Access the full text.
Sign up today, get DeepDyve free for 14 days.
Stem quality and damage was evaluated in mixed spruce-fir-beech stands. Moreover, an assortments structure was determined with their financial value. Results were compared with pure spruce (Picea abies [L.] Karst.), fir (Abies alba Mill.) and beech (Fagus sylvatica L.) stands. Repeated measurements on 31 long-term research plots, stand assortment models, assortment yield models and value yield models were used. Stem quality of fir and spruce was only slightly lower in mixed stands compared to pure stands but beech stem quality was considerably worse in mixed stands. Fir and spruce had slightly lower proportions of better A quality logs and higher proportions of B quality in mixed stands. Beech had worse assortment structure than spruce and fir, in general. Pure beech stands had higher proportions of better IA quality assortments than mixed stands by 17%. Fir and spruce average value production ( m3) culminated at about 56 and 62 cm mean diameters. Almost the same value production was found in pure stands. In these stands it culminated at the mean diameter of 58 and 60 cm. Beech produced substantially less value on the same sites. In mixed stands, its value production culminated at the mean diameter of 40 cm. In pure stands, it culminated at the mean diameter of 36 cm. Although the production was found to be similar in both mixed and pure forests, higher damage intensity and less stem quality in mixed forests suggest that the pure forests can be more profitable. Key words: silver fir; Norway spruce; European beech; mixed stands; assortments production Editor: Jaroslaw Socha 1. Introduction Mixed stands are usually expected to have higher production, which has repeatedly been proven (Pretzsch 2009; Forrester 2014). Mixed stands can be more producte than pure stands, however this depends on the site conditions, stand age and how the species interact. A lot of mixed-stand studies quantify growth or yield of indidual tree species by height or diameter growth (Künstle 1962; Monserud & Sterba 1996; Knoke et al. 2008; Petrás et al. 2014a), as well as by their production volume and increments (Kennel 1966; Prudic 1971; Míchal 1969; Hink 1972; Pretzsch 1992; Pretzsch & Schütze 2009; Lebourgeois et al. 2014; Petrás et al. 2014b). For Central Europe, these were mainly based on measurements on simultaneous plots in pure or mixed parts of the stand, and only few studies were based on long-term research plots in mixed stands. In the search for the causes of different growth and production in mixed stands, most authors focus on site, climate, tree species composition, the type of mixture and the stand age (Magin 1954; Kennel 1965, 1966; Hausser & Troeger 1967; Mitscherlich 1967; Hink 1972; Mettin 1985; Kramer et al. 1988; Pretzsch 2009; Pretzsch et al. 2010). Few authors prode detailed evaluation of the quality and value of wood produced in either pure forests (Karaszewski et al. 2013; Michalec et al. 2013) or mixed stands (Hausser & Troeger 1967; Kramer et al. 1988; Saha et al. 2012, 2014), and most of the above-mentioned authors agree that mixed stands have many advantages over pure stands, because the former more readily resist damage and have posite effects on soil properties. Mixed stands better utilize both above-ground and below-ground parts, especially when the tree species have different biological properties and requirements light, water and nutrient availability. These factors explain why higher wood production is expected in mixed stands than in pure on some sites. Knowledge on wood quality especially that of mixed-species stands, are essential for decision making in forestry. There is not only financial interest, but also in carbon management such as different wood products store carbon for different time periods. There is, however, a lack of knowledge on wood quality and value in mixed forests (Saha et al. 2012, 2014; Stefancík & Bosea 2014). Therefore, our aim is to fill the knowledge gap and go beyond the traditional quantitate production research by assessing assortment structure of mixed forests in Central Europe. We quantify differences in wood quality and financial yield between mono-specific and mixed-species forests. We also present an integrated methodological concept based on long-term experimental data and integrated models of wood quality and yield production. The study particularly aims (i) to evaluate stem quality and damage in mixed forests in the Western Carpathians; () to determine their assortment structures and financial value; and () to compare results between mixed and single species forests of Norway spruce (Picea abies L. Karst), silver fir (Abies alba Mill.) and common beech (Fagus sylvatica L.) *Corresponding author. Michal Bosea, e-mail: firstname.lastname@example.org, phone: +420 5206 310 in similar growth conditions. We hypothesise that, although the quantitate production is supposed to be higher in mixed forests, species-pure forests might produce higher value production because less-quality wood is expected to be produced. 2. Material and methods 2.1 Research plots Empirical material included repeated measurements from 31 long-term research plots (LTPs). These plots were established in the Western Carpathians (Fig. 1) in the 1960's and 1970's to study the growth and production of pure and mixed forest stands (Table 1). The plots were situated in the western and eastern parts of the Slovenské Rudohorie Mountains; the western parts in the Hriová region and the eastern ones in the Spis and Hnilecká dolina valley. The altitude ranged between 480 and 970 m a.s.l. The prevailing climatic-geographic subtype is a cold mountain climate, which gradually changes to mild and slightly warm mountain climate (Lapin et al. 2002). Plots were established in and represent the following forest types: beech-fir fertile forests; fir-beech forests on eutrophic to moderately oligotrophic soils; beechfir forests with spruce on oligotrophic soils and beech-fir forests with sessile oak (Quercus petraea Matt.) on oligotrophic soils. The tree species mixture differed between LTP; with all three species being present on 16 LTPs; spruce with fir on 13 LTPs; and fir with beech and spruce with beech each on one LTP. Fir had the highest proportion on the LTPs, followed by spruce, and then beech. Stand age at the time of LTP establishment varied from 32 to 159 years. All research plots were repeatedly measured and tended with negate thinning from below; most often at regular 5-year intervals. The same thinning method was applied in all the LTPs; both established in mixed and pure forests. The majority of the plots were measured four to eight times. The rectangle-shaped LTP area ranged from 0.2 to 1 ha, with all trees numbered and the place of diameter measurement marked. The height of all trees in the plots was only measured at the first and last measurements, while a sample of trees were selected for height measurement throughout the entire period. These sample trees were selected from the entire DBH range to enable developing the height-diameter model. The model was then used to estimate the height of the all remaining trees. 2.2. Assessment of stem quality and damage Using the Kraft classification system (Kraft, 1884) (predominant, dominant, co-dominant, intermediate, suppressed/ overtopped), trees were classified into 15 tree classes (, and their stem quality and damage were assessed. Stem quality was determined in the following three classes at each inventory prior to 1990: (1) best quality stems, straight and without technical defects; (2) average-quality stems with small technical defects and (3) lowest quality stems with large technical defects. This grading had been applied without consideration of the timber end-use, and more appropriate stem-quality classification was introduced in 1991 as new assortment models were developed in Slovakia (Petrás & Nociar 1991). Stems were then categorized in A (High quality stems, almost without knots (only healthy knots under 1 cm in diameter at the base), twisting (spiral growing), and without other technical defects.), B (Average quality stems, with small technical defects. In the case of hardwood species all of the healthy or unhealthy knots with diameters under 4 cm are allowed. For spruce and fir healthy or unhealthy knots under 4 cm and for Fig. 1. Location of study sites in the Western Carpathians. Table 1. Basic information on surveyed LTPs: t0 is the age at plot establishment, tn is the age at last measurement and G denotes stand basal area. LTP 15 44 45 46 47 50 51 52 53 54 56 60 61 63 79 80 81 82 83 89 91 93 94 107 110 111 112 114 115 118 119 Area [ha] 0.40 0.36 0.49 0.49 0.48 1.00 0.30 0.43 0.66 0.28 0.49 0.44 0.65 1.00 0.24 0.42 0.40 0.30 0.20 0.23 0.67 0.56 0.64 1.00 0.81 0.49 1.00 0.96 0.60 0.35 0.54 Altitude [m] 480 760 730 560 650 724 588 775 865 740 968 885 890 686 600 900 640 690 790 630 700 560 770 717 820 670 839 770 818 705 705 fir 81.5 68.3 65.1 94.1 84.0 69.2 92.3 81.7 82.9 77.4 92.4 12.5 7.2 63.8 89.6 66.5 91.1 84.8 94.4 83.6 64.5 40.1 33.0 83.4 90.7 18.0 61.0 9.9 45.3 31.5 Proportion [% of G] spruce 6.3 4.2 16.6 5.9 10.7 7.7 9.5 17.1 22.6 7.6 87.5 89.3 31.3 10.4 23.7 8.9 15.2 5.6 16.4 15.1 9.2 47.8 7.8 9.3 70.0 36.8 5.7 69.5 52.2 68.5 beech 12.2 27.5 18.3 5.3 30.8 8.8 fir 31 30 35 29 30 27 31 22 30 31 29 33 32 26 31 29 31 35 30 29 31 27 29 34 34 37 36 38 34 36 Site index [1 m] spruce 32 28 36 29 32 33 23 32 31 31 33 33 26 32 30 31 37 37 33 32 26 32 38 35 38 39 39 38 34 39 Age beech 27 30 30 21 23 16 t0 65 77 82 104 94 159 47 141 110 52 121 73 83 140 53 74 47 32 36 40 88 80 81 142 140 69 95 103 89 99 95 tn 108 120 123 145 135 202 88 185 152 93 162 114 124 184 96 114 88 73 79 80 124 122 111 181 166 110 134 144 115 125 136 Note: G stand basal area, t0 age at establishment, tn age at the last measurement. Scots pine less than 6 cm are allowed.), C (Low quality stems with large technical defects, with high frequency of branches (densely branched trees), twisting up to 4% of straight length axis. Healthy knots without limit for the size (diameter) are allowed, unhealthy knots up to a diameter of 6 cm in the case of softwood species, and up to 8 cm for hardwood species.) and D (Poor quality stems with unhealthy knots over 6 cm for softwood species and over 8 cm for hardwood species, which are also affected by rot. The stems are only utilized as fuelwood.) classes, dependent on quality assessment of their lower third portion. For this study, the new classification was only used in order not to affect results and interpretations. Damaged stems (sually assessed on standing trees) significantly predict inside-wood defects such as rot, and the red heart often found in beech trees. Therefore buttress and surface roots were evaluated in addition to surface stem damage; with damage presence only recorded, disregarding its size, intensity and position. The proportions of AD classes and damaged stems were calculated for each inventory after 1990; with average percentages and standard deations determined for each tree species. The same variables were calculated for pure fir, spruce and beech stands by assortment yield models (Petrás & Mecko 1995; Petrás et al. 1996). The proportion of the AD stem quality classes is a function of q site index (Equation 1). Here, site index is the mean stand height at 100 years standard age, dered from height growth models developed for Slovakian yield models (Halaj & Petrás 1998). The proportion of damaged stems, p%, is a function of stand age t. A, B, C, D% = f (q)  p% = f(t)  As follows from the models the stands with higher site index produce a higher proportion of better quality stems, and the proportion of damaged stems increases with the stand age. 2.3. Estimation of assortment structure Assortment structure was estimated for each LTP and tree species using stand assortment models (Petrás & Nociar 1991; Petrás 1992). These models prode assortment proportions S% for each tree species as a function of the following factors: mean diameter dv; proportion of stem quality classes kv%; proportion of damaged stems p%; and for beech trees also as a function of stand age t. S% = f (dv, kv%, p%, t)  Indidual assortments represent log classes based on log quality and diameter. The proportion of the following clas- ses results from Equation 3: End-use I cut veneer, special sports and technical equipment, plywood, matches and sports equipment, saw logs (better quality A, worse qua(A, B) lity B), building timber and sleepers, pulpwood, chemical and mechanical processing for V cellulose and wood-based panels production, fuel-wood. IB classes are split into 16+ diameter classes in the stand assortment model. Class class. In addition, the 2% of poor quality D class increased overall worst quality of beech in the mixed stands. Standard deations suggested that fir had the lowest between-plot variability in the all quality classes, followed by spruce, with the highest variability in beech. The coefficients of variation for their most represented B class were 11% for fir and 26% for spruce, with 30% for C class beech. % 80 70 60 50 40 30 20 The assortment structure of fir, spruce and beech single species stands was dered from assortment yield models (Petrás & Mecko 1995; Petrás et al. 1996), where assortment proportions S% is a function of stand age t and site index q. 2.4 Defining the assortments value Assortment value was calculated as the product of assortments volume and wood prices for each log quality and diameter class (Fig. 2). Wood prices were taken from the price list published by Slovak state forest enterprise in 2013. 10 0 A B C D Fig. 3. Proportion of AD stem quality classes by tree species in mixed stands. The whiskers denots 95% confidence intervals. % 80 70 Fir, spruce Beech Value [ m3] A.6+ A.1 A.2 A.3 A.4 A.5 I.6+ .2 .3 .4 .5 .6+ I.4 I.5 B.1 B.2 B.3 B.4 B.6+ B.5 0 A B C D Assortment category Fig. 2. Wood prices ( m3) by I qualitate classes, and by 16+ diameter classes of fir, spruce and beech. Fig. 4. Differences in A-D stem quality classes between mixed and pure stands. Structure and production value were calculated in the following two variants to evaluate the mixed stand production. These variants were chosen with regard to input data source for each variant: Variant Source of input data (stem quality and damage, mean diameter) 1 All input data emanates from LTP measurements. 2 All input data comes from the models developed for pure stands. 3. Results 3.1. Stem quality and damage The proportions of stem quality classes on LTPs in mixed stands indicate that B class dominates in fir and spruce with 62 to 66% (Fig. 3). The beech stem quality decreased during the study period and the highest proportion of approximately 57% was found in class C. This percentage was higher than both the average quality B class and the highest quality A In comparison to the quality of pure stands growing on the same sites (Fig. 4), fir and spruce had higher proportions of both best A stem quality class by 45% and C class by 913%. In contrast, the proportion of average B quality class was lower by 1417%. In addition, beech had 24% less best A quality class stems in mixed than pure stands as well as 13% less B class quality. This 37% sum leaves higher proportions of poor quality C class stems. We can clearly conclude that conifers in mixed stands produced more stems of both best and worst quality than pure stands, and the average-quality stems diminished. In contrast, the opposite was found for beech. Beech mixed with fir and spruce had a lower proportion of average quality stems by 13%, but the proportion of the best quality stems was even 24% lower compared to pure beech forests. Stem damage (e.g. after logging, debarking by a deer species, etc.) substantially reduces the wood quality. The proportion of damaged stems was between 49 and 53% for all the LTPs and all the tree species (Fig. 5). In the pure stands (as simulated by the models) the proportions were different. Spruce had the highest proportion of damaged stems (61%), followed by fir (46%) and beech (23%). % 40 30 20 10 0 A -10 -20 -30 B C D The assortment structure of beech is worse than that of both spruce and fir. While timber volumes increased steadily between I and V assortment category, pure stands had simultaneously higher proportions of better quality assortments (IA category) than mixed stands by approximately 17%, but this situation was reversed for lower quality B classes. 3.3. Assortment and value production Value of assortment and timber production is additionally influenced by actual prices. We found the proportions of the assortments of IA class calculated from the prices (Fig. 7) were higher than the proportions dered from their volumes (Fig. 6). Fir was found to have a higher proportion by 13%, spruce by 25% and beech by 28%. In contrast, lower proportions were found for B assortment classes; fir by 15%, spruce by 17% and beech by 110%. Fig. 5. Damaged stem proportions in mixed and pure stands. 3.2. Assortment structure Fir and spruce exhibited very similar assortment structure, where A and B saw-log classes prevailed with 3050% (Fig. 6). These were followed by pulpwood assortments in V class with 1015% and the most valuable assortments of I and class with 35% and then fuel-wood amounting approximately to 1%. Differences in assortment structure between the variants are far smaller. For both species, the proportions of the highest quality assortments (I and ) in mixed forests (1st variant) were only a few tenths of percent higher than in pure stands (2nd variant). Saw logs, however, had contrasting proportions. Mixed stands had a slightly lower proportion of A assortment and higher proportion of worse quality B assortment than pure stands. % 50 45 40 35 30 25 20 15 10 5 0 I % 50 45 40 35 30 25 20 15 10 5 0 I % 50 45 40 35 30 25 20 15 10 5 0 V Fir Mixed Pure Fir Mixed Pure Spruce Spruce Beech Beech Fig. 7. Value proportions of I quality classes logs in mixed and pure fir, spruce and beech stands. Fig. 6. Volume proportions of I quality class logs in mixed and pure fir, spruce and beech stands. 102 The value of wood production in mixed forests is not only influenced by assortment structure and prices, but also by the different timber volume of indidual tree species. The average production value ( m3) was calculated for each tree species and each variant to compare tree species production (Fig. 8, 9), and these were assessed as a function of mean diameter and site index. The value production pattern of fir and spruce followed a very similar course and culminated at 56 and 62 cm in mixed stands, at approximately 79 m3. Simulations by the Slovakian yield models showed almost the same production in pure stands, where it culminated at mean diameters of 58 and 60 cm with approximately 79 and 78 m3. These values approximate both their culmination and mean diameter range. In contrast, beech produced significantly less on the same site index; where mixed stand production culminated at 40 cm mean diameter and just below 54 m3. It culminated earlier in pure stands at 36 cm mean diameter and by 10 m3 higher value. y = 0.0169x + 1.8725x + 27.58 2 R = 0.8793 y = 0.0086x2 + 1.0765x + 44.85 R2 = 0.6601 y = 0.0228x2 + 1.8113x + 17.976 R2 = 0.4908 Mean stand diameter [cm] Fig. 8. Average value of fir, spruce and beech wood ( m3) produced in mixed stands. y = 0.0116x2 + 1.3501x + 39.838 R2 = 0.9518 y = 0.0092x2 + 1.117x + 44.001 R2 = 0.9641 Value [ y = 0.0902x2 + 6.4136x - 53.064 R2 = 0.3 and peeling. Beech stems generally have harder wood, but stem damage increases the probability of red heart (Petrás 1996a, b). Although overall stem damage was higher in pure stands, our results highlight that fir and especially beech suffered less damage in pure than in the mixed stands compared to spruce which had a higher damage in pure forests. This was probably because bark of spruce is one of the natural food sources in winter (Fino & Petrás 2011). Stem quality and damage is reflected in assortment structure. Fir and spruce had very similar assortment proportions in both mixed and pure stands. Thicker stem branches in mixed stands led to a slightly lower proportion of higher quality A class logs and a higher proportion of B. However, beech reached essentially lower timber quality in mixed forests. Wiedemann (1951) and Krammer et al. (1988) also suggested that beech usually has higher potential for best quality assortment in pure stands than in mixed. For this reason, Wiedemann (1951) and Prudic (1971) suggested that maximum beech proportion in mixed stands is usually limited to 2030%. Financial values comprehensely reflected the production capabilities of these stands. Our results confirmed that fir and spruce are the major value producers in mixed stands, with beech significantly lagging in this respect (Wiedemann 1951; Prudic 1971) and also performing worse in pure stands. Hauser & Troeger (1967) reported that fir produces 9% greater value than spruce in mixed spruce-fir stands because of their greater diameter. Here, it is important to realize that assortment tables do not consider stem quality and damage; these rely solely on dimensions for production value calculation. m ] 3 Value [ m3] 5. Conclusions 50 60 70 Mean stand diameter [cm] Fig. 9. Average value of fir, spruce and beech timber ( m3) produced in pure stands. 4. Discussion Spruce, fir and beech are ecologically and economically the most important tree species in the Western Carpathians and these naturally form both pure and mixed stands. Our results indicated slightly worse stem quality in mixed forests for all the species. Wiedemann (1951) suggested this was due to vertical and horizontal structure of mixed forests where less dense crown canopy enables longer surval and consequent branch roughening than in pure stands with their more concentrated single-layer canopy. Furthermore, strong heliotropism negately influences beech lengthwise and crosswise shape and also its spiral grain (Krammer et al. 1988; Pretzsch & Schütze 2009). Mechanical stem damage introduces a secondary factor; caused mainly by inappropriate technology in logging and by red deer bark-stripping This study suggested that conifers had only slightly worse stem quality in mixed than pure stands. However, beech had considerably lower stem quality in mixed forests While the proportion of damaged stems in mixed stands was high for all the tree species, fir and especially beech stems experienced less damage in pure stands. Spruce trees, in contrast, suffered higher damage in pure stands In mixed forests, beech was found to have overall worse assortment structure than spruce and fir. This study suggested that wood quality and assortment structure was considerably lower in mixed forests only for beech, while almost no differences were found for conifers. This thus encourage forestry practice to prefer mixed-species forests, especially when static stability and resistance to climate change should be taken into account. Acknowledgements This work was supported by the Slovak Research and Development Agency under contract No. APVV-0255-10, APVV-0439-12 and SK-RO-0006-12.
Forestry Journal – de Gruyter
Published: Jun 1, 2016
Access the full text.
Sign up today, get DeepDyve free for 14 days.