Restore Soil to Restore Sustainable Mixedwood Forests on Industrial Sites

Transcription

1 Restore Soil to Restore Sustainable Mixedwood Forests on Industrial Sites D David H. McNabb ForestSoil Science Ltd. Edmonton, Alberta

2 Wide Range of Industrial Activities

3 Why Restore Soil?

4 Sustainable Soils: An Evolving Concept Natural capital, ecosystem services, and soil change: Why soil science must embrace an ecosystems approach (Robinson et al Vadose Zone Journal) Finite resource with an almost insatiable demand Dynamic changes are being quantified: acidification, carbon changes, drainage class (Startsev and McNabb Can. J. Soil Sci. 89:45-56) Soil profile is now the Vadoze Zone aerated soil above the permanent water table

5 Sustainable Soils / Sustainable Ecosystems Can Soil Reclamation Restore Sustainable Mixedwoods? Soil is not an elastic material Severity depends on type of traffic and soil strength (wetness) Ecological consequences of physical changes are complex?

6 Forest Soils are the Platform for Sustainable Forests Forest productivity Climate, topography, soil properties Most productive soils are probably the most resistant and resilient to natural disturbances Most important soil property Quantity and quality of soil (Coile 1952) Deep, medium-textured soils for eastern oaks (Carmean 1972) Central BC, dominant soil property determining white spruce productivity is drainage class (Wang 1994) Alberta Ecosite Classification soil 1-2 m deep, w/o restrictive layer Deep soils in NE Alberta have 30 to 60% of soil/forest floor nitrogen and organic matter below 20cm. Restrictive layers, natural and anthropogenic, commonly reduce the depth of root penetration (Stone and Kalisz 1991)

7 How Deep Is Deep Soil in the Mixedwoods? Effective Rooting Depth 80+ % of roots are found in top 20 cm of soil Roots that we can see When do we look Few roots are needed to extract water Mycorrhizae assist in water uptake Temporary water tables require roots to regenerate A more practical answer: How deep do soils dry? White spruce windthrow northeast of Peace River, Alberta

8 Machine Impacts on Soil Relatively Low Impact Skidding Machines Effects of skidding traffic on soils physical properties, persistence, and effect on tree growth in western-alberta sites - wide tracked skidding vehicles

9 Machine Impacts on Soil - 2 Alberta study: Summary of Cutblock Compaction Significant compaction when soil is wetter than field capacity for wide-tired skidders Most compaction occurs in 3 cycles Changes in porosity limited to large pores - aeration Infiltration, and hydraulic conductivity significantly reduced Reduced soil aeration changed drainage class in 3-4 years Rutting was not addressed McNabb et al. 6 papers

10 Machine Impacts on Soil - 3 Where do skidding equipment with high floatation skidders fit on a Compaction Curve? Soil Density Increasing Maximum Density Undisturbed Soil Optimum Water Content Soil Moisture Increasing Field capacity at -10 kpa Field Capacity

11 Machine Impacts on Soil 3a Where do skidding equipment with high floatation skidders fit on a Compaction Curve? Soil Density Increasing Maximum Density Undisturbed Soil Optimum Water Content Soil Moisture Increasing Field capacity at -10 kpa Field Capacity NOTE: Skidders today are about 25% heavier and fewer have wide tires a different curve applies

12 Temporary Summer Logging Roads Roads are compacted to maximum density by truck traffic. (McNabb For. Ecol. & Mgnt. 66: ) Machine Impacts on Soil - 4 Study of soil water retention in undisturbed samples of a road and adjacent soil (McNabb Proc. Symp. XX IUFRO World Congress p )

13 Machine Impacts on Soil - 5 Truck Traffic Also Alters Pore Size Distribution: 60+ cm Pore sizes DECREASE Aeration Available Water Porosity Holding Capacity (Macropores) Field (Mesopores) Permanent (Micropores) Capacity) Wilting Point Unavailable Water Interpretation As soil density increases: Macroporosity decreases Which reduces soil aeration and the hydrologic function of the soil Mesoporosity decreases Which reduces available water storage capacity of the soil

14 Bulk Density, Mg/m3 Machine Impacts on Soil -7 Soil Density in Relation to Compaction Curve During Construction and Reclamation Standard Proctor Compaction Test Max. Density = 1.64 Opt. Moisture = Soil Water Content, kg/kg Soil Density = (Soil water, kg/kg) R 2 = 0.90, F = 0.000

15 Machine Impacts on Soil -8 Trafficking of soil wetter than optimum for compaction destroys soil structure, which can create a massive, structureless soil. Massive soils may not be significantly compacted (increase in density) but the hydrologic function of the soil profile is severely impacted.

16 Soil Density Increasing Ecological Consequences of Soil Impacts Maximum Density Undisturbed Soil Optimum Water Content Soil Moisture Increasing Compacted and Massive Soil High soil density results in a loss of macro and water holding pore space in drier soil Wetter soil, soil structure is destroyed with loss of larger pores Common denominator is impaired hydrologic function - limits infiltration of water into the soil - limits the vertical and horizontal movement of water in soil - reduces the ability of roots to access water - increases periodic and seasonal root mortality

17 Impaired Hydrologic Function Massive soil from trafficking wet soil Temporary watertable over a massive subsoil

18 Natural Recovery is Ineffective in Subsoil Freeze/process is mostly a surface phenomenon cm and most effective in medium textured soils Ice formation heaves the surface soil but it returns to same position on thawing Most of the change in soil volume and permeability occurs in first 1-3 cycles (soil engineering literature) Early wagon roads across the prairies of Alberta still have a significant increase in penetration resistance below 15 cm after yrs. Compacted subsoil in early wagon road southwest of Lethbridge, Alberta

19 Summary of Ecological Consequences of Trafficking Forest soils are frequently wet Higher soil wetness limits compaction but damages soil structure Compacted soil and/or massive soil have an impaired hydrologic function the common denominator Thin traffic pans can impair hydrologic function as well Poor soil aeration and/or soil drought is the common biological outcome Natural processes are unlikely to restore hydrologic function in the subsoil

20 Restoring Forest Soils Restoring soil capable of supporting sustainable forest ecosystems Practices have to restore hydrologic function Retain forest floor and topsoil Rapid revegetation for soil occupancy Build site nitrogen capital

21 Restoring Forest Soils - 2 There is a Critical Depth That Rippers and Tinges are Effective - Raper Appl. Engrg Agricul. 21:

22 Restoring Forest Soils - 3 Non-Conventional Tillage of Summer Haul Road

23 Restoring Forest Soils - 4 Why Does Rough Tillage Work? Because it maximizes the effectiveness of freeze/ thaw process in several ways: Increases depth and rate of frost penetration After 1 year Allows lateral expansion of soil during freezing Increases the melting of snow in early fall and late spring - Increases soil wetness - Increases early soil freezing

24 Restoring Forest Soils - 5 Non-Conventional Tillage Trial Restoring Soil Productivity Rough tillage made freezethaw process more effective After 1 year Subsoil density initially less than undisturbed soil Natural leveling of the surface occurs over time (foreground) Topsoil and organic debris returned without compaction (background) After 2 years Elevated planting sites are warmer and better drained

25 Restoring Forest Soils - 6 Non-Conventional Tillage Trial 10-Year-Old Planted Lodgepole Pine Trees averaged 4.5 m in height and 6 cm in DBH 9 year-old pine Context: Some of the largest 10-yr old pine in Alberta Trees were 15 to 20% larger than in cutblock Mortality was half of the cutblock control and stable Site Index (@50 yrs) = 25 + m Trees were well rooted Uniform stand (survival was 90+%) No evidence of nutrient deficiencies

26 Restoring Forest Soils - 7 Topsoil: Important for Forest Productivity but Critical for Supporting Forest Biodiversity - BC Research indicates homogenization of soil layers is detrimental (Krzic et al Can. J. Soil Sci. 89:25-34.) Bare soil at 12 years w/o topsoil Understory on topsoil at 12 yrs

27 Advances in Deep Soil Tillage Practices RipPlows since 2005

28 Effective Deep Tillage Practices - Plow through the topsoil - Deep tillage is required, minimum of 70 cm and deeper is preferred - Leave soil as rough and porous as possible - Maximize potential for freeze/thaw process to restructure soil - Last step don t traffic soil after plowing Kakwa Wellsite ConocoPhillips

29 Kakwa Wellsite 4 Years After Plowing Depth,cm Plowed Control P.Sign. Soil Density, Mg/m Water, g/g Volumetric Water, cm3/cm Aeration Porosity, %

30 Deep Plowing Increases Total Soil Porosity RipPlows increase soil elevation about 15 cm. About 30% of elevation retained after 4 years. Logepole pine height and diameter is significant greater after 4 years.

31 New Practices for Forest Roads

32 White Spruce on Temporary Forest Roads 4 yr old spruce on heavily used winter road with little topsoil and competition. Start of 4 th year spruce on temporary road plowed with topsoil in place

33 Poplar Planted on Temporary Road Plowed road with 3 yr rooted sticks (left) and 15 cm sticks (center) Unplowed road with poor topsoil recovery

34 Effectively Restored Soil = Sustainable Forest Cover Original plow and pullback road planted to lodgepole pine after 18 years. Untreated road in left foreground. Left photo: tree on the right is 9.5 m tall and 14.5 cm dbh.

35 Conclusions Acknowledgements - Mixedwoods use and require a larger volume of soil than commonly assumed - Impaired hydrologic function of soil is the common impact, is generally deep, and does not recover - Effective deep tillage practices are effective and sustainable - Effective deep tillage improves soil quality for all plants - Retention of topsoil is important for maintaining soil quality and supporting plant diversity - Restoring the quantity and quality of soil on trafficked soil is the foundation of sustainable mixedwoods - Alberta Environmental Centre/ARC - Alberta Forest Service for first tillage trial - Weyerhaeuser for original road reclamation trials: Weyerhaeuser, Canfor, Hinton Forest Products, Sundance Forest Industries,Sunpine Forest Industry, Alberta Newsprint Company - 6 companies funding the skidder soil compaction study - Alberta Forestry Research Institute for wellsite reclamation research - Weyerhaeuser - ConocoPhillips - Alberta Pacific for new road reclamation practices