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Selected biological and chemical properties of forest floors across bedrock types on the north coast of British Columbia J.M. Kranabetter and A. Banner
Abstract: We examined some of the factors related to nutrient availability of forest floors developed over saprolitic and colluvial mineral soils of four bedrock types (granodiorite, gneissic diorite, schist, and limestone) on the outer northern coast of British Columbia. All sites were relatively well drained with old-growth coniferous forests. Forest floor morphology was quite similar across sites, with friable, moderately aggregated horizons dominating the profile. There were significant differences in concentrations of total nitrogen, available phosphorus, total sulphur, and condensed tannins across bedrock types. We found detritivores such as sowbugs, millipedes, and potworms across all sites. We could not detect differences in turnover rates (via laboratory respiration) of organic matter between bedrock types. Turnover rates instead were negatively correlated with forest floor carbon and total canopy cover. Overall, forest floor properties were quite similar across the range in parent materials because of the strong influence of climate and vegetation on soil development. Résumé : Nous avons examiné quelques facteurs reliés à la disponibilité des nutriments dans les couvertures mortes formées sur des sols minéraux issus du saprolithe et de colluvions de quatre types d’assise rocheuse (granodiorite, diorite gneissique, schiste et calcaire) sur la côte nord extérieure de Colombie Britannique. Tous les sites étaient relativement bien drainés et couverts de vieilles forêts conifériennes. La morphologie de la couverture morte était assez semblable d’un site à l’autre, avec des horizons friables et modérément structurés dominant le profil. Il y avait des différences significatives dans les concentrations d’azote total, de phosphore disponible, de soufre total et de tanins condensés entre les différents sites. Nous avons trouvé des détritivores tels les cloportes communs, les millipèdes et les vers dans tous les sites. Nous n’avons pu détecter de différence entre les taux de renouvellement (par mesure de la respiration en laboratoire) de la matière organique sur les différents types d’assise rocheuse. Le taux de renouvellement était plutôt relié négativement au carbone de la couverture morte et au couvert total de la canopée. Dans l’ensemble, les propriétés de la couverture morte étaient pratiquement similaires, indépendamment de la roche-mère, à cause de la forte influence du climat et de la végétation sur le développement du sol. [Traduit par la Rédaction]
Kranabetter and Banner
Introduction The hypermaritime forests of northern coastal British Columbia have extensive areas of western redcedar (Thuja plicata Donn ex D. Don in Lamb.) and yellow-cedar (Chamaecyparis nootkatensis D. Don in Lamb.), but there is uncertainty surrounding the feasibility and sustainability of harvesting these wet, slow-growing forests. The HyP3 project (Pattern, Process, and Productivity in Hypermaritime forests of coastal British Columbia) was initiated by the B.C. Ministry of Forests to develop ecologically based management guidelines for these forests. As part of this research effort, we are examining soil processes across forest types to better understand the interaction of soil nutrients and moisture on site productivity. The terrain of the northern coast is gentle and low lying on the outer coastal Hectate Lowlands, to rugged and steep further inland on the Kitimat Range (Holland 1976). The Received July 12, 1999. Accepted January 25, 2000. J.M. Kranabetter1 and A. Banner. British Columbia Ministry of Forests, Bag 5000, Smithers, BC V0J 2N0, Canada. e-mails:
[email protected] and
[email protected] 1
Corresponding author.
Can. J. For. Res. 30: 971–981 (2000)
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most common parent material on the Kitimat Range is colluvium, deposits of which are often shallow veneers over bedrock (Valentine et al. 1978). Organic veneers and blankets over saprolitic veneers are typical of the Hectate Lowlands. We have observed that bedrock geology, from igneous intrusive to metamorphic and sedimentary rock, reflects trends in vegetation communities and forest productivity across these landscapes. Although parent material is a significant soil-forming factor (Jenny 1980; Pritchett and Fisher 1987), its influence is reduced as weathering and pedogenic processes proceed (Buol et al. 1973). In similar soils from southeastern Alaska, for example, Heilman and Gass (1974) found chemical properties were quite uniform in upper mineral soil horizons, despite the wide differences in parent materials. Soils on the northern coast undergo accelerated leaching from high levels of precipitation, while forest vegetation continually recycles nutrients back to soil surfaces. Since this organic matter accumulation at the surface has the majority of tree rooting, we investigated whether forest floors would reflect any nutritional differences between bedrock types. Nutrient availability, via forest floors, depends upon the nutrient content of the organic matter and its turnover rate (Edmonds et al. 1989). Richer, more productive coniferous © 2000 NRC Canada
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972 Fig. 1. Site locations across the CWHvh2 on the north outer coast of British Columbia.
forest soils typically have forest floors with relatively higher pH, total nitrogen (N), mineralizable N (Min. N), and lower carbon/ nitrogen (C/N) ratios than poorer soils (Courtin et al. 1988; Klinka et al. 1994; Wang 1997; Chen et al. 1998; Vesterdal and Raulund-Rasmussen 1998). Soils with low N, phosphorus (P), or pH can lead to lower quality plant litter (high in lignin and tannins) and subsequently lower decomposition and nitrification rates (Handley 1961; Davies et al. 1964; Lamb 1976; Jones and Richards 1977; Flanagan and Van Cleve 1983; Northrup et al. 1995). Soil faunal communities can also change across forest and soil types (Staaf 1987; Beyer and Irmler 1991; Teuben and Smidt 1992; Blair et al. 1994) and directly affect nutrient cycling and decomposition through communition and microbial grazing (Baath et al. 1981; Setälä et al. 1988; Williams and Griffiths 1989). We could expect, therefore, that both the nutrient content and turnover rate (through differences in litter quality or faunal activity) of the forest floors would reflect differences in site productivity. We sampled forest floors from saprolitic and colluvial mineral soils of four bedrock types (granodiorite, gneissic diorite, schist, and limestone) for some of the biological and chemical factors related to nutrient status, including nutrient (macro and micro) and condensed tannin concentrations, soil faunal communities, and turnover rates (via respiration in a laboratory incubation). The objective of this study was to determine how these properties differed after forest floor development across bedrock types on the outer northern coast of British Columbia.
Methods Site description The Coastal Western Hemlock zone (CWH) occurs at low to middle elevations mostly west of the coastal mountains, along the
Can. J. For. Res. Vol. 30, 2000 Fig. 2. Schematic diagram of respiration jar, with tripod, glass vial, rubber cap, and syringe.
Table 1. ANOVA table for forest floors (with subsamples) and mineral soil, foliar (without subsamples). ANOVA without subsamples
ANOVA with subsamples Source
df
Error term
Source
df
Bedrock Plot (bedrock) Error Total
3 8 24 35
Plot (bedrock)
Bedrock Error Total
3 8 11
entire British Columbia coast and on into Alaska and Washington– Oregon (Meidinger and Pojar 1991). The CWH corresponds to Köppens’s Cfb region, a temperate, rainy climate with warm summers (Krajina 1969). Study sites were located within the very wet hypermaritime portion of the CWH zone (CWHvh2), located on the outer northern coast of British Columbia (Fig. 1). The CWHvh2 ranges in elevation from 0 to 600 m and has a cool, very mild climate (mean annual temperature 8°C) with little snow but foggy and rainy year round (-3000 mm/year) (Banner et al. 1993). Three replicates of four bedrock types were chosen from geological maps (Hutchinson et al. 1979) and site examination: granodiorite (including quartz diorite), igneous intrusive rocks with a high content of quartz, feldspar and some biotite; gneissic diorite, an igneous intrusive rock with less quartz and more biotite, garnet, and some hornblende; schist, a sedimentary amphibolite metamorphic rock with a high mica, biotite, and hornblende content; and limestone, a sedimentary rock, high in CaCO3.
Sampling Sampling took place between July 5 and July 10, 1998. At each site a 20 × 20 m plot area was established, where plant species and percent cover were recorded, along with a site and soil description. © 2000 NRC Canada
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Table 2. Site and soil descriptions for each plot. Bedrock, plot No., and location
Humus classa
Forest floor descriptiona (horizons and depth)
Soil classb
Mineral soil (horizon, depth, texture; total % coarse fragments)b
Granodiorite 1 Rainbow Lake
Resimor
L 25–22 cm; Hr 22–7 cm; Hh 7–0 cm L 46–45 cm; Hr 45–0 cm L 6–5 cm; Fm 5–0 cm
O.FHP
Ae 0–7 cm, LS; Bhf 7–20 cm SiL; C 20–25 cm SCL; R 25+; 0% cf C 0–1 cm, LS; R 1+; 0% cf Bm (C) 0–8 cm; R 8+; 25% cf
6 Giltoyees Inlet 11 Campania Island Gneissic diorite 4 Diana Lake
Resimor Hemimor Resimor
5 Smith Island
Resimor
8 Boat Bluff
Humimor
Schist 2 Alwyn Lake
Resimor
3 Diana Lake, north
Resimor
7 Work Island
Resimor
Limestone 9 Aristazabal Island
Resimor
10 Emily Carr Inlet
Resimor
12 Hanmer Island
Resimor
HE.FO O.DYB
L 11–10 cm; Fm 10–9 cm; Hr 9–1 cm; Hh 1–0 cm L 15–14 cm; Hr 14–3 cm; Hzi 3–0 cm L 18–17 cm; Hr 17–12 cm; Hh 12–0 cm
O.FHP
L 11–10 cm; Hr 10–1 cm; Hh 1–0 cm L 24–22 cm; Hr 22–2 cm; Hhi 2–0 cm L 11–10 cm; Hr 10–2 cm; Hh 2–0 cm
O.HFP
L 8–7 cm; Hr 7–0.5 cm; Hh 0.5 –0 cm L 13–12 cm; Fm 12–10 cm; Hr 10–0 cm L 22–21 cm; Fm 21–17 cm; Hr 17–7 cm; Hh 7–0 cm
O.HFP
O.FHP O.FHP
O.HFP O.HFP
O.DYB O.FHP
Bhf1 0–15 cm, SiL; Bhf2 15–50+ cm, SiL; 40% cf Ae 0–1 cm; Bhf 1–40 cm, SiL; BC 40–90 cm, SiL; R 90+; 20% cf Bhf 0–40+ cm, SiL; 60% cf
Ae 0–1 cm; Bf1 1–6 cm, fSL; Bf2 6– 50+ cm, SL; 70% cf Ae 0–1 cm, Bfh 1–42 cm, SiL; BC 42+ cm, CL; 50% cf Ae 0–5 cm, Bf 5–150 cm, fSL; R 150+; buried Ae horizons; 12% cf Bf 0–30 cm SiL, Bhf 30–32 cm SiL; R 32+; 5% cf Bm 0–30 cm, LS; Bhf 30–32 cm, SL; R 32+; 15% cf Ah 0–7 cm, Si; Ae 7–15 cm, Si; Bhf 15–30 cm, Si; BC 30–40 cm, SiL, C 40–50+ cm; 0% cf
a
Green et al. (1993). Canadian Soil Survey Committee (1987).
b
A sample of bedrock and mineral soil (0–20 cm depth, or less for shallower soils) was taken from the soil pit. Three forest floor subsamples were taken from each site. The subsample was 30 × 30 cm wide and 10 cm deep but sometimes shallower in microsites with forest floors
