JRuuska

Slide1: 

Effect of retained trees on growth and structure of young Scots pine stands Juha Ruuska, Sauli Valkonen and Jouni Siipilehto Finnish Forest Research Institute, Vantaa, Finland

Green tree retention: 

Maintain specific ecological processes (habitats) Create structurally complex stands Maintain aesthetic values Promote regeneration Objectives Green tree retention An integral part of contemporary forestry in Europe

Slide3: 

Poorly stocked gaps around retained trees (poor sites in N. Finland) Loss of harvested volume Logging damage, higher logging costs Poor stability in solitary distributions Problems

Hypotheses: 

Hypotheses In the vicinity of Retained Trees (RT), Seedling stand density is lower Seedling height and diameter growth is slower Influence on diameter growth is greater than on height growth, and seedlings are slimmer (height-diameter ratio) Seedlings have smaller and less branches and An aggregated RT distribution is less harmful than a dispersed distribution

Study stands: 

Study stands 9 stands in Southern Finland Most Scots pine upland sites covered Seedling stand dominant height of 2-7 m Scots pines retained for 8-18 years Variable RT densities (32 - 117 ha-1) Variable but mostly scattered spatial distributions No significant tree removals or mortality A sample of planted or naturally generated Scots pine seedling stands with RT

Sampling: 

Sampling 8 seedling sample plots per RT sample tree Plots systematically at 1, 3, 6 and 10 m distance from RT Seedlings measured for h, dbh, coordinates One sample seedling per plot per species selected among main crop seedlings (h, dbh, cr, cw, h growth, d growth, branch diameters etc.) One additional sample seedling per species to represent non-main crop seedlings All RT mapped, measured for dbh, h 10 sample RT per stand measured for trunk and crown variables, t, dbh growth

Approach: 

Approach Growth models For pine seedlings, RT Individual tree, spatially explicit Models for branching Max branch diameter and branch cross sectional area of 3 whorls; for pine only Simulation Seedling diameter and height growth Branching variables Subject to site, density of the seedling stand, number and diameter of RT, and RT spatial distribution

Overstory influence: 

Overstory influence Light interception is not the critical factor Low interception rate with pine (15 % with 50 RT ha-1) Root competition is Water, nutrients Greatest on poor sandy soils Extent Roots up to >10 m Greatest near RT base Great variation in shape Root density and distance from a retained Scots pine tree (Kalela 1954)

Description of tree competition: 

Description of tree competition A spatial competition index Incl. RT and seedlings Ecological field theory: resource availability (Wu et al. 1985) Index = f(diameter, distance) Max value = 1 (with max RT d in data and zero distance) Competition effect of one tree by diameter and distance

Results1. RT effect on seedling stand density: 

Results 1. RT effect on seedling stand density Seedling stands were dense 3,700-37,000 Scots pine seedlings ha-1 Virtually no RT influence on pine density Clearly less birch near RT Greater RT effect in Northern Finland (Niemistö et al.1993)

2. Seedling height growth : 

2. Seedling height growth Cumulative growth = height Clearly smaller pine seedlings near RT Smaller effect than in Northern Finland (Niemistö et al.1993) Relative height of pine seedlings and RT distance and diameter

Slide12: 

Cumulative growth = diameter RT effect negligible compared to that of stand density Equal RT influence on height and diameter growth Tree form not influenced by RT 3. Seedling diameter growth Diameter of 5 m high pine seedlings, RT distance and diameter, and seedling stand density

4. Maximum branch diameter: 

4. Maximum branch diameter Diameter of the thickest branch of a pine seedling Slightly smaller near RT for given seedling height Effect was minor compared to that of Site index Competition from other seedlings Influence of RT diameter and distance, site (H100), and seedling stand density on the maximum branch diameter of a 5 m high pin seedling

5. Total branching: 

5. Total branching Sum cross-sectional area of branches in 3 whorls Clearly less near RT More pronounced than on maximum branch diameter Site index and competition from other seedlings also had a strong effect Influence of RT diameter and distance, site (H100), and seedling stand density on the total branch Cross-sectional area of 3 whorls of a 5 m high pine seedling

Slide15: 

With retention Without

6. Spatial distribution of RT: 

6. Spatial distribution of RT Simulated alternatives 16 to 48 RT ha-1 Average RT dbh 25 cm and height 21 m 15-year simulation period Random, regular and clustered RT distribution Results RT spatial patterns had only a marginal effect on growth and branching of pine seedlings 48 RT ha-1 reduced average seedling height 15%, diameter 11-16% and maximum branch diameter 9-10% compared to no retention

Conclusions (I): 

Conclusions (I) RT do not reduce seedling stand density in S Finland as much as in N Finland Can help control birch on problem sites Influence on diameter growth is not greater than on height growth, and height-diameter ratio is not affected much Seedlings have smaller and less branches, but the maximum branch diameter is not reduced much Reduction in branching is small compared to that achieved by higher density, site-species match An aggregated RT distribution is only little less harmful than a dispersed distribution

Conclusions (II): 

Conclusions (II) In that sense, the current practice with 5-10 trees ha-1seems not to have a great effect on wood production Growth effects are small No unstocked patches in the south Not effective in quality improvement It is a small improvement that groups are now placed near stand edges, or on special uncut sites Retention is practiced for ecological and aesthetical purposes. It is not mandated by law but is strongly suggested for example during a certification process.