United States 

Department of 

Agriculture 

Forest Service 

Pacific Southwest 

Research Station 

Research Paper 

PSW-205 

Site Preparation Affects Survival, 

Growth of Koa on Degraded 

Montane Forest Land 

Paul G. Scowcroft Kenneth T. Adee 
Scowcroft. Paul G.: Adee. KenncthT. 1991. Site orenaretion 

. . sNectssurvival, growth of 

LOY on degraded rnonlanc forest lund. Rer. Paper PSW-205. Berkelcy. CA: Pacific 

Southwest Rercarch Station, Forest Scrvice. U.S. Department of Agriculturc: 7 p. 

Banana poka vines (Possifloro mollisrimo) and kiiyu pass (Pennirerurn clondestinum) 

can limitkoa(Acociokoo)rreforertation in Hawaii. Performanceofplanted koaseedlings was 

studied in relation to type of site preparation: broadcast spraying of Roundup herbicide at 

threerates (2.M.4.05, and 6.07 kg active ingredient per hectare) andhand scalping vegetation 

fmm each planting spot. One year after planting, survival and growth of koa seedlings were 

significantly greaterinplotsspraycd with a he~vydoseofRoundup thanincon~Ip1ots. Tenyear survival and height were significantly greater for the heavydose treatment than for the 

scalp ueament, but none of the Utes in thc control treatment were alive. Site preparation 

must control competing vegetation over the entire planting area, to give koa a competitive 

edge during establishment. 

Rcrrievol Tern: Acocio Iroo, Possiforo mollissirno, Pennisetum clandesrinurn, competition, 

Hawaii, reforestation 

The Authors: 

PAUL G. SCOWCROFT is a research farestcr assigned to the Forest Management Research Unit in Hawaii at the Station's Institute of Pacific Islands Foresuy. headquartered in 

Honolulu. KENNETH T. ADEE was aresearchfmsterassizned - to thcNativeHawaiian 

Forest Ecosystems Rescarch Unit at the Station's Institute of Pacific Islands Forestry 

headquartered in Honolulu. He currently works as programmer analyst with hd Managcment~lanning, WiUamctte National ire st, ~ugek, Oregon 

Acknowledgments: 

Research in Hawaii by the Forest Service. U.S. Depanment of Agriculture, is conduetcd 

in cwwration with lhe Division of Faresw and Wildlife. Hawaii Depanment of Land and 

~aturk Resources. 

We lhmk Gerald Waltcrs and Howard Sakai for help in study design and establishment; 

lamer Baldwin for statistical guidance: and Gene Conrad. Howard Horiuchi. Roben 

Memiam.Audrey Newman,RabenStrand,and Charles Wakidsforreviewing anearlier draft 

of this manuscript. 

Publisher: 

Pacific Southwest Research Station 

P.O. Box 245, Berkeley, California 94701 

March 1991 
Site Preparation Affects Survival. 

Growth of Koa on Degraded 

Montane Forest Land 

Paul G . Scowcroft Kenneth T . Adee 

CONTENTS 

.. In Brief .............................................................................................................................. 11 

Introduction ...................................................................................................................... 1 

Study Area ........................................................................................................................ 1 

Methods ............................................................................................................................. 2 

Data Analysis , .................................................................................................................. 2 

Survival ....................................................................................................................... 3 

Stem Height ................................................................................................................. 4 

Stem Diameter ............................................................................................................. 5 

. . Other Stand Charactenstics ......................................................................................... 5 

Relative Height Growth Rates ..................................................................................... 5 

. . Seedling Posit~on and Vigor ........................................................................................ 6 

Block Effects ............................................................................................................... 6 

ManagementImplications ............................................................................................... 7 

References ......................................................................................................................... 7 

USDA Forest Service Res . Paper PSW.205 . 1991 . 
IN BRIEF. . . 

Scowcroft, Paul G.; Adee, Kenneth T. 1991. Site preparation 

affects survival, growth of koa on degraded montane 

forest land. Res. Paper PSW-205. Berkeley, CA: Pacific 

SouthwestResearchStation,ForestService,U.S.Department 

of Agriculture; 7 p. 

Retrieval Terms:Acacia koa, Passifora mollissima, Pennisetum 

clandestinum, competition, Hawaii, reforestation 

Restoring native, mixed-species forests on degraded montane 

lands of Hawaii has become a desirable goal forFederal, State, 

and private land owners. For some owners the main objective is 

to restore habitat for recovery of threatened and endangered 

forest species. For others the main objective is to grow commercial-size koa and other high-quality native hardwoods. And for 

still others the objective is to reestablish the flow of multiple, 

forest-derived benefits. Regardless of the objective forrestoring 

native forests, owners share a common concern-what can be 

done to establish and speed development of such forests? 

The question is difficult to answer partly because many 

aggressive introduced plants and animals have become naturalized; they compete intensely with native forest species. Cattle 

grazing is incompatible with maintenance and restoration of 

nativeforests. Koa(Acacia koa), oneof the two main overstory 

trees inHawaiian forests and a key species in reforestationplans, 

is particularly vulnerable to damage by cattle. Banana poka 

(Passflora mollissima) and kikuyu grass (Pennisetum 

clandestinum) are two introduced plant species that can limit 

reforestation success in Hawaii. 

This paper reports the results of alternative types of site 

preparation on survival and growth of planted koa seedlings in 

an area heavily infested with banana poka and kiuyu grass. A 

randomized complete blockdesign was used to study theeffects 

of (a) broadcast spraying of Roundup herbicide at three rates 

(2.02,4.05, and 6.07 kg active ingredient per hectare) and (b) 

handscalping ofvegetationfroma0.3 square-meter areaaround 

each planting spot. 

The heavy-dose herbicide treatment most effectively controlled competing vegetation during seedling establishment. 

One year after planting, 74 percent of the seedlings were above 

competing vegetation in the heavy-dose treatment, only 22 

percent were bent over or covered by banana pokavines, and 95 

percent had acceptable to high vigor. In contrast, none of the 

seedlings were above competing vegetation in the control, 82 

percent were bent over or covered by banana poka vines, and 

only 45 percent had acceptable to high vigor. This difference in 

degreeofcompetitioncontrolresultedinsignificantly greater 1- 

year survival, height, and relative growth rate of koa seedlings 

in the heavy-dose treatment than in the control. 

Ten years after planting, none of the trees in the control 

treatment were alive. Ten-year survival, total height, height to 

crown, and height to first major fork were significantly greater 

for the heavy-dose treatment than for the scalp treatment. Type 

of treatment did not significantly affect 10-year mean stem 

diameter, which ranged from 8.7 to 12.4 cm at breast height. 

Successful establishment of koa on sites occupied by banana 

pokaand dense stands of kikuyu grass depends on adequate site 

preparation to control competition. A heavy dose of Roundup 

proved an effective means of imposing such control. If a 

manager decides to use herbicide, werecommend that the entire 

planting area be treated rather than just the small area around 

each planting spot. Disk plowing of grasslands is an alternative 

form of site preparation that has been used successfully on the 

Island of Hawaii. We also recommend that planted areas be 

periodically weeded for5 to 10 years to keep bananapokavines 

from damaging the developing stands. 

USDA Forest Service Res. Paper PSW-205. 1991. 
INTRODUCTION 

ore than 1,000 hectares of cattle pasture and degraded 

montane forest on the Island of Hawaii may be planted 

withkoa (Acacia koa)duringthe 1990's toacceleraterestoration 

of nativemixed-species forest habitat for threatened and endangered buds (i.e., the Hakalau Forest National Wildlife Refuge) 

or to help build an economically viable timber resource. Koa 

was selected for planting because (a) it is an important component ofhabitatforendangeredforest buds, suchas theakiapolaau 

(Hemignuthus munroi), Hawaii creeperfOreomystismana), and 

akepa (Laxops coccineus) (Scott and others 1986); @) it is a 

nitrogen-fixing, pioneer species in disturbed habitats during 

secondary succession, thus creating conditions favorable to 

reestablishment of other native plants (Mueller-Dombois and 

others 1981); and (c) its commercial value exceeds that of all 

other native Hawaiian trees (Skolmen 1968). 

The areas targeted for reforestation-portions of the eastem 

flank of Mauna Kea between 1,500- and 2,000-m elevationsupported koa and ohia-koa forests before 1800. But with the 

advent of cattle and sheep ranching in themid-l800's, extensive 

tracts of closed-canopy forests were converted to open pastures 

and grazed woodlands (Cuddihy and Stone 1990). Forests 

adjacent to the ranches were degraded by the frequent incursion 

of livestock. 

Two of the more formidable obstacles to successful reforestation are cattle grazing and interspecific competition. Cattle 

grazing isincompatible with koareforestation, especially during 

stand establishment and early development. Koa reproduction 

is completely suppressed by cattle grazing (Baldwin and 

Fagerlund 1943, Mueller-Dombois and others 1981, Scott and 

others 1986, Whitesell 1964). Cattle prefer young koa to grass 

(Skolmen 1990). Saplings are straddled and trampled by cattle 

in their quest for succulent foliage (Whitesell 1964). and both 

saplings and pole-size koa are barked by cattle. No one knows 

how long cattle must be excluded from a koa reforestation site 

before the trees become resistant to these types of injury. 

However, managers generally agree that cattle no longer damage koa once the bark becomes thick, rough, and scaly (Horiuchi 

and Wakida 1989). 

Numerous grass species have been introduced to improve 

forage quality. Some of these grasses form thick, dense stands 

that compete with woody seedlings for water, nutrients, and 

light; kikuyu grass (Pennisetum clandestinum) is one of these. 

We suspect that, of the grasses, it poses the greatest threat to 

regeneration of native forest species. However, the seriousness 

of the threat from kikuyu grass is still open to question. 

Banana poka (Passiflora mollissima), an aggressive introduced vine, is also a serious threat to reforestation. Readily 

dispersed by feral pigs (Sus scrofa) and introduced fruit-eating 

birds (Cuddihy and Stone 1990). poka shrouds seedlings, saplings, and evenmoderately largeadult trees in a blanket of vines. 

Reduced growth, lodging, and breakage of koa trees result. 

Successful reforestation will probably require development 

and application of a silvicultural plan that addresses issues such 

as seed source (location and quality of the parent tree), nursery 

practices, site preparation, planting and replanting practices, 

post-planting maintenance practices, and protection against 

animal damage. Research can provide information to help 

develop reforestation plans. 

This paper reports the results of site preparation on survival 

and growth of planted koa seedlings in an area heavily infested 

with kikuyu grass and banana poka. 

STUDY AREA 

The mesic study site lies on the northeast slopes of Mauna 

Kea at 1,550 m elevation in the Humuula section of the Hilo 

Forest Reserveon the Island of Hawaii. Median annual rainfall 

is about 2,300 mm (Division of Water and Land Development 

1982). The period May through Septemberisthedriestseasononly 25 percent ofthe annual rainfall occurs during the 5-month 

period. Mean annual temperature is about 15 "C (Division of 

Water and Land Development 1970). Formed in volcanic ash, 

the well-drained silt loam soilis a thixotrophic, isomesic, Hydric 

Dystrandept of thePuu Ooseries (Sato and others 1973). These 

soils are high insurfacelayerorganic matterand, generally, they 

have a large capacity to fix phosphorus into forms unavailable 

to plants. The topography is undulating with 6 to 12 percent 

slopes. 

The forest is an open koa-ohia type. Mature and senescent 

emergent koa trees dominate the overstory. Scattered ohialehua (Metrosiderospolymorpha), pilo (Coprosma spp.), and 

tree fern (Cibotium spp.) arealso present. Kiuyu grass, banana 

poka, the native Hawaiian raspberry (Rubrrs hawaiiensis), and 

blackberry (Rubusargutus) dominate the shrub and herbaceous 

layers. Velvet grass (Holcus lanatus), puu-lehua grass 

(Microleana stipoides), knotweed (Polygonum glabrum), 

nipplewort (Lapsana communis), bracken (Pteridium 

aquilinium), and laukahi (Dryopteris paleacea) are also common ground cover species. 

We chose this degraded forest area because it was typical of 

other portions of the windward side of Mauna Kea targeted for 

koareforestationanditwaseasily accessible. Thestudy areahad 

beengrazed in the past, but atthe timeof thisstudy allcattle had 

been removed. Feral pigs were common. Kiuyu grass and 

banana poka infestations were heavy. and natural koaregeneration was sparse. 

USDA Forest Service Res. Paper PSW-205. 1991 
Table 1-Avcmge pemcnt change of bnmm poka and grass cover three 

months aJ?e/for applying hrrb{cidcs in herbicide screening trials' 

METHODS 

We conducted apreliminary study to determine which herhicide' to use in the chemical treatments-Roundup2 [N- 

@hosphonomethyl)glycinel or a mixture of Dowpon W [2,2- 

dichloropropionic acid] andKarmexZ 13-(3,4-dichloro-phenyl)- 

1,l-dimethylurea]. Roundup was tested at two concentrations--4.05 and 8.10 kg active ingredient (a.i.) per hectare. 

Dowpon andKarmex were testedin three mixhlres--8.29kga.i. 

Dowpon and 8.96 kg a.i. Karmex per ha; 8.29 kg a.i. Dowpon 

and 16.8 kg a.i. Karmex per ha; and 12.43 kg a.i. Dowpon and 

17.92 kg a.i. Karmex per ha. Each herbicide was sprayed on a 

separate set of three 5-by 5-m testplots. The percent loss oflive 

bananapokacoverand grass cover was estimated 3 months after 

spraying. 

Data obtained in the herbicide screening test was subjected to 

one-way ANOVA and the Bonferroni method of multiple comparisons (Neter and Wasserman 1974) using a family Type I 

error rateof no more than 0.025. Resultsindicated thatRoundup 

was more effective at controlling banana poka than any of the 

DowponKarmex mixtures (table I). Roundup was as effective 

at controlling grasses as the DowponKarmex mixtures. On the 

basis of these results, we selected Roundup [or use in the main 

study. 

We used a randomized complete block design to study the 

elfect of chemical and mechanical site preparation on survival 

and growth of koa seedlings. Three blocks, each large enough 

to conlain five 10- by 10-m treatment plots and their associated 

2.5-m bufler strips, were delineated in an area that we believed 

was representative of the upper portion of the Humuula forest. 

Two of the blocks lay side-by-side; the third block lay about 75 

m north of the others. All three blocks were in the open and not 

shaded by nearby mature koa trees. The blocks were fenced to 

exclude cattle and feral pigs. 

Five treatments were randomly assigned toplots within each 

block-three chemical treatments, one mechanical treatment, 

and a control treatment. The chemical site preparation treatrnenLv were Roundup applied at three rates: 2.02 kg a.i. per ha 

(light dose), 4.05 kg a.i. per ha (moderate dose), and 6.07 kg a.i. 

per ha (heavy dose). Herbicides wereapplied to entireplots, not 

just to planting spots. The mechanical treatment involved hand 

scalpingof thevegetationina0.3 square-meterareaaroundeach 

planting spot. 

Koa seedlings were grown at the Division of Forestry and 

Wildlife, Central Tree Nursery. The seed collection area was 

about 2.5 km from the study site and located within the 

Laupahoehoe section of the Hilo Forest Reserve between 1.400 

'This papermilher recommends thc pesticide uses reponed nor implies that 

he pesticides have been registered by the appropriate gavernmcntal sgmdes. 

'Tradenamesorwmmercialbrand~arementionedsole1yforiomaon. No 

cndonement by the U.S. Department of Agriculture ir implied. 

I Treatment 

(kg a.iJhn2) 

Roundup: 

4.1 

8.1 

------------percent 

-70 (8) -97 (0) 

-86 (4) -97 (0) 

DowponKamcx mix: 

8.3:9.0 

8.3:16.8 

124:17.9 

'Standard errors of the means (to the nearest percent) are rhourn in 

parentheses. 

'kg a.i./ha = kilograms of active ingredient per hectare. 

I 

Type of cover 

0 (0) -95 (1) 

-34(18) -99 (1) 

-23(14) -100 (0) 

Control 

to 1,800 m elevation. Planting was done in February 1978, 8 

weeks after herbicides were applied. Sixty-four dibble seedlings were planted in each treatment plot on a squarespacing of 

1.25 m. Scalping was doneat timeof planting. No weeding was 

done during the first year of growth. 

Only the 36 inner trees per plot were used to evaluate 

treatment effects. Height, vigor class (high, acceptable, low, or 

dead), and position with respect to surrounding vegetation 

(shorter, same height, or taller) were recorded foreach seedling 

at time of planting, and at 3,6, and 12 months after planting. 

Heights were measured from the root collar to the terminal 

irrespective of the lean of the tree. 

No additional data were collected until October 1987 when 

we measured height, diameter at breast height (1.4 m above 

ground), disease class (yes or no), height to the base of live 

crown, and height to the firstmajor fork. During theintervening 

years, bananapokavines and other overtopping vegetation were 

cut from surviving trees several times. No other weeding or 

maintenance was done. 

Banana poka 

+19(10) 0 (0) 

DATA ANALYSIS 

Grasses 

Differences in survival were evaluated at one year and ten 

yearsafterplantingnsingone-way ANOVA with threeobservations per treatment. Proportions were subjected to angular 

transformation for analysis. Because the 36-tree plot was the 

sampling unit, not the individual seedling, the treatment-block 

interaction was used as the error term for hypothesis testing in 

this and all other ANOVA's. Differences among treatment 

means wereevaluated by Tukey's method of multiplecompariUSDA Forest Service Rer. Paper PSW-205.1991 
sons. Mean survival data and associated standard errors in 

arcsine units were back-transformed for presentation. 

Differences in mean stem height were examined one year 

after planting using two-way ANOVA. The factors were 

treatment and block. Differences among treatment means were 

evaluated using Tukey's method of multiple comparisons. Because of differences in mortality, there were an unequal number 

of seedlings per cell. 

The preceding analysis couldnot beused with the tenth-year 

height data because some experimental blocks had no survivors 

(e.g., none of the trees in control plots survived). Instead, 

differences in heights among treatments were evaluated using 

theGames and Howell procedure for multiplepainvisecomparisons (Games and Howell 1976). The Bonferroni t statistic 

(Bailey 1977) wasused as the criticalvaiueforrejecting thenull 

hypothesis. Degrees of freedom were calculated using the 

Satterthwaite approximation (Games and Howell 1976). There 

were six comparisons. Each comparison was done at a significance level that achieved an overall Type I error rate of at most 

5 percent. 

Differences in mean stem diameter at breast height were 

evaluated for the tenth year only. The Games and Howell 

procedure was used to assess treatment effects. 

Periodic height growth of the seedlings during the fust year 

after planting was examined using mean relative growth rate. 

Height data for the periods 0 to 3 months, 3 to 6 months, and 6 

to 12 months were used tocalculate relative growth rate (RGR) 

based on the formula 

RGR = (Ht,/H,,) 1'(t2-tL) -1 Eq. 1 

whereH I, and H , are stem heights at time t, and t,, respectively. 

RGRcan beinterpreted as the rate of interest on thecapital, that 

is, the rate of height growth per unit of initial height. Units for 

RGR are centimeters of growth per centimeter of initial stem 

height per month or percent height growth per month. 

- 

Meanrelative growthrate ( RGR ij) for aplot was calculated 

- nij 

RGRij=(z RGR,3hFj Eq. 2 L.- 1 

whereRGR**is the relative growth rate forthe k*seedling in the 

j* block and P treatment, and nij is the number of trees in each 

plot. 

Treatment and block effects were examined using the SAS 

general linear models (GLM) procedure (SAS Institute 1985). 

Only those seedlings that were alive 12 months after planting 

were used to calculate mean RGRs. Differences among treatments were tested using Tukey's multiple comparison procedures. Each comparison was done at a significance level that 

achieved an overall Type I error rate of at most 5 percent. 

RESULTS 

Survival 

Average seedling survival one year after planting ranged 

fromahighof 85 percent(f8.4percents;)forplotssprayed with 

a heavy dose of Roundup to a low of 30percent (k 14 percents;) 

forcontrol plots Lfig I). Theimprovement in first-yearsurvival 

in plots sprayed with a heavy doseof herbicide was statistically 

significant. Survival in herbicided plots treated with moderate 

and light doses of Roundup and in scalped plots was not 

significantly different from that in control plots. 

Treatment 

- Heavy Roundup 

-----. Moderate Roundup 

a ---- Light Roundup 

Scalp 

Control 

0 2 4 6 8 10 

Elapsed time (years) 

Figure I-Survival of planted koa as a function of elapsed time since planting and type of site preparation treatment. Ten-year means followed by the 

same letter are not significantly different at the overall significance level of 0.05 (Bonferroni 1-test). 

USDA Forest Service Re. Paper PSW-205. 1991. 3 
Ten years afterplanting, 51 percentof the koain plotsinitiaUy 

sprayed with a heavy dose of Roundup were still alive (fig. 1). 

In contrast, none of the koain control plots were still alive. The 

heavy herbicide treatment was the only one that significantly 

improved 10-year survival compared with thecontrol. In figure 

1, the moderate herbicide treatment and the scalp treatment 

appear to have better survival than the control. But large 

variability among replicates and small sample size prevented 

detection of significant treatment effects (table 2). 

We attributed the improvement in survival mainly to the 

beneficial effects of site preparation, not to the beneficial effects 

of plot maintenance. All plots were weeded at identical times 

and with equal thoroughness. All trees should have benefited 

from weeding equally, regardless of site preparation treatment. 

Differences in site preparation affected how often weeding 

was needed. For example, weeding wasneeded mostfrequently 

in the control treatment andleast frequently in the heavy herbicide treatment Butweedingwasnotdoneona~as-neededbasis. 

Rather it was done infrequently and at irregulaiintervals. In the 

interim, competing banana poka vines tended to overwhelm koa 

in all except the heavy herbicide treatment. We believe that the 

initialcompetitiveedgeconferredon treesin theheavy herbicide 

treatment lasted several years. Whatever competitive edge was 

given to trees in theother site preparation treatments was not as 

longlasting. Hence, trees growing in plols with such treatments 

were adversely affected by competition between weedings. 

Stem Height 

One year after planting, the mean height of koa seedlings 

ranged from 0.6 m (+ 0.1 m s:) in scalped plots to 1.7 m (k 0.1 

Table 2--Mean' survival, lree height, diomclcr nl bras1 heighl (1.4 m), 

heighl lo crown, and height lofirst fork of koa lrecr lOyeorsnfterplanling, 

by treOrmcnP 

Treaunent 

'Means within a column followed by the same letter do not differ significantly at the 0.05 level of statirtical significance (Bonfenoni t-test). 

'No koa trees in the control treatment survived. 

'?he 95 pct confidence intervals are in parentheses. Confidence interval = 

mean i (t)(d: alpha 5 0.05: 

Roundup: 

Heavy 

dorc 

ModElate 

dose 

Light 

dare 

Scalp 

df = n - 1: s-;= (C +I ~$1") 0.5: mean = il ixiln 

'Mean percent survival bared on n = 3. 

Sample 

dze 

3 

2 

2 

3 

m s;) in heavy-dose plots. Trees planted in plots sprayed with 

heavy or moderate doses of Roundup were significantly taller 

than those in control or scalped plots (fig. 2). 

Ten years after planting, the mean height of surviving koa 

trees in the heavy-dose plots (8.4 m) was still greater than in the 

scalpedplots (5.8 m); thedifference was significant (table2). A 

similar comparison between the heavy-dose and control treat0 

1 10 

Elapsed time (years) 

Survival 

Treatment 

Heavy Roundup 

Moderate Roundup 

Light Roundup 

Ezl Scalp 

Control 

Figure 2-Average height of koa trees one year and ten years after planting, by type of site preparation treatment. No trees in the control treatment 

were alive at 10 years. Treatments grouped under a common horizontal line are not significantly different at the overall significance level of 0.05 

(Bonferroni 1-test). 

Height 

4 USDA Forest Scrvicc Res. Paper PSW-205. 1991 

Stem 

diameter 

Height to. . . Crown I Fork 
0 

, 0 HcavyRovndvp 

0 Malsrals Roundup 

20 1 ; L.i$;Rw"d~p 

Figure 3--Relationship between percent survival (stand density) and 

mean tree height and mean stemdiameter at breast height (1.4 m) of koa 

ten years after planting, by type of site preparation treatment. 

ments could not be made because all trees in control plots died 

before our last measurement. None of the other differences 

among treatments were statistically significant (jig. 2). 

Generally, tree height is unaffected by stand density, over a 

wide range of densities (Spurr and Barnes 1980). We found no 

evidence that height of 10-year-old trees was affected by survival, i.e., stand density (jig. 3A), except in the heavy herbicide 

treatment. In that treatment, average height of koa was negatively correlated with survival. Such negative effect of stand 

densityon tree height normally occurs in only verydensestands. 

Stem Diameter 

Ten years after planting, mean stem diameters ranged from 

8.7 cm in moderate-dose plots to 12.4 cm in light-dose plots 

(table 2). There was considerable variability in diameter at 

breast height (dbh) within treatments. For example, the dbh of 

trees growing in scalped plots varied from 0.6 to 27.9 cm. 

Differences in mean dbh among treatments were not significant 

at ten years of age, partly because of this large variability. 

We found no consistent effect of survival (i.e., stand density) 

on stem diameter of 10-year-old trees (jig. 38). Generally, the 

mean diameter of trees in a stand decreases nonlinearly with 

increasing stand density (Spurr and Barnes 1980). Such a 

relationship was evident only in plots treated with a heavy dose 

of Roundup. 

Other Stand Characteristics 

Mean height of the base of the live crown was significantly 

greater in plots prepared with a heavy dose of Roundup than in 

plots prepared by scalping (table 2). The heavy-dose plots had 

more than twice the stem basal area of any other treatment. We 

believe that shade within plots treated with a heavy dose of 

Roundup was deep enough to cause branch death in the lowest 

portion of the crowns. Differences among other pairs of treatment means were not significant. 

Thefustmajorforkin thetrunkoccurredatanaverage height 

of about 5 m in plots prepared with a heavy dose of Roundup. In 

scalped plots, forking occurred at about 3 m above the ground. 

We suspect that this statistically significant difference between 

the two treatments (table 2) was a function of survival and 

canopy closure. Because of relatively high survival, trees in 

plots sprayed with a heavy doseofRoundup were crowded, and 

their crowns closed early in stand development. The low light 

levels within these stands resulted in thedeath of lower branches. 

Thus, major forks could not develop low on the tree trunks. In 

contrast, the relatively low survival of trees in scalped plots 

created moreopen stands. Light levels within these stands were 

high enough to allow lower branches to survive and major forks 

to develop. 

More than 70 percent of the surviving 10-year-old koa in 

heavy-dose, light-dose, and scalp plots showed symptoms of 

disease-swollen, oozing portions of the main stem, mistletoe, 

or fungal fruiting bodies. About 50 percent of the koa in plots 

treated with a moderate dose of Roundup were obviously diseased. 

The prevalence of diseased trees may be unimportant in the 

longrun. Koastockinginanunmanaged,matureohia-koaforest 

typically averages less than 35 trees per hectare. For the sake of 

argument, however, we will assume that 100 mature koa per 

hectare can be grown in a managed forest. In our study, tree 

density in the least stocked plot treated with a heavy dose of 

Roundup was 1,100 trees per hectare at 10 years. If all of the 

diseased trees died by the time the stand reached maturity, 

density would still be three fold greater than the site could 

support. The stand would have to sufferan additional loss of 70 

percent of the healthy trees for stand density to reach 100 trees 

per hectare. 

Relative Height Growth Rates 

Thefirstthreemonthsafterplanting, heightgrowth was slow 

as seedlings recovered from transplant shock and adjusted to a 

new environment. MeanRGRs (eq.2)forseedling heights were 

generally between 4 and 7 percent per month during that period 

of growth. Treatment effects were not significant (jig. 4). 

The second threemonths afterplanting, height growth accelerated. RGRs averaged up to 52 percent per month (heavy dose 

of Roundup). There were no significant differences in RGR 

among the three herbicide treatments nor was there a significant 

difference between the scalp and control treatments (jig. 4). 

RGRs for the three herbicide treatments were significantly 

greater than those for the scalp and control treatments. 

USDA Forest Service Rer. Paper PSW-205. 1991. 5 
Figure &-Mean relative rate of height growth of koa for selected 

intervals during thel2-month period after planting, by type of site preparation treatment. Within an intewal, treatments grouped undera common 

horizontal line are not significantly dinerent at the overall significance 

level of 0.05 (Bonferroni t-test). 

In all treatments, RGRs during the 3- to 6-month period were 

significantly greater than those during the 0- to 3-month period. 

The ac'celeration in growth was most noticeablein plots treated 

withRoundup. DifferencesinRGRbetweenthefustandsecond 

3-month periods were as much as 4.5 times greater in plots 

treated with Roundup than in control or scalp plots fig. 5). 

During theperiod from 6 to 12 months afterplanting, growth 

slowed significantly in alltreatments. Seedlingsin plots sprayed 

with a heavy dose of Roundup slowed from aRGR of 52percent 

permonth toless than lOpercentpermonth, whichwas themost 

rapid rate observedfor any treatment during the 6- to 12-month 

period. RGRs were not significantly different among the heavy 

dose, medium dose, and scalp treatments nor between the light 

doseand control treatmentsforthe 6- to 12-month period fig. 4). 

Treatment effects on mean relative rate of height growth 

(percent per month) for the first 12 months after planting were 

as follows: 

Heavy dose Moderate dosc Light dose Scalp Control 

17.6 a 15.6 a 13.4 ab 8.4 bc 7.6 c 

where means followed by the same letter are not significantly 

different. It is apparent that all three herbicide treatments 

resulted in improved rates of height growth compared to the 

control. Butthisresultmustbe tempered by treatmenteffectson 

survival. As noted previously, only the heavy-dose herbicide 

treatment significantly improved survival in comparison to that 

achieved in the control. 

Seedling Position and Vigor 

Information about seedling position relative to surrounding 

vegetation and seedling vigor gave us clues to help explain 

treatmenteffects on survivalandearly growthof 1-year-old koa 

seedlings (table 3). In control plots, more than 80 percent of the 

surviving seedlings were lodged or covered with banana poka 

vines. None of thekoa crowns was above the level ofcompeting 

vegetation. As a result. only 45 percent were classed as having 

Time interval 

50 

+ lsl Ulrep monlhs 

0 2nd Ulree months 

.- Y 20- 

id 

10 - 1 H~v-~g&l 1 

Roundup 

Trsatmonl 

Figure 5--Magnitude of differences in mean relative rate of height 

growth between the first three and second three months of growth, by 

type of site preparation. 

acceptable to high vigor. In contrast, only 22 percent of the 

survivors in the heavy Roundup plots were lodged or covered 

with poka vines; 74 percent were above competing vegetation. 

Theneteffect was that 95 percent of the seedlings had acceptable 

to high vigor. These data reflect the degree of competition 

control brought about by each treatment-heavy > medium > 

light 2 scalp > control. 

Block Effects 

Differences in growth were observed among blocks during 

the first year afterplanting. Growth was significantly slowerin 

block 3, which was located on a separate ridge about 75 meters 

away from the other two blocks. At one year of age, trees in 

block 3 averaged 83 cm in height; those in blocks 1 and 2 

averaged 145 cm and 130 cm in height, respectively. We 

attribute the poorer performance in block 3 to severe competition with banana poka vines. Even from the start of the study, 

banana poka was more abundant in and around block 3 than in 

and around the other blocks. 

Tsblr %Percmfogr of surviving koo frees one year ojlw plonfing, by 

lre,,lmcnf 

6 USDA Forest Scrvicc Res. Paper PSW-205. I991 

Treatment 

Roundup: 

Heavy dose 

Moderate dose 

Light dose 

Scalp 

Control 

Class of surviving koa ~cc 

Lcdged or covered 

wilh banana poka vines 

percent 

22 74 95 

58 30 78 

74 6 61 

17 12 63 

82 0 45 

Above competing 

vegetation 

Acceptable lo 

high vigor 
MANAGEMENT IMPLICATIONS 

Successful establishment of koa on sites occupied by banana 

poka and dense kikuyu grass depends on adequate site preparation toco~~trolcompetition. Inthis study, only heavy application 

of Roundup to the entire planting area sufficiently suppressed 

competing vegetation to give koa seedlings a competitive edge. 

Survival, height, and rate of growth of koa growing in plots 

treated withaheavy doseof Roundup weregreaterthan achieved 

by koa growing in control plots. 

Planting spots are often prepared by hand hoeing the surrounding ground vegetation. Where the ground vegetation is 

sparse, short, or slow growing, scalping has proved a sufficient 

method for controlling competition during seedling establishment. The site used in the present study had dense, tall, rapidly 

growing ground vegetation. Scalping provided only short-term 

control of competition. The deep rhizomes of kikuyu grass were 

not affected, and rapid regrowth occurred. 

Amoredrastic form of scarificationmay be calledforonsites 

similartoourstudysite. Forexample,diskplowingisbeingused 

toprepareplantingareas in theHakalauForestNationa1 Wildlife 

Refuge. The sites are about 10 km south of our study area and 

at about the same elevation. Kiyu grass and other pasture 

grasses are dense, but banana poka has not yet become established. With disk plowing, the soil is thoroughly turned over. 

Preliminary study showed that two or three passes of the disk 

plow reduced grass density for about 6 months. 

In areas occupied by kikuyu grass and banana poka, neither 

mechanical nor chemical spot treatment of groundvegetatiou is 

likely to free koa seedlings from the adverse effects of competition formore than 3 months. Forexample, we believe that spot 

spraying of a heavy doseof Roundup wouldbenomoreeffective 

than spot scalping; itis amatter of scale. Surrounding vegetation 

could quickly reinvade the treated areas, and pokavines rooted 

just outside the sprayed spots could rapidly climb into koa 

canopies. Treatments have to be applied to an area larger than 

that in the immediate vicinity of a koa seedling. 

In areas infested with banana poka, site preparation alone 

without follow-up maintenance will not ensure long-term stand 

survival and growth. Even if an entire planting area were 

sprayed with herbicide (as done in our Roundup treatments), 

cleaning and weeding would be necessary to combat reinvading 

pokavines. A case in point is the poorperformance of seedlings 

in block3 of this experiment. Nodoubt the abundanceof banana 

poka vines in and around block 3 created intense competition, 

which wasnot aseffectively controlledby theinfrequentweedigs 

as it wasin theother two blocks. Theneed formaintenance wilt 

lessen if and when biological control of banana poka (Markin 

1989) becomes a reality. 

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USDA Forest Service Rcs. Paper PSW-205. 1991. 
The Forest Service, U.S. Department of Agriculture, is responsible for Federal leadership in forestry. 

It carries out this role through four main activities: 

. Rotection and management of resources on 191 million acres of National Forest Systcm lands 

. Cooperation with State and local governments, forest industries, and private landowners to help 

protect and manage nou-Federal forest and associated range and watershed lands .. 

. Participation with other agencies in human resource and wmmunity assistance programs to 

improve living conditions in nual areas 

. Research on all aspects of foreshy, rangeland management, and forest resources utilization. 

The Pacilic Southwest Research Ststion 

. Repments the research branch of the Forest Service in California. Hawaii, American Samoa 

and the western Pacific. 

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with any handicapping wnditions arc welwme to use and enjoy 

all facilities, programs, and services of the U.S. Department of 

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policy, and shculd be reported to the Scc~~tary of Agriculture. 

Washington. DC 20250.