USDA United States 

Department of 

Agr~culture Reexamination of Effects 

Forest Service of Paraformaldehyde on 

Northeastern lorest 

Experiment Station Tissues Around Tapholes 

Research Paper NE-706 in Sugar Maple Trees 

David R. Houston 

J. Chris Fagan 
Abstract 

Pellets containing paraformaldehyde (PFA) are sometimes placed behind spouts in 

tapped sugar maples to prolong sapflow and increase the yield of sap used to make 

maple syrup.The practice is controversial because the chemical has been shown 

experimentally to promote decay and is reported to cause cambial dieback around 

tapholes. This study reexamined the effects of PFA on tapped sugar maple and 

determined how these effects also are influenced by the time of tapping and spout 

removal, and by taphole flushing. A survey of sugarbushes In Wisconsin revealed no 

re la ti oils hi^ between PFA use and cambial dieback and rate of ta~hole closure. 

Other fact& including poor tapping techniques and practices, drought, and old age 

affected these taphole attributes more than PFA. A trial conducted in eastern New 

York using young, vigorous sugar maple trees showed that PFA increased the size 

of discoloration columns associated with taphole wounds. Discoloration columns 

were smaller around the PFA tapholes made at onset of sapflow. Decay incidence 

around PFA taps was 60 to 75 percent compared to 25 percent for controls. The 

presence of decay columns increased size of discoloration columns. Tapholes 

from which PFA residues were flushed with water when spouts were pulled had the 

most and largest decay columns; columns were especially large around tapholes 

made prior to sapflow (January). Taphoies with spouts pulled just before growth 

resumed (May) had fewer and smaller decay columns than those removed earlier 

(April). 

The Authors 

DAVID R. HOUSTON was Principal Plant Pathologist at the Northeastern Center for 

Forest Health Research in Hamden, Connecticut, a laboratory of the USDA Forest 

Service Northeastern Forest Experiment Station. He joined the Forest Service in 

1961 after receiving his Ph.D. in Plant Pathology from the University of Wisconsin 

and for over 30 years he has worked primarily on dieback-decline diseases of 

deciduous hardwoods, especially beech, maple and oak. 

J. CHRIS FAGAN is Research Associate at the Center for Forest Health Research in 

Harnden, Connecticut. He obtained his B.S. in Forestry from SUNY at Syracuse in 

1972 and joined the Forest Pathology Research Team in 1974. 

Manuscript received for publication 11 December 1996 

Acknowledgments 

We thank the National Maple Syrup Council, which funded this study (Grant No. 23- 

680) and appreciate the assistance of G. Walton, USDA Forest Service, who guided 

the design and analysis of data, J. Cummings-Carlson. Wisconsin Department of 

Natural Resources, who helped locate the Wisconsin sugarbushes, and the many 

suga&ush owners who allowed us to poke and prod their trees. We also thank 

Clarence Putnam, NewYork State Department of Environmental Conservation, who 

located the site and facilitated the experimental phase of the work in New York, the 

many laboratory assistants who helped dissect and measure the insides of treated 

sugar maples, and J. Cummings-Carlson, W. Shortie, P.M. Wargo, and K.T. Smith for 

reviewing earlier drafts of the manuscript. 

PuMished by: 

USDA FOREST SERVICE 

5 RADNOR CORP CTR STE 200 

RADNOR PA 19087-4585 

For additional copies: 

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Publications Distribution 

359 Main Road 

Delaware, OH 43015 

May 1997 
Introduction 

Sap from sugar maple (Acersaffiharum Marsh.) trees can be 

collected and concentrated by boiling to produce maple 

syrup.The use of pellets containing paraformaldehyde 

(trioxymethylene) (PFA) to prolong the period of sapflow and 

thus increase the yield of sap from tapped trees is 

controversial. Dewlopment of the PFA pill to be placed behind 

spouts in taphdes followed research to determine why 

seasonal sapflows often stopped prematurely, especially 

during periods of warm weather. This research suggested that 

microorganisms present in tapholes in some way caused 

Rows to stop (Shenernan et al. 1959; Ching and Mericle 1960). 

PFA inhibited the growth of these organisms in the laboratory, 

and its influence on mow seemed confirmed by trials which 

showed reduced microbial populations in sap, and signifkantly 

increased sap yields and prolonged sap Rows when PFA was 

used (e.g., MacArthur and Blackwood 1966; Sheneman et al. 

1959). Pellets containing 250 mg PFA became widely 

accepted as a means to sanitize tapholes (Costilow et al. 

1962; Sheneman and Costilow 1959; Sheneman et al. 1959). 

With time, reports (by sugarbush owners and operators) of 

tapholes not closing, of cambial dieback around tapholes, 

and of unusual amounts of decay in wood surrwnding 

tapholes treated with PFA suggested the possibility that the 

chemical was injuring tree tissues. A series of studies 

comparing PFA-treated tapholes with untreated tapholes on 

the same tree suggested that PFA was toxic to tree tissues 

(Shigo and Laing 1970; Walters and Shigo 1978. 1979). In 

these studies, some treated trees were dissected after 2 

months and others at intervals thereafter over the next 5 

years. While the rate of taphole closure and incidence of 

cambial dieback were not affected, the incidence and extent 

of discoloration and especially of decay were significantly 

oreater in wood around ta~h0leS treated with PFA. Walters 

and Shigo (1978) concluded that PFA prolonged sapflow not 

because it inhibited microorganisms but because it inhibited 

the development of gums and other changes that comprise 

the protective barrier zones which normally develop in 

healthy tissues around wounds. 

Despite this evidence, proponents of its use maintain that 

PFA is more beneficial (economically) than harmful 

(biologically) (e.g., Reynolds 1989). and many sugarbush 

operators have reported no observed (external) damage to 

trees even where PFA has been used for many years. 

The seemingly variable damage anributable to PFA may 

result from differences in inherent or stress-induced 

responses to the chemical or to wounding, seasonal 

patterns of growth, tree condition, or tapping practices that 

affect when and how long tissues are exposed to PFA 

relative to the period of sapflow or the resumption of 

cambial activity. 

The objectives of this study were to: (1) reexamine the 

eftects of PFA on taphole closure, and on the development 

wer time of discoloration and decay associated with 

tapholes; and (2) determine whether these variables are 

influenced by dates of tapping and spout removal, or by 

flushing PFA from tapholes. Preliminary reports have been 

published (Houston 1998; Houston and Fagan 1996). 

Materials and Methods 

The study consisted of two parts: a survey of taphole 

conditions In Wisconsin sugarbushes with and without 

histories of PFA use, and an experiment that compared both 

taphole closure and the development over time of 

discoloration and decay around tapholes treated or not 

treated with PFh 

Survey of Wisconsin Sugarbushes 

In June 1991,16 sugarbushes (50 trees in each sugarbush) 

in Wisconsin (Fig. 1) in which PFA had (9) or had not (7) 

been used in recent years were surveyed for external 

evidence of damage by PFA. Each owner was interviewed to 

determine the history of PFA use, method of sap collection, 

and other possible stress factors. Measurements were made 

of tree diameter at 1.4 m (d.b.h.); crown canopy position 

(dominant, codominant. intermediate, overtopped); crown 

condiSon (healthy, c10 percent dead upper and outer crown 

branches; fair, 10 to 50 percent dead upper and outer crown 

branches; poor, >SO percent upper crown branches dead); 

number of taphdes that were open and oozing (an indication 

of microbial infection); and amwnt of cambial dieback, if 

present, that occud around (up to) three open tapholes. 

Outer bark around open tapholes was removed carefully to 

reveal the extent of cambial dieback. 

Experimental Effects of PFA 

Trees. In all. 162 sugar maples growing on a 10-acre (4-ha) 

portion of Bear Swamp State Forest near Dorloo, New York, 

were used.The trees. 20 to 25 cm in diameter at 1.4 m, 

were intermediate to codominant crown class, 43 to 47 years 

old, and part of a relatively pure stand of sugar maples that 

had colonized an old farm field that sloped 5 to 20 percent to 

the east. 

In each tree, two standard tapholes 1 .I cm in diameter and 

5.1 cm deep were drilled opposite each other on the west 

and east sides at 1.2 m above ground line. Standard plastic 

spouts were inserted into each hole. Care was taken to avoid 

drillino into frozen bark or to set the soouts too deedv. Each 

tree was assigned randomly to a gro"p of three tr& and 

received two treatments assigned systematically so that 

there were two replicates of each treatment for each tree 

group. 
Figure 1 .-Locations of 16 Wisconsin sugarbushes surveyed for external evidence of damage caused 

by PFA (sugarbush 6 was not used).The encircled areas encompass those sugarbushes affected 

severely by drought in 1988-89. Sugarbushes in the central area were affected most severely. 

Sugarbush Locations 

Without paraformaldehyde 

WtIh paraformaldehyde 

Figure 2.--Schedule of taphole treatments and tree harvests. 

Treatments Installed Trees Harvested and Measured 

1991 

Jan Feb Mar April May 

8 21 15 5 4 

1992 1993 1994 

Sept Sept Sept 

28 29 27 

trees tapped spouts pulled 

taps flushed 

A sapflow began 

$ sapflow ended 

8 budbreak began 
Reatments. The three main treatments were: 1) no PFA 

placed in the taphdes (controls), 2) a 250-mg pellet of PFA 

placed in tapholes behind the spouts, 3) same as treatment 

2 except that the tapholes were flushed with sterile water 

after spouts were removed. All spouts were fitted with a 1 - 

foot (30.5cm) length of open plastic tubing that was curled 

upward and held in place by a spout clip. This simulated a 

closed tubingcdlection system. Whik, sap could Row out of 

the open tubing, the sap-filled loop restricted the entrance of 

air and microbes into the taphde. 

Trees were tapped at three times selected to bracket Me 

1991 sapflow period in the stand (Fig. 2). Different gmups of 

54 trees (1 8 of the three-tree groups) were tapped on 8 

January (before), 21 Feb~ary (at), and 15 March (well after) 

the onset of sapflow. 

Spouts from hail of the trees in each treatment were carefully 

pulled 'earfy" on April 5 (soon after sapRow caased) or gate' 

on May 4 (just prior to cambial activity and budbreak) (Fig. 2). 

At the time spouts were removed. half of the PFA-treated 

tapholes were flushed with sterile water to remove all traces 

of the PFA pellet. 

Harvests and Measurements 

Groups of 54 trees each (18 of the threetree groups selected 

randomly) were felled in September of 1992,1993, and 1994 

(1 8 to 20,30 to 32, and 42 to 44 months after treatment 

hereinafter noted as two, three, and four growing seasons after 

treatment) to assess the influence of tLne on the dewbpment 

of discoloration and decay. A 2-m-long bolt centered about 

the tapholes was cut from each tree and returned to the 

laboratory where it was dissected and measured after its 

tapholes were examined for dowre and any cambial dii 

measured. Intact bolts were first cross sectioned thmwh each 

taphole and a disk was removed. Measurements of the width 

and depth of the discoloration columns and of the decay 

columns if present around the tapholes were made on the 

Eaces of disks (Fig. 3a). Bolts were then splii longitudinally 

through the opposing taphole columns and overall lengths of 

the discdoration and decay cdumns were measured (Fig. 3b). 

Small, narrow streaks of discolored wood extending beyond 

the main columns were not included in the measurements of 

column length. For this sludy, discdored wood was wood 

altered in color without a loss of strength; decayed wood was 

wood altered in wlor and determined to be softer or weaker 

than surrounding tissues when probed with a sharp scalpel. 

Analysis 

The following variables measured on tapholes were 

evaluated: 

1. Tapholes open or dosed at time of hanrest 

2 Area of cambial dieback calculated as: 

length x width of theopening 

3. Volume of discoloration columns calculated as: 

yartical x radial depth of discdored 

2 column 

4. Number of tapholes with decay 

5. Volume of decay columns calculated as: 

vx radial depth of decay 

2 columns 

Results 

Survey of Wisconsin Sugarbushes 

The 16 sugarbushes surveyed were well distributed within 

the state (Fig. 1). Overall, there was no apparent 

relationship between the use of PFA and any of the taphole 

attributes measured (Table 1). Some sugarbushes with long 

histories of PFA use ranked among the lowest (least 

damage) for some attributes and among the highest for 

others, while several stands with high values had never 

been treated with PFA (Table 2).There was no correlation 

between these attributes and tree size (d.b.h., crown class), 

though there was a significant correlation (p=0.02, 

Rk0.28) between the amount of cambial dieback and tree 

condition. 

Interviews with sugarbush owners and personal observations 

revealed that other factors, often unique to individual 

sugarbushes, influenced the external taphole attributes more 

than PFA. Poor pmctices such as overtapping, tapping small 

trees in overly dense stands, and leaving spouts in trees 

were observed in some sugarbushes. Bark splii above and 

below tapholes, common in some sugarbushes, resulted 

fmm inserting wuts too deeply or from tapping into frozen 

bark. 

The severe drought of 1988-89 in Wixonsin adversely 

affected the condition of trees in some sugakushes. 

especially in the central part of the state. The approximate 

area where drought damage was most intense. as revealed 

through interviews with owners and others, is shown in 

Figure 1 .The stress history and other stand data, together 

with mean tree condition and mean cambial dieback br eight 

representative sugarbushes, are listed in Table 3. 

Experimental Effects of PFA 

Taphole closure. Pearson's chi square used in 2x2 

contingency table analyses revealed no simple 

correspondence between the use of PFA and taphde 

dosure. After two growing seasons, about half of the controls 

and two-thitds of the PFA-treated taps had closed. By the 

third and fourth growing seasons, these percentages had 

risen to 95 peM and 97 percent, (controls) and 93 to 99 

percent (PFA), respectively. 

Dlscoloratlon. Columns of discolored sapwood were 

associated with every taphole and were larger around the 

PFA-treated taphdes, especially the PFA-flushed tapholes, 

than in the controls (Fig. 4). However, analysis of variance 
Figure 3.--(a) cross-sectional disk and (b) split bolts with typical discoloration and decay associated 

with the tapholes.Taphole "w" (with decay) received PFA; the othertaphole did not. 
indicated some high-order interactions between the 

independent variables, especially those related to timing of 

treatments. A dassification tree model using all possible 

values of all possible Variables was used to help identify the 

most important interactions. 

Using PFA (flushed or not) always was the most important 

factor affecting column volume. However, columns 

associated with PFA-treated tapholes, made either before or 

well after sapflow began, were larger than those of tapholes 

made at onset of sapflow (TaMe 4). The largest columns 

were associated with PFA-flushed tapholes installed before 

sapflow with spouts pulled early (Tables 4-5). The smallest 

after four growing seasons were around controi taphdes 

made at onset of sapflow with spouts pulled late (Tables 4-5). 

Regardless of when tapping was done, discoloration 

columns increased in size over the four gmwing seasons. 

Decay. Decay incidence (number of tapholes with decay 

columns) was much higher for tapholes treated with PFA, 

espedally those that were flushed. than for the controls (Table 

6). Incidence increased over time for PFA-treated tapholes. 

After four growing seasons, 75 percent of the flushed and 80 

percent of the nonflushed PFA tapholes had demy columns 

compared to less than 25 percent of the controls. 

After two growing seasons (1992), there were no evident 

differences in decay incidence related to tapping dates. 

However, by the next year, significantly fewer PFA tapholes 

made at onset of sapflow had decay columns than PFA 

tapholes made either earlier or later (Fig. 5).This pattern 

murred after four growing seasons as well. 

When spouts were removed strongly influenced the 

occurrence of decay. For controls, while there were no 

Table l.-Avemge values (50 tmea) for trees in 16 sugarbushes in 

Wloconsin where PFA had (9) or had not (7) been used 

Paraformaldehyde 

Item (+) (4 

D.b.h. (cm) 40.1 39.3 

Crown dass (1 -4). 2.1 2.3 

Condition (1-3)b 1.3 1.3 

open taps (no.) 3.0 3.2 

Taps with dieback (no.) 2.1 2.3 

Diebadc area (cm2) 5.3 5.2 

Taps 

Open, oozing (no.) 0.6 0.4 

Closed, oozing (no.) 0.1 0.1 

1 =dominant tree; 4 = overtopped, suppressed tree. 

1 = healthy, full crowned tree; 3 = poor tree, > 50 percent upper crown 

branches dead. 

Table 2.4ubabushes ranked bv mean values for taDhOls attribulms for 50 trees in each of 16 

Wlacondn sugarbushso whem PFA had (9) or had not (7) ken uw for each attribute, sugarbushso 

am ranked as high (left), moderate (center), or low (rlght) with range of mean values in parenthesea 

Attribute High values Moderate values Low values 

Open tapholes 14 11. 13' 8 15. C? 2. 10 12 7. 17 16 Y1'3.4 

.... .... .................. ...................... ..... (no.) (5.4 to 3.9) (3.7 to 2.2) (2.1 ....to 1.6) 

Tapholes with 1411a13' 8 9 7. 17 15' 10 5' 12 16 2'1.3' 4 

tieback (no.) (4.8 .... to .... 2.9) (2.5 .................. to ...................... 1.7) (1.5 ....to ..... 0.9) 

Dieback area 11. 14 9' P 12 6 17 13' 5. 4 15- 10 1. 2'16 3. 

(an? (8.7 .... to .... 5.7) (5.5 .................. to ...................... 3.8) (3.5 ....to ..... 2.1) 

Open tapholes 11. 2. P 1. 14 9' 12 8 5. 10 15. 17 16 13' 3. 4 

oozing (no.) (0.89 .. to .. 0.80) (0.76 ................to .................... 0.30) (0.26 ..to... 0.02) 

Paraformaldehyde used. 

0 NO PFA, controls 

PFA 

4 234 234 

Growing Seasons after Tapping 

Figure 4.--Mean volume of discoloration columns by treatment over time. Columns were measured 

in September of 1992,1993, or 1994 two, three, or four growing seasons after tapping in 1991. 

TaMe 4.--Mean volume fcml of dlscoloratlon columns around tapholes treated or not 

tmated with PFA bebre(~st;uary), at (February), or after (March) the onset of sapflow in 

1991 In tmea harvested two, three, or four growing seasona after tapping 

Growing seasons after tapping 

Treatment Jan Feb Mar Jan Feb Mar Jan Feb Mar 

No PFA 306 Bb 26P 303 190b 209 345 332 537 

PFA 437 2sOb 506 393 368 362 552 379 537 

PFA-flushed 555 299 348 555 25gb 440 722. 597 508 

Note: Means followed by "a" are significantly different (p < 0.05) from those followed by "b" as 

determined by Tukey's Studentized Range Test. 

differences after two growing seasons, about 40 percent 

more of the tapholes with spouts pulled late had decay 

columns after three and four growing seasons (Table 6). By 

contrast, the proportion of PFA tapholes with decay columns 

was much higher in all three harvest years when spouts were 

pulled early. 

LBaq sewfjly. Decay severity (volume of decayed wood) 

can be expressed as the average for all tapholes in a given 

treatment, whether or not a taphole had a decay column 

(the treatment means), or as the average amount for only 

those tapholes that were decayed. 

The average volumes of decay for the two PFA treatments 

were consistently and markediy greater than for controls. For 

the latter, mean decay volume was greatest about those 

tapholes with spouts pulled late (TaMe 7). For PFA tapholes, 

decay volumes were greatest for two of the three harvest 

years when spouts were removed early (Table 7) from 

tapholes installed before or after sapflow (Table 8). There 

were no differences related to time of installation for the 

controls (Table 8). 

Except for the PFA tapholes that were examined after three 

growing seasons (where average decay columns were about 
Table S.-Maan volume (cm3 of discoloration columns around tapholes 

treated or not treated wlth PFA and where spouts wera pulled early (Aprll) 

or late (May) two, three, or lour growing seasons after tapplng in 1991 

Growing seasons after ta~~ina 

2 3 4 

Treatment Eariv Late Earlv Late Eariv Late 

No PFA 27 27zb 19gb,' Zagb 474b 34gb 

PFA 440 343 356O 399 55ga 450 

PFA-flushed 484 32Zb 407 422 711. 527a 

Note: Means followed by 'a" are significantly different (p < 0.05) from those 

followed by 'b"; those followed by %" are significantly different from those 

followed by 'd" as determined by Tukey's Studentized Range Test. 

Table 6.--Percentage of tapholes treated or not with PFA and whose spouts were 

pulled early (April) or late (May) with decay two, three, or fwr growing seasons 

after tapping in 1991 (number of observations In parentheses) 

Growing seasons after tapping 

2 3 4 

Treatment Early Late Early Late Early Late 

NO PFA 29(17) 32(19) 14(22) 40(15) 13(16) 33(21) 

PFA and 59 (37) 43 (35) 65 (40) 14 (29) 81 (32 ) 56 (39) 

PFA-flushed 

one-third the size of their corresponding discoloration 

columns), decay columns were 20 to 24 percent the size of 

their associated discoloration mlumns regardless of treatment 

or time after tapping (Table 9). Regression of the mean 

discoioration wlumes against mean decay volumes (Fig. 6) 

revealed a highly significant relationship (P=0.01. R2=0.54). 

Discussion 

Taphole Closure 

Treating tapholes with PFA did not muse dieback of cambium 

around tapholes nor prevent or slow taphole closure in this or 

previous experiments (Walters and Shigo 1978. 1979). Factors 

other than the use of PFA appear responsible for these effects, 

for example, cambial dieback and slow closure have been 

attributed to stressors such as defoliation (Wargo 1977). 

Wounds in trees in~riabiy result in the development of 

discoioration columns whose size and shape are delimited 

by the tree's inherent ability to establish barriers against both 

the inroads of air and the invasion of microorganisms (Shigo 

1984; Shortle 1979). With respect to discoioration. the 

questions addressed in this study are: To what extent does 

the use of PFA alter the natural ability of the tree to set and 

maintain its defensive barriers around tapholes? And to what 

extent are these defenses influenced by when the wounds 

are made and when spouts are removed? 

For some time after tapping, complex interactions among 

timing of tapping and spout removal as well as treatment 

influenced the processes of discoloration. With time, 

though, the time of spout removal became less important. 

By the fourth growing season, the use of PFA and to a 

lesser extent the timing of tapping relative to the onset of 

sapflow were the principal factors influencing discoloration 

column size. 

That PFA strongly increases the volumn of discoloration 

columns is an important finding where sap production is 

concerned. Columns of discolored tissues neither store 

sugars nor transport sap. Consequently, their presence 

determines the availability of future tapping sites. Also, their 

size and shape establishes the potential limits of subsequent 

decay columns (Shigo and Hillis 1973). The complex 

interactions between discoioration and decay was further 

demonstrated by Shortle et al. (1995) and by our findings, 

which indicate that the soatial limits of discoloration (column 

sizes) are increased by ihe presence of decay fungi.'yet the 

question remains: Are these effects important to the tree or 

to the sugarbush? 

One way to address this question is to project our results 

over time-given certain assumptions of practice and tree 
Times When Tapped 

0 

loo 

d * 80 

L-9 

60 z 

2 40 

-0 

% 20 8 

6 0 

. 

NO PFA PFA- NO PFA PFAflushed flushed 

NO PFA PFAflushed 

Treatments 

Figure 5.--Percentage of tapholes decayed by treatment wer time in relation to time of 

tapping (January, Feb~aw, or March) in 1991 . Tapholes were examined in September of 

condition. Thus, if we assume that a tree will be tapped only 

after reaching 12 inches (30.5 cm) in diameter, that there will 

be two taps per year, that tapping and its effects will be 

limited to a 4-foot (1.2 m) section of stem, and that the tree 

will grow 1 inch in diameter every 10 years, we project the 

following: 

1) W'mout PFA, about 9 percent of the outer 3 inches of 

wood in the tapped section will be discolored in 10 years 

and about 15 percent of the outer 4 inches will be 

discolored after 20 years. 

2) With PFA, these values will be about 15 percent (10 

years) and 23 percent (20 years), and thus, in this 

hypothetical tree, represent an increase of 6 to 8 percent 

(compared to no PFA) in sapwood rendered unsuitable 

for tapping by the presence of discoloration. 

The fact that columns of discoloration continued to increase 

in size for at least four gmwing seasons after tapping, and 

especially about tapholes that had contained PFA, indicates 

that the chemical's influence is long lasting.Yet Me largest 

columns were about tapholes Mat had been both made and 
Table 7.--Mean volumes (cm3 of decay in tapholes treated or not treated 

wRh PFA two, three, or four growing seasons after tapplng In 1991, and 

whose spouts were removed early (Aprll) or late (May) 

Growing seasons after taming 

2 3 4 

Treatment Earlv Late Earlv Late Earlv Late 

No PFA lab 23b 2M 2P 2" 42b 

PFA 5P 60b 75 IllC 53b 

PFA-flushed Mb 3Bb 70P 64 171. 79 

Note: Means followed by "a" are significantly different from those followed by 

'b" (D c 0.05): those followed bv %"are sianificantlv different (D c 0.05) from 

those follow&l by "d" as determined by ~ukey's ~Gdentized dange ~&t. 

Table &-Mean volume (em3 of decay around tapholes treated or not trented wlth PFA before 

(January), at (February), or after (March) the onset of sapflow in 1991 In trees harvested two, 

three, or bur growing seasons after tapping 

Growing seasons after tapping 

2 3 4 

Treatment Jan Feb Mar Jan Feb Mar Jan Feb Mar 

No PFA 23 27 1 Ob 6b 3b 21 37 20 16 

PFA 104 39 62 85 41 72 67 46 125 

PFA-flushed 46 63 27 102 55 72 141' 96 124 

Note: Means followed by 'a" are signifiintly different (p c 0.05) from those followed by "b" as 

determined by Tukey's Studentized Range Test. 

Table 9.--Mean volumes (cm3 of the decay columns that occurred and assoclated 

discoloration columns, by growing seasons after tapplng and treatment 

MY Discoloration 

Growing seasons after tapping Growing seasons after tapping 

Treatment 

No PFA 73.9 51.3 101.6 338.2 251.8 509.9 

(SE=11.7-87.7) n=10 n=7 n=9 (21 .8). (20.4) (19.9) 

PFA 112.4 165.2 132.6 472.0 484.0 638.2 

(SE=l7.7-88.7) n=16 n=15 n=21 (23.8) (34.0) (20.8) 

PFA-flushed 98.4 143.0 172.7 461.0 432.9 711.5 

(SE=19.9-108.2) n=17 n=18 n=25 (21.3) (33.0) (24.3) 

' Numbers in parentheses are the relative proportion of the discoloration columns occupied 

by the decay columns. 
0 

0 25 50 75 100 125 150 

Mean decay column volume (cm3) 

Figure 6.4egressim of mean discoloration column vdumes on means of decay column volumes 

(R2=0.54. P=0.01); discoloration data fmm Table 4, decay values from Table 8. 

flushed of PFA residues the earliest.This suggests that PFA Decay 

may influence the discdoration process in two ways: 1) 

thrwgh an initial and rapid eftect on surrounding wood Decay develops in trees that are wounded, i.e., within tissues 

tissues that impairs the formation of anatomical or chemical that have become discolored. However, unlike diiloration, 

decay after mounding is not inevitable. With respect to decay, 

defense barriers, a biocidal invading therefore, the questions of concern are: TO what extent does stain-causing and decay-causing microorganisms. It has 

been suggested that PFA inactivates defense-plugging PFA increase the likelihood of decay? To what extent does it 

mechanisms and chemicals, lnduding oxidized phenols facilitate the decay process? And to what extent does the 

presence of decay increase the size of the associated (Walters and Shigo 1978; Morselli 1995).The microbiocidal discoloration dumns? Most ecay-caus ing tungi succeed 

or sanitizing effects of PFA might be reduced if 'still active" 

residues were flushed fmm tapholes, particularly if done only in woundaltered woody tissues, and then usually only 

early to allow a longer period for organisms to invade and after such tissues have been altered further by earlier 

colonizers including bacteria and stain fungi (Shio and Hiliis 

grow in Wefenseless" tissues prior to the tree's resumption 1973), of active spring gmwth. 

It is not km whether discdoration columns will contirme to Using PFA resulted in more than twice as many decayed 

increase in size or at the same rate as they did during the tapholes and, correspondingly, twice as much volume of 

study period. Walters and Shigo (1978) found that such decay compared to the controls. However, we found that the 

columns associated with tapholes increased in length volume of decayed wood amund tapholes was relatively 

thrwgh 44 months (four growing seasons) but ceased small. Using our results and the tapplng assumptions given 

thereafter. previously, we project that when PFA is used, about 22 

percent (10 years) to 3.4 percent (20 years) of the tapable 
sapwood will be decayed compared to 0.6 and 0.9 percent 

with no PFA. In oractice. taoholes often are concentrated in . . stem sections kuch shorter than 1.2 m long. In such cases, 

the proportion decayed, especially of cross-sectional areas, 

would be much greater--perhaps more than twice that 

calculated here.That our data and the findings of Shortle et 

al. (1995) clearly show that discoloration columns increase in 

size when invaded by decay organisms reveals an additional 

and perhaps even more important effect of decay on sap 

production. 

Practices and factors that could alter these values even more 

adversely include tapping slow-growing trees stressed by 

inadequate light, moisture, or nutrients (overly dense 

sugarbush), external stress factors that slow growth and 

prevent rapid taphole closure (e.g., drought and insect 

defoliation), and wertapping (increased tapping intensity or 

tapping undersize trees). While trees in this study were 

smaller than recommended (e.g., Houston et al. 1990) for 

operational sugarbushes, they were young and vigorous. 

closed taphole wounds quickly, and probably established 

internal compartment barriers rapidly. It is likely that decay 

volumes would be larger in old trees or trees under stress. 

An important factor is the distribution of tapholes with 

discoloration and decay.Tnus, in a tree 12 to 14 inches in 

diameter, even 23 percent of the tapable wood with 

discoloration distributed as many separate columns would be 

damaging, particularly if they were concentrated in a limited 

area. Decay rapidly spreads outward into the tissues around 

new tapholes that penetrate into preexisting decay columns. 

Of course, this volume of decay will be a significantly larger 

proportion of the available sapwood in trees smaller than 12 

inches in diameter and in trees tapped for longer periods. 

Literature Cited 

Ching, T. M.; Mericle. L. W. 1960. Some evidence of 

premature stoppage of sugar maple sap pmductlon. 

Forest Science. 6: 270-275. 

Costilow, R. N.; Robbins, P. M.; Simmons. R. J.; Willits, C. 0. 

1962. The efficiency and practicability of different 

types of paraformaldehyde pellets for mntrolllng 

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Lansing, MI: Michigan State University Agricultural 

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Houston, D. R. 1996. A reexamination of the effects of 

paraformaldehyde on tapped sugar maples. I. Survey 

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8A(2): 12-16. 

Houston, D. R.; Alien, D. C.; Lachance. D. 1990. Sugarbush 

Management: a guide to maintaining tree health. Gen. 

Tech. Rep. NE-129. Radnor, PA: US. Department of 

Agriculture, Forest Service, Northeastern Forest 

Experiment Station. 

Houston, D. R.; Fagan, J. C. 1996. A reexamination of the 

effects of paraformaldehyde on tapped sugar maples. 

II. Development of discoloration and decay around 

tapholes. Maple Syrup Digest. 8A(3): 20-30. 

MacArthur, J. D.; Bladorvood. A. C. 1968. Taphole sanltatlon 

pellets and sugar maple sap ylelds. Forestry Chronicle. 

42(4): 380-386. 

Morselli. M. 1995. Effects of the use of paraformaldehyde 

sterlllsing pellets on sugar maple health: a revlew. In: 

Caring forthe forest: research in a changing world: 

abstracts of invited papers; 1995 August 6-12; Tampere, 

Finland.Tampere, Finland: IUFRO XX World Congress: 

410. Abstract. 

Reynolds, L. 1989. Editorial. Maple Syrup Digest. lA(1): 16- 

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Sheneman. J. M.; Costilow. R. N. 1959. ldentificatlon of 

microorganisms tmm maple tree tapholes. Food 

Research. 24: 14&151. 

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J. E. 1959. Correiatlon between mlcmblal populations 

and sap ylelds from maple hses. Food Research 24: 

152-159. 

Shigo. A. L. 1984. Compartmentallzatlon: a conceptual 

framework for understanding how trees grow and 

defend themselves. Annual Review of Phytopathology. 

22: 189-214. 

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wood, and mlcmorganlsms in living trees. Annual 

Review of Phytopathology. 11: 197-222. 

Shigo, A. L.; Laing, F. M. 1970. Some effects of 

paraformaldehyde on wood surrounding tapholes in 

sugar maple trees. Res. Pap. NE-161. Upper Darby, PA: 

US. Department of Agriculture. Forest Service, 

Northeastern Forest Experiment Station. 

Shortle, W. C. 1979. Compartmentallzatlon of decay in red 

maple and hybrid poplar trees. Phytopathology. 69: 410- 

413. 

Shortle, W. C.; Smith, K. T.; Dudzik, K. R.; Parker, S. 1995. 

Response of maple sapwood to Injury and lntectlon. 

European Journai of Forest Pathology. 25: 241-252. 

Walters, R. S.; Shigo, A. L. 1978. Dlscoloratlon and decay 

associated wlth paraformaldehydstreated taphoies in 

sugar maple. Canadian Journal of Forest Research. 8(1): 

54-60. 

Waiters, R. S.; Shigo, A. L. 1979. Paraformaldehyde-treated 

tapholes: effects on wood. National Maple Syrup Digest. 

12(2): 13-18. 

Wargo, P. M. 1977. Wound closure in sugar maple: 

adverse effects of defoliation. Canadian Journal of 

Forest Research. 7: 410-414. 
Houston, David R.: Fagan, J. Chris. 1997. Reexamlnatlon of etleets of 

paraformaldehyde on tlaaues around tapholes In sugar maple trees. Res. 

Pap. NE-706. Radnor, PA: US. Department of Agriculture, Forest Sewiw, 

Northeastern Forest Experiment Station. 12 p. 

Pellets containing paraformaldehyde (PFA) are sometimes placed behind spouts 

in tapped sugar maples to prolong sapflow and increase the yield of sap used to 

make maple sywp.The practice is controversial because the chemical has Wen 

shown to promote decay and is reported to cause cambial dieback around 

tapholes.This study reexamined the effects of PFA on tapped sugar maple and 

determined how these effects also am influend by time of tapping and spOut 

removal, and by taphole flushing. A survey of sugarbushes in Wisconsin revealed 

no relationship between PFA use and cambial dieback and rate of taphole 

closure. Other factors including poor tapping techniques and practices, drought, 

and old age affected these taphde attributes more than PFA. 

I b~Wot'ds: sugar mwle, paraformaldehde. taphoies, discoloration, decay 

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Headquarters of the Northeastern Forest Experiment Station is in Radnor, 

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