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Effect of radiata pine on soil chemical characteristics
Forest Ecology and Management, 11 (1985) 257--270 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
257
EFFECT OF RADIATA PINE ON SOIL CHEMICAL CHARACTERISTICS
JOHN TURNER and JOSEPH KELLY Forestry Commission of New South Wales, P.O. Box 100, Beecroft, N.S.W. 2119 (Australia) (Accepted 1 February 1985)
ABSTRACT
Turner, J. and Kelly, J., 1985. Effect of radiata pine on soil chemical characteristics. For. Ecol. Manage., 11: 257--270. Soil nutrient contents and distributions beneath planted mature pine (P. radiata) have been compared with those beneath adjacent native eucalypt at two sites (Wee Jasper and Billapaloola) in the Tumut District, N.S.W. The soil nutrients studied included total nitrogen, phosphorus, potassium, calcium, magnesium and sodium, together with exchangeable aluminium, calcium, magnesium, potassium and sodium. Planting of pine resulted in a redistribution of nutrients within the ecosystem. At Wee Jasper, nutients accumulated in the pine- stand and it appeared that this had occurred from deeper rooting in the soil profile, while at Billapaloola, nutrients were removed to a greater degree from the soil surface. Changes in total quantities of nutrients were small and there was no evidence of a potential productivity decline in the subsequent rotation from these changes.
INTRODUCTION Pinus radiata D. D o n p l a n t a t i o n s in A u s t r a l i a n o w e x c e e d 6 0 0 0 0 0 h a w i t h a p l a n t i n g r a t e o f a p p r o x i m a t e l y 20 0 0 0 h a y - ' . T h e s e p l a n t a t i o n s are generally e f f i c i e n t w o o d p r o d u c e r s w i t h p e r i o d i c a n n u a l i n c r e m e n t (p.a.i.) g r o w t h rates e x c e e d i n g 2 5 - - 3 0 m 3 h a - ' y - L H o w e v e r , R o u t l e y a n d R o u t l e y ( 1 9 7 5 ) a n d o t h e r s h a v e a r g u e d t h a t c o n i f e r o u s p l a n t a t i o n s in Australia r e d u c e soil f e r t i l i t y a n d c o n s e q u e n t p r o d u c t i v i t y . T h e c o n c e p t s f o r r e d u c e d p r o d u c t i v i t y c o m e f r o m w h a t was c o n s i d e r e d o r a s s u m e d t o b e a parallel s i t u a t i o n in E u r o p e , w h e r e r e p l a c i n g b r o a d l e a v e d species w i t h a c o n i f e r o u s species {spruce) was t h e c a u s e o f p o d s o l i z e d a n d i n f e r t i l e soils. H o w e v e r , t h e m o s t e x t r e m e cases o c c u r r e d o n v e r y p o o r sands ( D a s m a n n , 1972). E a r l y r e s e a r c h w o r k in A u s t r a l i a t e n d e d t o s u p p o r t a d e c l i n i n g yield c o n c e p t ( H a m i l t o n , 1 9 6 5 ) b y i n d i c a t i n g decreases in organic m a t t e r w h e n e u c a l y p t w o o d l a n d s w e r e c o n v e r t e d t o P. radiata p l a n t a t i o n s . T h e decline in s e c o n d r o t a t i o n p r o d u c t i v i t y o f pines in S o u t h A u s t r a l i a ( K e e v e s , 1 9 6 6 ) w a s c o n s i d e r e d as f u r t h e r c o n f i r m a t i o n o f this view ( R o u t l e y a n d Routley, 1975).
0378-1127]85/$03.30
O 1985 Elsevier Science Publishers B.V.
258 Although these observations have been accepted b y m a n y as evidence for soil fertility changes and a declining yield under pine, and thus as an argument against the planting of conifers, the case is n o t that definitive. Soil formation theory and experimental evidence (Jenny, 1980) established that the effect of a tree species on soil chemical properties is a function of a series of factors including the nutrient requirements of the particular species, its nutrient cycling characteristics, soil type, and properties of leachates from bark, foliage, roots and litter, as well as the length of time the species has affected the soil. S o m e soil properties m a y change when species are altered, but the estimation of the form and magnitude of change is more difficult. It is even more difficult to predict subsequent changes in productivity. Reliable results as to the effect of a particular species on soil properties and subseqeunt properties can only be obtained from well designed experiments. Soil and productivity changes associated with different species can be studied under field conditions using natural vegetation distribution or b y designed changes. An example o f the first t y p e of m e t h o d is the effect of red alder in Northwestern America (Tarrant and Miller, 1963; Franklin et al., 1967). Use of this m e t h o d assumes that other soil forming factors, such as parent material, are constant. The alternative m e t h o d is to use situations where different species have been planted on the same original soil, or to establish different species, and follow soil properties over a sequence of years (Alban, 1982). In b o t h cases species effects must be separated from any differences which may arise from management practices or from variations in initial soil or parent materials. The effects of management practices such as land clearing, burning, and compaction may be difficult to separate from species effect. This latter m e t h o d has been widely used because of the shorter time required to obtain results, b u t sometimes w i t h o u t sufficient control of variables. For instance, in the early work of Hamilton (1965), a series of six paired dry sclerophyll sites (pine and eucalypt) in the A.C.T. were studied, and declines were found in surface soil organic matter and nitrogen under P. radiata (five o u t of six sites). However, the results for phosphorus and cations suggested that soil boundaries were probably crossed in at least two cases. At site 5, the soil total phosphorus under the pine was higher than that under the eucalypt b y a very large a m o u n t (498 p p m and 294 p p m respectively) and this was the reverse of the general trend. Hopmans et al. (1977) intensively sampled and compared pine (P. radiata) and eucalypt sites on uniformly nutritionally p o o r sandy soils in Victoria. Although all nutrient levels were low, the surface soils under pine were significantly higher in nitrogen, magnesium and potassium. The differences were small and were also predominantly related to organic matter changes. Turner and Kelly (1977) compared surface and deeper horizon soils of a Douglas-fir plantation (Pseudotsuga menziesii Mirb. Franco) which had never been thinned (thus reducing potential management effects on soft)
259 with those of adjacent natural eucalypts. Both these studies t o o k into account the original clearing effects. While the mineral soil organic matter and nitrogen had declined, nutrients had accumulated in the litter and A-horizon, and when elements in the tree biomass were taken into a c c o u n t (Turner, 1980) there were no changes in total nutrients. There were redistributions and changes of form of nutrients within the Douglas-fir system compared with the eucalypt system, but no nutrient losses from the system. Because of the importance of pine to Australian forestry production and the need to understand more fully the possible changes in soil properties and eventual productivity under pine, a long-term research programme has been established in New South Wales. The programme uses the m e t h o d o l o g y which compares soil properties under paired (on similar soils and parent materials) pine and natural eucalypts stands. This paper represents the initial report and presents results from a comparison of pine and eucalyptus on a moderately productive site near Tumut. SITE AND METHODS Two study sites were selected within Buccleuch S.F., these being in the Wee Jasper section and in the Billapaloola section. The selected sample areas were in relatively old radiata pine stands (40 years plus) adjacent to naturally-occurring eucalypt species. There was no apparent geological change, as assessed from rock samples taken at each sampling point, across the boundary from pine to eucalypt at time of sampling, and the t o p o g r a p h y was uniform. General features of the study areas have been summarized in Table I. Within each area, pairs of plots were selected, each pair being at least 50 m apart and consisting of one location in the pine stand and another in the eucalypt stand in a similar micro-topographical situation. The factors considered were slope, position on slope, and relative degree of concavity or convexity. Seven pairs of plots were selected at Wee Jasper and eight at Billapaloola. The plot size was 0.1 ha. The pine areas had originally been cleared of eucalypts and broadcast burned prior to planting, and hence any land preparation effects in the area were across the whole area, rather than being concentrated in features such as windrows. Disturbances have occurred in pine areas as a result of the selection thinnings carried o u t a b o u t every five years after age fifteen. The Wee Jasper eucalypt area has been maintained as rough grazing land with frequent burning, while the Billapaloola eucalypt site has n o t been grazed or burned. No definite ages were known for the eucalypts b u t t h e y were probably uneven-aged stands with the larger trees older than the pine. At each plot, soil was sampled from the 0--5 cm and 5--10 cm depth, each sample being a bulking of 10 subsamples. In addition bulk density samples were taken at b o t h depths using a standard round corer with fitted brass rings, giving a soil sample 10 cm in diameter and 4 cm deep. A n y compression occurring was assumed to occur across all sites. These t w o
260 TABLE 1 General characteristics of stands in the Wee Jasper and Billapaloola sections of Buccleuch S.F.
Physical aspects Elevation (m) Geology Soil Topograhpy Aspect Eucalypt Stand Species
Dominant height (m) History Pine Stand Planted Compartment Stem ha -1 (with regrowth) Basal area (m 2 ha -I ) Natural regeneration Mean dominant height (m)
Wee Jasper
Billapaloola
1000--1100 F i n e - - m e d i u m grained granodiorite Red earth Gently sloping Northeast
820 Medium grained granodiorite and quartz p o r p h o r y Red podzolic Gentle depression West
E. dalryrnpleana E. radiate E. macrorhyncha 27 Burnt for grazing
E. radiata E. dalrympleana E. bridgesiana 25 Unburnt
1931 27 240 37 Medium 42
1932 35 200 33 Dense 42
depths were selected because previous studies have shown t h e m to be the most sensitive to change, having the highest fine r o o t density and inputs from the forest floor (Turner and Kelly, 1977). The depths sampled did n o t cross a soil horizon boundary. Soil pits were dug to assess possible differences at depth, such as the crossing o f a soil boundary. Six forest floor samples per plot were taken using a 0.1-m 2 steel ring and oven dried at 70°C before sorting. Those from the Wee Jasper site were sorted into the c o m p o n e n t s of leaves {needles), stick, bark, fine material and understorey, b u t only the total sample was analysed at Billapaloola. Bark was underestimated in the eucalypts because of the bark 'halo' effect at the base of some trees {Turner and Lambert, 1983). Fine material was undefinable in origin. Samples were analysed individually. Soil samples were air dried and sieved to pass a 2-mm sieve and the p r o p o r t i o n of stone was estimated. The samples were analysed for pH, organic matter, nitrogen, phosphorus, and exchangeable calcium, magnesium, potassium, sodium and aluminium using procedures according to Lambert {1976). Total soft cations were digested b y the m e t h o d of Bernas {1968) and estimated b y atomic absorption s p e c t r o p h o t o m e t r y . Forest floor samples were oven dried at
261
70°C, sorted, ground to pass an approximately 2-mm mesh, and analysed for phosphorus, calcium, magnesium, potassium, sodium and nitrogen (Lambert, 1976). Statistical analyses were carried o u t as in Sokal and R o h l f (1969). Estimates of nutrients removed in thinning pine were made b y using known estimates of timber volume removed from the age class and using mean P. radiata w o o d and bark nutrient concentration from the area (Lambert, 1976). First thinning records were incomplete, so the removal estimates were considered to be underestimates. RESULTS
The soil chemical characteristics under eucalypts for b o t h the Wee Jasper and the Billapaloola area (Table 2) were fairly similar. Although the average analyses for total exchangeable bases and phosphorus (Table 3) were slightly higher at Wee Jasper than at Billapaloola, the differences were n o t statistically significant. Compared with other pine forest softs in N e w South Wales, however, these sites are relatively high in nutrient reserves, particularly phosphorus, calcium and magnesium (Humphreys, 1974; Kelly and Turner, 1978; Turner, 1981). Wee Jasper soils The 0--5 cm soil depth under pine at the Wee Jasper site was significantly higher in organic matter than that under the eucalypt stand. Decreased bulk density and increased exchangeable cations also occurred, and, although n o t statistically significant, the differences were probably related to the organic matter changes. Estimates of exchangeable cations were assumed to be available quantities, whereas concentrations of total cations provided estimates of nutrient reserves. While less than 10% o f magnesium and potassium were in exchangeable forms, almost 50% of the total calcium was in this form. There was a significant increase in soil total calcium under pine at both the 0--5 cm and 5--10 cm depths and a decrease in total potassium at the surface (Table 3). The P. radiata soil at the 5--10 cm depth was significantly higher in exchangeable calcium and total exchangeable bases than the eucalypt soil. With the exception of pH, potassium and aluminium, the 5--10 cm depth showed trends with species similar to those in the surface horizon. The nutrient mass per unit area of forest floor and soil, together with statistical analyses, are shown in Table 4. There was a greater forest floor mass under the eucalypt stand, largely resulting from the higher bark and stick mass, but there was little difference b e t w e e n the pine and eucalypt litter nutrients, except for calcium and magnesium contents. When the total soil nutrients (0--10 cm) were included with the litter nutrient contents, neither nitrogen nor phosphorus was significantly different. However, under pine there was an increase in calcium and a decrease in potassium and magnesium, compared with eucalypt.
0.88 0.85 n.s.
5--10 cm depth Eucalypt Pine S.D.B.M.
0.94 0.88 n.s.
5--10 cm depth Eucalypt Pine S.D.B.M. 5.29 5.31 n.s.
8.51 7.73 n.s.
6.06 7.67 1.6"
2.1"*
8.76 12.74
27 43 11
n.s.
n.s.
0.11 0.07 0.03
28 37
27 29 n.s.
25 35 8"*
C/N
0.17 0.12
0.13 0.15 n.s.
0.20 0.21 n.s.
N (%)
5.52 5.50 n.s.
n.s.
5.53 5.29
5.30 5.34 n.s.
5.33 5.06 n.s.
pH H20
4.02 4.63 n.s.
n.s.
6.72 5.15
3.92 6.57 2.70**
6.55 8.28 n.s.
Ca
1.56 1.40 n.s.
n.s.
2.00 1.80
2.04 1.95 n.s.
2.66 2.39 n.s.
Mg
0.70 0.55 n.s.
n.s.
0.81 0.71
0.71 0.66 n.s.
1.28 1.26 n.s.
K
Exchangeable (meq. %)
0.07 0.07 n.s.
n.s.
0.08 0.14
0.58 0.52 n.s.
0.05 0.08 n.s.
Na
6.36 6.64 n.s.
n.s.
9.61 7.80
7.25 9.70 2.80*
10.50 12.01 n.s.
T.E.B. a
aT.E.B. = total exchangeable bases (excluding aluminium). bS.D.B.M. = significantdifference between means; *, 5 % level; ** 1 % level;n.s. = not significant.
0.90 0.85 n.s.
0--5 c m d e p t h Eucalypt Pine S.D.M.B.
Billapaloola
0.81 0.76 n.s.
Bulk Organic density matter (gcc -I) (%)
0--5 c m d e p t h Eucalypt Pine S.D.B.M. b
Wee Jasper
Site
M e a n results o f soil analyses u n d e r P. radiata a n d Eucalyptus spp. at Wee J a s p e r a n d B i l a p a l o o l a
TABLE 2
0.34 0.30 n.s.
n.s.
0.36 0.52
0.63 0.56 n.s.
0.34 0.46 n.s.
Al
20.7 21.2 n.s.
n.s.
25.9 25.5
22.8 28.1 3.5*
26.6 32.8 n.s.
32 30 n.s.
n.s.
37 31
30 32 n.s.
35 36 n.s.
(%)
C.E.C. Base (meq.%) saturation
b~ O~ b~
263 TABLE 3 Soil total p h o s p h o r u s and t o t a l a n d e x c h a n g e a b l e c a t i o n q u a n t i t i e s u n d e r P. radiata and Eucalyptus spp. at Wee J a s p e r a n d Billapaloola Site
To~lP (ppm)
To~lcatio~
(me%)
E x c h a n g e a b l e / T o t a l (%)
Ca
Mg
K
Na
Ca
Mg
K
Na
Wee Jasper 0--5 cm d e p t h Eucalypt Pine S.D.B.M. a
385 415 n.s.
13.6 18.1 3.2**
35.1 33.1 n.s.
17.4 15.1 2.1"
6.1 6.6 n.s.
48.1 45.7 2.5*
7.6 7.2 n.s.
7.4 8.3 2.0*
0.8 1.2 n.s.
5--10 c m d e p t h Eucalypt Pine S.D.B.M.
325 430 n.s.
9.9 13.1 2.5*
36.6 35.0 n.s.
18.4 17.2 n.s.
5.9 7.5 n.s.
39.6 50.2 6.2*
5.6 5.6 n.s.
3.9 3.8 n.s.
9.8 6.9 n.s.
0--5 c m d e p t h Eucalypt Pine S.D.B.M.
270 310 n.s.
17.7 14.5 2.1"
19.6 18.1 n.s.
21.3 19.6 n.s.
5.1 3.8 n.s.
38.0 35.5 n.s.
10.2 9.9 n.s.
3.8 3.6 n.s.
1.6 3.7 n.s.
5--10 c m d e p t h Eucalypt Pine S.D.B.M.
230 270 n.s.
11.7 10.3 n.s.
19.9 18.3 n.s,
21.4 19.7 n.s.
4.9 4.0 n.s.
34.4 45.0 n.s,
7.8 7.7 n.s.
3.3 2.8 n.s.
1.4 1.8 n.s.
Billapaloo la
aS.D.B.M. = significant d i f f e r e n c e b e t w e e n m e a n s ; *, 5% level, ** 1% level; n.s. = n o t significant.
The quantities of nutrients in the litter and surface soil do n o t differ significantly between the pine and eucalypt stands at Wee Jasper. When the quantity of nitrogen already removed in thinning from the pine site is taken into account, there is an excess of 400 kg N ha -1 in the pine site. The existing standing crop was n o t taken into account, which leads to an underestimate. The quantity of nitrogen accumulated in the pine stand amounts to between 8 and 9 kg ha -1 y-l, which supports the findings of Richards (1962). This accumulation may be either from deeper d o w n the soil profile or from fixation. An alternative explanation is that there have been losses from the eucalypt stand, b u t the process by which these occurred is n o t immediately obvious. The other nutrients in the pine stand also appear to have been drawn from further d o w n the profile. Phosphorus quantities (kg ha -1) tended to be higher under the pine than under the eucalypt for both areas. The pine litter had a higher phosphorus concentration than the eucalypt litter. Decomposition of organic matter and accumulation in the mineral soil gave a higher organic phosphorus con-
--
--
0-10 c m
T o t a l soil +forest floor
1396
1272
740
124.3
15.3 10.8 15.8 67.4 15.0
310
298
155
11.6
1.2 1.0 1.0 7.0 1.3
(453)
5986
2030 (150) 5953 (420)
32.5
4.5 3.8 4.1 17.0 3.0
2206 (1127)
1080 (520) 1939 (860)
267
58.4 42.4 32.2 131.4 2.0
Ca
3574 (261)
1579 (120) 3543 (230)
30.8
5.6 4.1 3.5 15.3 2.4
Mg
--
--
--
1 4 1 5 n~"
1299
778
116.4
326 ~
314
154
11.6
1.0
10.9
21 150
9.4
89.5
2 120 10 4 1 0 1 830
1.2
16.0
P
6 790
N
aO.M. ffiorganic matter. **, * = 1 % and 5 % significance level between eucalypt and pine; n.s. = not significant.
--
Soil 0-5 c m
26 8 6 0
Total
910 580 850 170 350
7 3 2 12 2
K
O.M.
P
O.M. a
N
Pine
Eucalypt
Forest Floor Stick Bark Leaf or n e e d l e Fine material Understorey
Component
2.5
5615" (344)
2161 (180) 5582 (310)
34.1
1.1
30.5
K
2551"* (1280)**
1335 (610) 2431 (1160)
120
3.8
99.3
15.8
Ca
3194" (210)*
1389 (100) 3175 (200)
18.9
0.3
16.3
2.3
Mg
Biomass a n d n u t r i e n t c o n t e n t (in kg h a -~) o f t h e f o r e s t f l o o r t o g e t h e r w i t h t o t a l n u t r i e n t s c o n t a i n e d in t h e t o p 10 c m o f soil in t h e pine and e u c a l y p t stands at Wee Jasper. Soil e x c h a n g e a b l e c a t i o n s are i n p a r e n t h e s e s
TABLE 4
O~ ht~
265 centration in the 0--5 cm layer. Thinning the pine stand removed 6 kg P ha -1 (Table 5), but this small q u a n t i t y would n o t have affected the above estimates. It was estimated that thinning the pine would have removed approximately 84, 147 and 25 kg ha -I of potassium, calcium and magnesium respectively (Table 5), and therefore differences of this order could be expected between the pine and eucalypt sites. Based on surface soils and litter, eucalypts exceeded pine by 370 and 380 kg ha -1 for potassium and magnesium respectively, but pine was 345 kg ha -1 higher in calcium. Obviously these differences cannot be explained by differences in thinning removals (Table 5) and there was no evidence for extensive leaching losses. When soil exchangeable potassium and magnesium were considered (Table 4), levels in eucalypt were 109 and 42 kg ha -1 higher than in pine for potassium and magnesium respectively. These differences may be the result of thinning losses, and the total differences may be an artifact because of higher variability in total estimates. Calcium is apparently more weatherable and mobile in these soils, as indicated by the high ratio of exchangeable to total calcium, and it would appear to be accumulated from deeper in the profile in a comparable manner to phosphorus. TABLE 5 Average removal of nutrients (in kg ha -j ) in thinning for Wee Jasper and Billapaloola. Biomass removals estimated from known quantities of thinnings removed and the specific gravity of the wood and bark Component
Biomass (kg ha -j)
N
P
K
Ca
Mg
Bark Wood Total
17 000 97 000 114 000
44 337 381
1.7 4.3 6.0
25 59 84
62 85 147
19 25
6
Billapaloola soils At Billapaloola, there were no statistically significant differences in nutrient concentrations at the 0--5 cm depth, although trends indicated lower organic matter, nitrogen and cations, and higher phosphorus under P. radiata. The nitrogen concentration at the 5--10 cm depth was significantly lower under P. radiata compared with the eucalypt soil, and there were differences in the trends of the exchangeable cations. The major change in total cations at Billapaloola was a decrease in calcium under pine. The total concentrations of the other cations were not significantly different between the two forest types. The litter and soil data from Billapaloola (Table 6) showed a decrease in nitrogen under the pine compared with the eucalypt, but no significant
n.s.
360**
n.s.
231
220
120
11
230** (50)**
7351 (291)
3684 (140) 7320 (260)
31
655* (420)*
2873 (1207)
1595 (606) 2696 (960)
247
Ca
n.s. n.s.
2132 (218)
1078 (110) 2104 (190)
28
Mg
24 000
--
--
24 000
961
812
508
149
N
14
241
227
118
P
39
6945 (239)
3692 (110) 6906 (200)
K
1950 (1021)
1235 (430) 1777 (847)
174
Ca
1741 (174)
808 (80) 1717 (150)
24
Mg
aO.M. = organic matter. bS.D.B.M. = significant difference between means of eucalyt and pine; *, 5% level; **, 1% level; n.s. = not significant.
S.D.B.M. b
1374
Total Soil and Forest Floor
734
127
1247
26 800
26 800
K
O.M.
P
O.M. a
N
Pine
Eucalypt
0--10 cm
Soil 0--5 cm
Forest Floor
Component
Biomass and nutrient content (in kg ha -~) of the forest floor together with total nutrients contained in the top 10 cm of soil in the pine and eucalypt stands at Billapaloola. Figures in parentheses are exchangeable quantities
TABLE 6
O~
b3
267 change in phosphorus. The total and exchangeable cations decreased under pine, but this was not significant for magnesium. These declines occurred in the litter and the 0--5 cm and 5--10 cm depths, indicating a decrease in all estimated pools. When nutrients were expressed per unit area (kg ha -1) (Tables 4 and 6), some differences were observed. In the case of nitrogen at Billapaloola, there was less nitrogen in the combined litter and surface soil of the pine forest compared with that of the eucalypt. When the concentration of nitrogen in the soil profile was assessed (Fig. 1), there appeared to be a uniform distribution of nitrogen under pine, while it was concentrated near the surface under eucalypt. Unfortunately, samples from only one pair of soil pits were analysed in detail and no statistical analysis was possible. At Billapaloola under pine there have been decreases in nitrogen, potassium, calcium and magnesium of 415, 406, 923, and 391 kg ha-' respectively, using total nutrients as the estimate. In the case of exchangeable cations, the decreases were 52, 186 and 44 kg ha-' for potassium, calcium and magnesium respectively, and these are approximately equivalent to nutrient removals in logging. Phosphorus levels were higher under pine, but not significantly so. Therefore, it may be concluded t h a t the changes on this site are a result of tree uptake and that this is reflected in exchangeable and total cation estimates. SOIL NITROGENI%) 0.05 0.1 0.15 0.2 i
i
l
SOIL NITROGEN(%) 0.05 0.1 0.15 0.2
i
i
i
i
|
0 pine.,
pin~,/~ /eucalypf
10,
7
10
E
i 20,
20
o 30,
3O
0
40 5C
if'
I
50.
BILLAPALOOLA
WEE JASPER
Fig. 1. Mean nitrogen concentrations for the profiles of the pine and eucalypt soils at Billapaloola and Wee Jasper.
DISCUSSION
The role o f i m p o r t a n t but study the soils been compared
vegetation in soil-forming processes is acknowledged to be its effects are often difficult to quantify. In the present beneath mature, managed, planted radiata pine stands have with softs beneath adjacent natural eucalypt stands in which
268 disturbances were only due to g a z i n g and fire. T h a t is, assessment of the net changes was basically based on the species alteration from eucalypt to pine and the subsequent effect of pine management, such as thinning. At the Wee Jasper site there has been a general t e n d e n c y towards increased concentrations of nutrients at 0--5 cm soil d e p t h under the P. radiata and there has been an overall upward redistribution of nutrients within the soil profile. If nutrient removals as a result of thinning are also taken into account, nutrients must have been recycled f r o m deeper than 10 cm in the profile to account for the differences. At Billapaloola there has been a decrease in several of the nutrients in the soil surface, but when thinning losses were considered, equal quantities of nutrients occurred on both the pine and eucalypt sites. At the Billapaloola s t u d y site, the difference between the pine and the eucalypt was equivalent to the thinning loss, as may be expected. The stand appears to have been growing p r e d o m i n a n t l y in the surface soil with little drain on nutrients further in the profile. It is hypothesised t h a t the Wee Jasper pines accumulated nutrients on the surface from deeper in the profile and that the trees have more fully utilized the depth of soil than was the case at Billapaloola. A combination of several factors m a y have affected the nutritional status of these soils. It is possible that regular fires in the eucalypt stand at Wee Jasper have played an important part and t h a t over an extended period (at least 40 years in this case) n u t r i e n t losses have occurred, such as volatilization of nitrogen. On the other hand, the fire protection system practised at Billapaloola in the eucalypts and' in the management o f the pine stands has maintained the nutrient capital, and any losses were those predictable as a result of wood removal from the site. With native eucalypts as a base comparison, both sites studied have shown that pine planting has affected n u t r i e n t distributions. The quantities redistributed were equivalent to those accumulated in a typical standing crop of pine of this age and quality. The sites differ in that pine at Wee Jasper, growing on a Red Earth, appears to have more thoroughly utilized the deeper soil profile, while at Billapaloola, on a Red Podzolic, there has been less volatilization deeper within the profile, thus leading to an apparent nutrient deficit in the soil. The total soil cations do n o t give a reasonable indication of change, but the proportion of exchangeable to total cations provides an indicator of nutrient reserves. Thus, at Wee Jasper 40% or more of the calcium is in exchangeable form and at BiUapaloola this is more than 30% {Table 3). Comparable estimates for magnesium and potassium were less than 10%, indicating that calcium is the most vulnerable cation for nutrient depletion. Page {1968) assessed observable soil properties such as horizon depth and litter thickness under three coniferous species in England. The species were neither compared with each other nor with another species as a base line, rather changes in relation to stand development were ascribed when
269
the parameter used for assessing stand development was stand current top height rather than age. By this means the a u t h o r overcame the problem of variation in stand quality. M a x i m u m top stand height was about 37 m and most changes in terms of horizon and litter depth, moisture content, pH and bulk density occurred in the 16--25 m top height range, after which stage there was a gradual equilibration reverting to levels f o u n d in the original situation. This equilibration was considered to be due to thinning, and many of the changes observed could be related to changes in litter depth. If the effect found by Page (1968) were to apply under Australian conditions, significant changes chould be apparent in a radiata pine stand at 10--20 years of age, the time of rapid stand development and heavy drain on nutrient reserves. After this stage, thinning and consequent return of nutrients and opening of the stand should tend to return the soil to near pre-planting conditions. McIntosh (1980) compared 45-year-old P. radiata to native L e p t o s p e r m u m in New Zealand in a similar way to the present study. The soils were derived from ash and were more permeable. The lower nitrogen, organic matter, phosphorus and cations under P. radiata were attributed to nutrient uptake, mineralization and different organic acids. This study was carried o u t towards the end of a P. radiata r o t a t i o n and included the effects of management (for example thinning) rather than pine planting per se. A larger effect may have occurred in the 10--20 year age period, when the greatest drain on soil reserves would occur. The soils have n o t been significantly reduced in nutrients and when the nutrient content of slash from clearcutting is included, the nutrient status of the soil should be equivalent to that at the c o m m e n c e m e n t of the first rotation. Therefore one would n o t expect a productivity reduction in the n e x t rotation.
REFERENCES
Alban, D.H., 1982. Effects of nutrient accumulation by aspen, spruce and pine on soil properties. Soil Sci. Soc. Am. J., 46: 853--861. Bernas, B., 1968. A new method for decomposition and comprehensive analysis of silicatesby atomic absorption spectrometry. Anal. Chem., 40 : 1682--1683. Dasman, R.F., 1972. Environmental Conservation. Wiley, N e w York, NY, 473 pp. Franklin, J.F., Dyrress, C.T., Moore, D.G. and Tarrant, R.F., 1967. Chemical soil properties under coastal Oregon stands of alder and conifers. In: J.M. Trappe, J.F. Franklin, R.F. Tarrant and G.M. Hansen (Editors), Biology of Alder. Pac. Northwest For. Range Exp. St. For. Serv., U S D A , Oregon, pp. 157--172. Hamilton, C.D., 1965. Changes in the soil under Pinus radiata. Aust. For., 29: 275--289. Hopmans, P., Flinn, D.W. and Squire, R.O., 1977. Soil chemical properties under eucalypt forest and radiata pine plantations on coastal sands. Forests Commission, Victoria, Res. Branch Rep. 102, 9 pp. Humphreys, F.R., 1974. The nutrient status of pine plantations in central N e w South Wales. Appita, 18: 111--121.
270 Jenny, H., 1980. The Soil Resource, Origin and Behaviour. Springer-Verlag, N e w York, NY, 377 pp. Keeves, A., 1966. Some evidence of loss of productivity with excessive rotations of Pinus radiata in the south-east of South Australia. Aust. For., 30: 51--63. Kelly, J. and Turner, J., 1978. Soil nutrient--vegetation relationships in the Eden area, N.S.W.I. Soil nutrient survey. Aust. For., 41: 127--134. Lambert, M.J., 1976. Methods of Chemical Analysis. Forestry Commission of N e w South Wales Tech. Pap. No. 25, 187 pp. McIntosh, P.D., 1980. Soil changes under radiata pine in Kiangaroa State Forest, central North Island, N e w Zealand. N.Z.J. Sci., 23 : 63--92. Page, G., 1968. S o m e effects of conifer crops on soil properties. C o m m . For. Rev., 47: 52--62. Richards, B.N., 1962. Increased supply of soil nitrogen brought about by Pinus. Ecology, 43 : 538--541. Routley, R. and Routley, V., 1975. The Fight for the Forests. The takeover of Australian forests for pinewood chips and intensive forestry. Research School of Social Services, Aust. Nat. Univ., Canberra, 407 pp. Sokal, R.R. and Rohif, F.J., 1969. Biometry - - The Principles and Practice of Statistics in Biological Research. W.H. Freeman and Co., San Francisco, CA, 776 pp. Tarrant, R.F. and Miller, R.E., 1963. Accumulation of organic matter and soil nitrogen beneath a plantation of red alder and Douglas-fir. Soil Sci. Soc. Am. Proc., 27 : 231-234. Turner, J., 1980. Nitrogen and phosphorus distributions in naturally regenerated Eucalyptus spp. and planted Douglas-fir. Aust. J. For. Res., 10: 289--294. Turner, J., 1981. Nutrient s u p p l y in relation to immobilization in biomass and nutrient removal in harvesting. In: Proc. Australian F o r e s t r y Nutrition Workshop Productivity in Perpetuity. C.S.I.R.O., Melbourne, pp. 263--275. Turner, J. and Kelly, J., 1977. Soil chemical properties under naturally regenerated Eucalyptus spp. and planted Douglas-fir. Aust. For. Res., 7: 163--172. Turner, J. and Lambert, M.J., 1983. Nutrient cycling within a 27-year-old Eucalyptus grandis plantation in New South Wales. For. Ecol. Manage., 6: 155--168.
257
EFFECT OF RADIATA PINE ON SOIL CHEMICAL CHARACTERISTICS
JOHN TURNER and JOSEPH KELLY Forestry Commission of New South Wales, P.O. Box 100, Beecroft, N.S.W. 2119 (Australia) (Accepted 1 February 1985)
ABSTRACT
Turner, J. and Kelly, J., 1985. Effect of radiata pine on soil chemical characteristics. For. Ecol. Manage., 11: 257--270. Soil nutrient contents and distributions beneath planted mature pine (P. radiata) have been compared with those beneath adjacent native eucalypt at two sites (Wee Jasper and Billapaloola) in the Tumut District, N.S.W. The soil nutrients studied included total nitrogen, phosphorus, potassium, calcium, magnesium and sodium, together with exchangeable aluminium, calcium, magnesium, potassium and sodium. Planting of pine resulted in a redistribution of nutrients within the ecosystem. At Wee Jasper, nutients accumulated in the pine- stand and it appeared that this had occurred from deeper rooting in the soil profile, while at Billapaloola, nutrients were removed to a greater degree from the soil surface. Changes in total quantities of nutrients were small and there was no evidence of a potential productivity decline in the subsequent rotation from these changes.
INTRODUCTION Pinus radiata D. D o n p l a n t a t i o n s in A u s t r a l i a n o w e x c e e d 6 0 0 0 0 0 h a w i t h a p l a n t i n g r a t e o f a p p r o x i m a t e l y 20 0 0 0 h a y - ' . T h e s e p l a n t a t i o n s are generally e f f i c i e n t w o o d p r o d u c e r s w i t h p e r i o d i c a n n u a l i n c r e m e n t (p.a.i.) g r o w t h rates e x c e e d i n g 2 5 - - 3 0 m 3 h a - ' y - L H o w e v e r , R o u t l e y a n d R o u t l e y ( 1 9 7 5 ) a n d o t h e r s h a v e a r g u e d t h a t c o n i f e r o u s p l a n t a t i o n s in Australia r e d u c e soil f e r t i l i t y a n d c o n s e q u e n t p r o d u c t i v i t y . T h e c o n c e p t s f o r r e d u c e d p r o d u c t i v i t y c o m e f r o m w h a t was c o n s i d e r e d o r a s s u m e d t o b e a parallel s i t u a t i o n in E u r o p e , w h e r e r e p l a c i n g b r o a d l e a v e d species w i t h a c o n i f e r o u s species {spruce) was t h e c a u s e o f p o d s o l i z e d a n d i n f e r t i l e soils. H o w e v e r , t h e m o s t e x t r e m e cases o c c u r r e d o n v e r y p o o r sands ( D a s m a n n , 1972). E a r l y r e s e a r c h w o r k in A u s t r a l i a t e n d e d t o s u p p o r t a d e c l i n i n g yield c o n c e p t ( H a m i l t o n , 1 9 6 5 ) b y i n d i c a t i n g decreases in organic m a t t e r w h e n e u c a l y p t w o o d l a n d s w e r e c o n v e r t e d t o P. radiata p l a n t a t i o n s . T h e decline in s e c o n d r o t a t i o n p r o d u c t i v i t y o f pines in S o u t h A u s t r a l i a ( K e e v e s , 1 9 6 6 ) w a s c o n s i d e r e d as f u r t h e r c o n f i r m a t i o n o f this view ( R o u t l e y a n d Routley, 1975).
0378-1127]85/$03.30
O 1985 Elsevier Science Publishers B.V.
258 Although these observations have been accepted b y m a n y as evidence for soil fertility changes and a declining yield under pine, and thus as an argument against the planting of conifers, the case is n o t that definitive. Soil formation theory and experimental evidence (Jenny, 1980) established that the effect of a tree species on soil chemical properties is a function of a series of factors including the nutrient requirements of the particular species, its nutrient cycling characteristics, soil type, and properties of leachates from bark, foliage, roots and litter, as well as the length of time the species has affected the soil. S o m e soil properties m a y change when species are altered, but the estimation of the form and magnitude of change is more difficult. It is even more difficult to predict subsequent changes in productivity. Reliable results as to the effect of a particular species on soil properties and subseqeunt properties can only be obtained from well designed experiments. Soil and productivity changes associated with different species can be studied under field conditions using natural vegetation distribution or b y designed changes. An example o f the first t y p e of m e t h o d is the effect of red alder in Northwestern America (Tarrant and Miller, 1963; Franklin et al., 1967). Use of this m e t h o d assumes that other soil forming factors, such as parent material, are constant. The alternative m e t h o d is to use situations where different species have been planted on the same original soil, or to establish different species, and follow soil properties over a sequence of years (Alban, 1982). In b o t h cases species effects must be separated from any differences which may arise from management practices or from variations in initial soil or parent materials. The effects of management practices such as land clearing, burning, and compaction may be difficult to separate from species effect. This latter m e t h o d has been widely used because of the shorter time required to obtain results, b u t sometimes w i t h o u t sufficient control of variables. For instance, in the early work of Hamilton (1965), a series of six paired dry sclerophyll sites (pine and eucalypt) in the A.C.T. were studied, and declines were found in surface soil organic matter and nitrogen under P. radiata (five o u t of six sites). However, the results for phosphorus and cations suggested that soil boundaries were probably crossed in at least two cases. At site 5, the soil total phosphorus under the pine was higher than that under the eucalypt b y a very large a m o u n t (498 p p m and 294 p p m respectively) and this was the reverse of the general trend. Hopmans et al. (1977) intensively sampled and compared pine (P. radiata) and eucalypt sites on uniformly nutritionally p o o r sandy soils in Victoria. Although all nutrient levels were low, the surface soils under pine were significantly higher in nitrogen, magnesium and potassium. The differences were small and were also predominantly related to organic matter changes. Turner and Kelly (1977) compared surface and deeper horizon soils of a Douglas-fir plantation (Pseudotsuga menziesii Mirb. Franco) which had never been thinned (thus reducing potential management effects on soft)
259 with those of adjacent natural eucalypts. Both these studies t o o k into account the original clearing effects. While the mineral soil organic matter and nitrogen had declined, nutrients had accumulated in the litter and A-horizon, and when elements in the tree biomass were taken into a c c o u n t (Turner, 1980) there were no changes in total nutrients. There were redistributions and changes of form of nutrients within the Douglas-fir system compared with the eucalypt system, but no nutrient losses from the system. Because of the importance of pine to Australian forestry production and the need to understand more fully the possible changes in soil properties and eventual productivity under pine, a long-term research programme has been established in New South Wales. The programme uses the m e t h o d o l o g y which compares soil properties under paired (on similar soils and parent materials) pine and natural eucalypts stands. This paper represents the initial report and presents results from a comparison of pine and eucalyptus on a moderately productive site near Tumut. SITE AND METHODS Two study sites were selected within Buccleuch S.F., these being in the Wee Jasper section and in the Billapaloola section. The selected sample areas were in relatively old radiata pine stands (40 years plus) adjacent to naturally-occurring eucalypt species. There was no apparent geological change, as assessed from rock samples taken at each sampling point, across the boundary from pine to eucalypt at time of sampling, and the t o p o g r a p h y was uniform. General features of the study areas have been summarized in Table I. Within each area, pairs of plots were selected, each pair being at least 50 m apart and consisting of one location in the pine stand and another in the eucalypt stand in a similar micro-topographical situation. The factors considered were slope, position on slope, and relative degree of concavity or convexity. Seven pairs of plots were selected at Wee Jasper and eight at Billapaloola. The plot size was 0.1 ha. The pine areas had originally been cleared of eucalypts and broadcast burned prior to planting, and hence any land preparation effects in the area were across the whole area, rather than being concentrated in features such as windrows. Disturbances have occurred in pine areas as a result of the selection thinnings carried o u t a b o u t every five years after age fifteen. The Wee Jasper eucalypt area has been maintained as rough grazing land with frequent burning, while the Billapaloola eucalypt site has n o t been grazed or burned. No definite ages were known for the eucalypts b u t t h e y were probably uneven-aged stands with the larger trees older than the pine. At each plot, soil was sampled from the 0--5 cm and 5--10 cm depth, each sample being a bulking of 10 subsamples. In addition bulk density samples were taken at b o t h depths using a standard round corer with fitted brass rings, giving a soil sample 10 cm in diameter and 4 cm deep. A n y compression occurring was assumed to occur across all sites. These t w o
260 TABLE 1 General characteristics of stands in the Wee Jasper and Billapaloola sections of Buccleuch S.F.
Physical aspects Elevation (m) Geology Soil Topograhpy Aspect Eucalypt Stand Species
Dominant height (m) History Pine Stand Planted Compartment Stem ha -1 (with regrowth) Basal area (m 2 ha -I ) Natural regeneration Mean dominant height (m)
Wee Jasper
Billapaloola
1000--1100 F i n e - - m e d i u m grained granodiorite Red earth Gently sloping Northeast
820 Medium grained granodiorite and quartz p o r p h o r y Red podzolic Gentle depression West
E. dalryrnpleana E. radiate E. macrorhyncha 27 Burnt for grazing
E. radiata E. dalrympleana E. bridgesiana 25 Unburnt
1931 27 240 37 Medium 42
1932 35 200 33 Dense 42
depths were selected because previous studies have shown t h e m to be the most sensitive to change, having the highest fine r o o t density and inputs from the forest floor (Turner and Kelly, 1977). The depths sampled did n o t cross a soil horizon boundary. Soil pits were dug to assess possible differences at depth, such as the crossing o f a soil boundary. Six forest floor samples per plot were taken using a 0.1-m 2 steel ring and oven dried at 70°C before sorting. Those from the Wee Jasper site were sorted into the c o m p o n e n t s of leaves {needles), stick, bark, fine material and understorey, b u t only the total sample was analysed at Billapaloola. Bark was underestimated in the eucalypts because of the bark 'halo' effect at the base of some trees {Turner and Lambert, 1983). Fine material was undefinable in origin. Samples were analysed individually. Soil samples were air dried and sieved to pass a 2-mm sieve and the p r o p o r t i o n of stone was estimated. The samples were analysed for pH, organic matter, nitrogen, phosphorus, and exchangeable calcium, magnesium, potassium, sodium and aluminium using procedures according to Lambert {1976). Total soft cations were digested b y the m e t h o d of Bernas {1968) and estimated b y atomic absorption s p e c t r o p h o t o m e t r y . Forest floor samples were oven dried at
261
70°C, sorted, ground to pass an approximately 2-mm mesh, and analysed for phosphorus, calcium, magnesium, potassium, sodium and nitrogen (Lambert, 1976). Statistical analyses were carried o u t as in Sokal and R o h l f (1969). Estimates of nutrients removed in thinning pine were made b y using known estimates of timber volume removed from the age class and using mean P. radiata w o o d and bark nutrient concentration from the area (Lambert, 1976). First thinning records were incomplete, so the removal estimates were considered to be underestimates. RESULTS
The soil chemical characteristics under eucalypts for b o t h the Wee Jasper and the Billapaloola area (Table 2) were fairly similar. Although the average analyses for total exchangeable bases and phosphorus (Table 3) were slightly higher at Wee Jasper than at Billapaloola, the differences were n o t statistically significant. Compared with other pine forest softs in N e w South Wales, however, these sites are relatively high in nutrient reserves, particularly phosphorus, calcium and magnesium (Humphreys, 1974; Kelly and Turner, 1978; Turner, 1981). Wee Jasper soils The 0--5 cm soil depth under pine at the Wee Jasper site was significantly higher in organic matter than that under the eucalypt stand. Decreased bulk density and increased exchangeable cations also occurred, and, although n o t statistically significant, the differences were probably related to the organic matter changes. Estimates of exchangeable cations were assumed to be available quantities, whereas concentrations of total cations provided estimates of nutrient reserves. While less than 10% o f magnesium and potassium were in exchangeable forms, almost 50% of the total calcium was in this form. There was a significant increase in soil total calcium under pine at both the 0--5 cm and 5--10 cm depths and a decrease in total potassium at the surface (Table 3). The P. radiata soil at the 5--10 cm depth was significantly higher in exchangeable calcium and total exchangeable bases than the eucalypt soil. With the exception of pH, potassium and aluminium, the 5--10 cm depth showed trends with species similar to those in the surface horizon. The nutrient mass per unit area of forest floor and soil, together with statistical analyses, are shown in Table 4. There was a greater forest floor mass under the eucalypt stand, largely resulting from the higher bark and stick mass, but there was little difference b e t w e e n the pine and eucalypt litter nutrients, except for calcium and magnesium contents. When the total soil nutrients (0--10 cm) were included with the litter nutrient contents, neither nitrogen nor phosphorus was significantly different. However, under pine there was an increase in calcium and a decrease in potassium and magnesium, compared with eucalypt.
0.88 0.85 n.s.
5--10 cm depth Eucalypt Pine S.D.B.M.
0.94 0.88 n.s.
5--10 cm depth Eucalypt Pine S.D.B.M. 5.29 5.31 n.s.
8.51 7.73 n.s.
6.06 7.67 1.6"
2.1"*
8.76 12.74
27 43 11
n.s.
n.s.
0.11 0.07 0.03
28 37
27 29 n.s.
25 35 8"*
C/N
0.17 0.12
0.13 0.15 n.s.
0.20 0.21 n.s.
N (%)
5.52 5.50 n.s.
n.s.
5.53 5.29
5.30 5.34 n.s.
5.33 5.06 n.s.
pH H20
4.02 4.63 n.s.
n.s.
6.72 5.15
3.92 6.57 2.70**
6.55 8.28 n.s.
Ca
1.56 1.40 n.s.
n.s.
2.00 1.80
2.04 1.95 n.s.
2.66 2.39 n.s.
Mg
0.70 0.55 n.s.
n.s.
0.81 0.71
0.71 0.66 n.s.
1.28 1.26 n.s.
K
Exchangeable (meq. %)
0.07 0.07 n.s.
n.s.
0.08 0.14
0.58 0.52 n.s.
0.05 0.08 n.s.
Na
6.36 6.64 n.s.
n.s.
9.61 7.80
7.25 9.70 2.80*
10.50 12.01 n.s.
T.E.B. a
aT.E.B. = total exchangeable bases (excluding aluminium). bS.D.B.M. = significantdifference between means; *, 5 % level; ** 1 % level;n.s. = not significant.
0.90 0.85 n.s.
0--5 c m d e p t h Eucalypt Pine S.D.M.B.
Billapaloola
0.81 0.76 n.s.
Bulk Organic density matter (gcc -I) (%)
0--5 c m d e p t h Eucalypt Pine S.D.B.M. b
Wee Jasper
Site
M e a n results o f soil analyses u n d e r P. radiata a n d Eucalyptus spp. at Wee J a s p e r a n d B i l a p a l o o l a
TABLE 2
0.34 0.30 n.s.
n.s.
0.36 0.52
0.63 0.56 n.s.
0.34 0.46 n.s.
Al
20.7 21.2 n.s.
n.s.
25.9 25.5
22.8 28.1 3.5*
26.6 32.8 n.s.
32 30 n.s.
n.s.
37 31
30 32 n.s.
35 36 n.s.
(%)
C.E.C. Base (meq.%) saturation
b~ O~ b~
263 TABLE 3 Soil total p h o s p h o r u s and t o t a l a n d e x c h a n g e a b l e c a t i o n q u a n t i t i e s u n d e r P. radiata and Eucalyptus spp. at Wee J a s p e r a n d Billapaloola Site
To~lP (ppm)
To~lcatio~
(me%)
E x c h a n g e a b l e / T o t a l (%)
Ca
Mg
K
Na
Ca
Mg
K
Na
Wee Jasper 0--5 cm d e p t h Eucalypt Pine S.D.B.M. a
385 415 n.s.
13.6 18.1 3.2**
35.1 33.1 n.s.
17.4 15.1 2.1"
6.1 6.6 n.s.
48.1 45.7 2.5*
7.6 7.2 n.s.
7.4 8.3 2.0*
0.8 1.2 n.s.
5--10 c m d e p t h Eucalypt Pine S.D.B.M.
325 430 n.s.
9.9 13.1 2.5*
36.6 35.0 n.s.
18.4 17.2 n.s.
5.9 7.5 n.s.
39.6 50.2 6.2*
5.6 5.6 n.s.
3.9 3.8 n.s.
9.8 6.9 n.s.
0--5 c m d e p t h Eucalypt Pine S.D.B.M.
270 310 n.s.
17.7 14.5 2.1"
19.6 18.1 n.s.
21.3 19.6 n.s.
5.1 3.8 n.s.
38.0 35.5 n.s.
10.2 9.9 n.s.
3.8 3.6 n.s.
1.6 3.7 n.s.
5--10 c m d e p t h Eucalypt Pine S.D.B.M.
230 270 n.s.
11.7 10.3 n.s.
19.9 18.3 n.s,
21.4 19.7 n.s.
4.9 4.0 n.s.
34.4 45.0 n.s,
7.8 7.7 n.s.
3.3 2.8 n.s.
1.4 1.8 n.s.
Billapaloo la
aS.D.B.M. = significant d i f f e r e n c e b e t w e e n m e a n s ; *, 5% level, ** 1% level; n.s. = n o t significant.
The quantities of nutrients in the litter and surface soil do n o t differ significantly between the pine and eucalypt stands at Wee Jasper. When the quantity of nitrogen already removed in thinning from the pine site is taken into account, there is an excess of 400 kg N ha -1 in the pine site. The existing standing crop was n o t taken into account, which leads to an underestimate. The quantity of nitrogen accumulated in the pine stand amounts to between 8 and 9 kg ha -1 y-l, which supports the findings of Richards (1962). This accumulation may be either from deeper d o w n the soil profile or from fixation. An alternative explanation is that there have been losses from the eucalypt stand, b u t the process by which these occurred is n o t immediately obvious. The other nutrients in the pine stand also appear to have been drawn from further d o w n the profile. Phosphorus quantities (kg ha -1) tended to be higher under the pine than under the eucalypt for both areas. The pine litter had a higher phosphorus concentration than the eucalypt litter. Decomposition of organic matter and accumulation in the mineral soil gave a higher organic phosphorus con-
--
--
0-10 c m
T o t a l soil +forest floor
1396
1272
740
124.3
15.3 10.8 15.8 67.4 15.0
310
298
155
11.6
1.2 1.0 1.0 7.0 1.3
(453)
5986
2030 (150) 5953 (420)
32.5
4.5 3.8 4.1 17.0 3.0
2206 (1127)
1080 (520) 1939 (860)
267
58.4 42.4 32.2 131.4 2.0
Ca
3574 (261)
1579 (120) 3543 (230)
30.8
5.6 4.1 3.5 15.3 2.4
Mg
--
--
--
1 4 1 5 n~"
1299
778
116.4
326 ~
314
154
11.6
1.0
10.9
21 150
9.4
89.5
2 120 10 4 1 0 1 830
1.2
16.0
P
6 790
N
aO.M. ffiorganic matter. **, * = 1 % and 5 % significance level between eucalypt and pine; n.s. = not significant.
--
Soil 0-5 c m
26 8 6 0
Total
910 580 850 170 350
7 3 2 12 2
K
O.M.
P
O.M. a
N
Pine
Eucalypt
Forest Floor Stick Bark Leaf or n e e d l e Fine material Understorey
Component
2.5
5615" (344)
2161 (180) 5582 (310)
34.1
1.1
30.5
K
2551"* (1280)**
1335 (610) 2431 (1160)
120
3.8
99.3
15.8
Ca
3194" (210)*
1389 (100) 3175 (200)
18.9
0.3
16.3
2.3
Mg
Biomass a n d n u t r i e n t c o n t e n t (in kg h a -~) o f t h e f o r e s t f l o o r t o g e t h e r w i t h t o t a l n u t r i e n t s c o n t a i n e d in t h e t o p 10 c m o f soil in t h e pine and e u c a l y p t stands at Wee Jasper. Soil e x c h a n g e a b l e c a t i o n s are i n p a r e n t h e s e s
TABLE 4
O~ ht~
265 centration in the 0--5 cm layer. Thinning the pine stand removed 6 kg P ha -1 (Table 5), but this small q u a n t i t y would n o t have affected the above estimates. It was estimated that thinning the pine would have removed approximately 84, 147 and 25 kg ha -I of potassium, calcium and magnesium respectively (Table 5), and therefore differences of this order could be expected between the pine and eucalypt sites. Based on surface soils and litter, eucalypts exceeded pine by 370 and 380 kg ha -1 for potassium and magnesium respectively, but pine was 345 kg ha -1 higher in calcium. Obviously these differences cannot be explained by differences in thinning removals (Table 5) and there was no evidence for extensive leaching losses. When soil exchangeable potassium and magnesium were considered (Table 4), levels in eucalypt were 109 and 42 kg ha -1 higher than in pine for potassium and magnesium respectively. These differences may be the result of thinning losses, and the total differences may be an artifact because of higher variability in total estimates. Calcium is apparently more weatherable and mobile in these soils, as indicated by the high ratio of exchangeable to total calcium, and it would appear to be accumulated from deeper in the profile in a comparable manner to phosphorus. TABLE 5 Average removal of nutrients (in kg ha -j ) in thinning for Wee Jasper and Billapaloola. Biomass removals estimated from known quantities of thinnings removed and the specific gravity of the wood and bark Component
Biomass (kg ha -j)
N
P
K
Ca
Mg
Bark Wood Total
17 000 97 000 114 000
44 337 381
1.7 4.3 6.0
25 59 84
62 85 147
19 25
6
Billapaloola soils At Billapaloola, there were no statistically significant differences in nutrient concentrations at the 0--5 cm depth, although trends indicated lower organic matter, nitrogen and cations, and higher phosphorus under P. radiata. The nitrogen concentration at the 5--10 cm depth was significantly lower under P. radiata compared with the eucalypt soil, and there were differences in the trends of the exchangeable cations. The major change in total cations at Billapaloola was a decrease in calcium under pine. The total concentrations of the other cations were not significantly different between the two forest types. The litter and soil data from Billapaloola (Table 6) showed a decrease in nitrogen under the pine compared with the eucalypt, but no significant
n.s.
360**
n.s.
231
220
120
11
230** (50)**
7351 (291)
3684 (140) 7320 (260)
31
655* (420)*
2873 (1207)
1595 (606) 2696 (960)
247
Ca
n.s. n.s.
2132 (218)
1078 (110) 2104 (190)
28
Mg
24 000
--
--
24 000
961
812
508
149
N
14
241
227
118
P
39
6945 (239)
3692 (110) 6906 (200)
K
1950 (1021)
1235 (430) 1777 (847)
174
Ca
1741 (174)
808 (80) 1717 (150)
24
Mg
aO.M. = organic matter. bS.D.B.M. = significant difference between means of eucalyt and pine; *, 5% level; **, 1% level; n.s. = not significant.
S.D.B.M. b
1374
Total Soil and Forest Floor
734
127
1247
26 800
26 800
K
O.M.
P
O.M. a
N
Pine
Eucalypt
0--10 cm
Soil 0--5 cm
Forest Floor
Component
Biomass and nutrient content (in kg ha -~) of the forest floor together with total nutrients contained in the top 10 cm of soil in the pine and eucalypt stands at Billapaloola. Figures in parentheses are exchangeable quantities
TABLE 6
O~
b3
267 change in phosphorus. The total and exchangeable cations decreased under pine, but this was not significant for magnesium. These declines occurred in the litter and the 0--5 cm and 5--10 cm depths, indicating a decrease in all estimated pools. When nutrients were expressed per unit area (kg ha -1) (Tables 4 and 6), some differences were observed. In the case of nitrogen at Billapaloola, there was less nitrogen in the combined litter and surface soil of the pine forest compared with that of the eucalypt. When the concentration of nitrogen in the soil profile was assessed (Fig. 1), there appeared to be a uniform distribution of nitrogen under pine, while it was concentrated near the surface under eucalypt. Unfortunately, samples from only one pair of soil pits were analysed in detail and no statistical analysis was possible. At Billapaloola under pine there have been decreases in nitrogen, potassium, calcium and magnesium of 415, 406, 923, and 391 kg ha-' respectively, using total nutrients as the estimate. In the case of exchangeable cations, the decreases were 52, 186 and 44 kg ha-' for potassium, calcium and magnesium respectively, and these are approximately equivalent to nutrient removals in logging. Phosphorus levels were higher under pine, but not significantly so. Therefore, it may be concluded t h a t the changes on this site are a result of tree uptake and that this is reflected in exchangeable and total cation estimates. SOIL NITROGENI%) 0.05 0.1 0.15 0.2 i
i
l
SOIL NITROGEN(%) 0.05 0.1 0.15 0.2
i
i
i
i
|
0 pine.,
pin~,/~ /eucalypf
10,
7
10
E
i 20,
20
o 30,
3O
0
40 5C
if'
I
50.
BILLAPALOOLA
WEE JASPER
Fig. 1. Mean nitrogen concentrations for the profiles of the pine and eucalypt soils at Billapaloola and Wee Jasper.
DISCUSSION
The role o f i m p o r t a n t but study the soils been compared
vegetation in soil-forming processes is acknowledged to be its effects are often difficult to quantify. In the present beneath mature, managed, planted radiata pine stands have with softs beneath adjacent natural eucalypt stands in which
268 disturbances were only due to g a z i n g and fire. T h a t is, assessment of the net changes was basically based on the species alteration from eucalypt to pine and the subsequent effect of pine management, such as thinning. At the Wee Jasper site there has been a general t e n d e n c y towards increased concentrations of nutrients at 0--5 cm soil d e p t h under the P. radiata and there has been an overall upward redistribution of nutrients within the soil profile. If nutrient removals as a result of thinning are also taken into account, nutrients must have been recycled f r o m deeper than 10 cm in the profile to account for the differences. At Billapaloola there has been a decrease in several of the nutrients in the soil surface, but when thinning losses were considered, equal quantities of nutrients occurred on both the pine and eucalypt sites. At the Billapaloola s t u d y site, the difference between the pine and the eucalypt was equivalent to the thinning loss, as may be expected. The stand appears to have been growing p r e d o m i n a n t l y in the surface soil with little drain on nutrients further in the profile. It is hypothesised t h a t the Wee Jasper pines accumulated nutrients on the surface from deeper in the profile and that the trees have more fully utilized the depth of soil than was the case at Billapaloola. A combination of several factors m a y have affected the nutritional status of these soils. It is possible that regular fires in the eucalypt stand at Wee Jasper have played an important part and t h a t over an extended period (at least 40 years in this case) n u t r i e n t losses have occurred, such as volatilization of nitrogen. On the other hand, the fire protection system practised at Billapaloola in the eucalypts and' in the management o f the pine stands has maintained the nutrient capital, and any losses were those predictable as a result of wood removal from the site. With native eucalypts as a base comparison, both sites studied have shown that pine planting has affected n u t r i e n t distributions. The quantities redistributed were equivalent to those accumulated in a typical standing crop of pine of this age and quality. The sites differ in that pine at Wee Jasper, growing on a Red Earth, appears to have more thoroughly utilized the deeper soil profile, while at Billapaloola, on a Red Podzolic, there has been less volatilization deeper within the profile, thus leading to an apparent nutrient deficit in the soil. The total soil cations do n o t give a reasonable indication of change, but the proportion of exchangeable to total cations provides an indicator of nutrient reserves. Thus, at Wee Jasper 40% or more of the calcium is in exchangeable form and at BiUapaloola this is more than 30% {Table 3). Comparable estimates for magnesium and potassium were less than 10%, indicating that calcium is the most vulnerable cation for nutrient depletion. Page {1968) assessed observable soil properties such as horizon depth and litter thickness under three coniferous species in England. The species were neither compared with each other nor with another species as a base line, rather changes in relation to stand development were ascribed when
269
the parameter used for assessing stand development was stand current top height rather than age. By this means the a u t h o r overcame the problem of variation in stand quality. M a x i m u m top stand height was about 37 m and most changes in terms of horizon and litter depth, moisture content, pH and bulk density occurred in the 16--25 m top height range, after which stage there was a gradual equilibration reverting to levels f o u n d in the original situation. This equilibration was considered to be due to thinning, and many of the changes observed could be related to changes in litter depth. If the effect found by Page (1968) were to apply under Australian conditions, significant changes chould be apparent in a radiata pine stand at 10--20 years of age, the time of rapid stand development and heavy drain on nutrient reserves. After this stage, thinning and consequent return of nutrients and opening of the stand should tend to return the soil to near pre-planting conditions. McIntosh (1980) compared 45-year-old P. radiata to native L e p t o s p e r m u m in New Zealand in a similar way to the present study. The soils were derived from ash and were more permeable. The lower nitrogen, organic matter, phosphorus and cations under P. radiata were attributed to nutrient uptake, mineralization and different organic acids. This study was carried o u t towards the end of a P. radiata r o t a t i o n and included the effects of management (for example thinning) rather than pine planting per se. A larger effect may have occurred in the 10--20 year age period, when the greatest drain on soil reserves would occur. The soils have n o t been significantly reduced in nutrients and when the nutrient content of slash from clearcutting is included, the nutrient status of the soil should be equivalent to that at the c o m m e n c e m e n t of the first rotation. Therefore one would n o t expect a productivity reduction in the n e x t rotation.
REFERENCES
Alban, D.H., 1982. Effects of nutrient accumulation by aspen, spruce and pine on soil properties. Soil Sci. Soc. Am. J., 46: 853--861. Bernas, B., 1968. A new method for decomposition and comprehensive analysis of silicatesby atomic absorption spectrometry. Anal. Chem., 40 : 1682--1683. Dasman, R.F., 1972. Environmental Conservation. Wiley, N e w York, NY, 473 pp. Franklin, J.F., Dyrress, C.T., Moore, D.G. and Tarrant, R.F., 1967. Chemical soil properties under coastal Oregon stands of alder and conifers. In: J.M. Trappe, J.F. Franklin, R.F. Tarrant and G.M. Hansen (Editors), Biology of Alder. Pac. Northwest For. Range Exp. St. For. Serv., U S D A , Oregon, pp. 157--172. Hamilton, C.D., 1965. Changes in the soil under Pinus radiata. Aust. For., 29: 275--289. Hopmans, P., Flinn, D.W. and Squire, R.O., 1977. Soil chemical properties under eucalypt forest and radiata pine plantations on coastal sands. Forests Commission, Victoria, Res. Branch Rep. 102, 9 pp. Humphreys, F.R., 1974. The nutrient status of pine plantations in central N e w South Wales. Appita, 18: 111--121.
270 Jenny, H., 1980. The Soil Resource, Origin and Behaviour. Springer-Verlag, N e w York, NY, 377 pp. Keeves, A., 1966. Some evidence of loss of productivity with excessive rotations of Pinus radiata in the south-east of South Australia. Aust. For., 30: 51--63. Kelly, J. and Turner, J., 1978. Soil nutrient--vegetation relationships in the Eden area, N.S.W.I. Soil nutrient survey. Aust. For., 41: 127--134. Lambert, M.J., 1976. Methods of Chemical Analysis. Forestry Commission of N e w South Wales Tech. Pap. No. 25, 187 pp. McIntosh, P.D., 1980. Soil changes under radiata pine in Kiangaroa State Forest, central North Island, N e w Zealand. N.Z.J. Sci., 23 : 63--92. Page, G., 1968. S o m e effects of conifer crops on soil properties. C o m m . For. Rev., 47: 52--62. Richards, B.N., 1962. Increased supply of soil nitrogen brought about by Pinus. Ecology, 43 : 538--541. Routley, R. and Routley, V., 1975. The Fight for the Forests. The takeover of Australian forests for pinewood chips and intensive forestry. Research School of Social Services, Aust. Nat. Univ., Canberra, 407 pp. Sokal, R.R. and Rohif, F.J., 1969. Biometry - - The Principles and Practice of Statistics in Biological Research. W.H. Freeman and Co., San Francisco, CA, 776 pp. Tarrant, R.F. and Miller, R.E., 1963. Accumulation of organic matter and soil nitrogen beneath a plantation of red alder and Douglas-fir. Soil Sci. Soc. Am. Proc., 27 : 231-234. Turner, J., 1980. Nitrogen and phosphorus distributions in naturally regenerated Eucalyptus spp. and planted Douglas-fir. Aust. J. For. Res., 10: 289--294. Turner, J., 1981. Nutrient s u p p l y in relation to immobilization in biomass and nutrient removal in harvesting. In: Proc. Australian F o r e s t r y Nutrition Workshop Productivity in Perpetuity. C.S.I.R.O., Melbourne, pp. 263--275. Turner, J. and Kelly, J., 1977. Soil chemical properties under naturally regenerated Eucalyptus spp. and planted Douglas-fir. Aust. For. Res., 7: 163--172. Turner, J. and Lambert, M.J., 1983. Nutrient cycling within a 27-year-old Eucalyptus grandis plantation in New South Wales. For. Ecol. Manage., 6: 155--168.