UBC Faculty Research and Publications

Vegetation and soil nutrient properties of Black spruce and Trembling aspen ecosystems in the boreal.. Klinka, Karel; Kayahara, Gordon J.; Krestov, Pavel; Qian, H.; Chourmouzis, Christine 2001-04-17

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Scientia Silvica Extension Series, Number  31, 2001Vegetation and Soil Nutrient Properties of Black Spruce and TremblingAspen Ecosystems in the Boreal Black and White Spruce ZoneIntroductionChanges in  forest ecosystem vegetation also bring about changes to  the associated soil.   In order to maintain forestproductivity, it is important to know the effects of tree species upon the soil, especially the influence of deciduous versusconiferous tree species. Many deciduous species increase pH, nitrogen, base saturation and/or accumulation of organicmatter in the forest floor. The chemical properties of the forest floor may, in turn, influence the chemical properties of theunderlying mineral soil. If a tree species significantly alters the soil, then silviculturists may consider crop rotation betweendeciduous and coniferous trees or growing mixed-species stands to maintain greater nutrient availability and maintain siteproductivity.Trembling aspen (Populus tremuloides) and black spruce (Picea mariana) may occupy similar sites in the North Americanboreal forest.  Shade-intolerant aspen is generally a seral species while shade-tolerant black spruce can be a seral speciesbut also forms a major component in late successional stages. This study investigated differences in nitrogen-related soilproperties between trembling aspen and black spruce stands on upland sites in the BWBS zone of northeastern BC. Weasked two questions: (1) are the differences in soil nutrient properties manifested in both forest floor and mineral soil? (2)To what extent are these differences reflected in the floristic composition of understory vegetation?MethodsWe described vegetation and sampled the forest floor and top 30 cm of mineral soil in 40 spruce stands and 58 aspenstands. Vegetation was analyzed by tabular comparison and multivariate analysis, and soils were analyzed for acidity, totalC, total N, mineralizable N, and extractable K, Ca, and Mg.ResultsDespite large  differences in  some  forest  floor  measures between the  two  stand  types,  there  were few  differencesbetween the associated mineral soils (Table 1, Figure 1). There were significant differences (alpha = 0.05) in pH, total N, C:Nratio,  mineralizable N, and extractable Ca, Mg, and K between the  humus forms  associated with the  spruce  standscompared to the aspen stands. The mineral soil associated with the spruce stands had lower pH and significantly lowerconcentrations of mineralizable N, extractable Mg and K. Significant differences in extractable bases could not be detectedbetween the stands. This comparison suggests that aspen forest floors are richer in nutrients than spruce forest floors.In view of profound differences in the forest floor nutrient properties between black spruce and trembling aspen stands,we expected analogous differences in understory vegetation. Non-parametric multidimensional scaling analysis showedno overlap in vegetation between the spruce and aspen stands (Figure 2). This pattern gives a convincing demonstrationthat the spruce and aspen stands have distinctly different flora and hence, represent different plant community types.Although black spruce and aspen stands share a number of species that are characteristic of the boreal forest, they aredistinguished from each other by a combination of several differential species (Table 2). The major differences includepreponderance of mosses in spruce stands, and preponderance of shrubs, herbs and grasses in aspen stands. Comparedto the moss-dominated understory in spruce stands, aspen stands support well-developed shrub and herb layers.Total N (%) aspen(A)mineralizable N (ppm)0100200300400500600spruce aspen(B)sum of exchangeable (Ca, Mg, K) (ppm)0200040006000800010000120001400016000spruce aspen(C) Black spruce Trembling aspen P-value Forest floor    pH  4.34 (0.09)  5.37 (0.07)  <0.0001 Total C (%)  36.9 (1.67)  39.1 (0.55)  0.2146 Total N (%)  0.95 (0.03)  1.38 (0.03)  < 0.0001 C:N ratio  40.5 (2.6)  28.9 (0.5)  0.0001 Mineralizable N (ppm)  109.9 (9.5)  551.2 (27.5)  <0.0001 Extractable Ca (ppm)  1715 (271)  11734 (349)  <0.0001 Extractable Mg (ppm)  731 (85)  1342 (70)  <0.0001 Extractable K (ppm)  635 (33)  1287 (40)  <0.0001 summation(Ca, Mg, K) (ppm)  4755 (344)  14363 (412)  <0.0001 Mineral soil      pH  4.79 (0.14)  5.27 (0.09)  0.0030 Total C (%)  1.38 (0.18)  1.44 (0.14)  0.8067 Total N (%)  0.08 (0.01)  0.09 (0.01)  0.4516 C:N ratio  16.5 (0.9)  16.0 (0.3)  0.6097 Mineralizable N (ppm)  8.6 (1.5)  15.9 (2.1)  0.0062 Extractable Ca (ppm)  874 (139)  994 (127)  0.5317 Extractable Mg (ppm)  238 (44)  131 (18)  0.0453 Extractable K (ppm)  46 (5)  75 (6)  0.0002 summation(Ca, Mg, K) (ppm)  1158 (179)  1211 (145)  0.8181 G3Table 1. Mean nutrient measures (standard error in parentheses) forhumus form and the upper 30 cm of the mineral soil for black sprucestands (n = 40) and trembling aspen stands (n = 58) with the associatedp-value for the t-test comparing spruce to aspen measures.Figure 1. Concentrations of total N, mineralizable N, and sum of exchangeable cations (Ca, Mg, K) in the forest floors(white area) and in the upper 30 cm of the mineral horizons (shaded area) in black spruce stands (n = 40) versustrembling aspen stands (n = 58) on upland sites in the BWBS zone. Error bars represent 95% confidence intervals.G24G56G53G48G51G36G53G55G58G46._G48G2eG28G3cPlant species common to both spruce and aspen standsG3Plant species occurring predominantly in spruce standsG3Plant species occurring predominantly in aspen stands   Spruce  Aspen    Spruce Aspen   Spruce  Aspen Cornus canadensis   V1  52  IV  5  Hylocomium splendens   V  7  II 2 Aster conspicuus   I  t  III  4 Ledum groenlandicum   IV  5  III  5  Peltigera aphthosa   III  3 I 1 Calamagrostis canadensis   I  h  IV  3 Linnaea borealis   IV  4  V  3  Picea mariana   V  7 I 2 Elymus innovatus       IV  4 Petasites frigidus   IV  2  IV  3  Pinus contorta   IV  6 I 2 Epilobium angustifolium   III + V  4 Picea glauca   III  6  IV  4  Pleurozium schreberi   V  7 I 2 Fragaria virginiana   I  h  III  2 Vaccinium vitis-idaea   IV  5  III  3  Ptilium crista-castrensis   IV  6 I h Galium boreale   I  h  III  3 Viburnum edule   III  2  III  4  Lathyrus ochroleucus   I  +  V  3 Mertensia paniculata   III  +  II  2  Maianthemum canadense   I  h  IV  3 Orthilia secunda   III  +  II  1  Populus tremuloides   II  4  V  8 Shepherdia canadensis   II  3  III  4  Pyrola asarifolia   I  h  III  3 Rosa acicularis   III 1 V  5 Rubus pubescens   I  +  III  3 Salix sp.       IV  4 Spiraea betulifolia   I  t  III  2 Vaccinium myrtilloides       III  5 1  Presence is printed as presence class: I = 0 - 20%; II = 21 - 40%; III = 41 - 60%; = 61 - 80%; V = 81-100%; bold type indicates  presence greaterequal 41%.  2  Mean cover is average cover value for ecosystem unit; scale used for cover values is the Domin-Krajina scale; percent cover ranges for symbols printed: t = 0.001 - 0.009; h = 0.010 - 0.099; + = 0.100 - 0.299; 1 = 0.300 - 0.499; 2 = 0.500 - 0.999; 3 = 1.000 - 1.999; 4 = 2.000 - 4.999; 5 =5.000 - 9.999; 6 =- 10.000 - 19.999; 7 =- 20.000 - 49.999; 8 = 50.000 - 69.999; 9 = 70.000 - 100.000. G3Table 2. Differentiated summary table indicating floristic differences between upland black spruce and trembling aspen standsin the BWBS zone of British Columbia. Only the species with presence class greaterequalIII in one or both columns are given.  Speciespresence class1 and significance2 for 40 black spruce and 58 aspen stands.Figure 2. The distribution pattern ofblack spruce and trembling aspenstands along the first three axes ofnon-parametric multidimensionalscaling ordination.DiscussionDifferences in forest floor chemistry between black spruce and aspen stands did not cause marked differences in themineral soil. Except for pH and extractable K, forest floor has not modified nutrient properties of the mineral soil since thelast stand-destroying event (> 50 years). Regardless of site differences, forest floors in aspen stands were richer than inspruce stands, particularly in nitrogen as indicated by a low C:N and high mineralizable N. In turn, aspen forest floors areexpected to have a higher nitrogen mineralization rates as these increase with decreasing C:N. As differences in nutrientavailability must result from differences in the type and decomposition rate of forest floor materials, they should bereflected in forest floor morphology and humus form.Scientia Silvicais published by the Forest Sciences Department,The University of British Columbia, ISSN 1209-952XEditor: Karel Klinka (klinka@interchange.ubc.ca)Research: G. Kayahara (Gordon.Kayahara@mnr.gov.on.ca), K. Klinka, P.V. Krestov (farrex@vtc.ru), and H.Qian (hqian@interchange.ubc.ca)Production and design: Christine Chourmouzis (chourmou@interchange.ubc.ca)Financial support: Site Productivity Working Group, BC Ministry of ForestsFor more information contact: Gordon KayaharaCopies available from: www.forestry.ubc.ca/klinka orK. Klinka, Forest Sciences Department, 3036-2424 Main Mall, UBC, Vancouver, BC  V6T 1Z4Since both spruce and aspen stands occupy similar environments, humus formation must be influenced only by microclimaticconditions (temperature and moisture conditions in the forest understory) and chemical and physical characteristics oflitter (including understory vegetation).  These, in turn, determine the abundance and composition of flora and fauna in theforest floor. Using humus form classification, spruce stands had well developed Mor (Hemimor) humus forms which arecharacterized by incomplete decomposition and nutrient immobilization.  A variety of Moder humus forms have developedin aspen stands. Moders have intermediate properties between Mors and Mulls.  In contrast to Mors that form as a resultof fungal decomposition, Moder and Mull formation result from soil fauna-mediated decomposition.The common humus form in aspen stands was Lamimoder, although Mors also occurred rarely. In the lower humus formhorizons there were many roots of aspen and herbaceous vegetation. Root distribution takes advantage of the humus layersince the main source of nutrients, warmest soil temperature, good aeration, and water availability occur just below theground surface.The ameliorating effect of aspen on the surface soil horizon is widely acknowledged. Nutritional studies of aspen-dominatedecosystems indicate that aspen takes up large quantities of nutrients and stores them in woody tissues and foliage. Incontrast, black spruce is one of the few tree species well adapted to acid and nitrogen-deficient soils. White spruce, whichis less tolerant of such conditions (more nutrient-demanding) and grows more productively with increasing nutrient availability,is  found more frequently than  black spruce regenerating in  the  understory of aspen stands (Table 2).   Therefore, weattribute the differences in the patterns and processes in the forest floors to the influence of tree species and the understoryvegetation that has developed in different microenvironments under spruce and aspen.ConclusionsThe major differences in nitrogen-related soil properties between black spruce and trembling aspen stands on upland sitesin the montane boreal forest were detected in the forest floors.  These differences were reflected in the floristic compositionof understory vegetation and the types of humus forms.  The forest floors in spruce stands were strongly acid, nitrogen-and base-poor, and exemplified by Mor humus forms, those in aspen stands were weakly acid, nitrogen- and base-rich,and exemplified by Moder humus forms. While ericaceous shrub and mosses were dominant in spruce stands, deciduousshrubs, herbs, and graminoids dominated the understory of aspen stands. We concluded that each study species has astrong effect on the forest floor but not on the underlying mineral soil.ReferenceG. J. Kayahara G.J., K. Klinka, P.V. Krestov, and H. Qian. 2000. Comparison of vegetation and soil nutrient propertiesbetween black spruce and trembling aspen ecosystems in the Boreal Black and White Spruce Zone of British ColumbiaSubmitted for publication to Canadian Journal of Forest Research 00/11.


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