|Post-fire mulching experiment|
Case Study Experiment - Soil Erosion
Post-fire mulching in forests
Burnt areas in forests can reveal some extreme responses in runoff generation and associated sediment losses. Such responses exacerbate the direct effects of fire on vegetation and on the soil physical, chemical and biological properties, compromising their recovery from heat-induced changes. Post-fire soil erosion also represents a serious threat to off-site "values-at-risk", through flood generation and transfer of sediments, organic matter, nutrients and pollutants to downstream water bodies. Recent field trials in the Portugese case study area have clearly demonstrated that mulching with forest logging residues (widely available in the region) is highly effective in reducing erosion in recently burnt areas. The RECARE experiment is testing the effectiveness of mulching to reduce post-fire soil (fertility) losses. It involves mulching with eucalyptus logging slash at 2 contrasting application rates.
A. the two mulch application rates tested in the field (2.5 vs. 8 Mg ha-1) had a statistically significant effect on various ground cover categories throughout the first year after the fire, including the litter cover that was targeted by the treatment. Immediately after mulching, the litter cover was, on average, 4% in the untreated plots and 48 and 77% in the little- and much-mulch treatments, respectively, corresponding to increases in protective cover of 12 and 19 times.
B. the two mulch application rates also produced major reductions in mineral soil losses over the first year after the fire as these losses amounted, on average, to 6.3 Mg ha-1 y-1 in the case of the untreated plots and to 0.9 and 0.2 Mg ha-1 y-1 in the plots with little- and much-mulch, respectively. As such, the overall effectiveness of the two mulch treatments in reducing soil loss was 86 and 97%, effectiveness in % being quantified as: (loss_untreated – loss_treated) / loss_untreated * 100. Similar results were obtained for organic matter losses (weight-loss-on-ignition method), with the two mulching treatments being, on average, highly effective (88 and 94 %) in reducing the 1.7 Mg ha- y-1 losses from the untreated plots.
J.J. Keizer, M.A.S. Martins, S.A. Prats, S.R. Faria, O. González-Pelayo, A.I. Machado, M.E. Rial-Rivas, L.F. Santos, D. Serpa, M.E.T. Varela (20015) Within-in flume sediment deposition in a forested catchment following wildfire and post-fire bench terracing, north-central Portugal. Cuadernos de Investigación Geográfica Vol 41, No. 1 doi: http://dx.doi.org/10.18172/cig.2700
A.I. Machadoa, D. Serpaa, R.V. Ferreiraa, M.L. Rodríguez-Blancob, R. Pintoa, M.I. Nunesa, M.A. Cerqueiraa, J.J. Keizera(2015) Cation export by overland flow in a recently burnt forest area in north-central Portugal Science of the Total Environment Volumes 524–525, 15 August 2015, Pages 201–212 doi: 10.1016/j.scitotenv.2015.04.026
Ferreira R.V., Serpa D., Cerqueira M.A., Keizer J.J. (2016) Short-time phosphorus losses by overland flow in burnt pine and eucalypt plantations in north-central Portugal: A study at micro-plot scale. Published in: Science of the Total Environment 551–552, 631–639 https://dx.doi.org/10.1016/j.scitotenv.2016.02.036
Campos I., Abrantes N., Keizer J.J., Vale C., Pereira P. (2016) Major and trace elements in soils and ashes of eucalypt and pine forest plantations in Portugal following a wildfire. Published in:Science of the Total Environment 2016 Dec 1;572:1363-1376 https://dx.doi.org/10.1016/j.scitotenv.2016.01.190
Tavares Wahren F., Julich S., Nunes J.P., Gonzalez-Pelayo O., Hawtree D., Feger K.-H., Keizer J.J. (2016) Combining digital soil mapping and hydrological modeling in a data scarce watershed in north-central Portugal. Published in: GEODERMA 264, part B, 350- 362 http://dx.doi.org/10.1016/j.geoderma.2015.08.023
Further information about the case study activities in Portuguese can be found here
The study region is located in north-central Portugal. The Caramulo mountains have an Atlantic-Mediterranean climate, with prolonged, dry summers promoting wildfire ignition and high annual rainfall (≥ 1200 mm) promoting plant biomass production and, thus, fuel load accumulation. The present-day landscape is dominated by tree plantations of Maritime Pine (10 %) and especially eucalypt (40 %), which are both highly flammable species and, thus, promote the structural wildfire risk.
Post-fire erosion risk in the RECARE study region is comparatively high, due to the elevated rainfall erosivity and the terrain's pronounced relief, with slopes typically of 20-25o. Whilst post-fire erosion rates of ≥ 5 Mg.ha-1.y-1 are not exceptional, even rates lower than 1 Mg.ha-1.y-1 – the widely accepted threshold for "tolerable" soil loss - cannot be disregarded. The soils in the study region, like in many parts of the Mediterranean, are in general shallow (< 40 cm deep) and very stony, reflecting their long land-use history but, most importantly, it highlights their fragility. Furthermore, these sediment losses comprise a substantial organic matter component.
Main soil threat
The main soil threat in the Caramulo mountains in north-central Portugal is soil erosion by water, particularly following wildfires. Recently burnt areas can reveal some extreme responses in runoff generation and associated sediment losses. Such responses exacerbate the direct effects of fire on vegetation and on the soil physical, chemical and biological properties, compromising their recovery from heat-induced changes. Post-fire soil erosion also represents a serious threat to off-site "values-at-risk", through flood generation and transfer of sediments, organic matter, nutrients and pollutants to downstream water bodies.
In the past four decades, wildfires have become a frequent phenomenon in Portugal and have affected, on average, some 100,000 ha.y-1. Of the RECARE study region, almost 40% was burnt at least once during the period 1975-2011. This fire regime reflects climatic conditions propitious to wildfire but also past changes in land use, in particular, the widespread planting of flammable tree species in combination with land abandonment. Post-fire land management in Portugal is largely restricted to "regular" forestry operations as logging, ploughing and bench terracing. Ploughing was found to further increase soil erosion in recently burnt areas. Unlike in the USA, emergency measures for mitigating post-soil erosion have hardly been employed in Portugal and, until quite recently, were also barely supported by field experiments in the country's principal forest types.
Recent field trials have clearly demonstrated that mulching with forest logging residues (widely available in the region) is highly effective in reducing erosion in recently burnt areas. Nonetheless, there remain various knowledge gaps on post-fire erosion prevention. They include technical issues:
i) mulching's effectiveness at lower-than-hitherto-tested (and thus cheaper) application rates;
ii) its effectiveness at the landscape scale, using innovative, spatially-explicit application schemes (e.g. mulch strips);
iii) effectiveness of novel measures such as PAM, possibly combined with mulching; and
iv) impacts of erosion-prevention measures on other soil functions (e.g. seed bank, carbon sequestration).
The poor adoption of post-fire erosion prevention measures by private and public stakeholders in Portugal is another fundamental topic for further research, addressing adoption constraints from financial and social, institutional and legal perspectives.
Geology & Soils
The SJM-M Case Study site is part of the Hesperic Massif, one of the region’s major physiographic units, and its bedrock consists of granites and, to a somewhat lesser extent, of a complex of schists and greywackes. The granites are of Hercynian origin, whereas the schists-greywackes are of pre-Ordovician age. Overall, the slopes on granite are less steep than those on schists-greywackes. While the ESDB depicts the area as dominated by Mollic Cambisols (Figure 2.2), soils of the study region, including the SJM-M case study site, are mapped – at a scale of 1:1,000,000 – as a complex of Humic Cambisols and, to a lesser extent, Dystric Litosols (not shown). The predominant soil types are Cambisols, Litosols and Coluvisols, to a large extent mapped as complexes, whereas also zones dominated by granite outcrops occupy large areas. No soil profile descriptions or data on specific soil properties are available from the SJM-M case study site, but various studies in the wider region (e.g. Malvar et al., 2013) have reported that forest soils are typically shallow, stony, coarse-textured (sand being the dominant fraction) and rich in organic matter (5-10 % in the topsoils).
Soil groups and materials (left) and Land Use in the Case Study site of São João do Monte and Mosteirinho (right). Source: JRC
Land Cover and Use
At present, the SJM-M case study site is predominantly covered by forest, amounting to almost 90 % of the area, with some dispersed croplands and hardly any built-up area - see below. This forest cover mainly consists of plantations of fast-growing eucalypt trees (Eucalyptus globulus Labill.), represented in the CORINE 2006 map as broad-leaved forest, mixed forest and transitional woodland-shrubland. In the Caramulo mountain range as a whole, eucalypt plantations have increasingly come to substitute plantations of maritime pine (Pinus pinaster Ait.), especially since the 1980s. In turn, the pine stands had been widely planted during the early 1900s, including for reasons of erosion control and substituting a mixed landscape of (semi-) natural oak-dominated woodlands, shrublands and pastures. The large-scale reforestation with eucalypt has supposedly been driven by the demand for eucalypt wood by the paper pulp industry in the region, and has been accelerated by wildfires, of which the large wildfires of 1986 deserves special mention for burning some 60 km2 of mainly pine plantations. Eucalypt has a much shorter production cycle than maritime pine, amounting to 10-15 years as opposed to 40-45 years. Worth mentioning is that eucalypt trees can typically be logged twice, subsequently resprouting vigorously from multiple stems, without the need for establishing a new plantation. In recent years, the establishment of new eucalypt plantations in the Caramulo mountain range has increasingly been involving the construction of bench terraces using bulldozers. In the SJM-M case study site, almost 10% of the eucalypt plantations are currently on bench terraces
Left: Present-day main land-cover classes in the case study site of SJM-M; right: Wildfire recurrence in the case study site of SJM-M since 1975
The Caramulo mountain range has an Atlantic-Mediterranean climate, with prolonged dry and warm summers that are propitious to fire occurrence, and wet winters that promote plant biomass production and, thus, fuel load accumulation. According to the Köppen system, the climate can be classified as Csb (DRA-Centro, 2001).
The above figure summarizes the monthly temperature and rainfall records at various meteorological stations in the region during the period 1971-2000. Mean monthly temperatures vary between around 10oC during the winter months (December – February) and around 20oC during July and August, whereas the mean monthly rainfall ranged from over 200 mm during the November-February period to around 20 mm in July and August.
Drivers and pressures
Like many parts of Portugal, the SJM-M Case Study site has repeatedly been affected by wildfires since 1975 (see above). This map indicates a total of seven wildfires, occurring in 1984, 1985, 1986, 1990, 1991, 1995 and 2013, with the latter having particularly large dimensions. Around 75% of the forest area in the SJM-M Case Study site was burnt at least once during the last three decades, whereas 35 and 2% was burnt twice and thrice, respectively, over the same period. Worth stressing is that crucial information for estimating wildfire impacts on soil properties and functions is (currently) missing for these past wildfires, including the most recent one. Examples of such crucial information are wildfire severity as well as rainfall conditions, vegetation recovery and land management operations after the wildfires. Likewise, no information is available on the causes of ignition of these specific wildfires. In general, wildfire ignition in Portugal is mainly due to human activities and, in particular, negligence. Also the underlying causes of the present-days fire regime in Portugal are better established for the country as a whole than for a specific location such as the SJM-M Case Study site. Key socio-economic and policy-related factors behind the intensified fire regime of the past three decades are widely held to include/relate to a rural exodus and associated land abandonment starting in the 1950s, and to the above-mentioned widespread planting of fire-prone tree species as maritime pine and eucalypt. The large-scale migration from rural to urban areas in Portugal after the 1950s also took place in the SJM-M Case Study site, with a reduction in resident population of around 50% over the past five decades. At present, the resident population amounts to 1079 persons (see below) and corresponds to an extremely low population density of 16.6 inhabitants per km2. The exodus also had a marked influence on the age structure of the resident population, with roughly 30% being older than 64 years. Besides demographic processes, also land ownership structure is generally held to play an important role in the tendency towards decrease in forest management activities such as wood and fodder collection for domestic use, grazing and fuel load reduction. The facts that around 90% of the Portuguese forest area is privately owned and that the bulk of these private properties is small, at least in north and central Portugal, represents a seriously constraint to the management options that are feasible, especially also from an economic point of view (Valente et al., 2013). These same facts also help explain why post-fire land management is typically limited to logging and reforestation with eucalypts (Ribeiro et al., 2010). The role of policy-related factors is perhaps best illustrated by the Law 1971 from 5 June 1938, prohibiting grazing and burning and, thereby, leading to the accumulation of highly combustible fuels on forest floors and an increase in fire risk.
Status of soil threat
Since the late 1980s, several field studies have been performed in the wider study region on runoff and sediment losses following wildfire and post-fire land management, including measures to control soil erosion. None of these studies, however, actually took place in the SJM-M case study site. Some examples are Shakesby et al. (1994, 1996), Ferreira et al. (2005), Malvar et al. (2011), Prats et al. (2012, 2014) and Martins et al. (2013). Overall, these studies have shown that: (i) sediment losses during the first one to two years after a wildfire vary markedly, from (well) below the rate of 1 Mg ha–1 y–1 that Verheijen et al. (2009) proposed as threshold for tolerable soil loss till 10 times that threshold figure; (ii) high-impact forestry operations in recently burnt areas can lead to sediment losses as high as 14 Mg ha–1 y–1 following bench terracing (Martins et al., 2013) and 37 Mg ha–1 y–1 following rip-ploughing in downslope direction (Shakesby et al., 2002); (iii) elevated post-fire sediment losses can be markedly reduced by soil conservation measures, with hydro-mulching and mulching with forest residues reducing overall losses by 80-90% (Shakesby et al., 1996; Prats et al., 2012, 2013, 2014). It is worth mentioning that sediment losses both without and with forest residue mulching could be predicted to a satisfactory extent using the Morgan-Morgan-Finney model (Vieira et al., 2014). Nonetheless, major knowledge gaps with respect to the hydro-geomorphological effects of wildfires and post-fire land management in the study region exist. These include the role of past land use (supposedly, contributing markedly to the strong variation in observed erosion rates), key aspects of fire regime (fire severity and recurrence), specific forestry operations (especially logging) as well as the effects beyond the scale of plots and in terms of soil fertility losses (organic matter/carbon, nutrients, cations) as well as mobilization of pollutants (polycyclic hydrocarbons (PAHs), metals). In a nutshell, the current state of knowledge would appear too limited for a reliable reconstruction of the cumulative sediment losses caused by the wildfires that have occurred in the SJM-M Case Study site since 1975. Therefore, an expert-based approach will be used for a first assessment of the state of soil degradation, using fire recurrence, high-impact forestry operations and terrain characteristics as principal factors.
Maps on the current state of land use, soil degradation and soil conservation in the case study area have been produced using the WOCAT (World Overview of Conservation Approaches and Technologies) methodology
The steps of this process are as follows:
1) The area to be mapped is divided into distinctive land use systems (LUS). 2) The team gathers the necessary data on soil degradation and conservation for each LUS using a standardised questionnaire, in close consultation with local land users, and supported where possible by remote sensing or field data. 3) For each LUS, the soil degradation type, extent, degree, impact on ecosystem services, direct and indirect causes of degradation, as well as all soil conservation practices, are determined. 4) Once collected, the data is entered in the on-line WOCAT-QM Mapping Database from which various maps can be generated.
Following the principles of all WOCAT questionnaires, the collected data are largely qualitative, based on expert opinion and consultation of land users. This allows a rapid and broad spatial assessment of soil degradation and conservation/SLM, including information on the causes and impacts of degradation and soil conservation on ecosystem services.
More details about the methodology used to produce these maps and their interpretation can be found here.
Land Use (click on maps to expand)
The degree of degradation reflects the intensity of the degradation process, whilst the rate of degradation indicates the trend of degradation over a recent period of time (approximately 10 years).
The "effectiveness" of conservation is defined in terms of how much it reduces the degree of degradation, or how well it is preventing degradation. The Effectiveness trend indicates whether over time a technology has increased in effectiveness.
Effect of soil threat on soil functions
Table below provides a summary description as well as a ranking of the effects of post-fire runoff and erosion on the seven widely-recognized soil functions for the SJM-M Case Study site and the Caramulo mountain range in general.
|Functions of soil||Explanation||Effect|
|Biomass production||Reduction of the soil stock and especially the loss of the nutrient- and organic matter-rich topsoil negatively affect biomass production, especially where soils are already shallow.||M|
|Environmental interactions||Reduction of the soil stock and removal of the topsoil negatively affects soil water storage capacity, organic matter and nutrients, its resistance to the impact of raindrops and overland flow, and its capacity to buffer rainfall from extreme events.||H|
|Gene reservoir/ Biodiversity pool||Overland flow can transport organism dwelling on or near the soil surface (including soil seed bank) and removal of topsoil can negatively affect soil habitat quality and diversity.||L|
|Physical medium||Runoff and soil erosion can cause damage to off-site infrastructures such as bridges, roads, houses (especially in flood zones) and reservoir dams.||L|
|Source of raw materials||Soils in the study site/region are not used as source of raw materials.||U|
|Carbon pool||Reduction of the soil stock and especially removal of the topsoil can negatively affect the soil carbon pool.||M|
Administrative and socio-economic setting
The administrative unit of Caramulo pertains to the municipality of Tondela of the Viseu District. Two parishes constituting one local administrative unit – i.e. the “União de freguesias” of São João do Monte and Mosteirinho (SJM-M) - are selected as primary Case Study site. At present, the Institute for the Conservation of Nature and Forests (ICNF), pertaining to the Ministry of Agriculture and Sea, is the high authority for forest management in Portugal. Its mission is to propose, accompany and assure the execution of the policies for nature and forest conservation. ICNF comprises the Central Services as well as Decentralized Services, in each of the five regions (North, Centre, Lisbon and Tagus Valley, Alentejo, Algarve). In addition, at the municipal level, Forest Technical Offices (GTFs) are responsible for supporting the implementation of forest policies, including the definition of the Municipal Plan for Forest Protection against Fires (PMDFCI). Furthermore, nowadays many regional and even local organizations of private forest producers exist, reflecting the fact that around 90% of the forest area in Portugal is privately owned and that most properties are less than 10 ha, in particular in the North and Central Region. The forest sector in Portugal, however, also includes some large companies, in particular the international consortium Soporcel-Portucel with 120,000 ha of forest holdings and the European company ALTRI managing 84,000 ha of forest.
The National Forest Strategy and the Regional Plans for Forest Management and Planning provide the general guidelines for the Portuguese forest sector. While specific policies on post-fire management do not exist, the legal framework for the Plan for Forest Protection against Fires does integrate a line of action on ecosystem rehabilitation and restoration. Furthermore, the Rural Development Program (PRODER) includes a sub-action that is directed towards the application of so-called post-fire emergency stabilization measures (i.e. sub-action 22.214.171.124 “Planning and recovery of forest plantations for emergency stabilization”). In fact, the “união de freguesias” of SJM-M was one of various “freguesias” in the study region that recently applied to PRODER funding under this sub-action, after three wildfires had burnt over 90 km2 of the Caramulo mountain region between August 20 and September 2 2013.
Population in Caramulo (left) and GDP per capita trends for Portugal and the Euro Area (right)
Post-fire land management in Portugal is typically restricted to standard forestry practices such as logging and (re-)planting, often following ground preparation operations and, in particular, rip-ploughing or bench terracing. Logging, rip ploughing and bench terracing in recently burnt areas can all produce marked increases in soil erosion by water (Fernández et al., 2007; Martins et al., 2013; Shakesby et al., 1994). Soil conservation measures aiming to mitigate post-fire erosion, however, have hardly been employed in Portugal. Nonetheless, recent field trials have clearly demonstrated that especially mulching with forest logging residues (widely available in the region) is highly effective in reducing overland flow generation and especially erosion in recently burnt pine and eucalypt plantations (Prats et al., 2012, 2014).
During the last century, the Portuguese central administration has been changing and multiplying the number of planning, legislative, regulatory and financial tools to create a suitable framework for the forest sector (Mendes, 2008). This instability has contributed to the fact that the level of implementation of these forest policies is rather limited. For the case of fire management, there is a strong focus, including in budgetary terms, on fire suppression at the expense of fire prevention as well as post-fire management (Moreira et al., 2012).
The PRODER sub-action 126.96.36.199 “Planning and recovery of forest plantations for emergency stabilization” has been operational since 2008. However, a systematic evaluation of its performance has not been carried out, neither in terms of the selection process of the potential emergency stabilization measures nor in terms of the effectiveness of the implemented measures. Operational aspects would also deserve special attention as wildfires typically occur at the end of the summer season while the first autumn rains often include extreme events.
Long-term post-fire management should include the implementation of measures for the restoration of heavily degraded ecosystems affected by, e.g., multiple wildfires, post-fire drought conditions hampering vegetation recovery or particularly intense erosion processes. More in general, long-term management will require the development of an integrated strategy, combining fire prevention (e.g. through prescribed fires), fire suppression and post-fire management. Such a strategy will require the active involvement of the full range of forest stakeholders in Portugal, not only for defining the strategy but also for implementing it, possibly through Forest Intervention Areas (Valente et al., 2013) or other management models.
Relevant end-users and local stakeholder groups include:
• Private forestry land owners and associations thereof such as the Baixo Vouga Forestry Association
• Public forest management committees of common lands and municipal Technical Forestry Offices, especially of Águeda, Albergaria-a-Velha, Sever do Vouga
• RAIZ – Research Institute for Forestry and Paper
• Paper and pulp industry such as the Soporcel-Portucel Consortium (manages 120,000 ha of private forest lands)
• Companies providing water-related services such as the "Associação de Municípios do Carvoeiro" (drinking water supply) and Greenvouga (hydric energy supply).
The aim is for the above-mentioned institutional stakeholders to be actively involved throughout the entire process of defining, implementing, monitoring and evaluating the prevention/remediation measures, and of setting-up the demonstration sites. The involvement of local stakeholders will be sought immediately following the selection of a burnt area during the summer of 2014. In the initial phase of stakeholder involvement, full stock will be taken of the team's ongoing field trials.
Gender and stakeholder workshops
Both men and women stakeholders are invited to the study site workshops. Most of the participants are men representing landowners, land managers and the private sector. Both men and women represent research, governmental and non-governmental organizations. All participants said they would greatly benefit from changes in SLM.
This web page is authored by:
J.J. Keizer, S. Prats, S. Valente, M. Rial and C. Ribeiro from University of Aveiro, Portugal
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