Growth and Structure Development of Semi-Natural Larch-Spruce-Fir (Larix

Forest Ecology and Management 240 (2007) 165–177 www.elsevier.com/locate/foreco

Growth and structure development of semi-natural larch-spruce-ﬁr (Larix olgensis–Picea jezoensis–Abies nephrolepis) forests in northeast China: 12-year results after thinning Xiangdong Lei a,*, Yuanchang Lu a, Changhui Peng b, Xiaopeng Zhang c, Jie Chang d, Lingxia Hong a a Institute of Forest Resource Information Techniques, Chinese Academy of Forestry, Beijing 100091, PR China b Institute of Environment Sciences, University of Quebec at Montreal (UQAM), Montreal H3C 3P8, Canada c Institute of Automation, Chinese Academy of Science, Beijing 100080, PR China d College of Life Sciences, Zhejiang University, Hangzhou 310012, PR China Received 20 February 2006; received in revised form 13 December 2006; accepted 20 December 2006

Abstract Analyzing and understanding the structure and growth dynamics of semi-natural plantations is useful for their management. Since 1987, 16 plots with 4 treatments (CT: control; LT: light thinning; MT: medium thinning; and HT: heavy thinning) by 0, 20, 30 and 40% of basal area removal, respectively, and four replications were established in semi-natural larch-spruce-fir forests in northeast China. The structure and growth dynamics of semi-natural larch-spruce-fir stands and the effects of thinning on the growth, structure and diversity were examined. A mixed model repeated measures analysis of variance (RMANOVA) was used to test the effects of treatment and time. Results showed that differences in periodic annual increment (PAI) of stand basal area and volume and the individual diameter and volume among treatments changed over time in a complex statistical interaction. Thinning, however, had a significant effect on growth at tree and stand levels 12 years after thinning while the PAI of the diameter, basal area and volume was positively correlated with thinning intensity. No significant differences were found in the total stand yield among treatments. Composition of tree species group (larch, other conifers and deciduous trees) during monitoring years did not change significantly. Moreover, no significant differences were observed in tree species and size diversity among treatments in the years following thinning. Both thinning and control plots had similar understory plant diversity after the 12 year period. Univariate point pattern analysis revealed that clumped and random distributions were dominant for tree species groups in this study. The current species composition and regeneration dynamics within these semi-natural plantations suggested a development towards mixed coniferous and broad- leaved forests. Management implications for the transformation from larch plantations towards mixed broad-leaved Korean forests with a more diverse structure, the climax vegetation in this region, were discussed. # 2006 Elsevier B.V. All rights reserved.

Keywords: Thinning; Semi-natural larch plantation; Growth; Stand structure; Stand development

1. Introduction 31.51% of the total forested area according to the Sixth National Forest Resources Inventory (Department of Forest China is currently shifting its forestry strategy from timber Resources, 2005). However, most timber plantations operate at production to ecological rehabilitation (Zhou, 2004). Forest a low management level. Their composition, moreover, is plantations play an important role in both timber production single, consisting of one tree species. Consideration must be and ecological protection since China has the most extensive given to the serious problems concerning the use of plantations and largest plantation program in the world. The total plantation including low forest productivity, soil fertility decline, area in China is estimated about 53.25 million ha occupying improper tree species composition and age group structure as well as damage from forest pests and diseases (Li and Zhou, 2000; Department of Forest Resources, 2005). These problems * Corresponding author. Tel.: +86 10 62889199; fax: +86 10 62888315. indicate that forest management is still an important issue for E-mail address: [email protected] (X. Lei). now and future in China. Thinning is the most widely employed

0378-1127/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2006.12.019 166 X. Lei et al. / Forest Ecology and Management 240 (2007) 165–177 management practice being a major tool for achieving the goal Forestry Bureau, Jilin Province, situated on the middle lower in increasing tree growth or improving tree quality and species hill region of Changbai Mountain in northeastern China. composition on a sustainable basis (Zeide, 2001, 2004). The Elevation ranges from 550 to 1100 m asl with an annual rainfall effects of thinning have long been a focus for research in how it from 600 to 700 mm. The mean annual temperature is 4 8C. affects forest growth and yield (Hibbs et al., 1989; David, 2002; Mean monthly maximum and minimum temperatures range Johnstone, 2002; Simarda et al., 2004; Ma¨kinen and Isoma¨ki, between 22 and 32 8C, respectively. Soil type is dark brown 2004a,b; Kojola et al., 2004; Juodvalkis et al., 2005), forest forest soil (Editorial Committee of Jilin Forest, 1988), and the structure (Bailey and Tappeiner, 1998; Crow et al., 2002; La¨hde original vegetation type is mixed broad-leaved Korean pine et al., 2002; Parrotta et al., 2002; Montes et al., 2005a,b) and (Pinus koraiensis) forest. Most primary forests, however, have diversity (Thomas et al., 1999; He and Barclay, 2000; Sullivana been altered to form other forest types such as spruce-fir et al., 2002; Lindh and Muir, 2004; Homyack et al., 2005). dominated mixed coniferous forests, birch-aspen mixed broad- Some controversy still exists concerning how thinning affects leaved forests and plantations consisting of larch, spruce, fir and growth, structure and diversity due to high variations in stand pine, for example, after long-term management practices and density, origin, tree species composition, site quality, stand age, disturbances. observation periods and thinning methods. Stands used in this study were originally larch forests planted As one of the most common species and an important timber in clear-cut areas with some fir, spruce and broad-leaved trees resource in China, larch is typical in cold and medium temperate remaining between 1962 and 1964. Thinning experiments were zones (Chen et al., 1997). It is also one of the most widely established by the Wangqing Forestry Bureau in 1987 when the employed plantation tree species in China. Research has been larch trees were 23–25 years old. Most stands developed into previously carried out on soil fertility (Liu et al., 1998), biomass mixed forests by that time, dominated by Changbai larch (Larix and productivity (Zhou et al., 2002), growth models (Li, 1995; olgensis Henry), spruce (Picea jezoensis var. microsperma Sun, 1999; Hu, 2003), understory plant community structure (Lindl.) Cheng et L.K. Fu) and fir (Abies nephrolepis (Trautv.) (Cun et al., 1995), thinning effects on tree growth (Yin, 1987; Maxim.). Other tree species composing the stands include Dong, 2001), diameter distribution (Dong et al., 2000) and the Korean pine (Pinus koraiensis Sieb. et Zucc.), asian white birch physical mechanic properties of wood (Chen et al., 2001) in larch (Betula platyphylla Suk.), ussuri popular (Populus ussuriensis plantations. Most research, however, was executed in pure Kom.), ribbed birch (Betula costata Trautv.), linden (Tilia forests. While in the past forest management was merely focused amurensis Rupr.), elm (Ulmus propinqua Koidz.), maple (Acer on timber production, recent management strategies emphasize mono Maxim.), ash (Fraxinus mandshurica Rupr.) and corktree that forests should be managed according to the multiple-use (Phellodendron amurense Rupr.). These forests are referred to in concept. Diverse stand structure can contribute to its multiple this study as semi-natural larch-fir-spruce forests. Originally, the uses (Malcolm et al., 2001). Stand structure characteristics are aim of the sample plots was to monitor the effects of thinning on increasingly being recognized for their theoretical and practical stand growth and compare the growth and yield between thinned importance in understanding and managing forest ecosystems and control stands. Four treatments were tested: CT, control; LT, (Franklin, 2002). Some larch plantations in northeast China were light thinning (20% of basal area removal); MT, moderate originally established by planting larch with surviving or thinning (30% of basal area removal); HT, heavy thinning (40% invading natural trees species such as spruce, fir and broad-leaved of basal area removal). Thinning method was thinning from trees. These forests were named semi-natural plantations. They below. Randomized block design was used for the four have some characteristics of natural forests and are expected to treatments and four replications establishing 16 rectangular develop potentially into mixed coniferous and deciduous forests sample plots with a maximum area of 0.25 ha and a minimum or broad-leaved Korean pine forests with complex structures and area of 0.0775 ha (Table 1). multiple benefits under right management. To date, very little is known about the structural dynamics of these semi-natural larch 2.2. Stand measurement stands. The effects of thinning on growth, structure and biodiversity in mixed larch forests have not yet been investigated The following measurements were made at each plot every 2 in northeast China. or 3 years from 1987 to 1999 after thinning events (1987, 1990, The objectives of this study are: (1) to examine the structure 1992, 1994, 1997, 1999): tree species, diameter at breast height and growth dynamics of semi-natural larch-spruce-fir stands; (dbh) and crown class of all living trees (dbh > 5.0 cm), the (2) to analyze thinning effects on growth, structure and dominant and average tree height of larch as well as elevation, diversity; (3) to apply the results to the better management of aspect, slope, soil, and other variables. At the most recent larch plantations in northeast China. inventory (1999), all trees with a dbh more than 5 cm were mapped to observe stand structure development. Understory 2. Methods and data vegetation diversity was also investigated by recording species name, number of individual species and the average height and 2.1. Study area and experimental design cover in five subplots measuring 5 m 5 m for shrub layers and 1 m 1 m for herb layers. Regeneration was counted by The study area is located at the Jingouling Experimental tree species with a diameter less than a 5 cm threshold in areas Forest Farm (130850–1308200E, 438170–438250N), Wangqing within five subplots measuring 2 m 2 m. All five subplots X. Lei et al. / Forest Ecology and Management 240 (2007) 165–177 167

Table 1 Experimental design and sample plots information at the time of establishment in 1987 Block Treatment Plot number Size (ha) Elevation (m) Slope (8) Density (stems ha1) Basal area (m2 ha1) I CT 302 0.0775 760 10 1587 26.1 LT 304 0.0975 760 10 1200 22.5 MT 303 0.13 760 10 1461 23.9 HT 301 0.0775 760 10 1277 24.7 II CT 306 0.2 780 7 2015 29.4 LT 307 0.2 780 18 1965 29.7 MT 305 0.2 780 18 1850 28.9 HT 308 0.2 780 10 1815 27.8 III CT 309 0.25 660 6 1208 21.5 LT 311 0.25 670 6 1316 25.1 MT 310 0.25 670 10 1328 25.2 HT 312 0.25 680 10 1552 26.6 IV CT 320 0.1 600 9 1660 24.1 LT 317 0.1 615 7 1720 21.3 MT 319 0.1 605 9 1420 21.4 HT 318 0.1125 610 7 1600 23.0 CT: control; LT: light thinning; MT: medium thinning; and HT: heavy thinning. were distributed in the same manner in each plot: one subplot to spatial pattern, species diversity, mixture, size variability or was located at the center of each plot while the other four were differentiation and coarse woody debris (Buongiorno et al., located near the four vertexes at each cardinal direction. Table 1 1994; Gadow and Hui, 1999; Staudhammer and LeMay, 2001; provides experimental design and sample plot information. The Ralston et al., 2004; Kint, 2005; McElhinny et al., 2005). Tree density of the plots varied from 1200 to 2015 stems ha1 with a species spatial patterns, tree species and size diversity as well as basal area from 21.3 to 29.7 m2 ha1 at the time of the study’s understory plant diversity were variables selected for this study. establishment in 1987. 2.3.2.1. Spatial pattern. The L-function (Besag, 1977) 2.3. Measurement of tree growth, stand structure and derived from Ripley’s K-function (Ripley, 1977) that linearizes diversity and stabilizes the variance of the K-function was chosen for spatial pattern analysis. Their estimates Kˆ ðdÞ and LˆðdÞ are 2.3.1. Tree growth at individual and stand levels expressed as: Since species composition was variable among plots, tree A Xn Xn species were divided into three groups: a dominate larch, Kˆ ðdÞ¼ dðd Þ; i 6¼ j (2) n2 ij another coniferous group (spruce, pine and fir) and a deciduous i¼1 j¼1 group. The periodic annual increment (PAI) values for sffiffiffiffiffiffiffiffiffiffi individual trees and stands in each plot were calculated by Kˆ ðdÞ LˆðdÞ¼ d (3) Pressler’s formula (Philip, 1994) for each measurement period p based on the values of living trees that were tagged at the time of the study’s establishment: where A is the plot area, n the number of trees on the plot, d a distance used as a radius of a circle around each tree, trees are ya yan 200 pn ¼ (1) counted within this circle, dðdijÞ an indicator function repre- ya þ yan n senting 1 if dij d and 0 if dij > d, and dij is the distance where pn is PAI, n the number of years between inventories, ya between the ith and jth trees. the measure (diameter, basal area or volume) in inventory a, Univariate spatial analysis was used to examine the spatial and yan is the measure in inventory a n. distribution pattern of all trees regardless of species within each Ingrowth and death rates during the observational period plot as well as the three species groups separately. The spatial were counted as the number of stems per hectare per year. Stand pattern can then be described as either clumping, random or yield 12 years after thinning was calculated by the sum of the regular at any distance d up to half the length of the shortest side volume in the 12th year and the volume removed. The number of rectangular plot if the L calculation is greater than, equal to of seedlings per hectare was used for regeneration analysis by or lower than the 99% confidence envelope (Dixon, 2002). tree species groups. Significance is achieved by applying Monte Carlo simulation with a 99% confidence envelope. Four-hundred and ninety-nine 2.3.2. Stand structure simulations were used for all Monte Carlo tests according to Numerous variables were used for examining stand structure Perry (2004). For edge effects, weighted edge correction development and management effects, especially those related (Goreaud and Pe´lissier, 1999) for rectangular plots was used. 168 X. Lei et al. / Forest Ecology and Management 240 (2007) 165–177

SpPack (Perry, 2004) was the software used for univariate intensity and time since thinning, were treated as fixed effects analyses. following the SAS MIXED Procedure (Moser et al., 1990; SAS Institute Inc., 2001). ANOVA with least mean squares 2.3.2.2. Tree species and size diversity. The Shannon–Wiener and Tukey comparisons were performedtotesttheeffectsof diversity index (Magurran, 2004), having been applied widely treatments on PAI for both single trees and stands, ingrowth in stand structure literature (Buongiorno et al., 1994; Lin et al., and death rates as well as stand structure diversity. Treatment 1996; Kuuluvainen et al., 1996; Staudhammer and LeMay, effects were also analyzed over time. The existence of 2001; Varga et al., 2005), was used to characterize the diversity significant differences in stand conditions, thinning removal, of tree species and diameter distributions. The formula is understory vegetation diversity and regeneration among expressed as: treatments during one sampling time was also tested using univariate ANOVA in SAS. A p-value of 0.05 or less was Xs 0 defined as statistically significant. H ¼ pi log pi (6) i¼1 3. Results where pi is the proportion of basal area in the ith species or diameter class. The width of the diameter class was 2 cm. 3.1. Stand conditions prior to and after thinning

2.3.2.3. Understory vegetation diversity. Understory vegeta- ANOVA indicated no significant difference in any stand tion diversity was measured by species richness and species characteristic among treatments prior to thinning (Table 2). The diversity. Species richness denoted the total number of species mean removal varied significantly, ranging from 5.0 to sampled for both herbs and shrubs while species diversity was 9.6 m2 ha1 in basal area, and from 32.4 to 67.6 m3 ha1 in based on the Shannon–Wiener diversity index (Magurran, stock volume (Table 2). The quadratic mean diameter (QMD) 2004). The diversity index was calculated separately for herb of LT, MT and HT treatments was 12.2, 13.5 and 14.2 cm, and shrub layers. respectively. However, no significant difference in species composition of removal among treatments was detected. The 2.4. Statistical analysis basal area removed mainly consisted of larch with a proportion of over 40%. Since several inventories were carried out at each plot, After thinning, significant differences in stand parameters growth measurements from individual plots were supposed to between control and thinning plots appeared except in QMD correlate. The data were analyzed with a mixed model and species composition (Table 2). Average stand density, basal repeated measures analysis of variance (RMANOVA) in area and volume in control plots were significantly higher than which a block was treated as a random effect, and thinning those in thinning plots.

Table 2 Stand characteristics before and after thinning and removal amount Treatment Density (stems ha1) Basal area (m2 ha1) Stock volume (m3 ha1) QMD (cm) Basal area composition (%) Larch Other coniferous group Deciduous group CT 1617(331) 25.3(3.3) 172.9(21.3) 14.2(0.7) 58.4(6.0) 27.9(10.4) 13.7(1.3) LT 1550(355) 24.6(3.7) 166.6(26.4) 14.4(1.4) 65.0(10.1) 22.6(14.7) 12.4(2.6) MT 1515(230) 24.9(3.1) 171.9(25.0) 14.5(0.7) 60.4(12.2) 26.0(8.9) 13.6(4.0) HT 1561(221) 25.5(2.1) 177.3(14.8) 14.5(0.9) 61.3(4.4) 23.2(11.6) 15.5(2.8) ANOVAa NS NS NS NS NS NS NS LT 446(132)a 5.0(0.8)a 32.4(4.8)a 12.2(1.6)a 40.8(21.6) 33.9(15.8) 25.3(6.7) MT 529(152)ab 7.3(0.8)b 50.3(7.7)b 13.5(2.0)b 54.6(16.4) 25.4(13.4) 20.0(6.0) HT 660(250)b 9.6(1.3)c 67.6(7.3)c 14.2(2.8)b 48.1(16.1) 25.8(10.4) 26.1(5.7) ANOVAb * *** *** * NS NS NS CT 1617(331)a 25.3(3.3)a 172.9(21.3)a 14.2(0.7) 58.4(6.0) 27.9(10.4) 13.7(1.3) LT 1104(266)b 19.6(3.0)b 134.2(22.1)b 15.2(1.8) 70.9(8.3) 20.0(7.4) 9.1(2.0) MT 986(177)b 17.6(2.3)bc 121.6(19.4)bc 15.1(1.0) 62.8(10.8) 26.2(8.0) 11.0(3.4) HT 901(37)b 15.9(1.1)c 109.7(10.2)c 15.0(0.5) 68.7(7.4) 21.9(11.6) 9.4(3.0) ANOVAc ** *** *** NS NS NS NS Values are means with standard error in parentheses. Different letters indicate signiﬁcant differences between treatments (LSD, t-test p < 0.05). QMD: quadratic mean diameter; CT: control; LT: light thinning; MT: medium thinning; and HT: heavy thinning. NS: not signiﬁcant; *p < 0.05, **p < 0.01, ***p < 0.001. a Before thinning. b Removal amount. c After thinning. X. Lei et al. / Forest Ecology and Management 240 (2007) 165–177 169

Fig. 1. Means of stand basal area (a) and volume (b) at measurement years and PAI of basal area (c) and volume (d) in ﬁve periods for different treatments.

3.2. Growth were increased by 34, 38, 38 and 40% for the basal area and 40, 42, 43 and 45% for the growing stock volume, respectively. 3.2.1. Diameter, basal area and volume increment at tree Both increased with thinning intensity. Similar results were and stand level found at the individual tree level. The individual diameter of The a and c graphs in Fig. 1 illustrated the effects of thinning CT, LT, MT and HT, for example, was increased by 29, 30, 33 on the mean stand basal area and volume after the 12 year and 36% and volume by 71, 86, 90 and 98%, respectively response period. Stands in different treatments had very similar (Fig. 2a and c). It was observed at ﬁve periods since thinning growth trends. During monitoring years, CT, LT, MT and HT that the PAI of the basal area and volume in thinning plots

Fig. 2. Means of individual dbh (a) and volume (b) at measurement years and PAI of dbh and volume in ﬁve periods for different treatments. 170 X. Lei et al. / Forest Ecology and Management 240 (2007) 165–177

Table 3 individual diameter and volume was significantly influenced by p-Values for test of hypothesis for treatment, time and their interaction effects treatment, time, and time treatment interaction (Table 3). on stand and tree level variables after thinning in RMANOVA There were also significant differences in the PAI of the Variable Pr > F diameter and volume between control plots and MT and HT Treatment Time Treatment time treatments (Table 4). The PAI of the diameter and volume still increased with thinning intensity. Thinning had significant Stand level PAI of basal area (%) 0.0316 0.0001 0.0436 effects on the PAI of individual diameters and volumes for all PAI of volume (%) 0.0242 0.0001 0.0314 periods (ANOVA: p < 0.05 in all cases). Ingrowth rate 0.0548 0.4296 0.6047 1 1 (stems ha year ) 3.2.2. Mortality and ingrowth Mortality rate 0.0107 0.2072 0.2447 Stand development during the years following thinning was (stems ha1 year1) Shannon tree species 0.6513 0.8760 0.9790 characterized by high mortality in the control plots. diversity index RMANOVA detected significant treatment effects on the Shannon tree size 0.5296 0.0001 0.5044 mortality rates, but failed to detect significant time and diversity index time treatment interaction effects (Table 3). Significant Tree level differences were also observed in the mortality rates between PAI of DBH 0.0083 0.0001 0.1010 control and thinning plots (Table 4). Heavy mortality rates PAI of volume 0.0145 0.0001 0.0180 occurred in larch and deciduous groups irrespective of PAI: periodical annual increment; CT: control; LT: light thinning; MT: medium treatments. MT plots had the lowest mortality volume and thinning; HT: heavy thinning. CT the largest (ANOVA: F =6.966,p =0.01).RMANOVAdid not detect any significant treatment, time and their interaction effects on the ingrowth rates. Few ingrowth trees occurred. For generally exceeded those in control plots (Fig. 1b and d), as did example, there were no larch species ingrowth trees at all the PAI of individual trees (Fig. 2b and d). In general, the PAI of within the control plots. Most ingrowth trees occurred in LT the basal area and volume at stand level and the diameter and plots in the form of spruce and fir while control plots had the volume at tree level decreased during periods following most deciduous ingrowth trees. HT plots showed the most thinning. ingrowth in the form of korean pine. Repeated measures analysis of variance (RMANOVA) for all data in different measurement years at stand level suggested 3.2.3. Total yield that time, treatment and their interaction had significant effects Significant differences were observed in stand volume on the PAI of stand basal area and volume (Table 3). The PAI of between thinning and control plots in the 1st year following the stand basal area and volume varied significantly among thinning (Table 2), but the differences ceased to exist after 12 treatments at all periods (ANOVA: p < 0.05 in all cases) except years growth (Table 5). Thinning did not significantly affect for the PAI of the basal area in the first period ( p = 0.0956). total yield (existing volume plus removal). But significant Significant differences were found between thinning and difference in mortality volume existed between CT and MT control plots for the whole period, but not between thinning plots (ANOVA: F = 6.966, p = 0.01), and CT and MT plots had plots themselves (Table 4). Moreover, the PAI of the stand basal the largest and smallest mortality volume, respectively. LT plots area and volume increased with thinning intensity. had almost the same yield as control plots. In general, the yield We also performed RMANOVA for all data during different in thinning plots was higher than that in control plots, and the measurement years at individual tree level. The PAI of total yield increased with thinning intensity.

Table 4 Least squares means of stand and tree level variables after thinning in RMANOVA Variable Treatment S.E. CT LT MT HT Stand level PAI of basal area (%) 2.040a 3.579b 3.927b 4.071b 0.459 PAI of volume (%) 2.510a 4.237b 4.543b 4.701b 0.475 Ingrowth rate (stems ha1 year1) 6.65 7.80 3.25 4.95 2.04 Mortality rate (stems ha1 year1) 28.95a 12.10b 7.9b 9.4b 4.03 Tree species diversity index 1.368 1.002 1.144 1.061 0.215 Tree size diversity index 1.906 1.915 1.912 1.791 0.068 Tree level PAI of DBH (%) 1.452a 1.932ab 2.143b 2.391b 0.159 PAI of volume (%) 3.411a 4.471ab 4.988b 5.529b 0.391 Different letters (a and b) indicate signiﬁcant differences between treatments (LSD, t-test p < 0.05). S.E.: stand error; PAI: periodical annual increment; CT: control; LT: light thinning; MT: medium thinning; and HT: heavy thinning. X. Lei et al. / Forest Ecology and Management 240 (2007) 165–177 171

Table 5 Total yield for treatments during 12 years after thinning (m3 ha1) Treatment VB Removal volume VA VF TY CT 172.9(21.3) 0(0)a 172.9(21.3)a 246.8(15.7) 246.8(15.7) LT 166.6(26.4) 32.4(4.8)a 134.2(22.1)b 214.5(4.7) 246.9(5.1) MT 171.9(25.0) 50.3(7.7)b 121.6(19.4)bc 209.9(4.7) 260.2(8.5) HT 177.3(14.8 67.6(7.3)c 109.7(10.2)c 195.8(14.6) 263.4(15.0) ANOVA NS *** ** NS NS VB: volume before thinning; VA: volume after thinning; VF: volume in the 12th year following thinning; TY: total yield during 12 years following thinning. Values are means with standard error in parentheses. Different letters (a–c) indicate signiﬁcant differences between treatments (LSD, t-test p < 0.05). CT: control; LT: light thinning; MT: medium thinning; and HT: heavy thinning; NS: not signiﬁcant; *p < 0.05, **p < 0.01, ***p < 0.001.

Fig. 3. Tree species and size diversity indices for treatments at measurement years following thinning.

3.3. Regeneration time effects on tree size diversity (Table 3). The tree species diversity index for different years after thinning was very Regeneration occurred in all plots for all tree species except similar, but the tree size diversity index increased with time larch in which seedlings were only found in one LT plot. duration after thinning (Fig. 3). Control plots had the richest Regeneration density increased orderly for Korean pine, broad- tree species diversity. All plots had almost the same tree size leaved tree species as well as for spruce and fir. However, no diversity in the 12th year after thinning with the exception of significant differences was found among treatments (ANOVA: HT plots. F = 1.240, p = 0.357 for Korean pine; F = 0.889, p = 0.487 for larch; F = 0.352, p = 0.789 for the deciduous group; and 3.4.3. Understory plant diversity F = 0.071, p = 0.974 for spruce and fir group). Vegetation within the shrub layers sampled in these stands mainly included Acer tegmentorum Maxim., Acer ukurun- 3.4. Stand structure and biodiversity duense Jrautv. et Mey., Syringa reticulata (Blume) Hara var. amurensis (Rupr.) Lonicera japonica Thunb., Syringa amar- 3.4.1. Species composition ensis Rupr. and Corylus mandshurica Maxim. Herb layers were No significant differences were found for tree species group composed primarily of Thalictrum aquilegifolium Linn. var. composition among treatments in the 12th year following sibiricum Regel et Tiling, Stellaria media (Linn.) Cyr., Oxalis thinning (ANOVA: F = 0.699, p = 0.576 for larch; F = 0.281, acetosella L., Aegopodium alpestre Ledeb, Brachybotrys p = 0.838 for other coniferous group; and F = 2.661, p = 0.112 pariformis Maxim., Deyeuxia Langsdorffii (Link.) Kunth, for the deciduous group). Paired t-test analysis on the same Maianthemum bifolium (Linn.) F.W. Schmidt and Carex treatment at post-thinning and the 12th year after thinning also calltrichos (Franch.) V. Krecz. ANOVA did not show indicated no significant differences for tree species group significant differences in species diversity for shrub and herb composition ( p > 0.05 in all cases). Therefore, tree species layers among treatments (Table 6). This concluded that they composition among treatments in the 12th year after thinning had very similar species diversity after 12 years. and at post-thinning, and the 12th year after thinning on the same treatment was very similar, suggesting that tree species 3.4.4. Spatial structure composition may be relatively stable. When point pattern analysis was applied with all stems combined, the spatial distribution was significantly random in 3.4.2. Tree species and size diversity every control plot (Fig. 4a). However, the spatial patterns of RMANOVA did not detect significant effects of treatment, thinning plots showed high variability. Eight of 12 plots time, and time treatment interaction except for significant exhibited random distribution with the exception of regularity 172 X. Lei et al. / Forest Ecology and Management 240 (2007) 165–177

Table 6 to 11 m although random at less than 3 m and over 11 m Understory plant diversity indices for treatments in the 12th year after thinning (Fig. 5f). Treatments Sp H0 Other coniferous trees within control plots exhibited either a Herb random or clumping tendency (Fig. 6a and b). Most were CT 11.2(0.8) 1.717(0.095) clumped within thinning plots (Fig. 6c) with the exception of LT 11.3(0.8) 1.628(0.111) one that exhibited a random tendency (Fig. 6d). MT 11.8(0.9) 1.745(0.233) Deciduous trees in control plots showed significant random HT 11.3(0.8) 1.785(0.076) tendencies at less than 2 or 3 m and clumping tendencies at other ANOVA NS NS scales (Fig. 7a and b), while four thinning plots showed a random Shrub tendency, other plots showed a random tendency at less than 2 m CT 4.1(0.9) 1.096(0.170) and a clumping tendency at other scales (Fig. 7c and d). LT 4.6(0.5) 1.256(0.113) MT 4.8(0.7) 1.223(0.373) 4. Discussion and conclusion HT 4.8(0.9) 1.192(0.079) ANOVA NS NS 4.1. Growth Values are means with standard error in parentheses. Sp: species richness index; H0: species diversity index; NS: no significant; CT: control; LT: light thinning; Differences in PAI at stand and tree levels among treatments MT: medium thinning; and HT: heavy thinning. changed over time in a complex statistical interaction. Significant differences, however, were detected between distribution at a distance of less than 2 m (Fig. 4b). Two were thinning and control plots for the whole study period while significantly clustered (Fig. 4c) while the other two showed the PAI of the dbh, basal area and volume was positively random distribution at a distance of less than 6 m and wider correlated with thinning intensity. Similar results were found in than 14 m and clumped at a distance from 6 to 14 m (Fig. 4d). most of the previous studies (Dong, 2001; Ma¨kinen and All larch trees within control plots had a clumping tendency Isoma¨ki, 2004c). when tree species groups were considered separately (Fig. 5a). As the study has shown, higher mortality rates in control In 12 thinning plots, two were completely random (Fig. 5b); rather than thinning plots exist. MT had the least mortality five were random less than 2 m and clumped over 2 m (Fig. 5c); volume. Larch and deciduous trees accounted for the largest two were clumped (Fig. 5d); two were regular less than 2 m and proportion of mortality rates due to their shade intolerance. random from 2 to 10 m (Fig. 5e); and one was clumped from 3 Korean pine had the least proportion of mortality rates in LT

Fig. 4. Spatial pattern analysis with all stems combined. X. Lei et al. / Forest Ecology and Management 240 (2007) 165–177 173

Fig. 5. Spatial pattern analyses for larch. since it is shade tolerant during early development years. and control plots 12 years following thinning. There were some Several studies have also revealed that heavy mortality was inconsistent results concerning thinning effects on plant associated with high stand densities in control plots (Simarda diversity. For example, Deal and Tappeiner (2002) detected et al., 2004; Zhang et al., 2005). no significant changes between uncut and partially cut stands in No significant differences were detected in total yield among tree species composition and stand structure in Sitka spruce treatments, suggesting that thinning did not significantly affect dominated forests. He and Barclay (2000) found that after 27 yields, although the yields increased with thinning intensity. years, thinning and fertilization had little effect on understory Montero et al. (2001) and Can˜ellas et al. (2004) also reported no vegetation whether in terms of species richness or vegetation significant differences in total yield between treatments; total cover in a Douglas fir plantation. However, Thomas et al. yield of stands with the heaviest thinning was slightly lower (1999) found that silvicultural thinning and fertilization can than control stands. have significant effects on understory plant diversity and community composition in a set of 21–27 year old Douglas fir 4.2. Structure plantations. Treatment effects were not a simple function of understory light levels (Thomas et al., 1999), relating also to Tree species composition, understory plant diversity and tree years after thinning, thinning methods, forest types and other size diversity showed no significant changes between thinning environmental or ecological factors. However, this current 174 X. Lei et al. / Forest Ecology and Management 240 (2007) 165–177

Fig. 6. Spatial pattern analyses for other coniferous trees. study suggests that thinning had no signiﬁcant effect on species spatial structures including competition, dispersal, gap crea- diversity 12 years after development following thinning. tion, spatial structure of the environment, disturbance history, Spatial pattern is an important characteristic of stands. There edaphic factors, and meteorological events (Watt, 1947; Moeur, are many processes and factors that contribute to small-scale 1993; Kuuluvainen et al., 1996; Schwarz et al., 2003; Davis

Fig. 7. Spatial pattern analysis for deciduous trees. X. Lei et al. / Forest Ecology and Management 240 (2007) 165–177 175 et al., 2005). Spatial structure in turn affects the vital processes broad-leaved tree species, including some rare tree species such of growth, birth and death. Point pattern analysis of all species as Korean pine and ash. The current species composition and combined revealed random distribution in all control plots. individual occurrence of spontaneous tree regeneration in these Random distribution of trees could either be due to random semi-natural plantations showed a development towards natural events, including mortality and seed dispersal, or the mixed coniferous and broad-leaved forests, and even mixed simultaneous action of competition and small-scale environ- broad-leaved Korean forests. In another study on comparison of mental heterogeneity (Wolf, 2005). Thinning plots showed plant species diversity of four forest types in Northeastern more variable patterns from random to clumped distribution China (Lei et al., 2003), we found that these larch plantations and similar patterns within the same blocks. Moreover, no had similar species composition with mixed coniferous and consistent trend in thinning intensity was found. Compared to broad-leaved forest through DCA ordination. However, other thinning plots, the two clumped plots mentioned above recruitment was found to be poor although a lot of regeneration had higher mortality rates for larger trees which may create seedlings of different species occurred. The study did not detect gaps for clumped distribution. Gap dynamics and favorable significant changes in species composition during monitoring microsites were important factors for clumped distribution years suggesting that the current composition is relatively (Pe´lissier, 1998). Also we found that all thinning plots in the stable, being a long-term and dynamic process. Additional same block had almost the same distribution pattern for blocks management practices (e.g., thinning and selective logging) can 3 and 4, which may result from environmental heterogeneity. be helpful to accelerate regeneration. Kint et al. (2003) found that tree species were either randomly positioned or showed a tendency towards regularity as a result 4.4. Implications for forest management of larch of the long-term randomization effect of thinning in Scot pine plantations: is it possible to develop into broad-leaved forests. Montes et al. (2005a) also reported clustered or random Korean pine forests? distribution in thinned coppice forests. Although larch was planted, it showed a spatial pattern far China has developed new forestry strategies focusing on removed from regular distribution after nearly 35 years of ecological rehabilitation. Chinese society is increasingly development. Clumped distribution for larch trees in control demanding that forests should be managed for multiple plots may be related to their high mortality rates and may benefits. However, large area plantations employing a low consequently result in gaps. Regularity was only found at less management status is an ongoing issue. A greater diversity of than 2 m in thinning plots. Random and clumped distribution forest structure is one way of satisfying these requirements may be explained by the interaction between thinning and (Malcolm et al., 2001). How can China manage these forests environmental heterogeneity. and transform them into more diverse structures at the same Other coniferous and deciduous trees in both thinned and time? Thinning is one important strategy in increasing stand control plots showed either a random or clumping tendency. structural diversity. Moreover, maintaining a mixture of Similar results were found in the same study area, revealing that different species is important for structural diversity (Busing random or clumped distribution existed for tree species such as and Garman, 2002). Tree species composition in this study Korean pine, spruce, fir, birch, aspen, linden, maple and ash (Li, provided a reference model and therefore may provide a species 1986; Sun and Zhao, 1997; Hou and Han, 1997). compositional model for the transformation from the current Several aspects of this study differed from previous pure larch plantation. Thinning can be performed to maximize treatments studies for pure plantations (Yin, 1987; Dong tree size and height diversity in order to promote understory et al., 2000; Dong, 2001). For example, plantations used in this development and to allow shade tolerant species to be recruited study incorporated some remaining natural mature trees. Also, into the overstory. the original distribution of these trees was not known. Mixed broad-leaved Korean pine forests, as the central and Moreover, some tree species invaded the plots before the primary vegetation in northeastern China (Editorial Committee study’s establishment. Additionally, several tree species were of Jilin Forest, 1988), have an important role for stability and grouped into one species group since they were few in number species richness for natural forest rehabilitation, having been and not dominant. Due to this, the spatial pattern may be more appointed as the target for secondary forest development in this complex and uncertain. region. Planting conifers and protecting broad-leaved trees as an appropriate intervention measure to accelerate succession of 4.3. Future stand development secondary forest development has been widely implemented in the northeastern forest regions, with some success (Chen et al., An essential component of future stand development is the 1993). Recently, Chen et al. (2003) used a simulation model to establishment of the next generation of trees. As the study has study how to accelerate the succession for restoration of mixed shown, larch cannot be regenerated under a canopy and broad-leaved Korean pine forests. No specific measures, subsequently develop into larch forests successfully since it is a however, have been enacted for larch plantations. Is it possible heavy light demanding tree species (Editorial Committee of for larch plantations to develop into mixed broad-leaved Jilin Forest, 1988). It will consequently be replaced by shade Korean pine forests? tolerant and middle shade tolerant tree species. In this study, For larch plantations, management must create stand condi- regeneration mainly occurred in both other coniferous and tions that support regeneration for target-oriented development 176 X. Lei et al. / Forest Ecology and Management 240 (2007) 165–177 or transformation. The transformation process, that is, to Chen, D.K., Zhou, X.F., Zhu, N., Wang, Y.H., 1993. Structure, Dynamics and introduce or protect other conifers and native broad-leaved tree Function of Natural Secondary Forests. Press of Northeast Forestry Uni- versity, Harbin (Chinese). species, can be performed by natural regeneration or human- Chen, G.S., Guo, M.H., Huang, Z., 2001. The effect of thinning density on wood induced natural regeneration. Currently, Korean pine cutting physical mechanics properties of larch plantation. J. Northeast Forestry has been prohibited in some areas of northeast China, but Univ. 29 (3), 13–16 (in Chinese with English abstract). appropriate management practice should be applied during Chen, L.Z., Chen, Q.L., Liu, W.H., 1997. Forest Diversity and Its Geographical different stand development stages according to the biological Distribution in China. Science press, Beijing, p. 235 (in Chinese). Chen, X.W., Li, B.L., Lin, Z.S., 2003. The acceleration of succession for the characteristics of tree species. Korea pine, for example, requires restoration of the mixed-broadleaved Korean pine forests in northeast shade in its initial stage and sunlight for rapid growth in late China. For. Ecol. Manage. 177 (1–3), 503–514. stage. Gaps appear to be important for seedling establishment Coates, K.D., 2002. Tree recruitment in gaps of various size, clearcuts and (Coates, 2002). They provide an adequate sunlight environment undisturbed mixed forest of interior British Columbia, Canada. For. Ecol. required for these stands since most broad-leaved tree species Manage. 155, 387–398. Crow, T.R., Buckley, D.S., Nauertz, E.A., Zasada, J.C., 2002. Effects of used in the study are shade intolerant or middle shade management on the composition and structure of Northern hardwood forests intolerant. These species can be accompanying species with in upper Michigan. For. Sci. 48 (1), 129–145. Korean pine. Zang et al. (1999) and Yu et al. (2000) found that Cun, G.F., Yang, W.H., Xiao, J., Han, J.Y., Cao, S.H., Liu, L.S., 1995. regeneration density was higher in gaps than in canopies in Community structure dynamics of larix plantation. For. Sci. Technol. 20 mixed broad-leaved Korean pine forests. Therefore, for those (4), 4–6 (in Chinese with English abstract). David, P., 2002. Twenty-year results of precommercial thinning in a balsam fir Korean pine and native broad-leaved trees in the plantations, stand. For. Ecol. Manage. 168, 177–186. thinning or selective logging can be performed in order to Davis, M.A., Curran, C., Tietmeyer, A., Miller, A., 2005. Dynamic tree accelerate regeneration and growth. Subsequently, semi-natural aggregation patterns in a species-poor temperate woodland disturbed by larix plantations are expected to develop into mixed broad- fire. J. Veg. Sci. 16, 167–174. leaved Korean forests. Moreover, further studies are still needed Deal, R.L., Tappeiner, J.C., 2002. The effects of partial cutting on stand structure and growth of western Hemlock-Sitka Spruce stands in Southeast for transformation possibilities of pure larch plantations Alaska. For. Ecol. Manage. 159, 173–186. especially long-term observations from semi-natural planta- Department of Forest Resource, State Forestry Administration of China, tions. 2005. The Sixth National Forest Resource Inventory and the Status of Forest Resource. Green China, January 9–12 (in Chinese with English abstract). Acknowledgements Dixon, P.M., 2002. Ripley’s K function. Encyclopedia Environ. 3, 1796–1803. Dong, X.B., 2001. Impacts of cutting intensity on the growth of Larch forest. J. Northeast Forestry Univ. 29 (1), 43–47 (in Chinese with English abstract). The authors would like to thank numerous people involved Dong, X.B., Li, Y.X., Jiang, L.C., 2000. The effects of thinning on stand in establishing and maintaining the permanent plots over the structure for Larch plantation. J. Northeast Forestry Univ. 28 (1), 16–18 (in past years: Mrs. Donglan Li, Mr. Zelu Zhang, Xiaoguang Chen, Chinese with English abstract). and Baosheng Chen from Wangqing Forestry Bureau, Jilin Editorial Committee of Jilin Forest, 1988. Jilin Forest. China Forestry Press, Province as well as Dr. Jishan Du, Dr. Huiru Zhang, Dr. Hong Beijing, p. 462 (in Chinese). Franklin, J.F., 2002. 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