Black Spruce Growth and Understory Species Diversity with and without Sheep Laurel

Richardson and Hall, 1973a, p. 63, 1973b, p. 46; Wall, 1977, p. 55). Competition and allelopathic effects of Growth and understory species diversity of black spruce [Picea sheep laurel have been attributed to the regeneration mariana (Miller) B.S.P.] planted in central Newfoundland at contiguous sites with and without dense cover of sheep laurel (Kalmia angusfailure and poor growth of conifers (Mallik, 1987, 1990, tifolia L.) were compared. Black spruce stem density and volume per 1992, 1996; Mallik and Roberts, 1994). In eastern and hectare were calculated by sampling 10 circular quadrats (50 m2), and central Newfoundland, large areas of moderately prothe cover of all plant species was determined by sampling 20 quadrats ductive black spruce forests with sheep laurel un(1 m2) in each site. In addition, 10 randomly sampled planted black derstory have been converted into sheep laurel domispruce samplings from each site were analyzed for stem height, basal nated heath following forest disturbance (Mallik, 1995). diameter, and foliar chemistry. Results showed a significantly lower A regeneration survey of 5888 plots in black spruce stem height and basal diameter (65 and 51%, respectively) at the site plantations found that 55% of them contained sheep with dense sheep laurel cover (36%) compared with the site with laurel (English and Hackett, 1994, p. 12). Black spruce sparse sheep laurel cover (,1% sheep laurel cover, and henceforth in sheep laurel infested sites exhibits typical symptoms: referred to as the non-sheep laurel site for simplicity). Black spruce grown at the sheep laurel dominated site contained significantly higher Poor plant height and diameter growth and short and quantities of Ca, Al, Fe, and K in the needles than that grown at the chlorotic needles, as observed in other conifers in the non-sheep laurel site. The sheep laurel dominated site also had a presence of different ericaceous plants (Handley, 1963; significantly higher mean organic matter depth of 8.3 cm compared Gimingham, 1972; de Montigny and Weetman, 1990; with 5.6 cm at the non-sheep laurel site. Canonical correspondence Fraser, 1993, p. 166; Inderjit and Mallik, 1996a; Jaderanalysis (CCA) of the species cover data clearly separated the sheep lund et al., 1997). Black spruce forests that are domilaurel dominated plots from the non-sheep laurel plots. The sheep nated by sheep laurel tend to have a reduced species laurel dominated site had reduced species richness of vascular plants richness and deficiency in available nutrients (Damman, but increased species richness for lichens compared with the non1971). Recently, Yamasaki et al. (1998) reported that sheep laurel site. Allelopathy associated with phenol-induced soil black spruce seedlings in close proximity of sheep laurel nutrient imbalance and nutrient stress is a possible cause for black spruce growth inhibition at the sheep laurel dominated site. (,1 m) experience lower height, biomass, root/shoot ratio, foliar N and P, and lower mycorrhizal infection than those growing farther (.1 m) away from sheep laurel. R growth of sheep laurel after clear cutting Damman (1971, 1975) suggested that long-term occuand fire in sheep laurel–black spruce communities pancy of a site by sheep laurel causes irreversible soil has been widely observed in eastern Canada, particudegradation, leading to a stable heath formation by prelarly at sites with organic and coarse textured mediumcluding forest regeneration. Apparently sheep laurel, quality soil types (Page, 1970, p. 7; van Nostrand, 1971, like other ericaceous plants, is able to grow in nutrient p. 68; Damman, 1975). The natural regeneration of black poor conditions where black spruce growth is very much spruce at these sites is poor, and planted black spruce restricted. There is evidence suggesting that the ericaseedlings exhibit stunted growth (Candy, 1951, p. 224; ceous plants are able to access the N that is bound in the protein–polyphenol complex through the ericoid Dep. of Biol., Lakehead Univ., Thunder Bay, ON, Canada P7B 5E1. mycorrhizae, but this N is not available to the conifers Received 25 Jan. 2000. *Corresponding author (azim.mallik@ lakeheadu.ca). Abbreviations: CCA, canonical correspondence analysis; IAA, indoleacetic acid. Published in Agron. J. 93:92–98 (2001). MALLIK: BLACK SPRUCE GROWTH AND SPECIES DIVERSITY WITH SHEEP LAUREL 93 through their ectomycorrhizal association (Bending and Species Composition and Richness Read, 1996). It is also possible that the nutrient requireThe cover of all the understory plants was determined by ments of sheep laurel are lower than those of black sampling 10 randomly placed 1-by-1-m quadrats in each of spruce. The rapid proliferation of sheep laurel after the sheep laurel and non-sheep laurel sites. The thickness of clear cutting and fire and the associated black spruce the organic and Ae horizon was determined from 25 soil pits that were randomly dug in each of the sheep laurel and nongrowth inhibition is a serious problem for forest mansheep laurel sites. agement in central Newfoundland. Recognizing this problem, the provincial government of Newfoundland and Labrador has implemented new forest management Statistical Analysis guidelines that discourage forest harvesting in sites with A paired t-test was used to determine the significant differdense sheep laurel cover. Although poor black spruce ence of the growth parameter and foliar nutrient means of growth in the presence of dense sheep laurel cover has black spruce at the sheep laurel and non-sheep laurel sites. been widely observed in Atlantic Canada, to this day PC-ORD (McCune and Mefford, 1995) was used to ordinate no quantitative evaluation of black spruce growth has the 20 sampling plots with and without sheep laurel based on been made in plots with and without sheep laurel. The the species cover data. The species–environment relationships objectives of the present study were to compare (i) the were analyzed using CCA with Pearson correlation. growth and foliar nutrient concentrations of planted black spruce and (ii) the species composition, richness, RESULTS and diversity of understory plants in contiguous plots with and without sheep laurel. Black Spruce Growth Response Black spruce stem height and basal diameter were STUDY AREA AND METHODS significantly less (65 and 51%, respectively) at the site The study area belongs to the north-central subregion of with dense cover (36%) of sheep laurel compared with the central Newfoundland ecoregion that is characterized by the non-sheep laurel site (Fig. 1). Consequently, after a high maximum summer temperature and a lower rainfall 15 yr there was 85% less black spruce volume at the and higher fire frequency than anywhere on the island sheep laurel dominated site compared with the non(Meades and Moores, 1994, p. 226). Because of the high fire sheep laurel site (Fig. 1). Black spruce height growth frequency, the area is dominated by pure black spruce stands of seed origin and aspen (Populus tremuloides Michaux) was consistently less at the sheep laurel dominated site stands originating from root suckering. The soil is typically a than at the non-sheep laurel site (Fig. 2). The stem coarse textured humo-ferric podzol. The area has rolling to density of black spruce was 34% less at the sheep laurel undulated topography that is characterized by shallow, medominated site compared with the non-sheep laurel site dium-quality till with a soil texture ranging from sandy loam (Fig. 1). The current stem density of the two sites conto loam. Black spruce after disturbance in this relatively low sists of planted seedlings as well as natural regeneration moisture, coarse-textured soil suffers from regeneration failof black spruce. However, the natural regeneration of ure, particularly when sheep laurel occurs as a dense unblack spruce at the sheep laurel site was about onederstory (Meades and Moores, 1994, p. 226). third (900 stems ha21) of that of the non-sheep laurel This study was conducted in a 15-yr-old black spruce plantation in Sandy Pond, central Newfoundland (488509 N, 558249 site (2400 stems ha21). W; altitude of 153 m). The area was harvested by clear cutting Black spruce grown at the sheep laurel plots conin 1979, scarified in 1981, and planted with containerized black tained significantly higher concentrations of Ca, Al, Fe, spruce in 1982—15 yr before this study. The planting density and K in the needles than that in the non-sheep laurel was 2100 seedlings ha2. Approximately half of the 10-ha plots (Table 1). The sheep laurel dominated plots had plantation contained on an average of 36% sheep laurel cover a significantly higher organic matter depth (8.3 cm) than that was fairly uniformly distributed while the other half of the non-sheep laurel plots (5.6 cm). The organic matter the plantation had ,1% sheep laurel cover. The sheep laurel depth was strongly related to the x-axis (r 5 20.841) dominated site had a thicker organic layer than the non-sheep while the Ae horizon depth was strongly related to the laurel site. Both sites had coarse-textured freely drained sandy y-axis (r 5 298.2). The y-axis did not separate the samloam soil with a 0.5 to 2 cm thick Ae horizon. pling plots into levels of sheep laurel condition, sugBlack Spruce Growth Response Table 1. Foliar nutrient concentrations of planted black spruce Ten 50-m circular quadrats were randomly placed in each in sheep laurel and non-sheep laurel sites. Values are the means of the sheep laurel and non-sheep laurel areas. The stem of 10 samples 6 SD. height and basal diameter of all black spruce saplings were Nutrient Sheep laurel Non-sheep laurel determined in each quadrat. From these data, the stem density and volume of black spruce were determined. Ten randomly N, % 1.028 6 0.038 1.028 6 0.033 selected planted black spruce saplings were destructively samP, mg kg21 8.7211 6 0.347 8.2359 6 0.278 K, mg kg21 3495 6 205.95a 4403 6 217.31b pled from each site to determine their age and yearly growth Al, mg kg21 0.7525 6 0.084a 0.5184 6 0.053b increment by measuring their annual ring widths in two direcCa, mg kg21 56.949 6 8.146 56.1466 6 4.717 tions perpendicular to each other. The planted black spruce Cu, mg kg21 0.0218 6 0.004 0.032 6 0.005 seedlings were recognized by their presence in the lines with Fe, mg kg21 0.2821 6 0.018a 0.2247 6 0.014b Mg, mg kg21 9.8706 6 0.52 9.592 6 0.689 regular spacing. Foliar samples were collected at the mid canMn, mg kg21 19.5179 6 2.437 15.2522 6 3.184 opy level from 1-yr-old branches of black spruce for chemiZn, mg kg21 0.3863 6 0.046 0.4611 6 0.046 cal analysis. 94 AGRONOMY JOURNAL, VOL. 93, JANUARY–FEBRUARY 2001 Fig. 1. (A) Mean stem height, (B) basal diameter, (C) stem density, (D) and volume of black spruce in sheep laurel and non-sheep laurel plots at Sunday Pond, NF, Canada 15 yr after planting. gesting that this axis had picked up within-site variwith a stem density of 4500 stems ha21, the non-sheep ability. laurel site is comparable with Site Index 10 (Newton, 1992). By contrast, the sheep laurel dominated site is Black Spruce Crown Closure and Understory comparable to Site Index 7 (Newton, 1998). Species Cover, Richness, and Diversity Sheep laurel cover at the two sites was 48.5 and 1.0%, respectively. The sheep laurel dominated site was also With smaller black spruce, the sheep laurel dominated associated with dense cover of blueberry (Vaccinium site had relatively open canopy 15 yr after planting, with angustifolium Aiton) and schreberi moss [Pleurozium only 8.5% black spruce cover. In contrast, the contiguschreberi (Brid.) Mitt.]—29.5 and 44.5%, respectively, ous non-sheep laurel site was approaching canopy cloin contrast to 18.0 and 20.0% at the non-sheep laurel sure, with 56% black spruce cover (Table 2). In the site. The cover of bunchberry (Cornus canadensis L.), context of the stand density management diagram for however, remained similar (12.3 and 14%) at the two Newfoundland (Newton and Weetman, 1993) black spruce crown closure approaching at the age of 16 yr sites (Table 2). Fig. 2. Mean cumulative black spruce height in sheep laurel and non-sheep laurel plots. MALLIK: BLACK SPRUCE GROWTH AND SPECIES DIVERSITY WITH SHEEP LAUREL 95 Table 2. Species cover, richness, and diversity in sheep laurel and non-sheep laurel sites. Values are calculated from 10 quadrats (1 by 1 m) in each site. % Cover Richness Diversity Species Sheep laurel Non-sheep laurel Sheep laurel Non-sheep laurel Sheep laurel Non-sheep laurel Vascular plants 12 16 1.24 1.23 Picea mariana 8.5 6 9.9 56 6 25.6 Betula papyrifera 2 6 3.5 0.3 6 0.95 Larix laricinia 0 2.1 6 4.9 Populus tremuloides 0 1.8 6 3.8 Prunus pensylvanica 0 1.3 6 2.2 Nemopanthus macronuta 0.4 6 1.3 0 Viburnum cassinoides 0.4 6 1.3 0 Kalmia angustifolia 48.5 6 27.0 1 6 2.1 Rhododendron canadense 3 6 9.5 0 Vaccinium spp. 29.5 6 9.6 18.1 6 16.7 Gaultheria hispidula 3.3 6 6.7 10.8 6 11.6 Cornus canadensis 3.5 6 5.8 14 6 6.6 Linnaea borealis 0 0.5 6 1.6 Soidago rugosa 0 1 6 2.1 Epilobium angustifolium 0 0.5 6 1.1 Potentilla anserina 0 0.5 6 1.6 Cypripedium reginae 0 0.4 6 0.8 Vaccinium vitis-idaea 5.4 6 9.5 0 Mitella nuda 3.8 6 4.6 1 6 3.2 Maianthemum sp. 0.3 6 0.95 2.3 6 4.6 Bryophytes and Pteridophytes 7 9 1.01 .95 Pleurozium schreberi 44.5 6 28.8 20.1 6 22.2 Hylocomium splendens 1.5 6 3.4 0.8 6 1.8 Ptilium crista-castrensis 9 6 7.4 2.8 6 3.5 Sphagnum spp. 1 6 3.1 0 Polytrichum spp. 4.9 6 5.6 0 Dicranum scoparium 1.8 6 3.5 2.2 6 2.2 Dicranum polyseptum 11.7 6 3.5 9.8 6 4.4 Lycopodium dendroideum 0 0.3 6 0.95 Lycopodium annotinum 0 1 6 3.2 Lichens 9 5 .69 .89 Cladina rangiferina 1 6 3.2 0 Cladina alpina 0 1 6 1.1 Cladina arbuscula 0.3 6 0.95 4.4 6 4.7 Cladina spp. 0 4.8 6 5.0 Permelia sulcata 4.9 6 5.4 0 Cladonia cenotea 1.8 6 2.6 0 Cladonia cornicraea 6.6 6 5.7 1.8 6 3.2 Cladonia fimbriata 0 1.2 6 1.5 Peltigera apthosa 0.5 6 1.6 0 Although the overall species richness of the sheep of black spruce. Although the stem density of black laurel and non-sheep laurel sites was comparable with spruce at the sheep laurel dominated site (|3000 stems only 28 to 30 species, the two sites were markedly differha21) was less than that of the non-sheep laurel site ent in terms of the species composition, richness, and (|4500 stems ha21) (Fig. 1), this difference is not critical diversity of the vascular plants and lichens. The sheep from a resource management perspective because a denlaurel dominated site contained 12 species of vascular sity of 3000 stems ha21 is considered sufficient for black plants and five species of lichens, whereas the non-sheep spruce regeneration. What is more important, however, laurel site contained 16 species of vascular plants and is that the height and volume of black spruce in the nine species of lichens (Table 2). A CCA of the species sheep laurel dominated plots is consistently less than cover data separated the sheep laurel dominated plots that of the non-sheep laurel plots. from the non-sheep laurel plots (Fig. 3) along the Similar growth inhibition of black spruce has been x-axis (Eigenvalue 5 0.22), which explained 12.7% of found in labrador tea dominated sites (Inderjit and Malthe variance in the species data. lik, 1996a). However, at the labrador tea dominated site, conifer growth tended to improve 7 yr after planting. A poor early growth and eventual increased growth of DISCUSSION black spruce associated with a labrador tea dominated site was also reported by LeBarron (1948, p. 60). In the Both the stem density and growth of black spruce were significantly less at the sheep laurel dominated site present study, the sheep laurel dominated site exhibited significantly slow growth, and no subsequent growth in (Fig. 1). Significant natural regeneration has occurred in both sites because the planting density was 2100 seedheight of black spruce was observed 15 yr after planting. Thus, the growth inhibitory effect of sheep laurel on lings ha21. However, recruitment of black spruce in sheep laurel dominated site was about one-third that of black spruce seems to be more long-term than the effects of labrador tea. Damman (1971) suggested that longthe non-sheep laurel site, indicating that the presence of sheep laurel interfered with the natural regeneration term occupancy of a site by sheep laurel can cause irre96 AGRONOMY JOURNAL, VOL. 93, JANUARY–FEBRUARY 2001 Fig. 3. Canonical correspondence analysis (CCA) of sheep laurel and non-sheep laurel plots showing the significance of sheep laurel cover and organic matter depth in their separation. versible habitat degradation, converting conifer forests The primary objective of the present paper was to quantify the growth differences of black spruce at coninto ericaceous heath. He attributed this vegetation shift to the high rate of organic accumulation, soil acidificatiguous sheep laurel and non-sheep laurel sites. Perhaps it is safe to assume that the contiguous sheep laurel and tion, and nutrient sequestration in the presence of sheep laurel. non-sheep laurel sites initially belonged to the same site type, and the invasion of sheep laurel transformed it The height and diameter (at breast height, DBH) of the destructively sampled planted black spruce of the into a lower site index type (Damman, 1964, p. 62, 1971). What is not known for sure is how long sheep laurel sheep laurel and non-sheep laurel sites were compared with the site index curves of naturally regenerating pure has been occupying the site. A study of disturbanceinduced sheep laurel proliferation at a chronosequence black spruce in central Newfoundland (Newton, 1992). It was found that the black spruce at the non-sheep and associated black spruce regeneration failure and habitat degradation will elucidate the role of sheep laulaurel site fit close to Site Index 12 and that of the sheep laurel dominated site was comparable to Site Index 10. rel in this vegetation shift. Inderjit and Mallik (1996a) compared the growth and Using the site index curves of Newton (1992), the projected height of black spruce at the age of 50 in the nonfoliar nutrients of planted black spruce in labrador tea and non-labrador tea sites. They attributed the poor sheep laurel and sheep laurel dominated sites would be 12.18 and 10.32 m, respectively. However, the values growth of black spruce in labrador tea dominated sites to a lower foliar N and to a soil nutrient imbalance that for the black spruce growing at the sheep laurel dominated site may have been overestimated for at least a was due to the high phenolic content of the labrador tea litter. In this study, the black spruce grown at the couple of reasons. First, trees at the sheep laurel dominated plots were too small to determine a meaningful sheep laurel dominated site had smaller needles but did not have lower concentrations of foliar N compared diameter at breast height, and secondly, as Newton (1992) cautioned, the site index curves of age classes 1 with the non-sheep laurel site. These values are very similar and within the adequate range (0.95–1.10%) for to 20 may not be very accurate for the small sample size of his model. In a subsequent paper, Newton (1998) black spruce according to Lowry and Avard (1968, p. 54). Swan (1970), however, considered 1.20% foliar N presented a more realistic site index for black spruce in sheep laurel sites by developing successional vectors to be low for black spruce growth. There is no evidence in the present data to suggest that foliar N deficiency based on the size–density relationship (Newton and Weetman, 1993). He suggested that delayed crown clois a cause of the growth limitation of black spruce in the sheep laurel dominated plots. However, other nutrisure due to poor spruce growth and seedling mortality in the presence of sheep laurel will lower the site index ent and heavy-metal imbalances may be responsible. Significantly higher concentrations of foliar Al and Fe to 7 or even 4, depending on the black spruce stem density and the density and longevity of sheep laurel at were found in the black spruce at the sheep laurel dominated site compared with that of the non-sheep laurel a site. He further suggests that even a productive black spruce–moss forest type on sandy loam or loamy sands site. Comerford and Fisher (1984) have shown that normal tree growth may be impaired by nutrient imbalmay be degraded into an unproductive sheep laurel– black spruce type of significantly lower site index if the ances. The high phenolic content of sheep laurel leaf and litter has been implicated as a soil depositional site is occupied by dense sheep laurel after forest harvesting. factor that reduces N availability elsewhere (Inderjit MALLIK: BLACK SPRUCE GROWTH AND SPECIES DIVERSITY WITH SHEEP LAUREL 97 and Mallik, 1996b; Northup et al., 1999), but the imporfrom sheep laurel leaves. These authors have shownthat genticic and o-hydroxyphenylacetic acid at 0.5 totance of this process at this site may depend on further5 mM concentrations, and the others at 1 to 5 mMlitter inputs over time. An invasion by sheep laurelconcentrations, can inhibit the primary root and shootseems to more quickly bring about a reduction of nutri-growth of black spruce (Mallik and Zhu, 1995). How-ents other than N, and at present, resource deficiencyever, the involvement of these phenolic acids in theby a critical concentration of K (Swan, 1970) or in-growth inhibition of larger black spruce seedlings undercreased Fe, Al, and Mn toxicity may have created soil Nfield conditions has not yet been studied.deficiency and nutrient imbalance (Inderjit and Mallik,A reduced richness and diversity of vascular plants1996b). This in turn may have created the growth inhibi-was obtained in presence of sheep laurel compared withtory effect on black spruce.the non-sheep laurel site. Habitat stress induced by theAt the sheep laurel dominated sites of central New-ericaceous plants may be suggested as a filtering mecha-foundland, field trials with spot fertilization of blacknism leading to heath formation where the species capa-spruce with three formulations of Gromax Transplantble of tolerating nutrient stress persist. The failure ofFertilizer (TPFS 4, 5, and Gromax Plus) at the time ofground-level vascular species to invade sheep laurelplanting produced a significant height increase of blackdominated sites allows cryptogams to occupy the soilspruce that lasted only for 2 yr (English, 1997, p. 10).surface. It can be argued that the high diversity of stressAfter that, there was no significant difference in blacktolerant lichens at the sheep laurel dominated site is aspruce height between the fertilized and unfertilizedreflection of the stress condition of the habitatplants, and the author concluded that the fertilizer-(Grime, 1977).treated seedlings were not able to capitalize on the initialheight growth boost to overcome the sheep laurel ACKNOWLEDGMENTSgrowth inhibition. These results seem to suggest thatthe black spruce growth inhibition phenomenon in theThe work was supported by a research grant from the Natu-presence of sheep laurel is more than just a case of ral Science and Engineering Research Council (NSERC). Inutrient deficiency.thank Abitibi Consolidated, Grand Falls-Windsor for theirlogistical help during the field work and Robin Bloom andResults from the ericaceous litter amending experi-Felix Eigenbrod for their help in data analyses. The commentsments of Inderjit and Mallik (1996a, 1997) showed thatof Dr. W.H. Carmean and two anonymous reviewers weresheep laurel and labrador tea litter can lower pH andhelpful in revising the manuscript.increase the total phenolic content of soil; these changescan reduce the available N and P and increase Fe, Al,REFERENCESCa, Mn, Zn, Cu, and Ba (Brady, 1990, p. 619). The Appel, H.M. 1993. Phenolics in ecological interactions: The impor-authors attributed this soil nutrient imbalance to thetance of oxidation. J. Chem. Ecol. 19:1521–1552.high phenolic content of the ericaceous litter becauseBending, G.D., and J.R. Read. 1996. Nitrogen mobilization from pro-phenolics are known to influence the availability, accu-tein–polyphenol complex by ericoid and ectomycorrhizal fungi.mulation, and uptake of nutrients (Rice, 1984; Appel,Soil Biol. Biochem. 28:1603–1612.Brady, N.C. 1990. The nature and properties of soil. MacMillan Publ.,1993). 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