Concept and application of uneven-aged silviculture in China: A case study of larch plantations in Northeast China 9 th IUFRO: Uneven-aged Silviculture 2014, Birmensdorf ZH, Switzerland Zhu JJ, Yan QL, Yu LZ State Key Laboratory of Forest and Soil Ecology, Qingyuan Experimental Station of Forest Ecology, Institute of Applied Ecology, Chinese Academy of Sciences (CAS), China June

Two stages of China forest management since 1949 Forest management for timber harvest (before 1998) Characterized by excessive cutting, and ignoring the ecological functions of forests Caused problems such as depletion of forest resources, soil erosion and desertification. Especially, flood (Yangtze River and Nenjiang River in 1998), Sustainable forest management (after 1998) ★ Six large scale plantation and rehabilitation projects ★ Strict regulations on forest resources management ★ National program: motivations mechanism to conserve forest resources ( Li, 2014 )  Uneven-aged silviculture as one of the most conducive measures in improving sustainable forest management has been paid a widespread attention recently 2 Concept of uneven-aged silviculture in China

Background Purpose Methods and Results Summary Acknowledgement Outline of Presentation 3 Application of uneven-aged silviculture in Northeast China ——A case study of larch plantations

General information of forests in China Background 8 th (2009–2013) National Forest Inventory Data (State Forestry Administration, 2014) Total forest area: 208 million ha Forest coverage: ca. 22% ca. 1/3 in Northeast China Plantation forests: 69 million ha (1/3 of national forest) 4

Playing important roles in conserving water resource & timber production (providing 40% of timber for the country) Background Forests in Northeast China: Secondary forests (SF) Heavy timber harvest in the past century  70% of them were mixed broadleaved secondary forests  could not provide timber as before 5

Background A large area of secondary forests had been replaced by larch (Larix spp.) plantations in order to meet increasing timber demand since 1950’s Larch plantations: amount to 2 million ha, around 55% of the planted forests in Northeast China Forming mosaic plantation/secondary forest landscapes (Mason and Zhu, 2014) Secondary ForestLarch plantation Mosaic landscapes Forests in Northeast China: Larch plantations (LP) 6

Background Compared with the adjacent secondary forests, larch plantations induced decrease of water conservation capacity and runoff water acidification  Water-holding capacity in larch plantations decreased by 20%  Runoff water pH 6.3 in secondary forests 7 (Xu et al., 2012)

Background Compared with the adjacent secondary forests, larch plantations induced soil fertility decline  Soil organic matter (SOM) of 40-year larch plantation decreased by 33.5% at 0-5 cm soil layer; by 42.6% at 5-15 cm soil layer 8 (Yang et al., 2010) Major reason caused the problems: mono-species composition of larch plantations  Soil fertility decline, water conservation capacity decrease and acidification

Purposes Try to change species composition by promoting the regeneration of broadleaved species  to convert the larch plantations into uneven-aged mixed forests  For larch plantations surrounded by secondary forests: Find out a suitable distribution pattern of larch plantations planted within the secondary forest ecosystems; for improving regeneration potentials and the possibility inducing LP into uneven-aged mixed forests Determine the effects of thinning trials on natural regeneration of broadleaved species in larch plantations  For larch plantations not surrounded by secondary forests: Test the feasibility of introducing broadleaved species into the thinned larch plantations by artificial assistance 9

Precipitation: mm Mean T: 4.7 ℃ Max. T: 36.5 ℃ Min. T: ℃ Frost-free P: 130 days Growing season: late Apr-late Sep Experimental forests: 1350 ha, composed of mixed broadleaved secondary forests and larch plantations; common and typical in Northeast Study site Qingyuan Experimental Station of Forest Ecology, CAS Shenyang Shenyang 10

Experiment forests  Secondary forest  Mosaic patterns  Larch plantation Mixed broadleaved Secondary Forests Larch plantation Major forest types in Qingyuan Station Larch plantation surrounded by secondary forest Larch plantation Secondar y forest 11 (Not surrounded by SF, out of the station)

Larch plantations surrounded by secondary forests —two distribution patterns of larch plantations within secondary forests  The Contour Type (CT): SF and LP locating at the same slope position/aspect side by side  The Up-Down Type (UDT): LP locating at the down slope of adjacent SF in the same aspect Contour Pattern Secondary forest Larch plantation Sample belt Sample point Up-Down Pattern Sample belt Sample point Secondary forest Larch plantation  Survey plots: 4-paired stands 12 Methods— Effects of two typical distribution patterns of LP on seed, seedling and sapling banks

Transects and quadrats setting Contour Type (CT) Up-Down Type (UDT)  3 transects, each separated by 10m  11 sampling points, at intervals of 2, 4, 8, 16 and 32 m (1 m 2 )  132 sampling quadrats (1 m 2 ) 13 Methods— Effects of two typical distribution patterns of LP on seed, seedling and sapling banks

 Litter cover and depth, vegetation cover, measured at more than nine random points in each sample plot  Canopy openness, estimated in each month of growing season at the sample plots 14 Methods— Effects of two typical distribution patterns of LP on seed, seedling and sapling banks

Results— Effects of two typical distribution patterns of LP on seed, seedling and sapling banks Seed density for all tree species in soil SFLPSF LP The Contour Type stands Boundary  varied as a quadratic curve from SF to LP, and peaked at the boundary of SF/LP The Up-Down Type stands  increased linearly from SF to LP; More suitable for seed invasion Number of seeds m -2 Positions Number of seeds m -2 Positions 15

Seed density for specific tree species in soil-- Fraxinus rhynchophylla SF LP SFLP The Contour Type stands  declined logarithmically from SF to LP, and seeds only appeared at 4m in LP The Up-Down Type stands  increased as a quadratic curve from SF to LP Positions Number of seeds m -2 Positions Number of seeds m Results— Effects of two typical distribution patterns of LP on seed, seedling and sapling banks Boundary

Seed density for specific tree species in soil-- Acer mono The Contour Type stands  no significant changes from SF to LP The Up-Down Type stands  increased as a quadratic curve from SF to LP SF LP SF LP Number of seeds m -2 Positions 17 Results— Effects of two typical distribution patterns of LP on seed, seedling and sapling banks Boundary

Seedling/sapling density for all species in UDT stands SF Boundary LP Number of seedlings m -2 Positions SF Boundary LP Number of saplings m -2 Positions SF Boundary LP Number of seedlings m -2 Positions SF Boundary LP Number of saplings m -2 Positions  Both seedlings and saplings of broadleaved species established in the larch plantation  formed uneven aged larch-broadleaved forests naturally 18 Results— Effects of two typical distribution patterns of LP on seed, seedling and sapling banks

Relationships between seed/seedling/sapling densities and canopy openness in Up-Down Type stands  Canopy openness is the key factor in affecting regeneration of broadleaved species in larch plantations 19 Results— Effects of two typical distribution patterns of LP on seed, seedling and sapling banks

From the view of improving regeneration potential and inducing larch plantations into the larch- broadleaved forests, the pattern of Up (SF)-and- Down (LP) may be more feasible for seed invasion and seedling or sapling establishment Problem: How to promote the regeneration of broadleaved species in larch plantations for Contour Type stands? Thinning, the most important measure, has been applied in improving the regeneration… we examined the effects of thinning on the regeneration of broadleaved species in the larch plantations 20 Results— Effects of two typical distribution patterns of LP on seed, seedling and sapling banks

Thinning intensity Stem density (trees ha -1 ) Basal area (m 2 ha -1 ) Canopy openness (%) Number of plots 30%1620/ /28.1/23.5Plots A1-A2 50%1920/ /25.9/34.0Plots A3-A5 Regime A: Larch plantation was planted in 1965, thinned (10, 20, 30, & 50%) in 2004 with random thinning patterns Methods— Effects of thinning on forming uneven aged larch-broadleaved forests 21 Larch plantations surrounded by secondary forests —two thinned stands of larch plantations (data: before/after thinning) Regime A (2004 thinned larch stand) : to test the effect of recent thinning on emergence and survival of broadleaved species. Species number and seedling density of all regenerated broadleaved species were investigated soon after thinning in 2004 & 2005

Methods— Effects of thinning on forming uneven aged larch-broadleaved forests 22 Thinning intensity Stem density (trees ha -1 ) Basal area (m 2 ha -1 ) Canopy openness (%) Number of plots 40%1513/ /38.8/14.2Plots B1-B2 60%1546/ /35.0/16.8Plots B3-B4 Regime B: Larch plantation was planted in 1960, thinned in 1994 with random thinning patterns (20, 30, 40 & 60%) Regime B (1994 thinned larch stand) : to confirm the effect of thinning on establishment of broadleaved species after 10 years of thinning. Seedlings (5-50 cm) and saplings ( cm) of all broadleaved species were recorded in The sapling height and base diameter were measured in 2005

Broadleaved species regeneration in 2004 thinned stands: species number and seedling density  Number of broadleaved species: 15 species, with abundant species of F. rhynchophylla, A. mono, Phellodendron amurense, Cornus controversa  Seedling density of broadleaved species: 3-11 seedlings m -2  Seedling density in 2005 > in 2004  More seedlings in 50% than in 30% 23 (surveyed in 2004 and 2005) Methods— Effects of thinning on forming uneven aged larch-broadleaved forests

Regeneration establishment in 1994 thinned stands  Number of regenerated broadleaved species: 10 with abundant species of A. mono, F. rhynchophylla, F. mandshurica and Quercus mongolica etc.  Density of regenerated broadleaved species: 1-8 seedlings per m 2, 2-7 saplings per 10 m 2  Seedling density: 40% > 60%, Sapling density : 60% > 40% Seedlings: 5–50 cm in height Saplings: 50–500 cm in height Results— Effects of thinning on forming uneven aged larch-broadleaved forests 24 (surveyed in 2005)

25 Sapling growth in 1994 thinned stands (surveyed in 2005) Results— Effects of thinning on forming uneven aged larch-broadleaved forests  Basal diameter and height of saplings in 60% were higher than those in 40%, but they both established.  The regeneration of broadleaved species was successful in 40% and 60% thinning treatments after 11 years.

For larch plantations surrounded by secondary forests, it may be feasible to develop uneven-aged larch-broadleaved forests through thinning; the thinning intensity should be large enough to satisfy the survival and growth of seedlings or saplings For larch plantations not surrounded by secondary forests, whether can we promote the regeneration of broadleaved species by artificial assistance? 26 Results— Effects of thinning on forming uneven aged larch-broadleaved forests

Methods— Seed germination & seedling growth of introduced broadleaved species in LP stands 27 Larch plantations not surrounded by secondary forests —nine stands in a thinned larch plantation (10.3 ha, 20yrs) in 2011 Thinning intensity Stem density (trees ha -1 ) 0 (CK) %675 50%450 25±1% 11±1% 21±1% Canopy openness 100%0 Dominant broadleaved species: Fraxinus mandshurica & Juglans mandshurica

 Treatments: Fraxinus & Juglans seeds were collected and directly seeded at five positions by simulating the states of seeds after falling off in thinned stands in autumn (2011) Methods— Seed germination & seedling growth of introduced broadleaved species in LP stands 28 Seed germination in thinned larch plantations not surrounded by secondary forests (Oct 2011-Oct 2013) pressed half- way into the soil ( ST ) under 1cm soil with 4cm litter cover ( LS1 ) on top of the litter cover ( LT ) under 1cm soil without litter cover ( S1 ) beneath the litter of 4 cm depth ( LS )  Germination, seedling emergence and survival were monitored after seeding (50 seeds×3 replications)

Results— Seed germination & seedling growth of introduced broadleaved species in LP stands Seed germination—J. mandshurica ST: pressed half-way into soil; LT: on top of litter; LS: beneath litter; S1: under soil without litter cover; LS1: under soil with litter coverage  Highest: 25% & 50% thinned stands; S1/LS1: 19.2±2.2%/ 21.3±2.2%  Lowest: 100% & CK; LT: 5.4±2.2% 50% 100% CK 25% 29 Seed germination rate (%)

Seed germination—F. mandshurica ST: pressed half-way into soil; LT: on top of litter; LS: beneath litter; S1: under soil without litter cover; LS1: under soil with litter coverage Seed germination rate (%)  Highest: 50% thinned stands, next CK, 25%; S1/LS1: 34.7±2.0%/ 37.7±2.3%  Lowest: 100% (17.7±2.5%), ST/LT: 20.3±2.3%/ 22.0±2.4% Results— Seed germination & seedling growth of introduced broadleaved species in LP stands 30 CK 25% 50% 100%

Seedling emergence and survival  J. mandshurica: lower survival rates in general, less than 4%; Control plot exhibited the lowest survival; The highest: 25%/S1 10.7%, 50%/LS1: 10.3%  F. mandshurica: 14% survival in average; The highest: 50%/S1 23% Results— Seed germination & seedling growth of introduced broadleaved species in LP stands 31 J. mandshurica F. mandshurica

For larch plantations not surrounded by secondary forests, 25% (675 stems per hectare) and 50% thinning (450 stems per hectare), and under soil seeding are necessary for the germination and emergence of Juglans and Fraxinus. But, the survival of the seedlings after germination was very poor. Problem: Is it possible to plant the seedlings of broadleaved species in the thinned larch plantations to promote the regeneration of broadleaved species? Results— Seed germination & seedling growth of introduced broadleaved species in LP stands 32

 Treatments: 1-year & 2-year FM & JM seedlings were planted randomly in each stand in spring (50 seedlings×3 replications) Methods— Seed germination & seedling growth of introduced broadleaved species in LP stands 33 Planting seedlings in thinned larch plantations not surrounded by secondary forests (May-Oct 2013)  Seedling survival was monitored at interval of one month from May to Oct.  Seedling harvest was conducted in autumn. Height, collar diameter, root length, biomass, leaf δ 13 C, non-structural carbon content were measured 1-yr-old 2-yr-old 0.5cm J. Mandshurica F. mandshurica

Seedling survival Results— Seed germination & seedling growth of introduced broadleaved species in LP stands 34  Lowest: at 100% thinned stands (33% for F. mandshurica; 58% for J. mandshurica)  Highest: CK, 25% & 50% thinning stands (45% for F. mandshurica, 86% for J. mandshurica)

 It may be caused by the water stress because of lower soil water contents and higher light intensities in the clear- cutting plot  δ13C of leaves: carbon isotope was the highest in seedling leaves of clear-cutting plot, which confirmed the deduction Water use efficiency δ 13 C (‰) 1-yr- old 2-yr- old Results— Seed germination & seedling growth of introduced broadleaved species in LP stands 35 Soil water content in 0-20 cm Light regime at 100 cm

Seedling growth Results— Seed germination & seedling growth of introduced broadleaved species in LP stands 36  Height/diameter: no significant differences between thinning intensities for both aged seedlings (short observed period)  Growth trend: diameter growth of both species showed the increasing trend with the increase of thinning intensities

 For the larch plantations not surrounded by secondary forests, artificial assistance (thinning, and planting seedlings of dominant broadleaved species) has potential to improve the regeneration of broadleaved species in the larch plantations.  Further observations are being carried out… Results— Seed germination & seedling growth of introduced broadleaved species in LP stands 37

Summary  For larch plantations (LP) surrounded by secondary forests (SF), the natural regeneration of broadleaved species have established with Up secondary forest and Down larch plantation pattern. Therefore, it is feasible for the Up-Down pattern larch plantations to develop the uneven-aged larch- broadleaved forests  For LP surrounded by SF, when they located side by side, it is likely to form an uneven-aged larch-broadleaved forest by thinning with appropriate canopy openness  For LP not surrounded by SF, artificial assistance, including thinning larch plantations and planting broadleaved species seedlings, has potential to promote the regeneration of broadleaved species in the larch plantations. But, the further observations are needed 38

Thank you for your attention! Qingyuan Experimental Station of Forest Ecology, CAS Questions & Comments Acknowledgement National Basic Research Program of China (973) (2012CB416900) & National Natural Science Foundation of China ( ) provided the financial support The member in Research Group of Ecology & Management of Secondary Forests, IAE, CAS gave the helps in field observations and valuable suggestions

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