sugar bush stands (p =.75, Table 4). Again the pattern of variation was similar. Table 5. Frequency of transparency for dominant and codominant sugar maple. Transparency (% of trees at each transparency level) Region level (%) Canada > Ontario > Quebec > N.B./N.S >

14 13 Mean Cluster Dieback % 6 15% 16 25% Kilometres Figure 6. Location of NAMP monitoring sites by dieback levels in Table 6. Comparison of average annual cluster dieback between sugar bush (SB) and non-sugar bush (NSB) stands of dominant and codominant sugar maple in each region. (average dieback standard error) Region Canada SB 9. ±.8 a 8.2 ±.8 a 7.6 ±.6 a 7.7 ±.6 a 8. ±.6 a 7.1 ±.5 a NSB 6.2 ±.5 b 5.7 ±.4 b 6.1 ±.3 b 6.5 ±.4 a 6.7 ±.4 a 6.3 ±.4 a Ontario SB 7. ±.8 a 8.4 ±.8 a 7.8 ± 1. a 8.1 ± 1.3 a 8.3 ± 1.2 a 6.6 ± 1.1 a NSB 5.2 ±.9 a 6.2 ±.7 b 6.8 ±.6 a 6.7 ±.7 a 6.7 ±.8 a 6.1 ±.9 a Quebec SB 11.8 ± 1.7 a 9.5 ± 1.7 a 8.6 ± 1.1 a 7.8 ±.7 a 8.6 ± 1. a 7.9 ±.7 a NSB 7. ±.7 b 5.4 ±.6 b 5.9 ±.6 b 6. ±.5 a 6.5 ±.6 a 6.6 ±.5 a N.B./N.S. SB 7.7 ±.8 a 5.7 ±.3 a 5.8 ±.4 a 6.9 ±.8 a 6.6 ±.7 a 6.4 ±.6 a NSB 6.3 ±.5 a 5.4 ±.2 a 5.4 ±.3 a 7. ±.5 a 7.1 ±.9 a 6.1 ±.2 a Note: Means comparing sugar bush (SB) to non-sugar bush (NSB) annual dieback within each region are not significant if followed by the same letter (p.5).

15 14 Table 7. Stem damage by dieback class of dominant and codominant sugar maple in Dieback level (%) Percent of trees with damaged stems > Between Regions The average annual dieback was not significantly different between regions or in sugar bush and non-sugar bush stands, except during 1988 when plots in Quebec had higher levels of dieback than the other provinces (Table 8; Fig. 6). Analysis of crown transparency showed significant differences between regions in some years (Table 9). Transparency data varied widely from year to year and sometimes among provinces. This suggests that transparency is strongly influenced by local environment. Any stress on the tree, such as drought, defoliation, or windstorm, could cause these differences. Table 8. Average cluster dieback of dominant and codominant sugar maple in sugar bush (SB) and non-sugar bush (NSB) stands, (average dieback ± standard error) Region SB Ontario 7. ±.8 a 8.4 ±.8 a 7.8 ± 1. a 8.1 ± 1.3 a 8.3 ± 1.2 a 6.6 ± 1.1 a Quebec 11.8 ± 1.7 b 9.5 ± 1.7 a 8.6 ± 1.1 a 7.8 ±.7 a 8.6 ± 1. a 7.9 ±.9 a N.B./N.S. 7.7 ±.8 ab 5.7 ± 1.5 a 5.8 ±.4 a 6.9 ± 1.3 a 6.6 ±.7 a 6.4 ± 1.1 a NSB Ontario 5.2 ±.9 a 6.2 ±.7 a 6.8 ±.6 a 6.7 ±.7 a 6.7 ±.8 a 6.1 ±.9 a Quebec 7. ±.7 a 5.4 ±.6 a 5.9 ±.6 a 6. ±.5 a 6.5 ±.6 a 6.6 ±.5 a N.B./N.S. 6.3 ±.5 a 5.4 ±.2 a 5.4 ±.3 a 7. ±.5 a 7.1 ±.9 a 6.1 ±.2 a Note: Means within a column followed by the same letter are not significantly different (p.5). Table 9. Average cluster transparency of dominant and codominant sugar maple in sugar bush (SB) and non-sugar bush (NSB) stands, (average transparency ± standard error) Region SB Ontario 13.9 ± 1. a 19.3 ± 2.2 a 15.2 ± 1.2 a 11.7 ±.7 a 16.6 ±.9 a 15.8 ±.9 a Quebec 24.1 ± 2. b 24.3 ± 1. a 16.6 ± 1.5 a 13.2 ±.4 a 16.5 ±.8 a 8.6 ±.5 b N.B./N.S. 12. ± 1. a 19.8 ± 2. a 14. ±.7 a 11.8 ± 1.2 a 8.7 ±.7 b 9.2 ±.9 b NSB Ontario 11.7 ± 1.1 a 16.1 ± 1.8 a 14.4 ± 1.5 a 11.5 ±.8 a 15. ± 1.1 a 16.3 ±.8 a Quebec 21.7 ± 2.7 b 23.3 ±.9 b 14.8 ±.8 a 12.5 ±.4 a 16. ±.8 a 9.4 ± 1. b N.B./N.S. 1.6 ±.6 a 2.3 ± 1.8 ab 13.7 ±.7 a 11.3 ± 1. a 9.5 ±.9 b 9.1 ±.4 b Note: Means within a column followed by the same letter are not significantly different (p.5).

16 15 Between Tree Diameter Classes Due to the small sample size of larger diameter trees, sugar bush and non-sugar bush plots were combined for the analysis. Average crown dieback and transparency were significantly higher in the larger diameter classes (Tables 1, 11). The percentage of trees with lower levels of dieback (Fig. 7) and transparency (Fig. 8) decreased with increasing diameter in all years. For dieback, the proportion of healthy trees declined from 94% to 82% and from 98% to 75% with increasing diameter classes in 1988 and in 1993 respectively. Table 1. Average dieback by dbh class of dominant and codominant sugar maple. dbh Class (average dieback ± standard error) (cm) ±.2 a 5.7 ±.2 a 5.7 ±.2 a 6.4 ±.2 a 6.4 ±.2 a 5.8 ±.2 a (n = 1465) ±.3 ab 6.9 ±.2 b 6.8 ±.2 b 7. ±.2 a 7.2 ±.2 a 6.3 ±.2 a (n = 153) ±.5 b 8. ±.4 bc 7.4 ±.3 b 7.4 ±.3 ab 8.3 ±.4 b 7.5 ±.3 b (n = 387) ±.7 c 9.6 ±.6 c 8.5 ±.5 bc 8.8 ±.5 bc 9.5 ±.5 b 8.5 ±.5 b (n = 172) > ± 1.1 bc 1.5 ±.9 c 1.4 ±.8 c 11.8 ±.8 c 13. ±.8 c 12.5 ±.7 c (n = 74) Note: Means within a column followed by the same letter are not significantly different (p.5). n = Number of trees in Table 11. Average transparency by dbh class of dominant and codominant sugar maple. dbh Class (average transparency ± standard error) (cm) ±.3 a 2.2 ±.2 a 13.8 ±.2 a 11.4 ±.1 a 11.6 ±.2 a 1. ±.2 a (n =1465) ±.3 b 21.3 ±.3 ab 15.2 ±.2 b 12. ±.2 ab 14.7 ±.2 b 11.4 ±.2 b (n = 153) ±.5 b 22. ±.5 bc 16.7 ±.4 c 12.8 ±.3 b 16.2 ±.4 c 12.2 ±.3 bc (n = 387) ±.8 c 23. ±.7 bc 15.7 ±.5 bc 12.6 ±.4 ab 17.8 ±.6 c 13.2 ±.5 cd (n = 172) > ± 1.2 c 25.4 ± 1.1 c 18. ±.8 c 13.3 ±.7 ab 18.8 ±.8 c 14.7 ±.7 d (n = 74) Note: Means within a column followed by the same letter are not significantly different (p.5). n = Number of trees in 1988.

17 16 1 (a) Dieback (b) Dieback >61 dbh Class >61 dbh Class 15% 16 55% >55% Figure 7. Percent of trees with low, moderate, and high levels of dieback in (a) 1988 and (b) 1993 by dbh class of dominant and codominant sugar maple. 1 (a) Transparency (b) Transparency >61 dbh Class >61 dbh Class 15% 16 35% >35% Figure 8. Percent of trees with low, moderate, and high levels of transparency in (a) 1988 and (b) 1993 by dbh class of dominant and codominant sugar maple.

18 17 Tree Mortality Mortality rate is a good indicator of forest health when averaged over several years and if the development stage of the stand is considered. This is also an easy and rapid parameter to measure. NAMP stands are mostly semi-mature and thus mortality caused by natural stand thinning should be low. The data include trees that died from natural cause(s), some of which were subsequently cut, but they do not include living trees that were cut for management purposes. Average annual mortality for 1988 to 1993 was below 1% for dominant/codominant trees everywhere except for sugar bush trees in Quebec, where initial dieback was highest (Table 12). Mortality rates were lowest in the New Brunswick/Nova Scotia plots. Mortality was consistently Table 12. Average annual mortality (%) of dominant and codominant sugar maple, Region Sugar bushes Non-sugar bushes Canada.62.6 Ontario Quebec N.B./N.S higher for trees in the intermediate/suppressed crown classes than in the dominant or codominant classes (Fig. 9). This is a normal situation for semi-mature stands where competition for space affects mainly suppressed, less vigorous trees. There does not appear to be a difference in mortality rates between sugar bush and non-sugar bush sites. Within the dominant and codominant trees, the mortality rate increased with dbh. Fewer large trees (dbh >49 cm) died in sugar bush plots, likely a result of removal of decayed or moribund trees. Dieback and Deposition Levels One of the objectives of NAMP is to evaluate the relationship between levels of dieback and transparency and wet acidic deposition. Plots were established in areas of low, medium, and high levels of deposition. The levels for sulfate were low, 15 kg/(ha yr); medium, kg/(ha yr); and high, >25 kg/(ha yr). For nitrates, the levels were low, 15 kg/(ha yr); medium, 16 2 kg/(ha yr); and high, >2 kg/(ha yr). No consistent relationships were found between sulfate and nitrate deposition levels and dieback or transparency (Tables 13, 14). However, for nitrate deposition, the data suggest a tendency of greater dieback at higher levels of deposition. Dieback averages were in general slightly higher at higher levels of deposition, but differences were % Mortality Dominant/Codominant Sugar bush (n = 1641) Non-sugar bush (n = 1528) Intermediate/Suppressed (n = 633) (n = 586) Figure 9. Annual mortality of sugar maple by crown position and stand type.

19 18 statistically significant in only 2 out of the 6 years (1989, 199) and only between low and high levels of nitrate deposition. The differences are less than 3% and probably not biologically significant, although the possible effects over time are unknown. The transparency data suggest a weak relationship with deposition levels but there are exceptions to any trend. In the case of the sulfate deposition zones, transparency levels were statistically higher at the medium level of deposition compared with the low one in 1988 and 1992, and at the high level compared with the medium in However, the transparency levels were also lower, though not statistically significant, at the high level of deposition compared with the medium one in all years from 1988 to 1992 inclusively. The absence of a clear trend in Table 13 as well as the annual variation in transparency levels complicates the interpretation of results (Figs. 2 5). A statistically significant difference in average transparency was observed between low and medium levels of sulfate and nitrate deposition, both in 1992, and between low and high levels in 1988 and 1993 (Tables 13 and 14). This trend of increased transparency with higher levels of nitrate deposition is weak. Transparency levels vary significantly from year to year (1988 vs vs. 199) irrespective of deposition levels, so that a possible trend in the data in one year may be contradicted the following year. For example, the trend in 1988 of increasing transparency from low to high deposition is not consistent with the data of In addition, differences in transparency levels of 4% 6% are probably not biologically significant. Sulfate and nitrate deposition is generally low in New Brunswick/Nova Scotia, and high west of Lake Ontario (Figs. 1, 11). In between, there are four sites with high sulfate deposition in Quebec and a mixture of high and medium Table 13. Average dieback at low, medium, and high excess sulphate deposition levels for dominant and codominant sugar maple. Excess sulfate deposition levels (average dieback ± standard error) Dieback Transparency Low Medium High Low Medium High ± 1.3 a 7.9 ±.7 a 7.4 ± 1.2 a 11.2 ± 2.3 a 18.2 ± 1.2 b 15.7 ± 1.2 ab ± 1. a 7.3 ±.6 a 7.3 ± 1. a 2.6 ± 1.7 a 21.6 ±.9 a 17.4 ± 1. a ±.8 a 6.8 ±.4 a 8.1 ±.8 a 13.7 ± 1.1 a 15.7 ±.6 a 13.6 ±.8 a ±.8 a 6.9 ±.5 a 7.8 ±.8 a 11.3 ±.6 a 12.6 ±.4 a 11. ±.8 a ±.9 a 7.4 ±.5 a 7.5 ±.9 a 9.1 ±.9 a 16.2 ±.5 b 14.4 ±.9 b ±.8 a 6.9 ±.4 a 6.4 ±.8 a 9.3 ± 1.2 a 11.8 ±.7 a 14. ±.8 b Note: Excess sulfate levels: Low = 15 kg/ha (n = 12); medium = kg/ha (n = 38); high = >25 kg/ha (n = 12). Means within a row followed by the same letter are not significantly different (p.5). Table 14. Average dieback and transparency levels at low, medium, and high nitrate deposition levels for dominant and codominant sugar maple. Nitrate deposition levels (average dieback ± standard error) Dieback Transparency Low Medium High Low Medium High ± 1. a 7.3 ± 1. a 8.1 ±.8 a 12.7 ± 1.8 a 15.8 ± 1.8 ab 19.2 ± 1.4 b ±.8 a 6.7 ±.8 ab 8.1 ±.6 b 2.6 ± 1.4 a 2. ± 1.5 a 2.9 ± 1.1 a ±.6 a 6.3 ±.6 ab 8.2 ±.5 b 13.5 ±.9 a 14.9 ± 1. a 15.8 ±.7 a ±.6 a 6. ±.7 a 8. ±.5 a 11.6 ±.5 a 11.8 ±.6 a 12.4 ±.4 a ±.7 a 6.9 ±.7 a 8.1 ±.6 a 1.2 ±.7 a 16.8 ±.7 b 15.9 ±.6 b ±.6 a 6.4 ±.6 a 7.2 ±.5 a 9.5 ±.9 a 11.1 ± 1. ab 13.6 ±.7 b Note: Nitrate levels: Low = 15 kg/ha (n = 18); medium = 16 2 kg/ha (n = 16); high = >2 kg/ha (n = 28). Means within a row followed by the same letter are not significantly different (p.5).

20 19 NAMP Plot Locations at Excess Sulfate Levels 1 2 Kilometres Low ( 15 kg/ha) Medium (16 25 kg/ha) High (>25 kg/ha) Figure 1. Location of NAMP monitoring sites by excess sulfate deposition levels, NAMP Plot Locations at Nitrate Levels 1 2 Kilometres Low ( 15 kg/ha) Medium (16 2 kg/ha) High (>2 kg/ha) Figure 11. Location of NAMP monitoring sites by nitrate deposition levels,

21 2 Mean Cluster Transparency % 16 35% Kilometres Figure 12. Location of NAMP monitoring sites by transparency levels in deposition levels of nitrate. Comparing this with the 1988 dieback and transparency situations, which were relatively severe in that year, there is a weak relationship between these parameters only in New Brunswick/Nova Scotia, where all three parameters are low (Figs. 6, 12). On the other hand, dieback and transparency were at low levels west of Lake Ontario, where deposition is high. Only 2 of the 4 high dieback sites in Quebec in 1988 correspond with high deposition levels (Fig. 6). The other sites in Quebec and Ontario do not follow any pattern. It is probable that site characteristics, such as soil depth, soil fertility, buffering capacity, drainage, site exposure, insect defoliations, and drought or freezing, have more impact on dieback and transparency levels than deposition. In addition, deposition of pollutants varies in intensity and location from year to year so that some individual plots may be in different deposition zones in different years. Overall, these results are similar to those reported by Allen et al. 1992, which did not show a relationship between dieback and transparency and levels of pollutant deposition. Changes in Crown Condition To detect and evaluate change in stand conditions the mean dieback and transparency level for each cluster of plots was calculated and grouped over time. Dieback classes used here were % 5%, 6% 15%, 16% 25%, and >25%. Transparency classes were % 15%, 16% 35%, and >35%. The data for show the changes over the period (Figs. 13, 14). In 1993, about 23% of the sites had improved by one dieback class over 1988, while almost 65% remained in the same class. Dieback was higher on the remaining 12% of the sites. Differences between provinces were noted (Fig. 13). In Ontario, 79% of the sites remained in the same dieback class, only one site deteriorated. In New Brunswick/Nova Scotia with dieback levels relatively low in 1988, 43% of the sites remained unchanged, while half the remainder improved or deteriorated. Transparency varied from year to year according to current growth conditions. Thus, a poor growing season in 1988 could be compared with a good one in 1993, and the conclusion reached that the trees were more vigorous. However, a change in growing conditions could quickly alter tree vigor the following year. Large differences were observed between provinces with respect to transparency from 1988 to 1993 (Fig. 14). In New Brunswick/Nova Scotia, 86% of the sites remained unchanged and the rest improved. In Quebec, a similar picture of stability and improvement emerged

22 21 NAMP Plot Dieback Trends Kilometres Reduced dieback No change Increased dieback Figure 13. Changes in dieback level of sugar maple by at least one 1% class between 1988 and NAMP Plot Transparency Trends Kilometres Reduced transparency No change Increased transparency Figure 14. Changes in transparency level of sugar maple by at least one 1% class between 1988 and 1993.

23 22 but here only 33% of the sites remained stable, while all others improved. In Ontario, 54% of the trees had higher transparency in 1993 compared with 1988, while 12% improved. The impact of drought and defoliation by the forest tent caterpillar in the early 199s affected transparency levels in Ontario. Fate of Trees Predictions of the future condition of trees could help sugar bush managers decide when to cut a tree affected by dieback. To develop such a tool, trees were placed into four classes according to the level of dieback in 1988: % 15%, 16% 35%, 36% 55%, and >55%, and their dieback levels were followed until 1993 (Fig. 15; Table 15). Most of the trees in the % 15% dieback class in 1988 were still healthy 5 years later; only 2.2% of them died, a relatively normal condition for a forest stand. Most trees (69%) in the 16% 35% dieback class in 1988 (69%) improved to 15% or less dieback. Total mortality was 1.5% or about 2% per year, again a normal rate. However, trees in the 36% 55% dieback class fared less well. Only about 43% improved to the relatively healthy class of 15% or less; and 31.4% died during the period, about 6% annually. The group of trees with more than 55% dieback continued to deteriorate and after 5 years, only 8% were healthy, 12% improved to the 16% 35% dieback class, and 75% died (Fig. 15). Thus, once a tree has more than 55% dieback, it will likely die within 5 years. A comparable study with different levels of dieback showed a similar trend (Paradis 1993). During a 4-year period, more trees died and fewer trees improved among the trees that were originally in high dieback classes compared with those in the lower classes. Although mortality rates were somewhat lower for the higher dieback classes, similar trends were observed. Gross (1991) showed that 2% of dominant/ codominant trees with >4% dieback died after 2 seasons. Paradis (1993) showed that 25% of trees with >6% dieback died after 4 seasons. It is important to differentiate between the fate of stands of trees and that of an individual tree. A tree in a relatively healthy stand may have a high level of dieback. In a stand severely affected by dieback, the increase in light intensity and possibly temperature, as well as the reduced competition because of the dying or dead trees, may benefit and stimulate the regeneration and growth of trees in the lower Table 15. Fate of dominant and codominant sugar maple at various dieback levels. Fate Dieback (% of trees at each dieback level) category (%) level (%) > Dead > Dead > Dead > > Dead

24 23 1 (a) Dieback 15% 1 ;; (b) Dieback 16 35% ;; (c) Dieback 36 55% 1 ; ; ;; ;; ; 8 ;; 6 ;; 4 ;; (d) Dieback >55% ;; 8 ;; ;; 6 ;; ;; ;; ;; 4 ;; ;; ;; ;; 2 ;; % 16 35% 36 55% >55% Dead Figure 15. Fate of dominant and codominant sugar maple in 1993 in relation to dieback levels in 1988: (a) % 15% (n=2519); (b) 16% 35% (n=172); (c) 36% 55% (n=35); and (d) >55% (n=24).

25 24 1 (a) Transparency 15% 1 (b) Transparency 16 35% ;;;; (c) Transparency >35% 1 ;; ;; ;; % 16 35% >35% Dead Figure 16. Fate of dominant and codominant sugar maple in 1993 in relation to transparency levels in 1988: (a) % 15% (n=1583); (b) 16% 35% (n=14); and (c) >35% (n=63).

26 25 canopy. These may rapidly fill in the gaps in the original canopy and result in a healthy-appearing stand in a few years. By then, trees severely affected by dieback will probably have died. The pattern of change in transparency is similar to that of dieback, except that annual variations are larger and the importance of a given level of transparency on tree vigor is less evident. There was an increase in the number of dead trees from 1988 to 1993, from 2.% to 11.%, with increasing transparency classes of % 15%, 16% 35%, and >35% (Table 16). After 5 years, in all three transparency classes the proportion of relatively healthy trees (% 35% transparency) was in the range of 88% to 97% of those in the original classes (Fig. 16). Thus, transparency does not appear to be a good predictor of future tree vigor or health. Dieback and Taphole Closure The relationship between levels of dieback and the speed of taphole closure was examined. The average number of open tapholes on trees was grouped according to four levels of dieback (Table 17). A taphole was considered open when a pencil could be inserted in the hole. The trend towards more open tapholes on trees with more dieback is evident, suggesting a reduced ability to heal wounds with increased dieback. Table 16. Fate of dominant and codominant sugar maple at various transparency levels. Fate Transparency (% of trees at each transparency level) category (%) level (%) > Dead > Dead > > Dead Table 17. Average number of open tapholes within each level of crown dieback for dominant and codominant sugar maple. Percent of crown dieback (average number of open tapholes) 5% 6 15% 16 35% >35% ±.7 a 2.6 ±.12 b 2.6 ±.19 b 5.84 ±.3 c ±.5 a 2.2 ±.12 b 2.64 ±.17 b 5.49 ±.29 c ±.5 a 1.99 ±.13 b 2.68 ±.2 b 3.97 ±.3 c ±.5 a 1.42 ±.1 b 2.48 ±.2 c 5.4 ±.33 d ±.5 a 1.71 ±.9 b 2.19 ±.2 b 5.81 ±.33 c ±.4 a 1.39 ±.1 b 2.43 ±.19 c 3.19 ±.38 c Note: Means within a row followed by the same letter are not significantly different (p.5).

27 26 Conclusions The North American Sugar Maple Project (NAMP) was established to monitor the rate of change in the crown condition of sugar maples. The NAMP conditionmonitoring method is sensitive enough to detect annual changes in transparency and yet stable enough in terms of dieback measurements to show trends. Transparency is a good indicator of current stress on trees and of variations in stress from year to year and within and between regions. There was an improvement nationally in the crown condition of sugar maples between 1988 and No significant differences between years in any region were noted for dieback. Most improvement in crown condition occurred in Quebec, while tree condition in the Maritimes remained stable. In Ontario, some sites improved, while most others remained stable. There was a general improvement in transparency over the period. Transparency increased in areas that sustained severe drought and defoliation in the early 199s. The data were consistent with other CFS reporting of forest conditions. There was no relationship between levels of acidic deposition and crown condition. A slight trend to higher transparency with increasing deposition, particularly for nitrates, was noted. Therefore, the possible impact of pollutants on sugar maple cannot be eliminated, given that other factors, such as soil properties, may synergize with deposited levels. Other stressors, including drought, insect defoliation, and soil properties, had a greater impact on crown condition. A longer term study would permit evaluation of the effect on forest health of pollutants and other stresses. Levels of dieback in stands actively managed for sap were slightly higher (but not significantly higher statistically) than in natural stands. This may be caused by the frequent incursions in sugar bushes causing more stress on the trees. This additional stress may originate from soil compaction, tree wounding, frequent light thinnings, and tapping. All stands, whatever the original condition, improved during 1989 and 199 to a level of good health. This level was maintained except in the presence of stressful environmental conditions. At the individual tree level, however, there is a significant difference in the extent and in the rate of recovery, depending on the initial level of dieback. Many of the trees with more than 55% dieback are likely to die within 5 years. Plot site selection was not made at random; thus, the only inference from original conditions can be made from NAMP data. Although the number of sampling sites is relatively low, the trends observed in general crown condition may be typical for a larger area surrounding the monitoring sites. Comparisons with results of nearby provinces or states, as well as with similar studies by other organizations, tend to support these deductions. Constant monitoring is necessary to explain the causes of stand forest decline. Stands are sensitive to environmental stress, which varies with site. The site integrates the below-ground properties with the above-ground conditions of climate and anthropogenic stresses. Changes in crown condition were explained by stressors such as drought and insect defoliation. In a recent experiment near Duchesnay, Quebec, a decline of mature sugar maple was initiated by preventing normal snow accumulation on the ground in winter, thereby causing the soil to freeze (Bertrand et al. 1994). This indicates that acute stress is more likely to trigger decline than light chronic stress such as ambient levels of pollution. The latter is probably more likely to induce a gradual, subtle change in a stand than a decline. If we are to draw conclusions on the state of the health of our forests, it is imperative that we continue to monitor forest conditions. References Allen, D.C.; Barnett, C. J.; Millers, I; Lachance, D Temporal change ( ) in sugar maple health, and factors associated with crown condition. Can. J. For. Res. 22: Bertrand, A.; Robitaille, G; Nadeau, P.; Boutin, R Effects of soil freezing and drought stress on abscisic acid content of sugar maple sap and leaves. Tree Physiol. 14: Bureau de la Statistique du Québec Statistiques Agro-alimentaires, 1 er semestre Chapitre II L acériculture. Québec. Burkman, W. G.; Millers, I.; Lachance, D Quality assurance aspects of the joint USA Canada North American Sugar Maple Decline Project. In Proceedings of the 3rd Annual Quality Control Workshop, April, 199. Burlington, Ont. Can. Centre Inland Waters, Environ. Can., Burlington, Ont. p Coons, C.F Sugar bush management for maple syrup producers. Rev. ed. Ont. Minist. Nat. Resour., Toronto. 48 p.