Post-fire Forest Residue Mulch
Portugal - acolchoado, aplicação de restos vegetais
left: Forest residue mulch being scattered in a recently burnt area.
right: Detail of a forest residue mulch composed by eucalypt chopped bark mulch.


Forest residue mulch is spread immediately after a wildfire in order to prevent soil erosion and reduce overland flow.

In two areas of eucalypt plantations affected by wildfires in central Portugal in 2007 and 2010, the research team of the University of Aveiro set up two experiments in order to test the effect of forest residue mulching as a soil erosion mitigation technique. Forest residues such as chopped eucalypt bark mulch was spread over a group of erosion plots, and was compared to an untreated group of plots. The mulching was applied at ratios of 8.7 and 10.8 Mg ha-1 provided an initial ground cover of 70 to 80%, and was found to reduce post-fire runoff by 40-50% and soil erosion by 85-90%, respectively.
The increase in ground cover will decrease post-fire soil erosion by reducing raindrop impact over the ashes and bare soil, and decrease the runoff amount by increasing water surface storage, decreasing runoff velocity, and increase infiltration. Ideally, post-fire mulching must be carried out immediately after the fire, in order to prevent that the first autumn rainfall events fall over the bare and unprotected burnt soils. It is intended for places in which burnt severity was moderate to high and where there are important values at risk, such as water reservoirs, populations, industries, human and wild life.
The chopped bark mulch was obtained at a depot 20 km from the burnt area, where eucalypt logs are debarked and then transported to a paper pulp factory. The bark is chopped into fibers and are typically transported to a biomass energy plant. We used these 10–15 cm wide 2–5 cm long bark fibers as the source for our mulching experiment. The chopped bark mulch decays very slowly (around 20% less ground cover per year) which was very useful in cases of low re-growth of natural vegetation.
The eucalypt trees in the region are typically planted as monocultures for paper pulp production, and harvested every 7-14 years. The landscape reflects a long history of intense land management, with a mosaic of (semi-)natural and man-made agricultural and afforested lands. Since the 1980´s, however, wildfires have increased dramatically in frequency and extent, aided by a general warming and drying trend but driven primarily by socio-economic changes.
Location: Portugal/Beira Litoral
Region: Sever do vouga/ Pessegueiro do Vouga, Ermida
Technology area: 1.0E-5 km2
Conservation measure: agronomic
Stage of intervention: prevention of land degradation, mitigation / reduction of land degradation
Origin: Developed through experiments / research, recent (<10 years ago)
Land use type:
Forests / woodlands: Plantations, afforestations
Climate: subhumid, temperate
WOCAT database reference: T_POR003en
Related approach: not applicable ()
Compiled by: Sergio Prats Alegre Prats, Universidad de Aveiro
Date: 2013-04-25
Contact person: Jan Jacob Keizer /Jacob, Assisstant Researcher CESAM –Centro de Estudos do Ambiente e do Mar, Universidade de Aveiro. Phone: + 351 234 370200 ext. 22612. e-mail: jjkeizer@ua.pt.

                


Classification
Land use problems:
- Increased runoff and soil erosion, resulting in a decrease of on-site fertility and derived off-site effects such as loss of water quality, reservoirs water volume storage, higher risk of flooding and human beings damage. (expert's point of view)
- Loss of wood resources and productivity. (land user's point of view)


Land useClimateDegradationConservation measure
Land use Subhumid
Plantations, afforestations
plantation forestry
subhumid
Soil erosion by water: loss of topsoil / surface erosion, Water degradation: change in quantity of surface water, decline of surface water quality
Agronomic: Vegetation/soil cover
Stage of interventionOriginLevel of technical knowledge
   Prevention
   Mitigation / Reduction
   Rehabilitation
   Land users initiative
   Experiments / Research: recent (<10 years ago)
   Externally introduced
   Agricultural advisor
   Land user
Main causes of land degradation:
Direct causes - Human induced: crop management (annual, perennial, tree/shrub), deforestation / removal of natural vegetation (incl. forest fires), disturbance of water cycle (infiltration / runoff)
Direct causes - Natural: Heavy / extreme rainfall (intensity/amounts), other natural causes, Sediment deposition can decrease the storage volume of reservoirs.
Main technical functions:
- control of raindrop splash
- control of dispersed runoff: retain / trap
- control of concentrated runoff: retain / trap
- control of concentrated runoff: impede / retard
- control of concentrated runoff: drain / divert
- improvement of ground cover
- improvement of water quality, buffering / filtering water
- sediment retention / trapping, sediment harvesting
Secondary technical functions:
- control of dispersed runoff: impede / retard
- increase of infiltration
- increase / maintain water stored in soil

Environment
Natural Environment
Average annual rainfall (mm)Altitude (m a.s.l.)    LandformSlope (%)
> 4000 mm
3000-4000 mm
2000-3000 mm
1500-2000 mm
1000-1500 mm
750-1000 mm
500-750 mm
250-500 mm
< 250 mm

> 4000   
3000-4000   
2500-3000   
2000-2500   
1500-2000   
1000-1500   
500-1000   
100-500   
<100   

    plateau / plains
    ridges
    mountain slopes
    hill slopes
    footslopes
    valley floors

flat
gentle
moderate
rolling
hilly
steep
very steep

Soil depth (cm)

0-20
20-50
50-80
80-120
>120

Soil texture: medium (loam)
Soil fertility: high
Topsoil organic matter: high (>3%)
Soil drainage/infiltration: medium
Ground water table: 5 - 50 m
Availability of surface water: good
Water quality: good drinking water
Biodiversity: medium
Tolerant of climatic extremes: temperature increase, seasonal rainfall increase, seasonal rainfall decrease, heavy rainfall events (intensities and amount), wind storms / dust storms, droughts / dry spells
Sensitive to climatic extremes: floods

Human Environment
Forests / woodlands per household (ha)

<0.5
0.5-1
1-2
2-5
5-15
15-50
50-100
100-500
500-1,000
1,000-10,000
>10,000
Land user: employee (company, government), Small scale land users, common / average land users, men and women
Population density: 50-100 persons/km2
Annual population growth: negative
Land ownership: communal / village
Relative level of wealth: average, which represents 50% of the land users;

Importance of off-farm income: less than 10% of all income:
Access to service and infrastructure: low: employment (eg off-farm), market, energy; moderate: health, education, technical assistance, roads & transport, drinking water and sanitation, financial services
Market orientation: commercial / market
Purpose of forest / woodland use: timber


blob_id=3101Technical drawing

Forest residue mulch is spread as homogeneous as possible over steep areas (steeper than 15º) burnt at high fire severity (represented in green and 1). Other areas which are flat (2) and burnt at low severity or only partially burnt (3) must be avoided. ()

Implementation activities, inputs and costs
Establishment activitiesEstablishment inputs and costs per ha
- Manpower
- Transportation (small truck for carrying persons and material)
- Eucalypt chopped bark mulch
- Others
InputsCosts (US$)% met by land user
Labour 192.00 100%
Equipment  
  - machine use 51.20 100%
Agricultural  
  - forest residue mulch 307.60 100%
Other  
  -  64.10 100%
TOTAL 614.90 100.00%

Maintenance/recurrent activitiesMaintenance/recurrent inputs and costs per ha per year
-
InputsCosts (US$)% met by land user
Labour 0.00 0%
Equipment  
  - machine use 0.00 0%
TOTAL 0.00 NaN%

Remarks:
Accessibility and steepness will raise the costs, but selecting forest residues with lower densities as well as applying them in horizontal strips along the slope can reduce the application rates and the costs. For large and inaccessible areas some researchers indicated that helicopters can reduce the costs.
The prices were determined in winter 2012 for central Portugal. It is intended that mulch is applied only once, and thus maintenance is not needed. In other regions other forest residues can have a higher availability. Straw, needles, deciduous leaves or chopped shrubs are lighter compared to eucalypt chopped bark, slash stems or wood chips, and thus, can be easier to apply and transport. However, the lighter the material, the easier it can be blown away in windy areas.

Assessment
Impacts of the Technology
Production and socio-economic benefitsProduction and socio-economic disadvantages
   increased irrigation water availability quality
   reduced demand for irrigation water
   increased expenses on agricultural inputs
Socio-cultural benefitsSocio-cultural disadvantages
   improved conservation / erosion knowledge
   conflict mitigation
Ecological benefitsEcological disadvantages
   improved soil cover
   reduced soil loss
   increased water quality
   reduced surface runoff
   increased soil moisture
   reduced evaporation
   recharge of groundwater table / aquifer
   reduced hazard towards adverse events
   increased soil organic matter / below ground C
   increased beneficial species
Off-site benefitsOff-site disadvantages
   reduced downstream siltation
   reduced groundwater river pollution
   improved buffering / filtering capacity
   reduced wind transported sediments
   reduced damage on neighbours fields
   reduced damage on public / private infrastructure
   increased water availability
   reduced downstream flooding
Contribution to human well-being / livelihoods
   Public awareness of the technology is very limited. It is necessary to show it to landowners and stakeholders and increase dissemination.

Benefits /costs according to land user
Benefits compared with costsshort-term:long-term:
Establishmentpositiveneutral / balanced
Maintenance / recurrentslightly positiveslightly positive

Acceptance / adoption:
0% of land user families (0 families; 0% of area) have implemented the technology with external material support. The technology has been tested by scientific researchers and it is very effective, but not broadly implemented.
0% of land user families (0 families; 0% of area) have implemented the technology voluntary. The technology has been tested by scientific researchers researchers and it is very effective, but not broadly implemented.
There is no trend towards (growing) spontaneous adoption of the technology.

Concluding statements

Strengths and how to sustain/improveWeaknesses and how to overcome
It is a technology very easy to apply, with low failure possibilities and a strong soil erosion control Some researchers found better performance by grinding the mulch and selecting only the longest fibres.
The material is readily available (residues from the main forest specie affected by the wildfire)
It will prevent sediment movement and accumulation over roads and downslope properties
When applying high density mulches the application labour requirements and costs will be higher Distribute the mulch in strips, use lighter mulches, grind to remove the fine fibres or maybe try to reduce the application rate. It is also possible to use in-situ chopping tree machines or to use aerial application methods, such as helicopters to reduce the application costs.
The costs are not very high, but enough to discourage the landowners to cover the expenses. Look for Government funding, educate land owners about soil erosion conservation techniques.


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