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Relationships between foliar nutrient status of second growth Douglas-fir and forest floor chemical properties Davis, Geralyn Daphane


The objective of this study was to examine the relationships between Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) foliar nutrient status and forest floor chemical properties. Foliar nutrient analysis data were collected on 27, 50- to 140-year-old Douglas-fir stands, for which the forest floor chemical properties had previously been analysed. The 27 sites encompassed a broad geographical area within the Coastal Western Hemlock Biogeoclimatic Zone. Foliar samples were individually analysed for total S, N, P, K, Ca, Mg, B, Cu, Zn, Fe, Al, Mn and for AFe (active iron). Four foliar nutrient ratios (N/S, N/P, K/Ca, Ca/Mg) were additionally calculated. As the foliar sampling intensity was often below that recommended in the provincial sampling guidelines, the precision of the within-site foliar nutrient variable mean values was examined for the lowest sampling intensity used in this study (n=8). Foliar nutrient and ratio variances from 6 of the 27 sites, for which 15 trees per site had been sampled, were used as population variance estimates. A sampling intensity of n=8 was found to be sufficiently large to provide foliar nutrient variable mean estimates with an allowable error of 20% (∝ =0.5) for all but the following foliar nutrients and ratios: B, Cu, Ca/Mg and K/Ca. Two combinations of forest floor horizons were examined for possible relationships with foliar nutrient variables: L plus F and L plus F plus H. These two combinations of forest floor horizons were referred to as the LF and the LFH layers. The two criteria used to select forest floor chemical properties are as follows: (1) the precision of the forest floor chemical property site estimate was less than or equal to 20% (∝=0.5) for the field sampling intensity used, or (2) the forest floor chemical property was an established measure of nutrient availabilty. The 12 LF and 16 LFH chemical properties selected included: LF and LFH: pH (CaCl₂), total-S, -N, -P, -Cu, -Zn, -Mg, -K, -C, Min-N (anaerobic mineralizable N), KC1-N (KC1 extractable N, A (lipids), and LFH (only): exK, exCa, exMg (1M NH₄OAC exchangeable bases) and extP (Bray P₁ extractable P). Simple linear relationships between foliar nutrient variables and LF and LFH chemical properties were initially examined. Strong negative associations were found between foliar S and certain forest floor chemical properties, namely LF: pH, LMg and LFH: pH, LMg, LexMg, LexCa, LexK (here and following, L signifies the natural logarithm). It was hypothesized that these relationships reflected the effect of the different sources of plant available sulphur predominant on the higher (17 sites) and lower (10 sites) forest floor pH sites. Organic sulphur mineralization and mineral weathering were suggested as the major sources of plant available sulphur for the higher forest floor pH sites; anthropogenic atmospheric sulphur was suggested as the major source of plant available sulphur for the lower forest floor pH sites. The efficacy of forest floor (LF and LFH) chemical properties for predicting and classifying foliar nutrient status was examined through the use of multiple regression and discriminant analysis, respectively. These analyses were performed for the four foliar nutrient variables for which a range in sufficiency and possible deficiency (actual or inducible) was indicated for the stands sampled: foliar N, S, AFe and N/S. One regression model of potential predictive value was found for foliar LS. Together, LFH pH and LFH LCu statistically accounted for 79% of the observed variation in foliar LS. Several LF and LFH chemical properties were able to reliably classify stands into the following total foliar S groupings: sufficient and deficient (actual or inducible). LF LMg and LF A provided the best classification of stands into the groupings: S sufficiency and N-inducible S deficiency, as defined by foliar N/S. Three LFH chemical properties: P, S, and LexK provided the best classification of stands in terms of adequate and slight to severely deficient foliar N status. LF and LFH chemical properties were only poorly able to classify foliar AFe status. It was concluded that the relationships found in this study could not be extrapolated beyond the present study, due to the unforeseen, yet probable, influence of slightly acidic precipitation on both nutrient cycling and foliar nutrient status for 10 of the 27 stands examined.

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