United States 

Department of A Preliminary Identification 

Agriculture of Morphological Indicators 

Forest Service of Field Performance in 

Bare-Root Nursery Stock 

Southeastern Forest 

Experiment Station H. David ?/fuse and Glyndon E. Hatchell 

Research Paper 

SE-283 
A Preliminary Identification 

of Morphological Indicators 

of Field Performance in Bare-Root 

Nursery Stock 

ABSTRACT 

A general method for identifying key morphological attributes of bare-root 

nursery stock as indicators of early field performance is presented. The 

method is exploratory with emphasis on relating attributes of individual 

seedlings to their early field performance. The approach is illustrated 

using data from a recent study of longleaf pine (Pings palztstris Mill.) 

seedling quality. 

I<eywords: Experimental design, nursery data analysis, field data analysis, 

seedling quality, Pinus palxstris. 

Historically, the approach t,o determining seedling quality has 

involved setting a definition of seedling quality follo.vved by 

outplanting a group of seedlings thus defined to observe average 

field performance (Brissette 1984). However, various relationships 

of morphological characteristics of bare-root nursery stock of the 

southern pines to field performance have eluded researchers in 

their attempts to identify or separate seedlings according to their 

potential for survival and growth in the field. fir example, Wakeley 

(1953) concluded that his grading rules for morphological characteristics were inadequate. In many tests, lie had found that grade 

1 seedlings usually made the best growth arnong three grades but 

that they generally did not survive as well as grade 2 and sornetimes not as well as grade 3 seedlings, which ordinarily were culled. 

Our approach features broad flexibility to infer seedling quality 

based on i~ldividual seedling field perfor~rtance. Tllis method evolved 

during a fongleaf pine seedling quality study based on LYake1ey.s 

(1954) grades 1 and 2 and reported by Iflatchell and Muse (1990). 
The objective of this Paper is to develop a general method for 

identifying key morphological attributes of bare-root nursery stock 

as indicators of field performarrce. Areas of corrsideratio~l irlclude 

nursery and outplarltirlg study objectives, field data analysis. and 

seedlirlg quality inference. The resuiting tijethod is illustrated using 

data from the above-111e1lt ioned longleaf pi~re seiiclling quality st tici). 

Methods 

Our method focuses on the ~norphological characteristics of individual seedlings at lifting time in relation to subsequent field performance. Since an attribute may vary considerabty anlong seedlings, 

large sample sizes are needed; otherwise, the joint consiclera tiori 

of two attributes in relation to field performatice would probably 

not be feasible. Also, large sample sizes are needed for powerful 

analysis of ~lorninal scale field data such as survival. Siirce seedling 

survival is a necessary condition for further study of field performance, the first stage of our method addresses ~lre identification 

of key n~orpllological attributes related to survival. The resulting 

sample stratification could provide either a basis for delitreating 

seedling quality or a basis for utilizing a seconci measure of field 

performarrce to infer seedliilg quality. 

Our primary objective in the nursery phase is to produce a large 

set of plantable seedlings for each nursery treatrilent regime. A 

mininlum of 1,000 seedlings is desirable wit11 pact1 seedling identified. 

tagged, and measured at lifting time. For study purposes, culling. 

if any, should be limited to seedlirlgs on which darnage or disease 

has substa.tltial1y altered a morpllological attributrl of primary 

interest. 

Our main objective in outplanting experimental design is to "b able 

to draw inference about seedling quality for each nursery-field 

t>reatment conlbination of interest. Therefore, a large set of plantable seedlings is needed for each of these combinations. 

Our approach utilizes the assunlption that individual seedling field 

responses are independent. Consequently, the field design should 

feature the random msignment of seedlings produced under each 

nursery treatment regime to single-tree plots associated with each 

field treatment. 
Our approach to seedling quality inference involves partitioning the 

data set into a sequence of nested sets associated with one or more 

attlributes such that advancing nested sets possess higher sample 

seedling quality. kfore specifically, let GI, G2, . . . , Gk denote I< 

nested sets where Gp is contained in GI, Gg is nested in G2, etc., 

and sample quality increases with the set subscript. For survival 

studies, GI is the set of all plantable seedlings. If the field response is not survival, then GI may be a subset of the set of 

plantable seedlings such that sr~rvival rate is accept,able. In any 

event, the object is to find a set GJ, j > 1, such that the sample 

quality for GJ is significantly higher than the sample quality 

for GI. If such a set exists, there may also exist a set G,*, j* > j, 

such that the sample quality for G,* is sigl~ificantly higher 

than the sample quality for G,. Consequently, levels of seedling 

quality may be inferred. For large samples, the null hypothesis 

of no change in seedling quality from G, to GJ, j > i, versus the 

alternative hypothesis that seedling quality increases from 6, to 

GJ can he tested using the following procedures: 

1. If the field response is a nominal scale measure involving exactly two levels of response, say acceptable and unacceptable, then 

under the null hypothesis, the test statistic Z is an approximate 

standard normal statistic 

where 

and where 

XJ = the number of acceptable seedlings in GJ, 

n, = the total number of seedlings in GJ, 

G, - GJ = the set of seedlings contained in G, but not in GJ. 

W, = the number of acceptable seedlings in G, - G,, 

rn, = the totaI number of seedlings in G, - GJ, 

fi = X,/nJ, and f, = W,/m,. 

Although the above statistic 'L compares the performance levels lior 

G, and G, - Gj, it is appropriate for testing tire above hypothesis 
involving G, and GJ. This can be seen from the following derivation where ZI is appropriate for comparing the performance 

levels of 6, and Gj. Usirig the above notation, let 

Z, = Y/ Jestimated var(Y), 

where 

Y = Xj/nj - (Wi + Xj)/(mi + nj) 

= (miXj/nj - Wi)/(mi + nj) 

= mi(fj - fi)/(mi + nj), 

Wi + X, = the number of acceptable seedlings in G;, 

mi + nj = the total number of seedlings in G,, 

and 

estimated var(Y) = mi2[fJ(l - f,)/n, 

+ f,(l - fi)/rn,]/(mi + nj)2. 

Substituting for Y and estimated var(Y), Z1 reduces to Z. 

2. If the field response is a nominal scale measure involving 

exactly q levels of response, q > 2, then under the null hypothesis, 

the test statistic Z is an approximate chi-square statistic with 

q - 1 degrees of freedom 

where 

Z = C;-i(fih - fili)?/[fjh(1 - fJh)/llI + f,i;(l - fih)/r%l. 

nj, G, - GJ, and rn, are defined in procedure 1 above, 

Xjh = the number of seedlings in Gj exhibiting a level b 

response, 

W,h = the number of seedlings ir! G, - GJ exhibiting a 

level h response, 

fJh = Xjh/ni and flh = \Vlh/m,. 
Note that the statistic given in procedure 1 can also be used if 

the q levels of response can be condensed to two rneailingful levels 

of response. 

3. If the field response involves interval scale data, then under 

the null hypothesis, the test statistic Z is an approximate standard 

normal statistic where Z, Y, nJ, G, - GJ, and rn, are defuned in 

procedure 1, 

Xj = the observed total for seedlings from GJ, 

W, = the observed total for seedlings from G, - GJ, 

and 

estimated var(Y) = mi2(Si2/mi + Sj2/nj)/ (mi + %)2 

where S,2 and SJZ denote the sample variances for sets 

Gi - GJ and C;j, respectively. Survival, vigor, and height are 

examples of early field performance measures for which the 

three approaches are applicable. 

Since partitioning the data set into a sequence of nested sets of 

increasing quality is not a uniquely defined process, some guidelines would be useful. In our study, sample seedling quality 

tended to increase as the morphological attribute of interest 

increased. Therefore, each set in the nested sequence of sample 

quality sets could be defined by increasing the lower bound of an 

attribute used to define the previous set in the sequence. If the 

sequence is based on one ~norphological attribute. then the partitioning is straightforward. If the sequence is based on two or 

more attributes, then several approaches are possible. In our approach, one attribute at a time was allowed to increase, thereby 

obtaining a trial set G, - G,+, for each attribute involved in 

defining the sequence. Since G, - denotes the set of seedlings deleted at the (i + 1) stage of the nesting process, the trial 

set having lowest sample quality is an attractive set to delete. 

G,+, was defined on this basis. The above approach is easily 

generalized to the case where sample quality peaks within the 

interval of observed values for one or more attributes. 
An Illustration 

The above method was developed in conjrinctiot~ with a lo~lgleaf 

pine study reported by Batchell (1987) and Hatchell and hluse 

(1990). The nursery phase of this study involved a 2 x 2 x 2 

factorial experinlent laid out in four replications in a completely 

randomized design. The factors were: vertical root pruning versus 

nonpruned control; seedbed density, 65 or 129 seedlings per square 

meter; and seed drill spacing, 15 or 30 centimeters. At lifting 

time, 50 plantable seedlings, based on Wakeley's (1954) criteria 

for grades 1 and 2 stock, were randornly selected from each of the 

32 plots in the nursery. Individual seedling attributes measured 

included root-collar diameter (RCD) in inilli~neters; number of 

strong, first-order lateral roots (NSFOLR), which included only 

those with diameters larger than 1 milliineter (I<ormailik 1986); 

and fibrosity, an ocular rating of the akuridance of fibrous roots. 

Assigned fibrosity ratings were low (L), rnecliunz (M), and high 

(H). These seedlings were subsequently outplanted on a site at the 

Savannah River Forest Station, Aiken, SC, using one field treatment and a completely randomized design with single- tree plots. 

Seedlings were measured after the second growing season. 

As the study progressed and our approach to seedling quality inference evolved, two shortcomings of the study became evident. First, 

using Wakeley's specificatioii for grades 1 and 2 stock may have 

been too restrictive. In any event, our inferences about seedling 

quality were limited to the subpopulation of grades 1 and 2 

seedlings. Second, each nursery treatment regime resulted in only 

200 seedlings; thus, sample sizes were small. Subsequent analysis 

of variance indicated that pooling across levels of drill spacing 

and density in the nursery were justified, thereby resulting in 

pooled sets of size 800 for pruned and nonpruned seedlings. 

Since the survival rate as significantly higher (P = 0.01) for 

pruned seedlings (69%) than for nonpruned seedlings (48%), 

the pruned seedling data set was chosen for our illustration. 

Active height growth results are included for completeness. 

Results reported in table 1 indicate that fibrosity classes could 

be used to delineate levels of relative seedling quality. 2lediumor high-fibrosity seedlings had a significantly higher survival 
rate (72%) than all pla~ltable seedlings (69%). High-fibrosity 

seedlings performed significantly better (82%) than mediurnplus high-fibrosity seedlings (72%). The rate of act,ive height 

growth (height > 10 cm) was also significantly higher for 

high-fibrosity seedlings (78%) than for medium- plus 

high-fibrosity seedlings (7 1%). 

Values in table 2 indicate that NSFOLR offers several alternatives 

for defining relative seedling quality. Fbr example, if fibrosity is 

M or R, then the sample survival rate for G5 (NSFOLR > 3) is 79 

percent, and 80 percent of survivors have active height growth by 

age 2. The corresponding data for the complementary set GI - Gs, 

the set of seedlings contained in G1 but not G5, can be easily 

derived. Using the counts and survival percentages for G1 and 

G5, survival counts for GI and G5 are 472 and 355 seedlings, 

rcspective!y. Therefore, GI - G5 contairls 652 - 448 -- 204 

seedlings with 472 - 355 = 117 surviving, and the survival rate 

for G1 - G5 is 57 percent. Using survival counts and active height 

growth percentages for G1 and G5, respective height growth counts 

for G1 and G5 are 337 and 284. Therefore, GI - G5 contains 

337 - 284 = 53 seedlings in active height growth, and the percentage in active height growth is 45. Consequently, for medium- or 

high-fibrosity seedlings, G5 represents a statistically significant 

improvement in quality over GI - G5. Furthermore, G5 constitutes 

a large proportion of the sample seedling population with 69 

percent of the medium- or high-fibrosity seedlings and 56 percent 

of all plantable seedlings represented. As a second example, 

consider G6 with fibrosity unrestricted (fibrosity = L, M, or H). 

The sample survival rate for G, is 75 percent with 80 percent in 

active height growth; corresponding data for G1 - G6 include a 

59-percent survival rate with 48 percent in active height growth. 

Again, the delineation in relative seedling quality is striking. 

Continuing the example, GI - G, could be further partitioned into 

two sets of significantly different quality. Survival and active 

height growth rates for G1 - Gq (NSFOLR < 3) are 55 and 39 percent, 

respectively, while the corresponding rates for Gq - G6 (NSFOLR = 

3 or 4) are 63 and 59 percent. Hence, three levels of significantly 

different seedling quality have been defined. 
Results pertaining to RCD are given i11 table 3. Again several alternatives for delineating sample quality are evident. In particular, 

G4 (RCD > 8) contains seedlings of significantly higher quality 

than GI - Gq. If fibrosity = M or H, the survival and active 

height growth rates for Gq are 76 and 75 percent, respectively; 

the corresponding rates for GI - Gq are 53 and 45 percent. If 

fibrosity is not restricted, the survival rate and active height 

growth rates for Gq are 72 and 73 percent, respectively; the 

corresponding rates for GI - Gq are 53 and 47 percent. 

Table 4 contains results for RCD and NSFOLR as joint indicators 

of seedling quality. Each set G,+l, i = 2. . . . , 10, in the nested 

sequence was generated from G, by: (I) allowing the lower bound 

for RCD to increase while holding the lower bound for NSFOLR 

constant to produce a trial set G, - GI+,, (2) repeating the process 

with the roles of RCD and NSFOLR reversed to produce a secc~id 

trial set, and (3) setting Gi+l, to be the portion of G, complementary 

to the trial set of lowest seedling quality based on survival. Sets 

G2, G3, and G4 are based on increases in RCD, while the remailling 

sets involve increases in NSFOLR. Results based on table 4 are 

comparable to table 2 results except that sample quality levels 

for sets G4 through Gll of table 4 are higher than the corresponding sample quality levels of table 2. Tlle largest difference 

in sample quality occurs for G4 of table 4 versus GI of table 2; 

however, as the nested Level increases, the correspondirig differences 

in sample quality tend to decrease. Co~iseque~~tly,he advantages 

of joint consideration of RCD and NSFOLR in table 4 versus 

NSFOLR or RCD alone for assessing seedling quality are 

probably negligible. 

From the above discussioti, the exploratory nature of our tnetilodology is evident. Nevertheless, the approach oEers considerable 

flexibility for relating nursery morphological at tributes to early 

field performance, Based on our experience with the lorrgleaf pine 

quality study, the preliminary method presented in this Paper 

provides a strong basis for ident,ifying key morpfiological 

attributes of bare-root nursery stock as potential indicators of 

field performance. 
Literature Cited 

Brisset te, John C. 1984. Summary of discussions about seedling 

quality. In: Proceedings 1984 southern nursery conferences, Western Session, 1984 June 11-14; Alexandria, LA, and Eastern Session, 1984 July 24-27; Asheville, NC. Atlanta, GA. U.S. Department of Agriculture, Forest Service, Region 8: 127-128. 

Hatchell? Glyndon E. 1987. Nursery cultural practices, seedling 

morphology, and field performance of longleaf pine. In: Phillips, 

Douglas R., comp. Proceedings of the fourth biennial southern 

silvicultural research conference; 1986 November 4-6; Atlanta, 

GA. Gen. Tech. Rep. SE-42. Asheville, NC: U.S. Department 

of Agriculture, Forest Service, Southeastern Forest Experiment 

Station: 61-66. 

Hatchell, Glyndon E.; Muse, H, David. 1990. Nursery cultural 

practices and morphological attributes of longleaf pine bare-root 

stock as indicators of early field performance. Res. Pap. SE-277. 

Asheville, NC: U.S. Department of Agriculture, [Forest Service, 

Southeastern Forest Experiment Station. 34 pp. 

Kormanik, Paul P. 1986. Lateral root ~noryllology as an expressioil 

of sweetgurn seedling quality. Forest Science 32(3): 595-604. 

Wakeley, Philip C. 1954. Planting the southern pines. Agric. Monogr. 

18. tvashington, DC: U.S. Department of Agriculture, Forest 

Service. 233 pp. 
Table 1-Fibrosity ag an indicator of second-year survivd and active 

height growth given vertical root-pruned seedings 

Nested Fibrosity Initial Survival Active heiaht nowth 

sets rating1 number Count Percent Count Percent 

Within columns, survival and active height growth percentages followed by the 

same letter do not differ significantly (P - 0.05). The percentage in active 

height growth is based on surviving seedlings. 

'E = low; M = medium; H = high. 
Table 2-Number of strong, first-order lateral roots (NISFOLR) as an indicator of second-year survival 

and active height growth in vertically root-pruned seedlings with specified Abrositieer 

Initial number by Survid by Active height growth 

Nested fibrosi tv class1 fibrosi tv class1 

sets NSFBLR L, M, or W M or W L, M, or H M or H L, M, or H M or P3[ 

--- Percent - - - - - - Percent - - - 

Within, calurnm, survival and active height growth percentages foUowed by the same letter do not differ sidficaly 

(P = 0.05). The percentage in active height growth is based on surviving seedlings. 

'L = low; M = medium; H = high. 
Table 3-Root-collar diameter (RGD) as an indicator of second-year survival and active height growth 

of vertically root-pruned seedlings with specified fibrosibies 

-- - -- 

Lnitial number by Survival by Active height gzowth 

Nested fibrosi tv class1 fibrosi tv class1 fibrosi tv clsssl 

sets RCD L, M, or H Nor H L, M, or H h4 or H L, M, or W M or H 

--.x. Percent - - - --- Percent - - - 

Within colms, survid and active height growth percentages followed by the same letter do not differ 

si~ficantly (P = 0.05). The percentage in active height growth is based on surviving seedlings. 

'L = law; M = medium; H = high. 
Table 4---Number of strong, first-order lateral roots (NSFOLR) and root-collar diameter (RGI)) as joint 

indicators af second-year survival and active height growth of vertically root-pruned seedlings with 

specified fl hrosi ties 

Initial number by Survival by Active height growth 

Nested fibrosi ty class1 fibrosi ty class1 

sets NSFOLR RCD L, M, or H M or H L, M, or H M or H 

fibrosi ty class1 

L, M, or W M or 14 

--- Percent - - - --- Percent - - - 

Within colums, survival and active height growth percentages followed by the same letter do not differ si@fic&ly (P = 0.05). 

The percentage in active height growth is based on surviving seedlings. 

- 'L = law; M = rnediurn; H = high. w 
--- --__.----_I______..-_-l_l_.-__)______ 

I 

I 

i Muse, H. David; Hatchell, Glyx~don E. 1992. A preliminary 

identification of morphological indicators of field performatlce in 

I 

I bare-root stack. Res. Pap. SE-283. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southeastern Forest 

I 

I Experiment Station. 13 pp. 

I 

I The preliminary method presented in this Paper provides a strong 

I basis for identifyirig key niorphological attributes of bare-root 

nursery stock as potential indicators of field performance. 

I 

I Keywords: Experimental design, nursery data analysis, field 

f data analysis, seedling quality, Pznus pnlustrzs. 

I 

Muse, H. David; Hatchell, Glyndon E. 1992. A preliminary I identification of morphological indicators of field performance in 

I bare-root stock. Res. Pap. SE-283. Asheville, NC: U.S. Depart- I ment of Agriculture, Forest Service, Southeastern Forest 

I ExperimentStation.13pp. I 

I The preliminary method presented in this Paper provides a strong 

I basis for identifying key morpho!ogica! attributes of bare-root 

I nursery stock as potential indicators of fieid performance. I 

I Keywords: Experimental design, nursery data analysis, field 

I data analysis, seedling quality, Pznus palusiris. 

I