Mitigação da erosão do solo após os incêndios florestais

Doutoramento em Ciências do Mar e do Ambiente - Planeamento e Gestão AmbientalThis study aims to measure the effectiveness of four post-fire emergency techniques for reducing overland flow and soil erosion on the central-Portugal typical forest. The selection and development of these techniques was based on the review of the scientific background, but specially after checking throughout field rainfall simulation experiments which factors were the key for runoff and soil erosion on the specific case of high repellent soils. The forest residue mulch, a new treatment never tested before, was highly effective in reducing runoff and soil erosion in recently burnt eucalypt forest. The logging slash mulch had no obvious effect, but it was attributed to the small amounts of runoff and sediments that the untreated plots produced due to the extensive needle cast following a low severity fire. The hydromulch, a mixture of water, organic fibres, seeds, nutrients and a surfactant used in cutted slopes rehabilitation was also highly successful and was specially indicated for especially sensible areas. The utilization of polyacrylamides, a chemical agent with good performance in agricultural erosion, was not successful in post-fire runoff and soil erosion control, once that did not alter the most important key factor for soil erosion: the ground cover. The development of a new fibre optic turbidity sensor was a successful development on the soil erosion determination methodology, and its patent is being processed in the mean time.O presente trabalho centra-se na avaliação da efetividade de quatro técnicas de controlo da escorrência e da erosão após incêndios florestais, adaptadas para o caso de povoamentos florestais no centro norte de Portugal. A seleção e desenvolvimento das técnicas foi efetuada após revisão bibliográfica alargada, mas sobre tudo após a comprovação no campo, efetuando simulações de chuva, de quais os fatores determinantes da erosão nos solos típicos do centro norte do País, caracterizados por serem altamente repelentes ainda antes dos incêndios. O “mulch” com restos de casca de eucalipto triturada foi um tratamento pioneiro nunca antes testado e deu bons resultados no controlo da escorrência e da erosão em eucaliptais ardidos. O “mulch” com restos florestais não triturados (ramos, paus e folhas) aplicados em um pinhal recentemente ardido não pode ser bem testado devido à protecção natural que forneceram as agulhas do pinheiro que caíram das árvores. No entanto, a sua alta taxa de aplicação desaconselham a sua utilização. O “hidromulch”, uma variante do “mulch” composto por água, fibras orgânicas e sementes utilizadona restauração de taludes e pedreiras, também deu resultados altamente efetivos e foi indicado para o tratamento de áreas especialmente sensíveis. Por outro lado, a utilização de poliacrilamidas (PAM), um agente aglutinante com bastante êxito na redução da erosão em terrenos agrícolas e com alto potencial devido ao seu baixo custo, não obteve resultados satisfatórios, uma vez que não alterou o principal fator envolvido na geração da erosão: o coberto do solo. No decorrer destas experiências, foi ainda desenvolvido um sensor óptico de turvação que permite facilitar a determinação da concentração de sedimentos nas amostras de escorrência das parcelas de erosão. Atualmente, foi realizado o pedido de patente de um novo protótipo de sensor de turvação da água mais desenvolvido

Impacts of agricultural intensification on soil erosion and sustainability of olive groves in Alentejo (Portugal)

Context Olive groves are key features of Iberian Mediterranean landscapes. With the intensification of olive grove production, some negative environmental impacts on soils must be considered to achieve farm sustainability. Objectives To estimate, theoretically and empirically, soil erosion in olive groves of Alentejo (Portugal) considering different planting densities and soil managements (i.e. conventional, integrated, organic), and related impacts on soil loss and farm sustainability. Methods Soil erosion was empirically calculated using sediment traps. Soil loss was modelled using the Universal Soil Loss Equation (USLE) model. The impact of erosion on farm sustainability was assessed by simulating future projections to 100 and 500 years. Results An overestimation of theoretical erosion rates for all olive management models compared to the empirical results was observed. Plant cover strongly contributed to reduce soil loss. Temporal simulations based on experimental data showed a longer sustainability of intensive groves than expected according to theoretical values. Conclusions Despite the negative impacts of intensive agriculture, this study highlights that it is essential to consider soil management impacts on erosion, an aspect that influences farm sustainability, regardless of planting density. Future studies should expand our experiments across a wider sample and locations of olive groves, to better discern how olive sustainability is impacted by different agricultural management options and decisions.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. The implementation of this research was additionally funded by a Margarita Salas postdoctoral contract for the training of young PhDs (multiannual call for the requalification of the Spanish University System for 2021–2023; https://www.ucm.es/ct31-21), by University Complutense of Madrid through the Ministry of Universities, Government of Spain and the European Union – NextGenerationEU. The implementation of this study has been secondarily funded by the FCT (Fundação para a Ciência e a Tecnologia – Portugal), the CHANGE laboratory and MED—Mediterranean Institute for Agriculture, Environment and Development (University of Évora), funded by Project UIDB/05183/2020. This study has been supported by the SUSTAINOLIVE project (https://sustainolive.eu/?lang=en; PRIMA EU Programme)

Hydrologic Implications of Post-Fire Mulching Across Different Spatial Scales

Besides direct damage, wildfires can produce striking direct and indirect impacts, including extreme runoff–erosion responses with serious negative consequences for land-use sustainability and downstream values at risk. The best way to reduce post-fire runoff is the rapid application of mulch: a protective cover of straw, needles, wood-based material, or other ground cover. In this study, we assessed the efficacy of forest residue mulching for reducing post-fire runoff across spatial scales on a logged and burnt eucalypt hillslope. Additionally, we assessed the underlying processes involved in the hydrologic responses of burnt areas in central Portugal during the first 2 years after a wildfire, with special focus on soil moisture, soil water repellency, and rainfall. Forest residue mulch reduced post-fire runoff by 50% in both micro-plots (0·25 m2) and hillslope scale silt fence plots (100 m2) during the first year after the wildfire. Runoff in the micro-plots was tenfold higher than the larger plots, regardless of mulching. The main controlling factors for the volume of runoff were rainfall amount (direct correlation) and soil moisture (inverse correlation). Soil water repellency and soil moisture were not affected by the mulch but played a role in the hydrologic response. In contrast, there was no decrease in runoff rate within the first two post-fire years. Forest residue mulching can be an effective post-fire treatment for reducing runoff rates, and the consistent decrease in runoff rates between the two spatial scales suggests that the scaling of runoff was not affected by the mulch. Copyright © 2015 John Wiley & Sons, Ltd

Effect of fire frequency on runoff, soil erosion, and loss of organic matter at the micro-plot scale in north-central Portugal

Wildfire is a natural phenomenon that is a common ecological factor in Mediterranean ecosystems. The increase in occurrence in recent decades has raised widespread concern about the impact of repeated wildfires on runoff and erosion, a topic that has not been widely studied. We addressed these concerns in an area of north-central Portugal by comparing runoff at the micro-plot scale and the associated transport of sediments and organic matter (OM) in unburnt, once burnt, and repeatedly burnt plantations of Maritime Pine. We selected nine sites following a large wildfire in September 2012 that affected roughly 3000 ha of the Viseu municipality. Three of the sites had not been burnt since 1975 and acted as controls, with covers of pine trees, shrubs, and annual vegetation; three sites had burnt only in 2012 and contained burnt pines but no shrubs or annual vegetation; and three degraded sites had suffered from three wildfires prior to 2012 and contained no vegetation. We established nine micro-plots (0.25 m2) at each site and collected runoff, eroded soil, and OM losses in tanks after each rain from October 2012 to September 2014. The repeated wildfires strongly increased the runoff coefficient and the risk of downstream flooding after heavy rains. OM losses were nearly half the volume of the eroded soil in the degraded sites due to the transport of ash in the runoff. Runoff and soil losses occurred not only after erosive rainstorms following a fire but also after a subsequent period of drought. Soil cover, rain intensity, and soil moisture were key factors in the amount of runoff and erosion. The insights provided by this study can contribute to pre- and post-fire activities and management in protect areas and can thus improve post-fire recovery

Mid-term and scaling effects of forest residue mulching on post-fire runoff and soil erosion

© 2016 Elsevier B.V. Mulching is an effective post-fire soil erosion mitigation treatment. Experiments with forest residue mulch have demonstrated that it increased ground cover to 70% and reduced runoff and soil loss at small spatial scales and for short post-fire periods. However, no studies have systematically assessed the joint effects of scale, time since burning, and mulching on runoff, soil loss, and organic matter loss. The objective of this study was to evaluate the effects of scale and forest residue mulch using 0.25 m2 micro-plots and 100 m2 slope-scale plots in a burnt eucalypt plantation in central Portugal. We assessed the underlying processes involved in the post-fire hydrologic and erosive responses, particularly the effects of soil moisture and soil water repellency. Runoff amount in the micro-plots was more than ten-fold the runoff in the larger slope-scale plots in the first year and decreased to eight-fold in the third post-fire year. Soil losses in the micro-plots were initially about twice the values in the slope-scale plots and this ratio increased over time. The mulch greatly reduced the cumulative soil loss measured in the untreated slope-scale plots (616 g m− 2) by 91% during the five post-fire years. The implications are that applying forest residue mulch immediately after a wildfire can reduce soil losses at spatial scales of interest to land managers throughout the expected post-fire window of disturbance, and that mulching resulted in a substantial relative gain in soil organic matter

Use of coupled biochar and straw mulch as a technique to mitigate soil erosion and improve soil carbon stocks in burned soils of southern iberian peninsula

Comunicación oral presentada en el ISMOM 2019 - 8th International Symposium on Interactions of Soil Minerals with Organic Components and Microorganisms: 23-28 june, Sevilla (Spain)Wildfires typically increase runoff as well as soil erosion due to exposure of soil to direct raindrop impact. In addition, wildfires may cause a drastic alteration of soil structure by decreasing organic matter content and quality aggregate stability and carbon cycling. Post-fire mulching is the most widely accepted measure to mitigate soil erosion effectively but unfortunately mulch materials and application rates can vary greatly affecting its effectiveness. Some mulch materials such as straw have been used widely but others such as biochar which can improve soil quality has never been used in burned areas and has the potential to mitigate soil losses and improve soil quality in burned areas. While the CESAM group at the University of Aveiro has extensive experience in evaluating methodologies for erosion control the Organic Matter group from IRNASCSIC institution has studied soil quality and soil conservation strategies. This work aims to show examples of tools applied to mitigate post-fire erosion and their effects on soil quality. A total of 40 microplots (1 m2) were installed in September 2018 in two areas where wildfires burned at high severity (sandy and loamy soils) of southern Portugal and Spain respectively. Soil and sediment samples are being collected to assess soil erosion and carbon stocks via TG and DSC analysis. Treatments are: Burned (controls) Brushed (ash and stones removed) Straw mulch (at a rate of 1 Mg ha-1) Straw+Biochar (at a rate of 1+15 Mg ha-1) Pine slash and Marine algae. Preliminary results show that Straw and Straw+Biochar mulch strongly reduced soil erosion in 67- 60% compared to Burned plots or the Brushed plots which did not differ from each other. These findings indicate that applying both Straw together with Biochar can be an effective way to increase not only the labile soil organic matter fraction (derived from mulch itself) but also retain more recalcitrant native soil organic matter fractions (derived from the lack of erosion) and possibly also increase recalcitrant organic matter derived from biocha

EVALUACIÓN DE LA EROSIÓN EDÁFICA EN PAISAJES MEDITERRÁNEOS DE OLIVAR BAJO DIFERENTES SISTEMAS DE MANEJO

Los países de la cuenca Mediterránea producen casi el 70% del aceite de oliva mundial. Debido al incremento de la demanda de aceite, los olivares están sufriendo una rápida expansión e intensificación, con incrementos del uso de herbicidas químicos, laboreo, ferti-rega, y densidades de plantación. Este proceso es evidente en el Alentejo Portugués, conllevando impactos que amenazan su sostenibilidad (i.e. erosión, degradación de hábitats). El objetivo principal de este estudio consiste en evaluar los impactos de los diferentes modelos de manejo del olivar en el Alentejo (Portugal) sobre los procesos erosivos a diversas escalas espacio-temporales, considerando factores como la edad de los árboles, la densidad de plantación, y la gestión de la vegetación herbácea. En este sentido se está realizando un control experimental de la erosión a través de parcelas a escala localizada (1 m2) y de ladera (300 m2), además de evaluar la capacidad de secuestro de carbono de estos olivares y analizar qué factores son los condicionantes de los procesos erosivos. Los resultados preliminares (septiembre 2021-febrero 2022) evidenciaron que, a pesar de ser un año seco (i.e. 149 mm), la pérdida de suelo en ladera fue superior en los olivares con herbicidas respecto a aquéllos de reciente implantación, siendo insignificante en parcelas con laboreo y control mecánico de la vegetación herbácea. Sin embargo, a escala localizada la pérdida de suelo fue superior en fincas con laboreo respecto a las plantaciones en las que usaron herbicidas. Merece la pena destacar cómo la pérdida de materia orgánica fue superior para niveles erosivos inferiores. Estos resultados sirven como argumento para la concienciación de los agricultores sobre los problemas ligados a la gestión convencional de los paisajes de olivar, sirviendo para realizar recomendaciones hacia una gestión alternativa del olivar que incremente su sostenibilidad

Polyacrylamide application versus forest residue mulching for reducing post-fire runoff and soil erosion

For several years now, forest fires have been known to increase overland flow and soil erosion. However, mitigation of these effects has been little studied, especially outside the USA. This study aimed to quantify the effectiveness of two so-called emergency treatments to reduce post-fire runoff and soil losses at the microplot scale in a eucalyptus plantation in north-central Portugal. The treatments involved the application of chopped eucalyptus bark mulch at a rate of 10–12 Mg ha−1 , and surface application of a dry, granular, anionic polyacrylamide (PAM) at a rate of 50 kg ha−1 . During the first year after a wildfire in 2010, 1419 mm of rainfall produced, on average, 785 mm of overland flow in the untreated plots and 8.4 Mg ha−1 of soil losses. Mulching reduced these two figures significantly, by an average 52 and 93%, respectively. In contrast, the PAM-treated plots did not differ from the control plots, despite slightly lower runoff but higher soil erosion figures. When compared to the control plots, mean key factors for runoff and soil erosion were different in the case of the mulched but not the PAM plots. Notably, the plots on the lower half of the slope registered bigger runoff and erosion figures than those on the upper half of the slope. This could be explained by differences in fire intensity and, ultimately, in pre- fire standing biomass