6 Protection Quarterly VoI.9(1) 1994 Since ]986 broom has continued to spread at . Seeds may be The changing ecological impact of broom (Cytisus dispersed over long distances by streams, scoparius) by animals (horses, pigs, humans) and on at Barrington Tops, or in vehicles and machinery (Smith and Ha rl en 1991) . This has led to establish­ J. M. B. Smith, Department of Geography and Planning, University o f New ment of new individ uals and stands along England, Armidale, NSW 2351, . streams, in open, grazed places, and par­ ticularly along tracks and roads even sev­ eral kilome tres from previous infesta­ Summary tions. In recent years attempts have been The invasive European shrub broom a nd tree regene ra tion in the area made by the Forestry Commission, Na­ (CytisJls scoparills) was introduced to of Barrington Tops in 1986. Broom stands tional Parks and Wildlife Service, local the Barrington Tops plateau during the up to several hectares in area were then landholders and other land managers to 18405 and has spread particularly rap­ generally very dense and shady; the larg­ chemically or physically control such out­ id ly since 1969. In the Polblue area est shrubs at her study sites were aged by lying populations, and to keep road edges stands are now mainly over ten years old cOW1ting growth rings in basal stem discs, and o ther heavily frequented a reas dear and consist of fewer, larger and more and found to be 4-12 years old. She found of broom . Long-term control of the plant prostrate individuals than stands in the at fourteen paired sites tha t after broom is complicated by the presence of a large, Same area studied previously. Four invasion, the number of herbaceous spe­ long-lived soi l seed bank (Smith and broom growth stages are described. As cies per five square metres feU from ]7-35 Harl en 1991) from which the plant rap' stands age, partial recovery of ground to 4-22, foliage projective cover of ground idly regene ra tes after shrubs have been cover occurs, though not by all pre--exist­ stratum veg~ta t ion fell from 59-104 to destroyed. ing species, and without s uccessful re­ 1-53%, and the number of e ucalypt sap­ Stands of broom away from such places generation by broom and original lings per 25 square metres fell from 6-37 have generally been left W1trea ted, overstorey trees. Implications for the fu­ to 0-1 (30 and 35 in two anomalous plots induding in the Polblue area, and have lure of broom-invaded vege tation are with a history of recent fire). At two discussed.

Introduction Broom (Cytisus scoparius (L.) Link, Fabaceae) is a European shrub which has established itself in several othe r parts of the world as a n aggressive weed of pas­ tures and regene rating forests, where it may prevent growth of herbaceous Road Town and tree seedlings. Po lblue Swamp Though probably present elsewhere in 10 km New South Wales earlie r in the nine­ L...... J teenth century, broom was introduced as Road a garden ornamental to the property Stream "Tomalla " in the northern part of the Contour (m) Barrington Tops plateau in the 1840s. Its history in the a rea has been described by @ Study site Waterhouse (1986, 1988). Initia l spread Woodland was not recorded at the time; broom was Grassland apparently not widespread across the pla­ teau up to the 1940s, being restricted to Wetland the vicinity of cattle wateri ng pOin ts. In the succeeding two decades further , spread occurred a long logging tracks and \ fire trails, but only after cessation of ca ttle 7$00 graz ing and associated burning in 1969 \ , was rapid expansion of the broom popu­ .~. lation noticed . By 1986 broom grew across an estimated 10000 ha of Barring­ ton Tops platea u, mainly in e ucalypt woodlands and grasslands (both cleared and natural), in National Park and State Forest as well as on privately owned graz­ in g land (Waterhouse 1988). This repre· sents the largest a nd most significa nt in ­ festation by this plant in Australia, though broom is an even la rger p roblem elsewhere, notably in New Zealand (Williams 1983) and the Pacific North­ west of America (Bossard 1991). Figure 1. Locations of Polblue Swamp, Barrington Tops (top) and s tudy Waterhouse (1986, 1988) studied the im· sites at Pol blue (bottom). Broom is widespread and abundant in woodland pact of broom on herbaceous vegetation and grassland. Plant Protection Quarterly VoI.9(1) 1994 7 straddling the edges of broom stands Table 1. Characteristics of study sites; tree species (p - (both at Site a, Figure 1) which have been paucif/ora, s - E. stel/ulata, d - E. dalrylllpleana) are listed in order of monitored annually since 1986, outvvard abundance at sites where more than one occurs. expansion of 2-4 m has occurred during the seven years of observation, both by Site a b c d e lean and growth of exbting plants and by Aspect (degrees) 150-170 170 320-50 210-220 220-275 the establishment of new seedlings. Vig­ Slope (degrees) 5-7 5-12 5-10 5-10 2-10 orous regeneration by broom has also oc­ Tree Species p sp ps pds s curred locally after disturbance (herbi­ No.5 x 5 m plots 2 1 1 cide, slashing, burning). Nevertheless, No.1 x 1 m plots: most broom stands in the Polblue area no broom/Stage 1 9 10 10 9 (and probably generally on the plateau) Stage 2 2 2 1 4 15 now consist mainly of plants older than Stage 3 15 25 5 9 7 those studied by Waterhouse in 1986. Stage 4 21 23 22 In contrast to its lifespan of 10-15 years in its native Europe (Waloff 1968), broom at Barrington Tops can live for at least 23 groW1d achieved by the same plants sel­ of native vegetation beneath broom years (Smith and Harlen 1991), the great­ dom reaches half this value. This process shrubs, and permits further evaluation of est age fOWld by COWlting growth rings in of physical collapse is accelerated in some possible ecological outcomes of broom in­ basal stem discs from plants at Polblue. winters by snow. Broom flattening by vasion speculated upon by Waterhouse Even greater ages are probably achieved, snow was observed in August 1990 and (1986). The present paper describes the though this is difficult to demonstrate due from observations of similar damage is physiognomic change accompanying to the scarcity of very old stands in the presumed to have also occurred earlier in broom ageing, and reports and discusses area and to the fact that very old plants 1990 as well as in the winters of 1986 and some of its ecological consequences. commonly experience some rotting of 1992. heartwood making ring COWlting impos­ The collapse of older broom plants Broom growth stages sible. As they grow older, broom plants at means that broom shading of the groWld Observations were made in the Polblue Polblue lean and eventually become pros­ is reduced and becomes markedly un­ area of Barrington Tops (31 ' 57'S, 151 ' trate, so that while stem lengths exceed­ even. This might have great significance 26'E, Figure 1), the same area as that in ing 6 m are found, height above the for broom regeneration and for recovery which studies reported by Waterhouse (1986, 1988) and Smith and Harlen (1991) ¢ , were Wldertaken; these authors provide STAGE 1: 1-2YR general descriptions of the study area. Sites described as a, band c by Smith and Harlen (1991) are given the same letters in 1 metre the present paper. All sites lie at about 1450 m altitude, in eucalypt-rlominated woodlands or open forests. Further site details are given in Table 1 and their loca­ tions shown in Figure 1. Four 5 x 5 m plots at Polblue have been STAGE 2: 3-4(-7) YR monitored for 7-8 years; all broom plants except small seedlings (counted per square metre) were tagged, mapped, and their size recorded annually. These long­ term observations have provided a good picture of changing broom physiognomy, although ages of plants in these plots have not been accurately determined since this involves their destruction, and results from this continuing work are not fully reported here. To elaborate this Wl­ derstanding, eleven broom plants of vari­ ous sizes and typical growth forms were destructively sampled in November 1992 STAGE 3: (4-)5-9(-20) YR to record their structure and age. Based on all these data, four growth stages were delineated; they are illustrated in Figure 2, which is closely based on measured in­ dividuals. Stage 1 is the seedling stage, including the first two years of broom life. Seedlings generally establish themselves in partly open microsites (between grass tussocks, on wallaby paths, in pig-dug areas etc.) and typically achieve heights of 5-20 em STAGE 4: (8-)10-23(7-28+) YR in their first year and 20-50 em in their second. Most seedlings appear in spring Figure 2. Growth stages of broom at Pol blue, Barrington Tops. (October to November) and mortality in 8 Plant Protection Quarterly VoI.9(1) 1994 Table 2. Mean values for broom age, height and foliage projective cover; In Figure 3 the numbers of broom plants number of plant species excluding broom and overstorey eucalypts; and with stem basal areas of 1.0-9.9 cm2, and 2 percentage ground cover by snowgrass (Poa sieberiana), all other plants more than 10 (to 75) cm , recorded a t each except broom and eucalypts, and bare ground and/or litter, in 1 x 1 m occasion are plotted against approximate broom age. The plot at Site b was first de­ quadrats in broom stands at four stages of growth. scribed in late 1985 when most of its Mean Mean Mean No. plants were at growth Stage 2. Snowfall Broom Broom Broom Other the next winter (only a few weeks after Stage Age Height FPC Spp. % Pca % Others % Bare Water·house's observations) abruptly (y) (m) (%) transformed most of them into Stage 3 plants, an event which over the next two I 0.1 0.0 0.1 10.9 60.7 26.0 13.3 years was followed by a drop from 58 to 2 4.3 1.88 36.9 4.8 62.7 8.1 29.2 22 in the number of plants in the smaller 3 8.7 2.28 59.8 4.1 34 .2 8.4 57.3 size category. Only a minor part of this 4 11.5 1.96 53.4 5.1 29.6 16.0 54.4 drop was due to recruHment into the larger size category, which increased summer is heavy, especially in some and often even branches, and the canopies from 14 to 21, the re mainder resulting years, apparently associated with periods at their ends usually rise only 1.0-2.5 m from mortality. Numbers in the larger of soil dryness. At Stage 1 broom plants above the grolUld. Broom individ uals size category reached a peak of 30 when are vulnerable to being grazed (by progressively die (usually associated with the stand was about twelve years old, macropods and horses) but can recover suppression by another one lying on with several plants by then in Stage 4. well; if this is repeated, low, closely them) while the survivors continue to Continuous declines in both size catego­ branched growth forms may result, but pass through further cycles of upward ries thereafter ca n be extrapolated be­ this only occurs where isolated seedlings growth and coll apse. The largest plants tween ages 14 and 22 years, to where data grow in grassland areas which are rela­ have stems more than 6 m long and over from the Site c plot (aU plants at Stage 4) tively heavily grazed. Ungrazed, vigor­ 10 em in diameter. Extraordinary growth show further declines towards nine plants ous seedlings in well -lit places typically forms occur in wh ich long, bare stems, in the la rger size category a nd none in the make the transition to Stage 2 in their commonly showing healed splits and smaller after 28 years. third year. partial breaks, lie a long the ground, arch The overall picture is of an initially In Stage 2, which lasts for a further two over logs and boughs and eventually ter­ dense population of erect, young adult years (or longer if winters are free of minate in a canopy, parts of which may broom plants progressively thinning out heavy snowfa lls), plants remain erect and variously be supported by euca lypts or as it ages and as its plants collapse onto may achieve h eights of more than two other broom plants and in flower or fruit, each other: the plots are occupied by pro· metres. They tend to have canopies which or suppressed and dying. gressively fewer, larger p lants whose are at least as tall as they are wide, which As individual broom plants in a stand combined canopy becomes increasingly are dense and begin to have a marked ef· pass through these growth stages, the patchy. Unexpectedly, though, despite fect on herbaceous vegetation beneath population structure of the stand a lso the increase in illumination that results them, especially where they are relatively changes. This is demonstrated by the from thiS, there has been no broom closely spaced. Broom plants at Pol blue numbers of plants of different sizes re· regeneration in the plots. YOlUlg seedlings usually fi rst fl ower in their third year, but corded in two 5 x 5 m plots located within are routinely recorded a t densities of 2- 10 produce few seeds in that year or the next broom stands which became established per square metre, but most disappear (Smith and Harlen 1991). in about 1964 and 1981 respectively (Sites within a year, and a ll within 2-3 years. The succeeding Stage 3 marks the start c and b). These plots have been monitored The reasons for this total mortality are of broom plant collapse, in which stems for seven and eight years respectively. unknown, although the partial broom develop pronounced leans, though with­ out yet becoming prostrate. Directions of Site b ~ lean are towards the light, so different 60 stems from an isolated plant or within a small isolated clump may lean radially '"E to 2 outwards in all directions, whereas all C\I b. Basal area 1.0-9.9cm stems tend to lean away from a nearby ~ Q) Basal area >1 0.Ocm 2 large tree, established b room stand, or c. 40 o (/) steep slope. Only where the lean is pre­ E vented by an obstruction, such as a tree, 2 do broom plants remain erect once their (f) stems achieve lengths of 2-4 metres (char­ E acteristic of this stage) or more. Plants are eo fu lly reproductive, although parts of the [D 20 canopy which become shaded by other ci parts collapsing onto them stop fl owering z and begin to die back. Collapse progresses as stems grow longer, as suppressed, supporting stems i------~ '" die and decay, and with further episodes i i of heavy snow. The transition to Stage 4 10 15 20 25 30 typica ll y happe ns after about 10 years. Broom Age(years) Stems by that age are 4-5 m long but have become Virtually prostrate. More than Figure 3. Numbers of broom stems in two size categories growing in half their length is bare of twigs, foliage 5 x 5 m plots at various times after initial broom invasion. Plant Protection Quarterly VoI.9(1) 1994 9

60 60 !1: Bare/Litier iii > 0 0 ~ ..> .. 0 2 40 > 0 40 E ti .. .. Cl :E g Cl "e c: Snowgrass 'iii "- .. I A .. ~ Height Cl 1 .!1 .. 0 Foliage Cover 20 (; "- 20 u.. Other plants

0.1 4.3 8.7 11.5 0.1 4.3 8.7 11.5 (Stage 1) (Stage 2) (Stage 3)(Stage 4) (Stage 1) (Staga 2) (Stage 3)(Stage 4) Age(yr) Mean Broom Age(years) Figure 4. Mean values for broom height and foliage Figure 5. Mean percentage values for ground cover by projective cover in 1 x 1 m quadrats at each broom snow grass, all other ground cover plants, and bare or growth stage. litter-covered ground, in 1 x 1 m quadrats at each broom growth stage. shade still present in the plots is probably Unfortunately the latter observations growth stages d efined above, which in­ partly responsible. Auto-allelopathy were made (in January 1993) nine weeks volve the progreSSive collapse of indi­ might also be involved, but has not yet later than the former, possibly leading to vidual plants and reduction of the popu­ been investigated. more species and/or higher cover values lation. This is clearly refl ected in the being recorded than would have been the present data which show broom reaching Impact of broom on herbaceous case at the earlier time, due to plant its greatest mean height and foliage pro­ vegetation growth in the interim. jective cover at Stage 3, with subsequent The herbaceous flora of woodlands being in each of a total of 190 quadrats the fol­ drops in Stage 4 (Figure 4). inspection of invaded by broom in the Polblue area has lowing data were recorded: slope aspect the raw data showed that variations been described by Waterhouse (1986), and a ngle, foliage projective covcr by and around the mean values were particularly and broader accounts of the plateau's identity of overstorey trees, percentage of wide at Stage 4. Recorded heights in vegetation a nd flora prior to widespread ground without herbaceous plant cover quadrats at that stage ranged from 0.65 m broom invasion were provided by Fraser (bare or covered by litter), identity and in a quadrat in which broom had recently and Vickery (1937, 1939). in the present percentage cover of all spe­ become prostrate and had not yet g rown account, detailed fl oristic data are not cies in the ground cover, and for those upwards again, to 4.0 m in anothe r in provided, only the m ost significant spe­ quadrats with broom, its growth stage, which a broom plant had found support cies being named. greatest height above the ground, age (by against a eucal ypt stem. Similarly, indi­ Observations were made upon both cutting the largest contributing individual vidual quadrat values for foli age projec­ broom and ground cover, in 1 x 1 m at its base and counting the growth rings), tive cover of broom at Stage 4 ranged quadrats arranged on transects running and number of broom seedLings less than from 10 to 90%. This is also to be expected through broom stands at five sites (Sites one year old and 1-2 years old. because by this stage, when broom plants a-e, Fi gure 1). Sites were selected to all be Details of slope angle and aspect and of are typically large but prostrate, there is at the same altitude and in the same area, the overstorey canopy are summarized in considerable resultant patchiness at the to include sites from which other data Table 1. Broom seedlings were recorded scale of the quadrat size due to some have already been collected, and to cover in small numbers at Stage 1 and very vari­ places being occupied by collapsed, over­ a representative range of slope aspects, ably at later stages. Mean numbers of lapping broom ca nopies, but others only broom growth stages, and overstorey eu­ seedlings less than a year old recorded by bare stems. calypt species (Table 1). Wate rhouse per square metre at broom growth Stages As has been noted previously (e.g., (1986, 1988) showed that understorey 1-4 were 0.1.1.0,3.9 and 2.9 respectively, Waterhouse 1986, 1988) the number of vegetation and the structure and ecologi­ and for seedlings 1-2 years old were 0, plant species present at a site declines af­ cal impact of broom vary little between 1.8, 0.4 and 0.7. te r its invasion by broom, probably woodlands dominated by diffe rent euca­ Other quadrat data are summarized in mainly as a result of shading. Present data lypt species or on different slope aspects. Table 2. The full data se ts for the param­ confirm this, but also show that the re is Transects were placed horizontally eters included in Table 2 were tested for some recovery in species richness a t (along the contour) through broom thick­ statistical signifi cance using the Kruskal­ Stage 4 as the broom ca nopy begins to ets, quadrats being systematically located Wallis one-way analysis of variance, and open. Mean numbers of species (not on the upslope side of the measuring tape in every case the chance of the patterns counting broom and overstorey e uca­ used, separated by gaps of one metre. At being obtained from the same population lypts) recorded per square me tre declined four sites supplementary transects were was found to be less than 0.00 1. Differ­ from 10.9 at Stage 1 to 4.8 and 4.1 at Stages studied in the same way just o utside the ences betvveen broom growth stages over­ 2 and 3, but climbed to 5. 1 at Stage 4. broom thickets, in order to sample veg­ all are therefore highly significant in all However, this was not simply a partial etation prior to its invasion by broom or cases, and further discussion centres on return to the pre-broom invasion condi­ in Stage 1 of broom growth (no suitable mean values only. tion, as indicated by percentage cover val­ vegetation existed for such study at Site b). As broom ages, it passes through the ues fo r the dominant ground cover plant 10 Plant Protection Quarterly VoI.9(1) 1994 Poa siebenana Spreng. (snow grass), and birds typical of tall open-forests and rain­ thickets for shelter and probably bring in for all other species (Table 2, Figure 5). forest margins rather than woodlands. nutrients; these may be involved in the Snowgrass cover did not decline until Appearing in broom thickets at study success of nitrophilous species such as Stage 3, perhaps due to persistence under sites for the first time in 1993 were Urt ien incisa during Stage 4. Nutrient en­ inadequate light conditions by this peren­ leeches, another animal which presum­ richment of soil may also result from ni­ nial plant for up to a few years through ably had spread from more mesic, dense trogen fixation in broom roots, although utilization of food reserves, and a possi­ vegetation. Some larger animals includ­ in a pilot study Waterhouse (1986) was ble tendency during data collection to ing pigs and rnacropods utilize broom tulable to demonstrate this. record mainly dead snowgrass with only a few green leaves as providing full cover. KEY After a decline at Stage 3 it then failed to recover at Stage 4, and in fa ct showed Acacia dealbata some continuing decline (including total 2 absence from some quadrats) despite a. Cytisus scoparius thinning of the broom ca nopy above it. By ~ Elaeocarpus holopetalus contrast, combined cover by other ground ~ Eucalyptus dalrympleana cover species (not including broom and 10m Eucalyptus pauciflora overstorey eucalypts) fell to low levels at ~ Stages 2 and 3, but showed a pronotulced ~ purpurascens SCALE recovery at Stage 4 when it brought about a drop in the percentage of bare or litter­ covered grotuld. A. PRE-INVASION Several plants became more common at Stage 4 than they were at earlier stages in­ cluding before broom invasion and it is these species which were mainly respon­ sible for the increase in grotuld cover. They included some tall forbs, especially Senecio lnutus Forst. f. ex Willd., S. millitJItis Poiret and Urtien illeisa Poi ret and some low, creeping or rhizomatous plants in­ cluding Asperula gUllllii Hook. f. and Pratin pedtmculnta (R.Br.) Benth. Apart from the widespread S. laut_us, the tall forbs hardly occurred in the study area away from broom except in very mesic si tes. Plants frequent at Stage 1 which nei­ B. 25 YEARS AFTER INVASION ther remained nor became frequent at Stage 4 (e.g., species of Acnel1n, Glycine, Gnapilalillm, GOllocarplls, Luzula, Oreo­ myrrhis, Verol1ica and Wahlellbergin) ap­ peared to all be typical of relatively well­ lit and well-drained situations in the study area, where they grew with snowgrass.

Discussion and conclusions Broom is inducing complex ecological changes involving more than simple re­ duction of grotuld cover and its late r re­ covery as the broom canopy begins to open. The pre-existing species-rich herba­ C. 75 YEARS AFTER INVASION ceous ground cover dominated by snowgrass is partly eliminated by shad­ ing during Stages 2-3, and does not re­ cover during Stage 4. Instead, ecological conditions move towards a more mesic habitat in which some plants become more common than they were before broom invasion. The fatula appears to re­ fl ect this change. Reptiles (in particular skinks) which are abtuldant in tulinvaded Figure 6. Profile diagrams showing observed and projected stages in places, arc rare or absent from Stages 2-4. vegetation development following invasion by broom: By con trast, as Bell (1990) has demon­ i) before invasion, ii) c. 25 years after invasion, iii) c. 75 years after inva­ strated , several birds have colonized broom thickets although remaining rare sion . in uninvaded places nearby, especially i) and ii) are based on measurements of native trees and shrubs made in 2 Eastern Whipbird (which nested at Site b m wide transects at site a and of broom plants at sites a and c, iii) is specu­ in 1992) and White-browed Scrubwren, lative (see text). Pla nt Protection Quarterly VoL9(1) 1994 11 The substantial failure of woody plants, These condition s have been shown to Bossard, c.c. (1 991). The role of habitat including broom, to rep rod uce in broom­ prevent euca lypt regeneration, so Wlless disturba nce, seed preda tion and ant invaded areas is also of inte rest, as dem­ major d isturbance occurs (perhaps in the dispersa l on establishment of the exotic onstrated for eucalypts in Stages 2-3 form of bush fire, for example), it might shrub Cytisus scopariu s in California. broom by Wate rhouse (1 986, 1988). The be expected that in coming decades, as Americal1 Midlal1d Naturalist 126, 1-1 3. present investigation was not designed to ageing e ucalypts die, tree cover over Fraser, L. and Vi ckery, j.W. (1937). The elaborate this finding, although the re­ broom stands will diminish . However, ecology of the Upper Williams River corded presence of e ucalypt seedlings or other tree and tall shrub taxa grow nearby and Barring ton Tops districts. 1. intro­ small saplings (to 1.5 m) in several Stage 1 which may have diffe rent regeneration duction. Proceedings of the Linnean quadrats but in no Stages 2-4 quadrats is requirements and which may invade th e Society of NSW 62, 269-83. consistent with it. stands. They include trees of cool temper­ Fraser, L. and Vickery, jW. (1939). The Broom seedling data collected at all ate rainforest and of the narrow stands of ecology of the Upper Willia ms River sites in the present project confirm data rainforest-like vegetation growing along and Barrington Tops districts. 3. The from the long-term 5 x 5 m quadrats at some streambanks. One such species, the euca lypt forests and general discussion. Sites a, band c, in showing that the re is tall shrub Tasmannia purpumsceI1s (Vick.) Proceedings of the Linnean Society of continuous recruitment of seedlings at a A.C. Smith, common on rainforest ma r­ NSW 64, 1-33 . site afte r broom plants reach rep roductive gins and in we tter sites in e ucalypt open­ Smith, j.M.B. and Harlen, R.L. (1991). Pre­ maturity, but that after Stage 2 few of forests in the Polblue area, already occurs liminary observations on the seed dy­ these survive more than a year and possi­ as occasional seedlings and small saplings namics of broom (Cytisus scopariu s) a t bly none more tha n two years. Only in broom stands. Further in vasion, espe­ Barrington Tops, New South Wales. where there is substantial dis turbance ci ally by this and other bird-dispersed Plant Protection Quarterly 6(2), 73-8. (e.g ., cutting or h erbicidal treatment of trees, including Elaeocarpus holopetalu s Waloff, N . (1968). Studies on the insect existing broom) d oes s uccessful broom F. MueH., ma y progressively create a fa una on Scotch broom Sarothmlll1 us regeneration take place. This is d espite the novel vegetation whose origins depend scoparius (L. ) Wimmer. Advances ill Eco­ fact that in.itial broom invasion o f wood­ upon broom, but which (as the trees logiml Research 5, 87-208. lands and grasslands in the area can be overtop and shade lower strata) would Waterhouse, B.M. (1 986). Cytisus scoparius demonstrated to be continuing in the ab­ include decreasing amounts of broom. (broom) on Barrington Tops. Honours sence of any disturbance (other than mi­ This p ossible sequence is illustrated in Thes is, Dept of Geography and Plan­ nor natural processes such as branch-fall Fi gure 6. Similar fa cilitation by broom of ning, University of New England. by trees and activities of macropods), al­ the establishment of shade-tolerant native Wa terhouse, B.M. (1988). Broom (Cytis us though it does occur more ra pidly (where trees has pre vi ously been noted in New scopariu s) at Barring ton Tops, New seeds a re available) at grossly disturbed Zealand (Williams 1983). Such a change South Wales. Australian Geographical sites. would have considerable significance for Studies 26, 239-48. This leads to speculation about the fu­ land uses such as recrea tion and forestry, Williams, PA (1983). Secondary vege ta­ ture of broom-invaded vegetation at and for conservation. tion succession on the Port Hills Banks Barrington Tops. On the basis of her data, Furthe r specula ti on is not warranted , Peninsula, Canterbury, New Zealand. Waterhouse (1986) suggested three possi­ especially as broom's ecological situation New Zealand Journa l of Botany 21 , 237- ble scenarios: decline of broom and sub­ is changing in other unpredictable ways 47. stan tial recovery of the pre-existing veg­ which a re likely to influence long-te rm etation; continuing broom d ominance vegetational outcomes. Foremost is the and a decline in the tree overstorey; and introduction of herb ivorous invertebra tes replacement of broom by shad e-tole rant, in a n attemp t at bi ological control of native woody plants. Present d ata allow broom. Release of the firs t of th ese, the some evaluation of such possible long­ stem-mining moth Leucop tera spa rt ifoliella term outcomes. Hubner, took p lace in February 1993 (one From present results, it seems unlikely release loca tion being Site a), and intro­ that the dense Stages 2-3 thickets typical duction of othe r broom-feeding inve rte­ of the area in recent years, and studied by brates is planned. It is hoped tha t as a re­ Waterhouse (1 986, 1988), will recreate sult of this program the vigo ur, longevi ty themselves unless disturbed. However, it and ecologica l impact of broom will also see ms unlikely that the re will con­ be curtailed , but to what extent and tinue to be no broom regeneration at aU as with what long-term vegeta tional conse­ stands pass through Stage 4 and become quences is not yet known. ever more open. In experimental plots in a Stage 4 stand at Site c, all broom plants AckllOlvledgmel1/s were cut at their bases, but even when the I a m grateful to th e Aus tral ian Rese.:lrch cut plants were left 'in situ' and there was Council and the UniverSity of New Eng­ no other disturbance, many healthy seed­ la nd for financial assistance; to all those, lings up to arOlmd 35 cm tall were present especially G. D.Williamson, who helped within one year. An intermediate out­ with data collection in the fi eld ; and to H. come might be partial recovery by broom, Weinan d for st.:ltis ti cal and computing as individual bushes become established advice. in the increasingly large ga ps between the dying old plants, throug h survival of a References small proportion of those broom seed ­ Be ll , S.A J (1990). Effects of the weed lings which appear every year. This could Scotch broom on bird communities in well result in ecological conditions simi­ open forests on Ba rring ton Tops. Hon­ lar to those of present Stage 4 stands be­ o urs Thesis, Dept Geogra phy, Unive r­ ing maintained over long period s. sity of Newcastle, NSW.