Abstract

Resprouting in the oil mallee, Eucalyptus kochii Maiden & Blakely subsp. plenissima Gardner (Brooker), involves generation of new shoots from preformed meristematic foci on the lignotuber. Numbers of such foci escalated from 200 per lignotuber in trees aged 1 year to 3000 on 4‐ to 5‐year‐old trees. Removal of shoot biomass by decapitation 5 cm above ground in summer (February) or spring (October) resulted in initiation of 140–170 new shoots, but approx. 400 shoots were induced to form if crops of new shoots were successively removed until sprouting ceased and rootstocks senesced. Initially, the new shoot biomass of regenerating coppices increased slowly and the root biomass failed to increase appreciably until 1·7–2·5 years after cutting. Newly cut trees showed loss of fine root biomass, and structural roots failed to secondarily thicken to the extent shown by uncut trees. After 2 years, the biomass of shoots of coppiced plants was only one‐third that of uncut control trees and shoot : root dry mass ratios of coppiced plants were still low (1·5–2·0) compared with those of the controls (average ratio of 3·1). Spring cutting promoted quicker and greater biomass recovery than summer cutting. Starch in below‐ground biomass fell quickly following decapitation and remained low for a 12–18 month period. Utilization of starch reserves in naturally regenerating coppices was estimated to provide only a small proportion of the dry matter accumulated in new shoots. Results are discussed in relation to their impact on coppicing ability of the species under natural conditions or when successively coppiced for shoot biomass production.

Received: 10 December 2001; Returned for revision: 31 January 2002; Accepted: 18 April 2002

INTRODUCTION

The ability of herbaceous and woody species to generate new shoots from older basal regions of their shoots is well displayed throughout the plant kingdom and is prominent amongst both shrub and tree components of temperate ecosystems (Blake, 1983; Bell et al., 1984; Del Tredici, 2001). Plants with this ability are commonly referred to as ‘sprouter’, ‘resprouter’ or ‘coppicing’ species. They collectively exhibit a broad range of morphological and physiological characteristics conducive to rapid regeneration of new shoots. In most cases, resprouting is initiated only after part or all of the original shoot system has been damaged, stressed or killed by natural agencies, or following deliberate removal of shoot biomass by man in harvesting for fodder, timber, paper pulp, firewood or biomass for generation of electricity.

Regardless of life form and sprouting morphology, early growth of shoot sprouts is associated with some degree of mobilization of previously accumulated reserves of nutrients, starch, sugars and other soluble and insoluble energy reserves (Woods et al., 1959; Zimmerman, 1971; Canadell and López‐Soria, 1998; Garcia et al., 2001). Where comparisons have been made between cohabiting groups of shrubby species of resprouting capacity (sprouters) or those killed by fire (obligate seeders) within Western Australian fire‐prone ecosystems, root reserves of starch occur in consistently greater amount in the sprouters (Pate et al., 1990; Bell et al., 1996). Sprouters are also typically slow growing, slow to commence reproduction and much longer lived than counterpart obligate seeders (Bell et al., 1984).

‘Mallee’ eucalypts are characterized by multiple woody stems arising from an underground lignotuber (Kerr, 1925; James, 1984). The latter houses a large store of potential bud‐forming sites carrying the capacity for rapid regeneration of a canopy after decapitation. A lignotuber typically contains several thousand of such ‘meristematic foci’ (Noble, 2001), each of which is capable of producing several individual shoots (Noble, 1989; Burrows, 2000, 2002). Opinions differ as to whether the lignotuber is also important as a major storage site of non‐structural carbohydrate reserves (Carrodus and Blake, 1970; Bamber and Mullette, 1978; Del Tredici, 2001; Noble, 2001).

Mallees are very long lived, with some species (e.g. the Meelup mallee, Eucalyptus phylacis) reaching ages possibly exceeding 6000 years (Rosetto et al., 1999). With the death of central parts and peripheral fragmentation of the plate‐like lignotuber, close groupings of genetically identical individuals may be formed around a single parent tree. Such clones are likely to have experienced numerous cycles of shoot destruction and replacement and accordingly carry a continued capacity to implement coppicing processes at fairly frequent intervals during their life (Mullette, 1978; Tyson et al., 1998; Rosetto et al., 1999; Noble, 2001).

Regularly coppiced plantings of mallee eucalypts are being trialled in the Western Australian wheatbelt for the generation of bio‐electricity, extraction of essential leaf oils and production of activated carbon from shoot biomass (Enecon Pty Ltd, 2001). Suitable ‘oil mallee’ species such as E. kochii subsp. plenissima, E. horistes and E. loxophleba subsp. lissophloia (Wildy et al., 2000b) are typically established in narrow belts across conventional cereal and grazing land where they benefit from the ‘edge effect’ of greater access to soil moisture, nutrients and light than would occur if they were competing in plantation layout. The incorporation of a deep‐rooted, summer‐active component into farming systems such as one based on oil mallee is also viewed as being importance in restoring the hydrological balance in situations where continued use of inadequately transpiring annual crop and pasture species has led to dangerous rises in water tables and resulting dryland salinization of cleared landscapes (State Salinity Council, 2000). High yielding biomass production on a continuous basis is important for the economic viability of an integrated bio‐energy production industry (Enecon Pty Ltd, 2001).

Rates of regenerative growth of coppicing species are generally influenced by both the original vigour of the uncut plant (Jacobs, 1955; Hillis and Brown, 1984; Sims et al., 1999) and the season of cutting. In Mediterranean climates, it is well established that autumn cuts result in poorer eucalypt regeneration than winter or early spring cuts (Milthorpe et al., 1994; Wirthensohn and Sedgley, 1998; Wildy et al., 2000b; Noble, 2001). As described generally for the closely‐related Melaleuca genus (Murtagh, 1996), the optimal cutting time in temperate mallee eucalypts is one in which production of new shoot biomass coincides with the natural seasonal flush growth of intact plants of the species. In Mediterranean climates, this generally corresponds to the late spring and early summer period when temperatures are warm and soil moisture has been replenished by winter rains (Noble, 1989; Specht, 1996; Wildy et al., 2000a).

Previous cutting history also appears to affect productivity and survival. When first cut at ages of 1–3 years and then repeatedly on 1–2 year rotations, plantation‐grown mallees can exhibit progressively reduced yields (Milthorpe et al., 1998) and increased mortality (Eastham et al., 1993; Wildy et al., 2000b). This parallels what has been experienced in non‐mallee eucalypts grown on 6–10 year rotations (Reidacker, 1973; Schönau, 1991; Barros and Novais, 1996; Nambiar, 1999) and in other temperate woody species (Ceulemans and Deraedt, 1999; Mitchell et al., 1999; Hytönen and Issakainen, 2001). Early research attempted to explain such declines through depletion of stored carbohydrate and nutrient reserves, but this may be only part of a complex set of interacting factors that are not well understood (Chapin et al., 1990; Sennerby‐Forsse et al., 1992). It is possible that, in part, too‐frequent cutting of slowly regenerating plants may not allow below‐ground reserves to be replenished. Similarly, root systems may cease to grow or partly senesce while regenerating plants are preferentially directing photosynthates to new shoots (Hodgkinson and Becking, 1977; Steinbeck and Nwoboshi, 1980; Dickmann et al., 1996). In addition, a disrupted shoot : root ratio may cause a large proportional burden in root respiration relative to meagre photosynthate returns from coppiced shoots (Noble, 2001), and regularly cut stumps are also likely to be more susceptible to disease (Christersson et al., 1992).

To further understand the coppicing ability of an oil mallee species [E. kochii Maiden & Blakely subsp. plenissima Gardner (Brooker)], which has been widely planted over the past 8 years in the drier zones of the wheatbelt of south‐west Western Australia, we first examined the morphology of lignotuber development in planted stands differing in age. Then, using a 4–5‐year‐old stand for detailed investigation, we studied coppicing responses in terms of recovery of shoot biomass, changes in root biomass and quantification of below‐ground starch contents under contrasting cutting regimes in comparison with uncut trees. The overall aim was to describe the general biology of coppicing in the species and thereby provide a basis for the design of management practices to enable continual production of shoot biomass from short‐rotation coppicing stands.

MATERIALS AND METHODS

Principal site for studying coppicing under different cutting regimes

At the principal trial site (30°09′S, 117°12′E) (Fig. 1A and B) near Kalannie, in the central wheatbelt of Western Australia, alley plantings of E. kochii subsp. plenissima had been established as seedlings in July 1994 immediately after ripping and scalping of topsoil to remove weeds. Fertilizer was not applied since the soil was relatively fertile through continuous use of fertilized crops of wheat and nitrogen‐fixing lupins (Lupinus spp.). Each belt of trees consisted of two rows 2 m apart, with an average of 1·8 m spacings between trees within rows. The average alley width available for crop/pasture between belts of trees was 90 m. Planting density was 2820 trees per hectare in that part of the land surface devoted to trees, or the equivalent of 121 trees ha–1 across the whole ecosystem at the time of planting. Since only 85 % of seedlings survived the dry year of establishment (238 mm rainfall in 1994), the effective density at the start of the study was reduced to 103 trees ha–1. Measurements were made between February 1999 (when trees were 4·6 years old) and October 2001 (trees aged 7·2 years).

The extra‐dry Mediterranean climate (Beard, 1984) of the Kalannie region of the wheatbelt (Table 1) typically features hot, dry summers (December–February) and cool, wet winters (June–August). The long‐term (74 year) annual average rainfall at Kalannie is 319 mm (Bureau of Meteorology, Australia). However, 1999 was an exceptionally wet year (504 mm falling at the principal study site) and unusually heavy summer rain fell in 1999–2000 and again in 2000–2001 (see Table 1). The soil at the principal study site was a gradational yellow sand (Gn 2·21: Northcote, 1979) overlying a siliceous hardpan of ‘silcrete’ at varying (1–8 m) depths across the study site. Roots of planted and native mallees in the region were found to have penetrated through weak zones in the silcrete, thereby possibly gaining access to groundwater below this layer.

Lignotuber development and increases in potential resprouting capacity with age

Lignotuber development was studied in February 1999 by random sampling across a range of differently aged (0·6–4·6 years) plantings of as yet uncut saplings selected in the Kalannie area. All sites involved deep yellow sands similar to those at the principal site. Five trees of each age class were excavated, including one set of 4·6‐year‐old trees from the principal study site referred to above. Residual soil and the rough outer bark around the shoot : root junction were removed, thus enabling counts to be made of the number and size (outer diameter) of the distinct swellings present on the lignotuber and adjacent lower shoots (Fig. 1C–E). All bark down to cambium level was peeled off the lignotuber, surrounding stem and upper root to expose the closely spaced groups of pimple‐like ‘meristematic foci’ (approx. 1 mm diameter) typically encountered within each swollen region on or in the vicinity of the lignotuber (Fig. 1F).

Decapitation and shading regimes

At the principal study site, a random series of 100 m long quadrats of tree belt was selected (Fig. 1A and B show the junction of coppicing and uncut trees) and stems of all trees were cut with a chainsaw to 5 cm above ground level. The quadrats designated for cutting were sited within a fully randomized block design comprising 16 quadrats cut in late summer (February), a further 16 cut the following spring (October) of 1999 and a matching set of 16 quadrats of uncut saplings incorporated as controls. Following initial cutting, mortality was only 2·0 and 0·5 % for trees cut in February and October, respectively.

In each of the 16 coppice quadrats used for the two seasons of cutting, most trees were allowed to regenerate naturally for the duration of the study (CN treatment, Table 2), while two in each quadrat were subjected to additional decapitations on a 3‐monthly basis (CR treatment). To further test the resprouting ability of rootstocks, another three tree stumps (CS treatment) in each quadrat were left to regenerate while caged in multiple layered shade cloth (permitting penetration of approx. 25 % of ambient light and designed to maintain young shoots at or near their CO2 compensation point), and, finally, two trees were subjected to both shading and repeated 3‐monthly decapitation (CSR treatment, Table 2).

Counts of resprouting shoots

Numbers of shoot sprouts [equivalent to the fascicles of Noble (2001)] arising from lignotubers were counted at 3‐monthly intervals after decapitation (see Table 2). Counting was carried out non‐destructively for CN plants while for CR and CSR plants, shoots were counted at the time of each 3‐monthly decapitation.

Measurement of shoot and root biomass

Shoot biomass of control uncut trees and trees regenerating naturally from cutting in February or October 1999 (CN) was measured at ten sampling dates between February 1999 and February 2001 (Table 2). At each sampling date, 42 randomly selected trees of these treatments were cut to 5 cm above ground level and weighed fresh in the field. Sub‐samples of leaf, twig and larger stems were collected, weighed fresh and then oven‐dried at 70 °C to constant weight for fresh : dry weight conversions.

For CR and CSR trees, shoot biomass produced after initial decapitation was measured at each further 3‐monthly decapitation event. Shoot biomass of CS plants was measured 1 year after decapitation. Shoots were oven‐dried at 70 °C to constant weight before weighing.

Below‐ground biomass was excavated to assess root and lignotuber biomass using a bobcat which progressively transferred soil plus root material onto a mobile mechanical sifting device. The readily recognizable lignotuber was removed with a chainsaw at the point of root proliferation and weighed fresh. Root biomass was separated visually into lateral (flaking bark, straight) and sinker (non‐shedding bark, contorted shape) roots. These were then weighed fresh, fed through a garden chipper, and a small sub‐sample frozen immediately pending oven‐drying for fresh : dry weight conversions and starch analysis (see below). A section taken through the lignotuber using a chainsaw was also frozen for starch analysis and fresh : dry weight conversions. For control saplings and CN plants, the average ratio of lignotuber weight : rest‐of‐shoot weight for each treatment at each root harvest was used to estimate total shoot biomass (i.e. shoot including lignotuber) of the corresponding 42 trees from a treatment and sampling date (described above).

Root and lignotuber biomass was harvested for control saplings and CN trees from ten plants per treatment at each sampling date and at 2–5 month intervals during the study period. Root biomass of CR, CS and CSR plants was sampled for ten plants from each treatment at one final sampling date 12 months after the initial decapitation of the plants (February or October 2000) (Table 2).

The regularly employed root harvesting procedure involved a ‘standard’ excavation 1 m deep and extending 1 m out from the tree stump into the alley (with no trees) and similarly out to the midpoint between neighbouring trees (Fig. 2). To estimate the proportions of lateral and sinker root biomass not likely to be recovered by the ‘standard’ procedure, selected trees were subjected to a series of more ‘extensive’ excavations executed in 1 m stages to a depth of 4 m and 5 m out into alleys (see Fig. 2). These were carried out on three trees (including both uncut and coppiced plants) at five sampling occasions throughout the study period. Such excavations were found to harvest virtually all lateral root biomass and all but the lowermost parts of deeply penetrating sinker roots. By following the attenuation in recovery of sinker root biomass for each successive 1 m level of excavation, it was estimated that unrecovered root biomass extending below the 4 m depth limit would be equivalent to only 4–8 % of the total root biomass of trees of the age class under study. Comparisons of data from these ‘standard’ and occasional ‘extensive’ excavations indicated that the standard (incomplete) excavation would typically recover 80 % of the lateral root biomass and 50 % of that of sinker roots.

Shoot : root dry weight ratios were determined for the excavated CN and intact trees at each sampling date. Throughout the text, the term ‘root’ refers to the full extent of the root system, excluding lignotuber biomass, while ‘shoot’ includes both the aerial canopy removed in a normal harvest procedure (leaf + stem) plus the shoot stump remaining above ground and the lignotuber. Conversely, the term ‘below‐ground biomass’ refers to the calculated full extent of roots + lignotuber (i.e. that remaining after shoot harvest).

Study of the effect of coppicing on secondary growth of roots

An anatomically based technique for evaluating possible inhibitory effects of cutting on root growth of coppiced (CN trees) compared with uncut trees was initiated 3 months after setting up the summer or spring coppice treatments (May 1999 or January 2000, respectively). It involved non‐destructive exposure of one or two major sinker and lateral roots of each of 16 randomly selected coppicing or uncut trees and removal of a small 0·5 cm2 window of bark down to the cambium to expose the outer layer of xylem. The portion removed in each case involved less than 12 % of the root circumference and was therefore unlikely to have a major deleterious effect on subsequent secondary growth of the root. Treated roots were re‐covered with soil and left for 21 months (until February or October 2001). A 10 cm length of root including the ‘window’ was then harvested and transversely sectioned to assess the extent of increase in root stele diameter in undamaged radial sections of the root to that of the non‐growing exposed portion underlying the window. Comparative estimates were thus made of the proportional extents to which secondary growth of roots of coppicing trees had been reduced over the 21‐month period relative to that exhibited by uncut trees.

Starch concentrations and total starch reserves of below‐ground biomass

For each tree excavated for root biomass between July 1999 and February 2001, starch concentrations were determined separately for lignotubers, lateral roots and sinker roots. Dried sub‐samples of material of each plant part were finely ground to pass through a final mesh width of 0·5 mm. Starch was extracted from a 0·1 g sub‐sample using the perchloric acid method (Pucher et al., 1948) and then assayed using the phenol method (Dubois et al., 1956; Pate et al., 1990) giving reproducible recoveries of starch, including both amylose and amylopectin. Starch concentrations in roots and lignotubers are given on a weight for weight basis (g starch per g organ dry matter) and are expressed as percentages.

Since determinations of starch in root biomass collected from standard excavations required extrapolations based on more extensive excavations, it was necessary to test whether the starch concentration in outer‐lying root biomass differed appreciably from that obtained from more proximally located roots recovered in standard excavations. Three uncut saplings and coppicing CN trees from both seasons of initial cutting were sampled in this way in July 2000 and February 2001. The resulting data (Table 3) showed general trends towards an increased concentration of starch in root biomass with distance out along a lateral or down a sinker root (e.g. see Kolb and McCormick, 1991). An appropriate correction factor was therefore applied when scaling up starch contents of both lateral and sinker roots from a standard excavation to provide a more accurate assessment of total starch concentration (and consequently total starch storage) within the entire below‐ground biomass of each tree investigated.

RESULTS

Development of lignotuber and resprouting potential with age

Distinct opposing and usually paired sets of swellings developed at, or above, the cotyledonary node of juvenile trees during their first season of growth (Fig. 1C). Further swellings then arose at various positions close to the initial pair (Fig. 1D and E) until some 15–20 such structures were typically present on rootstocks of second and third year trees (Fig. 3A). As the swellings enlarged further, they fused laterally with others to form an aggregate collar‐like lignotuber of greater diameter than that of adjacent parts of stem and root (Fig. 1E), and the mean number of distinctly separate swellings began to decrease (Fig. 3A). Remnant rootstocks of very old trees of E. kochii removed during clearing of virgin bush for agriculture possessed lignotubers of truly massive proportions, with a complex complement of thick lateral and tap roots arising at various positions below the lignotuber (Fig. 1G).

Counts of meristematic bud foci on debarked stumps (Fig. 1F) showed 2‐year‐old trees to possess approx. 500 foci per lignotuber, rising to 1000 in 3‐year‐old trees and then to 3000 per lignotuber for 5‐year‐old trees (Fig. 3A). When cut at age 4·6 (February cutting) or 5·2 (October cutting) years, stumps coppicing unhindered (CN treatment) showed similar intensities of coppice shoot production, viz. 140–170 per lignotuber (Fig. 3B).

Resprouting of repeatedly decapitated and/or shaded stumps (CR, CS and CSR treatments)

Repeated 3‐monthly shoot removal after initial cuts in either February or October 1999 [treatments CR (repeated decapitation) and CSR (shading + repeated decapitation); see Table 2] resulted in eventual death of the plants. Each successive regeneration event released between 40 and 170 accessory shoots per plant (Fig. 4A) to give cumulative numbers over the four regeneration intervals of approx. 400 shoots per tree. There were no significant differences in shoot numbers produced by matching pairs of shaded (CSR) and unshaded (CR) trees at any sampling date, thus data for shaded and unshaded trees were combined. Significantly more shoots (P < 0·05) were produced at the initial resprouting event than in the final decapitation event for trees cut originally either in February or October. The new shoot biomass produced at successive harvests for the same treatments (Fig. 4B) showed greatest amounts of coppice shoot biomass produced during the natural period of shoot extension of the species, regardless of the number of previous coppice crops that had been removed.

Table 4 summarizes data for the end of the 1‐year period following initial decapitation of saplings in either February or October. Shaded trees (CS and CSR together) produced significantly less new shoot biomass over this period (0·11–0·29 kg d. wt per plant) than repeatedly cut, unshaded plants (CR) (0·27–0·47 kg d. wt per plant) (P < 0·001).

Shoot biomass of uncut trees and CN coppice from a summer or spring cut

Coppice shoots recovering naturally from a single decapitation event in February or the following October (CN) showed slow recovery in the first year after cutting, and this was especially apparent for plants cut in February (Fig. 5A). After 2·0 years of coppice regrowth, February‐cut plants had restored only 53 % of their original shoot biomass, compared with 76 % for October‐cut trees (Fig. 5A). Increments in shoot biomass production over the 2·7‐year study period were greatest for uncut saplings ageing from 4·6–7·2 years (20 kg d. wt per plant) (Fig. 5A).

Excavations of root biomass

Excavations showed that all trees had developed a number of deeply penetrating sinker roots, originating directly below the stem (see Fig. 1E), and also from shallow lateral roots that radiated out to 5 m at most from the stem base. Most trees also possessed horizontally extending lateral roots that developed from sinker roots at depths down to 2–3 m. Lignotubers were calculated to comprise on average 17 % of total below‐ground biomass compared with 41 % for lateral roots and 42 % for sinker roots.

Observations on excavated root systems of all decapitated plants showed that large amounts of fine roots (<2 mm) had senesced. Root biomass of plants subjected to repeated decapitation and/or shading was consistently lower than the original root biomass measured at the time of cutting (Table 4). Occasionally, the root system of these plants had also been attacked by fungi and borer insects. Net increases in root biomass of CN trees ceased over a period of 1·7 years for October‐cut trees and 2·5 years for February‐cut trees (Fig. 5B). By contrast, root biomass increased three‐fold for uncut saplings over the study period (Fig. 5B). For the treatments sampled temporally, root biomass varied significantly with time (P < 0·001, uncut saplings; P = 0·001, February‐cut CN trees; P = 0·046, October‐cut CN trees).

Root secondary thickening following decapitation

As shown in Table 5, marked depressions in secondary growth of major roots of cut (CN) plants relative to uncut plants were also recorded for roots that had been partly debarked and left to grow for 21 months. Combining data for lateral and sinker roots (separately for the two 21 month periods) showed significantly greater increases (P < 0·001 for both) in root secondary thickening in uncut control trees (75–130 %) compared with February‐cut trees (14–26 %) or October‐cut trees (23–30 %).

Shoot : root ratios

Shoot : root dry matter ratios for uncut saplings ranged from 2·5 to 3·5 (Fig. 5C). This variation resulted from the different phenologies of root and shoot growth (e.g. Specht, 1996). In contrast, shoot : root dry matter ratios of decapi tated CN trees increased continuously until July 2001, but failed to reach the values of uncut plants.

Starch concentrations and below‐ground starch reserves

Concentrations of starch measured in regularly excavated portions of below‐ground biomass were significantly higher in uncut saplings (mean of all starch samples 2·9 %) than in coppices regenerating unhindered from a single decapitation in either February or October (1·4 and 1·7 %, respectively; P < 0·001). Lignotubers had significantly lower (P < 0·05) concentrations of starch (generally less than 1 %) than either lateral or sinker roots in all of the above treatments (Table 6).

Combining dry weight values for the full extent of below‐ground biomass with the starch concentration data above (appropriately corrected for higher starch concentrations in outlying roots as shown in Table 3) gave calculated values for mean below‐ground starch concentrations in the range of 2–6 % of dry mass for uncut saplings and 1–5 % for regenerating CN coppice (Fig. 6A). Below‐ground starch concentrations varied significantly with season (P < 0·001 combining CN and uncut treatments), with uncut saplings showing peak starch concentrations just prior to the period of main shoot extension growth in spring of 1999 and 2000, followed by a decline in starch content in summer. Fluctuations in the total below‐ground starch reserve pools (Fig. 6B) followed similar patterns, except that the smaller root biomass of coppiced plants (see Fig. 5B) resulted in total starch reserves in below‐ground parts remaining significantly lower (P < 0·05) than those of uncut saplings until February 2001. October‐cut trees possessed a significantly greater total below‐ground starch store than the February‐cut trees (P = 0·003) despite starch concentrations not varying significantly between the two (see Fig. 6A).

DISCUSSION

Lignotuber development in the mallee eucalypt, Eucalyptus kochii subsp. plenissima, showed a similar pattern to that recorded for a wide range of eucalypts (Chattaway, 1958; Carrodus and Blake, 1970; Graham et al., 1998). Meristematic foci from which shoot buds can arise increased markedly in number as lignotubers aged, with several hundred present on 2‐year‐old seedlings and over 1000 on 4‐year‐old saplings. Once the shoot system of 4‐ to 5‐year‐old E. kochii was removed, in excess of 100 new shoots developed from each lignotuber. Subsequently, a large proportion of the smaller of these new shoots senesced within the first year (Fig. 3B). With further attrition over subsequent years, coppice shoot numbers would be expected to reduce much further until only 12 or so shoots remain (see scheme of Noble, 1989), as is typically observed during resprouting of naturally occurring, fire‐decapitated populations of the species at sites close to the plantings at Kalannie.

A greater number of meristematic foci could be induced to commence growth if each crop of new growth was removed (e.g. see Zammit, 1988; Canadell and López‐Soria, 1998). However, the 400 shoots produced by such repeatedly decapitated plants was far fewer than the potential 3000 or so discernible on 5‐year‐old lignotubers. Regardless of the fact that lignotuber size and potential bud number would be unlikely to increase further for more than a year after cutting (Table 4), the large store of remaining foci available for new growth would still be expected to allow coppicing to take place even if young trees were repeatedly cut on rotations of less than 1 year.

Lignotubers of E. kochii appear less important as starch storage organs than they are as providers of replacement shoot meristems after decapitation (c.f. Bamber and Mullette, 1978; Del Tredici, 2001). Lignotubers in this study possessed consistently lower starch concentrations than roots (see Table 6), which may be attributed to a lack of suitable storage tissue (Carrodus and Blake, 1970; Noble, 2001). Combined with the fact that the lignotuber contributed on average only 17 % of the below‐ground biomass, this organ would have contributed just 5–10 % of the starch reserves of the recently decapitated E. kochii plants in this study.

The variations in above‐ground coppicing performance between trees of E. kochii from contrasting decapitation treatments (see Table 4) did not appear to be explained by the size of the lignotuber reserve of meristematic foci nor by the number of shoots emerging after each decapitation event. For example, similar numbers of shoots were produced after decapitation treatments in February or October (Fig. 3B), but trees of the latter treatment restored their new canopies more rapidly (Table 4). Similarly, despite a slowly declining number of shoots produced successively by repeatedly decapitated (unshaded) plants following an initial cutting in February, the biomass of new shoots produced after each harvest was actually significantly greater at the final decapitation event. Thus, once initiated, shoot growth was clearly more related to climatic conditions than to the actual number of sprouts produced in this case. Indeed, poor correlations between sprout number and survival or productivity are generally found in coppicing tree species (Sennerby‐Forsse et al., 1992).

This study clearly showed that removal of shoots resulted in greatly inhibited production and secondary thickening of root biomass during the first 1·7–2·5 years of shoot regeneration, compared with continual unimpeded increases in root biomass of uncut trees. In other woody species, reports of reductions in root growth following shoot removal are common (Kny, 1894; Hodgkinson and Becking, 1977; Schroth and Zech, 1995; Crombie, 1997; Ruess et al., 1998) but not universal (Dickmann et al., 1996; Kosola et al., 2001).

Interpreting the literature pertaining to the wide variety of root responses following shoot removal in other species, and evidence from this study, suggest that E. kochii sheds fine root biomass while the superstructure of the root system is retained. Soon after reformation of the canopy, fine roots may start being produced again in balance with the regenerating shoot, but further investment in structural roots or lignotubers remains slow until the functional shoot : root ratio nears restoration (Reidacker, 1973; Hodgkinson and Becking, 1977; Steinbeck and Nwoboshi, 1980; Reis and Kimmins, 1986; Kummerow et al., 1990; Fownes and Anderson, 1991; Dickmann and Pregitzer, 1992; Schroth, 1995; Ruess et al., 1998; Farrar and Jones, 2000). Indeed, the apparent slowing of the dry mass‐based shoot : root ratio at a level below that of uncut plants towards the end of this study (see Fig. 5C) may belie a functionally restored shoot : root ratio (Thornley, 1977; Wilson, 1988; Farrar and Jones, 2000) given the approx. 50 % greater photosynthetic activity of coppice shoots measured over the study period (D. T. Wildy and J. S. Pate, unpubl. res.).

Root respiration would, of course, place a large burden on the reserves of recently decapitated trees, especially in species with naturally low shoot : root ratios such as E. kochii. While the carbon cost of root systems of coppiced E. kochii plants showing reduced rates of fine root production could be lower than that of an actively expanding root system (e.g. see Nobel et al., 1992; Ryan et al., 1996; Keith et al., 1997), it is possible that below‐ground maintenance would still comprise a sink of equal or greater magnitude to that of the new shoot (Smith et al., 1992; Farrar and Jones, 2000; Noble, 2001). Much of the observed loss of starch from root systems might then be committed to respiration rather than contributing to dry matter gain of new coppice shoots. However, it is possible that translocation of organic compounds and carbohydrates, such as sugars and wall‐based polysaccharides, from senescing roots might partially offset this cost. Since these potential sources and sinks of carbon were not examined in this study, it is not possible to evaluate their impact on the early carbon economy of a coppicing tree. Nevertheless, as suggested by Noble (2001), this potentially large respiratory tax on coppicing trees may be a major factor in the relatively slow regeneration of E. kochii after coppicing, particularly when canopy restoration coincides with winter months of low photosynthetically active radiation.

Greater below‐ground starch concentrations available for coppicing in spring‐cut plants (Fig. 6A) could, in part, explain the superior coppice shoot production of October‐cut trees (see Cremer, 1972). However, most evidence points to only a small contribution by starch reserves to the development of new canopies in E. kochii (Deans and Ford, 1986; Garcia et al., 2001). For example, the minimal difference in new shoot growth between shaded and unshaded trees after repeated decapitation in winter months might suggest a similar role for starch in the development of shoots at this time in both treatments. This would indicate that the magnitude of such a contribution is less than 40 g per plant (Fig. 4B), though this may also be confounded by generally slow growth in winter months. In the case of naturally regenerating plants, the 0·1–0·2 kg lost from the below‐ground starch stores would probably only account for a small fraction of the 0·9–2·5 kg of shoot biomass produced after 1 year if starch was the only source of carbon for both root respiration and development of a new shoot. Possible further evidence for the importance of starch only in the very early stages of canopy regeneration was the rapid decline of root starch contents after decapitation followed by a constant low level (Fig. 6).

Thus, the importance of such reserves in the decline of poorly managed coppice stands is debatable in E. kochii (c.f. Woods et al., 1959; Canadell and López‐Soria, 1998; Latt et al., 2000). Although the final low starch levels could constitute a simple explanation for the eventual death of the repeatedly harvested and/or shaded trees in this study, we believe that in this case it is more probable that these are symptoms associated with the general decline of these plants (Taylor et al., 1982; Chapin et al., 1990; Kosola et al., 2001). For example, the analyses showed that a significant fraction of starch remained in plants just prior to their death (Table 4), and, though low, these were only marginally below values shown by naturally regenerating coppice (Fig. 6A) (see Chapin et al., 1990). It was also apparent that such presumed low levels of starch in February‐cut plants subjected to their fourth consecutive 3‐monthly shoot removal (Fig. 4A) did not stop these trees producing their largest coppice crop, coinciding with the regular season for shoot growth. Finally, despite starch concentrations of naturally regenerating trees having returned to those of uncut trees by 1–1·5 years after decapitation (Fig. 6A), other studies on the same species still recorded declining yields and increasing mortality when harvested repeatedly at similar, or slightly longer, intervals (Eastham et al., 1993; Milthorpe et al., 1998).

The results from this study suggest that management of E. kochii for long‐term productivity over repeated decapitation events would firstly need to take account of the greater biomass produced by less frequently cut plants (see Table 4). In addition, cutting on 2‐ or 3‐year intervals, or more (depending on season), may avoid gradual rootstock decline by allowing active secondary growth between harvests.

ACKNOWLEDGEMENTS

We thank Lesley Sefcik for field assistance and carrying out starch analyses, the many volunteers who further assisted in field data collection, I. and R. Stanley for the use of the site, and Kevin Smith and Max Waters for building the mobile mechanical soil sifting device. Lars Christersson and Jim Noble provided valuable comments on an earlier version of the manuscript. The research was funded primarily by the Rural Industries Research and Development Corporation, Australia, and also by the Department of Conservation and Land Management, Western Australia, and the Land Institute, Kansas, USA.

Fig. 1. A, General view of study site showing hedges of decapitated (arrows) and intact 4·6‐year‐old Eucalyptus kochii trees at the time of first cutting in February 1999. B, Close‐up of adjacent uncut and coppicing trees in February 2001 (note 3 m high marking pole dividing quadrats). C, Six‐month‐old seedling showing swellings on and above hypocotyl region. D, Older (2·6 year) seedling showing greater enlargement of swellings especially in the hypocotyl region. E, Sapling aged 4·6 years showing fusion of swellings into a lignotuber completely enveloping the lower base of the shoot. F, Surface of cambial face of one of the composite swellings on a lignotuber with bark removed showing ‘pimple‐like’ meristematic foci, any of which can generate new shoots. Bar = 10 mm. G, Remains of lignotuber and lateral and sinker roots of an old E. kochii plant removed during clearing of the land prior to the current study.

Fig. 1. A, General view of study site showing hedges of decapitated (arrows) and intact 4·6‐year‐old Eucalyptus kochii trees at the time of first cutting in February 1999. B, Close‐up of adjacent uncut and coppicing trees in February 2001 (note 3 m high marking pole dividing quadrats). C, Six‐month‐old seedling showing swellings on and above hypocotyl region. D, Older (2·6 year) seedling showing greater enlargement of swellings especially in the hypocotyl region. E, Sapling aged 4·6 years showing fusion of swellings into a lignotuber completely enveloping the lower base of the shoot. F, Surface of cambial face of one of the composite swellings on a lignotuber with bark removed showing ‘pimple‐like’ meristematic foci, any of which can generate new shoots. Bar = 10 mm. G, Remains of lignotuber and lateral and sinker roots of an old E. kochii plant removed during clearing of the land prior to the current study.

Fig. 2. Stylized root systems and dimensions of excavations used in sampling root biomass for mallees grown in twin‐row hedges, as shown by an aerial view (A) and a cross‐sectional view through the soil profile (B). The ‘standard’ excavation (bold lines) was 1 m deep and extended from to midpoint between neighbours and 1 m out into the alley (with no trees). Occasional ‘extensive’ excavations (non‐bold lines) allowed regular standard excavations to be scaled‐up to include all root biomass, which included the estimated 4–8 % of deeply penetrating sinkers that were not recovered in the extensive excavation.

Fig. 2. Stylized root systems and dimensions of excavations used in sampling root biomass for mallees grown in twin‐row hedges, as shown by an aerial view (A) and a cross‐sectional view through the soil profile (B). The ‘standard’ excavation (bold lines) was 1 m deep and extended from to midpoint between neighbours and 1 m out into the alley (with no trees). Occasional ‘extensive’ excavations (non‐bold lines) allowed regular standard excavations to be scaled‐up to include all root biomass, which included the estimated 4–8 % of deeply penetrating sinkers that were not recovered in the extensive excavation.

Fig. 3. A, Number of swellings on the hypocotyl region and lower stem of uncut saplings of Eucalyptus kochii of various ages showing an initial increase and then coalescence of the swellings (see Fig. 1C–E) as trees aged, and the overall increase with plant age in the number of meristematic foci (see Fig. 1F) of the lignotuber. B, Number of new shoot sprouts arising from stumps of 4‐ to 5‐year‐old trees decapitated in summer (February 1999) or the following spring (October 1999) (CN treatment). Note that the original complement of shoots was reduced through senescence of smaller shoots. Vertical bars represent 2 s.e.

Fig. 3. A, Number of swellings on the hypocotyl region and lower stem of uncut saplings of Eucalyptus kochii of various ages showing an initial increase and then coalescence of the swellings (see Fig. 1C–E) as trees aged, and the overall increase with plant age in the number of meristematic foci (see Fig. 1F) of the lignotuber. B, Number of new shoot sprouts arising from stumps of 4‐ to 5‐year‐old trees decapitated in summer (February 1999) or the following spring (October 1999) (CN treatment). Note that the original complement of shoots was reduced through senescence of smaller shoots. Vertical bars represent 2 s.e.

Fig. 4. Number of new coppice sprouts (A) and new sprout biomass (B) produced per tree by shaded (diamonds) and non‐shaded (triangles) Eucalyptus kochii stumps subjected to repeated decapitation following initial cutting in February 1999 (closed symbols) or October 1999 (open symbols). Vertical bars represent 2 s.e.

Fig. 4. Number of new coppice sprouts (A) and new sprout biomass (B) produced per tree by shaded (diamonds) and non‐shaded (triangles) Eucalyptus kochii stumps subjected to repeated decapitation following initial cutting in February 1999 (closed symbols) or October 1999 (open symbols). Vertical bars represent 2 s.e.

Fig. 5. Comparisons of shoot biomass (A), root biomass (B) and shoot : root dry weight ratio (C) of 4‐ to 7‐year‐old trees of Eucalyptus kochii left intact (uncut saplings, closed circles) or coppiced (CN treatment) in summer (February 1999 cut, closed squares) or the following spring (October 1999 cut, open squares). Dashed lines indicate time of cutting. Vertical bars represent 2 s.e.

Fig. 5. Comparisons of shoot biomass (A), root biomass (B) and shoot : root dry weight ratio (C) of 4‐ to 7‐year‐old trees of Eucalyptus kochii left intact (uncut saplings, closed circles) or coppiced (CN treatment) in summer (February 1999 cut, closed squares) or the following spring (October 1999 cut, open squares). Dashed lines indicate time of cutting. Vertical bars represent 2 s.e.

Fig. 6. Changes in concentration (A) and total below‐ground reserves (B) of starch in total below‐ground biomass of 4‐ to 7‐year‐old trees of Eucalyptus kochii left intact (uncut saplings, closed circles) or coppiced (CN treatment) in summer (February 1999 cut, closed squares) or the following spring (October 1999 cut, open squares). Dashed lines indicate time of cutting. Vertical bars represent 2 s.e.

Fig. 6. Changes in concentration (A) and total below‐ground reserves (B) of starch in total below‐ground biomass of 4‐ to 7‐year‐old trees of Eucalyptus kochii left intact (uncut saplings, closed circles) or coppiced (CN treatment) in summer (February 1999 cut, closed squares) or the following spring (October 1999 cut, open squares). Dashed lines indicate time of cutting. Vertical bars represent 2 s.e.

Table 1.

Monthly rainfall and temperature data for Kalannie, Western Australia

 
Rainfall (mm)             
 1999 25 113 11 147 49 40 22 29 18 20 26 
 2000 56 156 15 40 19 17 11 
 2001 72 22 24 51 18 19 11 
Long‐term average rainfall (mm) 14 16 24 24 44 57 50 38 19 14 10 
Mean max. daily temp. (°C) 33 33 29 26 21 18 16 17 21 25 29 34 
Mean min. daily temp. (°C) 19 19 16 14 10 13 18 
 
Rainfall (mm)             
 1999 25 113 11 147 49 40 22 29 18 20 26 
 2000 56 156 15 40 19 17 11 
 2001 72 22 24 51 18 19 11 
Long‐term average rainfall (mm) 14 16 24 24 44 57 50 38 19 14 10 
Mean max. daily temp. (°C) 33 33 29 26 21 18 16 17 21 25 29 34 
Mean min. daily temp. (°C) 19 19 16 14 10 13 18 

Rainfall data for 1999–2001 (recorded at the principal trial site) and mean daily temperatures (the average of data recorded at Kalannie between 1999 and 2001) were provided by Agriculture WA. The long‐term (74‐year) average monthly rainfall for Kalannie was supplied by the Bureau of Meteorology, Perth.

Table 2.

Experimentation, general treatment codes, sampling frequency and numbers of replicates in the study of coppicing in Eucalyptus kochii subsp. plenissima at Kalannie, Western Australia

  Measurements    
Code Treatment Shoot biomass Shoot number Below‐ground biomass Below‐ground starch 
 Uncut saplings (control) 2‐ to 5‐monthly (42) – 2‐ to 5‐monthly (10) 2‐ to 5‐monthly (10) 
 Decapitated trees     
CN  No further intervention 2‐ to 5‐monthly (42 × 2 seasons) 3‐monthly (16 × 2 seasons) 2‐ to 5‐monthly (10 × 2 seasons) 2‐ to 5‐monthly (10 × 2 seasons) 
CS  Shading Final (48 × 2 seasons) – Final (10 × 2 seasons) Final (10 × 2 seasons) 
CR  Repeated 3‐monthly         decapitation 3‐monthly (32 × 2 seasons) 3‐monthly (32 × 2 seasons) Final (10 × 2 seasons) Final (10 × 2 seasons) 
CSR  Shading + repeated         decapitation 3‐monthly (32 × 2 seasons) 3‐monthly (32 × 2 seasons) Final (10 × 2 seasons) Final (10 × 2 seasons) 
  Measurements    
Code Treatment Shoot biomass Shoot number Below‐ground biomass Below‐ground starch 
 Uncut saplings (control) 2‐ to 5‐monthly (42) – 2‐ to 5‐monthly (10) 2‐ to 5‐monthly (10) 
 Decapitated trees     
CN  No further intervention 2‐ to 5‐monthly (42 × 2 seasons) 3‐monthly (16 × 2 seasons) 2‐ to 5‐monthly (10 × 2 seasons) 2‐ to 5‐monthly (10 × 2 seasons) 
CS  Shading Final (48 × 2 seasons) – Final (10 × 2 seasons) Final (10 × 2 seasons) 
CR  Repeated 3‐monthly         decapitation 3‐monthly (32 × 2 seasons) 3‐monthly (32 × 2 seasons) Final (10 × 2 seasons) Final (10 × 2 seasons) 
CSR  Shading + repeated         decapitation 3‐monthly (32 × 2 seasons) 3‐monthly (32 × 2 seasons) Final (10 × 2 seasons) Final (10 × 2 seasons) 

All measurements on decapitated trees were carried out both for plants first cut in February 1999 or in October 1999. Sampling frequency is indicated as ‘final’ for CS, CR and CSR where a single measurement was made at the end of the experiments (when approx. 15 % of plants had died, after approx. 12 months). These final measurements were then made on the remaining plants. For all treatments, the number of trees (replicates) sampled at each date is shown in parentheses. Note that below‐ground starch measurements were made between July 1999 and February 2001 only.

Table 3.

Starch concentrations (± s.e.) in Eucalyptus kochii roots in the ‘standard’ excavation zone (see Fig. 2) and in the remainder of roots collected in ‘extensive’ excavations beyond the standard excavation zone

 Uncut saplings (% of dry mass) February‐cut coppice (% of dry mass) October‐cut coppice (% of dry mass) 
Lateral roots     
 In standard excavation 2·1 (± 1·0) 1·4 (± 0·4) 1·7 (± 0·4) 
 Beyond standard excavation 3·8 (± 0·9) 2·6 (± 0·9) 3·5 (± 2·0) 
Sinker roots    
 In standard excavation 1·6 (± 0·7) 1·6 (± 0·7) 1·3 (± 0·2) 
 Beyond standard excavation 3·8 (± 1·6) 1·2 (± 0·5) 2·9 (± 0·7) 
 Uncut saplings (% of dry mass) February‐cut coppice (% of dry mass) October‐cut coppice (% of dry mass) 
Lateral roots     
 In standard excavation 2·1 (± 1·0) 1·4 (± 0·4) 1·7 (± 0·4) 
 Beyond standard excavation 3·8 (± 0·9) 2·6 (± 0·9) 3·5 (± 2·0) 
Sinker roots    
 In standard excavation 1·6 (± 0·7) 1·6 (± 0·7) 1·3 (± 0·2) 
 Beyond standard excavation 3·8 (± 1·6) 1·2 (± 0·5) 2·9 (± 0·7) 
Table 4.

Summary of changes in above‐ and below‐ground pool sizes following contrasting decapitation regimes in Eucalyptus kochii growing at Kalannie, Western Australia, over a 1‐year period for 4‐ to 5‐year‐old plants cut initially in either February or October 1999

 Total shoot biomass produced over period (kg d.wt per plant) Change in root biomass (kg d.wt per plant) Change in lignotuber biomass (kg d.wt per plant) Final below‐ground starch conc. (% of d.wt) Calculated change in below‐ground starch store (kg per plant) 
Between February 1999 and February 2000 (February‐cut trees) 
 Uncut controls 6·56* +1·64* +0·31 4·7†a +0·03 
 CN 0·88* –0·40* –0·01  2·1†b –0·18 
 CR 0·27 –0·57 –0·00 0·5c  –0·24 
 CS 0·14 –0·54 –0·10 0·9bc –0·11 
 CSR 0·11 –0·28 –0·10 0·7c  –0·23 
 
Between October 1999 and October 2000 (October‐cut trees) 
 Uncut controls 6·83* +1·58* +0·31 5·7†a +0·13 
 CN 2·46* –0·50* +0·02 4·6†a –0·09 
 CR 0·47 –0·64 –0·21 1·0b  –0·29  
 CS 0·29 –1·27 –0·16 0·4b  –0·31 
 CSR 0·24 –1·10 –0·16 0·9b  –0·28 
 Total shoot biomass produced over period (kg d.wt per plant) Change in root biomass (kg d.wt per plant) Change in lignotuber biomass (kg d.wt per plant) Final below‐ground starch conc. (% of d.wt) Calculated change in below‐ground starch store (kg per plant) 
Between February 1999 and February 2000 (February‐cut trees) 
 Uncut controls 6·56* +1·64* +0·31 4·7†a +0·03 
 CN 0·88* –0·40* –0·01  2·1†b –0·18 
 CR 0·27 –0·57 –0·00 0·5c  –0·24 
 CS 0·14 –0·54 –0·10 0·9bc –0·11 
 CSR 0·11 –0·28 –0·10 0·7c  –0·23 
 
Between October 1999 and October 2000 (October‐cut trees) 
 Uncut controls 6·83* +1·58* +0·31 5·7†a +0·13 
 CN 2·46* –0·50* +0·02 4·6†a –0·09 
 CR 0·47 –0·64 –0·21 1·0b  –0·29  
 CS 0·29 –1·27 –0·16 0·4b  –0·31 
 CSR 0·24 –1·10 –0·16 0·9b  –0·28 

Coppice treatments were CN (regenerating naturally after the initial cut), CR (repeated 3‐monthly decapitation), CS (shaded) and CSR (shaded + repeated decapitation) and are compared with control saplings left uncut. Significant differences (P < 0·05) in starch concentrations in total below‐ground biomass are shown by different superscript letters separately for both of the year‐long periods.

* Data calculated from Fig. 5.

Data taken from Fig. 6.

Original starch concentration at time of cutting estimated as 250 g per plant from extrapolation of Fig. 6B since comprehensive starch analyses were not carried out until July 1999.

Table 5.

Secondary root thickening over a 21‐month period in control Eucalyptus kochii trees compared with trees decapitated once

 Comparison 1 Comparison 2 
             February‐cut coppice                         Uncut sapling                         October‐cut coppice                         Uncut sapling 
Stem – 88 (± 9) –             213 (± 36) 
Lateral roots                         26 (± 10) 86 (± 17) 23 (± 9)             129 (± 23) 
Sinker roots         14 (± 8) 74 (± 9) 30 (± 7)             70 (± 17) 
 Comparison 1 Comparison 2 
             February‐cut coppice                         Uncut sapling                         October‐cut coppice                         Uncut sapling 
Stem – 88 (± 9) –             213 (± 36) 
Lateral roots                         26 (± 10) 86 (± 17) 23 (± 9)             129 (± 23) 
Sinker roots         14 (± 8) 74 (± 9) 30 (± 7)             70 (± 17) 

Data are expressed as mean percentage increase (± s.e.) in wood cross‐sectional area.

Table 6.

Starch concentrations measured in excavated portions of below‐ground organs of uncut and naturally regenerating coppice of Eucalyptus kochii at Kalannie, Western Australia

 Mean of all samples (% of dry mass) Range of all means across harvests (% of dry mass) 
Uncut saplings   
 Lignotuber 0·77c 0·5–1·5 
 Lateral roots 3·59a 1·7–5·4 
 Sinker roots 4·07a 1·2–6·2 
February‐cut coppice   
 Lignotuber 0·41c 0·1–1·5 
 Lateral roots 1·81b 0·9–3·9 
 Sinker roots 1·85b 0·7–3·8 
October‐cut coppice   
 Lignotuber 0·37c 0·3–0·4 
 Lateral roots 2·21b 1·2–4·6 
 Sinker roots 2·29b 1·5–3·8 
 Mean of all samples (% of dry mass) Range of all means across harvests (% of dry mass) 
Uncut saplings   
 Lignotuber 0·77c 0·5–1·5 
 Lateral roots 3·59a 1·7–5·4 
 Sinker roots 4·07a 1·2–6·2 
February‐cut coppice   
 Lignotuber 0·41c 0·1–1·5 
 Lateral roots 1·81b 0·9–3·9 
 Sinker roots 1·85b 0·7–3·8 
October‐cut coppice   
 Lignotuber 0·37c 0·3–0·4 
 Lateral roots 2·21b 1·2–4·6 
 Sinker roots 2·29b 1·5–3·8 

Different superscript letters indicate significant differences (P < 0·05) between organs across all treatments using Tukey’s pairwise comparison.

References

BamberRK, Mullette KJ.
1978
. Studies of the lignotubers of Eucalyptus gummifera (Gaertn. & Hochr.). II Anatomy.
Australian Journal of Botany
 
26
:
15
–22.
BarrosNF, Novais RF.
1996
. Eucalypt nutrition and fertilizer regimes in Brazil. In: Attiwill PM, Adams MA, eds. Nutrition of eucalypts. Melbourne: CSIRO,
335
–355.
BeardJS.
1984
. Biogeography of the kwongan. In: Pate JS, Beard JS, eds. Kwongan: plant life of the sandplain. Perth: University of Western Australia Press,
1
–26.
BellDT, Hopkins AJM, Pate JS.
1984
. Fire in the kwongan. In: Pate JS, Beard JS, eds. Kwongan: plant life of the sandplain. Perth: University of Western Australia Press,
178
–204.
BellTL, Pate JS, Dixon KW.
1996
. Relationships between fire response, morphology, root anatomy and starch distribution in south‐west Australian Epacridaceae.
Annals of Botany
 
77
:
357
–364.
BlakeTJ.
1983
. Coppice systems for short‐rotation intensive forestry: the influence of cultural, seasonal and plant factors.
Australian Forestry Research
 
13
:
279
–291.
BurrowsGE.
2000
. An anatomical study of epicormic bud strand structure in Eucalyptus cladocalyx (Myrtaceae).
Australian Journal of Botany
 
48
:
233
–245.
BurrowsGE.
2002
. Epicormic strand structure in Angophora, Eucalyptus, and Lophostemon (Myrtaceae) – implications for fire resistance and recovery.
New Phytologist
 
153
:
111
–131.
CanadellJ, López‐Soria L.
1998
. Lignotuber reserves support regrowth following clipping of two Mediterranean shrubs.
Functional Ecology
 
12
:
31
–38.
CarrodusBB, Blake TJ.
1970
. Studies on the lignotubers of Eucalyptus obliqua L’Herit. I. The nature of the lignotuber.
New Phytologist
 
69
:
1069
–1072.
CeulemansR, Deraedt W.
1999
. Production physiology and growth potential of poplars under short‐rotation forestry culture.
Forest Ecology and Management
 
121
:
9
–23.
ChapinFS, Schulze E‐D, Mooney HA.
1990
. The ecology and economics of storage in plants.
Annual Review of Ecological Systematics
 
21
:
423
–447.
ChattawayMM.
1958
. Bud development and lignotuber formation in eucalypts.
Australian Journal of Botany
 
6
:
103
–115.
ChristerssonL, Ramstedt M, Forsberg J.
1992
. Pests, diseases and injuries in intensive short‐rotation forestry. In: Mitchell CP, Ford‐Robertson JB, Hinckley T, Sennerby‐Forsse L, eds. Ecophysiology of short rotation forest crops. Essex: Elsevier Science Publishers Ltd,
185
–215.
CremerKW.
1972
. Morphology and development of primary and accessory buds of Eucalyptus regnans.
Australian Journal of Botany
 
20
:
175
–195.
CrombieDS.
1997
. Water relations of jarrah (Eucalyptus marginata) regeneration from the seedling to the mature tree and of stump coppice.
Forest Ecology and Management
 
97
:
293
–303.
DeansJD, Ford ED.
1986
. Seasonal patterns of radial root growth and starch dynamics in plantation‐grown Sitka spruce trees of different ages.
Tree Physiology
 
1
:
241
–252.
Del TrediciP.
2001
. Sprouting in temperate trees: a morphological and ecological review.
Botanical Review
 
67
:
121
–140.
DickmannDI, Pregitzer KS.
1992
. The structure and dynamics of woody plant root systems. In: Mitchell CP, Ford‐Robertson JB, Hinckley T, Sennerby‐Forsse L, eds. Ecophysiology of short rotation forest crops. Essex: Elsevier Science Publishers Ltd,
95
–123.
DickmannDI, Nguyen PV, Pregitzer KS.
1996
. Effects of irrigation and coppicing on above‐ground growth, physiology, and fine‐root dynamics of two field‐grown hybrid poplar clones.
Forest Ecology and Management
 
80
:
163
–174.
DuboisM, Gilles KA, Hamilton JK, Rebers PA, Smith F.
1956
. Colorimetric method for determination of sugars and related substances.
Analytical Chemistry
 
28
:
350
–356.
EasthamJ, Scott PR, Steckis RA, Barton AFM, Hunter LJ, Sudmeyer RJ.
1993
. Survival, growth and productivity of tree species under evaluation for agroforestry to control salinity in the Western Australian wheatbelt.
Agroforestry Systems
 
21
:
223
–237.
Enecon Pty Ltd.
2001
. Integrated tree processing of mallee eucalypts. Canberra: Rural Industries Research and Development Corporation.
FarrarJF, Jones DL.
2000
. The control of carbon acquisition by roots.
New Phytologist
 
147
:
43
–53.
FownesJH, Anderson DG.
1991
. Changes in nodule and root biomass of Sesbania sesban and Leucaena leucocephala following coppicing.
Plant and Soil
 
138
:
9
–16.
GarciaH, Nygren P, Desfontaines L.
2001
. Dynamics of nonstructural carbohydrates and biomass yield in a fodder legume tree at different harvest intensities.
Tree Physiology
 
21
:
523
–531.
GrahamAW, Wallwork MA, Sedgley M.
1998
. Lignotuber bud development in Eucalyptus cinerea (F. Muell. ex Benth).
International Journal of Plant Sciences
 
159
:
979
–988.
HillisWE, Brown AG.
1984
. Eucalypts for wood production. Melbourne: CSIRO.
HodgkinsonKC, Becking HGB.
1977
. Effect of defoliation on the root growth of some arid zone perennial plants.
Australian Journal of Agricultural Research
 
29
:
31
–42.
HytönenJ, Issakainen J.
2001
. Effect of repeated harvesting on biomass production and sprouting of Betula pubescens.
Biomass and Bioenergy
 
20
:
237
–245.
JacobsMR.
1955
. Growth habits of the eucalypts. Canberra: Forestry and Timber Bureau.
JamesS.
1984
. Lignotubers and burls – their structure, function and ecological significance in Mediterranean ecosystems.
Botanical Review
 
50
:
225
–266.
KeithH, Raison RJ, Jacobsen KL.
1997
. Allocation of carbon in a mature eucalypt forest stand and some effects of soil phosphorus availability.
Plant and Soil
 
196
:
81
–99.
KerrLR.
1925
. The lignotubers of eucalypt seedlings.
Proceedings of the Royal Society of Victoria
 
37
:
79
–97.
KnyL.
1894
. On correlation in the growth of roots and shoots.
Annals of Botany
 
8
:
265
–280.
KolbTE, McCormick LH.
1991
. Relationship between total nonstructural carbohydrate concentration and root diameter in sugar maple.
Forest Science
 
37
:
343
–346.
KosolaKR, Dickmann DI, Paul EA, Parry D.
2001
. Repeated insect defoliation: effects on growth, nitrogen acquisition, carbohydrates, and root demography of poplars.
Oecologia
 
129
:
65
–74.
KummerowJ, Kummerow M, Trabaud L.
1990
. Root biomass, root distribution and the fine‐root growth dynamics of Quercus coccifera L. in the Garrigue of southern France.
Vegetatio
 
87
:
37
–44.
LattCR, Nair PKR, Kang BT.
2000
. Interactions among cutting frequency, reserve carbohydrates, and post‐cutting biomass production in Gliricidia sepium and Leucaena leucocephala.
Agroforestry Systems
 
50
:
27
–46.
MilthorpePL, Hillan JM, Nicol HI.
1994
. The effect of time of harvest, fertiliser and irrigation on dry matter and oil production of blue mallee.
Industrial Crops and Products
 
3
:
165
–173.
MilthorpePL, Brooker MIH, Slee A, Nicol HI.
1998
. Optimum planting densities for the production of eucalyptus oil from blue mallee (Eucalyptus polybractea) and oil mallee (E. kochii).
Industrial Crops and Products
 
8
:
219
–227.
MitchellCP, Stevens EA, Watters MP.
1999
. Short‐rotation forestry – operations, productivity and costs based on experience gained in the UK.
Forest Ecology and Management
 
121
:
123
–136.
MulletteKJ.
1978
. Studies of the lignotubers of Eucalyptus gummifera (Gaertn. & Hochr.). I. The nature of the lignotuber.
Australian Journal of Botany
 
26
:
9
–13.
MurtaghGJ.
1996
. Month of harvest and yield components of tea tree. I. Biomass.
Australian Journal of Agricultural Research
 
47
:
801
–815.
NambiarEKS.
1999
. Introduction to third workshop in Kerala, India. In: Nambiar EKS, Tiarks A, Cossalter C, Ranger J, eds. Site management and productivity in tropical plantation forests: a progress report. Kerala, India: Center for International Forestry Research,
1
–2.
NobelPS, Alm DM, Cavelier J.
1992
. Growth respiration, maintenance respiration and structural‐carbon costs for roots of three desert succulents.
Functional Ecology
 
6
:
79
–85.
NobleJC.
1989
. Fire regimes and their influence on herbage and mallee coppice dynamics. In: Noble JC, Bradstock RA, eds. Mediterranean landscapes in Australia: mallee ecosystems and their management. Melbourne: CSIRO,
168
–180.
NobleJC.
2001
. Lignotubers and meristem dependence in mallee (Eucalyptus spp.) coppicing after fire.
Australian Journal of Botany
 
49
:
31
–41.
NorthcoteKH.
1979
. A factual key for the recognition of Australian soils. Adelaide: Rellim Technical Publications.
PateJS, Froend RH, Bowen BJ, Hansen A, Kuo J.
1990
. Seedling growth and storage characteristics of seeder and resprouter species of Mediterranean‐type ecosystems of S.W. Australia.
Annals of Botany
 
65
:
585
–601.
PucherGW, Leavenworth CS, Vickery HB.
1948
. Determination of starch in plant tissues.
Analytical Chemistry
 
20
:
850
–853.
ReidackerA.
1973
. Les taillis d’Eucalyptus au Maroc.
Annales des la Recherche Forestière au Maroc
 
13
:
156
–163.
ReisMdGF, Kimmins JP.
1986
. Importance of the root system in the initial growth of Eucalyptus shoots.
Revista Arvore
 
10
:
196
–201.
RosettoM, Jezierski G, Hopper SD, Dixon KW.
1999
. Conservation genetic and clonality in two critically endangered eucalypts from the highly endemic south‐western Australian flora.
Biological Conservation
 
88
:
321
–331.
RuessRW, Hendrick RL, Bryant JP.
1998
. Regulation of fine root dynamics by mammalian browsers in early successional Alaskan taiga forests.
Ecology
 
79
:
2706
–2720.
RyanMG, Hubbard RM, Pongracic S, Raison RJ, McMurtrie R.
1996
. Foliage, fine‐root, woody‐tissue and stand respiration in Pinus radiata in relation to nitrogen status.
Tree Physiology
 
16
:
333
–343.
SchönauAPG.
1991
. Growth, yield and timber density of short rotation coppice stands of Eucalyptus grandis.
South African Forestry Journal
 
156
:
2
–22.
SchrothG.
1995
. Tree root characteristics as criteria for species selection and systems design in agroforestry. In: Sinclair FL, ed. Agroforestry: science, policy and practice. Dordrecht: Kluwer Academic Publishers,
125
–143.
SchrothG, Zech W.
1995
. Above‐ and below‐ground biomass dynamics in a sole cropping and an alley cropping system with Gliricidia sepium in the semi‐deciduous rainforest zone of West Africa.
Agroforestry Systems
 
31
:
181
–198.
Sennerby‐ForsseL, Ferm A, Kauppi A.
1992
. Coppicing ability and sustainability. In: Mitchell CP, Ford‐Robertson JB, Hinckley T, Sennerby‐Forsse L, eds. Ecophysiology of short rotation forest crops. Essex: Elsevier Science Publishers Ltd,
146
–184.
SimsREH, Senelwa K, Maiava T, Bullock BT.
1999
. Eucalyptus species for biomass energy in New Zealand – Part II: Coppice performance.
Biomass and Bioenergy
 
17
:
333
–343.
SmithGS, Clark CJ, Boldingh HL.
1992
. Seasonal accumulation of starch by components of the kiwifruit vine.
Annals of Botany
 
70
:
19
–25.
SpechtRL.
1996
. The influence of soils on the evolution of the eucalypts. In: Attiwill PM, Adams MA, eds. Nutrition of Eucalypts. Melbourne: CSIRO,
31
–60.
State Salinity Council.
2000
. The salinity strategy. Perth: Government of Western Australia.
SteinbeckK, Nwoboshi LC.
1980
. Rootstock mass of coppiced Platanus occidentalis as affected by spacing and rotation length.
Forest Science
 
26
:
545
–547.
TaylorJS, Blake TJ, Pharis RP.
1982
. The role of plant hormones and carbohydrates in the growth and survival of coppiced Eucalyptus seedlings.
Physiologia Plantarum
 
55
:
421
–430.
ThornleyJHM.
1977
. Root:shoot interactions. In: Jennings DH, ed. Integration of activity in the higher plant. Cambridge: Cambridge University Press,
367
–389.
TysonM, Vaillancourt RE, Reid JB.
1998
. Determination of clone size and age in a mallee eucalypt using RAPDs.
Australian Journal of Botany
 
46
:
161
–172.
WildyDT, Pate JS, Bartle JR.
2000
a. Variations in composition and yield of leaf oils from alley‐farmed oil mallees (Eucalyptus spp.) at a range of contrasting sites in the Western Australian wheatbelt.
Forest Ecology and Management
 
134
:
205
–217.
WildyDT, Bartle JR, Pate JS, Arthur DJ.
2000
b. Sapling and coppice biomass production by alley‐farmed ‘oil mallee’ Eucalyptus species in the Western Australian wheatbelt.
Australian Forestry
 
63
:
147
–157.
WilsonJB.
1988
. A review of evidence on the control of shoot:root ratio, in relation to models.
Annals of Botany
 
61
:
433
–449.
WirthensohnMG, Sedgley M.
1998
. The effect of pruning on regrowth of cut foliage stems of seventeen Eucalyptus species.
Australian Journal of Experimental Agriculture
 
38
:
631
–636.
WoodsFW, Harris HC, Caldwell RE.
1959
. Monthly variations of carbohydrates and nitrogen in roots of sandhill oaks and wiregrass.
Ecology
 
40
:
292
–295.
ZammitC.
1988
. Dynamics of resprouting in the lignotuberous shrub Banksia oblongifolia.
Australian Journal of Ecology
 
13
:
311
–320.
ZimmermanMH.
1971
. Storage, mobilization and circulation of assimilates. In: Zimmerman MH, Brown CL, Tyree MT, eds. Trees: structure and function. New York: Springer Verlag,
307
–322.

Author notes

1School of Plant Biology (Botany), Faculty of Natural and Agricultural Sciences, University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia

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