Soil heating during burning of forest slash piles Matt Busse, Ken - PowerPoint PPT Presentation

Soil heating during burning of forest slash piles Matt Busse, Ken Hubbert, Steve Overby, Carol Shestak U.S. Department of Agriculture Pacific Southwest Research Station Science that makes a difference

What conditions might lead to detrimental changes in soils?

Do pile burns act as short- term “hotspots” for nutrient release?

Soil heating Post-burn soil quality Tahoe Basin inventory

Step 1: Assess the range of pile conditions in the Tahoe Basin  75 inventory plots  Pile size  Fuel composition  Pile density (#/acre)  Ground cover  Thinning intensity

Inventory of current conditions 300 Number of piles 250 Pile size • Wide variety of pile sizes and densities 200 150 100 50 • Average diameter = 10 ft 0 1-2 2-3 3-4 4-5 5-6 6-7 >7 Diameter (m) • Large piles not uncommon 25 Number of plots Pile density • Everything from small slash to large wood piles 20 15 10 5 0 0 0 0 0 0 0 0 5 9 3 7 1 5 9 > - 1 1 2 2 2 0 - - - - - 5 0 0 0 0 0 9 3 7 1 5 1 1 2 2 Piles ha -1

How much ground is covered by piles within a unit? 3% cover 10% cover 20% cover 30% cover 25 Number of plots 20 • Average cover = 11% 15 10 • One-fifth of the plots exceeded 15% cover 5 0 5 0 5 0 5 0 5 • Ground cover = 3.75 + 0.223(stump BA) - 1 1 2 2 3 3 0 - - - - - - 5 0 5 0 5 0 1 1 2 2 3 Percent of land surface

Soil Quality Study Intensive plots (29 piles)  Soil heating  Soil and water chemistry  Water repellency  Soil physical properties  Riparian and upland soils

Each pile was measured for • pile size • fuel mass by size class

Measure heat pulse at 0, 5, 10, 30, 50 cm soil depths beneath pile center

What’s the big deal about soil heating? Mineralogy changes Soil C and N loss Loss of hydrophobic compounds Release of inorganic N and P Bacteria & Fungi death Root and seed mortality 0 100 200 300 400 500 600 700 800 900 Temperature ( o C)

So how hot does the soil get?

Pile type I • Dominated by bolewood • Upper North Canyon Soil temperature profile at North Canyon, NV (20 ft diam. pile) 700 600 Temperature ( o C) 500 0cm 400 5cm 300 10cm 200 30cm 100 0 0 6 12 18 24 30 36 42 48 54 60 66 72 78 Time (hours )

Pile type 2 • Mix of all fuel sizes • Bliss SP; Sugar Pine SP Soil temperature profile at Sugar Pine SP (20-ft diam. pile) 700 600 Temperture ( o C) 500 0cm 400 300 5cm 200 10cm 100 30cm 0 0 6 12 18 24 30 36 42 48 54 60 66 72 78 Time (hours)

Pile type 3 • Small diameter slash • Old Mill Soil temperature profile at Old Mill (10-ft diam. pile) 700 600 Temperature ( o C) 500 0cm 400 5cm 300 10cm 200 30cm 100 0 0 6 12 18 24 30 36 42 48 Time (hours)

Pile type 1 (wood) Pile type 2 Pile type 3 600 Temperature ( o C) 5 cm soil depth 500 400 300 200 100 0 6 8 10 12 14 16 18 20 22 24 Pile diameter (ft) 600 Temperature ( o C) 10 cm soil depth 500 400 300 200 100 0 6 8 10 12 14 16 18 20 22 24 Pile diameter (ft) 600 30 cm soil depth 500 Temperature ( o C) 400 300 200 100 0 6 8 10 12 14 16 18 20 22 24 Pile Diameter (ft)

How much spatial variability in heating is found beneath piles?

How much spatial variability in heating is found beneath piles? Pile center 400 Pile Pile Temperature ( o C) edge edge 300 200 0.6 m 0.6 m outside outside 100 0 0 30 60 0 30 60 0 30 60 0 30 60 0 30 60 0 30 60 0 30 60 0 30 60 0 30 60 Time after ignition (hours)

What about mopping up? 500 Soil depth Termperature ( o C) 400 0 cm 5 cm 300 10 cm Mop up 200 100 0 0 10 20 30 40 50 60 Time after ignition (hours)

Soil Heating Summary • Moderate to severe heating was found in the surface 10 cm beneath piles • Fuel composition was the driving force • Pile size was important only for wood-dominated piles • Spatial variability was high - about one-half of the pile area reaches maximum heating

Post-burn soil quality

Soil effects Nitrate Ammonium Total C, N, P N mineralization Nitrification Nutrients pH Fungi, bacteria Microbial biomass Respiration PLFA community structure Water infiltration Water repellency Water quality Bulk density NO3, PO4 Plant recovery Surface and subsurface Downslope Repeated sampling

Post-burn soil quality (0-5 cm) Soil C (24 months) 8 Pile burn 6 Control % C 4 2 0 Old Mill Bliss Sugar Pine Spooner1 Spooner2 Fire Severity

Post-burn soil quality (0-5 cm) Soil N (24 months) 0.4 Pile burn 0.3 Control % N 0.2 0.1 0.0 Old Mill Bliss Sugar Pine Spooner1 Spooner2 Fire Severity

Post-burn soil quality (0-5 cm) Fungal hyphae (24 months) 800 Pile burn Control 600 m/g 400 200 0 Old Mill Bliss Sugar Pine Spooner1 Spooner2 Fire Severity

Post-burn soil quality (0-5 cm) Soil solution NO 3 (24 months) 4 Pile burn 3 Control mg/kg 2 1 0 Old Mill Bliss Sugar Pine Spooner1 Spooner2 Fire Severity

Post-burn soil quality (0-5 cm) Multivariate analyses 0.4 Pile burn 0.4 0.3 Control Pile burn % N 0.3 Control 0.2 % N 0.2 0.4 0.1 Pile burn 0.3 Control 0.1 0.0 Old Mill Bliss Sugar Pine Spooner1 Spooner2 % N 0.2 0.0 Old Mill Bliss Sugar Pine Spooner1 Spooner2 Fire Severity 0.4 0.1 Fire Severity Pile burn 0.3 Control 0.0 Old Mill Bliss Sugar Pine Spooner1 Spooner2 % N 0.2 Fire Severity 0.4 0.1 Pile burn 0.4 0.3 Control 0.0 Old Mill Bliss Sugar Pine Spooner1 Spooner2 Pile burn % N 0.3 Control 0.2 0.4 Fire Severity Pile burn % N 0.2 0.3 Control 0.1 % N 0.2 0.1 0.0 Old Mill Bliss Sugar Pine Spooner1 Spooner2 0.0 0.1 Old Mill Bliss Sugar Pine Spooner1 Spooner2 Fire Severity 0.0 Old Mill Bliss Sugar Pine Spooner1 Spooner2 Fire Severity Fire Severity 0.4 Pile burn 0.3 Control % N 0.2 0.4 0.1 Pile burn 0.3 Control 0.0 Old Mill Bliss Sugar Pine Spooner1 Spooner2 % N 0.2 0.4 0.4 Fire Severity Pile burn Pile burn 0.1 0.3 Control 0.3 Control % N % N 0.0 0.2 0.2 Old Mill Bliss Sugar Pine Spooner1 Spooner2 0.1 0.1 Fire Severity 0.0 0.0 Old Mill Bliss Sugar Pine Spooner1 Spooner2 Old Mill Bliss Sugar Pine Spooner1 Spooner2 0.4 Pile burn Fire Severity Fire Severity 0.3 Control % N 0.2 0.4 Pile burn 0.1 0.3 Control 0.0 % N 0.2 Old Mill Bliss Sugar Pine Spooner1 Spooner2 0.1 Fire Severity 0.4 0.4 0.0 Pile burn Pile burn 0.4 Old Mill Bliss Sugar Pine Spooner1 Spooner2 0.3 Control 0.3 Control Pile burn % N % N 0.3 Control Fire Severity 0.2 0.2 % N 0.2 0.1 0.1 0.1 0.0 0.0 Old Mill Bliss Sugar Pine Spooner1 Spooner2 Old Mill Bliss Sugar Pine Spooner1 Spooner2 0.4 0.0 Old Mill Bliss Sugar Pine Spooner1 Spooner2 Fire Severity Pile burn Fire Severity 0.3 Control Fire Severity % N 0.4 0.2 Pile burn 0.3 Control 0.1 % N 0.2 0.0 Old Mill Bliss Sugar Pine Spooner1 Spooner2 0.1 Fire Severity 0.0 Old Mill Bliss Sugar Pine Spooner1 Spooner2 Fire Severity 0.4 0.4 Pile burn Pile burn 0.3 Control 0.3 Control % N % N 0.2 0.2 0.4 0.1 0.1 Pile burn 0.3 Control 0.0 0.0 Old Mill Bliss Sugar Pine Spooner1 Spooner2 Old Mill Bliss Sugar Pine Spooner1 Spooner2 % N 0.2 0.4 Pile burn Fire Severity Fire Severity 0.3 Control 0.1 % N 0.2 0.0 Old Mill Bliss Sugar Pine Spooner1 Spooner2 0.1 Fire Severity 0.0 Old Mill Bliss Sugar Pine Spooner1 Spooner2 Fire Severity 0.4 Pile burn 0.3 Control % N 0.2 0.1 0.0 Old Mill Bliss Sugar Pine Spooner1 Spooner2 Fire Severity

Post-burn soil quality (0-5 cm) Percent of unburned control Soil effects Nitrate 515% Nitrification 190% Ammonium 90% N mineralization 97% Total C 92% Total N 98% Total P 114% pH 103% Fungi hyphae 42% Bacteria biomass 35% Microbial biomass (SIR) 87% Respiration 109% PLFA community structure Water infiltration 20% Water repellency 200% Bulk density 107%

Burning of hand piles will not result in extreme or extensive soil heating except when: • piles are dominated by large wood • piles occupy a high percentage of the ground surface Expect short-term changes in certain soil properties. Are they a problem? U.S. Department of Agriculture Pacific Southwest Research Station Science that makes a difference