- Email: [email protected]
Changes in soil acidity and organic matter following the establishment of conifers on former grassland in New Zealand
Forest Ecology and Management 112 (1998) 245±252
Changes in soil acidity and organic matter following the establishment of conifers on former grassland in New Zealand HaÊkan Alfredssona, Leo M. Condronb,*, Marianne Clarholmc, Murray R. Davisd a
Department of Ecology and Environmental Research, Section for Soil Ecology, Swedish University of Agricultural Sciences, P.O. Box 7072, S-750 07 Uppsala, Sweden b Soil, Plant and Ecological Sciences Division, P.O. Box 84, Lincoln University, Canterbury, New Zealand c Department of Mycology and Pathology, Swedish University of Agricultural Sciences, P.O. Box 7026, S-750 07 Uppsala, Sweden d New Zealand Forest Research Institute, P.O. Box 29237, Fendalton, Christchurch, New Zealand Received 12 April 1997; accepted 25 May 1998
Abstract Effects of a land use change from grassland to coniferous plantation forestry (Pseudotsuga menzieii [Douglas ®r]; Pinus radiata [radiata pine]) on soil acidity and organic matter were assessed at two sites in New Zealand. The sites differed with respect to soils, climate, vegetation cover and type, relative maturity and management of the forest stands. Results obtained at the different sites were, therefore, not directly comparable, although they represented a comparison of a similar change in land use and some overall trends were evident. The change from grassland to conifers decreased levels of organic carbon, total nitrogen and exchangeable cations and increased exchangeable acidity in the upper 20±30 cm of soil. Exchangeable aluminium and exchangeable acidity were more sensitive measures of the effects of afforestation on soil acidity than pH. # 1998 Elsevier Science B.V. All rights reserved. Keywords: Plantation forestry; Exchangeable cations; Pseudotsuga menzieii; Pinus radiata
1. Introduction In New Zealand, plantation forestry based on exotic conifer species such as radiata pine (Pinus radiata) and Douglas ®r (Pseudotsuga menzieii) is attracting continued interest as a viable long-term land use option for hill and high country areas. Plantation forests cover approximately 1.7 million ha (ca. 7% total land area) in New Zealand at present and since 1992, 50±90 000 ha of new forest have been planted *Corresponding author. Tel.: +64-03-3252811; fax: +64-033253607; e-mail: [email protected]
each year. Furthermore, it is expected that new planting will continue at 50±70 000 ha per annum between 1997 and 2010 (Glass, 1997). The latest expansion in forest planting in New Zealand has occurred primarily on hill country land developed under extensive pastoral agriculture since European settlement. This change in land use has been mainly attributed to a combination of continued declines in economic returns from pastoral farming and the expectation of increased future returns from forestry. There is a commonly held belief that conifers degrade soil fertility in various ways, although Binkley (1995) concluded that there has been little con-
0378-1127/98/$ ± see front matter # 1998 Elsevier Science B.V. All rights reserved. PII: S0378-1127(98)00346-6
246
H. Alfredsson et al. / Forest Ecology and Management 112 (1998) 245±252
sistent scienti®c evidence for this. In Europe, forest soil deterioration was previously thought to be caused by the conifers themselves, but has later been ascribed to forest management practices and the continued removal of nutrients or the choice of poor sites to grow trees (Innes, 1993; Binkley, 1995). On the other hand, there is evidence that conifers can actually improve soil nutrient availability (Fisher, 1990; Davis and Lang, 1991; Belton et al., 1995; Davis, 1995; Condron et al., 1996). The nature of soil acidity and acidi®cation processes have been described by several research workers (Van Breemen et al., 1983; BerdeÂn et al., 1987; Yuan and Lavkulich, 1995; Binkley and HoÈgberg, 1997). Soil acidity measured as pH in a water suspension or in a weak salt solution gives an immediate picture of the situation and could be viewed as a empirical index of the amount of free H in solution (Binkley and Richter, 1987). This small pool of free H is in equilibrium with other less reactive `exchangeable' or `titratable' pools of H associated with soil mineral and organic constituents (McBride, 1994). Trees have both direct and indirect effects on soil which can affect soil acidity and organic matter. The major sources of soil acidity in pre-industrial forests were nutrient removal and dissociated carbonic acid and organic acids (Nilsson et al., 1982). The deposition of industrial pollutants containing strong mineral acids may contribute to increased forest soil acidity in some areas of the world, although the removal of nutrients by harvesting also plays an important role in increased forest soil acidity (Bredemeier et al., 1990; NordeÂn, 1994). In New Zealand inputs of strong acids derived from industry are very low (Holden and Clarkson, 1986), and the main sources of acidity are found within the forest ecosystem. Conifers may increase soil acidity through the production of organic acids from their mycorrhizal roots and uptake of nutrients (Sollins et al., 1981). Tree roots release H ions as they take up cations, although most of the cations taken up by trees are returned to soil in litter and root detritus (Attiwell and Adams, 1993). When trees are harvested and cations removed in wood products, the resulting effect on soil acidity may become permanent or persist for several decades (Nilsson et al., 1982; Johnson et al., 1991). Organic matter has a signi®cant in¯uence on soil chemical properties and processes, including cation
exchange and acidity (McBride, 1994). Furthermore, most of the total nitrogen and signi®cant proportions of the total phosphorus and sulphur in most topsoils are associated with organic constituents and, therefore, the cycling and availability of these nutrients is mainly determined by the nature and dynamics of soil organic matter (Kelley and Stephenson, 1996; Magid et al., 1996; Zhao et al., 1996). There is a need for research to be conducted under New Zealand conditions to determine the effect of land use change from grassland to coniferous plantation forest on the ability of the soil to sustain plant growth in the long-term. The objective of this research was to investigate changes in soil acidity and organic matter associated with the establishment of conifers on land developed under grassland in the absence of signi®cant anthropogenic atmospheric inputs. This involved comparing selected indices of acidity and concentrations of organic carbon and total nitrogen in pairs of adjacent soils under grassland and recently established conifers at two sites in the South Island of New Zealand. 2. Materials and methods 2.1. Site descriptions and soil sampling 2.1.1. Craigieburn This site was located at the Craigieburn Research Area, 100 km west of Christchurch (438100 S, 1718200 E). The altitude at the site was 870 m, the annual rainfall 1440 mm, and the mean monthly temperature was approximately 88C (Nordmeyer and Ledgard, 1993). The soil was classi®ed as a Tekoa stony loam (Orthic Brown Soil [New Zealand Soil Classi®cation], Dystrochrept [USDA Soil Taxonomy]) formed from greywacke colluvium. The original vegetation was mountain beech (Nothofagus solandri var cliffortioides) which was cleared and burnt more than 100 years ago (Nordmeyer and Ledgard, 1993). The area was used for extensive grazing until Douglas ®r was planted at approximately 2000 stems per ha in 1979; the stand age at time of sampling was 17 years and it is expected that the trees will be harvested at 50±60 years. The forest stand and adjacent grassland were situated on a south±east facing hillslope with 308 slope angle. No fertiliser had ever
H. Alfredsson et al. / Forest Ecology and Management 112 (1998) 245±252
been applied to the areas under forest or grassland. The stand had not been thinned at the time of sampling and the canopy was closed. Species present in the grassland area included tall tussock (Chionocloa macra), brown top (Agrostis capillaris), mountain daisy (Celmisia spectabilis) and native shrubs (Dracophyllum, Hebe, Cassinia and Discaria spp). A total of 24 bulked soil samples were obtained from 0±5 cm, 5±15 cm and 15±30 cm depth in 1996. There were no signs of understorey vegetation under Douglas ®r and the ground was covered by 3±5 cm of litter (mainly needles) which was removed before soil sampling. In the grassland area, soils were sampled along four transects commencing 10 m from the forest edge. Five soil cores (65 mm diameter) were taken at a distance 1 m between each other and bulked for each depth and transect. The transects were situated 5 m apart in the direction of the slope. Under the Douglas ®r stand, samples were taken on two transects 0.6 m on both sides of the tree rows. The tree rows were at the same slope position as the corresponding grassland transects. Sub-samples were taken at 1 m intervals along each 5 m transect. The samples were bulked for each tree row and depth. 2.1.2. Southland This site was located at Drummond, 32 km northwest of Invercargill (1688150 E, 468100 S) (O'Meara, 1995). It was situated on a west facing 358 terrace slope at 65 m above sea level. Mean annual rainfall at the site was approximately 850 mm and the mean annual temperature was 108C. The soil was classi®ed as an Aparima-Drummond silt loam (Pallic Soil [New Zealand Soil Classi®cation]; Humult [USDA Soil Taxonomy]) derived from greywacke alluvium and loess. The original tussock grassland (Chionochloa spp) vegetation was burned and replaced with pasture over 100 years ago. Extensive grazing had resulted in a steady decline in soil fertility, especially since very little fertiliser had been added due to the steep terrain. In 1980, radiata pine was established at a planting density of 2200 stems per ha, and the trees were progressively thinned to 450 stems per ha and pruned to 6 m, the ®nal operation being carried out in 1992. The mean tree diameter at breast height was 30 cm at the time of sampling; the stand age at time of sampling was 15 years and it is expected that the trees will be harvested at 25±30 years. A non-planted powerline
247
strip intersected the slope and was left with the original pasture. Species in the pasture were Yorkshire fog (Holcus lanatus), browntop (Agrostis capillaris), some white clover (Trifolium repens) and various weeds. The A horizon extended to 30 cm and roots were abundant to 20 cm under the pasture, although tree roots extended to more than 50 cm. There were no signs of understorey vegetation in the forest area and the forest ¯oor was covered by 2±3 cm of needles which were carefully removed before soil sampling. Soil samples from three depths (0±7.5 cm, 7.5±15 cm and 15±30 cm) were taken from pits excavated within three randomly located plots (1010 m) in the forest and adjacent grassland areas (O'Meara, 1995). 2.2. Soil analyses All soils were air-dried, crushed, and sieved (2 mm) after sampling. Soil pH was measured in 0.01 M CaCl2 (Blakemore et al., 1987). Exchangeable acidity and exchangeable aluminium (Al) were determined by double titration (Page et al., 1986) and exchangeable H was calculated as the difference between the two. Concentrations of exchangeable cations (Ca2, Mg2, K, Na, Mn2, Fe2) were determined according to the BaCl2-method described by Hendershot et al. (1993). The effective cation exchange capacity (ECEC) was calculated as the sum of all exchangeable cations. Total exchangeable cations (TEC) were de®ned as the sum of exchangeable Ca2, Mg2, K and Na and was also expressed as a percentage of ECEC (%TEC) (equivalent to total exchangeable bases [TEB] and base saturation [%BS] ± Blakemore et al., 1987). Concentrations of organic carbon (C) and total nitrogen (N) were determined by mass spectrometry. Soil data were statistically analysed using GENSTAT 5 for Windows (Lawes Agricultural Trust, 1993). Values for LSD at the 5% level between treatment pairs (grassland, forest) were determined for each site. 3. Results At the Craigieburn site, the only signi®cant difference in pH under Douglas ®r and grassland was at the 15±30 cm depth where pH was slightly lower under ®r, while exchangeable acidity and Al were higher under
248
H. Alfredsson et al. / Forest Ecology and Management 112 (1998) 245±252
®r at all depths (Table 1). Exchangeable Ca2, Mg2 and K levels were lower in soil under ®r at all depths except 0±5 cm for Ca2 and 15±30 cm for K (Table 1). Total exchangeable bases expressed as a percentage of ECEC (%TEC) were consistently and signi®cantly lower (16%±19%) under ®r compared with grassland (Table 1). Organic C and total N in the 0±5 cm soil were signi®cantly lower under ®r compared with grassland, while organic C was also slightly (but not signi®cantly) lower under ®r (5.4%) compared with grassland (6.6%) in the 5± 15 cm soil layer (Table 1). At the Southland site, differences between grassland and pine for most of the soil chemical properties measured were not statistically signi®cant (Table 2). Soil pH was lower under pine than grassland in the 0± 5 cm depth increment. Although there was a trend for exchangeable Ca2, Mg2 and K to be lower under pine, differences were not signi®cant for Ca2, and only signi®cant for Mg2 in the 0±7.5 cm and 7.5± 15 cm soil depths, and for K in the 7.5±15 cm and 15±30 cm depths. In contrast exchangeable Na tended to be higher under pine, although the difference was signi®cant only at the lowest depth (15±30 cm). While there was a trend for TEC and ECEC to be lower under pine, differences were only signi®cant for ECEC at the 7.5±15 cm and 15±30 cm depths (Table 2). Organic C and total N were slightly (but not signi®cantly) higher under pine compared with grassland in the 0±7.5 cm soil, but were signi®cantly lower in the 7.5±15 cm soil (Table 2). 4. Discussion Although there was no signi®cant difference in soil pH between grassland and Douglas ®r at Craigieburn in the upper layers and only a slight decrease under ®r in the lower layer, exchangeable Al and acidity increased under Douglas ®r in all soil depths sampled (Table 1). Thus, exchangeable acidity and Al provide more sensitive indicators of the development of acidity following afforestation than pH. Plant uptake was probably mainly responsible for the observed large decreases in levels of exchangeable cations (Table 1). Reductions in Bray-2 extractable (HCl/NH4F) K and Mg2 in topsoil (0±10 cm) under pine stands on similar soils in New Zealand high country were
reported by Davis and Lang (1991). However, under some older stands in lower rainfall areas cation availability in topsoils was found to be similar or greater than under grassland, possibly because of uptake from lower horizons and subsequent deposition at the surface in litterfall (Davis, 1998). In other studies levels of exchangeable Mg2 and Na were found to be greater under young pine stands compared with adjacent grassland in a coastal region of New Zealand, which was mainly attributed to increased interception of sea salts by the forest canopy (Giddens et al., 1997; Par®tt et al., 1997). The reduction in % TEC at the Craigieburn site occurred even though levels of organic C and total N, and thus ECEC, decreased in 0±5 cm soil under Douglas ®r compared with grassland. The % TEC would otherwise be expected not to decline under Douglas ®r if decreases in exchangeable cations were of a similar order of magnitude compared with decreases in ECEC. Thus, the soil has not been able to completely compensate for cation uptake by trees through weathering and, therefore, exchangeable acidity increased under trees compared with grassland at Craigieburn. However, despite these changes the level of soil acidity as measured by pH was maintained under the forest stand compared with grassland (Table 1), indicating that soil biological processes may not necessarily be negatively in¯uenced by afforestation. Concentrations of soil organic C and total N in topsoil (0±5 cm) were markedly lower under Douglas ®r compared with grassland at the Craigieburn site (Table 1). This is consistent with ®eld studies reported by Par®tt et al. (1997), while Davis (1995) also observed that radiata pine seedlings decreased levels of soil organic C and total N in a short-term glasshouse pot trial. The decrease in soil C and N may be attributed to changes in soil macro- and micro-¯ora associated with the root/rhizosphere systems of trees compared with grassland (Dighton and Boddy, 1988; Dighton, 1995). For example, ectomycorrhizal fungi associated with tree roots have been found to increase mineralisation of organic forms of N in soil via the production of extracellular hydrolase enzymes (e.g. proteinase) (Marschner and Dell, 1994; George and Marschner, 1996). On the other hand, signi®cant amounts of C and nutrients are added to soil via the roots (Vogt et al., 1986), and it has been estimated that roots and mycorrhiza are responsible for over 80% of
Fir Grassland LSDb
Fir Grassland LSDb
5±15
15±30
3.7 3.5 Ns
0.21 0.20 Ns
0.30 0.34 Ns
0.36 0.58 0.09
N (%)
18 17 Ns
18 19 Ns
19 20 Ns
C/N
0.31 0.57 0.09
0.82 1.56 0.47
4.40 5.62 Ns
Caa
0.14 0.23 0.03
0.31 0.56 0.16
0.99 1.71 0.53
Mga
0.19 0.30 Ns
0.27 0.55 0.14
0.51 0.79 0.20
Ka
0.002 0.002 Ns
0.005 0.005 Ns
0.004 0.006 Ns
Naa
0.045 0.024 0.008
0.057 0.044 Ns
0.122 0.102 Ns
Mna
0.016 0.024 0.008
0.030 0.023 Ns
0.035 0.025 0.004
Fea
4.75 3.79 Ns
6.88 6.66 Ns
8.83 9.62 Ns
ECECa
0.64 1.10 0.19
1.40 2.68 0.73
5.90 8.13 2.09
TECa
14 30 6
21 40 8
67 84 13
% TEC
4.36 4.51 0.12
4.33 4.42 Ns
4.75 4.70 Ns
pH (CaCl2)
Exchangeable cations/effective cation exchange capacity [ECEC]/total exchangeable cations [TEC]/exchangeable acidity [cmol()kgÿ1]. p<0.05.
b
a
7.0 11.9 2.6
Fir Grassland LSDb
0±5
5.4 6.6 Ns
C (%)
Depth (cm)
Table 1 Mean chemical analyses for soil sampled under Douglas fir and adjacent grassland at the Craigieburn site
3.71 2.45 0.85
4.96 3.63 0.81
2.48 1.16 0.98
Ala
0.33 0.19 0.13
0.43 0.29 0.11
0.30 0.20 Ns
Ha
4.04 2.64 0.91
5.39 3.92 0.86
2.78 1.36 1.08
Aciditya
H. Alfredsson et al. / Forest Ecology and Management 112 (1998) 245±252 249
Radiata Grassland LSDb
Radiata Grassland LSDb
7.5±15
15±30
2.2 2.0 Ns
0.16 0.15 Ns
0.16 0.22 0.03
0.31 0.28 Ns
N (%)
13 13 Ns
14 14 Ns
15 14 Ns
C/N
1.98 2.23 Ns
2.36 2.87 Ns
2.13 3.41 Ns
Caa
1.94 2.50 Ns
2.06 2.65 0.42
1.79 2.76 0.74
Mga
0.62 1.03 0.39
0.74 1.28 0.46
1.81 1.73 Ns
Ka
0.27 0.10 0.13
0.32 0.10 Ns
0.39 0.34 Ns
Naa
0.12 0.05 Ns
0.24 0.12 Ns
0.36 0.09 0.11
Mna
0.01 0.00 Ns
0.00 0.00 Ns
0.01 0.07 Ns
Fea
6.53 8.17 0.58
7.37 8.87 0.42
9.27 10.27 Ns
ECECa
4.81 5.86 Ns
5.48 6.90 1.28
6.12 8.24 Ns
TECa
73 72 Ns
75 78 Ns
66 80 Ns
% TEC
4.61 4.61 Ns
4.54 4.62 Ns
4.27 4.54 0.24
pH (CaCl2)
Exchangeable cations/effective cation exchange capacity [ECEC]/total exchangeable cations [TEC]/exchangeable acidity [cmol()kgÿ1]. p<0.05.
b
a
4.7 4.1 Ns
Radiata Grassland LSDb
0±7.5
2.2 3.0 0.6
C (%)
Depth (cm)
Table 2 Mean chemical analyses for soil sampled under radiata pine and adjacent grassland at the Southland site
1.42 2.02 Ns
1.42 1.60 Ns
2.37 1.58 Ns
Ala
0.17 0.23 Ns
0.20 0.24 Ns
0.42 0.29 Ns
Ha
1.59 2.25 Ns
1.62 1.84 Ns
2.79 1.87 Ns
Aciditya
250 H. Alfredsson et al. / Forest Ecology and Management 112 (1998) 245±252
H. Alfredsson et al. / Forest Ecology and Management 112 (1998) 245±252
the organic matter and N added to soil under Douglas ®r (Fogel and Hunt, 1983). There was some indication of differences in soil characteristics under radiata pine and adjacent grassland at the Southland site. Contrary to ®ndings at the Craigieburn site under Douglas ®r, amounts of organic C and total N in the mineral topsoil (0±7.5 cm) were slightly higher under radiata pine compared with grassland at Southland (Table 2). This may re¯ect differences in tree species and relative maturity at the different sites and the consequent effects on the amounts and fate of litterfall material. Biomass accumulation and turnover would have been substantially greater at the lower elevation radiata pine site than at the Douglas ®r site, and in addition thinning and pruning would have returned a large proportion of accumulated biomass and nutrients to the soil surface. It is also possible that decomposition and subsequent incorporation of forest litter into topsoil was greater at the Southland site compared with the Craigieburn site. Despite the relatively low soil pH (4.3±4.6) measured at the Southland site, a signi®cant number of earthworms were observed under radiata pine compared with the adjacent grassland (O'Meara, 1995). Thus accumulation and subsequent decomposition of litterfall may have reversed a possible earlier reduction in C and N levels under pine. The lower ECEC observed in the 7.5±15 cm soil under radiata pine compared with grassland was consistent with the corresponding lower level of organic C (Table 2). On the other hand, ECEC was signi®cantly lower under radiata pine compared with grassland in the 15±30 cm soil, despite the fact that soil pH and levels of organic C and total N were similar under radiata pine and grassland (Table 2). This may be attributed to changes in the chemical nature of the soil organic matter present under the different vegetation types at this depth, although the lower ECEC at this depth may also be due to enhanced weathering of clay minerals. The decline in pH under pine in the 0±7.5 cm soil is consistent with other studies which have shown pH of grassland soil to decline under afforestation (Davis and Lang, 1991; Hawke and O'Connor, 1993; Giddens et al., 1997; Par®tt et al., 1997). The absence of a pH decline under Douglas ®r in the upper horizons at Craigieburn, despite similar or greater reductions in TEC and increases in exchangeable acidity than under pine at the Southland site, may re¯ect the greater organic
251
matter content and consequent buffering capacity of the Craigieburn soil (Tables 1 and 2). The long-term impact of successive tree generations on soil fertility will depend on the amounts of nutrient exported in harvest in relation to the capacity of the soil regolith and atmospheric inputs to compensate for the losses and the meet needs of future tree generations (Binkley and HoÈgberg, 1997). Trees contains substantial amounts of nutrient that are locked up for a shorter or longer time while the forest litter also contains signi®cant quantities of nutrients, a proportion of which will be incorporated into the underlying soil in the long-term. Amounts of nutrient locked up in organic forms in forest systems are much higher than for grassland systems. For a more complete picture, it is necessary to follow the changes in nutrient pools and organic matter quantitatively, which was not possible in this study. When trees are harvested, it is important to determine the fate of cations and other nutrients present in the tree and litter, which in turn requires investigation over more than one forest rotation. Acknowledgements This study was jointly funded by the Swedish University of Agricultural Sciences and Lincoln University (New Zealand) and the authors would like to thank Leanne Hassall and Prof. Ian Cornforth (Lincoln University) and Alan Nordmeyer (New Zealand Forest Research Institute) for their assistance. References Attiwell, P.M., Adams, M.A., 1993. Nutrient cycling in forests. New Phyt. 124, 561±582. Belton, M.C., O'Connor, K.F., Robson, A.B., 1995. Phosphorus levels in topsoils under conifer plantations in Canterbury high country grasslands. New Zealand J. For. Sci. 25, 262±282. BerdeÂn, M., Nilsson, S.I., RoseÂn, K., Tyler, G., 1987. Soil acidification ± extent, causes and consequences. Report 3292. National Swedish Environment Protection Board, Solna, Sweden, 164 pp. Binkley, D., 1995. The influence of tree species on forest soils ± processes and patterns. In: Mead, D.J., Cornforth, I.S. (Eds.), Proceedings of the Trees and Soils Workshop. Lincoln University Press, New Zealand, pp. 1±34. Binkley, D., Richter, D., 1987. Nutrient cycles and H budgets of forest ecosystems. Adv. Ecol. Res. 6, 1±51.
252
H. Alfredsson et al. / Forest Ecology and Management 112 (1998) 245±252
Binkley, D., HoÈgberg, P., 1997. Does atmospheric deposition of nitrogen threaten Swedish forests? For. Ecol. Manage. 92, 119± 152. Blakemore, L.C., Searle, P.L., Daly, B.K., 1987. Methods for chemical analysis of soils. NZ Soil Bureau Scientific Report, 80. Lower Hutt, New Zealand, 103 pp. Bredemeier, M., Matzner, E., Ulrich, B., 1990. Internal and external proton load to forest soils in northern Germany. J. Environ. Qual. 19, 469±477. Condron, L.M., Davis, M.R., Newman, R.H., Cornforth, I.S., 1996. Influence of conifers on the forms of phosphorus in selected New Zealand grassland soils. Biol. Fertil. Soils 21, 37±42. Davis, M.R., 1995. Influence of radiata pine seedlings on chemical properties of some New Zealand montane soils. Plant Soil 176, 255±262. Davis, M.R., 1998. Soil impacts of afforestation in the high country. New Zealand Forestry 42, 34±38. Davis, M.R., Lang, M.H., 1991. Increased nutrient availability in topsoils under conifers in the South Island high country. New Zealand J. For. Sci. 21, 165±179. Dighton, J., 1995. Nutrient cycling in different terrestrial ecosystems in relation to fungi. Can. J. Bot. 73, 1349±1360. Dighton, J., Boddy, L., 1988. Role of fungi in nitrogen, phosphorus and sulphur cycling in temperate forest ecosystems. In: Boddy, L., Marchant, R., Read, D.J. (Eds.), Nitrogen, Phosphorus and Sulphur Utilization by Fungi. Cambridge University Press, Cambridge, pp. 269±298. Fisher, R.F., 1990. Amelioration of soils by trees. In: Gessel, S.P., Lacate, D.S., Weetman, G.F., Powers, R.F. (Eds.), 7th North American Forest Soils Conference. University of British Columbia, pp. 290±300. Fogel, R., Hunt, G., 1983. Contribution of mycorrhizae and soil fungi to nutrient cycling in a Douglas fir ecosystem. Can. J. For. Res. 13, 219±232. George, E., Marschner, H., 1996. Nutrient and water uptake by roots of forest trees. Z. Pflanz. Bodenk. 159, 11±21. Giddens, K.M., Parfitt, R.L., Percival, H.J., 1997. Comparison of some soil properties under Pinus radiata and improved pasture. New Zealand J. Agric. Res. 40, 409±416. Glass, B.P., 1997. A survey of afforestation intentions in New Zealand between 1996 and 2010. New Zealand Forestry 41, 34±37. Hawke, M.F., O'Connor, M.B., 1993. Soil pH and nutrient levels at Tikitere agroforestry research area. New Zealand J. For. Sci. 23, 40±48. Hendershot, W.H., Lalnade, H., Duquette, M., 1993. In: Carter, M.R. (Ed.), Soil Sampling and Methods of Analysis. Lewis Publishers, Boca Raton, Florida, USA, pp. 167±176. Holden, R., Clarkson, T.S., 1986. Acid rain: a New Zealand viewpoint. J. R. Soc. New Zealand 1, 1±15. Innes, J.L., 1993. Forest Health: Its Assessment and Status. CAB International, Wallingford, UK, 677 pp.
Johnson, D.W., Cresser, M.S., Nilsson, S.I., Turner, J., Ulrich, B., Binkley, D., Cole, D.W., 1991. Soil changes in forest ecosystems: evidence for and probable causes. Proc. R. Soc. Edinburgh 97B, 81±116. Kelley, K.R., Stephenson, F.J., 1996. Organic forms of N in soil. In: Piccolo, A. (Ed.), Humic Substances in Terrestrial Ecosystems. Elsevier, Amsterdam, pp. 407±427. McBride, M., 1994. Environmental Chemistry of Soils. Oxford University Press, New York, 406 pp. Magid, J., Tiessen, H., Condron, L.M., 1996. Dynamics of organic phosphorus in soils under natural and agricultural ecosystems. In: Piccolo, A. (Ed.), Humic Substances in Terrestrial Ecosystems. Elsevier, Amsterdam, pp. 429±466. Marschner, H., Dell, B., 1994. Nutrient uptake in mycorrhizal symbiosis. Plant Soil 159, 89±102. Nilsson, S.I., Miller, H.D., Miller, J.D., 1982. Forest growth as a possible cause of soil and water acidification: an examination of the concepts. Oikos 39, 40±49. NordeÂn, U., 1994. Influence of tree species on acidification and mineral pools in deciduous forest soils of south Sweden. Water Air Soil Pollut. 76, 363±381. Nordmeyer, A.H., Ledgard, N.J., 1993. Above-ground biomass, productivity, and nutrients in 15-year-old stands of Ponderosa pine, Corsican pine, Douglas fir and European larch in the Craigieburn range. New Zealand Stud. For. Suec. 191, 75±85. O'Meara, D.M., 1995. A comparison of soil fertility under Pinus radiata and pasture in Southland. Research Dissertation, Bachelor of Forestry Science, University of Canterbury, Christchurch, New Zealand, 48 pp. Page, A.L., Miller, R.H., Keeney, D.R., 1986. Methods of Soil Analysis, Chemical and Microbiological Properties, 2nd ed. American Society of Agronomy and Soil Science Society of America, Madison, Wisconsin, 1159 pp. Parfitt, R.L., Percival, H.J., Dahlgren, R.A., Hill, F., 1997. Soil and solution chemistry under pasture and radiata pine in New Zealand. Plant Soil 191, 279±290. Sollins, P., Sromack, K., Jr., Fogel, R., Li, Y.C., 1981. Role of lowmolecular-weight organic acids in the inorganic nutrition of fungi and higher plants. In: Wicklow, D.T., Carroll, G.C. (Eds.), The Fungal Community. Marcel Decker, New York, pp. 607± 619. Van Breemen, N., Mulder, J., Driscoll, C.T., 1983. Acidification and alcalinization of soils. Plant Soil 75, 283±308. Vogt, K.A., Grier, C.C., Vogt, D.J., 1986. Production, turnover and nutrient dynamics of above- and belowground detritus of world forests. Adv. Ecol. Res. 15, 303±377. Yuan, G., Lavkulich, L.M., 1995. Acid-buffering capacity of factors of forest soils. Comm. Soil Sci. Plant Anal. 26, 51±60. Zhao, F.J., Wu, J., McGrath, S.P., 1996. Soil organic sulfur and its turnover. In: Piccolo, A. (Ed.), Humic Substances in Terrestrial Ecosystems. Elsevier, Amsterdam, pp. 467±506.
Changes in soil acidity and organic matter following the establishment of conifers on former grassland in New Zealand HaÊkan Alfredssona, Leo M. Condronb,*, Marianne Clarholmc, Murray R. Davisd a
Department of Ecology and Environmental Research, Section for Soil Ecology, Swedish University of Agricultural Sciences, P.O. Box 7072, S-750 07 Uppsala, Sweden b Soil, Plant and Ecological Sciences Division, P.O. Box 84, Lincoln University, Canterbury, New Zealand c Department of Mycology and Pathology, Swedish University of Agricultural Sciences, P.O. Box 7026, S-750 07 Uppsala, Sweden d New Zealand Forest Research Institute, P.O. Box 29237, Fendalton, Christchurch, New Zealand Received 12 April 1997; accepted 25 May 1998
Abstract Effects of a land use change from grassland to coniferous plantation forestry (Pseudotsuga menzieii [Douglas ®r]; Pinus radiata [radiata pine]) on soil acidity and organic matter were assessed at two sites in New Zealand. The sites differed with respect to soils, climate, vegetation cover and type, relative maturity and management of the forest stands. Results obtained at the different sites were, therefore, not directly comparable, although they represented a comparison of a similar change in land use and some overall trends were evident. The change from grassland to conifers decreased levels of organic carbon, total nitrogen and exchangeable cations and increased exchangeable acidity in the upper 20±30 cm of soil. Exchangeable aluminium and exchangeable acidity were more sensitive measures of the effects of afforestation on soil acidity than pH. # 1998 Elsevier Science B.V. All rights reserved. Keywords: Plantation forestry; Exchangeable cations; Pseudotsuga menzieii; Pinus radiata
1. Introduction In New Zealand, plantation forestry based on exotic conifer species such as radiata pine (Pinus radiata) and Douglas ®r (Pseudotsuga menzieii) is attracting continued interest as a viable long-term land use option for hill and high country areas. Plantation forests cover approximately 1.7 million ha (ca. 7% total land area) in New Zealand at present and since 1992, 50±90 000 ha of new forest have been planted *Corresponding author. Tel.: +64-03-3252811; fax: +64-033253607; e-mail: [email protected]
each year. Furthermore, it is expected that new planting will continue at 50±70 000 ha per annum between 1997 and 2010 (Glass, 1997). The latest expansion in forest planting in New Zealand has occurred primarily on hill country land developed under extensive pastoral agriculture since European settlement. This change in land use has been mainly attributed to a combination of continued declines in economic returns from pastoral farming and the expectation of increased future returns from forestry. There is a commonly held belief that conifers degrade soil fertility in various ways, although Binkley (1995) concluded that there has been little con-
0378-1127/98/$ ± see front matter # 1998 Elsevier Science B.V. All rights reserved. PII: S0378-1127(98)00346-6
246
H. Alfredsson et al. / Forest Ecology and Management 112 (1998) 245±252
sistent scienti®c evidence for this. In Europe, forest soil deterioration was previously thought to be caused by the conifers themselves, but has later been ascribed to forest management practices and the continued removal of nutrients or the choice of poor sites to grow trees (Innes, 1993; Binkley, 1995). On the other hand, there is evidence that conifers can actually improve soil nutrient availability (Fisher, 1990; Davis and Lang, 1991; Belton et al., 1995; Davis, 1995; Condron et al., 1996). The nature of soil acidity and acidi®cation processes have been described by several research workers (Van Breemen et al., 1983; BerdeÂn et al., 1987; Yuan and Lavkulich, 1995; Binkley and HoÈgberg, 1997). Soil acidity measured as pH in a water suspension or in a weak salt solution gives an immediate picture of the situation and could be viewed as a empirical index of the amount of free H in solution (Binkley and Richter, 1987). This small pool of free H is in equilibrium with other less reactive `exchangeable' or `titratable' pools of H associated with soil mineral and organic constituents (McBride, 1994). Trees have both direct and indirect effects on soil which can affect soil acidity and organic matter. The major sources of soil acidity in pre-industrial forests were nutrient removal and dissociated carbonic acid and organic acids (Nilsson et al., 1982). The deposition of industrial pollutants containing strong mineral acids may contribute to increased forest soil acidity in some areas of the world, although the removal of nutrients by harvesting also plays an important role in increased forest soil acidity (Bredemeier et al., 1990; NordeÂn, 1994). In New Zealand inputs of strong acids derived from industry are very low (Holden and Clarkson, 1986), and the main sources of acidity are found within the forest ecosystem. Conifers may increase soil acidity through the production of organic acids from their mycorrhizal roots and uptake of nutrients (Sollins et al., 1981). Tree roots release H ions as they take up cations, although most of the cations taken up by trees are returned to soil in litter and root detritus (Attiwell and Adams, 1993). When trees are harvested and cations removed in wood products, the resulting effect on soil acidity may become permanent or persist for several decades (Nilsson et al., 1982; Johnson et al., 1991). Organic matter has a signi®cant in¯uence on soil chemical properties and processes, including cation
exchange and acidity (McBride, 1994). Furthermore, most of the total nitrogen and signi®cant proportions of the total phosphorus and sulphur in most topsoils are associated with organic constituents and, therefore, the cycling and availability of these nutrients is mainly determined by the nature and dynamics of soil organic matter (Kelley and Stephenson, 1996; Magid et al., 1996; Zhao et al., 1996). There is a need for research to be conducted under New Zealand conditions to determine the effect of land use change from grassland to coniferous plantation forest on the ability of the soil to sustain plant growth in the long-term. The objective of this research was to investigate changes in soil acidity and organic matter associated with the establishment of conifers on land developed under grassland in the absence of signi®cant anthropogenic atmospheric inputs. This involved comparing selected indices of acidity and concentrations of organic carbon and total nitrogen in pairs of adjacent soils under grassland and recently established conifers at two sites in the South Island of New Zealand. 2. Materials and methods 2.1. Site descriptions and soil sampling 2.1.1. Craigieburn This site was located at the Craigieburn Research Area, 100 km west of Christchurch (438100 S, 1718200 E). The altitude at the site was 870 m, the annual rainfall 1440 mm, and the mean monthly temperature was approximately 88C (Nordmeyer and Ledgard, 1993). The soil was classi®ed as a Tekoa stony loam (Orthic Brown Soil [New Zealand Soil Classi®cation], Dystrochrept [USDA Soil Taxonomy]) formed from greywacke colluvium. The original vegetation was mountain beech (Nothofagus solandri var cliffortioides) which was cleared and burnt more than 100 years ago (Nordmeyer and Ledgard, 1993). The area was used for extensive grazing until Douglas ®r was planted at approximately 2000 stems per ha in 1979; the stand age at time of sampling was 17 years and it is expected that the trees will be harvested at 50±60 years. The forest stand and adjacent grassland were situated on a south±east facing hillslope with 308 slope angle. No fertiliser had ever
H. Alfredsson et al. / Forest Ecology and Management 112 (1998) 245±252
been applied to the areas under forest or grassland. The stand had not been thinned at the time of sampling and the canopy was closed. Species present in the grassland area included tall tussock (Chionocloa macra), brown top (Agrostis capillaris), mountain daisy (Celmisia spectabilis) and native shrubs (Dracophyllum, Hebe, Cassinia and Discaria spp). A total of 24 bulked soil samples were obtained from 0±5 cm, 5±15 cm and 15±30 cm depth in 1996. There were no signs of understorey vegetation under Douglas ®r and the ground was covered by 3±5 cm of litter (mainly needles) which was removed before soil sampling. In the grassland area, soils were sampled along four transects commencing 10 m from the forest edge. Five soil cores (65 mm diameter) were taken at a distance 1 m between each other and bulked for each depth and transect. The transects were situated 5 m apart in the direction of the slope. Under the Douglas ®r stand, samples were taken on two transects 0.6 m on both sides of the tree rows. The tree rows were at the same slope position as the corresponding grassland transects. Sub-samples were taken at 1 m intervals along each 5 m transect. The samples were bulked for each tree row and depth. 2.1.2. Southland This site was located at Drummond, 32 km northwest of Invercargill (1688150 E, 468100 S) (O'Meara, 1995). It was situated on a west facing 358 terrace slope at 65 m above sea level. Mean annual rainfall at the site was approximately 850 mm and the mean annual temperature was 108C. The soil was classi®ed as an Aparima-Drummond silt loam (Pallic Soil [New Zealand Soil Classi®cation]; Humult [USDA Soil Taxonomy]) derived from greywacke alluvium and loess. The original tussock grassland (Chionochloa spp) vegetation was burned and replaced with pasture over 100 years ago. Extensive grazing had resulted in a steady decline in soil fertility, especially since very little fertiliser had been added due to the steep terrain. In 1980, radiata pine was established at a planting density of 2200 stems per ha, and the trees were progressively thinned to 450 stems per ha and pruned to 6 m, the ®nal operation being carried out in 1992. The mean tree diameter at breast height was 30 cm at the time of sampling; the stand age at time of sampling was 15 years and it is expected that the trees will be harvested at 25±30 years. A non-planted powerline
247
strip intersected the slope and was left with the original pasture. Species in the pasture were Yorkshire fog (Holcus lanatus), browntop (Agrostis capillaris), some white clover (Trifolium repens) and various weeds. The A horizon extended to 30 cm and roots were abundant to 20 cm under the pasture, although tree roots extended to more than 50 cm. There were no signs of understorey vegetation in the forest area and the forest ¯oor was covered by 2±3 cm of needles which were carefully removed before soil sampling. Soil samples from three depths (0±7.5 cm, 7.5±15 cm and 15±30 cm) were taken from pits excavated within three randomly located plots (1010 m) in the forest and adjacent grassland areas (O'Meara, 1995). 2.2. Soil analyses All soils were air-dried, crushed, and sieved (2 mm) after sampling. Soil pH was measured in 0.01 M CaCl2 (Blakemore et al., 1987). Exchangeable acidity and exchangeable aluminium (Al) were determined by double titration (Page et al., 1986) and exchangeable H was calculated as the difference between the two. Concentrations of exchangeable cations (Ca2, Mg2, K, Na, Mn2, Fe2) were determined according to the BaCl2-method described by Hendershot et al. (1993). The effective cation exchange capacity (ECEC) was calculated as the sum of all exchangeable cations. Total exchangeable cations (TEC) were de®ned as the sum of exchangeable Ca2, Mg2, K and Na and was also expressed as a percentage of ECEC (%TEC) (equivalent to total exchangeable bases [TEB] and base saturation [%BS] ± Blakemore et al., 1987). Concentrations of organic carbon (C) and total nitrogen (N) were determined by mass spectrometry. Soil data were statistically analysed using GENSTAT 5 for Windows (Lawes Agricultural Trust, 1993). Values for LSD at the 5% level between treatment pairs (grassland, forest) were determined for each site. 3. Results At the Craigieburn site, the only signi®cant difference in pH under Douglas ®r and grassland was at the 15±30 cm depth where pH was slightly lower under ®r, while exchangeable acidity and Al were higher under
248
H. Alfredsson et al. / Forest Ecology and Management 112 (1998) 245±252
®r at all depths (Table 1). Exchangeable Ca2, Mg2 and K levels were lower in soil under ®r at all depths except 0±5 cm for Ca2 and 15±30 cm for K (Table 1). Total exchangeable bases expressed as a percentage of ECEC (%TEC) were consistently and signi®cantly lower (16%±19%) under ®r compared with grassland (Table 1). Organic C and total N in the 0±5 cm soil were signi®cantly lower under ®r compared with grassland, while organic C was also slightly (but not signi®cantly) lower under ®r (5.4%) compared with grassland (6.6%) in the 5± 15 cm soil layer (Table 1). At the Southland site, differences between grassland and pine for most of the soil chemical properties measured were not statistically signi®cant (Table 2). Soil pH was lower under pine than grassland in the 0± 5 cm depth increment. Although there was a trend for exchangeable Ca2, Mg2 and K to be lower under pine, differences were not signi®cant for Ca2, and only signi®cant for Mg2 in the 0±7.5 cm and 7.5± 15 cm soil depths, and for K in the 7.5±15 cm and 15±30 cm depths. In contrast exchangeable Na tended to be higher under pine, although the difference was signi®cant only at the lowest depth (15±30 cm). While there was a trend for TEC and ECEC to be lower under pine, differences were only signi®cant for ECEC at the 7.5±15 cm and 15±30 cm depths (Table 2). Organic C and total N were slightly (but not signi®cantly) higher under pine compared with grassland in the 0±7.5 cm soil, but were signi®cantly lower in the 7.5±15 cm soil (Table 2). 4. Discussion Although there was no signi®cant difference in soil pH between grassland and Douglas ®r at Craigieburn in the upper layers and only a slight decrease under ®r in the lower layer, exchangeable Al and acidity increased under Douglas ®r in all soil depths sampled (Table 1). Thus, exchangeable acidity and Al provide more sensitive indicators of the development of acidity following afforestation than pH. Plant uptake was probably mainly responsible for the observed large decreases in levels of exchangeable cations (Table 1). Reductions in Bray-2 extractable (HCl/NH4F) K and Mg2 in topsoil (0±10 cm) under pine stands on similar soils in New Zealand high country were
reported by Davis and Lang (1991). However, under some older stands in lower rainfall areas cation availability in topsoils was found to be similar or greater than under grassland, possibly because of uptake from lower horizons and subsequent deposition at the surface in litterfall (Davis, 1998). In other studies levels of exchangeable Mg2 and Na were found to be greater under young pine stands compared with adjacent grassland in a coastal region of New Zealand, which was mainly attributed to increased interception of sea salts by the forest canopy (Giddens et al., 1997; Par®tt et al., 1997). The reduction in % TEC at the Craigieburn site occurred even though levels of organic C and total N, and thus ECEC, decreased in 0±5 cm soil under Douglas ®r compared with grassland. The % TEC would otherwise be expected not to decline under Douglas ®r if decreases in exchangeable cations were of a similar order of magnitude compared with decreases in ECEC. Thus, the soil has not been able to completely compensate for cation uptake by trees through weathering and, therefore, exchangeable acidity increased under trees compared with grassland at Craigieburn. However, despite these changes the level of soil acidity as measured by pH was maintained under the forest stand compared with grassland (Table 1), indicating that soil biological processes may not necessarily be negatively in¯uenced by afforestation. Concentrations of soil organic C and total N in topsoil (0±5 cm) were markedly lower under Douglas ®r compared with grassland at the Craigieburn site (Table 1). This is consistent with ®eld studies reported by Par®tt et al. (1997), while Davis (1995) also observed that radiata pine seedlings decreased levels of soil organic C and total N in a short-term glasshouse pot trial. The decrease in soil C and N may be attributed to changes in soil macro- and micro-¯ora associated with the root/rhizosphere systems of trees compared with grassland (Dighton and Boddy, 1988; Dighton, 1995). For example, ectomycorrhizal fungi associated with tree roots have been found to increase mineralisation of organic forms of N in soil via the production of extracellular hydrolase enzymes (e.g. proteinase) (Marschner and Dell, 1994; George and Marschner, 1996). On the other hand, signi®cant amounts of C and nutrients are added to soil via the roots (Vogt et al., 1986), and it has been estimated that roots and mycorrhiza are responsible for over 80% of
Fir Grassland LSDb
Fir Grassland LSDb
5±15
15±30
3.7 3.5 Ns
0.21 0.20 Ns
0.30 0.34 Ns
0.36 0.58 0.09
N (%)
18 17 Ns
18 19 Ns
19 20 Ns
C/N
0.31 0.57 0.09
0.82 1.56 0.47
4.40 5.62 Ns
Caa
0.14 0.23 0.03
0.31 0.56 0.16
0.99 1.71 0.53
Mga
0.19 0.30 Ns
0.27 0.55 0.14
0.51 0.79 0.20
Ka
0.002 0.002 Ns
0.005 0.005 Ns
0.004 0.006 Ns
Naa
0.045 0.024 0.008
0.057 0.044 Ns
0.122 0.102 Ns
Mna
0.016 0.024 0.008
0.030 0.023 Ns
0.035 0.025 0.004
Fea
4.75 3.79 Ns
6.88 6.66 Ns
8.83 9.62 Ns
ECECa
0.64 1.10 0.19
1.40 2.68 0.73
5.90 8.13 2.09
TECa
14 30 6
21 40 8
67 84 13
% TEC
4.36 4.51 0.12
4.33 4.42 Ns
4.75 4.70 Ns
pH (CaCl2)
Exchangeable cations/effective cation exchange capacity [ECEC]/total exchangeable cations [TEC]/exchangeable acidity [cmol()kgÿ1]. p<0.05.
b
a
7.0 11.9 2.6
Fir Grassland LSDb
0±5
5.4 6.6 Ns
C (%)
Depth (cm)
Table 1 Mean chemical analyses for soil sampled under Douglas fir and adjacent grassland at the Craigieburn site
3.71 2.45 0.85
4.96 3.63 0.81
2.48 1.16 0.98
Ala
0.33 0.19 0.13
0.43 0.29 0.11
0.30 0.20 Ns
Ha
4.04 2.64 0.91
5.39 3.92 0.86
2.78 1.36 1.08
Aciditya
H. Alfredsson et al. / Forest Ecology and Management 112 (1998) 245±252 249
Radiata Grassland LSDb
Radiata Grassland LSDb
7.5±15
15±30
2.2 2.0 Ns
0.16 0.15 Ns
0.16 0.22 0.03
0.31 0.28 Ns
N (%)
13 13 Ns
14 14 Ns
15 14 Ns
C/N
1.98 2.23 Ns
2.36 2.87 Ns
2.13 3.41 Ns
Caa
1.94 2.50 Ns
2.06 2.65 0.42
1.79 2.76 0.74
Mga
0.62 1.03 0.39
0.74 1.28 0.46
1.81 1.73 Ns
Ka
0.27 0.10 0.13
0.32 0.10 Ns
0.39 0.34 Ns
Naa
0.12 0.05 Ns
0.24 0.12 Ns
0.36 0.09 0.11
Mna
0.01 0.00 Ns
0.00 0.00 Ns
0.01 0.07 Ns
Fea
6.53 8.17 0.58
7.37 8.87 0.42
9.27 10.27 Ns
ECECa
4.81 5.86 Ns
5.48 6.90 1.28
6.12 8.24 Ns
TECa
73 72 Ns
75 78 Ns
66 80 Ns
% TEC
4.61 4.61 Ns
4.54 4.62 Ns
4.27 4.54 0.24
pH (CaCl2)
Exchangeable cations/effective cation exchange capacity [ECEC]/total exchangeable cations [TEC]/exchangeable acidity [cmol()kgÿ1]. p<0.05.
b
a
4.7 4.1 Ns
Radiata Grassland LSDb
0±7.5
2.2 3.0 0.6
C (%)
Depth (cm)
Table 2 Mean chemical analyses for soil sampled under radiata pine and adjacent grassland at the Southland site
1.42 2.02 Ns
1.42 1.60 Ns
2.37 1.58 Ns
Ala
0.17 0.23 Ns
0.20 0.24 Ns
0.42 0.29 Ns
Ha
1.59 2.25 Ns
1.62 1.84 Ns
2.79 1.87 Ns
Aciditya
250 H. Alfredsson et al. / Forest Ecology and Management 112 (1998) 245±252
H. Alfredsson et al. / Forest Ecology and Management 112 (1998) 245±252
the organic matter and N added to soil under Douglas ®r (Fogel and Hunt, 1983). There was some indication of differences in soil characteristics under radiata pine and adjacent grassland at the Southland site. Contrary to ®ndings at the Craigieburn site under Douglas ®r, amounts of organic C and total N in the mineral topsoil (0±7.5 cm) were slightly higher under radiata pine compared with grassland at Southland (Table 2). This may re¯ect differences in tree species and relative maturity at the different sites and the consequent effects on the amounts and fate of litterfall material. Biomass accumulation and turnover would have been substantially greater at the lower elevation radiata pine site than at the Douglas ®r site, and in addition thinning and pruning would have returned a large proportion of accumulated biomass and nutrients to the soil surface. It is also possible that decomposition and subsequent incorporation of forest litter into topsoil was greater at the Southland site compared with the Craigieburn site. Despite the relatively low soil pH (4.3±4.6) measured at the Southland site, a signi®cant number of earthworms were observed under radiata pine compared with the adjacent grassland (O'Meara, 1995). Thus accumulation and subsequent decomposition of litterfall may have reversed a possible earlier reduction in C and N levels under pine. The lower ECEC observed in the 7.5±15 cm soil under radiata pine compared with grassland was consistent with the corresponding lower level of organic C (Table 2). On the other hand, ECEC was signi®cantly lower under radiata pine compared with grassland in the 15±30 cm soil, despite the fact that soil pH and levels of organic C and total N were similar under radiata pine and grassland (Table 2). This may be attributed to changes in the chemical nature of the soil organic matter present under the different vegetation types at this depth, although the lower ECEC at this depth may also be due to enhanced weathering of clay minerals. The decline in pH under pine in the 0±7.5 cm soil is consistent with other studies which have shown pH of grassland soil to decline under afforestation (Davis and Lang, 1991; Hawke and O'Connor, 1993; Giddens et al., 1997; Par®tt et al., 1997). The absence of a pH decline under Douglas ®r in the upper horizons at Craigieburn, despite similar or greater reductions in TEC and increases in exchangeable acidity than under pine at the Southland site, may re¯ect the greater organic
251
matter content and consequent buffering capacity of the Craigieburn soil (Tables 1 and 2). The long-term impact of successive tree generations on soil fertility will depend on the amounts of nutrient exported in harvest in relation to the capacity of the soil regolith and atmospheric inputs to compensate for the losses and the meet needs of future tree generations (Binkley and HoÈgberg, 1997). Trees contains substantial amounts of nutrient that are locked up for a shorter or longer time while the forest litter also contains signi®cant quantities of nutrients, a proportion of which will be incorporated into the underlying soil in the long-term. Amounts of nutrient locked up in organic forms in forest systems are much higher than for grassland systems. For a more complete picture, it is necessary to follow the changes in nutrient pools and organic matter quantitatively, which was not possible in this study. When trees are harvested, it is important to determine the fate of cations and other nutrients present in the tree and litter, which in turn requires investigation over more than one forest rotation. Acknowledgements This study was jointly funded by the Swedish University of Agricultural Sciences and Lincoln University (New Zealand) and the authors would like to thank Leanne Hassall and Prof. Ian Cornforth (Lincoln University) and Alan Nordmeyer (New Zealand Forest Research Institute) for their assistance. References Attiwell, P.M., Adams, M.A., 1993. Nutrient cycling in forests. New Phyt. 124, 561±582. Belton, M.C., O'Connor, K.F., Robson, A.B., 1995. Phosphorus levels in topsoils under conifer plantations in Canterbury high country grasslands. New Zealand J. For. Sci. 25, 262±282. BerdeÂn, M., Nilsson, S.I., RoseÂn, K., Tyler, G., 1987. Soil acidification ± extent, causes and consequences. Report 3292. National Swedish Environment Protection Board, Solna, Sweden, 164 pp. Binkley, D., 1995. The influence of tree species on forest soils ± processes and patterns. In: Mead, D.J., Cornforth, I.S. (Eds.), Proceedings of the Trees and Soils Workshop. Lincoln University Press, New Zealand, pp. 1±34. Binkley, D., Richter, D., 1987. Nutrient cycles and H budgets of forest ecosystems. Adv. Ecol. Res. 6, 1±51.
252
H. Alfredsson et al. / Forest Ecology and Management 112 (1998) 245±252
Binkley, D., HoÈgberg, P., 1997. Does atmospheric deposition of nitrogen threaten Swedish forests? For. Ecol. Manage. 92, 119± 152. Blakemore, L.C., Searle, P.L., Daly, B.K., 1987. Methods for chemical analysis of soils. NZ Soil Bureau Scientific Report, 80. Lower Hutt, New Zealand, 103 pp. Bredemeier, M., Matzner, E., Ulrich, B., 1990. Internal and external proton load to forest soils in northern Germany. J. Environ. Qual. 19, 469±477. Condron, L.M., Davis, M.R., Newman, R.H., Cornforth, I.S., 1996. Influence of conifers on the forms of phosphorus in selected New Zealand grassland soils. Biol. Fertil. Soils 21, 37±42. Davis, M.R., 1995. Influence of radiata pine seedlings on chemical properties of some New Zealand montane soils. Plant Soil 176, 255±262. Davis, M.R., 1998. Soil impacts of afforestation in the high country. New Zealand Forestry 42, 34±38. Davis, M.R., Lang, M.H., 1991. Increased nutrient availability in topsoils under conifers in the South Island high country. New Zealand J. For. Sci. 21, 165±179. Dighton, J., 1995. Nutrient cycling in different terrestrial ecosystems in relation to fungi. Can. J. Bot. 73, 1349±1360. Dighton, J., Boddy, L., 1988. Role of fungi in nitrogen, phosphorus and sulphur cycling in temperate forest ecosystems. In: Boddy, L., Marchant, R., Read, D.J. (Eds.), Nitrogen, Phosphorus and Sulphur Utilization by Fungi. Cambridge University Press, Cambridge, pp. 269±298. Fisher, R.F., 1990. Amelioration of soils by trees. In: Gessel, S.P., Lacate, D.S., Weetman, G.F., Powers, R.F. (Eds.), 7th North American Forest Soils Conference. University of British Columbia, pp. 290±300. Fogel, R., Hunt, G., 1983. Contribution of mycorrhizae and soil fungi to nutrient cycling in a Douglas fir ecosystem. Can. J. For. Res. 13, 219±232. George, E., Marschner, H., 1996. Nutrient and water uptake by roots of forest trees. Z. Pflanz. Bodenk. 159, 11±21. Giddens, K.M., Parfitt, R.L., Percival, H.J., 1997. Comparison of some soil properties under Pinus radiata and improved pasture. New Zealand J. Agric. Res. 40, 409±416. Glass, B.P., 1997. A survey of afforestation intentions in New Zealand between 1996 and 2010. New Zealand Forestry 41, 34±37. Hawke, M.F., O'Connor, M.B., 1993. Soil pH and nutrient levels at Tikitere agroforestry research area. New Zealand J. For. Sci. 23, 40±48. Hendershot, W.H., Lalnade, H., Duquette, M., 1993. In: Carter, M.R. (Ed.), Soil Sampling and Methods of Analysis. Lewis Publishers, Boca Raton, Florida, USA, pp. 167±176. Holden, R., Clarkson, T.S., 1986. Acid rain: a New Zealand viewpoint. J. R. Soc. New Zealand 1, 1±15. Innes, J.L., 1993. Forest Health: Its Assessment and Status. CAB International, Wallingford, UK, 677 pp.
Johnson, D.W., Cresser, M.S., Nilsson, S.I., Turner, J., Ulrich, B., Binkley, D., Cole, D.W., 1991. Soil changes in forest ecosystems: evidence for and probable causes. Proc. R. Soc. Edinburgh 97B, 81±116. Kelley, K.R., Stephenson, F.J., 1996. Organic forms of N in soil. In: Piccolo, A. (Ed.), Humic Substances in Terrestrial Ecosystems. Elsevier, Amsterdam, pp. 407±427. McBride, M., 1994. Environmental Chemistry of Soils. Oxford University Press, New York, 406 pp. Magid, J., Tiessen, H., Condron, L.M., 1996. Dynamics of organic phosphorus in soils under natural and agricultural ecosystems. In: Piccolo, A. (Ed.), Humic Substances in Terrestrial Ecosystems. Elsevier, Amsterdam, pp. 429±466. Marschner, H., Dell, B., 1994. Nutrient uptake in mycorrhizal symbiosis. Plant Soil 159, 89±102. Nilsson, S.I., Miller, H.D., Miller, J.D., 1982. Forest growth as a possible cause of soil and water acidification: an examination of the concepts. Oikos 39, 40±49. NordeÂn, U., 1994. Influence of tree species on acidification and mineral pools in deciduous forest soils of south Sweden. Water Air Soil Pollut. 76, 363±381. Nordmeyer, A.H., Ledgard, N.J., 1993. Above-ground biomass, productivity, and nutrients in 15-year-old stands of Ponderosa pine, Corsican pine, Douglas fir and European larch in the Craigieburn range. New Zealand Stud. For. Suec. 191, 75±85. O'Meara, D.M., 1995. A comparison of soil fertility under Pinus radiata and pasture in Southland. Research Dissertation, Bachelor of Forestry Science, University of Canterbury, Christchurch, New Zealand, 48 pp. Page, A.L., Miller, R.H., Keeney, D.R., 1986. Methods of Soil Analysis, Chemical and Microbiological Properties, 2nd ed. American Society of Agronomy and Soil Science Society of America, Madison, Wisconsin, 1159 pp. Parfitt, R.L., Percival, H.J., Dahlgren, R.A., Hill, F., 1997. Soil and solution chemistry under pasture and radiata pine in New Zealand. Plant Soil 191, 279±290. Sollins, P., Sromack, K., Jr., Fogel, R., Li, Y.C., 1981. Role of lowmolecular-weight organic acids in the inorganic nutrition of fungi and higher plants. In: Wicklow, D.T., Carroll, G.C. (Eds.), The Fungal Community. Marcel Decker, New York, pp. 607± 619. Van Breemen, N., Mulder, J., Driscoll, C.T., 1983. Acidification and alcalinization of soils. Plant Soil 75, 283±308. Vogt, K.A., Grier, C.C., Vogt, D.J., 1986. Production, turnover and nutrient dynamics of above- and belowground detritus of world forests. Adv. Ecol. Res. 15, 303±377. Yuan, G., Lavkulich, L.M., 1995. Acid-buffering capacity of factors of forest soils. Comm. Soil Sci. Plant Anal. 26, 51±60. Zhao, F.J., Wu, J., McGrath, S.P., 1996. Soil organic sulfur and its turnover. In: Piccolo, A. (Ed.), Humic Substances in Terrestrial Ecosystems. Elsevier, Amsterdam, pp. 467±506.