Keserű, Zsolt

Rédei, Károly

Acta Silvatica et Lignaria Hungarica

University of Debrecen Electronic Archive

Acta Silv. Lign. Hung., Vol. 8 (2012) 165–170  
 
 
 
 
 
 
 
Target Diameter Models for Leuce Poplar Stands 
Growing on Sandy Soils 
 
 
Károly RÉDEI∗ – Zsolt KESERŰ 
 
Hungarian Forest Research Institute, Sárvár, Hungary 
 
 
 
Abstract – The fact that certain ecological factors fundamentally influencing tree growth have 
become unfavourable in Hungary in recent years, has led to the more extensive use of white poplar 
(and its hybrids) in afforestation and forest regeneration. An intensive integrated research and 
development work has been carried out on the growth of Leuce poplars on sandy soils, including 
primarily the white poplar (Populus alba) and its natural hybrid the grey poplar (Populus x canescens). 
The research revealed several factors influencing stand growth. The study presents a new, simplified 
tending operation model for Leuce poplar stands, as well as age, growing space and target diameter 
models suitable for qualitaty log production and for mass assortments. The simplicity of these 
practice-oriented models may foster the qualitative development of Leuce poplar management in 
Hungary. 
Leuce poplars / tending operation models / growing space regulation   
 
 
Kivonat – Homoki Leuce-nyár állományok célátmérő modelljei. A homoki Leuce-nyárakkal, dön-
tően a fehér nyárral (Populus alba) és természetes hibridjével, a szürke nyárral (Populus x canescens) 
kapcsolatos kutatómunka intenzívebbé tételét több tényező indokolja. A fatermesztést alapvetően be-
folyásoló ökológiai tényezők egy részének kedvezőtlenebbé válása előtérbe helyezte e fafaj (és hibrid-
jeinek) egyre kiterjedtebb alkalmazását az erdőtelepítések, illetve erdőfelújítások során. A tanulmány a 
nemzetközi szakirodalomban is hézagpótlónak tekinthető módon közli a fehérnyárasok új, egyszerűsített 
erdőnevelési modelljét, illetve a minőségi rönktermesztésre, valamint a tömeg-választékok előállítására 
alkalmas fehérnyárasok kor-növőtér-célátmérő modelljeit. A közölt gyakorlatorientált modellek egysze-
rűségüknél fogva nagyban segíthetik a Leuce- nyár termesztés minőségi fejlesztését Magyarországon. 
Leuce-nyárak / erdőnevelési modellek / növőtér szabályozás 
 
 
1 INTRODUCTION 
 
Leuce poplars, primarily white poplar (Populus alba) and its most important natural hybrid 
the grey poplar (Populus x canescens), are tree species native to Hungary (Kopecky 1962, 
Szodfridt − Palotás 1973, Kopecky 1978, Rédei 1991). Due to their favourable silvicultural 
and growth characteristics, as well as the possibilities for the utilisation of their wood, the 
area they occupy is increasing continuously. The most important task facing Hungarian poplar 
                                                 
∗
 Corresponding author: redei.karoly@t-online.hu, H-9600 SÁRVÁR, Várkerület 30/A. 
Rédei, K. – Keserű, Zs. 
 
 
Acta Silv. Lign. Hung. 8, 2012 
166 
growers is improving the quality and increasing the quantity of poplar stands for wood 
production (Rédei 2000). 
The area occupied by the two species in 2006 was 65 000 ha (3.2% of the total forest 
area), with a standing volume of 9.8 million m3 (163 m3 ha-1) (Führer et al. 2009). Their 
importance will continue to increase across the large areas of marginal land not suitable for 
the cultivation of hybrid poplars but able to accommodate these native species (Rédei 1991, 
1994, 2000).  
Other species that may be used for plantation forestry in addition to these poplar species 
are black locust, red oak and black walnut. Common walnut plantations may also play a role, 
but the silvicultural significance of this tree species is negligible. 
From among the above listed tree species, the models for tending operations and the 
tables for age-growth space-target diameter models are suitable for production of large, 
quality wood material as well as mass assortments produced in white and grey poplar stands.  
 
 
2 MATERIALS AND METHODS 
 
The models we developed  are based on a yield table for white and grey poplars. It was 
constructed from data gathered from 50 permanent and 40 temporary forest inventory sample 
plots (500–1000 m2). The stands sampled were located in the vicinity of N 46o 31’ 10” and E 
19o 26’ 46”. The age of the stands varied between 5 and 45 years. 
During the stand surveys, the key stand characteristics were measured. Stem volume was 
estimated using the following volume function (Sopp − Kolozs 2000): 
 
( ) [ ]32986.443.124236.0]3.1[10 2128 +++−−= − hdhdhhhdv  (1) 
where v  is stem volume (m3), d  is diameter at breast height (cm) and h  is tree height (m). 
The regression analyses were calculated using a computer-based statistics programme. 
The expected height values of the stands at the reference age (25 years) according to the yield 
classes are: 24.2 m, 21.6 m, 19.0 m, 16.4 m, 13.8 m and 11.2 m. On the basis of the guide 
curve and the reference age (100%), a percentage value was calculated at any age and for any 
yield class. The yield table was constructed using the following formulae and coefficients; 
(a detailed dataset is available from the authors): 
1. Age of stand (A)  
2. Hm = average height of stand (height of dominant and co-dominant trees) in m: 
Hm = 1.21592 × (1-e-0.09236A)1.8334 
3. Dm = average DBH of stand in cm:  
Dm = 1.58356 + 0.73502 × Hm + 0.01571 × H2m 
with R2 = 0.886 
4. Vm = volume of stand in m3 ha-1 
Vm = BAm × H × Fm, where 
H × Fm = form-height quotient 
H × Fm = 1.96791 + 0.40778 × Hm 
with R2  = 0.923 
5. BAm = basal area of stand  in m2  ha-1: 
BAm = m
m N
D
×
×
×
100004
2 pi
 
Target diameter models for Leuce Poplar stands 
 
 
Acta Silv. Lign. Hung. 8, 2012 
167 
6. Nm = stocking density of stand in trees ha-1: 
Nm = e8.75483-0.83879lnDm 
with R2=0.826 
 
 
3 SIMPLIFIED TENDING OPERATION MODEL FOR LEUCE POPLAR STANDS 
 
Leuce poplars are fast-growing species. Seedlings quickly emerge from competition with 
weeds. In-line and inter-row weeding is required in the first years after plantation 
establishment by means of seeding, as is the removal of failed plants. During tending 
operations, it is important to take into consideration the fact that plantations consist of trees of 
varied genetic make-up (genotype). In terms of the demand for light, it is worth remembering 
that Leuce poplar reacts extremely strongly to light availability. It also tolerates shade very 
well (Tóth 1996, Führer et al. 2009). 
Table 1 contains a simplified tending operation model for Leuce poplar (white and grey 
poplar) stands. The table was compiled using data obtained from 70 long-term yield and  
experimental tending operation plots. The choice of the most suitable spacing depends on 
the quality of the planting material and the particular site conditions. In this table, all of the 
data are presented in six yield classes. The mean tree height is the most important model 
factor because it determines the timing of the particular tending operation. Thinnings 
(to expand the available growing space) must be carried out when the stocking density 
approaches the stem number quoted in the table.   
In plantations planted at spacings of either 3 x 3 m or 3 x 2 m, there is no need for 
thinning, except where the sapling growth is unstable. With initial spacings narrower than 
3 x 1 m or 2.5 x 1 m, one or two thinnings are recommended for plantations established with 
white poplar clones.  
 
Table 1. Simplified tending operation model for Leuce poplars (white and grey popla) stands 
Tending operation Stocking density (stems ha-1) 
Tending operation 
 Number To be carried 
out in year… 
To be carried out at 
Hm (m) and   
yield class… before after 
1 5–10 6 I–VI >3000 3000 
Cleaning 
2 11–14  8–11 I–VI    3000 1300–1800 
1 15–20 12–17 I–V 1300–1800   650–1200 
Thinning 
2 21–25 16–23 I–IV   650–1200 350–600 
 
40 
30–35  
I–II 
III–IV  
350–400 
500–600 Final cutting 
 
25–30 
20–25  
V 
VI  
800–900 
1000–1100 
Remarks for the use of the tending operation model: 
− When planning the thinning operation, the better the estimated yield class, the lower the stem number value 
after thinning to be applied.   
− White poplar stands in yield classes V–VI are not suitable for quality wood production.  
 
 
Rédei, K. – Keserű, Zs. 
 
 
Acta Silv. Lign. Hung. 8, 2012 
168 
4 AGE, GROWING SPACE AND TARGET DIAMETER MODELS FOR LEUCE 
POPLAR STANDS 
  
In plantation forestry, the timing of the expansion of the available growing space is significant 
for reaching the target assortments by maintaining the near optimal stocking density per 
hectare (growth space). The ecological factors of the site essentially define the target 
assortments; for example, whether the opportunity for the production of sizeable, quality 
wood material (panel log, saw-log) exists or merely thinner wood assortments (cutting, pallet 
and box basic material), pulp, fibre, chippings and basic wooden board materials. 
The data in table 2 show that an opportunity for the production of quality, sizeable logs is 
possible in white and grey poplar stands classified yield class I-III. For white and grey poplar 
stands in yield class IV – assuming an average harvesting age of 30 years – a target diameter 
of 18 to 20 cm can be planned with great certainty. The sustainable stocking density per 
hectare depending on the yield class varies from 320 to 560 stems. 
Table 3 shows that stands of yield classes IV and V are suitable for the production of 
mass assortments, and possibly even white and grey poplar stands of yield class VI with a 
target diameter of 10 to 12 cm. However, the management of stands characterised by these 
two lowest yield classes are usually loss producing and so are unsuitable for plantation 
forestry.  
White and grey poplar stands growing under unfavourable ecological conditions also 
have an earlier harvesting age (generally between 25–30 years). The sustainable stocking 
density varies between 620–920 stems ha-1 depending on the yield class. In these stands, the 
reduction in stem number (thinning) carried out at age 15–17 does not lead to a significant 
increase in diameter growth. 
 
Table 2. Age-target diameter model for Leuce poplars (white and grey poplar) stands 
targeted for quality log production 
Planned target 
diameter (DBH) (cm) Yield class 
Years required to reach 
target diameter 
Stocking density 
(stems ha-1) 
18 I 14 
18 II 17 
18 III 21 
18 IV 28 
560±5% 
20 I 16 
20 II 18 
20 III 23 
20 IV 32 
515±5% 
25 I 21 
25 II 25 
25 III 37 
425±5% 
30 I 28 
30 II 42 365±5% 
 
Target diameter models for Leuce Poplar stands 
 
 
Acta Silv. Lign. Hung. 8, 2012 
169 
Table 3. Age-target diameter model for Leuce poplars (white and grey poplar) stands targeed 
for the production of mass assortments 
Planned target 
diameter (DBH) (cm) Yield class 
Years required to reach 
target diameter 
Stocking density 
(stems ha-1) 
10 IV 11 
10 V 14 
10 VI 19 
920±5% 
12 IV 13 
12 V 17 
12 VI 25 
790±5% 
14 IV 15 
14 V 24 
14 VI – 
690±5% 
16 IV 20 
16 V 31 
16 VI – 
620±5% 
 
 
5 CONCLUSIONS 
 
White and grey poplar plantation management for improved growth is becoming ever more 
significant in lowland forestry. This fact was taken into account in the conception of this 
study, and fed into the novel planning tools developed to help increase the value of the 
material produced in Leuce poplar stands. In recent decades, growth models based on stand 
level data have gradually been replaced by stand growth models predicated on stem number 
frequencies and individual tree growth models. Nevertheless, traditional tending operation 
models will remain very useful tools for forest management and forest inventory. The published 
models can be widely used in Leuce poplar management and forest inventory, such as:  
• harvest scheduling for Leuce poplar stands,  
• volume estimations,  
• further development of silvicultural (tending operation) models for Leuce poplar 
stands,  
• development of guidelines for local policies promoting native species, and 
• growth analysis of Leuce poplar stands.  
 
 
Acknowledgements: Research on the improvement of Leuce poplar was supported in part by 
the Kiskunsági Forest and Wood Processing Company (KEFAG ZRt., Kecskemét). 
 
 
Rédei, K. – Keserű, Zs. 
 
 
Acta Silv. Lign. Hung. 8, 2012 
170 
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Target diameter models for leuce poplar stands growing on sandy soils

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Target diameter models for leuce poplar stands growing on sandy soils

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