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Forest floor nutrient properties in single- and mixed-species stands of Western hemlock and Western redcedar Klinka, Karel; Collins, D. Bradley; Montigny, Louise E. M. de; Feller, M. C. (Michael Charles); Chourmouzis, Christine 2001

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Scientia Silvica Extension Series, Number  34, 2001Forest Floor Nutrient Properties in Single- and Mixed-speciesStands of Western Hemlock and Western RedcedarIntroductionThe influence of tree species on forest soils has been the subject of study for at least a century. Of particular interest havebeen western hemlock (Tsuga heterophylla (Raf.) Sarg.) and western redcedar (Thuja plicata Donn ex D. Don) - twoof the most common tree species in coastal and southern British Columbia, but each with a different nutrient amplitude. Ithas generally been found that acid, mycogeneous Mor humus forms develop in hemlock stands, while less acid and morezoogenous Mormoder, Moder, or even Mull humus forms develop in redcedar stands.The objective of this study was to determine the influence of hemlock and redcedar, growing separately and together, onforest floor nutrient properties.  The questions addressed were: (1) does each stand type have unique forest floor nutrientproperties? and (2) can any forest floor nutrient property discriminate between stand types?Study Stands and MethodsStudy stands were located in three areas: Capilano River (Capilano), University of British Columbia, Malcolm KnappResearch Forest east of Vancouver (Knapp), and Mission Tree Farm License No. 26 (Mission). Within  each area, 9stands were selected: 3 hemlock, 3 redcedar, and 3 mixtures of approximately equal proportion, by basal area. The studystands were naturally regenerated, unmanaged, closed-canopied, and even-aged (50 to 70 years at breast height), andrepresented the end of the stem exclusion stage of stand development. All stands were within the Submontane Very WetMaritime Coastal Western Hemlock (CWHvm1) variant, and were located on fresh, nutrient-medium sites.Within each stand a 30 x 30 m (0.09 ha) sample plot uniform in topography, vegetation, and soil was established.  Forestfloors were sampled at 12 random locations in each stand. The samples collected were amalgamated into 3 samples, sothat each composite sample consisted of 4 randomly chosen samples from the initial 12 samples.  All samples were air-dried to constant mass and ground on a Wiley  mill to  pass through  a 2-mm sieve.   Samples were analyzed for  pH,mineralizable nitrogen (min-N), and concentrations (%) of nitrogen (N), carbon (C), calcium (Ca), magnesium (Mg),potassium (K), phosphorus (P), and sulfur (S).Mean values of forest floor nutrient properties among the three stand types were compared with a one-way analysis ofvariance (ANOVA), utilizing a general linear regression model testing the stand type, location, and their interaction withnutrient properties:[1] Yi = b0 + b1STAND + b2LOC + b3 STANDxLOC + epsiloniwhere Yi is a nutrient property, b0 is an overall mean, STAND is stand type, LOC is location, STANDxLOC is stand typeby location interaction, and epsiloni is model error.Various discriminant function analyses were performed to determine those forest floor nutrient properties which significantlydiscriminate among stand types at alpha = 0.05.  These properties were then subjected to canonical discriminant analysis todetermine the degree of discrimination among stand types.Results and DiscussionANOVA by model [1] indicated that: (i) C, C:N ratio, and S were significantly related to stand type but not to location, (ii)min-N was significantly related to both stand type and location, (iii) a significant stand type x location interaction existedfor pH, Ca, and K, and (iv) N, Mg, and P were not significantly related to stand type or location (Table 1).Chemical property  Stand type  Location   Hw Hw-Cw Cw Significant Stand x location interaction  Capilano Knapp Mission pH 3.8 (0.1) 4.2 (0.2) 4.3 (0.2)  * 3.9 (0.1) 4.0 (0.1) 4.2 (0.2) C (%)  49.8a (6.0) 47.2a,b (6.7) 44.1b (5.6)  49.5 (5.4) 47.8 (5.8) 45.0 (7.5) N (%)  0.750 (0.120) 0.739 (0.099) 0.682 (0.093)  0.724 (0.117) 0.727 (0.102) 0.712 (0.112) C:N ratio  67.2a,b (8.5) 70.3a (12.7) 60.3b (8.9)  69.8 (12.2) 66.5 (10.3) 63.7 (9.3) Mineralizable N (ppm)  54.79b (8.03) 60.75a,b (9.20) 70.60a (15.14)   54.12b (7.26) 67.13a (13.97) 64.10a,b (10.08) Ca (%)  0.232b (0.072) 0.324b (0.080) 0.571a (0.107)  * 0.284 (0.082) 0.312 (0.086) 0.338 (0.082) Mg (%)  0.032 (0.016) 0.027 (0.014) 0.027 (0.007)  0.032 (0.016) 0.025 (0.007) 0.028 (0.014) K (%)  0.071 (0.021) 0.076 (0.026) 0.096 (0.019)  * 0.073 (0.025) 0.070 (0.021) 0.092 (0.021) P (%)  0.020 (0.004) 0.020 (0.003) 0.019 (0.002)  0.019 (0.004) 0.021 (0.003) 0.020 (0.003) S (%)  0.192a (0.040) 0.161a,b (0.039) 0.148b (0.040)  0.175 (0.032) 0.169 (0.045) 0.165 (0.053) G3Table 1. Means and standard errors (in parentheses) of forest floor nutrient properties of study stands, stratifiedaccording to stand type and location.  For a given chemical property, values in the same row with the samesuperscript are not significantly different (alpha = 0.05); no superscripts indicates no significant differences (p <=<0.05).Does each stand type have unique forest floor nutrient properties?The forest floors in the hemlock stands had significantly higher C and S concentrations than those in the redcedar stands.Although not significant, Mg and N concentrations appeared slightly higher in the hemlock stand type than in the mixed orredcedar types.  The forest floors in the redcedar stands had significantly higher min-N concentrations than the forestfloors within the hemlock stands (Table 1).  The significant stand type by location interactions found for pH, Ca, and Kprecluded multiple range testing of these forest floor properties between stand types. However, plots of these interactionsrevealed that the redcedar stand forest floors had higher pH and Ca concentrations than the hemlock stands, while notrend was observed for K concentrations.   The forest floors of the mixed stands had nutrient properties intermediatebetween the hemlock and redcedar, except in C:N ratio which was significantly greater than in the redcedar stand type.Concentrations of forest floor min-N increased with increasing presence of redcedar, although min-N was also significantlyrelated to location (Table 1).  When measured by anaerobic incubation, min-N represents N liberated from microbes. Thisis consistent with the increase in both pH and min-N with increasing influence of redcedar, as the higher pH of redcedarforest floors has been associated with increased microbial populations, decreased fungal biomass, and increased rates ofdecomposition in the forest floor, relative to hemlock.  These findings support the proposition that both species of treeshave different influences on the microbial populations, fauna, and properties of the underlying forest floor and soil, and thatthese influences affect min-N concentrations.  However, the significant differences in pH, min-N, and K among locationssuggest that the influence of the tree species on N availability is site-specific. Mean forest floor C:N ratios significantlydecreased with progression from the mixture to the hemlock to the redcedar stands.  This trend is neither strengthened norweakened by the findings of other studies and suggeststhat for hemlock and redcedar stands, C:N ratios are site-specific.Despite the interaction effect, Ca increased with increasing presence of redcedar.Figure 1. Ordination of 27 forest floor samples andmeans for each stand type as functions of the firsttwo canonical variables, based on forest floornutrient properties significantly discriminatingamong stand types (pH, C:N, Ca, and Mg) (p<0.10). Abbreviations for stand types are: Hw ?western hemlock, Cw - western redcedar, HwCw? western hemlock-western redcedar.Does any forest floor nutrient property discriminate between stand types?Significant differences between stand types were detected in 4 (C, C:N, min-N, S) of the 10 forest floor nutrient propertiesassayed, while 2 additional properties (pH, Ca) showed strong (but statistically insignificant) trends with respect to standtype.  No significant differences in N, Mg, and P concentrations were associated with stand type.  The canonical discriminantanalysis identified three properties: pH, C:N, and Ca. Ordination of the data based on these properties showed a gradualprogression of samples from the left to the right region of ordination, i.e., from hemlock to mixtures to redcedar stands(Figure 1). Cross-validation resulted in a low predicted overall misclassification error rate (p < 0.111), indicating gooddiscrimination among stand types by the 3 forest floor nutrient properties selected. The hemlock and redcedar stand typemeans are well separated with the mixed stands intermediate. This indicates that the forest floors in hemlock and redcedarstands have distinct nutrient properties, while the mixed stands are intermediate.ConclusionsThe forest floors under hemlock and redcedar stands had distinct nutrient properties, while hemlock-redcedar stands typehad intermediate forest floor nutrient properties.  Forest floor nutrient status generally improved with increasing presenceof redcedar.    Forest floor  pH, C:N ratio,  and Ca concentration effectively  discriminate  between stands of hemlock,redcedar, and their mixtures.ReferenceCollins, D.B., M.C. Feller, K. Klinka, and L. deMontigny. 2001. Forest floor nutrient propertiesin  single-  and mixed-species, second  growthstands of western hemlock and western redcedar.[submitted ms]Scientia Silvicais published by the Forest Sciences Department,The University of British Columbia, ISSN 1209-952XEditor: Karel Klinka (klinka@interchange.ubc.ca)Research: B. Collins (brad@locin.com), M.C. Feller (feller@interchange.ubc.ca), K. Klinka,and L.de Montigny (Louise.demontigny@gems2.gov.bc.ca)Production and design: C. Chourmouzis (chourmou@interchange.ubc.ca)Financial support: Natural Science and Engineering Council of Canada, CanadianForest Products Ltd., TimberWest Forest Ltd., and Weyerhauser of Canada Ltd., andBC Ministry of Forests.For more information contact: Brad CollinsCopies available from: www.forestry.ubc.ca/klinka orK. Klinka, Forest Sciences Department, UBC,3036-2424 Main Mall, Vancouver, BC,  V6T 1Z4CAN 1-3 -2 -1 0 1 2 3 4 5CAN2-3-2-101234CwHwCwHwCw MeanHwCw MeanHw Mean

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