Electronic Journal of Polish Agricultural Universities (EJPAU) founded by all Polish Agriculture Universities presents original papers and review articles relevant to all aspects of agricultural sciences. It is target for persons working both in science and industry,regulatory agencies or teaching in agricultural sector. Covered by IFIS Publishing (Food Science and Technology Abstracts), ELSEVIER Science - Food Science and Technology Program, CAS USA (Chemical Abstracts), CABI Publishing UK and ALPSP (Association of Learned and Professional Society Publisher - full membership). Presented in the Master List of Thomson ISI.
2005
Volume 8
Issue 1
Topic:
Forestry
ELECTRONIC
JOURNAL OF
POLISH
AGRICULTURAL
UNIVERSITIES
Orzeł S. , Socha J. , Forgiel M. , Ochał W. 2005. BIOMASS OF UNDERBRUSH AND CONDITIONS FOR ITS OCCURRENCE IN STANDS OF THE NIEPOŁOMICE FOREST, EJPAU 8(1), #14.
Available Online: http://www.ejpau.media.pl/volume8/issue1/art-14.html

BIOMASS OF UNDERBRUSH AND CONDITIONS FOR ITS OCCURRENCE IN STANDS OF THE NIEPOŁOMICE FOREST

Stanisław Orzeł, Jarosław Socha, Marcin Forgiel, Wojciech Ochał
Department of Forest Mensuration, Agricultural University of Cracow, Poland

 

ABSTRACT

This study showed that biomass of underbrush occurring in stands of a simple structure is significantly greater than biomass of underbrush in stands of a complex structure. A great spatial variation of underbrush occurrence is probably the cause of difficulties in determination of its relationship with stand characteristics. In stands growing on sites of mixed coniferous and mixed deciduous forests the degree of site moisture determines the quantity of biomass of the underbrush layer. Generally in Scots pine stands biomass of underbrush decreases with increase of stand density. In the Niepołomice Forest the total biomass of the underbrush layer in stands above 10 years of age, occupying the area of 9 459 (ha), is 20 705 tons, and it was estimated with the standard error ±1 296 tons.

Key words: underbrush, biomass, stand characteristics.

INTRODUCTION

Forests of the Niepołomice Forest District (Niepołomice Forest), situated in the fork of Vistula and Raba rivers, make the most westerly part of the Sandomierz Forest. The Niepołomice Forest District occupies the total area of 10 864 (ha), including 10 512 (ha) of forest land with about 10 086 (ha) of land covered with forest stands [21]. Nearly 64% of this area is occupied by stands with Scots pine predominance, over 19% with oak, and about 11% with alder predominance. The remaining main species of forest trees: larch, spruce, fir, beech, ash, hornbeam, birch, poplar, and lime occupy a little over 6% of the forest area [21].

In respect of forest site types 53.9% of area of the Niepołomice Forest District is occupied by sites of a mixed coniferous forest, 22.3% by sites of a deciduous forest, and 19.1% by sites of a mixed deciduous forest. In respect of moisture, sites in 82.6% are classified as moist, in 17.1% as fresh, and in about 0.3% as swampy.

This short description of growth conditions of forest stands indicates that in the Niepołomice Forest there are favourable conditions for growth of the forest of a rich species composition in all its layers.

The underbrush layer, the lowest layer of woody vegetation of stands, plays an important soil protection role, and favourably affects the microclimate of forest interior [5, 17]. This, often undervalued [9], but playing an essential phytomelioration role [1, 16], forest layer may sometimes be a more valuable source of information on site conditions than herbaceous vegetation of forest floor [4]. Its favourable effect on growth and stem self-pruning of Scots pine was demonstrated by Tuszyński [19].

The occurrence of underbrush is conditioned, apart from site conditions, by many other factors, including species composition [8, 5, 11], age [11], and crown closure [5] of stands.

A detailed analysis of species composition of underbrush in stands of the Niepołomice Forest, and also of structure of its biomass, have been presented by authors in another paper [6].

The purpose of the present study was to determine relationship between biomass of underbrush and characteristics of stands occurring in the Niepołomice Forest.

MATERIAL AND METHODS

A study material consisted of results of measurements carried out in sample plots established in stands above 10 years of age. The total forest area of such stands in the Niepołomice Forest District is 9458.69 (ha) [21]. In these stands 393 circular sample plots were established. They were systematically distributed in a network of squares, 500 (m) x 500 (m), and their size varied from 0.01 (ha) to 0.10 (ha), depending on stand age.

Centres of sample plots were marked on the stand map, and were found in the field by geodetic offsets from distinctive land marks. Tree dbh and height measurements included all trees above 7.0 (cm) in dbh present in sample plots. If there were less than 15 trees in a plot, then the plot area corresponding to a given stand age was enlarged by one order of magnitude. In each plot weight of the underbrush layer was determined. For this purpose shrubs and trees less than 7.0 (cm) in dbh, growing in area of 40 (m2), were cut and weight in a fresh state. The weights were rounded to 0.1 (kg). This measurement was completed in 4 circular areas, 10 (m2) each (with radius 1.73 (m)), situated in the distance of 5 (m) from plot centres in N, S, W and E directions. To save some of the trees belonging to the underbrush layer, they were not felled, while their weight was calculated by empirical formulae on the basis of their dbh and height. A general formula of the allometric equation assumed, formula parameters, and method of determination of dry mass of underbrush, have been given in another papers [6, 13].

Trees measured in sample plots were assigned to one of the two layers distinguished according to height. The first layer (storey) included trees of height greater than 2/3 of the mean height of 5 tallest trees in the plot, while the second layer (storey) included the remaining trees of dbh ³7.0 (cm). The stands were characterized on the basis of trees of the first storey only.

For methodical reasons the analysis of the relationship between biomass of underbrush and the stand density was carried out only for pure Scots pine stands. For each stand the real (N) and model (N6) numbers of trees per area unit (1 ha) were determined. The model number (N6) was calculated by formula worked out by Bruchwald [2]:

           (1)

where:
p6 - mean distance between trees in the stand managed in agreement with principles of the limiting model:

           (2)

where:
W - stand age
B - stand quality understood as the top height of the stand at the age of 100 years.

The index of tree density (wzag) was calculated as a quatient of the real (N) and model (N6) numbers of trees:

           (3)

The statistical analysis was carried out according to program STATISTICA 6 [15].

RESULTS

Relationship between biomass of underbrush and stand species composition

On the basis of the percentage of the principal species in volume of trees included in the first storey the stands were divided into two groups: stands of a simple structure (principal species ³0.8) and stands of a complex structure. In the Niepołomice Forest stands of a simple structure prevail (Table 1). Biomass of their underbrush widely varied from 0.000 to 13.257 (t ha-1), and its mean value of 2.286 (t ha-1) was greater by 0.261 (t ha-1) (12.9%) than mean underbrush biomass in stands of a complex structure. The Mann-Whitney U test showed that the difference was statistically significant at the level α = 0.05.

Table 1. Biomass of underbrush ind stands of simple and complex structure

Stand structure

Number of plots

Biomass (t ha-1)

Mean

Minimum

Maximum

Standard deviation

Simple

247

2.286

0.00

13.257

2.728

Complex

146

2.025

0.00

11.819

2.698

Total

393

2.189

0.00

13.257

2.717

In respect of the principal species 4 categories of stand species composition were distinguished:

In these groups of stands the mean biomass of underbrush varied from 2.147 (t ha-1) to 2.311 (t ha-1) (Fig. 1). The analysis of variance showed that these small differences, less than 0.2 (t ha-1), were insignificant at α = 0.05.

Fig. 1. Biomass of underbrush in groups distinguished in respect of a tree species of the main stand

It also turned out that biomass of underbrush did not depend on percentage of the principal species in the stand (Table 2). Although the difference between mean values for stands, in which the percentage of the principal species was less than 60%, and the remaining groups was considerable, varying from 0.616 (t ha-1) to 0.735 (t ha-1), it was statistically insignificant at the assumed level of significance of 5%. Undoubtadly a great variation in quantity of underbrush biomass in each of the distinguished groups was the cause of this lack of statistically significant differences. This was indicated by the range of extreme values, greater than 9 (t ha-1) in each case, as well as by standard deviation, not less than 2.380 (t ha-1).

Probably a great variation was also the cause of absence of significant differences between underbrush biomass of the distinguished groups, homogeneous in respect of the principal tree species and its percentage in stand´s structure (Table 2).

Table 2. Biomass of underbrush in groups distinguished in respect of percentage of the principle species in stand structure

Stands

Percentage of principal species

Number of plots

Biomass (t ha-1)

Mean

Standard deviation

Minimum

Maximum

Pine

<0.6

22

1.702

2.153

0.00

7.857

<0.6-0.8)

42

1.998

2.557

0.00

10.593

<0.8-1.0)

91

1.965

2.197

0.00

8.708

1.0

79

2.560

2.712

0.00

10.337

Total

234

2.147

2.447

0.00

10.593

Oak

<0.6

15

0.669

1.118

0.00

4.158

<0.6-0.8)

18

2.597

3.292

0.00

11.819

<0.8-1.0)

25

3.216

4.061

0.00

13.257

1.0

8

0.744

0.611

0.00

1.495

Total

66

2.169

3.237

0.00

13.257

Alder

<0.6

3

0.010

0.018

0.00

0.031

<0.6-0.8)

7

3.084

3.746

0.00

9.326

<0.8-1.0)

9

3.026

3.330

0.00

9.158

1.0

18

2.018

2.408

0.00

8.328

Total

37

2.302

2.876

0.00

9.326

Other

<0.6

27

2.276

2.947

0.00

9.306

<0.6-0.8)

12

2.862

3.194

0.00

9.182

<0.8-1.0)

10

2.697

4.006

0.00

11.242

1.0

7

0.949

1.655

0.00

4.049

Total

56

2.311

3.066

0.00

11.242

Together

<0.6

67

1.627

2.380

0.00

9.306

<0.6-0.8)

79

2.362

2.913

0.00

11.819

<0.8-1.0)

135

2.322

2.866

0.00

13.257

1.0

112

2.243

2.565

0.00

10.337

Total

393

2.189

2.717

0.00

13.257

Relationship between biomass of underbrush and stand age

The age of stands varied from 11 to 176 years. The analysis of the effect of stand age on underbrush biomass was carried out in 20-year age classes. The exceptions to this rule were stands of age class 1 (11-20 years) and class 8 (above 140 years). The mean weight of underbrush biomass of respective stand age classes varied considerably from 1.371 (t ha-1) in class 5 (81-100 years) to 3.180 (t ha-1) in class 2 (21-40 years) (Fig. 2). This was rather unexpected and difficult to interpred at a present research stage. Detailed analyses, however, showed that these considerable differences in biomass of the underbrush layer are accidental. The hypothesis of equality of means was confirmed by a non-parametric Kruskala-Wallis test using real values, as well as the analysis of variance carried out after the previous logarithmic transformation of data [18].

Fig. 2. Biomass of underbrush depending on the stand age class

Generally, biomass of underbrush slightly decreased with increase of stand age, independently of the principal tree species. The Sperman´s coefficient of rank correlation [14], determined for stands in which the percentage of the principal species was at least 80% of total volume, was negative, i.e. -0.1506 for pine stands, -0.1348 for oak stands, and -0.1957 for alder stands. For pine stands, for which this correlation was significant, the dependence of underbrush biomass on stand age is shown in Fig. 3.

Fig. 3. Biomass of underbrush in pine stands depending on stand age

Interesting was biomass of shrubs alone in distinguished age classes (Fig. 4). Its quantity increased from 0.116 (t ha-1) in age class 1 to 1.779 (t ha-1) in class 4, and then rapidly decreased to 0.786 (t ha-1) in class 5, but again it reached over 1.5 (t ha-1) in class 7. However the relation between the biomass of shrubs and the stand age was not significant, since the coefficient of correlation was only -0.0251 in pine stands, 0.0520 in oak stands, and -0.0932 in alder stands.

Fig. 4. Biomass of shrubs depending on stand age class

Relationship between biomass of underbrush and site conditions

The mean quantity of underbrush biomass in stands growing on a moist mixed deciduous forest site (1.534 (t ha-1)) turned out to be the smallest one in comparison with stand growing on sites of other types (Table 3). While the largest one was found in stands growing on a fresh mixed coniferous forest site, i.e. 2.619 (t ha-1). However, this considerable difference between extreme mean values amounting to 1.085 (t ha-1) turned out to be statistically insignificant at α = 0.05. This fact confirmed earlier results concerning the effect of stand species composition on biomass of the underbrush layer. Fertility of site considerably affects the stand species composition, but the species composition does not affect biomass of underbrush, as it has turned out.

The data in Table 3 show that in stands growing on sites of similar trophic conditions the underbrush biomass was greater in the case of sites of smaller moisture. This rule was true for sites of mixed deciduous and mixed coniferous forests.

Table 3. Biomass of underbrush in groups distinguished in respect of the forest site type

Forest site type

Number of plots

Biomass (t ha-1)

Mean

Standard deviation

Minimum

Maximum

Moist decid.

84

2.418

3.351

0.00

13.257

M.mix.conif.

176

2.211

2.472

0.00

10.593

M.mix.decid.

51

1.594

2.081

0.00

9.158

Fresh mix.c.

32

2.619

3.143

0.00

10.337

Alder

20

1.923

2.301

0.00

7.915

Fresh mix.d.

29

2.160

2.913

0.00

10.183

Total

392

2.190

2.720

0.00

13.257

Relationship between biomass of underbrush and stand density

The analysis of the relationship between biomass of the underbrush layer and stand density was carried out for 170 stands. It turned out that the coefficient of correlation for this relationship was not too high, i.e. -0.1957. However this correlation was statistically significant at α = 0.05. It means that in the sample of stands, investigated during this study, the underbrush biomass significantly depended on stand density, and it decreased with increase of that density (Fig. 5).

Fig. 5. Relationship between underbrush biomass and stand density

However, there was no such a relationship between stand density and biomass of shrubs alone, since the coefficient of correlation in this case was -0.0493, and it was statistically insignificant.

DISCUSSION

The occurrence of underbrush is conditioned by many factors. According to Obmiński [5] ..."mass of underbrush is distinctly conditioned by species composition and crown closure..., and its quantity considerably increases (under same site conditions) with age and loosening of the crown closure". This opinion Obmiński based also on results of investigations of Ovington carried out in 50-year-old pine stands of the quality class I. The cited data indicate that biomass of underbrush in stands with pine as the predominant species was on the average 4.2 (t ha-1), reaching its maximum value of (8.9 t ha-1). Biomass of undrgrowth in stands with oak as the predominant species was considerably smaller, i.e. 2.5 (t ha-1) on the average, and ranging from 0.6 (t ha-1) to 6.9 (t ha-1). These quantities differ considerably from quantities obtained for similar pine stands of age class 3, where estimated biomass of underbrush was 2.839 (t ha-1).

Stands of the Niepołomice Forest grow under favourable trophic conditions. The site moisture seem to be a factor determining the occurrence of underbrush. The greatest biomass was reached by the underbrush layer of stands growing on a fresh mixed coniferous forest site. On the average it was by over 0.4 (t ha-1) greater than underbrush biomass of stands growing on a moist mixed coniferous forest site. The difference was even greater, i.e. almost 0.6 (t ha-1), between a fresh mixed deciduous forest site and a moist mixed deciduous forest site. These results are fully in agreement with results of earlier studies of Orzeł and Wysocki [7] carried out in pine stands of the Kłobuck Forest District. Also there the underbrush biomass on a fresh mixed coniferous forest site (3.7 (t ha-1)) was greater than on a moist mixed coniferous forest site (1.4 (t ha-1)) and a moist mixed deciduous forest site (0.8 (t ha-1)).

The results of this study did not confirm the results obtained by Ostrom [8] who demonstrated a significant effect of the stand species composition on biomass of underbrush. A dry mass of this layer, as estimated by this author, was from 0.9 (t acre-1) (2.224 (t ha-1)) in stands of Thuja occidentalis to 2.3 (t acre-1) (5.683 (t ha-1)) for Larix laricina. According to Ostrom biomass of underbrush makes a significant part of the overground biomass in all types of forest (from about 0.4 % in stands of exotic species to 7.0% in stands of Larix laricina.

A great variation of underbrush biomass, even in stands of similar species composition and site conditions, indicates that a high accuracy in estimation of its quantity on the basis of stand characteristics should not to be expected. This opinion has been fully confirmed by the results of the present study, as well as the results obtained in mixed stands of the Ratanica forest complex [10] and forests of the Sąspówka creek drainage area in the Ojców National Park [12]. Biomass of underbrush in these two forest complexes of similar species composition and age structure of stands was quite different, i.e. 2.452 (t ha-1) in the Ojców National Park and 4.0 (t ha-1) in the Ratanica forest complex, and its percentage in the total biomass of stands was 1.0% and 2.5% respectively.

The results of this study also differ considerably from results of investigations conducted in the Niepołomice Forest in late 1970s and early 1980s [11]. The biomass of underbrush in pine stands of aclass V estimated at that time was 3.6 (t ha-1), and in stands of age class II 1.9 (t ha-1). While the quantity of underbrush biomass in oak stands of age class V was as much as 10 (t ha-1). Undoubtadly the cause of such large differences in quantity of underbrush biomass estimated in stands of the same forest complex lies in choice of stands for investigations. The results of Rieger et al. [11] concerned 9 stands, i.e. 3 stands in each of the respective categories of age and species composition. For this reason they are less representative for groups of stands occurring in the Niepołomice Forest, as listed above, than results of the present study based on a considerably greater material.

Using an objective method of selection of a study material makes sure that results obtained may be referred to the entire area of stands above 10 years of age occurring in the Niepołomice Forest (9 459 (ha)). The estimated quantity of biomass of their underbrush is 20 705 tons, with the standard error of ±1 296 tons.

CONCLUSIONS

REFERENCES

  1. Bobiński J., 1971. Oddziaływanie jałowca na glebę [The impact of juniperus on soil properties]. Las Polski 3: 15-16 [in Polish].

  2. Bruchwald A., 1988. Self-thinning in Scots pine stands - a mathematical approach. Ann. Warsaw. Agricult. Univ.-SGGW-AR, For.and Wood Technol. 36: 11-16.

  3. Krzysik F., 1978. Nauka o drewnie [Wood science]. PWN Warszawa [in Polish].

  4. Lesiński J., 1975. Przydatność badań podszytu do określania jego roli wskaźnikowej w zbiorowiskach leśnych. Zeszyty Probl [The aplicability of the investigations on brushwood for the determination of its index role in forest communities]. Post. Nauk Rol., z. 162: 473-478 [in Polish].

  5. Obmiński E., 1978. Ekologia lasu [Forest ecology]. PWN Warszawa [in Polish].

  6. Orzeł S., Socha J., Forgiel M., Ochał W., 2005. Struktura biomasy podszytu występującego w drzewostanach Puszczy Niepołomickiej [Biomass structure of the underbrush growing in pine stands of the Niepołomice Primeval Forest]. In press [in Polish].

  7. Orzeł S., Wysocki P., 2003. Struktura i przyrost biomasy wybranych drzewostanów sosnowych Nadleśnictwa Kłobuck [Biomass structure and increment in selected pine (Pinus sylvestris L.) stands of the Kłobuck Forest District]. Acta Sci. Pol. Silvarum Colendarum Ratio et Industria Lignaria 2(2): 61-70 [in Polish].

  8. Ostrom A. J., 1983. Tree and shrub biomass estimates for Michigan. USDA For. Serv. Res. Note NC-302

  9. Pomarnicki L., 1973. Nie lekceważmy podszytów [Do not disregard underbrushes]. Las Polski 6: 13 [in Polish].

  10. Raimer J., Rutkowska L., Grabczyński S., Orzeł S., Rieger R., 1990: Ocena biomasy i produkcyjności drzewostanów kompleksu leśnego "Ratanica" na Pogórzu Wielickim [Appraisal of biomass and productivity of "Ratanica" forest tract in Wieliczka Plateau]. Acta Agr. Silv., ser. Silv., 29, 89-103.

  11. Rieger R., Grabczyński S., Orzeł S., Raimer J., 1984. Growing Stock and Increment of Tree Stands. - rozdział w książce pt.: "Forest Ecosystems in Industrial Regions". Ecological Studies 49. Springer-Verlag Berlin Heidelberg New York Tokyo, 70-78.

  12. Rieger R., Grabczyński S., Orzeł S., Raimer J., Rutkowska L., Wimmer M., 1988. Zapas i przyrost drzewostanów kompleksu leśnego zlewni potoku Sąspówka w OPN oraz ocena ich biomasy i rocznej produkcji [Volume and increment of Sąspówka creek drainage area forest complex stands in OPN and assesment their biomass and annual productivity]. Records in the Dept. of Forest Mensuration, Agricultural University of Cracow. [in Polish].

  13. Socha J., Wężyk P. 2004. Empirical Formulae to Assess the Biomass of the Above-Ground Part of Pine Trees. Electronic Journal of Polish Agricultural Universities, Forestry, Volume 7, Issue 2.

  14. Stanisz A., 2000. Przystępny kurs statystyki z wykorzystaniem programu STATISTICA PL na przykładach z medycyny [Easy course of statistic using STATISTICA PL software on the examples from medicine]. Tom II. Kraków [in Polish].

  15. StatSoft, Inc. 2004. STATISTICA (data analysis software system), version 6. www.statsoft.com.

  16. Szujecki A., 1978. Wpływ podszytów dębowych na zgrupowanie ściółkowych kusakowatych (Col., Staphylinidae) borów sosnowych świeżych [Impact of oak understorey upon the community of litter-inhabiting staphylinidis (COL. STAPHYLINIDAE) in fresh pine forest]. Folia For. Pol., s. A, z. 23: 157-173 [in Polish].

  17. Szymański S., 1986. Ekologiczne podstawy hodowli lasu [Ecological basis of forest silviculture]. PWRiL, Warszawa [in Polish].

  18. Tadeusiewicz R., Izworski A., Majewski J., 1993. Biometria [Biometrics]. Wyd. AGH Kraków [in Polish].

  19. Tuszyński M., 1986. Czy wprowadzanie podszytów spełnia pozytywną rolę w pielęgnowaniu gleby i drzewostanu? [Does underbrush play a possitive role in soil and forest stand tending?] Postępy Techniki w Leśnictwie, 38: 14-18 [in Polish].

  20. Nadleśnictwo Niepołomice. [W:] Lasy i gospodarka leśna Regionalnej Dyrekcji Lasów Państwowych w Krakowie [Niepołomice Forest District [In:] Forest and forest economy in the Regional Directorate of the State Forests in Kraków]. Kraków 2000. [in Polish]

  21. Forest Management Plan for the Niepołomice Forest District for 2002 - 2011. [in Polish]

A study was carried out under the project No 3 P06L 01322 entitled:"Biomass and annual production of woody vegetation of the Niepołomice Forest" financed by the Committee of Scientific Research.


Stanisław Orzeł
Department of Forest Mensuration,
Agricultural University of Cracow, Poland
Al. 29 Listopada 46, 31-425 Cracow, Poland
email: rlorzeł@cyf-kr.edu.pl

Jarosław Socha
Department of Forest Mensuration,
Agricultural University of Cracow, Poland
Al. 29 Listopada 46, 31-425 Cracow, Poland
email: rlsocha@cyf-kr.edu.pl

Marcin Forgiel
Department of Forest Mensuration,
Agricultural University of Cracow, Poland
Al. 29 Listopada 46, 31-425 Cracow, Poland
email: rlforgie@cyf-kr.edu.pl

Wojciech Ochał
Department of Forest Mensuration,
Agricultural University of Cracow, Poland
Al. 29 Listopada 46, 31-425 Cracow, Poland
email: rlochał@cyf-kr.edu.pl

Responses to this article, comments are invited and should be submitted within three months of the publication of the article. If accepted for publication, they will be published in the chapter headed 'Discussions' and hyperlinked to the article.