Effect of long-term burn-pruning on the flora in a lowbush blueberry (Vaccinium angustifolium Ait.) stand

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1 Effect of long-term burn-pruning on the flora in a lowbush blueberry (Vaccinium angustifolium Ait.) stand B. G. Penney 1, K. B. McRae 2, and A. F. Rayment 3 1 Atlantic Cool Climate Crop Research Centre, Agriculture and Agri-Food Canada, P.O. Box 39088, St. John s, Newfoundland and Labrador, Canada A1E 5Y7 ( penneyb@agr.gc.ca); 2 Atlantic Food and Horticulture Research Centre, Agriculture and Agri-Food Canada, Kentville, Nova Scotia, Canada B4N 1J5; and Avenue, Leduc, Alberta, Canada T9E 5A3. Contribution no Received 12 April 2007, accepted 9 October Penney, B. G., McRae, K. B. and Rayment, A. F Effect of long-term burn-pruning on the flora in a lowbush blueberry (Vaccinium angustifolium Ait.) stand. Can. J. Plant Sci. 88: The effect of burn-pruning on the flora in a natural stand of lowbush blueberry was studied over a 24-yr period in Newfoundland and Labrador, Canada. Treatments were: not burned and burn-pruned every 2nd, 3rd, or 4th year. A vegetative survey was conducted before burning and periodically in succeeding years. Following statistical analyses, species were grouped according to their response to burning, as follows: those not significantly affected; those eliminated or whose frequency of occurrence was reduced; and those whose occurrence was increased. Initially, burning virtually eliminated Juniperus communis var. depressa, Empetrum nigrum, Cladina rangiferina, Lycopodium clavatum and Pleurozium schreberi, reduced the frequency of occurrence of nine species by 6 to 69%, and increased 13 others by 1 to 2050%. With burning, Polytrichum commune and Fragaria virginiana ssp. glauca, in particular, increased very early in the study to become two of the most prevalent species. Also, except for some initial effects of burning, the lowbush blueberry and some initially prevalent species (Festuca filiformis, Maianthemum canadense, Danthonia spicata, Cornus canadensis and Luzula multiflora var. acadiensis) remained among the most dominant species. Of the species studied, only seven each of those increased or decreased by burning were affected by the burnpruning cycle. In both groups, the greatest increases or decreases in the frequency of occurrence were obtained with the 2- yr burn-pruning cycle. Key words: Lowbush blueberry, Vaccinium angustifolium, burning, pruning, plant succession, weeds, fire, flora Penney, B. G., McRae, K. B. et Rayment, A. F Incidence de l e lagage-brûlis prolonge sur la flore d une bleuetie` re (Vaccinium angustifolium Ait.). Can. J. Plant Sci. 88: Les auteurs se sont intéresse s aux conséquences de l e lagage et des bruˆ lis sur la flore d un peuplement naturel de bleuet nain durant une pe riode de 24 ans, a` Terre-Neuve-et-Labrador, au Canada. Les traitements étaient les suivants : aucun bruˆ lis et e lagage-bruˆ lis aux 2, 3 ou 4 ans. Les auteurs ont analyse la ve gétation avant les bruˆ lis et pe riodiquement par la suite. Ils ont groupe les espe` ces comme suit, selon leur re action au traitement en recourant a` des me thodes d analyse statistique : plantes peu touche es; plantes supprime es ou moins abondantes; plantes plus abondantes. Au de part, les bruˆ lis ont virtuellement élimine Juniperus communis var. depressa, Empetrum nigrum, Cladina rangiferina, Lycopodium clavatum et Pleurozium schreberi, diminue la fréquence de neuf autres espe` ces de 6 à 69 % et accru l abondance de 13 autres de 1 à %. Apre` s les bruˆ lis, Polytrichum commune et Fragaria virginiana ssp. glauca ont vu leur population augmenter très rapidement au de but de l e tude pour devenir deux des espe` ces les plus courantes. Outre certains effets initiaux attribuables aux bruˆ lis, le bleuet nain et quelques espe` ces de ja` abondantes (Festuca filiformis, Maianthemum canadense, Danthonia spicata, Cornus canadensis et Luzula multiflora var. acadiensis) ont continue de figurer parmi les espe` ces dominantes. Sur les espe` ces examine es, sept seulement des groupes dont les bruˆ lis accroissaient ou re duisaient la population ont e té affecte es par le cycle d e lagage et de bruˆ lis. Dans ces deux groupes, la plus forte hausse ou baisse d abondance se produit avec le cycle d e lagage-bruˆ lis de deux ans. Mots clés: Bleuet nain, Vaccinium angustifolium, bruˆ lis, e lagage, alternance des plantes, mauvaises herbes, flore The lowbush blueberry (Vaccinium angustifolium Ait.) is a low-growing (927 cm) deciduous perennial shrub that is endemic to a major portion of northeastern North America (Vander Kloet 1988). It is typically found growing on Podzolic soils that are acidic, infertile and that usually have a surface organic layer (Trevett 1962). This plant is an important fruit crop in Maine, Quebec, Nova Scotia, New Brunswick, Prince Edward Island, and Newfoundland and Labrador with approximately ha (Yarborough 1997) of natural stands under management. The 5-yr ( ) average annual 351 production from these areas is approximately t with about 38% of total production from Atlantic Canada, 36% from Maine and 26% from Quebec (Yarborough 2007). Natural stands of the lowbush blueberry in Newfoundland developed as a result of accidental forest fires and wood cutting by residents over many years (Badcock 1965). Some plants that may be found growing with the lowbush blueberry in Newfoundland include lichens, club-mosses, grasses such as Agrostis capillaris L. ( A. tenuis Sibth.), Danthonia spicata (L.) Roem. &

2 352 CANADIAN JOURNAL OF PLANT SCIENCE Schult. and Festuca filiformis Pourret (F. tenuifolia Sibth., F. capillata Lam.) and herbs and shrubs such as Achillea millefolium L., Anaphalis margaritacea (L.) Benth., Centaurea nigra L., Cornus canadensis L., Fragaria virginiana ssp. glauca (S. Wats.) Staudt, Hieracium lachenalii K. C. Gmel. (H. vulgatum Fries), Kalmia angustifolia L., Leontodon autumnalis L., Maianthemum canadense Desf., Prenanthes trifolium (Cass.) Fernald, Rumex acetosella L., Sibbaldiopsis tridentata (Ait.) Rydb. (Potentilla tridentata Ait.), Solidago spp. and Veronica officinalis L. (Rayment 1965; Penney and McRae 2000). Many of these species may also be found in blueberry fields in Nova Scotia (McCully et al. 1991), New Brunswick (Hall 1955, 1959), and Quebec (Bouchard 1986; Lapointe and Rochefort 2001). In fact, the weed floras in blueberry fields in Nova Scotia, New Brunswick, Quebec and Maine prior to the widespread use of selective herbicides were similar (Jensen and Yarborough 2004). Techniques to improve and sustain high lowbush blueberry production include land improvements, pollination, fertilizer application, the use of pesticides to control weeds, insects and diseases and pruning, which is usually conducted biennially by burning or mowing fields (Blatt et al. 1989; Yarborough 1996). However, due to the high cost of fuel for burning, mowing has been widely adopted by growers (Yarborough 1996). In their review of weed management in the lowbush blueberry, Jensen and Yarborough (2004) state that the use of herbicides and the practice of mow-pruning has led to a twofold increase in the number of species and the appearance of some species that are normally associated with cultivated crops, e.g., Digitaria spp., Galeopsis tetrahit L. and Chenopodium album L. Furthermore, they suggest that since burning reduces weed seeds and is effective in controlling certain weeds, insects and diseases, it should be considered as part of an integrated approach to manage these problems. The short-term effects of burning on the flora of lowbush blueberry land have been documented (Hall 1955; Hoefs and Shay 1981), but we could not find any report of long-term studies on associated plant growth under repeated burn-pruning. To address this and other issues we conducted a 24-yr study to determine how 2-, 3- and 4-yr burn-pruning cycles affect blueberry production, the surface organic layer, and the flora. In this paper we present the short- and long-term effects of burn-pruning on the floral composition of a lowbush blueberry stand. MATERIALS AND METHODS This research was part of a study conducted on an unfertilized, natural stand of lowbush blueberry from 1962 to 1986 at the Atlantic Cool Climate Crop Research Centre s Blueberry Substation in Avondale, Newfoundland and Labrador (lat ?N; long ?W; altitude, 133 m above sea level) that determined the effects of burn-pruning on blueberry production and the soil surface organic layer (Penney et al. 1997). The site is an exposed ridge that is typical of the better blueberry growing areas in eastern Newfoundland. Documented information regarding the origin and history (with respect to fire) of the Blueberry Substation is limited. The Substation was likely originally forested, since it is mainly surrounded by trees. It was burned by a forest fire in 1892, and while no reports of additional fires between 1892 and 1953 could be found, it has been barren (except for the lowbush blueberry and lowgrowing weedy species) since as early as 1950 and was frequented at that time by local residents to pick blueberries (R. M. Doyle, personal communication). The Government of Newfoundland conducted nonchemical experiments (dates of ripening, hand-picking vs. raking) in 1952 (Anonymous 1953) and 1953 (Anonymous 1954) and thus the site may have been burn-pruned in In 1954, the Blueberry Substation, consisting of approximately 12 ha, was leased to the Federal Government of Canada (Anonymous 1966). Burn-pruning was conducted at the Blueberry Substation in 1954, but it is uncertain whether or not the specific area used for the experiment was also burned (H. W. R. Chancey, personal communication). To our knowledge, there was no burn-pruning between 1955 and initiation of experimental burn-pruning treatments in The soil is a moderately well-drained Orthic Humo-Ferric Podzol, classified locally as the Cochrane Series (Heringa 1981). The experimental design was a randomized complete block with four blocks, each having ten m plots separated from each other by a similarly-sized buffer area. Treatments for each block included: not burned (one plot); burned every 2nd year (two plots); burned every 3rd year (three plots); and, burned every 4th year (four plots). Multiple plots were used for each burn-pruning treatment so that each treatment could be initiated in more than one year. Thus, the 4-yr burnpruning treatment with four plots was initiated in 4 consecutive years and similarly for the 3- and 2-yr treatments with three and two plots per block, respectively. This procedure exposed the pruning treatments to a greater variation in seasonal weather conditions over the experimental period and permitted the collection of data (including crop) for each treatment, every year. This was particularly important for the less frequently burned plots considering the relatively short duration of this study. Burn-pruning was conducted each spring between early April and late May using straw applied at a rate of 21 t ha 1. No other crop management procedure was practised during the experimental period. A vegetative survey of all plots was conducted in the fall of 1961 (initial survey before burn-pruning in 1962) and thereafter annually from 1969 to 1982 and in All surveys were conducted between Sep. 11 and Oct. 17. The survey involved placing a prefabricated

3 PENNEY ET AL. * EFFECT OF BURN-PRUNING ON FLORA OF LOWBUSH BLUEBERRY m wire-framed grid consisting of seventyeight cm quadrats on each plot and recording the presence of species observed in each quadrat. Plant species identified by A. F. Rayment and B. G. Penney are as follows: Abies balsamea (L.) Mill., Achillea millefolium, Anaphalis margaritacea, Cornus canadensis, Kalmia angustifolia, Larix laricina (DuRoi) K. Koch, lowbush blueberry, Ledum groenlandicum Oeder, Osmunda cinnamomea L., Picea mariana (P. Mill.) B. S. P., Rumex acetosella, Sibbaldiopsis tridentata, Vaccinium sp., and, Voila sp. The following species were identified at the Eastern Cereal and Oilseed Research Centre (Agriculture and Agri-Food Canada, National Program on Environmental Health Biodiversity, Vascular Plant Herbarium, Central Experimental Farm, Ottawa, Ontario, Canada K1A 0C6), and the Canadian Museum of Nature (P. O. Box 3443, Station D, Ottawa, Ontario, Canada K1P 6P4): Agrostis capillaris, Centaurea nigra, Chamerion angustifolium (L.) Holub ssp. angustifolium (Epilobium angustifolium L.), Cladina rangiferina (L.) Nyl., Coptis trifolia (L.) Salisb. [C. trifolia ssp. groenlandica (Oeder) Hulte n], Danthonia spicata, Empetrum nigrum L., Euphrasia stricta J. F. Lehm. (E. rigidula Jord.), Festuca filiformis, Fragaria virginiana ssp. glauca, Hieracium lachenalii, Juniperus communis var. depressa Pursh ( J. communis L.), Leontodon autumnalis, Linnaea borealis L., Luzula multiflora var. acadiensis Fernald, Lycopodium annotinum L., Lycopodium clavatum L., Lycopodium obscurum L., Lycopodium sabinifolium Willd., Maianthemum canadense, Oclemena blakei (Porter) Nesom [Aster blakei (Porter) House], Pleurozium schreberi (Brid.) Mitt., Polytrichum commune Hedw., Rosa nitida Willd., Rubus setosus Bigelow, Solidago macrophylla Pursh, Solidago rugosa Mill., Spiraea alba var. latifolia (Ait.) Dippel [Spiraea latifolia (Ait.) Borkh.], Veronica officinalis, andviburnum nudum var. cassinoides (L.) Torr. & A. Gray (Viburnum cassinoides L.). Sources used for nomenclature were Darbyshire et al. (2000), Brodo et al. (2001) and the Integrated Taxonomic Information System (2007). After the initial survey, changes in the occurrence of individual species over the 24-yr period were documented by annual surveys and classified as follows: Period 1, ; Period 2, ; and, Period 3, Plots within blocks were classified according to the four burn-pruning treatments. The major cross-classification for statistical analysis consists of four blocks and four burn-pruning cycles by three periods. Year of initiation, within the 2nd-, 3rd-, and 4th-yr burnpruning treatments, was included as a minor classification. The full cross-classification for the analysis of variance (ANOVA) consists of 120 units: 4 blocks 3 periods 10 treated plots (i.e., four burn-pruning treatments6 initiation years within burn-pruning cycles). The pre-burn occurrence of species, observed in 1961, was used as a covariate to adjust for initial differences in floral composition. The partitioning of the sums of squares in the ANOVA follows standard conventions (Table 1). In the ANOVA, blocks, plots and initiation year within the burn-pruning cycles were taken to be random effects, and burn-pruning cycle with proportional replication and period (denoted by P) were estimated as fixed factors. The formal ANOVA model is: y ijkl yb i P j BP ij T k PT jk E 1(i;j;k) where y denotes the occurrences of a species; B denotes block, i1... 4; P denotes period, j1, 2, 3; E denotes the residual error; and T denotes burn-pruning cycle, k0, 2, 3, 4; and, the subscript l indexes the initiation year within blocks, periods and burn-pruning cycles with l1... k for k0; and where the random effects are normally distributed as BN (0, s 2 B), BPN (0, s 2 BP), and EN (0, s 2 ). Covariate effects were estimated in each experimental stratum. Standard contrasts partitioned the sums of squares for burn-pruning as follows: not burned vs. burn-pruned (mean of 2-, 3- and 4-yr burn-pruning cycles) denoted by B; and the contrasts 2-yr vs. mean of 3- and 4-yr cycles and 3-yr vs. 4-yr cycle denoted by C. Another view of the data was formed by classifying each plot-year combination within blocks and period by the blueberry cropping year after burn-pruning as follows: not burned, burn year, first-crop year, secondcrop year, and third-crop year. This classification defined 60 experimental units (4 blocks3 periods 5 cropping years). Partitioning of the degrees of freedom Table 1. Partitioning of the degrees of freedom in the ANOVA for the effect of burn-pruning cycles on the flora in lowbush blueberry plots over three production periods Source of variation Among field blocks 3 Covariate 1 Residual 2 Blocks and periods 8 Period 2 Covariate 1 Residual 5 Among plots within blocks and periods 108 Burn-pruning 3 Not burned vs. burn-pruned (2-, 3- and 4-yr 1 burn-pruning cycles) 2-yr vs. 3- and 4-yr burn-pruning cycles 1 3-yr vs. 4-yr burn-pruning cycle 1 Periodburn-pruning 6 Periodnot burned vs. burn-pruned 2 Period2-yr vs. 3- and 4-yr burn-pruning cycles 2 Period3-yr vs. 4-yr burn-pruning cycle 2 Covariate 1 Residual 98 Total 119 d.f.

4 354 CANADIAN JOURNAL OF PLANT SCIENCE for this ANOVA is shown in Table 2. The average occurrence of each species was calculated for each of the 60 unit-combinations by averaging the data over plots and years within periods, and in some cases averaging over the same plot. The formal ANOVA model is: y ijk yb i P j BP ij T k PT jk E k(i;j) where y denotes the occurrences of a species; B denotes block, i1... 4; P denotes period, j1, 2, 3; T denotes years after burn-pruning cycle within blocks and periods where knot burned, 0, 1, 2, 3, 4 yr; and E denotes the residual error; and where the random effects are normally distributed as BN (0, s 2 B), BPN (0, s 2 BP), and EN (0, s 2 ). This classification is useful for assessing the recovery or decline of species in the cropping years following burn-pruning. In both ANOVAs, the frequency of occurrence data for each species were scaled to occurrences per 1000 quadrats, transformed to the square root scale for statistical analysis, and the means back-transformed for presentation in the tables. Data for species with a maximum occurrence of B40 per 1000 quadrats (in the period burn-pruning interaction table) were considered insufficient for reliable statistical analysis. The frequency of occurrence data for Lycopodium sabinifolium and Lycopodium obscurum were combined and statistically analysed together due to uncertainty in field identification. Data for Solidago macrophylla and Solidago rugosa were similarly treated for the same reason. Each pair of combined species is considered as a single species for this study. The statistical programming language GenStat, Release 7.1 (Payne 2003) was used for all statistical analyses. Unless stated otherwise, Table 2. Partitioning of the degrees of freedom in the ANOVA for the direct effects on the flora in the burn-pruning year and the indirect effects in the lowbush blueberry cropping years after burn-pruning, ignoring the frequency of burn-pruning Source of variation Blocks 3 Period 2 Residual 6 Year after burn 4 Not burned vs. burn-pruned 1 Linear (years after burn-pruning) 1 Deviations 2 Periodyear after burn 8 Periodnot burned vs. burn-pruned 2 Periodlinear 2 Deviations 4 Residual 36 Total 59 d.f. the significance level for statistical tests was set at 5% (i.e., P50.05). Table 3 gives an overall view of species studied with respect to their prevalence in unburned plots early in the study and in burned plots over the three periods. Results for four species (Larix laricina, Osmunda cinnamomea, Picea mariana, andcoptis trifolia) were excluded from this report due to very low (B1 per 1000 quadrats) frequency of occurrences, as were two others (Vaccinium sp. and Viola sp. with occurrences of B20 and B30 per 1000 quadrats, respectively) due to incomplete identification and another due to an uncertain identification (possibly Pyrola sp. with B4 occurrences per 1000 quadrats). For discussion purposes, species are referenced as follows: minor, those with B100 occurrences per 1000 quadrats; intermediate, those with occurrences; and most prevalent, those with 500 occurrences. RESULTS AND DISCUSSION Overview A wide range in the occurrence of species was evident for the unburned check (Period 1, ) with 17 species (47% of the total flora) having more than 100 occurrences per 1000 quadrats and seven (19% of the total flora) of them with more than 500 (Table 3). The seven most frequently occurring species (except for Cladina rangiferina, which was eliminated by burning) remained as some of the more prevalent species throughout the experimental period. The intermediate group included 10 species initially, and it was this group that was most affected by burning (Table 3). During Period 1, one species (Fragaria virginiana ssp. glauca) increased sufficiently to become part of the most prevalent group and similarly for another species (Polytrichum commune) during Period 2. Furthermore, during Period 3 another species (Agrostis capillaris) also increased sufficiently to become part of the most prevalent group of species, and while two (Kalmia angustifolia, Anaphalis margaritacea) remained as intermediate species, five others [Pleurozium schreberi, Veronica officinalis, Lycopodium clavatum, Lycopodium spp. (L. sabinifoliuml. obscurum), Solidago spp. (S. macrophyllas. rugosa)] decreased sufficiently to be classified as minor species. The 21 initially minor species, except for Centaurea nigra, Achillea millefolium and Hieracium lachenalii, remained as minor species (Table 3). The occurrence of C. nigra, A. millefolium and H. lachenalii increased to more than 100 occurrences per 1000 quadrats during Period 1, 2 and 3, respectively, essentially replacing Pleurozium schreberi, Veronica officinalis, Lycopodium clavatum, Lycopodium spp. (L. sabinifoliuml. obscurum) and Solidago spp. (S. macrophyllas. rugosa) in the intermediate group and also Cladina rangiferina, one of the original most prevalent species.

5 PENNEY ET AL. * EFFECT OF BURN-PRUNING ON FLORA OF LOWBUSH BLUEBERRY 355 Table 3. Occurrence of plant species in a natural stand of lowbush blueberry in the unburned check in Period 1 and in burned plots over the three periods Frequency of occurrence (no. per 1000 quadrats) Unburned check plots Burned plots Species Period 1 ( ) Period 1 ( ) Period 2 ( ) Period 3 ( ) Significant effects z (P50.05) Table reference Lowbush blueberry B 7c Festuca filiformis P, Cy, PCy 4c, 6 Maianthemum canadense PB 4c Danthonia spicata B, C, Cy 4c, 5, 6 Cornus canadensis B, PB 7c Cladina rangiferina B, P 4a Luzula multiflora var. acadiensis B, C, Cy, P, PB 4c, 5, 6 Pleurozium schreberi B, P, PB 4b Veronica officinalis B, C, Cy, P, PB, PCy 4b, 5, 6 Kalmia angustifolia B, C, Cy, P 4c, 5, 6 Lycopodium clavatum B, C, Cy, PB 4b, 5, 6 Polytrichum commune B, P, Cy, PB 7b Lycopodium spp. y B, C, Cy, P 4b, 5, 6 Fragaria virginiana ssp. glauca B, C, PB 7b, 8 Solidago spp. x B, C, P 4b, 5 Anaphalis margaritacea B, C 7c, 8 Agrostis capillaris B, C, P, Cy 7c, 8, 9 Juniperus communis var. depressa B, P, PB 4a Centaurea nigra B, P 7b Empetrum nigrum B 4a Achillea millefolium B, C, Cy 7c, 8, 9 Leontodon autumnalis B, C, Cy 7c, 8, 9 Oclemenablakei B 4c Hieracium lachenalii B, P, Cy 7b Linnaea borealis P, PB 7a Rumex acetosella B, C, Cy, P, PB, PCy 7a, 8, 9 Euphrasia stricta B, C, P, PCy 7b, 8, 9 Lycopodium annotinum w Ledum groenlandicum Viburnum nudum var. cassinoides Rubus setosus Abies balsamea Spiraea alba var. latifolia Sibbaldiopsis tridentata Rosa nitida Chamerion angustifolium ssp. angustifolium z Bnot burned vs. burn-pruned; Pamong periods; Cylinear contrast among cropping years; Camong 2-, 3- and 4-yr burn-pruning cycles. y Lycopodium sabinifoliumlycopodium obscurum. x Solidago macrophyllasolidago rugosa. w occurrences wereb40 per 1000 quadrats and were insufficient for statistical analysis. Some species occurred more or less frequently in the unburned check plots over the three periods (Tables 4 and 7). These changes were likely due to natural succession, but influenced perhaps by repeated harvesting and species surveys on the same plots. The interaction between burn-pruning cycle and period was not significant for any species. This result indicates that the effect of burn-pruning cycle was similar to within-block sampling variation across the three periods and thus is reported as a single factor averaged over the three periods. The interaction between the contrast not burned vs. burn-pruned and period, however, was significant for many species. Species that Did Not Appear to be Affected by Burn-pruning The species Viburnum nudum var. cassinoides, Spiraea alba var. latifolia, Sibbaldiopsis tridentata and Rosa nitida did not appear to be adversely affected by burning, but this could not be confirmed by statistical analyses due to low (B40 per 1000 quadrats) occurrences (Table 3). No reports on the effect of burning on S. tridentata and R. nitida could be found, but Hall (1955) reports that burning resulted in the elimination of V. nudum var. cassinoides and the appearance of S. alba var. latifolia. He suggests that S. alba var. latifolia grew from seeds that were already in the soil or that were

6 356 CANADIAN JOURNAL OF PLANT SCIENCE Table 4. Plant species that were initially reduced or initially eliminated by burn-pruning Frequency of occurrence (no. per 1000 quadrats) z Species Burn-pruned Period 1 ( ) Period 2 ( ) Period 3 ( ) a. Species that were eliminated or nearly so in Period 1 and that did not re-occur Juniperus communis var. depressa no yes Empetrum nigrum no yes Cladina rangiferina no yes b. Species that continued to decrease over periods compared with those in unburned plots Lycopodium clavatum no yes Pleurozium schreberi no yes Lycopodium spp. y no yes Veronica officinalis no yes Solidago spp. x no yes c. Species that subsequently did not change significantly over periods compared with those in unburned plots Oclemenablakei no yes Kalmia angustifolia no yes Danthonia spicata no yes d. Species that subsequently recovered over periods compared with those in unburned plots Luzula multiflora var. acadiensis no yes Maianthemum canadense no yes Festuca filiformis no yes z Data arranged in descending order of reduction by burn-pruning within groups in Period 1. y Lycopodium sabinifoliumlycopodium obscurum. x Solidago macrophyllasolidago rugosa. brought in with the straw for burn-pruning. The different result of Hall (1955) with V. nudum var. cassinoides is puzzling considering that its rhizomes are usually found 4 cm deep in mineral soil (Flinn and Wein 1977), which presumably would provide some protection from fire injury. However, Hall s (1955) results are based on 2 consecutive years of burn-pruning that could have been severe enough to eliminate this species. Species that were Initially Reduced or Initially Eliminated by Burn-pruning Species in this group were subdivided according to their response over periods: those that did not re-occur (Table 4a); those that continued to decrease (Table 4b); those that did not change significantly (Table 4c); and those that recovered at least to pre-burn levels (Table 4d). Species that Did Not Re-occur over Periods The species Juniperus communis var. depressa, Empetrum nigrum and Cladina rangiferina were eliminated or nearly so by initial burning and did not re-occur in plots during the experiment (Table 4a). Both Lycopodium annotinum and Abies balsamea also appear to be eliminated by burning, but this could not be confirmed by statistical analyses due to low occurrence (B40 per 1000 quadrats) (Table 3). These results are in general agreement with others [L. annotinum, A. balsamea (Hall 1955); J. communis (Hobbs et al. 1984); and, C. rangiferina (Lynham et al. 1998)]. The poor survival of some species in this group was probably due to vulnerability of perennating parts to burning, as in the shallow stems and rhizomes of L. annotinum (Hall 1955) and E. nigrum (Hobbs et al. 1984), the surface placement of unprotected seeds in J. communis (Hobbs et al. 1984)

7 PENNEY ET AL. * EFFECT OF BURN-PRUNING ON FLORA OF LOWBUSH BLUEBERRY 357 and A. balsamea (Rowe 1983) and the thallus fragmentation of C. rangiferina (Johnson 1981). Species that Continued to Decrease over Periods The occurrence of Lycopodium clavatum, Pleurozium schreberi, Lycopodium spp. (L. sabinifoliuml. obscurum), Veronica officinalis and Solidago spp. (S. macrophyllas. rugosa) decreased by 96% (13 vs. 364 occurrences per 1000 quadrats), 89% (55 vs. 494), 69% (86 vs. 281), 67% (134 vs. 401) and 11% (193 vs. 218), respectively, in Period 1. While occurrences continued to decrease over time, each species was still present at the end of the experiment (Table 4b). Both V. officinalis and Solidago spp., appear to rely on seed for establishment after fire [V. officinalis (Mallik and Gimingham 1983; Hobbs et al. 1984); Solidago spp. (Hall 1955)] and thus their decline over periods may have been due, in part, to destruction of their seed reserves by frequent burning. Moore and Wein (1977) report that even a low-intensity fire would destroy a high proportion of seeds since many of them are in the litter and surface layers of the organic pad. Increased competition, particularly for V. officinalis (Hobbs et al. 1984), could also have contributed to their decline over periods. The decline in L. clavatum was probably due to its perennating parts being located on the soil surface (Fernald 1950; Wagner and Beitel 1993) thus making it more susceptible to fire injury. Similarly for P. schreberi, persistence after a fire depends on the survival of tissue for eventual regeneration by vegetative means (Hobbs et al. 1984). The species that comprise Lycopodium spp. appear to be somewhat more persistent than L. clavatum and P. schreberi and this is probably due to their subterranean stems (Fernald 1950; Everett 1981; Wagner and Beitel 1993). Species that Did Not Change Significantly over Periods The occurrence of Oclemena blakei, Kalmia angustifolia and Danthonia spicata was reduced by 68% (6 vs. 19 occurrences per 1000 quadrats), 54% (177 vs. 384) and 29% (576 vs. 813), respectively, in Period 1 by burning, but there were no significant changes over periods (Table 4c). Ledum groenlandicum also appears to respond similarly, but this could not be confirmed by statistical analyses due to low occurrence (B40 per 1000 quadrats) (Table 3). The survival and long-term persistence of these species was probably due to their rhizomes or other perennating parts being deep enough in the soil [K. angustifolia, L. groenlandicum (Flinn and Wein 1977)] to avoid or minimize fire damage. Another reason may be burn-pruning being conducted when the soil was wet or frozen (Penney et al. 1997) which would also minimize potential damage to these organs. Although a decline in L. groenlandicum and D. spicata after fire has been reported by Vogl (1964) and Swan (1970), respectively, the effect of burning on O. blakei has not previously been reported. Species that Recovered over Periods The occurrence of Luzula multiflora var. acadiensis, Maianthemum canadense and Festuca filiformis was reduced 28% (476 vs. 665 occurrences per 1000 quadrats), 14% (701 vs. 819) and 6% (823 vs. 878), respectively, in Period 1 by burning, but they recovered at least to pre-burn levels by Period 2 (Table 4d). The effect of burning on L. multiflora var. acadiensis, and F. filiformis has not previously been documented while results for M. canadense are inconclusive. Swan (1970) found that burning increased M. canadense while Hall (1955) reports a significant decrease with no recovery in a 4-yr study in which trees were cleared from the site in the first year followed by burning in the third and fourth years. Differences between our results for M. canadense and those of Hall (1955) could be due to less severe burning and/or the perennating organs being possibly deeper in the soil in our study. Flinn and Wein (1977) report that the depth of perennating organs of M. canadense in the soil varied fromb0.5 to 6 cm among 18 sites in New Brunswick. Effect of Burn-pruning Cycle on Species Decreased by Burn-pruning Of the 14 species in this group, only seven were significantly affected by burn-pruning cycle (Table 5). While all burn-pruning cycles reduced the occurrence of these species, the greatest decreases were obtained with the 2-yr cycle. Reductions for the 2-yr cycle in descending order of reduction for the various species were as follows: Lycopodium clavatum, 99% (3 vs. 306 occurrences per 1000 quadrats); Lycopodium spp. (L. sabinifoliuml. obscurum), 97% (11 vs. 338); Veronica officinalis, 91% (19 vs. 216); Kalmia angustifolia, 64% (177 vs. 496); Solidago spp. (S. macrophyllas. rugosa), 57% (111 vs. 258); Danthonia spicata, 38% (526 vs. 843); and, Luzula multiflora var. acadiensis, 23% (604 vs. 784). The lesser decreases of occurrence for species in the less frequently burned plots were probably due to recovery in the non-burn years (Table 6). While there were no significant differences (P0.086) among cropping years for Solidago spp. (S. macrophyllas. rugosa) there was a trend of increased occurrence (157, 192 and 200 occurrences per 1000 quadrats for the first, second and third year after burning, respectively) which may account for the increase in occurrence with a decrease in burning frequency. With respect to Festuca filiformis, the increase in occurrence following burning occurred only in Period 1 as indicated by the interaction PCy (Table 3). Furthermore, although there were no significant differences (P0.270) among burn-pruning cycles, a similar trend of increased occurrence for F. filiformis was observed in this period with a decrease in burning frequency. Occurrences per 1000 quadrats for this comparison were as follows: not burned, 878; 2-yr burn-pruning cycle, 787; 3-yr cycle, 808; and, 4-yr cycle,

8 358 CANADIAN JOURNAL OF PLANT SCIENCE Table 5. Effect of burn cycle on plant species whose frequency of occurrence was reduced by burn-pruning Frequency of occurrence (no. per 1000 quadrats) z Species Not burned 2-yr cycle 3-yr cycle 4-yr cycle Lycopodium clavatum Lycopodium spp. y Veronica officinalis Kalmia angustifolia Solidago spp. x Danthonia spicata Luzula multiflora var. acadiensis z Data arranged in descending order of reduction by the 2-yr burn-pruning cycle. y Lycopodium sabinifoliumlycopodium obscurum. x Solidago macrophyllasolidago rugosa. Table 6. Plant species whose frequency of occurrence was initially reduced by burn-pruning, but which increased in subsequent blueberry crop years 853. In Periods 2 and 3, occurrences for F. filiformis were near the maximum (950 per 1000 quadrats) with no significant differences among cropping years nor among burn-pruning cycles. Species whose Frequency of Occurrence was Increased Initially by Burn-pruning In this group, two species subsequently decreased (Table 7a), five subsequently increased (Table 7b) and six thereafter did not change significantly (Table 7c) over periods. Species occurrence in descending order of increase by burning for Period 1 was as follows: Rumex acetosella (2050%, 172 vs. 8 occurrences per 1000 quadrats); Hieracium lachenalii (200%, 39 vs. 13); Achillea millefolium (191%, 96 vs. 33); Fragaria virginiana ssp. glauca (177%, 609 vs. 220); Linnaea borealis (142%, 29 vs. 12); Agrostis capillaris (83%, 327 vs. 179); Polytrichum commune (67%, 489 vs. 292); Euphrasia stricta (67%, 5 vs. 3); Centaurea nigra (56%, 112 vs. 72); Leontodon autumnalis (50%, 45 vs. 30); Anaphalis margaritacea (34%, 247 vs. 184); Cornus canadensis (24%, 926 vs. 748); and lowbush blueberry (1%, 991 vs. Frequency of occurrence (no. per 1000 quadrats) Species Not burned Burn yr z Crop 1 yr y Crop 2 yr Crop 3 yr Lycopodium clavatum Lycopodium spp. x Veronica officinalis Kalmia angustifolia Danthonia spicata Luzula multiflora var. acadiensis Festuca filiformis w z Lowbush blueberry vegetative year. y First year after burning. x Lycopodium sabinifoliumlycopodium obscurum. w Occurrences per 1000 quadrats for the crop years during Period 1 ( ); occurrences were greater than 950 and not significantly different in Periods 2 ( ) and 3 ( ). 978). Both Rubus setosus and Chamerion angustifolium ssp. angustifolium also appear to increase by burning, but this could not be confirmed by statistical analyses due to low occurrence (B40 per 1000 quadrats) (Table 3). An increase or appearance after burning for some of these species has also been reported by other authors [R. acetosella (Hall 1955), F. virginiana (Hoefs and Shay 1981; Lynham et al. 1998), P. commune (Lynham et al. 1998), and C. angustifolium ssp. angustifolium (Vogl 1964; Johnson 1981; Lynham et al. 1998)]. Furthermore, while Hall (1959) did not study the effect of burning on P. commune and A. capillaris, he reports that these were two of the most prevalent species in blueberry fields developed from old abandoned hay-fields. Also, although he did not mention that these fields were burned, it is highly probable that burn-pruning was a part of the development process. With respect to A. millefolium, Swan s (1970) result differs from ours in that its occurrence was lower in burned than in unburned land. However, his report indicates that a large number of species increased after burning, so increased competition may be the reason for the low

9 PENNEY ET AL. * EFFECT OF BURN-PRUNING ON FLORA OF LOWBUSH BLUEBERRY 359 Table 7. Plant species whose occurrence was increased initially by burn-pruning Frequency of occurrence (no. per 1000 quadrats) z Species Burn-pruned Period 1 ( ) Period 2 ( ) Period 3 ( ) a. Species that subsequently decreased over periods compared with those in unburned plots Rumex acetosella No Yes Linnaea borealis No Yes b. Species that continued to increase over periods compared with those in unburned plots Hieracium lachenalii No Yes Fragaria virginiana ssp. glauca No Yes Polytrichum commune No Yes Euphrasia stricta No Yes Centaurea nigra No Yes c. Species that subsequently did not change significantly over periods compared with those in unburned plots Achillea millefolium No Yes Agrostis capillaris No Yes Leontodon autumnalis No Yes Anaphalis margaritacea No Yes Cornus canadensis No Yes Lowbush blueberry No Yes z Data arranged in descending order of increase by burn-pruning within groups in Period 1. occurrence of A. millefolium in burned land. With respect to the lowbush blueberry, while research by Lynham et al. (1998) supports our findings that burning increases its occurrence, others report no change (Hall 1955) or a decrease after burning (Vogl 1964). Similarly for C. canadensis, while Hall (1955) reports no change in occurrence after burning, Hoefs and Shay (1981) report an increase. The effect of burning on H. lachenalii, E. stricta, C. nigra, L. autumnalis and A. margaritacea has not previously been reported. For effects over periods, Rumex acetosella and Linnaea borealis were practically eliminated during Period 2 (Table 7a) while Euphrasia stricta, Hieracium lachenalii, Centaurea nigra, Polytrichum commune and Fragaria virginiana ssp. glauca continued to increase with increases of 1140% (62 vs. 5 occurrences per 1000 quadrats), 567% (260 vs. 39), 83% (205 vs. 112), 35% (662 vs. 489) and 20% (728 vs. 609), respectively, by Period 3 (Table 7b). However, Achillea millefolium, Agrostis capillaris, Leontodon autumnalis, Anaphalis margaritacea, Cornus canadensis and the lowbush blueberry did not change significantly (Table 7c). The lack of a significant increase over periods by species other than C. canadensis and the lowbush blueberry in Table 7c was probably due to increased competition from other species. The occurrences of C. canadensis and the lowbush blueberry were already near the maximum occurrence of 1000 in Period 1 and therefore could not increase further significantly. The increase in occurrence of Rumex acetosella and Linnaea borealis in Period 1 is puzzling considering their rapid declines in later periods. Hall (1955) reports an increase in Rumex acetosella after burning and suggests that it arose from seed in the soil or in the hay used for burn-pruning. Since R. acetosella is not normally a weed of cereals (K. I. N. Jensen, personal communication) it is unlikely that the increase after burning in our study was due to seed in the straw used for burn-pruning. More likely, the increase came from seed already in the soil. The decline in R. acetosella over periods was probably due to increased competition and/or the destruction of seeds by burning. With respect to L. borealis, while both Whittle et al. (1997) and Lynham et al. (1998) report that it was eliminated by burning, their results are reasonable considering that stolons of L. borealis are very close to the soil surface (McLean 1969).

10 360 CANADIAN JOURNAL OF PLANT SCIENCE Table 8. Effect of burn cycle on plant species whose frequency of occurrence was increased by burn-pruning Frequency of occurrence (no. per 1000 quadrats) z Species Not burned 2-yr cycle 3-yr cycle 4-yr cycle Rumex acetosella Euphrasia stricta Fragaria virginiana ssp. glauca Achillea millefolium Leontodon autumnalis Anaphalis margaritacea Agrostis capillaris z Data arranged in descending order of increase by the 2-yr burn-pruning cycle. However, as stated previously, the conditions under which burning was conducted in our study may have contributed to its survival in Period 1. Of the 13 species whose frequency of occurrence was significantly increased by burning, only seven were significantly affected by burn-pruning cycle (Table 8). With the exception of Euphrasia stricta and Leontodon autumnalis, the greatest increases were with the 2-yr burn-pruning cycle. Increases in the frequency of occurrence with the 2-yr cycle compared with the unburned check, in descending order of increase, were as follows: Rumex acetosella (12 700%, 128 vs. 1 occurrence per 1000 quadrats), E. stricta (1600%, 34 vs. 2), Fragaria virginiana ssp. glauca (760%, 808 vs. 94), Achillea millefolium (670%, 154 vs. 20), L. autumnalis (129%, 39 vs. 17), Anaphalis margaritacea (107%, 391 vs. 189), and Agrostis capillaris (58%, 502 vs. 318). For R. acetosella, A. millefolium, L. autumnalis and A. capillaris the lower increases in occurrence in the less frequently burned plots were likely due to decreases in successive non-burn years (Table 9). The same is probably true for E. stricta since, although there was no significant difference in the frequency of occurrence between the first and second cropping year after burning, there was a decline from the second to the third year after burning. With respect to F. virginiana ssp. glauca and A. margaritacea, there were no significant differences among cropping years. This result was probably due to the large initial variation in occurrences among plots for these species before treatment application (data not given). While covariance adjusted the differences among burn-pruning cycles for this initial variation and showed a significant decline in occurrence with longer intervals between burning, a corresponding decline in the years following burning was not evident from the analysis of cropping years, which did not incorporate the initial covariate. SUMMARY AND CONCLUSIONS This report documents the short- and long-term changes in floral composition in a lowbush blueberry field due to burn-pruning. Burning is immediately detrimental to some initially prevalent species such as Cladina rangiferina and Pleurozium schreberi, but has little long-term effect on the occurrence of the lowbush blueberry and initially dominant weed species including Festuca filiformis, Maianthemum canadense, Danthonia spicata, Cornus canadensis and Luzula multiflora var. acadiensis. However, it does increase substantially the occurrence of some less dominant species such as Polytrichum commune, Fragaria virginiana ssp. glauca, Agrostis capillaris, Anaphalis margaritacea, Centaurea nigra, Achillea millefolium and Hieracium lachenalii. Since burn-pruning is practised by some blueberry growers, it is important for them to know how it affects the flora associated with the lowbush blueberry and to be aware of which species are Table 9. Plant species whose frequency of occurrence was initially increased by burn-pruning, but which decreased in subsequent blueberry crop years Frequency of occurrence (no. per 1000 quadrats) Species Not burned Burn yr z Crop 1 yr y Crop 2 yr Crop 3 yr Rumex acetosella Euphrasia stricta Achillea millefolium Leontodon autumnalis Agrostis capillaris z Lowbush blueberry vegetative year. y First year after burning.

11 PENNEY ET AL. * EFFECT OF BURN-PRUNING ON FLORA OF LOWBUSH BLUEBERRY 361 increased by burning. Knowledge of which plant species are increased by burning may help growers develop effective crop management strategies and assist chemical companies to develop effective herbicides for blueberry production. ACKNOWLEDGEMENTS The authors are grateful to the late E. Vivian, J. T. Aucoin, R. M. Doyle, G. G. Boyles, J. J. Walsh, the late C. H. Butler, D. C. Cox, C. A. Gallagher and A. M. Salter for technical assistance; to W. O. Coles, the late J. M. Connolly, B. J. Connolly, K. F. Raymond, the late E. A. Fagan, H. G. Morry, the late T. J. McDonald, the late A. J. McDonald and the late M. J. McDonald for helping with annual field operations, and to G. R. Chubbs for library assistance. We are also grateful to B. R. Baum, P. M. Catling, J. Cayouette, W. J. Cody, C. Crompton, R. Day, R. R. Ireland, E. Small, A. E. Stahevitch, S. I. Warwick and P. Y. Wong for plant identification, and to K. I. N. 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