The effect of mechanical site preparation on water and soil

protection in radiata pine plantations in the Basque Country

Nahia Gartzia Bengoetxea

Inazio Martínez de Arano

Ander Gonzalez Arias

Goods and servicesprovided by forest in relation to soil function

• Maintain or restore productivity

• Protect other ecosystem compartments- Carbon sequestration- water quality/quantity

Sediment outputs

• Preserve soil ecosystem integrity

Starting Point

Forest play an important role in the protective functions of soil and water quality

• Forest cover disappears• Understory and litter removals• Soil disturbance (logging, traffic, site preparation)

Main difference between (commercial) Plantations & other Forests is the Inter-Rotation period.

Starting Point

time gap between harvest and the crown closure of the next rotation (Mead 1990).

Pinus radiata

High slopes increase disturbance risk

Starting Point

Mechanized operations have increased Since 1980s Are common on slopes under 40%

Physical damage linked to machinery use in harvest, logging and soil preparation operations is one of the key factors of forest soil sustainability (Constantini et al. 1997 Aust. For. 60/4 )

Objective

To describe the effect of commercial site preparation on productivity, soil properties and sediment exports.

To evaluate sustainability and the production of goods and services in relation to soil & water conservation

TRIAL DESIGN

4 site preparation industrial treatmentsManual ScalpingRippingDiscontinuous ripping

3 repetitions

3.3 ha30% slope

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Soil depth before site preparation

Soil depth

pH M.O (%)

N (%)

C/N P (mg kg-1)

Ca meq/100

Mg meq/100

K (mg kg-1)

A 5.68 3.26 0.18 10.34 1.07 8.00 0.69 92.33

Bw1 5.79 1.42 0.12 6.67 0.04 6.92 0.72 51.33

Bw2 6.75 0.80 0.11 4.21 0.09 14.65 0.74 39.00

1

Soil chemical properties before site preparation

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(i) Manual (M): Clearing harvest residues and existing vegetation by hand; planting holes were also manually made

(ii) Scalping (S): Harvest residues and existing vegetation were cleared with the front blade of a bulldozer and planting holes were done by hand

(iii) Ripping (R): Harvest residues and vegetation was cleared as in the S treatment and afterwards a ripper that dug a 40-50 cm deep trench in the line of maximum slope was used to facilitate plantation that was also made by hand

Site preparations:

Manual Scalping

Ripping

before site preparation

after site preparation

Soil fertility:

OM, total N, C/N, pH, Ca, Mg, K, CEC, P-Olsen

Soil Organic Matter dynamics:

In situ seasonal N mineralization over 1 year

Tree growth evolution:

All trees were measured twice per year from 2002 to 2005

Soil Erosion:

At all Plots, 1.4 m long, 40 cm deep and 40 cm wide ditch was established to monitor soil loss and sediments were recovered once per year. years yr 1-3

Soil Physics:

Resistance to penetration, bulk density, saturated hydraulic conductivity, water holding capacity at -33 KPa and -1500 Kpa yr2-tr4

Water run-off:

water volume (ml) was determined over 1 year in1 m2 run-off plots yr-1

1300 mm

500 mm

15 mm

RESULTS

No difference in height between manual and rippingScalping clearly behind in first 4 years

20% loss in productivity?

* differences in diameter are non significant

Productivity

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abri-03 sept-03

febr-04 juli-04 dici-04 mayo-05

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Manual Scalping Ripping Dis. Ripping

• 36% of soil carbon loss (1st year)• C/N shows top soil removal

Soil Carbon

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33,5

44,5

55,5

C org(%)4

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C/N

subsolado

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FORSEE Project

Changes in aggregate size distribution mayProduce long term changes in soil carbondynamics

40 yr old radiata stand Adjacent mechanized 1 yr old stand

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P-Olsen(mg/kg)

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Box PlotSplit By: treatment

Soil Chemistry

Olsen P ppmmuy bajo

bajo

adecuado

Nitrógeno Fósforo

Calcio

Cobre

magnesio

Potasio Azufre ing.

n=187 rodalesDiagnóstico según Will (1985)

• P is the most liming element in radiata pine plantations

Soil Chemistry

Manual Scalping rippingmean cv mean cv mean cv

N total 0,2 21% 0,15 26% 0,121 30%C/N 15,4 17% 12,4 23% 10,7 28%P-Olsen(mg/kg) 2,2 82% 1,1 82% 0,7 171%Ca (mg/kg) 1129,5 47% 2354,7 61% 1224,2 99%Mg (mg/kg) 103,5 24% 70,4 63% 66 68%K (mg/kg) 80,0 63% 50,3 58% 40,1 45%

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For all treatments, nutrient contents are not outside of normal radiata pine soils in the Basque Country

In situ N mineralization. 1st year after soil preparation

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Interaction Line Plot for N-NH4+(mg/kg)Effect: season * treatment

* Values are means with standard errors in parentheses. Within each column, significantly different treatment means based on one-way analysis of variance and Bonferroni/Dunn test are indicated by different lowercase letter

Bulk density (Mg m-3)

Soil Penetration Resistance

(MPa)

Moisture capacity

-0.033 MPa (%)

Moisture capacity -1.5 MPa

(%)

Saturated hydraulic conductivity

(cm h-1)

Manual 1.25 (0.0)a* 1.63 (0.48)a 36.30 (0.82)a 18.41 (3.08)a 3.79 (0.14)a

Scalping 1.50 (0.0)b 3.73 (0.89)b 32.83 (0.37)b 15.93 (0.79)a 0.46 (0.17)b

Ripping 1.49 (0.81)b 3.23 (0.51)b 31.02 (0.48)c 15.64 (0.60)a 0.98 (0.36)b

1

Soil Physical Properties yr 1

• 20% increase in Bulk density• x 2.5 increase in soil penetration resistance (10 cm)• Reduction to 26%-12% in Hydraulic conductivity• 12%-15% loss in water holding capacity

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• Soil moisture at root depth (yr 1) is afected• ripping treatment maintains more moisture in summer

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Runoff during year 1Water collected after every significant rain event

• x 3 increase in runoff on bladed• x 2 increase in runoff in ripped treatment

Soil Erosion yr 1-3

* Soil loss in kg/ha at constant weight

Mean erosion

Tons yr-1 ha-1

Management

induced

manual 0.018

scalping 1.105 X 60

ripping 1.642 X 89

Autumn 2002 Spring 2003 Autumn 2003 Autumn 2004Manual 26* 0 0 11Scalping 389 1031 631 162Ripping 423 1273 1136 457Disc. Ripping 369 723 2355 701

soil strenght first 30 cm

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Behekoaerdikoagoikoa

• 12%-26% increase in soil strength

Soil Strength yr 4

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Conclusions

• Mechanized site preparation has produced a significativeRemoval of topsoil, organic matter and nutrients

• Soil compactation and deterioration of hydraulic propertiesare limiting growth in the scalping treatment

• Ripping has alleviated compactation and improvedwater availability in the dry season.

• Deterioration of soil physical properties is severe andShows no recovery in the sort term (4 years).

• Sustained productivity cannot be the only criteria for Forest Soil sustainability

Two treatments show similar productivity butthey differ in:

+ x 80 sediment exports- x 2 in hydraulic conductivity- 35% in carbon stock- 15% in Water holding capacity- 20% in bulk density

• Genetically improved material and proper fertilizationCould mask observed differences in subsequent rotations

• Relevant in the long term?• Relevant at the land scape?

One treatment minimizes soil disturbance, produces very lowSediment exports, maintains carbon stocks with no penalty in productivity.

The good news!

Also it must be considered that there soil treatment is no homegeneous.

Finally,

Plantation Forestry may provide good and services in relationto soil, carbon and water conservation, but it may not.

Management at the interotation period is critical in this respect