The relationship between vegetation patterns and environment on the south coast of New South Wales

l’ores~~;ology Management Forest Ecology and Management 72 ( 1995) 7 l-80

The relationship between vegetation patterns and environment on the south coast of New South Wales I.A. Neave*, S.M. Davey’, J.J. Russell-Smith2, R.G. Florence3 Department ofForestry, Australian National University, Canberra, A.C. T. 0200, Australia

Accepted6 April 1994

Abstract Relationshipsbetween vegetation patterns and environmental factors on a forest on the south coast of New South Wales have been examined using analysis of variance and principal coordinate analysis.The gradient in vegetation from rainforest through tall-open (wet sclerophyll) forest to open (dry sclerophyll) forest and heath is associatedwith variations in the chemistry of soils-including those related to the level of aluminium within the soil. Differences in the competitive ability of specieson soilsvarying in physical and other site factors can modify the speciespatterns determined by soil chemistry. The fertility rangeof individual speciesis illustrated. Keywords: Vegetationpattern;Species-environment relationship;Soilchemistry;Soilfertility

1. Introduction

The classification-ordination technique has been used in a number of eucalypt forests to identify consistent plant community patterns and to establish the relationships of the communities to each other, for example Have1 ( 1975) and Wardell-Johnson et al. (1989) in Western Australia, and Russell-Smith ( 1979) and Davey ( 1989) in New South Wales. Davey extended Russell-Smith’s original pattern analysis within Corresponding authorat: CAREAustralia,GPOBox2014, Canberra,A.C.T. 2601,Australia. ’ Presentaddress: Bureauof ResourceSciences, CommonwealthDepartmentof Primary Industriesand Energy,BrisbaneAvenue,Barton,A.C.T. 2600,Australia. ’ Presentaddress: AustralianNatureConservationAgency, GPOBox 1260,Darwin,N.T. 0801,Australia. 3Presentaddress:Departmentof Forestry,AustralianNationalUniversity,Canberra,A.C.T. 0200,Australia. l

forests on the south coast of New South Wales, developing an improved community classification based on three formations (heath, sclerophyll forest and rainforest), and seven distinct alliances (Table 1) . Relationships between the individual communities making up these alliances have been illustrated by Moore et al. (1991). It is generally inferred that edaphic factors, especially soil chemistry, regulate species and community patterns on the south coast of New South Wales,but this has not been established in a definitive way. Russell-Smith ( 1979) believed his analysis portrayed a gradient in vegetation from rainforest through tall open (wet sclerophyll) and open (dry sclerophyll) eucalypt forest to heath, and that this gradient could be explained satisfactorily in terms of a corresponding gradient in soil fertility. There have been some localised studies on

0378-l127/95/$09.500 1995ElsevierScienceB.V. All rightsreserved XSDIO378-1127(94)03410-9

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Table 1 Description of vegetation communities at the 3 and 7 group level of the vegetation classification (divisions after Davey. 1989; community numbering after Moore et al., I99 1) Abbrevi- Vegetation ation description -___ 3 group level Vegetation formation E. piperita group

E. maculata group

Rainforest group

7 group level Vegetation alliance E. piperita-E. globoidea

E. piperita-heath

Epip

Emac

RF

P1

P2

Low quality dry sclerophyll and heath communities (Division 1, 2); 7 group level P 1 and P2 Moderate and high quality sclerophyll forest with an E. rnaculata component (Division 1, 2); 7 group level E 1, S 1 and S2 Rainforest and rainforest ecotonal (wet sclerophyll) communities characterised by high species richness of mesic species in the understorey (Division 1); 7 group level RI and R2

Low quality dry sclerophyll E. piperita-E. globoidea (peppermintstringybark) communities (Division 1, 2, 6; Community Numbers 110, 120, 130) Low quality E. pipe&a-heath communities (Division 1, 2,6; Community Numbers 140,145)

species-environment relationships (e.g. McColl, 1969; McCutchan, 1978 ) . Soil chemistry is seen to play a pivotal role in explaining complex community patterns, but the physieal properties of soils affecting root development and the stor-

Abbrevi- Vegetation ation description Ecotonal E. piperitaE. maculatu

El

Moderate quality E. maculata

Sl

Upper slope E. maculata

s2

Temperate rainforest

RI

Ecotonal wet sclerophyllrainforest

R2

Low to modcrarc quality ecotonal E plperltu-l’ macnlatu commumttcu characterised by xeric species in the understore\ (Division i. 7.4. 5: Community Numbers 10. 15, 20. 25. 30.40 1 Moderate and high quality 1.. maculata communities with a range of understorey types (Division I,?. 3. 5: Community Numbers 50. 55.60. 65, 80.85, ‘10, 220) High quahty upper slope communities with little understorey (Division I. 2. 3: Community Numbers 90.95. 100. 105 : Temperate rainforest (Division 1. 3: Community Numbers 150. 160) Ecotonal rainforest being dominated by Eucaijptus (Division i . 3: Community Numbers 170, 175, I 80, 190. 200)

ageand availability of water, are also regarded as important factors under some conditions. Against this background, a wider and more objective examination of species-environment relationships has been needed to establish, with greater confidence, ways in which species and community patterns may be responding to variations in a wide range of environmental factors. This study has been designed to do this.

LA. Neave et al. /Forest Ecology and Management

2. Materials and methods

72 (1995) 71-80

13

and major drainage lines were also recorded. These attributes formed the site factor data set.

2. I. Plot selection and sampling procedure 2.2. Data analysis

The study was undertaken on Kioloa State Forest (35”35’42”S, 150°17’22”E), located about 30 km north of Batemans Bay on the south coast of New South Wales. The study uses data collected from a stratified sub-sample of the 171 plots established by Russell-Smith ( 1979) and Davey ( 1989) for the purpose of analysing vegetation patterns. The stratification was based on a sample of 51 plots, covering the full range of parent material, landform units and community types present in the forest. At each of the 51 sites, soil was taken for chemical analysis from three auger holes at a number of intervals to 30 cm depth, and beyond this at 20 cm intervals to a maximum depth, where possible, of 165 cm. While all soil samples were analysed individually, average chemical information for the O-30 and 3 l-60 cm soil zones, has been taken to represent the A and B horizons, respectively. Total anions, nitrogen and phosphorus were determined using the Kjeldahl acid digestion technique on a Technicon Autoanalyser II continuous flow analytical instrument (TAA-II, 1977). Exchange able cations such as potassium, sodium, calcium, magnesium, aluminium and iron were determined using methods adopted by the Forestry Commission of New South Wales (Lambert, 1978). Organic matter was assessedusing the technique of loss on ignition. Along with pH, these nine attributes made up separate chemical data setsfor the A and B horizons. The depths of the A 1and total A horizons, and the depth to the C horizon and to parent material were measured. The texture of the A and B horizons, the gravel percentage and drainage class (based on soil profile and vegetation characteristics) were assessed.These formed the soil physical data set. Slope, radiation index, position on slope, general topography, parent material, basal rock type, the major soil formation patterns (in situ, colluvial, depositional, erosional) and proximity to permanent or intermittent surface water in creeks

The data were analysed to determine possible relationships between plant communities and a range of environmental factors using univariate and multivariate techniques. One-way analysis of variance was used to demonstrate the variation in the chemical properties of the soils which support the distinctive vegetation types. The analysis was performed on the soil nutrient data set derived from the A horizon, using the vegetation groups defined through numerical classification of the original 171 plots (Davey, 1989). The 3 and 7 group levels (formation and alliance levels, respectively; Table 1) were selected for this analysis as these are readily identifiable in the field. The assumptions of analysis of variance were fulfilled, and heterogeneity of variance was corrected by the use of log or square root transformations. Only untransformed means are referred to in the text. The ordination technique of principal coordinate analysis (Reddy, 1983) was performed separately on the physical, site factor, and A and B horizon chemical data sets. This enables variables to be considered simultaneously and allows the use of both quantitative and qualitative data. The 7 group level of the vegetation classification of plots was subsequently superimposed onto the arrangement of plots defined by vectors 1 and 2 from the ordination of the separate environmental data sets. The contrasts of vectors 1 and 2 against vector 3 were also considered, but no useful patterns could be elucidated. The results of the ordination of the B horizon nutrient data set are not presented becausethere was little successin defining vegetation-soil fertility gradients. 2.3. The soil fertility eucalypt species

ranges of rainforest and

The distribution of the 51 plots along vector 1 of the A horizon nutrient ordination has been used to indicate the soil fertility ranges of the rainforest communities and the main eucalypt

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species. The species ranges were defined by assigning ‘importance values’ to all tree species greater than 10 cm dbhob and 2 m in height within the confines of the plot. An importance value ( Yi) for a species (Xi) shows that species contribution to the total community as follows Yi = l/2 (Basal Area X,/Total Basal Area + Stocking Xj/Total Stems) x 100 Any plot in which a given species had an importance value of 10 or greater, was used to define the fertility range of that species.Hence the location of the two extreme plots (both containing a specieswith an importance value of 10 or greater) at the positive and negative ends of vector 1 of the A horizon nutrient ordination, were used to defme the approximate soil fertility range of the species. 3. Results 3.1. Analysis of variance of the A horizon nutrient data set

Analysis of variance demonstrated consistent differences in the chemistry of the A horizon at both the 3 and 7 group classification levels (Table 2 ) . At the 3 group formation level, A horizon soils supporting the Eucalyptus piperita group of communities had significantly lower concentrations of organic matter than the rainforest group of communities, and significantly lower concentrations of all nutrient elements except aluminium and iron. The A horizon soils supporting various Eucalyptus maculata and ecotonal communities had intermediate concentrations of all nutrient elements except aluminium. The ratio of exchangeable aluminium to total exchangeable bases (A 1:TEB ) for the E. piperita group was significantly larger than for either the E. maculata or rainforest groups. A finer distinction between communities can be made at the 7 group (alliance) level (Table 2). The lower quality dry sclerophyll P2 (E. piperita-heath ) and P 1 (E. piperita-Eucalyptus globoidea) groups had the lowest mean concen-

72 (1995) 71-80

trations of total nitrogen and phosphorus, and lowest mean concentrations of exchangeable sodium, potassium, and magnesium. The P2 soils also had the lowest exchangeable calcium concentration and percentage of organic matter of any group. At the other end of the spectrum, the rainforest groups R 1 (temperate rainforest) and R2 (ecotonal wet sclerophyll-rainforest ), and the S2 group (upper slope E. maculata) had the highest concentrations of nitrogen, phosphorus, potassium and magnesium, and the highest percentage of organic matter. The El (ecotonal E. piperita-E. maculata) and S1 (moderate quality E. maculata) groups were generally intermediate between these extremes. While there is a consistent relationship between characteristics of the vegetation alliances and the major soil nutrient elements, this does not apply to aluminium. Mean exchangeable aluminium values ranged from 103 to 277 ppm. Within this range, the rainforest group Rl had the lowest and R2 the highest aluminium concentrations. The P2 and P 1 concentrations ( 109 ppm and 240 ppm respectively) were similarly divergent. The relationship between the A 1:TEB ratio and vegetation pattern is affected by the variable aluminium level. Nevertheless, the P2 and Pl groups had the highest A 1:TEB ratios (0.46 and 0.64 respectively) and the Rl and S2 groups the lowest (0.12 and 0.13 respectively). The R2 ecotonal rainforest had a high Al :TEB ratio of 0.45. 3.2. Ordination set

of the A horizon nutrient data

This ordination demonstrates the degree of similarity of 51 plots with respect to eight nutrient elements, organic matter and pH within the O-30 cm soil horizon. The first two vectors (axes) explain separately 26.9% and 15.6% of the total variation in the data set. The relative positions of 51 plots with respect to A horizon nutrients is shown by contrasting vectors 1 and 2 (Fig. 1). Those attributes contributing to the definition of the first two vectors are listed in order of importance in Table 3. The nutrient elements magnesium, ni-

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Table 2 Ranking of means from analysis of variance of A horizon (O-30 cm) soil nutrient concentrations (ppm) and other chemical attributes for the 3 and 7 group levels of the vegetation classification Nutrient element 3 group levela Nitrogen Phosphorus Potassium Calcium Magnesium Sodium Aluminium Iron Organic matter I PH AI:TEB ratio

613a Epip 67a Epip 51a hip 127a Epip 113a Epip 74a Epip 170a Emac 27a RF 6.la E.pip 6.01a RF 0.30a RF

1219b Emac 130b Emac 120b Emac 280ab Emac 234b Emac IlOa Emac 193a Epip 32ab Emac 8.lb Emac 6.19a Epip 0.30a Emac

7 group levelb 1963~ RF 207~ RF 21oc RF 364b RF 289b RF 133b RF 198a RF 32b hip 9.7b RF 6.20a E.mac 0.58b Epip

429a P2 45a P2 37a P2 1OOa P2 87a P2 67a P2 103a RI 10a s2 4.5a P2 5.92a R2 0.12a RI

716ab Pl 80ab Pl 59a PI 133ab Sl 127ab Pl 77a PI 109a P2 19ab P2 7.3b El 6.04ab El 0.13a S2

1122b Sl lllb El 74ab El 142ab Pl 228bc El lOlab El 117a s2 25ab Rl 7.0b Pl 6.10ab Rl 0.31ab El

1170b El 125b Sl 133abc Sl 300abc R2 202c Sl 102ab s2 156ab El 28ab R2 7.6b Sl 6.12ab PI 0.36b Sl

1657~ S2 186c s2 149c R2 342bcd El 287cd R2 IlOab Rl 194abc Sl 34ab Sl 8.0bc Rl 6.23ab Sl 0.45bc R2

1895~ R2 204~ R2 17oc s2 440cd Rl 299cd RI 118ab Sl 240bc Pl 38ab El 11.3c s2 6.32ab P2 0.46bc P2

2046~ RI 21 Ic Rl 282c RI 671d s2 358d s2 I53b R2 277~ R2 39b PI Il.lC

R2 6.45b s2 0.64~ PI

a Vegetation formation (3 group level): Epip, low quality E. piperita group; Emac, moderate and higher quality E. maculuta group; RF, wet sclerophyll-rainforest group. ’ Vegetation alliance (7 group level); PI, E. piperita-E. globoidea; P2, E. piperita-heath; E 1, ecotonal E. piperita-E. maculata; S 1, moderate quality E. maculata; S2, upper slope E. maculuta; Rl, temperate rainforest; R2, ecotonal wet sclerophyll-rainforest. Means within a row followed by a different letter are significantly different at PC 0.05. Only untransformed means are shown.

Fig. 1. Ordination

of the A horizon nutrient data and imposition of the 7 group level vegetation classification.

trogen, phosphorus, calcium, potassium and sodium, and organic matter percentage decline in value from the negative to positive end of vector

1. This first vector represents a broad gradient in vegetation from rainforest and wet sclerophyll forest at the negative (high nutrient) end,

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Table 3 Attributes contributing to the definition of Vector (V) 1 and 2 as identified in principal coordinate analyses of the A horizon nutrient, soil physical and site factor data sets. Pseudo-F-statistic (in parentheses) ranks the relative contribution of each attribute to the ordination, with a cutoff point for listing attributes of i 0 -__I_.--___ _I_A horizon nutrients Soil physical attributes Site factor attributes” ---. Vl v2 VI v2 VI V:! ------. Al Drainageb Depth of A 1 hor. Permian (Pebbley Beach ) Alluvial Mg (222) (139) (100) (27) (109) (67) N Fe Depth to C hor. Texture of A hor. Ordovician In situ (203) (57) (48) (22) (74) (44) P Depth of A hor. % of gravel Erosional Permian (Snapper Point ) PH (171) (20) (211 (21) (34) (18) OM Surface water availability Slope Twwwhy (82) (13) (31) (17) Ca Colluvial Position on slope (15) (51) (19) K Basal rock type (19) (46) Fe (10) --a The site factor attributes associated with parent materials (Permian, Ordovician) and soil formation patterns (in situ, coltuvial, depositional, erosional) are based on their presence or absence. b The attribute ‘Drainage’ is a qualitative assessment of the moisture holding characteristics of the soil, ranging from very well drained to permanently waterlogged.

through a range of dry sclerophyll communities dominated by E. maculata, ecotonal E. maculata-E. piperita communities, to E. piperita-E. globoidea-heath communities at the positive (low nutrient ) end. The elements aluminium and iron, and soil pH, contribute to the definition of vector 2 (Table 3). Of the 7 groups defined by the vegetation classification, only the P2 (E. piperita-heath) and S2 (upper slope E. madata) communities seem to be effectively discriminated with respect to this vector. These groups have consistently low concentrations of both aluminium and iron in the O-30 cm soil zone. However, from the analysis of variance, it was apparent that aluminium was also a discriminator of the R 1 and R2 rainforest groups. This is reflected to a certain extent over vector 2 in that the majority of Rl plots are at the positive, lower aluminium end while the majority of R2 plots are at the negative, higher nutrient end. That the ordination has not succinctly separated the two rainforest groups is not unexpected since the other major attribute con-

tributing to the alignment of piots akrngvector 2 is iron. Rl and R2 plots have similar concentrations of soil iron (24.9 ppm and 28.0 ppm, respectively). 3.3. Ordination

of the soil physical data set

This ordination arranges the 51 plots with respect to soil physical attributes. There are a number of these attributes which seem to be contributing to the dehmitation of vegetntion communities. The first two vectors explain separately 17.0% and 13.2% of the total variation in the data set. The contrast of vector 1 and vector 2 (Fig. 2) shows the relative position of 51 plots with respect to this data set, and the attributes contributing to these vectors are listed in Table 3. The attribute ‘drainage class’ dominates the definition of vector 1 (x-axis) by a factor of two, and indicates a gradient in m6isture . Pluts at the negative end of vector 1 have a more freely draining soil profile, lessde@&to the C hoiizon,

I.A. Neave et al. /Forest Ecology and Management

rive T l

I

0

A

I

A

A A

o

The Sl (moderate quality E. maczdatu) and P2 (E. piperitu-heath) groups occupy the whole range of positions in Fig. 2, that is, there are few similarities in the physical soil attributes collected which allow either the S1 or P2 groups to be effectively discriminated. 3.4. Ordination

Fig. 2. Ordination of the soil physical data and imposition of the 7 group level vegetation classification. The key to the community group symbols is that given in Fig. 1.

and a higher gravel percentage than those at the positive end of the vector. Of the three attributes defining the arrangement of plots over vector 2, ‘depth of Al horizon’ and ‘depth of total A horizon’ are strongly associated. Both may reflect differences in the ability of soils to provide available nutrients and surface soil moisture. Plots at the negative end of vector 2 have shallower Al and A horizons, and a heavier textured A horizon than those at the positive end of the vector. The relationship between alliance groups and physical soil attributes is demonstrated by imposing the 7 group level vegetation classification on the arrangement of plots produced by the ordination (Fig. 2). The plots within three of the groups form tight clusters. Along vector 1, the S2 (upper slope E. maculate) group and the R2 (ecotonal wet sclerophyll-rainforest ) group, with the exception of one plot, are found on soils with good drainage, less depth to the C horizon and a high percentage of gravel. In contrast, the El ecotonal group, with the exception of one plot, and to a lesser extent the P 1 (E. piperitu-E. globoideu) group, are found on soils with more restricted drainage, a greater depth to the C horizon and a low gravel percentage. From the arrangement of plots along vector 2, the Rl (temperate rainforest) group is consistently found on soils with a lighter textured A horizon and deeper A 1 and total A horizons.

17

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of the site factor data set

This ordination arranges the 51 plots with respectto a number of physical site attributes (Fig. 3). Vectors 1and 2 explain separately 25.2% and 15.3% of the total variation in the data set. This is at least as successfulas the A horizon nutrient ordination in terms of variance explained and in the demonstration of relationships between vegetation and environmental site factors. Only the S2 and P2 groups tend to form tight clusters over vector 1 and vector 2; however, four of the remaining five vegetation groups are characterised by a specific set of site attributes over either vector 1 or vector 2. The four S2 (upper slope E. maculatu) plots are characterised by Ordovician parent materials, mudstone basal rock type, steep slopes within steep topography, soil formed in situ and subject to erosional processes,upper positions on slope and relatively large distances to surface water (Table 3). Plots supporting the P2 (E. piperitu-heath) group of communities occur on flat to undulating terrain where slope is lessthan 9’,

X AA

A

0

l

l A

-IYe

A I

Fig. 3. Ordination of the site factor data and imposition of the 7 group level vegetation classification. The key to the community group symbols is that given in Fig. 1.

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and mostly 2-3 ‘. The communities are not found near surface water, soil formation patterns are either in situ or colluvial, and rock type, with the exception of one plot, is sandstone. Plots comprising the R2 (ecotonal wet sclerophyll-rainforest ) group are at the negative end of vector 1and are associated with Ordovician parent materials and steep slopes within steep topography. Plots supporting the Rl (temperate rainforest) group of communities are found at the negative end of vector 2, and are characterised by Permian (Snapper Point) derived soils (with the exception of one plot), lower slope sites, and close proximity to surface water in the form of seepage or intermittent creeks. The PI (E. piperita-E. globoidea) group also tends to have a number of distinctive site attributes. As with the P2 plots, there are both in situ and colluvial soil formation patterns, slopes are lessthan 9O,topography is flat to undulating and there is no associated surface water. Finally the majority of S1 (moderate quality E. maculata) communities occur on sites which have steepto undulating topography, moderate slopes, an absence of surface water and in situ and colluvial soil formation patterns. 3.5. The soil fertility eucalypt species

ranges of rainforest and the

Eucalyptus globoidea, E. piperita, Eucalyptus gummifera and Eucalyptus pellita are restricted

to the lower end of the soil fertility gradient in these forests (Fig. 4), as defined by vector 1 of the A horizon nutrient ordination. Other species have a wider fertility range; Eucalyptus pilularis extends from the low to moderate fertility soils and E. maculata from the low to higher fertility soils.Speciescomprising the rainforest groups are found on the moderate to higher fertility sites only. 4. Discussion It is now more clearly established that the vegetation gradient from rainforest and wet sclerophyll communities, through a series of E. macu-

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fata and ecotonal communities, to dry sclerophyll (E. piperita) and heath communities, is associ-

ated with a soil fertility gradient, as defined by the A horizon nutrient data set. The ordination of the B horizon nutrient data failed to reveal relationships between vegetation patterns and environmental factors. Since the majority of fine, translocating roots are likely to be concentrated in the first 30 cm of the soil profile (Feller, 1980; Carbon et al., 1980), it is not surprising that a data set based on chemical soil attributes within the 3 l-60 cm zone is a weak indicator of soil fertility-vegetation relationships. This may also illustrate the importance of an active nutrient cycling process in maintaining the fertility status of A horizon soil. Where the community groups (alliances) defined by the vegetation classification are imposed on the separate A horizon nutrient, soil physical and site factor ordinations, six of the seven groups can be characterised by a number of attributes contained in one or more of the data sets. Only the Sl (moderate quality E. maculata) alliance failed to form distinctive clusters of plots within any ordination, suggesting that this group occurs on environmentally diverse sites.The reasons for this may be apparent later. By combining results from the analyses of variance and ordinations, it is possible to establish sets of site attributes which are consistently related to particular vegetation types, as defined by the vegetation classification. The Pl (E. piperita-E. globoidea) and P2 (E. piper&a-heath) alliances have a number of site characteristics in common. Most important, perhaps, is that soils supporting both alliances have relatively low concentrations of total nitrogen and phosphorus, and low concentrations of exchangeable potassium, calcium, sodium and magnesium. The characteristics of the P 1and P2 sites are those associated with more highly weathered landforms and soils, from which nutrients have either been leached; or immobilised in aluminium complexes. The differentiation of the Pl and P2 alliances seems to be related to soil aluminium. The Pl alliance is associated with a range of rock types, and soils with significantly higher levels of aluminium than those of

I.A. Neave et al. /Forest Ecology and Management Subgenera:

E.

(C)

Corymbia

(M)

Monocalyptus

(S)

Symphyomyrtus

E.

E. E.

I E.

t t t HIGH

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All

maculata

rainforest

pilularis

SOIL

piperita

FERTILITY

(11)

(C)

(17)

E.pellita

(10)

globoidea

(12)

I (Ml I(S)

(MJ

(12)

(28) species

gummifera

79

1(Ml I(C)

(11)

GRADIENT

LOW

1

Fig. 4. Fertility range of the rainforest communities and the major eucalypt species as defined by vector 1 of the A horizon nutrient ordination. The number of sites on which a species (with an importance value greater than 10) occurred is given in parentheses. Only species which occurred on ten or more sites are shown. See text for derivation of this figure.

the P2 (E. pipe&-heath) alliance. Nutrients may have been substantially leached from the P2 alliance soils which are derived mainly from a single sandstone rock. The Rl (temperate rainforest) and R2 (ecotonal wet sclerophyll-rainforest ) alliances and the S2 (upper slope E. maculatu) alliance all occur on soils of relatively high fertility. Their characteristics suggest more active soil-forming processesthan those of the P 1 and P2 alliances, and hence greater rates of nutrient cycling. The pure rainforest community (Rl ) appears to have a distinct competitive advantage where both nutrients and water are in good supply, that is deep soils associated with Permian parent material, and closeto drainage lines and surface water. The R2 and S2 alliances are found on soils derived from Ordovician parent material-with good drainage, a moderate depth to the C horizon, and steep slopes within steep topography. Another factor which may help differentiate the Rl and R2 communities is aluminium-which is lower in the soils of R 1 than R2 communities. The capacity of soils to supply important nutrients may be reflected in the relationship between aluminium and total exchangeable bases (Al :TEB ratios), given that aluminium is known to form insoluble complexes with nutrients essential for plant growth (Wild, 1961; McCall, 1969). Hence, accessto, and uptake of potassium, calcium, sodium, magnesium and other nutrients, may be greater in the soils of the RI

and S2 group of communities than it is for the R2, PI and P2 groups. The high aluminium levels and high Al :TEB ratios in the R2 soils are surprising. While there are also high levels of phosphorus, nitrogen, potassium and other bases, the chemistry of these soils warrants further study. The basket of communities forming ecotones between E. piperita and E. maculata sites (the E 1 group ) are generally found on soils of moderate fertility which are less welldrained than those supporting the R2 and S2 alliances. They also have a low percentage of gravel and a depth to a C horizon which is generally intermediate between that associated with the E. piperita and E. maculutu communities. The Sl (moderate quality E. maculata) alliance occurs on siteswith few distinctive attributes. The sites tend to be of moderate fertility with steep to undulating terrain and moderate slopes. Individual species have defined ranges along the soil fertility gradient-as established by vector 1 of the A horizon nutrient ordination. Eucalyptus maculata has a wide environmental amplitude. At the lower end of its fertility range, its competitive ability is likely to be weaker, so that communities consisting entirely of E. gummifera (bloodwood group of Corymbia) and a number of Monocalyptus species (mainly E. piperita, E. globoidea and E. pilularis) form a mosaic with E. maculutu communities throughout the forest.

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While variations in soil fertility may be primarily responsible for broader vegetation patterns in this way, variations in soil physical properties can also affect the distributions of individual species through the way they influence accessto water and nutrients. For example, at the lower end of its soil fertility range, E. maculata may be able to maintain itself in the community where other environmental factors enhance its competitive advantage, such as periodically dry soils or soils of higher bulk density (Neave, 1987). The distribution of E. maculata on Kioloa State Forest may reflect its strong competitive ability on moderately fertile but dry sites.On soils derived from Ordovician parent material, most E. maculuta communities tend to occur on steeper, upper slopes where the gravel content is relatively high and the depth to a C horizon or parent rock is relatively shallow. Eucalyptus macdatu may maintain a strong competitive advantage on such sites becauseit will produce relatively more root biomass at depth under drying soil conditions, than other south coast species (Neave, 1987). It develops a strong main taproot enabling it to explore fissures and cracks in underlying rock (J.R. Bartle, personal communication, 1986), and can extend its roots deeply into heavy soils (Forestry Commission of N.S.W., 1985). Thus the distribution of E. maculutu may be extended on soils of low to moderate fertility where it has greater accessto water than species of the E. piperita community which might otherwise replace it. This may be the reason that the Sl (moderate quality E. muculutu) alliance failed to form distinctive clusters of plots within any ordination, that is, it occurs on environmentaliy diverse sites.

We are grateful to the Forestry Commission of New South Wales for permission to work in the study area. The study was carried out while the senior author was in receipt of a Commonwealth Postgraduate Research Award.

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