The effect of mechanical site preparation on water and soil protection in radiata pine plantations in the Basque Country Nahia Gartzia Bengoetxea Inazio Mart ínez de Arano Ander Gonzalez Arias
Goods and services provided 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 treatments Manual Scalping Ripping Discontinuous ripping 3 repetitions 3.3 ha 30% slope
Soil chemical properties before site preparation
<ul><li>Manual (M): Clearing harvest residues and existing vegetation by hand; planting holes were also manually made </li></ul><ul><li>Scalping (S): Harvest residues and existing vegetation were cleared with the front blade of a bulldozer and planting holes were done by hand </li></ul><ul><li>(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 </li></ul>Site preparations:
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 m 2 run-off plots yr-1
No difference in height between manual and ripping Scalping clearly behind in first 4 years 20% loss in productivity? * differences in diameter are non significant Productivity
• 36% of soil carbon loss (1st year) • C/N shows top soil removal Soil Carbon 4 6 8 10 12 14 16 18 20 22 C/N subsolado roza al aire manual FORSEE Project Changes in aggregate size distribution may Produce long term changes in soil carbon dynamics 40 yr old radiata stand Adjacent mechanized 1 yr old stand
Soil Chemistry Olsen P ppm • P is the most liming element in radiata pine plantations
Soil Chemistry a b c a b c a b c a b a a b b a b b 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
* 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 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
• Soil moisture at root depth (yr 1) is afected • ripping treatment maintains more moisture in summer a a b b ab b b a
Runoff during year 1 Water 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 ripping scalping manual X 89 1.642 X 60 1.105 0.018 Management induced Mean erosion Tons yr -1 ha -1
• 12%-26% increase in soil strength Soil Strength yr 4 a b
• Mechanized site preparation has produced a significative Removal of topsoil, organic matter and nutrients • Soil compactation and deterioration of hydraulic properties are limiting growth in the scalping treatment • Ripping has alleviated compactation and improved water availability in the dry season. • Deterioration of soil physical properties is severe and Shows no recovery in the sort term (4 years).
• Sustained productivity cannot be the only criteria for Forest Soil sustainability Two treatments show similar productivity but they 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 fertilization Could mask observed differences in subsequent rotations • Relevant in the long term? • Relevant at the land scape?
One treatment minimizes soil disturbance, produces very low Sediment 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 relation to soil, carbon and water conservation, but it may not. Management at the interotation period is critical in this respect