FORESTS DEPART]UIENT of WESTERNAUSTRALIA SEEDPRODUCTION and SURVIVAL of SOME LEGUMES TN the FORESTSOF WESTERN AUSTRALIA ,.V* by P

'.-l ' ,, . -r- '- 1$ nl i .,,/i.,iL. i r oDC 177. 36 , t81.522 Research Paper 76 February l9B4 FORESTS DEPART]UIENT OF WESTERNAUSTRALIA SEEDPRODUCTION AND SURVIVAL OF SOME LEGUMES TN THE FORESTSOF WESTERN AUSTRALIA ,.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 Acacia 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 plants (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 plant 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.

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