Five Years of Vegetation Succession Following Vegetation Management Treatments in a Jack Pine Ecosystem Douglas G. Pitt, Canadian Forest Service, 1219 Queen St. E., Sault Ste. Marie, Ontario, Canada P6A 5M7; Andrée E. Morneault, Ontario Ministry of Natural Resources, Southcentral Sciences Section, 3301 Trout Lake Rd., North Bay, Ontario P1A 4L7; Philip Bunce, Domtar Inc., Forest Resources, 1 Station Rd., Espanola, Ontario P5E 1R6; and F. Wayne Bell, Ontario Ministry of Natural Resources, Ontario Forest Research Institute, 1235 Queen St. East, Sault Ste. Marie, Ontario P6A 5N5.
ABSTRACT: Five years of data on vegetation dynamics and succession are provided for six operational release treatments applied to three 2- to 4-yr-old jack pine (Pinus banksiana Lamb.) plantations in central Ontario. Treatments included 3 yr of annual noncrop vegetation removal, conventional aerial spray with glyphosate (1.42 kg ae/ha), ground application of glyphosate with a mist blower, basal-bark application of triclopyr, motor-manual cutting (brush saw), and no treatment. Conventional aerial spraying and annual removal resulted in the greatest jack pine crop growth, with trees exceeding 90% crown closure, 7 cm in groundline diameter, and 3 m in height (stem volume index = 5.1 dm3) after 5 growing seasons. The cover of herbaceous plants was highest (30–50%) in the aerial spray plots during the observation period. Deciduous tree, shrub, and fern species remained well represented on these plots, although total cover and height were low (≤ 35% and 1 m, respectively). Mist-blower and brush-saw plots contained mid-sized pine (3.5 dm3) with 69% crown closure. In contrast, untreated and basal-bark plots contained the smallest pine (2.3 dm3 and 31% crown closure), likely caused by heavy competition and herbicide damage, respectively. On mist-blower and basal-bark plots, good height growth was observed on untreated deciduous trees; low-shrub and fern cover remained high (46 and 30%, respectively); and herbaceous cover increased gradually to 22%. On brush-saw plots, recovery of woody cover was rapid, but height growth was relatively slow. Deciduous trees and tall shrubs dominated untreated sites (> 70% cover) by the end of the fifth growing season. Successional trends suggest that aerial spray and annual removal treatments will produce pure jack pine stands at maturity; mist blower, basal bark, and brush-saw treatments may produce mixedwood stands; and untreated plots will likely be dominated by hardwoods. North. J. Appl. For. 17(3):100–109.
NOTE: All correspondence should be directed to Douglas G. Pitt—Phone: (705) 949-9461, Fax: (705) 759-5700, E-mail:
[email protected]. Funding for this project was provided by the Vegetation Management Alternatives Program (VMAP) of the Ontario Ministry of Natural Resources (OMNR) and the former E.B. Eddy Forest Products Inc., now Domtar Inc. The authors are indebted to Bob Wagner for initiating and administering VMAP and Dianne Othmer (OMNR) for her hard work and dedication in plot establishment and data collection. Thanks also go to Brian Nicks (Domtar Inc.), for his thoughtful review of the tactical plan, experimental design, site location, and draft manuscript. The experimental treatments would not be possible without the help of Matt Wilkie and Dave McKean (Domtar Inc.), Gaetan Mercier (formerly DowElanco, now Dow AgroSciences), and Rick Hansel (OMNR). Trial establishment and data collection were shared by Bill Moryto, Nicole Laporte, Danny Arcand, Derrick Lalonde, Gilles Hebert, Jon Arthurs, Steve Ross, Chad Purcell, Stephen Kendall, Mark Brady, Jennifer Clayton, Derek Drake, Brent Hagan, and Rob Foster. The thoughtful advice of Colin Bowling, John Winters, Luc Desrochers, and Dave McKean on earlier drafts of this manuscript was greatly appreciated. Trudy Vaittinen’s jack pine drawings greatly enhanced Figure 6.
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Across Canada, forest vegetation management activities are undertaken for conifer release on nearly 200,000 ha annually. Of this total, approximately 135,000 ha are treated with glyphosate by aerial application and 53,000 ha are brushed manually.1 Despite the fact that annual forest herbicide use amounts to less than 10% of residential lawn and 2% of agricultural crop applications (Hunter and McGee 1994), controversy over the use of herbicides in Canada’s forests has increased since the late 1980s (Wagner et al. 1998). A 1989 national survey indicated that 71% of Canadians oppose the use of chemicals in the forest, and most believe that pesticides, in general, are harmful to wildlife and people (Environics Research Group 1989). In Ontario, a 1994 survey revealed 1
Figures collected in a 1998 poll of provincial and forest industry applicators.
that 82% of the public found aerial application of herbicides to be unacceptable (Buse et al. 1995). Since the majority (80%) of Canada’s forests are publicly owned and managed, it is imperative that those responsible for forest management acknowledge public concerns and practice due diligence in objectively quantifying herbicide impacts and seeking effective alternatives. The study reported here was initiated in 1993 as part of a larger effort to seek viable alternatives to the use of herbicides through the Vegetation Management Alternatives Program (VMAP; Wagner et al. 1994). At this time, forest managers were very concerned about the consequences of a loss or reduction in their ability to use aerial application and herbicides in general. Today, these concerns are still very real. The study objectives included comparison of six potential release options in a jack pine (Pinus banksiana Lamb.) ecosystem in terms of crop growth response, vegetation dynamics, and succession through 5 yr posttreatment. The treatments were chosen to reflect practical responses to increasing restrictions on herbicide use: 1. Three years of annual noncrop removal (AR)—representing unrestricted herbicide use and designed to define maximal growth potential of the planted jack pine crop.
crop, poplar (Populus spp.), as an alternate crop species, other tree and tall-shrub species, low-shrub species, herbaceous vegetation (including grasses), and fern species. The resulting comparative data offer a basis for weighing various management options for the maintenance of timber production, wildlife habitat, and other values, should herbicide use be modified, limited, or restricted. Specifically, our results apply to dry through moderately fresh, rapid to well-drained jack pine ecosites (ES13.1 and 15.1, Chambers et al. 1997) in Site Region 4E (Hills 1959). Caution should be exercised in extrapolating results to other ecosites, since successional patterns may differ from those documented here.
2. Conventional aerial spray with glyphosate (AS)—the standard operational release treatment, as a benchmark for comparison with the alternatives.
Vegetation Assessments Within each treatment plot, 20 representative jack pine seedlings were systematically located with a random start. Selection was based on an approximate 4 m × 4 m grid of 4 trees by 5 trees. Each tree was identified with a pin-mounted, numbered aluminum tag. Prior to treatment in August 1993, total height (nearest cm, from groundline to the base of the terminal bud) and root collar diameter (nearest mm, 1 cm above groundline) were recorded for each tree. Noncrop vegetation was then assessed within a 1.13 m radius circle of each tree’s center. Trees and tall shrubs [e.g., beaked hazel (Corylus cornuta Marsh.), pin cherry (Prunus pensylvanica L. f.)] were identified by species and evaluated for cover (%), average height (nearest 10 cm), and stem density (including new seedlings). Low shrubs [e.g., bush honeysuckle (Diervilla lonicera Mill.), blueberry (Vaccinium spp.)], herbaceous plants (including grasses), and ferns were identified by spe-
3. Back-pack mist-blower application of glyphosate (MB)— representing a ground-based, broadcast herbicide application, given a restriction on aerial application. 4. Basal-bark application of triclopyr (BB)—representing a directed herbicide application, given a restriction on broadcast application. 5. Motor-manual brush saw (BS)—virtually the only available alternative, given a restriction on herbicide use. 6. No vegetation control (C)—“letting nature take its course,” as often suggested by some members of the public. Treatment effects are documented on each of six vegetation components, including planted jack pine, as the primary
Methods Experimental Design Three jack pine plantations, scheduled for operational release in 1993, were identified on E.B. Eddy Limited’s Sustainable Forest License area northwest of Espanola, Ontario (Table 1). These plantations represented a crosssection of plantation ages and stock types requiring release on ecosites 13.1 and 15.1 (Chambers et al. 1997). The study was established as a randomized complete block design with six treatments (Table 2) on each of the three sites (blocks).
Table 1. Description of study areas. Block 1 (46º47¢N, 82º08¢W) Olinyk Twp. 2 (46º47¢N, 82º10¢W) Olinyk Twp. 3 (46º47¢N, 82º04¢W) Oshell Twp.
Preharvest stand conditions FRI† 1974: Pw5Pj3Bw2 Site Class 2 Age 150 Height 24 m Stocking 0.7
Harvest Clearcut; treelength, conventional cut and skid, 1988
Glacial outwash plain; silty loam (ES15.1)
FRI 1974: Pj7Sb2Po1 Site Class 2 Age 85 Height 20 m Stocking 0.8
Clearcut; treelength, conventional cut and skid, 1989
Young’s Teeth, 1990
Jack Pine, over-wintered FH408 paper pot, planted with Potti Putki, May 13–16, 1991.
Glacial outwash plain; silty, very fine sands to silty loams (ES15.1)
FRI 1974: Pj6Sb2Po2 Site Class 2 Age 90 Height 21 m Stocking 0.6
Clearcut; treelength, conventional cut and skid, 1989
Young’s Teeth, 1990
Jack Pine, current 165 Jiffy Pot, planted with Potti Putki, June 14, 1991.
Geology Glacial outwash plain; fine sands to silty loams (ES13.1)*
Site preparation Young’s Teeth, 1989
Planting Jack Pine, current 408 paper pot, planted with Potti Putki, June 27–29, 1989.
* Chambers et al. (1997). † Forest Resource Inventory; Pw = white pine, Pj = jack pine, Bw = white birch, Sb = black spruce, and Po = poplar. Subscripts refer to the proportion of total stocking (out of 10) occupied by a species.
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Table 2. Summary of treatment details.
Treatment reference Control (C)
Date time (person-hr/ha) —
Details Plots left undisturbed.
Plot size (ha) 50 ¥ 0 m (0.25)
Aerial Spray (AS)
4 L/ha of Vision® (356 g/L ae glyphosate as a water soluble liquid) applied in a total spray volume of 34 L/ha with a Bell 206 helicopter equipped with conventional boom and nozzle gear (36 D8-45 nozzles mounted on an 8 m boom, orientation 45º, boom pressure 234 kpa, air speed 120 km/h, track spacing 20 m). Morning application, temperatures 10–12ºC, RH 82–97 %, and wind speed 1 km/h.
August 21, 1993 (0.02 hr)
100 ¥ 00 m (2.00)
Mist Blower (MB)
0.8 L/ha* of Vision® applied in a total spray volume of 40 L/ha with a Gloria 181 backpack mist blower. Weather parameters as per aerial application. *Typically higher on areas treated; application was not uniform, as stated rate suggests.
August 21, 1993 (1.0–2.0 hr)
50 ¥ 00 m (0.50)
Basal Bark (BB)
Release® (480 g/L ae triclopyr as a butoxyethyl ester) was mixed as a 30% solution with Shell Pella A mineral oil and applied with a Swissmex SP1 backpack sprayer equipped with a Model 30 Gunjet (with a positive shutoff valve) and a TP#2504 nozzle. Applications were made to unwanted stems in a 5 cm band, 30 to 50 cm above groundline on both sides of the stem (known as the streamline method). Only stems within a 1 to 1.13 m radius of crop trees were treated. Approximately 5.4 to 11.4 L of product were applied per ha.
October 4, 5, 1993. (4 hr)
50 ¥ 0 m (0.25)
Brush Saw (BS)
All noncrop vegetation was cut at 25 cm above groundline with a Husqvarna 165 clearing saw.
October 4, 5, 1993. (4–8 hr)
50 ¥ 0 m (0.25)
Annual Removal (AR)
Annual directed foliar applications of a 2% solution of Vision® using a backpack sprayer and flat-fan nozzle. Plots were randomly located within Aerial Spray plots (aerial spray was the first removal). Note: plots did not require application in 1994.
August 93, June 1995, and June 1996
40 ¥ 0 m (0.16)
cies and evaluated for cover (%). Cover assessments were facilitated by placing two 2.26 m lengths of plastic pipe in an “X” over the subplot center (i.e., the crop tree) and visually estimating the proportion of ground occupied by the vertical projection of crown(s) (to the nearest 5%) for each quadrant. Trace amounts of vegetation were assigned 2% cover. All crop trees and vegetation subplots were reassessed at the end of the growing seasons of 1994, 1995, 1996, and 1998 (woody stem densities were not recorded in 1998). In the final measurement year, crown widths were also recorded for each crop tree (one measure parallel to the planted row and a second perpendicular to the row). Crown area (CA, m2) was estimated from these measures, assuming elliptical form (Zedaker and Miller 1991).
Data Analysis Response variables used for crop tree analyses included root collar diameter, total height, stem volume (assuming conical form), and percentage survival. Deciduous trees and tall shrubs were analyzed on the basis of cover (%), average height (weighted by cover), and stem density (number per ha). Separate analyses were conducted for poplar (Populus spp.; principally Populus tremuloides Michx.), and the sum of all other deciduous trees and tall shrubs. Total cover (%) was used to describe the remaining vegetation components: low-shrub, herbaceous (including grasses), and fern. Statistical comparisons were made pretreatment and five growing seasons posttreatment using analysis of variance 102
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(ANOVA) and the model appropriate for a randomized complete block design (Table 3). Contrasts were used to address specific hypotheses defined by the study objectives. In the analyses of crop growth, pretreatment values of the response variables were used as covariates to equalize initial differences in tree size. In addition, crop and noncrop response trends over time were compared among treatments using repeated-measures analyses of variance. For these analyses, orthogonal polynomial response functions were fit to the repeated measures of each experimental unit (i.e., each plot of each treatment) and the estimated coefficients (mean, linear, and quadratic) used as primary data in the underlying ANOVA structure of Table 3 [see Meredith and Stehman (1991) for details]. As such, each of the sources of variation listed in Table 3 was considered as being an interaction term with time. Orthogonal polynomial coefficients were obtained Table 3. General form of analysis of variance.
Source of variation Treatments (fixed) Planned contrasts: Treated vs. Control (T vs. C) Aerial Spray vs. Annual Removal (AS vs. AR) Aerial Spray vs. Mist Blower (AS vs. MB) Aerial Spray vs. Basal Bark (AS vs. BB) Aerial Spray vs. Brush Saw (AS vs. BS) Mist Blower vs. Basal Bark (MB vs. BB) Blocks (random) Treatment ¥ blocks (error) Total
Degrees of freedom 6–1 = 5 (1) (1) (1) (1) (1) (1) 3–1 = 2 10 17
for the unequally spaced years posttreatment (i.e., data weren’t collected in 1997) using the ORPOL function in SAS (SAS IML User’s Guide, Release 6.03, 1988). In all cases, model residuals were examined to verify that the assumptions of homogeneity of variance and normality were met.
Results Crop Growth Response At the initiation of this study, jack pine planted in Block 1 were in their fifth growing season and averaged 154 cm in height and 23 mm in diameter. In contrast, trees in Blocks 2 and 3 (in their third growing season) averaged 64 cm × 8 mm and 50 cm × 6 mm, respectively. The overall mean initial tree size to which subsequent results were adjusted via analysis of covariance (ANCOVA) was 89 cm in height and 12.4 mm in diameter (stem volume index = 87 cm3). Consistent with other studies (Morris et al. 1990, Longpré et al. 1994, Pitt et al. 1999, and Wagner et al. 1999) stem diameter was more responsive to release than tree height (Figure 1). Both variables increased linearly over the observation period (P < 0.01), with diameter growth rates exhibiting relatively clear treatment separation (P < 0.01). Diameter growth was most rapid in Annual Removal and Aerial Spray plots, moderate in Mist-Blower, Brush Saw, and Basal Bark plots, and the slowest in Control plots. These results were also reflected by ANCOVA of the fifth-year posttreatment data (P < 0.01), with averages of these three groupings being 74 mm, 55 mm, and 43 mm, respectively. Differences in height growth were more subtle, with the highest growth rates being observed in Aerial Spray and Annual Removal plots (P < 0.03) and the lowest in Control and Basal Bark plots (P < 0.01). Five years after treatment, the heights of jack pine in these two treatment groups differed by 14 to 48 cm. Trees in Basal Bark plots were the shortest (269 cm, P < 0.01), reflecting herbicide injury caused by excessive nozzle pressure and the deflection of herbicide droplets off of target stems and onto some crop trees. In contrast to diameter and height growth alone, stem volume trends over time were curvilinear (P < 0.01; Figure 1). Treatment responses clearly separated into three groups, with Aerial Spray and Annual Removal equally supporting the largest trees (5174 cm3), Mist Blower and Brush Saw mid-sized trees (3543 cm3), and Basal Bark and Control plots the smallest trees (2320 cm3). Caution should be exercised in extrapolating these growth trends beyond the fifth year, since jack pine on Annual Removal and Aerial Spray plots were just approaching full crown closure (94%; calculated from the crown area measurements made in 1998) and intraspecific competition may begin to influence future growth trends. In contrast, crop trees on Mist Blower and Brush Saw plots averaged 69% crown closure at post-treatment year 5; Basal Bark and Control plots averaged 31%. Jack pine survival through the course of this study was quite high, averaging 95% at the end of the fifth growing season following all treatments except Basal Bark, where survival was only 78% (P < 0.01). Crop injury and mortality following this treatment can be attributed to misapplication of the herbicide, as described above. Control plots
Figure 1. Mean growth of jack pine through five growing seasons posttreatment. Lines represent functions estimated by polynomial contrasts from repeated-measures analysis of covariance. Plotted points represent treatment means, after adjustment to common pretreatment size. AS ()= Aerial Spray, AR (●)= Annual Removal, MB (▲) = Mist Blower, BS (✚)= Brush Saw, BB (❇) = Basal Bark, and C (■) = untreated control. Numbers in brackets are standard errors for the year-5 least-squares means.
supported the second lowest survival at 88%; however, this was not statistically different from that of the other treatments (P = 0.33). Effects on Tree and Tall-Shrub Species At the time of treatment, poplar was the dominant woody competitor on all plots, representing between 9 and 22 percent cover, with 12,000 and 24,000 stems per ha. Other deciduous tree and tall-shrub species, combined, averaged 15% cover and 25,000 stems per ha and consisted of white birch (Betula papyrifera Marsh.), beaked hazel, pin cherry, and red maple (Acer rubrum L.) in approximate proportions of 30%, 30%, 25%, and 5%, by cover, respectively. Small amounts of alder (Alnus spp.), serviceberry (Amelanchier spp.), and willow (Salix spp.) were also present. Poplar cover in Control plots increased in a linear fashion over five growing seasons posttreatment (P < 0.01), averagNJAF 17(3) 2000
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ing 40% at the end of the measurement period (Figure 2). In contrast, all other treatments generally suppressed poplar cover to 11% or less throughout the same period (P < 0.01). Variability precluded clear treatment differences, but Mist Blower plots supported nearly 10% higher year 5 poplar cover than Aerial Spray plots (P = 0.07) and, while cover tended to remain constant in glyphosate-treated plots over time, slight increases were observed in Basal Bark plots (BB vs. AS, × time linear, P = 0.04). Aerial Spray and Annual Removal plots remained virtually free of poplar cover during the measurement period. In contrast, cover of other deciduous tree and tall-shrub species increased gradually over five growing seasons, regardless of the treatment applied (P < 0.01). With the exception of Annual Removal and Aerial Spray plots, cover increased above pretreatment levels by the end of the observation period. Cover in Control plots increased the most rapidly (T vs. C, × time linear, P = 0.06), ending the measurement period with the highest cover (33%, P = 0.02). Only marginal increases in cover were observed in Annual Removal plots (AS vs. AR, × time linear, P = 0.07), which supported the lowest cover at the end of the measurement period (4%). The relative species composition of this vegetation group tended to remain relatively constant from pretreatment to posttreatment, as well as across treatments. White birch, beaked hazel, and pin cherry accounted for approximately 85% of cover, in
Figure 2. Mean cover of poplar and other deciduous tree and tallshrub species through five growing seasons posttreatment. Plotted points represent least squares treatment means; values in brackets are their standard errors, from analysis of variance at each measurement period. AS ()= Aerial Spray, CR (●) = Annual Removal, MB (▲) = Mist Blower, BS (✚) = Brush Saw, BB (❇) = Basal Bark, and C (■) = untreated control (see text for details).
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equal shares, with red maple and other species making up the remainder. This suggests that none of the treatments differentially affected these other species. Treatment-related patterns in height growth resembled the cover patterns depicted in Figure 2. Untreated poplar exhibited the greatest height growth (P < 0.01), reaching 4.3 m by the end of the fifth growing season. Annual Removal and Aerial Spray treatments maintained poplar height below 0.5 m, while stems in Brush-Saw plots remained just above 1 m throughout the measurement period. Although greater height growth might have been expected on regrowth following cutting, site factors, including coarse-textured soils and mechanical site preparation that removed organic matter, may have reduced growth response. A similar result was reported for another motor-manual cutting study (Bell et al. 1999). Mist Blower and Basal Bark treatments resulted in poplar heights of 2.5 m by year 5 (AS vs. MB and AS vs. BB, × time linear, P ≤ 0.05; in year 5, P < 0.01; MB vs. BB, P = 0.10). The height growth of other deciduous woody species was less dramatic than observed on poplar, with Control plots reaching only 2 m in height by year 5. Rates of height growth were similar regardless of treatment (P = 0.12), but endpoints differed. By year 5, trees were taller on Control, Basal Bark, Mist Blower, and Brush Saw plots, at approximately 2 m, than Aerial Spray and Annual Removal plots, at 1.0 m (P < 0.02). Patterns in stem density reflected a gradient of treatment effects rather than clear treatment groupings. Poplar density in Control plots gradually declined over time, approaching 15,000 stems/ha by year 3. Densities in treated plots declined more sharply (P < 0.01), with Mist Blower plots supporting the highest values (11,000 stems/ha) (MB vs. AS, P = 0.03) and Annual Removal plots the lowest (1,000 stems/ha). Overall, these values are higher than one might expect because they include new seedlings. In contrast to poplar, the density of other species increased slightly over time, with Control plots approaching 27,000 stems/ha by year 3 and not differing statistically from the other treatments (P = 0.55). Annual Removal plots showed the smallest gains in density, reaching 9,000 stems and differing only marginally from the increases observed on Aerial Spray plots (AS vs. AR, × time linear, P = 0.09). Effects on Low-Shrub Species At the time of treatment, low-shrub cover averaged 14% across all plots (P = 0.43) and consisted of bush honeysuckle, low sweet blueberry (Vaccinium angustifolium Ait.), red raspberry (Rubus idaeus L.), and sweetfern (Comptonia peregrina [L.] J.M. Coult.). Trace amounts of Canada honeysuckle (Lonicera canadensis Bart.), Labrador tea (Ledum groenlandicum Oeder), bog laurel (Kalmia polifolia Wangenh.), and wild rose (Rosa acicularis Lindl.) were also present. Total low-shrub cover, averaged over five growing seasons posttreatment, separated into three distinct treatment groups (Figure 3). The highest cover occurred on Brush Saw plots, medium cover on Basal Bark, Mist Blower, and Control plots, and the lowest cover on Aerial Spray and Annual Removal plots (treatments, P < 0.01). Increases in cover
increased rapidly during the initial posttreatment period and declined gradually after year 3 (time quadratic, P < 0.01). On all other plots, increases in herb cover tended to be more subtle and constant throughout the observation period (AS vs. AR, MB, and BS, P < 0.01). Year-5 comparisons supported the treatment grouping shown in Figure 4, although differences weren’t as strong after the fourth and fifth year declines in Aerial Spray plots (AS vs. AR, P = 0.04; MB, P = 0.09; BB, P = 0.09; BS, P = 0.02). By year 5, Aerial Spray plots contained about 20% cover of other herbs, whereas the plots of the other treatments typically contained about half this amount. Large-leafed aster, which peaked at over 20% in Aerial Spray plots in year two, declined steadily to about 10% cover at the end of the observation period; the same level observed in the other plots. Fireweed (Epilobium angustifolium L.) and grass species were present at low levels (< 5%) following all treatments. Low levels of “other” herbaceous species precluded statistical analyses, but trends over time based on frequency of occurrence are worth noting. Species such as trailing arbutus (Epigaea repens L.), cow wheat (Melampyrum lineare Desr.), Dutchman’s breaches (Dicentra cucullaria [L.] Bernh.), pyrola (Pyrola spp.), twinflower (Linnaea borealis L. spp. logiflora [Torr.] Hultén), and wintergreen (Gaultheria procumbens L.) were very infrequent and showed no consistent response to the any of the treatments. Wild sarsaparilla, bunchberry (Cornus canadensis L.), starflower (Trientalis borealis Raf. spp. borealis), pearly-everlasting (Anaphalis margaritacea [L.] Benth. & Hook. f. ex C.B. Clarke) and bristly sarsaprilla increased in frequency, irrespective of
Figure 3. Mean cover of low shrub species through five growing seasons posttreatment. Plotted points represent least squares treatment means; values in brackets are the standard errors, from analysis of variance of total shrub cover at each measurement period.
tended to be rapid following treatment and more gradual toward the end of the observation period (time quadratic, P < 0.01). Posttreatment year-5 comparisons confirmed that Aerial Spray plots differed from Mist Blower (P = 0.03), Basal Bark (P = 0.03), and Brush Saw plots (P = 0.01) (MB vs. BB, P = 0.91). Raspberry accounted for a large proportion of the lowshrub cover on Aerial Spray and Annual Removal plots, whereas bush honeysuckle, sweetfern, and low sweet blueberry dominated on plots of the other treatments. Effects on Herbaceous Species Pretreatment herbaceous cover averaged 10% (P = 0.13) and consisted of large-leaved aster (Aster macrophyllus L.) and small amounts of other herbs, including spreading dogbane (Apocynum androsaemifolium L.), wild sarsaparilla (Aralia nudicaulis L.), bindweed (Polygonum cilinode Michx.), bristly sarsaparilla (Aralia hispida Vent.), and other asters. Total herbaceous cover, averaged over five growing seasons posttreatment, resulted in two distinct treatment groupings, with the highest cover occurring on Aerial Spray plots and generally lower cover on all other plots (Figure 4; P < 0.01). On the Aerial Spray plots, herbaceous cover
Figure 4. Mean cover of herbaceous species through five growing seasons posttreatment. Plotted points represent least squares treatment means; values in brackets are the standard errors, from analysis of variance of total herbaceous cover at each measurement period. NJAF 17(3) 2000
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treatment. Yellow clintonia (Clintonia borealis [Aiton] Raf.) and wild lily-of-the-valley (Maianthemum canadense Desf.), increased initially in all plots, and then decreased in the third year. Lesser herbaceous species exhibiting a differential treatment response included bindweed, spreading dogbane, and orange hawkweed (Hieracium aurantiacum L.). Bindweed appeared to respond positively to vegetation control, increasing in frequency following the Aerial Spray and Annual Removal, decreasing following Basal Bark and Mist Blower treatments, and remaining relatively infrequent in Brush Saw and Control plots. Spreading dogbane exhibited the opposite preference, increasing in Basal Bark, Brush Saw, and Control plots and not changing in Aerial Spray, Annual Removal and Mist Blower plots. Orange hawkweed emerged on the sites two years after treatment and was found most frequently on Aerial Spray and Annual Removal plots. None of the tending treatments applied in this study caused any herbaceous species to be eradicated. Effects on Fern Species Bracken fern (Pteridium aquilinum [L.] Kuhn. Var. latiusculum [Desv.] L. Underw. ex A. Heller) represented 88% of all fern occurrences on the plots, averaging 8% cover at the time of treatment (P = 0.28, Figure 5). Increases in cover over time were generally steady and constant (time linear, P < 0.01), but the rates of increase separated into three distinct treatment groups (treatment × time linear, P = 0.04). Over the 5 yr posttreatment period, ferns expanded to occupy about 50% cover on Basal Bark and Control plots, 30% cover on Brush Saw and Mist Blower plots, and less than 10% cover on Aerial Spray and Annual Removal plots.
Discussion The combination of height and cover express the dominance and degree of site occupancy of a species or vegetation
Figure 5. Mean cover of fern species (predominantly Bracken) through five growing seasons posttreatment. Plotted points represent least squares treatment means; values in brackets are the standard errors, from analysis of variance of total fern cover at each measurement period. AS () = Aerial Spray, CR (●) = Annual Removal, MB (▲) = Mist Blower, BS (✚) = Brush Saw, BB (❇) = Basal Bark, and C (■) = untreated control (see text for details).
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group. A schematic side-view of the average year-5 cover and height of each of the main vegetation components (Figure 6) offers a summary of the early successional patterns observed following the six tending options studied. This representation of year-5 vegetation conditions also provides some useful insights into future succession and a basis upon which to predict the composition of stands at maturity. On the sites studied, the conventional operational treatment (aerial spray with glyphosate) modified succession in a manner that heavily favored the planted jack pine, without completely eliminating any of the other vegetation components (Figure 6). In Aerial Spray plots, approximately 57% of total cover was allocated to the crop by year 5, while deciduous trees and small shrubs (all less than one-third of the crop’s total height) accounted for 18% of total cover. Herbaceous vegetation and ferns also remained well represented at 25% of total cover. Given this pattern of development to year 5, one can be fairly confident in predicting that long-term timber management objectives will be achieved with the pure jack pine forests that are likely to dominate these areas at maturity. However, the fact that other vegetation components remained well represented on these areas, at least to year 5, suggests that this treatment may also be compatible with objectives that call for the maintenance of other values. For example, the woody cover remaining on Aerial Spray plots consisted of more than 20,000 stems per ha less than 1.5 m tall and included important wildlife species such as hazel, cherry, raspberry, honeysuckle, sweetfern, and blueberry. This observation supports previous indications that the conventional treatment may prolong wildlife food-source availability (Newton et al. 1989, Lautenschlager 1992). Reducing the cover of these other species further through annual weeding did not result in increased crop growth, suggesting that vegetation control beyond a single release may not be cost effective or desirable on sites similar to those studied. A single aerial release with glyphosate typically costs between $1002 and $150 per ha, making it the least expensive treatment tested. The conventional operational treatment also resulted in the short-term suppression of herbaceous vegetation, followed by a rapid rebounding of these species through year 5. This pattern may be explained by the interaction between glyphosate activity on herbaceous species in the understory and woody species in the overstory. Glyphosate effectively controls most existing herbaceous plants, but has no effect on plants germinating posttreatment (i.e., the many annual herbs germinating the year following treatment). Such germination and growth was likely stimulated by increased light levels reaching the forest floor, due to the nearly complete removal of woody species in the overstory. Subsequent declines in herbaceous cover between years 3 and 5 on these plots are consistent with the crop trees approaching full crown closure during this period. Three years of weeding prevented herbaceous cover from following similar patterns on the Annual Removal plots. 2
All costs are in Canadian dollars.
Figure 6. Schematic side view of the average cover (%) and height (m) of major vegetation groups five growing seasons posttreatment.
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The remaining vegetation management treatments invoked successional trajectories that resulted in various mixtures of crop, deciduous trees, and tall shrubs (Figure 6). If one decided not to use aerial application of herbicides on these sites, both Basal Bark and Mist Blower treatments offer options for managing mixed jack pine and poplar stands. Approximately 7,000 stems/ha of surviving poplar, left untreated following these applications, were only marginally shorter than the crop trees at year 5 and will likely contribute to a mixedwood stand at maturity. Of the two methods, Basal Bark applications offer the greatest flexibility in stem selection and control over stand development. For example, a practical scenario for mixedwood establishment might be to plant a reduced number of pine (e.g., 1000/ha) and apply a combined basal bark pine release and poplar thinning one or two growing seasons later. Of course, it is imperative that proper application technique be used to protect crop trees from injury (both softwood and hardwood in this case). Dow AgroSciences currently recommends the use of a wandmounted, narrow-angle, flat-fan nozzle and a very low pump pressure, with the nozzle tip placed within 2 cm of the target stem during application (Darrell Chambers, Dow AgroSciences, personal communication). The cost of basalbark treatment varies widely with the number of stems treated, but typically ranges between $200 and $300/ha. Unlike the basal bark method, the mist-blower does not offer stem selectivity. In this study, approximately 50% of the aspen survived the treatment due to a lack of application uniformity. Applicators found the physical effort and logistics involved in water transport onerous, perhaps making this treatment impractical for anything but small (< 5 ha) blocks. Application costs would reflect these limitations, making backpack applications unsuitable on most sites. Skiddermounted mist blowing equipment may be more practical for sites with good road access, at $175 to $250/ha. Regardless, the potential for operator herbicide exposure with this method may be considerable and warrants further study. In terms of impacts on noncrop species, both of the ground applied herbicide treatments resulted in greater low shrub (except raspberry) and fern cover than observed in conventionally treated areas (Figure 6). Deciduous trees and tall shrubs were also more dominant on these areas, with greater cover and height than those in Aerial Spray plots. This pattern may have resulted in herbaceous levels remaining lower than observed on aerial spray plots (i.e., a response to reduced light levels) and suggests that browse opportunities may be in decline on these areas by year 5. If one decided not to use herbicides on these sites, mixedwood management may be feasible through motormanual cutting. As described for the Basal Bark treatment, high quality mixedwood stands may be encouraged by planting pine at low densities and then releasing them at the same time that surrounding desirable hardwoods are spaced. Overall, this may be less costly than planting a high density of pine and then attempting to achieve a pure conifer stand by manually releasing them from all surrounding hardwoods (as attempted in this study). Like basal bark treatment, the cost of motor-manual cutting varies with stem density, but can range between $200 and $450/ha. 108
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In this study, manual cutting provided some of the highest levels of noncrop vegetation cover observed (Figure 6), suggesting that this alternative is likely compatible with the maintenance of other values. However, one might take precautions to ensure that the competitive pressure exerted by this cover on both conifer and hardwood crop trees is minimized. Other studies have shown that the vigor of resprouts may be reduced, in the case of aspen, by cutting stems just below the height of live crown, during mid-growing season (Bell et al. 1999) and, in white birch, by cutting stems at 0.15 cm above ground (Jobidon 1997). In the future, it may also be possible to augment the efficacy of manual cutting by applying a formulation containing a decay-causing fungus directly to the cut stumps (Pitt et al. 1999). Finally, this study suggests that leaving a jack pine plantation untreated may be inconsistent with objectives that call for the regeneration of this species and will likely result in a significant loss of any reforestation investment. Seven to nine years after planting, untreated poplar (15,000 stems/ha) had gained more than a meter in height over jack pine and dominated in cover (40% vs. 32%, Figure 6). Early growth and mortality trends for jack pine suggest poor future performance and the likelihood of low conifer wood volumes under these conditions.
Conclusions Comparative data quantifying 5 yr of vegetation dynamics in a jack pine ecosystem suggest the following management implications: 1. If management objectives include the maintenance of jack pine in future stands, some form of release is required. Of the six vegetation management methods tested, untreated areas supported the lowest year-5 posttreatment jack pine volumes and crown closures (32%). By year 5, the height of poplar, other deciduous trees, and tall shrubs equaled or exceeded that of the planted trees and their combined cover was more than double that of the crop. 2. Conventional aerial glyphosate application (1.42 kg ai/ha) produced the highest observed jack pine volumes (equivalent to 3 yr of annual vegetation removal). While pines dominated cover on treated sites (93% crown closure), quantities of deciduous trees and tall shrubs (≤ 1 m tall), low shrubs, and considerable herbaceous cover (> 30%) were retained through five growing seasons after treatment. This treatment appears consistent with management objectives that favor timber production along with the maintenance of other values during early stand development, such as vegetation diversity and wildlife habitat. 3. Glyphosate applied by mist blower may offer an alternative to aerial application on well-accessed small areas, provided objectives for pine dominance can be relaxed. As employed in this study, successional trajectories suggest a mixedwood stand will result. In terms of noncrop vegetation control and crop growth response, the mist blower application was only about one-half to two-thirds as effective as aerial application. By year 5, jack pine on
treated sites were only slightly taller (25–50 cm) than poplar, other deciduous trees, and tall shrubs, and had attained a little more than twice the crown area (65% vs. 30%). 4. Basal bark treatment with triclopyr generally provided efficacy equivalent to the mist-blower glyphosate application. Unfortunately, crop growth response was jeopardized by herbicide injury, which occurred due to excessive nozzle pressure and improper application technique. With proper care during application, this method offers a viable alternative to aerial herbicide application, particularly if it is used to encourage mixedwood stand development. 5. Where choice or legislation exclude herbicide use, cutting offers a viable, although potentially expensive, alternative. As tested, brush-saw treatment in October provided crop growth response and efficacy equivalent to the mist blower/glyphosate application. Jack pine on treated sites were over 1 m taller than poplar, other deciduous trees, and tall shrubs and contained more than twice the crown area (73% vs. 33%). Like basal bark applications, this method may be most effective when used selectively, to create a quality mixedwood forest.
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