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Research Paper 76 February l9B4

FORESTS DEPART]UIENT OF WESTERNAUSTRALIA SEEDPRODUCTION AND SURVIVAL OF SOME LEGUMES TN THE FORESTSOF ,.v* by P. R.SKINNER SUMMARY The growth and seed production patterns of sone rnajor understorey species of Western Australia's south-west forests were studied.

Monitoring over an eight-year period showed that some shorter-lived species of legumes, namel"y Acacja browniana, A .l i \t^rd^hc A mtJrr; f^1 : - PutwttcJ J d dtte A. urophvTfa, reached maturity and connenced seed production in three years and then quickly succumbed to senescence and death. The longer lived legurne species pentadenia and Bossjaea 1i-nophqlla appeared to have simi.lar seed production patterns. Two other longer lJ.ved species studied, B. laid.Lawiana and TrqnaJiun spathufatun (not a legume), did not reach their ful1 seed produclion by age eight,

There was a distinct paLtern of alternate high and low seed production years, wi-th very high seed production occurring in some species. Differences in site factors, h'ithin the narrow range of soil and moisture conditions availabl.e for each species, had no apparent influence on height growth, survival or seed production.

The majority cf the leguminous species studied completed thelr life cycle and seerned to be promoted by prescribed burning on a six to nine year pattern, There were indicaLions that hot f j.res could significantly increase seed production, and that deaths occurred earlier on clear fe11ed areas. INTRODUCTION A, nqrtifoTia, A. pentadenia, A. puJchella, A. uzophgTTa, Bcssiaea laidlawiana, A large proportion of wet sclerophyll B. linophglla and TrgnaTiun spathuTatun. karrr (Eucalgptus diversico-Zor) and rnixed These species are all fire sensitive and karri,/marri (8. calophgTTa) forest regenerate from seed, vtith the exception of understorey is nade up of fire-sensitive, B. linophglia which regenerates nainly frorn hard-seeded legune species. The nitrogen subterranean rootstock. TrgnaTiun fixing properties of these legumes play an spaxhuTatun ( Rhannaceae) was the only non- important role in fcrest fertility, and leguninous species studied ' their production of f Lrngus-inh ibi ting mi cro-or gani srns reduces the susceptibility Two to four Plots were selected for of the forest to Phqtophthota cinnamani each of the nine species. within each plot (shea, 1,979). ten (narked and nunbered) were chosen a! random within 5 m of a central peg. The non-leguminous hazel lfrgnaLiun Plots were locaLed on the greatest possible spathufatu,n) , is a rnajor sFecies of the range of soil and forest types' within karri understorey on the better loams. a 50 km radius of Manjinup, at Blue Pot Road, Pine Creek Road, Scatter Road, Seeds of these species accurnulate in the Henwood Road, strickland Road, Maxch Road, soil and lilter' and can lie dormanl for crace Road, Ant Rcad and Deans Road' very long periods. For germination t-o (Map page 3) . occur, the seed coat needs to be made permeable to water (Beadle,1940) . This is study areas were selected vthere the usually caused by fire' which cracks date of the previous burn, and hence the open the seed coat and allotr's noisture to age of the plants, was known. Al1 plots enter. Thus tbe pre-dominant hard-seeded were established before the plants had understorey species germinate prolifically reached seed-bearing age, except for one after fire (Christensen & Kimber'1975). each of the A. browliana and E. Jaidlawiana plots, sited wit-hin an area of four-year-old Since 1953 the Forests Department has scrub aL Bl.ue Pot Road (Appendix l) ' adopted the practice of prescribed burning every six to nine years' tc reduce fuel Annual height growth was measured with j.od, levels in forest understorey. a height rod over a six-year per by which time nost species had reached their A study was needed of the life cycle maximum height. and seed production of preferred understorey species (legumes)' to Survival counts were nade annually and establish whether existing burning patterns continued for a further two years, after favoured their promotion. which 13 of the original 27 plots had been disturbed (burnt or cleared) and were Growth measurementsr survival counts unsuitable for further measurements. and seed production were monitored for nine species within 27 plots over an eight Seedfall was measured by placing three year period, that is between two grcund 0.4 m2 (one tenth mil-acre) wire mesh trays cleari ng oper at ions. at randcn points within each p1ot. seedfall totals are therefore an average collecticn The plots were placed to tesl a wide from the plots of each particular species, range of site factors. It rvas clearly not just fron the ten marked plants on each establ.ished that seven of the nine species plot. Seed trays were placed in the plots studied had completed their useful in early December, before the seed pods lifecycLe and peak seed producticn had ripened, and left until late February occurred ra'ithin six years. site factors before pickup. only the seed of the species had no significant effect on growth rates under study was counted. fU vtas assumed or seed production. that the proporticn of seed eaten by insects or birds was approxinately the METHODS AND MAIERIALS same within the trays as with that falling on the surrounding area. No excessive species chosen for the study were numbers of insects were seen in the trays ACaCJa prownJdnd, A. dlvetgecs, at any stage. ,1 BLUEPOT RD. 2 STRICKLANDRD, 3 SCATTERRD, 4 HENWOODRD, 5 PINECREEK FD. 6 MARCHRD. ? DEESIDEBD. GRACE RD. 8 ANTRD, 9 DEANRD. RESULTS height incrernent progressively decreased ti11 naturity. Acacia browniana and Height A, ngrtifolia had almost reached naximum height at age three, Acacia nqrtifoiia Wj.lhin each species. soil differences showed an overall decrease in height in had little effect on height, though the its seventh year, due to severe dying back narrow range of sites available nade of leading shoots in that year (Fig. t). comparisons diffj.cult (see Appendix 1). Acacia urophg-lfa was stil1 growing in with A. pufchefla for instance, height height at age seven, growth was better on the karri loan at Pine Creek than on the podsol at Scatter The larger species, A. penxadenia, Road, while the reverse was the case with B. laidlawiana and ?, spathufatun. gtew B. faidfawiana. a! much the sane initial rate as lhe smaller species, but sustai.ned their annual The smaller- to-medium sized species, growth increment over the six-year period A. diverg€ns and A. pu-Zciella, had reached of the tria1. IndiviCual A. pentadenia at well over half their final height by the Ant P-oadreached sorne 7.5 n in heiqht at end of their third yearn after vrhich annual aqe eiqht.

Acacia browniana A. pulchella A. divergens A. myrtifolia

o o) c) E .c .9 o -

Age (years)

Trymalium A. urophylla spathulatum A. pentadenia

o o o

'P E .9 o I

Age(years)

Figure 1. Mean heights of wet sclerophyll scrub species on all sites neasured over a six year period Survival and Longevity survival rate vras higher in the first five years. After their sixth year degeneration The smaller species, A. browniana and accelerated, A. ngzxifoiia suffering badly A. puTchelTa' were short-Iived, the from insect gall attack, defoliation and majority of them being either dead or in senescence. Although Lhe A. ngrxifoTia an advanced stage of senescence by their survival-s were greater at the time of eighth year. Acacia divetgens $ras sinilar measurementin year eight. the plants were Eo A. pulcheLla at year eight, though nost severely degraded, and within three months of the renaining plants were senescent at had all died. The A. urophglla plots still that stage (fig. 2). Acacia bzowniana had several survivors one vear after the generally had the shortest life span, with final measurernents. only one five-year-old surviving at March Road. As neasurenents commencednhen plants were two to three years old, Figure 2 does Acacia ngtxifolia and A, urophglla not reflect percentage casualties prior v,'ere al-so short-li.ved, although their to this.

Acacia browniana A. pulchella A, divergens A. myrtifolia

o (Eo ,P c o 70 o o 60 o. at E (u o o n l0

Age(years)

Bossia€€ Trymalium A. urophylla laidlawiana spathulatum A. pentadenia 1m (D o) 90 .E 80 C o) 70 (t C) 60 6 o cl 50 ID U' rl0 E E I (o 30 l! o o o n E 10 z 0

Age(yearsl Figure 2. Casualties in wet sclerophyll scrub species over an eight year period. There appeared to be sone relationship danage (plots destroyed by fire, clearing betvreen the Fresence of overhead canopy and or falling trees were excluded from the survival rates of the short-lived species. assessment). The exception was the plot of The najority of plots had tree canopy B, TaidTawiana at Pine Greek' where the varying from light to heavy, and there was first death occurred when the Plants were no discernible pattern of deaths in these. four years old' and a steady deterioration At March Road, which was the only completeLy took place in the plot until remaining open area' earlier deaths were more plants died in tbeir seventh year. The prevalent in A. brawniana, A, divergens, earlier deabhs appear to have been the and, A. nvrtifolja than in conparable Flots result of conpetition from ?. spathuLaxum. in other areas (Fig. 3). which becarne the dorninant species on this site, Of the three larger species, A. penxadenia, B. l-aidlawiana and Survival rates were better in the two ?. spatiu-latun' nost plants were still B. linophglla plots. with aI1 plants surviving at age eight' the only casualties rernaining healthy in their eighth year. apparently caused by suFpression or cyclone

Acacia brcwniana A. divergens A. myrtifolia 100 c) 90 (oCD 80 o o 70 o 60 o. 50 o & P(u 30 o o m 10 0 Age (years) MARCHROAD_OPEN SITE

A. browniana A, divergens A. myrtifolia

6' o, (g o o o. at, .P (E (l) o m l0 NIL 0 12345678 Age (years) DEANSROAD_CLOSEDCANOPY Figure 3. Percentage casualties of some acacia spec ies cornpared on an open site and with cl-osed canopy. Seed Production senescence and death of most of lhe short-Iived plants and the declining seed production of A. pentadetja ' the longest- Throughout the study Period an lived of the Acacia species. alternate high,/low pattern of seed production occurred in the mature plants' TABLE I irrespective of the age of the plant of seed production ln wet sclerophyll (Table 2) , (The only species in which this Age scrub sPecies. pattern l.ras absent was ?. spatAu fatun\ ' Tlie fluctuation was not aPparent' cause of this AGE IN YEARS SPECIES No seed trays were put out in December 345678 19?1, but observations were made of pod production of lhe Acacia browniana xxxxxx flowering and seed " trees at Blue Pot divergens xxxxxl three and four-year-old " xxxxoo (burnt 1968 - ngttifalia and Deeside Roads December n ^a-r)a^^;2 xxxxxl March 1969) . The very low production " puLcheTfa xxxxlo observed rnay have been a result of the ' utophgfLa xxxxxl plant's inunaturity, but is more likely to Eossiaea faidl.awiana xxxxxx ' xxxxxx have coincided with a poor seed year' In JinoPhgLfa Ttg na f i un I p atLtul" axum ffx>txx Decenber 19'72, the foltowing seedj'ng season' plots of the four specres (A. puicheTTa, A. urophgTla, B. Taidlawiana f - flowers, no seed Produced - and .B, ljnophgl-za) containing three-year- x seed producetl I - producti.on low old plants consistently produced very high seed figures. TABLE 2 seed production in wet sclerophyll Most speci.es Froduced some seed in understorey scrub species (seeds/rn2) their third year (Table 1), though the ccunt was generally loh'. Much of the aborted during Lhe YEAR early SPECIES flowering or budding stage. seed L972 r9?3 1914 1975 L976 production continued until age sj.x or Acacia brawniata 14577465575 seven in all the short-lived , 1325 LO 3a22 50 52 after which the deaths of many plants' and ' ngxxifolia 985 r0 1107 drastically 2225 50 272 42 5 senescence of the remainder' " puTcheTla 3905 65 395? a7 - reduced production. Acacia pentadenia . uroph|lla 4490 185 3705 s45 392 produced seed in its fourth year, Bossiaea laidlaviana 57 5 25 22 445 most n li.ophglla 130 21 1317 r27 70s after which production progressively rqnaTiun spaxhulaxun - 2 185 1t75 4800 decreased unti.I its eighth yearT while B, Tinophgtla appeared to reach its peak at six-years oId' as its production at sone species were consistently high eight-years was significantly lower seed producers, particularly A. divergens' (.001 level in chi-square test). A. puTchella and A. urophgTTa. Other species were uniforrnly lower seed producers- The longer-lived B. TaidTatr'jara and T. spathuJaxun had apParently still to Each species showed some variation reach full production when these trials between sites' however, j.t was concluded. ?rqmal"ium spathufatum, in nost cases. The exception produced no seed untj'I its fifth year' insj.gnif i.cant was the March Road site, which over the Although inflorescence occurred in this five-year period produced a significantly species at ages three and four, it greater quantity of seed (varying from aborted prior to seed forming. ,01 to .001 in indi.vidual years' Studentrs divergens, A. ngrtifoiia' The distinct pattern of high and low t tes!) for A, A. urophqLfa and B. linophgl7a. Acacia seed years is shown in Table 2, the browniana had significantly higher seed difference between both being significant production at March Road in 1972 (.001 by at the O.O5 level (student's t test). The Student's t test.) but by 1974 most plants lolv total seed production in 1976, which , were dead or senescent and production (according to the pattern) should have was low. been a high Year' was caused bY the DISCUSSION (0.05 level, S tudentrs t test), at Ieast throughout the terrn of this trial, but the reason for The effect of site differences on this was not clear. The high or 1ow seed year hej.ght grorrth was not established, the mean effect hras apparent height of each species on different sites in all species except ?. spatttulatun (the being similar, despite considerable only non-legume), in which seed production built gradually variation in individual plants. ft was up from the fifth year (Table 2) observed thal plants tended to more . bushy growth on the open sites. site and shade factors had no obvious €ffect on production, Soil type had no apparent effect on seed as indi.vidual plots survival xates as deaths nere recorded at under heavy shade achieved similar seed a fairly even rate within each species, counts to those grown in the open. The higb seed production over the whole range of sites. Dealhs were of a1I species at March Road slightly earlier at March Road. Though could have been due to the site beLng subjected prior monitoring was not carried out for any to a very hot burn to germination species frorn germinaticn to age two or nore, and subsequen! ashbed effects (Loneragan it was observed that many casualties and Loneragan, L964, . occurred in nost species durj.ng this period. OpLinum production Studies on the ecology of Boronia negastigma seed for the legune species appears shor{ that seedling death rate accelerates to fall well within the usually prescribed - frorn age one to age three, almost half the burning cycle of 6 9 years, and this patlern seedLings dyi.ng over this period. Mortality is suitable for the speciesr prornotion. is greatest where seedling density is However, best seed germination depends highest (Christensen and Skinner,1978). not on the frequency of burn, but bn the intensity and season of tha! burn. From the beginning of the trial (at two years old), the size of the existing seed on or j.s plants had no apparent relationship to within the litter layer mos! probably destroyed survival, as deaths occurred fairly evenly in the hot fire needed sCimulate germiantion throughout the height range in each plot. to of seed buried in the rnineral soil. A cooL fire is Seed bearing began in all the legume unlikely to induce any germination at species during their third year. ft was all, not established whether the low production Spring-induced gerninants observed in 1971 was due to the plantrs are susceptible to suruner immaturity. or ri'hether seed production r,Jas drought. and browsing by native fauna, generally low. Seed production reached a peak in the fourth to sixth year of growth Therefcre, in the shorter-lived species, then decreased although sufficient seed production is availabl.e over the next two years, by which time the for long tern maintenance of majority of plants were dead or in an legume scrub under current burning advanced state of deterioration. regimes, more research is needed into the season and techniques of prescribed burning; a conbination The longest-Iived species, A. penxadenia, of spring and autumn burns could be desirable, reached peak seed production j.n its fourlh year, but suffered a dramatic decrease in its sixth year (Table 2). Seed tray figures showed a continuing decline in seed production for the subsequent two years, and production ln the ninth year, after ACKNOWLEDGEMENTS these trail-s had finished, was observed to be alnost ni]. This poses the question: My thanks to those officers of the are early seeding and a relatively short Manjimup Fcrests Departnent Research seed producing life features of both Station who assisted h'ith the field work at short and long-lived Acacias of the various ti$es throughout the study. I karri forest? also wish to thank Dr. P. Chri.stensen and Mr. P, Kimber for their valuable hetp and rFha r.i ^r- --n I ^,. -r,-16 ^f r't l-arhrF^ rrr9rr qrru lew criticism. and Mj.ss F. Styles for her help seed producing years was significant hrith drafting and diagrans. l I t. REFERENCES CHRISTENSEN,P. and SKINNER, P. The ecology of Eoronia negastigna (Nees) in Western Australian forest areas. Research Paper No. 38, L978, Forests Departnent BEADLE,N.C.W. (1940). Soil tenperatures of Western Australia. during forest fires and their effect on the survival of vegetation. Journal LoNERAGAN,o.W. and LONERAGN,I,J.F, (1964). of Ecology 28, L80-L92. Ashbed and nulrients in the grolrth of seedlings of karri (Eucal-gpxus CHRISTENSEN,P.E. and KIMBER'P.C. (1975'. diversicoToz) F.v.M.J. RoyaL Society of Effect of prescribed burning on the Western Australi.a, 47, 75-80, flora and fauna of south-west Australian forests. Proceedings of the Ecologicai SHEA, S. Forest Focus No. 2I, April 1979. society of Australia 9, 85-106. Forests Department of Western Australia. ri ,l APPENDIX13 Delails of wet sclerophyll scrub 6Pecies Plots.

AGE AT DATE OF LOCALITY SPEClES SOII, TYPE !.ORESTTYPE ESTABLISHMENT I,AST BURN

BIue Pot Road Acacia btowniana 4 years old Nov. 1967 Loam Karri, dense undersLorey Sossiaea Taidlawiana

Deeside Road ecacja pentadenia Dec. 1968 Karri loam I[arri/karr! Acacia uraphglTa clear feLled coupe

March Road Acacia browniana Jan, 1969 Podsol clear felled coupe A^a^; - t1; t'a,dana toam (Karrilmarr i ) Acacia ngrtifolia PodsoL Acacia urophgTTa Loam Bossjaea linophgTTa Podsol

Ant Road Acacia divezgens 3 years oLd .tan. 1969 Silty loan Acacia pentadenia Karri loam

Deans Road Acac ia bzowniana March 1969 Podsol Jarrah/marri Acacia divergens Silty loam Clear felled couPe Acacia ngrtifoJia Podsol Jarrah/marr i Acacia pentadenia Loam clear felled coupe (karri) Tzgnaliun spathulatum Sandy loam

scatter Road Acacia pulcheTla Dec. 1969 Podsol Jarrah/karri

Henwood Road Bossiaea linophgTla Dec. 1969 sandy loam Marri/karri

Pine Creek Acacia puLchelTa 2 years old Dec. 1969 Karri loam Yrarr!/katti Road Acacia urophg 7Ia Karri Eossiaea TaidLawiana Karri

strickland Acacia pu7che77a April 1970 Loam Karri Road zaan i a trranhttl la Bossiaea laidlawiana

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