Environ Monit Assess (2018) 190:377 https://doi.org/10.1007/s10661-018-6754-8

Influence of interspecies competition on (Fagus orientalis Lipsky) and some features of stand in mixed broad-leaved forest

Kambiz Abrari Vajari

Received: 15 December 2017 /Accepted: 25 May 2018 # Springer International Publishing AG, part of Springer Nature 2018

Abstract Oriental beech (Fagus orientalis Lipsky) coexistence and planning mixtures in temperate is one of the most important commercial spe- broad-leaved forests. cies in the Hyrcanian region. This species is known to suffer from strong intra- and interspecific com- Keywords Broad-leaved tree . Competition index . petition for above- and below-ground resources in Temperate forest . Tree architecture temperate mixed stands. In the present study, a total of 26 beech trees and their surroundings trees as well as stand characteristics were evaluated for Introduction determining the interactions between them and competition index (CI) in mixed beech stand. The Competition is a relationship between trees for results showed that in mixed beech stand, there gaining the growing space and taking limited re- were positive correlation between CI and crown sources such as light, nutrients, and water via their ratio and height/diameter (HD) ratio of target beech growth and development (Van de Peer et al. 2017). trees, but negatively correlated to crown length, A major ecological process that makes key role in crown width, crown area, and crown volume. Total growing and species replacement (Maleki et al. height, DBH, and bole of target beech trees were 2015) and also in tree’s structure and composition decreased with increasing CI. Regression analysis (Fichtner et al. 2012) is competition among trees. showed that CI had positive significant correlation The interactions between make a vital role in with functional group of forb richness. The target controlling composition (Kunstler et al. 2011) beech trees characteristics including HD ratio and and influenced via a lot of parameters (Guo et al. crown ratio showed contrasting responses to some 2016). A lot of parameters control the growth of variables which were related to their known specif- trees, but one of them is competition among trees ic ecological strategies. This study demonstrates the which can be determined via silvicultural tools different responses of target beech trees in oversto- (Metz et al. 2013). For measuring tree competition, ry to competition in neighborhood conditions which several competition indices have been considered are an important factor in retaining species (Metz et al. 2013) and using competition indices are an important subject of forestry in the world (Pedersen et al. 2013). Several studies show the * K. Abrari Vajari ( ) responses of trees to competition factor in forest Faculty of Agriculture and Natural Resource, Lorestan University, Khorramabad, such as crown architecture (Barbeito et al. 2014; e-mail: [email protected] Bayer et al. 2013; Olivier et al. 2016), tree size e-mail: [email protected] (Antin et al. 2013;Thorpeetal.2010), basal area 377 Page 2 of 7 Environ Monit Assess (2018) 190:377 increment (Contreras et al. 2011), tree morphology of providing information for practical management (Lang et al. 2010), stem girth increment (Martín of beech stands in temperate forest, especially et al. 2014), and crown modeling (Metz et al. selecting the silvicultural methods. 2013). In all studies, competition appeared to be more important factor, which has been shown to impact crown size, architecture, and tree Materials and methods morphology through its various components within forests. Measuring some characteristics of trees Study area within forest stand and their interactions with other trees can be used for evaluating them in The research took place in Hyrcanian beech forest lo- order to design silvicultural operations. For cated (36°, 12′,37″ N and 53°, 25′,47″ E) in Northern example, Sharma et al. (2016) declared that the Iran (Mazandaran province) with an elevation range crownsizesareusedtoevaluatesometreecharac- from 1010 to 1020 ma.s.l. The parent material of this teristics including strength and health of trees, region is marl, conglomerate, and alluvial belonging to wood quality, resistant to wind, and stand density. Pliocene epoch. The predominant soil type is Tree competition can be used as important factor pseudogley. The study site is characterized by a humid for predicting growth of trees (Contreras et al. climate with a mean annual precipitation 858 mm and a 2011) and in mixed stand with complex structure; mean annual temperature of 10.5 °C. The forest area is it is believed that tree competition is considered as dominated by broad- trees and comprises an obvious process (von Oheimb et al. 2011). 58.5 ha. Four species, oriental beech (Fagus orientalis Quantifying the influences of competition on the Lipsky), Alder (Alnus subcordata C.A.Mey), ironwood different components of trees may be vital to un- (Parrotia persica C.A.Mey), and hornbeam (Carpinus derstanding tree responses and to predict species betulus L.), comprise the overstory layers within stand, ability to compete with neighboring trees with oriental beech more common at higher height. The (Barbeito et al. 2014). Oriental beech (Fagus beech-ironwood trees along with other tree species orientalis Lipsky), as shade-tolerant tree, is one of formed the mixed uneven aged forest type (high forest) the most important commercial tree species and it and the past applied silvicultural system was the selec- plays significant ecological role in the Hyrcanian tion system. region. Beech stands mixed with other broad-leaved species are known to suffer from strong intra- and Field measurements interspecific competition for above- and below- ground resources in temperate mixed stands. To Data sampling was performed during summer 2017 on investigate the influence of neighborhood competi- 26 plots which were selected in a 100 m × 150 m regular tion on target beech trees, the present study was grid within beech stand. At the center of each plot, a carried out in a mixed broad-leaved forest of ori- single stemmed beech trees were sampled in overstory ental beech, hornbeam, ironwood, and Alder in the as target trees (totally 26 trees).The position of the Hyrcanian region, Northern Iran. The main purpose neighbors to the target beech tree was defined by mea- of this study was to identify the correlation between suring the horizontal distance from stem base to stem distant-dependent competition index (CI) caused by base and all trees were determined to species level (von neighboring trees and oriental beech (Fagus Oheimb et al. 2011). The morphological parameters orientalis Lipsky) species and also some stand fea- were measured for each target tree including stem di- tures within mixed broad-leaf temperate forest in ameter at a height of 1.30 m (dbh > 10 cm), total tree the Hyrcanian region. The specific objectives of the height (m), crown length and width (m), crown area study were to (1) identify the correlation between (m2) and volume(m3), height to diameter ratio of the CI and target beech tree characteristics, (2) evaluate tree (the slenderness factor, H/D), crown ratio (crown the interaction between CI and some environmental length–tree height ratio), and bole (m). Crown radius factors in beech stand, and (3) determine the rela- was calculated as the mean value of radii in four differ- tionship of crown and HD ratio with target beech ent directions (N, E, S, W).The crown surface area tree structure. The results can be used with the aim (CSA) and the crown volume (CV) were calculated Environ Monit Assess (2018) 190:377 Page 3 of 7 377

(Promis et al. 2009), supposing that the crown of target normal distribution. Thus, for the comparison of CI in tree has a parabolic shape: different diameter classes of target beech trees, paramet- ÀÁ ric statistics (independent T test) was used. A one-way π Â R 1:5 CSA ¼ Â R2 þ 4 Â C2 −R3 ð1Þ ANOVA (analyses of variance) was performed for ana- Â 2 L 6 CL lyzing the effect of species neighbor identity on the distance parameter and also on the diameter at breast R2 Â C CV ¼ π Â L ð2Þ height (DBH) of trees. The S.N.K. test was used for 2 multiple comparisons of species neighbor identity in where CL (m) is the crown length and R is crown radius relation to distance parameter and DBH (cm) following (m). To calculate the competition index (CI), the follow- the results of ANOVA. To calculate interaction between ing distance-dependent competition index was used of CI and some features of target trees and ecological ’ (Xiang et al. 2013): factors, Pearson s correlation coefficient was used. All ÀÁ data were analyzed with the use of SPSS version 20.0 2 and the statistical significance was based on α =0.05 n dbh j=dbhi CI ¼ ∑ ð3Þ and 0.01. j¼1 distij þ 1 where n is the total number of neighbor trees within the

6–8 m radius of the target tree, dbhi and dbhj are dbh Results (cm) of a target tree (i) and its neighbor trees (j), and distij is the horizontal distance (m) between the target The diameter at breast height (DBH) differed signifi- tree (i)andtheneighbortree(j). The beech target trees in cantly among the three neighbor trees species in the mixed conditions were surrounded by other tree species mixed stand (Table 2). The diameter at breast height including hornbeam, ironwood, and beech. In addition, was significantly higher in beech than in the other some variables including humus and litter thickness species. (cm), forb and graminoid richness (SR), herb layer The size of the distance between adjacent crowns of diversity (Simpson’s index diversity), and beech regen- neighbor trees did not differ significantly in regard to the eration within each plot were measured for determining species pair considered (Table 3). Although trees grow- interaction between competition index and these param- ing next to beech trees came in very close contact but the eters. The target beech tree characteristics can be found crowns of the neighbors do not overlapped. in Table 1. Correlation analysis (Table 4)showedthatcompeti- tion index (CI) had positive significant correlation with Statistical analyses forb richness (P < 0.05), but there was no significant correlation with other parameters. Competition index All data were tested for a normality using the (CI) was significantly negatively correlated with crown Kolmogorov-Smirnov test and datasets indicated a width, crown length, crown volume, DBH, height, and bole (P < 0.05) and positively correlated with H/D ratio Table 1 Dimensions of target beech trees (n = 26) in sample plots and crown ratio for target beech trees (Table 5). (mean ± standard deviation)

Variable Mean(± SD) Unit

Total height 34.7 (± 4.4) m Table 2 Diameter at breast height (DBH) and proportion charac- terizing canopy structure for neighbor trees DBH 70.4 (± 21.4) cm Crown length 11.9 (± 1.6) m Variable Beech Hornbeam Ironwood Crown width 13.1 (± 2.4) m DBH (cm) 59.27 (± 5.16)a 36.7 (± 6.4)b 41.90 (± 5.22)b Crown surface area 114.7 (± 70.3) m2 Proportion (%) 38.77 24.48 32.65 Crown volume 856.7 (± 344.6) m3 No of trees 19 12 16 Crown ratio 0.36 (± 0.05) – HD (height/diameter ratio) 56.6 (± 18.7) – Different letters indicate significantly different means of the spe- cies (SNK test, P < 0.05, means ± SE) 377 Page 4 of 7 Environ Monit Assess (2018) 190:377

Table 3 Minimum crown distance (m) in the lateral contact zone Table 5 Pearson’s correlation coefficient between Competition between neighbor trees and target beech tree index (CI) and some characteristics of target beech trees

Neighbor n Distance (m) Distance proportion (%) Variable Competition index (CI) Mean (± SE)

Beech 19 5.45 (± 0.41)a 30.72 Crown length (m) r = − 0.453* P = 0.026 12.97 (± 0.34) Hornbeam 12 6.35 (± 0.47)a 33.79 Crown width (m) r = − 0.400* P = 0.043 13.18 (± 0.57) Ironwood 16 5.94 (± 0.38)a 33.48 Crown volume (m3) r = − 0.474* P = 0.05 856.76 (± 67.5) Crown area (m2) r =0.262ns P = 0.196 114.85 (± 13.7) The same letters indicate no significant different means of the species (SNK test, P < 0.05, means ± SE) Crown ratio r =0.411* P = 0.045 0.35 (± 0.01) H/D ratio r = 0.888** P = 0.000 57.68 (± 3.67) Correlation analysis (Fig. 1a–c) showed that crown DBH (cm) r = − 0.787** P = 0.000 70.44 (± 4.20) ratio was significantly positively correlated with crown Height (m) r = − 0.403* P = 0.041 36.78 (± 0.87) length (r =0.672, P ˂ 0.01), crown area (r = 0.592, Bole (m) r = − 0.410* P = 0.038 23.42 (± 0.77) ˂ ˂ P 0.01), and crown volume (r =0.591,P 0.01) and *, ** significant at level = 0.05 and 0.01; ns, non-significant there were no significant correlations between crown ratio and total height, crown width, and DBH overlapped (Table 3). This result is consistent with study (P ˂ 0.05).The correlations between HD (height to of Hajek et al. (2015) in an old-growth species-rich, diameter ratio) and DBH (r = − 0.918, P ˂ 0.01), total temperate broad-leaved forest. The crowns of many height (r = − 0.443, P ˂ 0.05), crown width (r = − 0.463, trees were highly asymmetric which in it could be P ˂ 0.05) were significantly negative (Fig. 1d–f) and related to response to past competition with other neigh- there were no significant correlations between H/D ratio bor trees, wind, snow injury, etc. based on Hajek et al. and crown length, crown area, and crown volume for (2015) and applied silvicultural system in beech stand. target beech trees within forest stand (P ˂ 0.05). Inde- In general, researches indicate that pressure of competi- pendent T test showed that mean of competition index tion is higher when neighboring trees are close and large was higher at class of 40–70 cm than class of 71–100 cm (Fraver et al. 2014).The relationships between trees are for DBH of beech target trees (Table 6). influenced by the structure of trees, because of its impact on tree’s responses (Juchheim et al. 2017). Although the relationship between litter and humus layers with CI is Discussion not significant, but the neighboring trees and target beech ones can influence on thickness of organic layer Results from this research afford perception into how (Table 4). Vockenhuber et al. (2011) declared that de- competition among individuals impacts beech tree composability of litter differs among trees which impact structure in the temperate forest. Parrotia, Carpinus, the amount of the organic layer. and Fagus as functional group of broad-leaved decidu- The impact of mixing tree species on forb functional ous trees growing next to target beech trees came in very group and slightly on graminoids can be related to close contact and the branches of the neighbors partly lighting needs within mixed beech stand (Table 4). Plant species in understory differ in light demanding and Table 4 Pearson’s correlation coefficient between competition canopy space which is related to tree layer characteris- index (CI) and some features of beech stand tics (Marozas et al. 2014). In mixed stand, the existence of various trees can create a diverse distribution of Variables Competition index (CI) resources that might make different composition of her- Forb richness r =0.443* P =0.030 baceous plants (Ampoorter et al. 2015).The analysis indicated that the structure of the oriental beech trees Graminoid richness r =0.201ns P =0.324 varied significantly between interspecific competition Herb layer diversity r =0.185ns P =0.386 (Table 5). The crown and trunk of trees can react to Humus thickness (cm) r =0.197ns P =0.367 various neighboring tree diversity and beech trees show Litter depth (cm) r =0.047ns P =0.837 high crown flexibility and potential of competition in Regeneration (n/plot) r = − 0.135ns P =0.583 capturing growing space (Juchheim et al. 2017).In this *, significant at level = 0.05; ns, non-significant study, H/D ratio varied significantly between Environ Monit Assess (2018) 190:377 Page 5 of 7 377

Fig. 1 Relationship between crown ratio and crown length (a), crown area (b), crown volume (c); and also correlation between H/D (height to diameter ratio) and DBH (d), total height (b), and crown width (c) for target beech trees

interspecific competition. The susceptibility of trees to wind injury is more in trees with higher HD ratio Table 6 Independent T test for comparing CI values in different diameter class for beech target beech trees (mean ± SE) (Juchheim et al. 2017); therefore, it can be stated that the target beech trees are exposed to wind damages Diameter class (cm) within beech stand. This research revealed strong evi- dence for variation in crown structure of beech trees in CI t df Sig. 40–70 71–100 response to the local neighborhood tree competition 3.46 24 0.002** 0.84 (0.19) 0.18 (0.03) (CI). Tree crown architecture strongly influences the ability to compete with neighboring trees (Barbeito **, significant at level = 0.01 377 Page 6 of 7 Environ Monit Assess (2018) 190:377 et al. 2014). Many works indicated that crown structure declared that competition for light acquisition made a reacts to different variables such as competition (Thorpe tough effect on the growth of small trees, but competi- et al. 2010). All target beech trees have high DBH and tion for nutrients impacts on trees with all sizes. Mean- height (Table 1) and also neighboring beech (high DBH, while, Aakala et al. (2013) stated that some parameters Table 2) and these conditions can be related to stage of including species, size, and position of a tree relative to stand development. It is possible that reaction of crowns its neighbors impact tree growth. Results of this confirm to neighbors will differ according to development of target trees in closed canopy stands and in the absence of stand, though there is a high flexibility of older beech major disturbance were influenced by neighboring tree trees to variations in canopy situations (Barbeito et al. competitive relationships in the upper story within 2014). mixed stand. The neighborhood tree competition (CI) had a posi- tive influence on crown area of target trees. The more competitive power the target tree had, the larger its DBH Conclusion (Tables 1, 2,and5) in comparison to the mean DBH of its neighbors, the more expanded was its crown. The Results from this study provide tools for understand- biotic factors including DBH and competition impact on ing role of interspecific competition and determine crown surface area (Lang et al. 2010). Crown size of how detailed information on species interactions can target beech trees is negatively related to the competition be used to inform the design of silvicultural systems index and it can be considered as a significant indicator in oriental beech stands. Target beech trees as a for evaluating tree growth in stand. Fichtner et al. (2013) broad-leaved species showed the interactions be- declared that rising competition changes the ability of tween some of their characteristics and competition trees for gaining resource by decreasing crown length index within mixed beech stand. Beech trees (Fagus and diameter. Crown area of tree is identified as a very orientalis Lipsky) mixed with other forest species subtle growth reaction to competition (von Oheimb exhibit higher DBH rates than neighboring trees and et al. 2011). Crown structure is affected by some forest this might be dependent on site conditions. Tree size stand conditions including climate, competition among variation and its interaction to interspecific compe- trees, and site quality (Sharma et al. 2016). The decreas- tition provide a greater diversity of structure and ing height of target beech trees with increasing CI can be habitats for forest plants. These findings indicate related to site condition, especially light intensity in that competition can influence on forest structure beech stands as Vallet and Perot (2016)declaredinter- in a temperate beech forest that has not experienced specific competition for light acquisition in a forest major disturbances. stand influenced on tree height growth. It is worth mentioning that the differences in the competition level by tree species can be related to the differences in shade References tolerance within forest stand. The positive correlation (Fig. 1a–c) among some characteristics of target beech Aakala, T., Fraver, S., D’Amato, A. W., & Palik, B. J. (2013). trees might be in related to its ecological character. The Influence of competition and age on tree growth in structur- crown flexibility of trees in temperate mixed deciduous ally complex old-growth forests in northern Minnesota, USA. Forest Ecology and Management, 308,128–135. forests is explained by an attribute of shade tolerance of Ampoorter, E., Baeten, L., Vanhellemont, M., Bruelheide, H., trees (Barbeito et al. 2014). Sharma et al. (2016)stated Scherer-Lorenzen, M., Baasch, A., Erfmeier, A., Hock, M., that crown dimension is related to the height and diam- & Verheyen, K. (2015). Disentangling tree species identity eter growth of tree. The H/D ratio of target beech trees and richness effects on the herb layer: first results from a German tree diversity experiment. Journal of Vegetation decreased with an increase in their BDH, total height, Science, 26(4), 742–755. and crown width (Fig.1d–f), which could be related to Antin, C., Pélissier, R., Vincent, G., & Couteron, P. (2013). Crown neighboring trees. The result indicates that competitive allometries are less responsive than stem allometry to tree interactions differ between DBH classes for beech target size and habitat variations in an Indian monsoon forest. Trees, 27(5), 1485–1495. trees (Table 6); it can be due to tree size and temporal Barbeito, I., Collet, C., & Ningre, F. (2014). Crown responses to differences in the span of competition according to neighbor density and species identity in a young mixed Fichtner et al. (2012). Coomes and Allen (2007) deciduous stand. Trees, 28(6), 1751–1765. Environ Monit Assess (2018) 190:377 Page 7 of 7 377

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