Litterfall, litter and associated chemistry in a dry sclerophyll eucalypt forest and a pine plantation in south-eastern Australia: 1. Litterfall and litter

Litterfall, litter and associated chemistry in a drysclerophyll eucalypt forest and a pine plantationin south-eastern Australia: 1. Litterfall and litter

R. H. Crockford� and D. P. RichardsonCSIRO Land and Water, Box 1666, Canberra, ACT 2601, Australia

Abstract:Litterfall was measured in a dry schlerophyll eucalypt forest and a nearbyPinus radiata plantation of similar tree

density and basal area near Canberra in south-eastern Australia. Total annual litterfall for the eucalypts was329 g mÿ2, compared with 180 g mÿ2 for the pines, with the bark component being 52 g mÿ2 for eucalypts andzero for pines. Barkfall did not occur for the eucalypts during the drought of 1982±1983 but complete bark

shedding occurred during the subsequent very wet year when barkfall was 177 g mÿ2 for Eucalyptus rossiiand 146 g mÿ2 for Eucalyptus mannifera (9.3 and 7�6 g mÿ2 of basal area, respectively). Barkfall of E. rossiiresponded to rainfall in the period autumn to early summer, whereasE. mannifera responded to summer rainfall.

In the eucalypt forest ¯oor-litter was strati®ed into a surface layer where the components were substantiallyintact, and a cohesive layer where the components were fragmented and bound together by fungal hyphae. Theamount and residence times of loose and cohesive ¯oor-litter were 1056 g mÿ2 and 3.2 years, respectively, for theloose litter layer; and 1164 g mÿ2 and 3.5 years for the cohesive layer. The litter biomass represented 17% of the

estimated total above-ground biomass of 127 tonnes haÿ1. A previous study showed roots to be 25% of totalbiomass, suggesting a total biomass of 167 tonnes haÿ1. # 1998 John Wiley & Sons, Ltd.

KEY WORDS litterfall; eucalypt forest; barkfall; rainfall; pine plantation; litterfall chemistry; barkfall

INTRODUCTION

This study is part of an extensive seven-year project, which examined the partitioning of rainfall intothroughfall, stem¯ow and interception, in a eucalypt forest and a pine plantation near Canberra in south-eastern Australia (Crockford and Richardson, 1990a,b,c,d), as well as the associated chemistry (Crockfordet al., 1996). Also studied was soil water repellency in the eucalypt forest (Crockford et al., 1991). The broadaim of the Yass Catchment Project was to obtain information about the e�ect of interception on the waterbalance and nutrient cycling of a mixed rural catchment. It was part of an Australia-wide representativebasins project (Australian Water Resources Council, 1975). These litter papers extend the range of informa-tion published from this project.

Nutrients are recycled in forests by litterfall and the chemical enrichment of throughfall and stem¯ow. Inthis study, litterfall was collected, separated into its components and analysed, for both forests. Litterfall isprimarily caused by natural senescence of leaves and other components of the biomass; but the amount oflitterfall, its component composition and its distribution through time is also a�ected by factors such asseason, rainfall amount and distribution, and wind speed.

For both forests, data are reported on the annual accession of litter. In addition, for the eucalypt forest,comparisons are made between total biomass, litterfall and ¯oor-litter.

CCC 0885±6087/98/030365±20$17�50 Received 3 November 1996# 1998 John Wiley & Sons, Ltd. Revised 20 March 1997

Accepted 4 April 1997

Hydrological ProcessesHydrol. Process. 12, 365±384 (1998)

� Correspondence to: R. H. Crockford at CSIRO Land and Water, Box 1666, Canberra, ACT 2601, Australia.

Description of site

The catchment is located in the Upper Yass Representative Basin (Australian Water Resources Council,1975), situated about 320 km north-east of Canberra at 358 15'S and 1498 20'E, and around 800 m elevation(Figure 1). The upper part of the basin is divided into ®ve catchments for which discharge was measured withsmall sharp-crested weirs. Vegetation consisted of blocks of dry sclerophyll eucalypt forest, native andimproved grassland and a Pinus radiata plantation. Mean annual climatic data for this catchment are:640 mm for rainfall, 74 rain days, with 1800 mm US Class A Pan evaporation.

Individual process study areas (PSA) were established within the catchment for both eucalypt and pine(Figure 2) for study of rainfall partitioning into throughfall, stem¯ow and interception, and the associatedchemistry. The slopes of both were 578. Measurements were obtained from three 20 m� 20 m plots withineach PSA.

The eucalypt dry sclerophyll forest (Figure 2) was a 100-year-old regrowth forest that had not been burntfor over 40 years, which, except for the southern side, was surrounded by grassland. The mean height of theforest is 10±12 m, with dead trees comprising 7% of the total tree basal area (BA). The major species and

Figure 1. Yass catchment location

# 1998 John Wiley & Sons, Ltd. HYDROLOGICAL PROCESSES, VOL. 12, 365±384 (1998)

366 R. H. CROCKFORD AND D. P. RICHARDSON

features of the eucalypt forest are given in Table I. Other eucalypt species that occur near the study plots, areE. dives and E. rubida. Grasses and shrubs are e�ectively absent.The pine plantation was planted in 1962 and had been branch-pruned to a height of 2 m several years

prior to the experiment. It was not thinned until the 1982±1983 summer. The basic characteristics are shownin Table I.

Figure 2. Location of process study areas

Table I. Major tree species in process study areas

Forest type Major species Trees haÿ1 Species DBH� total BA{ total(live) (%) haÿ1 (m) haÿ1 (m2)

Eucalypt E. rossii 700 46 103 14.6E. mannifera 433 28 72 10.8E. macrorhyncha 292 19 48 7.3E. melliodora 100 7 12 1.4

Total 1525 100 235 34.1

Pine Pinus radiata 1708 100 266 35.1

�DBH: diameter at breast height{BA: basal area


LITTERFALL, LITTER AND ASSOCIATED CHEMISTRY: 1 367

METHODS OF COLLECTION

Litterfall

Eucalypt and pine litterfall were collected from September 1980 to May 1982. Barkfall was collected fromApril 1981 to May 1984. Litter was collected in the V-section galvanized iron troughs used for measurementof throughfall in the rainfall partitioning experiment (Crockford and Richardson, 1990a). Each of the three20 m� 20 m plots in the eucalypts and pines contained three 5 m� 0�22 m troughs and one 20 m� 0�22 mtrough.

Litter was collected frequently as the rainfall partitioning experiment was attended on an event bias.Mostly, litter was collected after not more than one or two rainfall events. If rainfall was likely, and littercould not be collected, litter was swept to the top end of the troughs to limit leaching. Litter from allcollectors was bulked and samples taken for separation into leaf, bark, twigs and òther'.

Green leaf was a very small proportion of total litterfall, associated with intermittent strong winds and birdactivity. A substantial proportion of green leaf was attached to twigs. Woody tissue was separated into: wood�41 cm diameter), twigs (5±10 mm) and ®ne twigs �55 mm). The wood component was small and variableand was not collected. The òther' component was a mixture of stamens, opercula, fruit, buds, frass, verysmall leaves (approximately 3±6 mm in length) and small fragments of leaf and bark. The relative proportionsvaried through time. These were not separated, but careful observation showed that very small leaves pre-dominated in spring, the ¯owering components and frass in summer and fragmented leaf and bark in winter.

Pine litter was identi®ed as needles and òther'. The òther' component was a mixture of male cones(strobili), frass and broken needles.

Additional barkfall collection

This barkfall was collected from December 1980 to May 1984, from three 10 m� 10 m areas where thenewly fallen bark was collected from the ¯oor. These areas were close to the litterfall plots. This wasoriginally done to test the e�ciency of the 22 cm wide trough collectors. Eucalyptus rossii bark is often inlarge pieces and may not be retained by the troughs, whereas E. mannifera bark pieces are smaller and morelikely to be adequately sampled. Collection of bark from the ¯oor of the litterfall plots could not be donebecause of the disturbance caused by collection of the rainfall partitioning samples. Table II shows thecharacteristics of the smooth-barked species E. rossii and E. mannifera in the barkfall plots.

Table II. Trees in barkfall area

Species Trees haÿ1 DBH� (m2 haÿ1) BA{(m2 haÿ1)

E. rossii 1200 152 19.1E. mannifera 533 122 19.2

�DBH: diameter at breast height{BA: basal area

Almost all barkfall (greater than 99%) came from the smooth-barked species E. rossii and E. mannifera.The bark from these species was separated during collection, based on E. rossii bark having a smoothlongitudinal grain pattern, with pieces generally being long and narrow. The larger pieces of E. rossii barkranged between 50 and 80 cm in length. By contrast, the bark of E. mannifera has a varied grain pattern andthe pieces are more square than those for E. rossii, and rarely greater than 10 cm in length. The next mostcommon species, E. macrorhyncha, is a stringy bark where bark threads are retained and form a ®brous layerthat thickens with age.

Floor-litter

Floor-litter was collected from 10, 0.5 m2 sites in the eucalypt forest; chosen randomly, except thatkangaroo paths and resting places were avoided. The litter was in two distinct layers; a loose surface layer



composed of largely intact leaves overlying a cohesive layer where the leaves were fragmented and bound(along with the other components of this layer) by fungal hyphae. The loose and cohesive layers were similarto the L and F layers commonly reported, but the cohesive layer observed here was clearly separate from theloose litter and the soil A0 layer. The terms `loose' and `cohesive' describe these layers in the eucalypt forestmore clearly than L and F.

Small areas (50 cm2) of the A0 layer were sampled. This layer graded from 100% organic matter at itssurface to largely mineral soil at its base. Its thickness varied between about 2 and 20 mm. While the uppersurface of this layer was usually well developed, the lower limit or junction between the A0 and A1 horizonsmade quantitative assessment di�cult.

Total biomass of the above-ground trees

These data were derived from the tree components used by Crockford and Richardson (1990c) forestimation of canopy storage capacity. The procedure was as follows: a number of trees of each major specieswere selected from an area adjacent to the study plots. The trees selected were representative of the size rangeand types. Table III shows the diameter at breast height (DBH) data for the selected trees. The trees werefelled and the length and diameter of all parts of the structural wood were measured; and representativesamples taken from the range of wood diameters.All twigs 510 mm diameter (with attached leaves) were weighed; and random subsamples taken. These

subsamples were separated into leaves, ®ne twigs �56 mm diameter) and twigs (6±10 mm). The dry weightsof the subsamples were used to calculate the total biomass through allometric relationships, and the driedsamples were prepared for chemical analysis. Greater detail is shown in Crockford and Richardson (1990c).

Table III. DBH� of trees used in biomass study

E. rossii E. mannifera E. macrorhyncha

13.1 10.08 14.218.8 15.5 17.223.0 19.2 23.4

25.0 26.828.0

RESULTS AND DISCUSSION

Eucalypt litterfall

Annual litterfall for the eucalypt forest is given in Table IV. A winter to winter period is used because ofthe low litterfall over winter.

The leaf-fall in 1981±1982 was 20% less than that in 1980±1981, but the reverse occurred for the othercomponents. The largest di�erence was for barkfall, the year 2 value being three times that for year 1. Thehigher year 2 value suggests greater growth which could be the reason for greater òther' fall (year 2 is almosttwice year 1) and the lower leaf-fall. Òther', being mainly reproductive components during the growthseason, is associated with growth. Species-speci®c aspects of barkfall and rainfall are discussed in theseparate barkfall section below.

Figures 3±6 show the pattern of litterfall through time for all major components. Falls for all componentsare summer dominant, which is common to all temperate eucalypt forests in being related to growth andphysiological stress (Attiwill et al., 1978). The curves for leaf-fall and barkfall are similar (Figures 3 and 4),and the summer/winter di�erences are marked. However, the falls of twigs and òther' components (Figures 5and 6) are more dispersed over time, producing substantial di�erences in the relative proportions throughtime. For example, the contribution by twigs averaged 11% (Table IV), but ranged between 3 and 60%,depending on the relative contributions of leaf and bark.



The closest forest type for which there are published litterfall data is the E. obliqua-dominated forests insouth-eastern Australia, in climates similar to this study area. In an E. obliqua forest 25 km south-east ofAdelaide the total annual litterfall (mean of ®ve years) was 190 g mÿ2 (Lee and Correll, 1978). Thiscompares with a value of 267 g mÿ2 (mean of two years) for our study, after subtraction of the barkfallvalues. The barkfall values were subtracted because E. obliqua has ®brous bark over the entire wood massand sheds little bark. Attiwill et al. (1978), in an area 80 km north-east of Melbourne, reported annual leaf-fall of E. obliqua to be 164 g mÿ2, which is similar to our value of 189 g mÿ2, as was the 159 g mÿ2 reportedby Hutson (1985), for an E. obliqua forest in an area of the Hale Conservation Park in south-eastern South

Table IV. Annual litterfall for the eucalypt forest (g mÿ2)

Year Leaf Bark Twigs Òther' Total Total�

1980±1981 210 29 32 29 300 8.81981±1982 168 95 43 52 357 10.5

Mean 189 62 37 40 329 9.6

1980±1981{ 70% 10% 11% 10% 100%1981±1982{ 47% 27% 12% 14% 100%

Mean{ 59% 18% 11% 12% 100%

�As g mÿ2 mÿ2 of basal area{As % of total

Figure 3. Cumulative eucalypt leaf-fall from 22/9/1980 to 14/4/1982



Australia. An E. obliqua forest in a wetter area (1000 mm rainfall) in central Gippsland, Victoria, gave leaf-fall of 244 g mÿ2 (Baker, 1983).

Most litterfall studies have been done in forests that have potential commercial value. In such forests, totallitterfall can be as high as 1000 g mÿ2 for a karri (E. diversicolor F. Meull.) forest in Western Australia(O'Connell and Menage, 1982). Ashton (1975a) reported 650 g mÿ2 for a wet sclerophyll eucalypt forest,E. regnans. Total litterfall for this dry sclerophyll forest was 329 g mÿ2 (Table IV).

Although leaf-fall was not measured after April 1982, it was obviously very substantial during the 1982 to1983 drought year. Visual observation of the tree crowns during the drought suggested that the leaf areaindex (LAI) was probably less than 20% of its normal value (1.1; Anderson, 1981 Ð although it must beunderstood that this ®gure will vary substantially through the years owing to varying seasonal rainfallpatterns), which means that leaf-fall would have been about 300 g mÿ2 during the drought period, com-pared with a `normal' value of about 190 g mÿ2 (Table IV). The LAI was measured in March 1984 (after thevery wet year) and found to be 1.9 (Crockford and Richardson, 1990c). Very little leaf-fall was observedduring the 1983±1984 summer, but bark shedding was complete (see separate barkfall section). These datasuggest an inverse correlation between leaf-fall and debarking for this period. The extremes are: the droughtyear with very large leaf-fall and no debarking, and the very wet year with complete debarking and very littleleaf-fall. Of course, because of the large leaf loss in the dry year, the `wet year' leaves would be relativelyyoung and not likely to be shed, i.e. even adaptive leaf loss (Pook, 1985) would not occur. The suggestion ofan inverse relationship between leaf-fall and barkfall is supported by the relative leaf and barkfall for theyears 1980 to 1982, shown in Table IV. In the 1981±1982 period, leaf-fall was 42 g mÿ2 less than for the1980±1981 year, but barkfall was 66 g mÿ2 greater.

Figure 4. Cumulative eucalypt barkfall from 22/9/1980 to 14/4/1982



Pine litterfall

Pine litter was identi®ed as needles and òther'. The òther' component was a mixture of male cones(strobili), frass and broken needles. In spring, the main period when the òther' was most signi®cant, malecones were about 60% of the total, frass about 30% and needles about 10%. Litterfall in winter was almostentirely needles.

The mean annual total litterfall for the pines is 180 g mÿ2 (Table V), which is composed mainly ofneedles. There was little di�erence in litterfall between years, and little di�erence in composition. Figures 7and 8 show the cumulative litterfall through time. Needlefall occurred continuously throughout the wholeperiod, with higher intensity in the summer months of 1982. This high fall was probably a result of the lowrainfall during this period, only 32 mm in 1982, 25 mm of which occurred on 23 February. By contrast, therainfall in this period of 1981 was 132 mm, evenly distributed. For 1981 the summer and autumn needlefalls

Figure 5. Cumulative eucalypt twigfall from 22/9/1980 to 14/4/1982

Table V. Pine litterfall (g mÿ2)

Year no. Needles Òther' Total Total�

September 1980 1 158.3 22.9 181.0 5.2June 1981July 1981 2 150.4 28.0 178.0 5.1April 1982Mean 154.4 25.4 180.0 5.1

�As g mÿ2 mÿ2 of basal area



were similar. This pattern of needlefall is consistent with the ®ndings of Raison et al. (1992) in a studylocated 25 km west of this site, where water stress caused peak needlefall to occur in the summer/autumnperiod. Baker (1983) and Cromer et al. (1984) also found that in drier environments needlefall peaks duringsummer, whereas in areas with non-limiting rainfall or irrigation, it peaks from autumn to early winter (Will,1959; Versfeld, 1981; Raison et al., 1992). Falls of the òther' component (Figure 8), composed mostly ofstrobili, occur in spring, which is consistent with the ¯owering pattern (Cromer et al., 1984).

Comparison of the litterfall from pines and eucalypts

The mean annual total litterfall of 180 g mÿ2 for the pines (Table V) is much less than the 329 g mÿ2

for the eucalypts (Table IV). But eucalypt litter includes bark, whereas pines do not shed bark. How-ever, allowing for this di�erence, the eucalypt litterfall is 267 g mÿ2; still substantially greater than thepines.

The di�erence between the litterfall of the eucalypts and pines is large considering that the forests weresimilar in terms of stems haÿ1 and basal area haÿ1 (1525 and 1798 stems haÿ1, and 34.1 and 35�1 m2 haÿ1

basal area, respectively, see Table I). For the two years of litterfall measurement the eucalypt leaf-fall was23% greater than the pine needlefall (189 and 154.4 g mÿ2, respectively, see Tables IV and V).Factors in¯uencing the di�erence in eucalypt leaf/pine needlefall could be:

(1) The speci®c leaf area of Pinus radiata is approximately 10 m2 kgÿ1 (Raison et al., 1992), but was4.7 for this eucalypt forest (coe�cient of variation of 10%). The pines can potentially generate thesame photosynthetic activity with a much smaller mass of leaf (needles).

Figure 6. Cumulative eucalypt òther' fall from 22/9/1980 to 14/4/1982



(2) A proportion of senescent pine needles remain in the foliage and are leached and may partiallydecompose prior to falling, which would reduce the mass value of the needlefall. In contrast, theeucalypts quickly release senescent leaves after withdrawal of nutrients; they also hang vertically, ornear vertically, which enhances detachment.

(3) Net primary production and allocation to foliage di�ers between the two species.

There was also a large di�erence in twigfall. For the pines there was virtually no twigfall, but therewas 37 g mÿ2 for the eucalypts (Table IV). It seems that most pine twigs remained attached, and wouldleach and decompose while still attached to the branches Ð at least over the time period of two years.

Barkfall from the barkfall plots

The amounts collected from the barkfall plots for each species are shown in Table VI, on a June to Juneyearly basis. While collections for year 1 commenced in December 1980, there was virtually no barkfall in theprevious few months.

There was no new barkfall in the 1982±1983 year, which was a period of severe drought, with only197 mm rain against the average of 640 mm. The very small barkfall by E. mannifera was owing todetachment of small pieces of old bark. By contrast, the trees completely debarked in the 1983±1984 year,except for the bottom 5 or 10 cm of the trunks of some trees. This was one of the wettest and possibly themost consistently wet years on record, with 1200 mm of rainfall over 140 rain days. The mean number of raindays for this area is 74 and the mean annual rainfall is 640 mm.

Figure 7. Cumulative pine needlefall from September 1980 to May 1982



Figure 8. Cumulative pine òther' fall from September 1980 to May 1982

Table VI. Barkfall from the barkfall plots (g mÿ2)

Year Year no. E. rossii E. mannifera E. rossii� E. mannifera�(June to June) (g mÿ2 mÿ2) (g mÿ2 mÿ2)

1980±1981 1 5.0 52.7 0.3 2.71981±1982 2 84.9 45.8 4.4 2.41982±1983 3 0.0 0.5 0.0 0.031983±1984 4 177.2 146.2 9.3 7.6

Mean � 66.7 61.3 3.5 3.2

Expressed as % of total bark fall1980±1981 1 2.8 36.01981±1982 2 48.0 30.01982±1983 3 0 0.31983±1984 4 100 100

1994±1995 0.01 60.01995±1996 66.0 42.01995±1996{ 92.0 55.0

�As g mÿ2 mÿ2 of basal area{Black Mountain/Bruce Ridge site



The barkfall of E. rossii and E. mannifera di�ered for the 1980±1981 and 1981±1982 periods (Table VI).There was little E. rossii barkfall in 1980±1981, but the pattern reversed in 1981±1982. The relative values areclearer (Table VI) when expressed as percentages of the 1983±1984 values, the year of complete barkshedding. Figure 9 shows the cumulative barkfall through time. The main barkfall times are similar for thespecies, but the quantitative di�erences are substantial, and the àlmost no barkfall' 1982±1983 year is veryobvious.

Additional information about barkfall was found during the 1994±1995 and 1995±1996 periods. In 1995it was noticed, initially on Black Mountain in the ACT, that E. mannifera commenced debarking later thanusual (early to mid-March) and that E. rossii was not debarking. At completion in late April, debarking ofindividual E. mannifera trees varied between 30 and 100% of the total surface area. By contrast, except for afew small areas on a few trees, E. rossii did not debark. The same patterns were observed in other similarforests in the region.

Trees in the Yass Catchment eucalypt forest were found to exhibit a similar pattern, i.e. no bark sheddingby E. rossii, but substantial shedding by E. mannifera. The extent of debarking by individual E. manniferatrees in the barkfall plots varied between about 40 and 70%, with a mean of around 60%. Our visualassessment was checked against photographs taken during the 1981±1982 period and appeared satisfactory.Bark collection was not possible because stock and kangaroos had crushed much of it.

A possible reason for the di�erent bark-shedding behaviour of these two species was found in early April1995, after observation of the debarking behaviour of some E. rossii trees near the Australian National

Figure 9. Cumulative eucalypt barkfall, 1981 to September 1984



Botanic Gardens (on BlackMountain). Eight trees of E. rossii were debarking (from about 20 to 90%). Theywere located just outside the northern boundary fence near the perimeter sprinkling system. They were in asmall depression, downslope from a sprinkler. The trees in the centre of the depression were extensivelydebarking, whereas debarking by those further out wasmuch less; and trees only 7 or 8metres from this groupwere not debarking. The function of the perimeter sprinkler system is ®re protection. It is tested monthly,delivering about 2 mm of water over the spray area. This is not enough to promote trunk growth, becausetrees near other perimeter sprinklers were not debarking. The area of the àctive' sprinkler was unusuallygrassy with a vigorous growth of shrubs. A leaky connecting pipe was found to be the cause. This, combinedwith the downslope depression, caused the trunk growth/debarking behaviour of this group of trees. Trunkgrowth means growth of all wood components Ð all of which can decorticate after su�cient growth.

These observations caused us to examine carefully the rainfall data for this 1994±1995 period and theoriginal data from the Yass Catchment eucalypt PSA. There was clearly a rainfall amount/time factor thatallowed trunk growth for E. mannifera, but none for E. rossii. The May to September period of 1994 wasunusually dry (53 mm, normal 270 mm), but there was higher than average rainfall in late December(176 mm to 6 January, normal 60) and 152 mm later in January. It seems that E. mannifera responded to thisrain, commenced growth and started shedding bark in mid-March; it usually commences in early January. Incontrast, E. rossii did not respond to the January rain, and hence did not debark.Further observations were made during the 1995±1996 summer. We noticed di�erences in the amount of

bark being shed by trees at two di�erent sites with very similar forests, the Yass Catchment and BlackMountain/Bruce Ridge in Canberra Ð only 30 km west of the Yass Catchment site. As mentioned above,bark-shedding behaviour was previously observed to be very similar at these three sites. After bark sheddingwas complete (late March 1996), the proportions of total wood surface area that had shed bark were assessedat each site. The data were derived from examination of all trees in the barkfall sites at the Yass Catchment,and from 80 trees of each species at the Black Mountain/Bruce Ridge site. These data are listed in Table VI,and shown plotted against rainfall in Figure 10a for E. rossii, and Figure 10b for E. mannifera. The BlackMountain/Bruce Ridge site is labelled (B). The amount of rain that fell prior to commencement of barkfallthat was most closely related to the amount shed, was found to be the July to December (inclusive) period forE. rossii, and September to December for E. mannifera; i.e. these periods gave the best regressions betweenbarkfall and rainfall. The regressions from these periods were substantially better than for other periodstested.

First consider E. rossii (Table VI, Figure 10a). The regression shown does not include the 1982 pointbecause there was no barkfall. There is clearly a good relationship between rainfall and bark shedding(r2 � 0�98). The 95 and 95B points (Yass Catchment and Black Mountain/Bruce Ridge sites, respectively)shows the Black Mountain/Bruce Ridge site to have 39% more barkfall than the Yass Catchment site; andits rainfall was also higher (11%). These data are close to the slope of Figure 10a. Figure 10a suggests that ifthe July to December rainfall is less than 250 mm, E. rossii will shed little or no bark.

The bark shedding/rainfall relationship for E. mannifera is quite di�erent (Figure 10b). The regression(r2 � 0�40) does not include the 1982 point because there was no barkfall. The extremely wet year (1983)gives form to the relationship, i.e. the regression is profoundly in¯uenced by this point. When this point isexcluded, the other ®ve points show no bark shedding/rainfall relationship. An interesting point is that onlyin the drought year (1982) was there no bark shedding by E. mannifera; whereas for E. rossii there were threeyears with little or no barkfall.

These ®ndings suggest: (1) that bark shedding (growth) of E. rossii is predominantly in¯uenced by periodicrainfall, (2) E. rossii may have a `drought defence mechanism', (3) except for extremes of periodic rainfall,other climatic factors a�ect E. mannifera more profoundly, and (4) that these factors were common to theYass Catchment and Black Mountain/Bruce Ridge sites in 1995. Other climatic factors of in¯uence could bedistribution of rainfall and maximum and minimum temperatures. Given the great variability in the amountand frequency of yearly rainfall, it is possible that the mean values (Table VI) may represent long periodmeans. These data certainly show the extremes.



The 1994 data support the proposal that E. rossii may have a better drought defence mechanism thanE. mannifera, in that the late December/early January rainfall in 1994±1995 did not cause E. rossii to growand shed bark, whereas E. mannifera did; i.e. the very dry May to October period set a drought defencemechanism in place for E. rossii, which the wet late December/early January period did not switch o�.During the drought year (1982) E. mannifera was more seriously a�ected than E. rossii; there were fewer

live leaves and more cracks in the bark layer. In fact, some E. mannifera lost virtually all leaf and twigs, and

Figure 10. (a) Eucalypt barkfall versus rainfall for E. rossii (period July to December). (b) Eucalypt barkfall versus rainfall forE. mannifera (period September to December)



appeared to be dying. The bark of both species cracked owing to internal moisture stress, but the cracks inE. manniferawere greater in number and wider than those in E. rossii. The moisture content and thickness ofbark may be the factors responsible for these di�erent bark-cracking behaviours. For trees of equivalentdiameter, the trunk bark of E. mannifera is 40% thicker than that of E. rossii and its moisture content is 30%greater (100 and 130% of dry weight for E. rossii and E. mannifera, respectively). This information wasacquired in September 1981 by taking disc samples of bark from a range of tree sizes, measuring barkthickness then determining the moisture content. The di�erences in thickness and moisture were remarkablyconsistent for each species (coe�cients of variation of 10 and 12%). Another di�erence between these speciesis the grain pattern of the bark. The grain pattern of E. mannifera is quite varied (almost random) comparedwith E. rossii. The E. rossii bark grain pattern is uniformly linear (vertical). When its bark ®ssured, verticalcracks appeared, but with E. mannifera, vertical and horizontal cracks appeared, in much greater numbersthan in E. rossii. The greater number and width of the vertical ®ssures in E. mannifera could be related to itshigher moisture content and greater thickness; and the horizontal cracks to its random grain pattern. In spiteof this, no E. mannifera died. In the spring following the end of the drought, epicormic growth appeared andthe trees recovered, a process described by Pook (1985).

The apparent `drought defence mechanism' of E. rossiimay also relate to the E. rossii/E. manniferamix onthe slopes. The proportion of E. rossii always increases towards the top of the slope, regardless of the slopeangle. At the Yass Catchment site, where the slope angle was only 78, E. rossii was about 20% of the totalE. rossii/E. mannifera mixture near the bottom of the slope, and increased to about 80% on the ridge, only150 m upslope. At Black Mountain and Bruce Ridge, where the slopes are steeper and longer, E. rossiiranges from less than 10% of the E. rossii/E. manniferamix at the bottom, to greater than 90% upslope. Thissuggests that E. rossii can tolerate drier conditions than E. mannifera. This is consistent with E. rossii havinga `drought defence mechanism', although there could be other in¯uential factors such as sinker roots(Ashton, 1975b). These were found in a tree root survey we did on three E. rossii in 1978, but they were notthe large sinker roots described by Ashton for E. regnans; they were small roots (less than 1.5 cm diameter)branching from the laterals and going into cracks in the bedrock Ð the bedrock was at about 60 cm. Thesmall sinker roots would certainly assist E. rossii in the drier upslope positions. We have not examined theE. mannifera root system.

Tolerance to ®re is another property that may be in¯uenced by thickness, moisture content and grainpattern of the bark. In January 1995 a number of small spot ®res (up to 30 m� 30 m) occurred in the BlackMountain/Bruce Ridge site. Observation of the burnt areas provided some interesting ideas about thepossible in¯uence of bark characteristics on tree ®re tolerance. The ®re damage on the trunks of E. rossii wasmuch greater than on E. mannifera, both in extent (height) and bark detachment. The thicker, wetter bark ofE. mannifera may be the reason for the smaller trunk ®re damage. The bark pieces that detached fromE. mannifera were much larger, up to 20 times the size of detaching pieces of E. rossii bark, and detachedmuch more slowly. A result of this was that the exposed outer cambium layer of E. mannifera had many fewerheat-induced ®ssures than E. rossii.Another interesting question about drought is, `what are the e�ects on E. rossii if a summer drought

followed a normally wet mid-year to early summer period?', i.e. drought after the growth has been switchedon. The answer is suggested by a study conducted by Pook and Forrester (1984), who described the e�ects ofsuch a drought on E. rossii in this region Ð the worst drought on record. It occurred from January toAugust 1965 after a normally wet mid-year to early summer in 1964, and resulted in the death of the above-ground parts of 30% of E. rossii. The process involved may be, that on debarking, the newly exposed layerwould not have the same insulating e�ect on heat input and evaporative water loss as old bark (Jacobs,1955), resulting in serious damage to the new, outer layer. However, lignotuber regrowth occurred for almostall the apparently dead trees. The e�ect of the drought on E. mannifera cannot be considered because Pookand Forresters' study did not include this species.

The original purpose of the speci®c barkfall experiment was to ®nd out whether the trough collectors wereproviding accurate data. By using basal area data derived from Table III, it is possible to compare the



barkfall from this area with that from the troughs area by considering the combined year 1 and 2 barkfalldata for the species combined. The combined total for the barkfall area is 128 g mÿ2 (Table VI); for thetrough area it is 124 g mÿ2 (Table IV). For E. rossii and E. mannifera, the basal areas are 38�3 m2 haÿ1 forthe barkfall area (calculated from the DBH data in Table III) and 25�4 m2 haÿ1 for the troughs area(Table I). Application of the basal area ratio (0.66, i.e. 25.4/38.3) gives a troughs area value of 125 g mÿ2,which is almost identical to the actual value (124 g mÿ2). This means that for these two years the troughcollectors did not, as we had feared, underestimate barkfall.

Floor-litter

The ¯oor-litter data discussed here were collected in August 1994. A similar collection was made in 1978,before the ¯oor was disturbed during the rainfall partitioning study (late 1978 to early 1983). It was weighedin bulk and not separated into components. The 1978 ¯oor-litter value was 2100 g mÿ2, which is very similarto the 1994 value of 2220 g mÿ2 (Table VII). There were nine years of average rainfall prior to 1994, so the1994 ¯oor-litter values should represent the long-term mean. As mentioned in the site description, there hadbeen no ®re through this area for more than 40 years.

Table VII. Floor-litter in the eucalypt forest (g mÿ2)

Leaf Bark Twig Total

Loose litter 507 116 432 105648.0%� 11.2% 40.7% 100%

Cohesive litter 998 166 116485.7% 14.3% 100%

Total litter 2220

� As % of total

These 1994 ¯oor-litter data are contained in Table VII. As stated in the methods section, the ¯oor-litterwas collected in two fractions, loose litter and cohesive litter. The loose litter was separated into leaf, barkand twigs. The òther' component (mixture of stamens, opercula, fruit, buds and frass) of litterfall could notbe separated. It is likely that òther' was quickly incorporated into the cohesive layer. Because much of thematerial in the cohesive layer was fragmented and in an advanced state of decomposition, it was not possibleto separate leaf and bark con®dently. It was, however, possible to separate obvious twig pieces. This wasdone with some reservation, because much of it was in a fairly advanced stage of decomposition. A commenton the rate of decomposition of twigs can be made from comparison of the twig proportion in loose litter, thecohesive layer and litterfall. Twigs are 40.7% of loose litter, but only 14.3% of cohesive litter (Table VII) and11.0% of litter fall (Table IV). There is a concentration of twigs in the loose litter. The leaf in the loose litterlayer is probably more quickly incorporated into the cohesive layer than twigs; which would increase twigconcentration in the loose litter. That the `recognizable' proportion of twig in the cohesive layer is so lowmay be owing to a combination of its slow incorporation into the cohesive layer and rapid decompositionwhen it is incorporated. Because of its lower content of oils, its rate of decomposition may be greater thanthat of leaf, when in the cohesive litter layer.

The ratio of annual litterfall to ¯oor-litter mass is the litter decomposition constant k (Olson, 1963), whichis the inverse of the mean residence time (Johnson et al., 1982). For this study the k value for total litter is0.15 and the mean residence time is 6.7 years. Other eucalypt forests have k values ranging from 0.14 for anE. marginata forest in Western Australia (Hatch, 1955) to 0.37 for sandstone forests near Sydney (Hannon,1958). Ashton (1975a) found a k value of 0.36 for a mature E. regnans forest in Victoria; and Polglase andAttiwill (1992) calculated the k value, in an E. regnans stand, to decrease incrementally from 0.31 at stand age0 years, to 0.23 at age 250 years.



The k values for the loose litter and cohesive layers separately, are 0.31 and 0.28 respectively; and the meanresidence times are 3.2 and 3.5 years. This suggests that a mean period of 3.2 years is required for the looselitter layer to become incorporated into the cohesive layer, and 3.5 years for incorporation of the cohesivematerial into the A0 layer.

The low k value (0.15) for this forest may be caused by a lack of understorey and its exposure to windsfrom all directions except south (see Figure 2), i.e. the ¯oor-litter, particularly the loose surface layer, maydry fairly quickly after rain. The situation is further complicated by the somewhat water repellent nature ofthe cohesive layer. It is not as profoundly repellent as the A0 layer (Crockford et al., 1991), but repellencywill reduce the moisture content of the cohesive year and, subsequently, its rate of decomposition.

Avery important and quite unusual feature of this forest is the very long period without bush ®res. A more`normal' bush ®re frequency could have a substantial in¯uence by reducing ¯oor-litter and, subsequently, themean residence time. It would also e�ect the layering of the ¯oor-litter.

Total biomass of the eucalypt forest and its relationship to ¯oor-litter

Total wood volumes (41 cm diameter) and the mean values for wood density for each tree are shown inTable VIII. Wood density was e�ectively constant over diameter classes, and the variation in density throughthe samples of each tree were quite small, as shown by the coe�cients of variation (Table VIII).

Table VIII. Characteristics of biomass trees

Tree DBH� Volume Mean density CV{ for(cm) (m3) (g ccÿ1) density

E. rossii 1 18.8 0.149 0.56 4.6E. rossii 2 13.6 0.068 0.52 3.0E. rossii 3 23.0 0.287 0.56 2.8E. mannifera 1 10.8 0.041 0.57 8.8E. mannifera 2 15.5 0.126 0.52 2.7E. mannifera 3 19.2 0.200 0.54 2.9E. mannifera 4 25.0 0.286 0.56 3.5E. mannifera 5 28.0 0.693 0.54 2.9E. macrorhyncha 1 14.2 0.104 0.49 5.3E. macrorhyncha 2 17.2 0.136 0.48 9.9E. macrorhyncha 3 23.4 0.279 0.48 9.1E. macrorhyncha 4 26.8 0.527 0.51 7.8

�DBH: diameter at breast height{CV: coe�cient of variation

The low variation in wood density provides reliable estimates of the mass from measurements of woodvolume. These were extrapolated from the plots to the forest by establishing relationships between basal areaand wood volume. The regression coe�cients were 0.98 for E. rossii, 0.85 for E. manniferi and 0.93 forE. macrorhyncha. The biomass of species in tonnes haÿ1 is shown in Table IX; wood is given in three sizeclasses. Separation of size classes was done to accommodate the variations in wood chemistry (see Paper 2,following). Eucalyptus melliodora was not destructively sampled, because there were very few in the area.They were only 4% of the total tree basal area. However, E. melliodora has a similar structure to E. rossii andE. mannifera. On this basis the biomass of E. melliodora was estimated to be 5�1 tonnes haÿ1.The estimated total above-ground biomass of 127 tonnes haÿ1 (Table IX) is low by comparison with an

E. obliqua forest in south-eastern Australia measured by Attiwill (1979), which ranged between 242 and371 tonnes haÿ1 over a period of 22 years.

Comparison of total biomass (127 tonnes haÿ1, Table IX) and ¯oor-litter (22�2 tonnes haÿ1, Table VII)shows ¯oor-litter to be 17.4% of the total live, above-ground biomass; with the loose litter and cohesive litter



components being, individually, about half of this. It may be more appropriate to compare ¯oor-litter withthe sum of the leaf, twig and ®ne twig (11�2 tonnes haÿ1, Table IX), the components forming the great bulkof ¯oor-litter. These components of the biomass are about half the value of ¯oor-litter (11.2 and22�2 tonnes haÿ1, respectively). Given that the biomass survey was done near the end of a very wet yearwhen the leaf area was almost double the normal value, it is likely that twigs and ®ne twigs will be similarlya�ected; which suggests that in a `normal' year, these biomass components could be about one-quarter of the¯oor-litter mass. The mean residence time, 6.7 years (see ¯oor-litter section above), ®ts well with this whenthe slower rate of decomposition of twigs and ®ne twigs is considered.

In an earlier study (1979) unpublished, in a forest 1 km west of this site, the roots of three E. rossii (DBHsof 15, 18 and 25 cm) were harvested and found to be 23, 24 and 27% of the total tree biomass. If the mean ofthese values (25%) is applied to all species in the PSA, the total root mass would be 42 tonnes haÿ1, giving atotal biomass ®gure of 169 tonnes haÿ1.

CONCLUSIONS

An attempt was made to explain the di�erent litterfall yields of the eucalypt and pine forests; eucalypts beingmuch greater than pines. As the pines do not shed decorticating dark, the examination centred on eucalyptleaf and pine needles, and twigs of both. The fact that eucalypt leaf-fall was 23% greater than pine needlefallwas attributed to a combination of di�erent speci®c leaf area values for eucalypts and pines, and possibleretention of a proportion of senescent needles by the pines, during which they lost weight because of leachingand decomposition. The very small pine twigfall (virtually zero) was owing to retention of the twigs after allneedles had detached.

The period covered by the experiment went from an extended àverage' period into a ®rst decile drought,followed by a ®rst decile wet period. This abnormal drought year/wet year succession did not in¯uencethe general litterfall study, because it concluded just prior to the drought. For barkfall, however, thechance combination of a drought year followed by one of the wettest years on record, subsequent tomeasurement in two `normal' years, provided insights to the debarking process. There was no debarkingduring the drought and complete debarking during the wet year, indicating no e�ective growth of woodytissue during the drought year, and unusually high growth during the post-drought wet year. The leaf-fall/barkfall data in Table IV, the measured barkfall data in Table V and observations of leaf-fall during thedrought year and wet year suggest an inverse relationship between leaf-fall and barkfall. The relation-ship would not be the same for E. rossii and E. mannifera because E. rossii is more drought tolerant thanE. mannifera.

Table IX. Biomass of the eucalypt forest (tonnes haÿ1)

Species Leaf Fine Twig Wood A Wood B Wood C Total Biomasstwig wood total

E. rossii 2.8 0.6 1.7 32.9 8.0 4.1 45 50E. mannifera 1.7 0.6 0.8 31.2 6.7 3.0 41 44E. macrorhyncha 1.4 0.3 1.0 17.5 4.8 2.8 25 28E. melliodora 0.2 0.1 0.2 3.5 0.9 0.5 5.1 5.4

Total 6.0 1.6 3.6 85 20.4 10.4 116 127

Expressed as % of total biomassE. rossii 5.5A 1.1 3.4 65.8 15.9 8.3 89.1E. mannifera 3.8 1.5 1.9 70.8 15.3 6.8 93.0E. macrorhyncha 4.9 1.1 3.4 63.1 17.4 10.0 91.0E. melliodora 4.5 1.2 2.8 66.8 15.6 9.2 87.9

Wood sizes: Wood A>10 cm; Wood B 5±10 cm; Wood C 1±5 cm.



Additional barkfall information acquired in 1995 provided insights into the e�ects of amount and time ofrainfall on trunk growth, and subsequent debarking of E. rossii and E. mannifera. Eucalyptus rossii respondsto late winter to early summer rainfall, whereas E. manniferi responds to spring in summer rainfall. Also, thedi�erent bark type (thickness, moisture content and grain pattern) on these species may provide di�erentdegrees of drought and ®re tolerance. During summer drought the bark layer cracks, which increases themoisture stress, and possibly allows entry of pathogenic organisms. The cracking of E. mannifera bark wasmuch more extensive than that of E. rossii, and the trees were noticeably in much worse condition. It ispossible therefore that the thicker, wetter, random-grained bark may provide E. mannifera with betterprotection against ®re (external moisture stress), but less protection against drought (internal moisturestress). This is consistent with their relative slope positions. Eucalyptus rossii is dominant upslope (the drierarea) and E. mannifera is dominant downslope (where it is wetter), but where ®res may be more intensebecause of greater fuel quantity (more shrubs and grasses).Layering of ¯oor-litter into two fairly distinct layers (loose and cohesive) is common in dry sclerophyll

eucalypt forests in this part of Australia, although they are not often as distinct as in this forest. Such distinctlayers are found in west-facing, gently sloped regrowth forests. Where there is a shrub later, or some grass, asoccurs in less dense forests with di�erent aspects, the two layers can still be seen, but not as obviously. Eachlayer is equivalent to about 8.5% of the total above-ground biomass, i.e. a total of 17%. The di�erentcomposition of these layers is interesting; twigs being 41% of the loose litter layer and only 14% of thecohesive litter layer. Because of the previous nine years of `normal' rainfall, the component compositionshould be representative of the long-term state. If this is so then it seems that twigs in the cohesive layer mustdecompose more rapidly than in the loose layer. As it was di�cult to separate components of the cohesivelayer, and the twigs recognized were remnants of the larger sized twigs, it is possible that they do decomposerapidly. The data presented almost certainly represent the long-term state; in this case a long term withoutbush ®res. The in¯uence of bush ®res is di�cult to predict because it will depend upon severity andfrequency.

ACKNOWLEDGEMENTS

We wish to thank the following people for their help: Frank Watson, owner of the Old Cohen property,where this project was conducted; Leslie Lockwood of the Australian National Botanic Gardens, whoprovided information on the watering systems Ð information that was the key to our understanding of thebark shedding regimes; and Owen O�er of the Canberra Meteorological O�ce, who provided the necessaryrainfall data.

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Documents

Litterfall, litter and associated chemistry in a dry sclerophyll eucalypt forest and a pine plantation in south-eastern Australia: 1. Litterfall and litter