eucalyptus species for biomass energy in new zealand—part ii: coppice performance

Eucalyptus species for biomass energy in New ZealandÐPart II: Coppice performance

Ralph E.H. Sims*, Kingiri Senelwa, Tavale Maiava, Bruce T. Bullock

Institute of Technology and Engineering, College of Sciences, Massey University, Private Bag 11 222, Palmerston North, New

Zealand

Received 29 June 1998; received in revised form 8 April 1999; accepted 12 April 1999

Abstract

Coppice re-growth and related yields of twelve species of the subgenus Symphyomyrtus and seven species of thesubgenus Monocalyptus were monitored over ®ve 3-year rotations. Planted in small plots at an original planting

density equivalent to 2200 stems/ha, the resulting population densities (trees/ha and shoots/ha) varied with speciesand with each rotation as tree mortality increased to varying degrees following every successive harvest. Only eightof the 19 species planted had survival rates exceeding 50% of the initial population density after the ®fth and ®nal

harvest. E. brookerana and E. ovata were the most vigorous species with survival rates exceeding 80% of theoriginal planting. Eight of the species had died out completely before the ®nal harvest. Overall, species from thesub-genus Symphyomyrtus had higher survival rates than those from the sub-genus Monocalyptus.

Tree height, shoot stump diameter and above ground biomass dry weights varied between species, between sub-genera, and also between harvests. Biomass yields at comparative population densities tended to increase withsubsequent coppice harvests, even though no irrigation, fertiliser, pest management systems or weed controlmethods were applied. Six speciesÐE. brookerana, E. botryoides, E. botryoides � saligna and E. ovata of the sub-

genus Symphyomyrtus, and E. elata and E. obliqua of the sub-genus MonocalyptusÐgave satisfactory yields whichexceeded 10 ODt/ha/y in any one of the ®ve harvests. This provided mean annual incremental yields over the 15year period ranging between 12-34 ODt/ha/y for these species when grown in the small plots. Commercial scale crop

yields are likely to be considerably lower. However the six top yielding Eucalyptus species identi®ed can berecommended for consideration in commercial plantings of short rotation coppice forestry schemes when grown onfertile soils in a temperate climate. # 1999 Elsevier Science Ltd. All rights reserved.

Keywords: Biomass; Coppice; Eucalyptus; Short rotation forest; Monocalyptus; Symphyomyrtus; Yield

1. Introduction

The production systems used in short rotation

forestry (SRF) can be divided into either single

stem, (replanting after harvest), or coppice.

Biomass and Bioenergy 17 (1999) 333±343

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* Corresponding author. Fax: +64-6-3505640.

E-mail address: [email protected] (R.E.H. Sims)

Single stem systems can utilise conventional for-estry species, both hardwoods and softwoods,while coppice systems are restricted to hardwoodgenera such as Populus, Eucalyptus and Salix.

In a coppice system, once the single stem ®rstrotation of the establishment cycle is harvested,the cut stumps resprout to provide another crop.This can continue for several rotations dependingon the vigour of the plants comprising the plan-tation. The sprouting shoots grow rapidly afterharvest because the roots have already estab-lished access to soil water and nutrients. Theyalso contain stored carbohydrates which help sus-tain rapid re-growth rates [1]. However, not allspecies regenerate in this manner. Those that docoppice do so with varying degrees of success.Some may re-sprout successfully but die backsoon after; others may not regrow after two orthree harvests; whilst others may have su�cientvigour to regrow even after several harvests as aresult of low stool mortality.

Since replanting is an expensive operation,selection of a species with high coppicing vigourand long life will reduce the overall biomass pro-duction costs. The overall age of a stand beforereplanting becomes necessary depends on theresprouting vigour, the stool mortality rate, andthe overall yield of the remaining stand. Coppiceyields vary with species, stocking density, ro-tation length, time of harvest, and age of theroot stock. Yields may be higher than those fromthe ®rst single stem harvest [2]. For exampleKaumi [3] found that in Kenya the ®rst coppicerotation yielded double that of the establishmentsingle stem rotation; the second coppice rotationwas 50% more; while the yield of the third cop-pice harvest was less again, being similar to the®rst rotation harvest.

The optimum number of coppice harvestsbefore replanting is warranted is not known formost species. Three coppice rotations have beensuggested for Eucalyptus [4,5], although highernumbers of rotations have been reported [2,3,6±8]. The variation in the number of coppice ro-tations suggests that stump mortality followingrepeated coppice harvests may vary with species,time of harvest, and prevailing climatic con-ditions. Sims et al. [9] showed that some of the

variability in growth and yield among Eucalyptusspecies when ®rst harvested as single stems at 3years old was associated with their sub-genericdi�erences. Species of the sub-genusSymphyomyrtus resulted in higher yields thanthose of the sub-genus Monocalyptus whengrown in the Palmerston North region of NewZealand. Other studies had suggested that therewere physiological di�erences between the sub-genera, including di�erences in the formation ofthe eucalypt±fungal relationships, and also in theroot structures [10,11].

This study compared the growth performance,coppicing ability, coppice survival and yields of19 Eucalyptus species from two sub-genera after®ve repeated harvests of 3-year rotations. Thespecies selected were chosen in anticipation thatthey would be good performers when grownunder local conditions. The aim was to demon-strate their comparative yields and hence suit-ability for growing in a commercial shortrotation forest coppice scheme. Part I of thestudy compared the results from the ®rst harvestof the single stem trees at 3 years old and wasreported earlier [9]. The objective of this secondpart of the study was to identify the Eucalyptusspecies which gave good dry matter yields andsurvival rates when managed under a coppiceregime in small plot trials. It was realised thatthe yields as measured would probably not beachievable when grown on a commercial scale,but that any species identi®ed as high yielding inthe trials might well be suitable for use in suchplantations.

2. Materials and methods

Details of the experimental design, site, estab-lishment of the trials in 1982, growth of the plotsup to the ®rst harvest of the single stem crop,and the sampling and analysis methodologieswere described in Part I of the study [9]. Twoseparate ®eld trials were designed:

1. a screening trial (a) of 19 Eucalyptus species innon replicated plots of 10 trees; and

2. a randomised block design trial (b) of the ®ve

R.E.H. Sims et al. / Biomass and Bioenergy 17 (1999) 333±343334

Eucalyptus species anticipated to be the bestperforming from the species in trial (a), with12 replicates and 5 trees in each plot.

The ®rst harvest was conducted at 3 years old inNovember/December 1985. The cut stumps wereallowed to re-grow into the ®rst coppice cropwhich was then harvested in the spring(November/December) of 1988 (2nd harvest at 6years old). The cycle was repeated by harvestingin the springs (November/December) of 1991(3rd harvest at 9 years old); of 1994 (4th harvestat 12 years old); and ®nally of 1997 (5th harvestat 15 years old). The sampling and analysis meth-odologies described by Sims et al. [9] wereapplied in all harvests with the exception ofmeasuring each of the multi-stems of the coppiceregrowth as opposed to the single stems at ®rst

harvest. Rather than combine the diameters ofall the shoots on each stool of multi-stemmedtrees using the square root of the sum of squaresof individual shoot diameters (i.e., D=ZS(d 2

i ,d 2ii, . . . )) as described by MacDicken et al. [12],

each individual shoot with base diameter>40 mm was considered as an independent treeregardless of the number present. The rationalefor this approach becomes more obvious whenthe size of each shoot is considered (Fig. 1) rel-evant to the close plant spacing of 1.0 m in 4.5 mrows.

Two stocking densities were therefore de®ned:

1. the apparent stocking density being the num-ber of rootstocks per hectare, and

2. the e�ective stocking density being the numberof shoots per hectare.

Shoots with base diameters under 40 mm werenot regarded as in¯uencing the e�ective stockingdensity. The yield of such material was relativelysmall and was categorised as part of the materialthat would normally be left on site when conven-tional forestry harvesting machinery is used. Thisincludes tree tops <40 mm diameter, mostbranches and leaves. When harvested for energypurposes however, it was assumed that all theabove ground biomass would be utilised. Thesetree components have therefore been included inthe total biomass yields recorded.

At each harvest, the stems were cut manuallywith a chainsaw at 0.15 m above the ground,(referred to as stump height), delimbed and thencross cut at the 40 mm top stem diameter heightto obtain the weights of stemwood material andthe remainder of the biomass. The green weightsof (i) each whole stem; (ii) stemwood to 40 mmtop diameter; and (iii) tops, branches and foliage,were determined to the nearest 0.1 kg using acalibrated load cell within a portable weighingframe. From each tree, representative samples ofthe stem, branches, twigs and foliage were col-lected for subsequent dry matter determinations.These samples were oven dried at 808C to con-stant weight, from which the moisture content atharvest (dry weight basis), and dry matter werecalculated. The number of surviving trees perplot was used to calculate total biomass and

Fig. 1. Manual harvesting of 8 m tall, 3 year old coppice

regrowth stems on 9 year old rootstocks.

R.E.H. Sims et al. / Biomass and Bioenergy 17 (1999) 333±343 335

Fig. 2. Apparent population (root stocks/ha) and e�ective population (shoots/ha, ~) for the selected species at each of the ®ve har-

vests. } Species names followed by the same letter show that the populations (root stocks/ha | shoots/ha) over 15 years were not

signi®cantly di�erent. % Harvests followed by the same letter show that the populations (root stocks/ha | shoots/ha) were not sig-

ni®cantly di�erent.


stemwood yields in terms of oven dry tonnes perhectare equivalent (ODt/ha), and hence the meanannual increment (MAI, ODt/ha/y).

For the non-replicated screening trial (a),simple comparisons were made between thespecies means over all ®ve harvests. For theanalysis of the randomised block trial (b), theGeneral Linear Model procedure of the SASSystem of statistical analysis [13], was used to in-dicate variations between species, between thesub-genera, and also between each of the ®veharvests. Coppice growth and yield variationsbetween species and between the two sub-generawere compared with the single stem (®rst) har-vest. The comparison was based on the averagesfor all the species that survived to the ®fth and®nal harvest. The ®ve harvests were each treatedand analysed as repetitive measurements. Tests ofsigni®cance were performed at the 95% con®-dence level.

3. Results

Statistical analysis emphasised those specieswhich survived to the ®fth harvest (4th coppiceharvest) but also identi®ed the trends observed inthe species that did not survive. Analysis of therandomised block, replicated trial (b) showedstatistical di�erences between the ®ve species,between the two sub-genera, and also betweenthe ®ve harvests. Results from this trial were alsoused to con®rm or otherwise, any trendsobserved in the non-replicated screening trial (a).Here results from both trials are presentedtogether for ease of comparison.

3.1. Species survival and population densities

The variation in surviving population densitiesfollowing repeated harvests in both the screeningtrial (a) and replicated trial (b), is illustrated inFig. 2. Both population density measurementsare compared; the apparent stocking density (bargraphs showing the number of surviving root-stocks), and the e�ective stocking density (linebars showing the number of shoots with stumpdiameter exceeding 40 mm). E�ective stocking

density was calculated by multiplying the appar-ent stocking density with the number of shootsper tree. Since in the ®rst single stem rotation thenumber of trees per hectare was synonymouswith the number of shoots per hectare, no linebars are presented for the ®rst harvest.

The apparent stocking density tended to pro-gressively decline with each harvest. Species thatsurvived to the ®nal harvest showed that tree sur-vival was signi®cantly di�erent between species,and also between the ®ve harvests. By the ®nalharvest in 1997, only E. brookerana and E. ovatahad survival rates greater than 80% of the orig-inal planting density of 2200 seedlings per hec-tare. E. urningera, E. rodwayii and E. elata hadsurvival rates of approximately 70% while E.botryoides � saligna, E. botryoides and E. obliquahad survival rates of 50±63%. Ten species fromthe screening trial (a), E. botryoides, E. nitens, E.cordata, E. viminalis, E. leucoxylon, E. nitida, E.obliqua, E. pulchella, E. amygdaline, and E. cocci-fera had no trees surviving by the ®nal harvest(Fig. 2). Overall, the species representing the sub-genus Symphyomyrtus had more surviving treesper hectare with more shoots per hectare thanthose of the sub-genus Monocalyptus.

The e�ective stocking density was lowest at thesingle stem harvest and the di�erences betweenthe subsequent four coppice harvests were notsigni®cant, re¯ecting the declining number ofrootstocks. The highest number of shoots perhectare was recorded in E. brookerana at thefourth coppice harvest (11,264 shoots/ha). Otherspecies with a high number of shoots, eventhough recorded in di�erent rotations, includedE. ovata, E. botryoides � saligna, E. obliqua, E.botryoides, E. elata, E. rodwayii and E. urningera.

3.2. Tree dimensions

Tree dimensions at the time of each harvestvaried di�erently between sub-genera and species,and also between the harvests (Table 1). Treeheight varied with species but not with harvestexcept for the ®rst coppice harvest where theheight was lower overall for some unknownreason. Di�erences in shoot diameters betweendi�erent species in the replicated trial (b) were


Table

1

Averagetree

height(m

),diameter

(mm)anddry

weight(kg)of3yearold

Eucalypts

repeatedly

harvestedin

aSRFcoppiceregim

e1

Treespecies

Treeheight

(m)

Shootstumpdiameter

(mm)

Shootdry

weight

(kg)

Whole

tree

dry

weight

(kg)

Single

stem

Coppicecrop

harvests

Single

stem

Coppicecrop

harvests

Single

stem

Coppicecrop

harvests

Single

stem

Coppicecropharvests

1st

2nd3rd

4th

1st

2nd23rd

4th

1st

2nd

3rd

4th

1st

2nd

3rd

4th

Screeningtrial`a'

ÐSymphyomyrtussub-genus

E.botryoides�

saligna

7.1

5.8

7.6

6.9

7.7

a,b

166

89��

9185a

16.7

11.8

10.5

7.4

17.0

a23.9

47.2

42.0

23.4

64.6

b

E.brookerana

6.8

6.2

8.5

8.3

8.1

a160

77��

8181

14.9

9.3

10.7

9.7

17.0

a21.1

32.9

64.2

50.9

108.8

b

E.botryoides

6.4

105

9.1

20.3

E.urnigera

8.1

5.5

6.0

6.6

6.7

b105

67��

6368b

9.0

4.9

4.6

5.7

10.7

c20.0

19.6

13.8

9.8

28.9

b

E.ovata

7.5

5.7

8.1

8.6

7.8

a135

82��

8887a

12.3

6.9

9.6

8.2

18.1

a,b

18.9

27.6

48.0

34.6

90.6

b

E.rodwayii

7.4

5.5

5.6

7.3

6.8

b124

81��

8385a,b

8.5

6.8

5.8

6.8

18.1

b,c18.9

27.2

16.6

19.4

25.3

b

E.maideni

7.4

6.1

8.6

8.2

8.0

a151

83��

12093a

12.4

7.8

14.4

12.6

19.4

a20.7

23.4

43.2

21.0

44.6

b

E.sm

ithii

7.0

6.2

6.4

9.2

7.9

a,b

112

96��

8474a,b

12.2

10.8

16.8

11.9

17.0

a27.2

43.2

50.4

130.9

306.0

a

E.nitens

8.4

6.0

7.4

150

93��

14.3

7.0

14.9

31.7

28.0

14.9

E.cordata

6.8

4.9

3.6

109

71��

6.2

6.4

4.7

13.9

19.2

9.4

E.viminalis

7.2

2.1

129

79��

9.5

0.8

21.1

0.8

E.leucoxylon

5.1

3.1

4.2

96

50��

4.1

1.9

2.9

9.1

1.9

8.7

ÐMonocalyptussubgenus

E.nitida

6.8

108

7.0

15.3

E.elata

6.6

5.3

7.9

8.0

7.2

a,b

11

87��

10678a,b

8.5

7.6

10.9

12.0

15.2

a,b

13.1

15.2

29.6

32.6

60.8

b

E.obliqua

6.4

6.1

8.5

145

80��

13.2

10.2

48.1

18.8

30.6

48.1

E.pulchella

6.0

3.6

134

85��

9.1

3.6

13.1

10.8

E.globoidea

5.9

4.5

5.1

6.4

4.7

c142

85��

8086a

6.4

5.8

6.7

5.9

11.7

c14.3

11.6

16.8

14.8

46.8

b

E.amygdalina

6.7

5.7

136

106��

12.2

12.9

27.1

25.8

E.coccifera

5.5

3.8

101

82

3.8

7.1

8.4

7.1

Replicatedtrial`b'

ÐSymphyomyrtussub-genus

E.botryoides�

saligna

7.2

5.2

6.3

6.3

7.1

b143

9185

7181a

23.9

10.3

10.5

8.6

15.3

a23.9

34.6

49.8

36.9

85.3

a

E.brookerarna

6.7

5.7

7.8

8.0

7.5

a117

7889

8778a

21.1

8.1

13.9

10.7

14.5

a21.2

33.9

52.5

49

76.5

a

E.batryoides

6.2

4.6

5.5

6.2

6.7

b123

8082

7785a

16.2

6.1

7.6

8.6

14.3

a6.2

22.5

35.5

43.6

79.4

b

ÐMonocalyptussubgenus

E.pulchella

5.9

5.7

107

75

13.1

6.8

13.1

26.2

E.obliqua

6.5

5.4

6.0

6.1

6.7

b118

9270

5494a

18.8

10.4

11.4

19.1

15.7

a18.8

27.0

34.1

45

77.5

a,b

1Foranyparameter

inthespeciesthatsurvived

tothe®nalrotation,speciesorharvestvalues

withthesameletter

are

notsigni®cantlydi�erent.

2��

Indicatesdata

forstumpdiameter

(mm)atthesecondcoppiceharvestwasnotavailable.


not signi®cant. Similarly, coppice shoot diametersdid not vary between the four harvests but weresigni®cantly lower than the ®rst rotation singlestem diameters when there was only one shootper rootstock. It was noted that the overall shootbasal area increased with subsequent coppice har-vests due to the increasing number of shoots pertree.

Shoot dry weights in the replicated trial (b) didnot di�er signi®cantly between species over the®ve harvests. Whole tree dry weights increasedwith subsequent harvests due to the increasingnumber of shoots per tree and the decliningapparent stocking density giving less competitionper tree. The largest single tree over any 3 yearrotation was obtained from E. smithii in the 4thcoppice harvest with a total dry weight of 306kg. However the apparent stocking density bythat stage was down to approximately 270 treesper hectare or 12% of the original densityplanted. So there was little competition for soilnutrients, moisture or light. However low overallMAI yields of biomass resulted due to the lowpopulation.

3.3. Mean annual increment yields

The comparative accumulative dry matteryields of the 19 species in screening trial (a) weredivided into two groups based around the sub-genera Symphyomyrtus and Monocalyptus (Fig.3). Values from the replicated trial (b) are alsogiven, being averages from the 12 replicates ofeach treatment. With the notable exception of E.botryoides (which for some unknown reason diedout after the ®rst harvest in the screening trial(a)), the trends observed for the yields of the fourother species were similar to those in trial (b).

Dry matter production was highest for E. broo-kerana with the 15 year MAI from the smallplots exceeding 30 ODt/ha/y. Other species withhigh yielding potential included E. ovata with a15 year MAI yield exceeding 29 ODt/ha/y and E.botryoides � saligna exceeding 24 ODt/ha/y.Unfortunately, E. ovata was not originally chosento be included in the replicated trial (b).

Species of the sub-genus Symphyomyrtustended to have higher yields than those of the

sub-genus Monocalyptus though both had poorlyperforming species too. Coppice yields wereusually signi®cantly higher than yields from the®rst single stem rotation in the replicated trial(b). Yields tended to increase in subsequent har-vests except for the third coppice harvest whichindicated a poorer growth and yield over thatparticular 3 year period. For the species that sur-vived to the ®fth harvest (Fig. 3), the highestyields were generally obtained from the fourthcoppice harvest, the exceptions being E. rodwayiiand E. maidenii in the screening trial (a).

4. Discussion

The small size of the plots and the lack ofreplication in the screening trial (a) severely lim-ited the con®dence that could be placed on theresults as an indication of commercial plantingyields. It is however emphasised that the exper-iments were designed simply to compare speciesperformance when grown under similar con-ditions using a coppicing regime. Although stat-istical analysis gave emphasis to the morevigorous species that survived past the ®fth har-vest, the overall comparison included thosespecies that did not survive following one of the®ve subsequent harvests.

The number of trees per hectare in subsequentharvests could be seen as a direct measure of thecoppicing ability of each species while the num-ber of main production shoots per tree demon-strated coppicing vigour. The di�erences insurvival rates, number of shoots per tree, andshoot/tree sizes between di�erent species and fordi�erent harvests emphasised the variability inability of certain species to withstand repeatedharvesting. The better performing ones would bemore suitable for use in short rotation forestswhen using a coppicing regime. The ten specieswhich had died out before the ®nal harvestwould not be recommended for such systems. Inview of the increased e�ective stocking densityresulting from more shoots per rootstock follow-ing coppicing, an original stocking density of4000±5000 stems/ha as recommended by Sims etal. [9] may now need to be revised. However


Fig. 3. Species yields (ODt/ha/y) from each of the ®ve 3 year rotation harvests (one single stem, and four coppice) for 19 species in

the non-replicated trial (a) and for the 5 species selected for the replicated trial (b) } Species names followed by the same letter

show that average yields over 15 years were not signi®cantly di�erent. % Harvests followed by the same letter show that the yields

were not signi®cantly di�erent.


other factors such as time to reach crown cover

will need to be included in any recommendation.

Although it is generally considered that most

broad leaved species coppice well, there are sig-

ni®cant variations between species, within a

genus and sub-genus. Poor coppicing in some

species may be associated with the lack of one or

more of the physiological and morphological

requirements for coppicing such as the inability

of shoots to resprout (i) from dormant buds on

the stool; (ii) from adventitious buds in the cam-

bial layer around the edge of the cut stem sur-

faces; or (iii) from ligno-tubers [14±17]. High

mortality on the other hand could be associated

with diseases and pests which infect trees follow-

ing harvesting. The reason for the contrast in

survival of E. botryoides between the single plot

of 10 trees in the screening trial (a) and the six

plots of 5 trees each in the replicated trial (b),

both being in the same ®eld, was not clear.

The physiological basis for coppice regrowth

occurring was not investigated in this study. It

was simply assumed that any species which sur-

vived the repeated harvests possessed good coppi-

cing characteristics. These results therefore

provide some information for selecting

Eucalyptus species for coppice management sys-

tems. For example, selection of E. brookerana

with its excellent survival record could lead to

cheaper production costs in terms of $/MJ as the

overhead costs of establishment and replanting

would be spread over a greater number of har-

vests. For all the species evaluated, successive

coppice harvests resulted in a declining stocking

density which con®rmed there is a ®nite life to a

coppice plantation before replanting is required.

The variability between species and also

between harvests in the tree dimension par-

ameters measured (tree height, stem diameter,

stem weight, shoot weight) indicated possible

genetic di�erences between the species and

showed the varying abilities of the species to

adapt to similar growing conditions. Although all

parameters measured are important determinants

of the suitability of a tree species for a SRF

scheme [18], total biomass yield (ODt/ha/y) was

considered to be the most important as it best

indicated the amount of actual marketable pro-duct.

The higher yields of the coppice rotations maybe attributed to a more rapid occupation of theland area leading to higher e�ective stocking den-sities in terms of shoots/ha (Fig. 2), together witha higher total leaf area developing at an earlierstage after each harvest. In addition, coppicecrops do not experience the establishment shockthat seedlings do which a�ects the ®rst rotation.An established root system (developed by mostplants in the ®rst two years of growth) ensuresrapid leaf development especially when plantedat higher stocking densities. However, in sub-sequent coppice harvests, yields were expected tostart declining due to a combination of (i) mor-tality of the stumps from increased competition;(ii) root mortality/senescence; (iii) introduction ofdisease through the cut surfaces; (iv) depletion ofthe nutrient levels of the site; (v) infestation ofpests; and (vi) repeated disruption of the root/shoot ratios of the tree. Yields of subsequentcoppice generations may also decline when theactive age of the root stock reaches its naturallife (i.e., the older the tree, the lower the coppi-cing vigour anticipated leading to reduced yields).High tree mortality and a decline in yields overtime indicates species with low coppicing abilityand vigour. These would be unsuitable for SRFsystems if grown under a coppicing regime.

Species belonging to the sub-genusSymphyomyrtus had a combination of signi®-cantly higher population densities and larger in-dividual trees than those of the sub-genusMonocalyptus. These factors combined to providehigher yields over 15 years with higher MAIs. AllSymphyomyrtus species with average 15 yearMAIs exceeding 16 ODt/ha/y (E. brookerana, E.ovata, E. botryoides � saligna, and E. botryoides )were considered to have good potential for SRFschemes along with E. obliqua and E. elata fromthe sub-genus Monocalyptus. Unfortunately, E.elata, the best of the Monocalyptus sub-genus inthe screening trial (a), had not been selected forthe replicated trial (b). As noted in part I of thisstudy [9], it would, with hindsight, have been abetter choice than E. pulchella, though still sig-ni®cantly lower yielding than the best


Symphyomyrtus species. The higher average cop-pice yields for the species of sub-genusSymphyomyrtus indicated that any physiologicaladvantages resulting from the development ofeucalypt±fungal relationships [10], and of deeperroot structures [11] is maintained through the lifeof the rootstocks and continues to bene®t sub-sequent coppice harvests.

5. Conclusions

Of the 19 Eucalyptus species evaluated in thesesmall plot trials for fuelwood production under acoppice regime, by the end of the ®fth rotationonly ten species planted in the screening trial (a)had survival rates exceeding 50% of the initialpopulation density. Of these, only six speciesÐE.brookerana, E. botryoides, E. botryoides � saligna,and E. ovata of the sub-genus Symphyomyrtus,and E. elata and E. obliqua of the sub-genusMonocalyptus had MAIs averaging over 16 ODt/ha/y as measured in these small plots. These topyielding species can be recommended for con-sideration when planning commercial plantingsof a short rotation coppice forestry schemegrown in similar soils and climate to those ex-perienced in this study.

Eucalyptus species belonging to the sub-genusSymphyomyrtus tended to have superior survivalrates, larger trees, and hence higher yields thanthose of the sub-genus Monocalyptus. At compar-able stocking densities, yields tended to increasein subsequent harvests. Plant coppicing vigourand survival were critical factors that determinedyield. The survival rates after the ®fth harvestindicated the ability of each species to withstandrepeated harvests, and therefore identi®ed thespecies most suitable for selection and planting ina coppicing regime. It should be re-emphasisedthat the yield results from these small plots maynot be a direct indication of expected yields incommercial scale ®eld plantings. Nevertheless thecomparative results provide a basis for a morefocused species selection to suit a speci®c site.

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