Forest Road Detection Using LiDAR Data and Hybrid Classification

Knowledge about forest road networks is essential for sustainable forest management and fire management. The aim of this study was to assess the accuracy of a new hierarchical-hybrid classification tool (HyClass) for mapping paved and unpaved forest roads with LiDAR data. Bare-earth and low-lying vegetation were also identified. For this purpose, a rural landscape (area 70 ha) in northwestern Spain was selected for study, and a road network map was extracted from the cadastral maps as the ground truth data. The HyClass tool is based on a decision tree which integrates segmentation processes at local scale with decision rules. The proposed approach yielded an overall accuracy (OA) of 96.5%, with a confidence interval (CI) of 94.0–97.6%, representing an improvement over pixel-based classification (OA = 87.0%, CI = 83.7–89.8%) using Random Forest (RF). In addition, with the HyClass tool, the classification precision varied significantly after reducing the original point density from 8.7 to 1 point/m2. The proposed method can provide accurate road mapping to support forest management as an alternative to pixel-based RF classification when the LiDAR point density is higher than 1 point/m2This research was supported by: (1) the Project “Sistema de ayuda a la decisión para la adaptación al cambio climático a través de la planificación territorial y la gestión de riesgos (CLIMAPLAN) (PID2019-111154RB-I00): Proyectos de I+D+i - RTI”; and (2) “National Programme for the Promotion of Talent and Its Employability” of the Ministry of Economy, Industry, and Competitiveness (Torres-Quevedo program) via a postdoctoral grant (PTQ2018-010043) to Juan Guerra HernándezS

Modelling diameter distributions in radiata pine plantations in Spain with existing countrywide LiDAR data

We evaluated the use of low-density airborne laser scanning data to estimate diameter distributions in radiata pine plantations. The moment-based parameter recovery method was used to estimate the diameter distributions, considering LiDAR metrics as explanatory variables. The fitted models explained more than 77% of the observed variability. This approach can be replicated every 6 years (temporal cover planned for countrywide LiDAR flights in Spain). Context: The estimation of stand diameter distribution is informative for forest managers in terms of stand structure, forest growth model inputs, and economic timber value. In this sense, airborne LiDAR may represent an adequate source of information. Aims: The objective was to evaluate the use of low-density Spanish countrywide LiDAR data for estimating diameter distributions in Pinus radiata D. Don stands in NW Spain. Methods: The empirical distributions were obtained from 25 sample plots. We applied the moment-based parameter recovery method in combination with the Weibull function to estimate the diameter distributions, considering LiDAR metrics as explanatory variables. We evaluated the results by using the Kolmogorov–Smirnov (KS) test and a classification tree and random forest (RF) to relate the KS test result for each plot to stand-level variables. Results: The models used to estimate average (dm) and quadratic (dg) mean diameters from LiDAR metrics, required for recovery of the Weibull parameters, explained a high percentage of the observed variance (77 and 80%, respectively), with RMSE values of 3.626 and 3.422 cm for the same variables. However, the proportion of plots accepted by the KS was low. This poor performance may be due to the strictness of the KS test and/or by the characteristics of the LiDAR flight. Conclusion: The results justify the assessment of this approach over different species and forest types in regional or countrywide surveys.Spanish Ministry of Science and Innovation (AGL2008-02259/FOR); Galician Government, Xunta de Galicia, Dirección Xeral de Montes (09MRU022291PR); Norvento (Multinational energy company) (PGIDT09REM023E); Eduardo González-Ferreiro was financially supported by the Plan galego de investigación, innovación e crecemento 2011-2015 (Plan I2C) (Official Journal of Galicia – DOG nº 52, 17/03/2014 p. 11343, exp: POS-A/2013/049): Galician Government (Dirección Xeral de Ordenación e Calidade do Sistema Universitario de Galicia – Consellería de Educación e Ordenación Universitaria) and European Social Fund. Manuel Arias-Rodil was financially supported by an FPU grant (AP2012-05337) from the Spanish Ministry of Education.Spanish Ministry of Science and Innovation (AGL2008-02259/FOR); Eduardo González-Ferreiro was financially supported by the Plan galego de investigación, innovación e crecemento 2011-2015 (Plan I2C) (Official Journal of Galicia - DOG nº 52, 17/03/2014 p. 11343, exp: POS-A/2013/049) - Galician Government (Dirección Xeral de Ordenación e Calidade do Sistema Universitario de Galicia - Consellería de Educación e Ordenación Universitaria) and European Social Fund. Manuel Arias-Rodil was financially supported by an FPU grant (AP2012-05337) from the Spanish Ministry of Education.S

Evaluating the potential of ALS data to increase the efficiency of aboveground biomass estimates in tropical peat–swamp forests

Estimates of aboveground biomass (AGB) in forests are critically required by many actors including forest managers, forest services and policy makers. Because the AGB of a forest cannot be observed directly, models need to be employed. Allometric models that predict the AGB of a single tree as a function of diameter at breast height (DBH) are commonly used in forest inventories that use a probability selection scheme to estimate total AGB. However, for forest areas with limited accessibility, implementing such a field-based survey can be challenging. In such cases, models that use remotely sensed information may support the biomass assessment if useful predictor variables are available and statistically sound estimators can be derived. Airborne laser scanning (ALS) has become a prominent auxiliary data source for forest biomass assessments and is even considered to be one of the most promising technologies for AGB assessments in forests. In this study, we combined ALS and forest inventory data from a logged-over tropical peat swamp forest in Central Kalimantan, Indonesia to estimate total AGB. Our objective was to compare the precision of AGB estimates from two approaches: (i) from a field-based inventory only and, (ii) from an ALS-assisted approach where ALS and field inventory data were combined. We were particularly interested in analyzing whether the precision of AGB estimates can be improved by integrating ALS data under the particular conditions. For the inventory, we used a standard approach based on a systematic square sample grid. For building a biomass-link model that relates the field based AGB estimates to ALS derived metrics, we used a parametric nonlinear model. From the field-based approach, the estimated mean AGB was 241.38 Mgha −1 with a standard error of 11.17 Mgha −1 (SE% = 4.63%). Using the ALS-assisted approach, we estimated a similar mean AGB of 245.08 Mgha −1 with a slightly smaller standard error of 10.57 Mgha −1 (SE% = 4.30%). Altogether, this is an improvement of precision of estimation, even though the biomass-link model we found showed a large Root Mean Square Error (RMSE) of 47.43 Mgha −1 . We conclude that ALS data can support the estimation of AGB in logged-over tropical peat swamp forests even if the model quality is relatively low. A modest increase in precision of estimation (from 4.6% to 4.3%), as we found it in our study area, will be welcomed by all forest inventory planners as long as ALS data and analysis expertise are available at low or no cost. Otherwise, it gives rise to a challenging economic question, namely whether the cost of the acquisition of ALS data is reasonable in light of the actual increase in precisionWe are grateful to the Galician Government and European Social Fund (Official Journal of Galicia DOG n 52, 17 March 2014, p. 11343, exp: POS-A/2013/049) for financing the postdoctoral research stays of Eduardo González-Ferreiro at different institutionsS

Comparison of ALS based models for estimating aboveground biomass in three types of Mediterranean forest

This study aimed to develop ALS-based models for estimating stem, crown and aboveground biomass in three types of Mediterranean forest, based on low density ALS data. Two different modelling approaches were used: (i) linear models with different variable selection methods (Stepwise Selection [SS], Clustering/Exhaustive search [CE] and Genetic Algorithm [GA]), and (ii) previously Published Models (PM) applicable to diverse types of forest. Results indicated more accurate estimations of biomass components for pure Pinus pinea L. (rRMSE = 25.90-26.16%) than for the mixed (30.86-36.34%) and Quercus pyrenaica Willd. forests (32.78-34.84%). All the tested approaches were valuable, but SS and GA performed better than CE and PM in most casesThe study was supported by the ForEadapt project ‘Knowledge exchange between Europe and America on forest growth models and optimization for adaptive forestry’ (PIRSES-GA-2010-269257). The authors thank (i) the foresters of the Extremadura Forest Service for assistance with data collection, (ii) the Portuguese Science Foundation (SFRH/BD/52408/2013) for funding the research activities of Juan Guerra and (iii) the Galician Government and European Social Fund (Official Journal of Galicia – DOG nº 52, 17/03/2014 p. 11343, exp: POS-A/2013/049) for funding the postdoctoral research stays of Eduardo González-Ferreiro and iv) the anonymous Reviewers of the European Journal of Remote Sensing for their helpful feedback. The research was carried out in the Centro de Estudos Florestais: a research unit funded by Fundação para a Ciência e a Tecnologia (Portugal) within UID/AGR/00239/2013.S

Comparing Johnson’s SB and Weibull Functions to Model the Diameter Distribution of Forest Plantations through ALS Data

[EN] The analysis of the diameter distribution is important for forest management since the knowledge of tree density and growing stock by diameter classes is essential to define management plans and to support operational decisions. The modeling of diameter distributions from airborne laser scanning (ALS) data has been performed through the two-parameterWeibull probability density function (PDF), but the more flexible PDF Johnson's SB has never been tested for this purpose until now. This study evaluated the performance of the Johnson's SB to predict the diameter distributions based on ALS data from two of the most common forest plantations in the northwest of the Iberian Peninsula (Eucalyptus globulus Labill. and Pinus radiata D. Don). The Weibull PDF was taken as a benchmark for the diameter distributions prediction and both PDFs were fitted with ALS data. The results show that the SB presented a comparable performance to the Weibull for both forest types. The SB presented a slightly better performance for the E. globulus, while theWeibull PDF had a small advantage when applied to the P. radiata data. The Johnson's SB PDF is more flexible but also more sensitive to possible errors arising from the higher number of stand variables needed for the estimation of the PDF parametersSIThis research was funded by the Forest Research Centre, a research Unit funded by Fundação para a Ciência e a Tecnologia I.P. (FCT), Portugal (grant number UID/AGR/00239/2019). The research activities of Diogo N. Cosenza were funded by the Portuguese Science Foundation (grant number PD/BD/128489/2017). The eucalyptus data used in this work were acquired under the framework of the PTDC/AGR-CFL/72380/2006 project (supported by the FCT under grant PTDC/AGR-CFL/72380/2006, co-financed by the European Fund of Regional Development (FEDER) through COMPETE–Operational Factors of Competitiveness Program, POFC). The pine data were acquired under the framework AGL2008-02259/FOR project (supported by the Spanish Ministry of Science and Innovation

Modelling stand biomass fractions in Galician Eucalyptus globulus plantations by use of different LiDAR pulse densities

[EN] Aims of study: To evaluate the potential use of canopy height and intensity distributions, determined by airborneLiDAR, for the estimation of crown, stem and aboveground biomass fractions.To assess the effects of a reduction in LiDAR pulse densities on model precision.Area of study: The study area is located in Galicia, NW Spain. The forests are representative of Eucalyptus globulusstands in NW Spain, characterized by low-intensity silvicultural treatments and by the presence of tall shrub.Material and methods: Linear, multiplicative power and exponential models were used to establish empiricalrelationships between field measurements and LiDAR metrics.A random selection of LiDAR returns and a comparison of the prediction errors by LiDAR pulse density factorwere performed to study a possible loss of fit in these models.Main results: Models showed similar goodness-of-fit statistics to those reported in the international literature. R2ranged from 0.52 to 0.75 for stand crown biomass, from 0.64 to 0.87 for stand stem biomass, and from 0.63 to 0.86for stand aboveground biomass. The RMSE/MEAN · 100 of the set of fitted models ranged from 17.4% to 28.4%.Models precision was essentially maintained when 87.5% of the original point cloud was reduced, i.e.a reductionfrom 4 pulses m–2to 0.5 pulses m–2.Research highlights: Considering the results of this study, the low-density LiDAR data that are released by theSpanish National Geographic Institute will be an excellent source of information for reducing the cost of forestinventoriesSIGalician Government, Xunta de Galicia, DirecciónXeral de Montes(09MRU022291PR); Norvento (Mul-tinational energy company) (PGIDT09REM023E);Galician Government, Dirección Xeral de Ordenacióne Calidade do Sistema Universitario de Galicia (Con-sellería de Educación e Ordenación Universitaria)and European Social Fund (Official Journal of Galicia –DOG nº 9, p. 2246, exp. 2011/14

Aplicación da tecnoloxía LiDAR na análise do medio físico

[GA] Impártense os coñecementos básicos necesarios para o estudo do medio físico, a través do tratamento dos datos capturados polo sensor activo LiDAR (Light Detection and Ranging) aerotransportado, xa que este sensor permite a captura de datos xeográficos dunha forma áxil e precisa, mentres que o tratamento dos seus datos permite a xeración de modelos que describen o terreo e os obxectos situados enriba del. Así na actualidade, a tecnoloxía LiDAR revelouse como a máis efectiva para a produción de Modelos Xeográficos de alta resolución e calidade

Modelling the vertical distribution of canopy fuel load using national forest inventory and low-density airbone laser scanning data

[EN] The fuel complex variables canopy bulk density and canopy base height are often used to predict crown fire initiation and spread. Direct measurement of these variables is impractical, and they are usually estimated indirectly by modelling. Recent advances in predicting crown fire behaviour require accurate estimates of the complete vertical distribution of canopy fuels. The objectives of the present study were to model the vertical profile of available canopy fuel in pine stands by using data from the Spanish national forest inventory plus lowdensity airborne laser scanning (ALS) metrics. In a first step, the vertical distribution of the canopy fuel load was modelled using the Weibull probability density function. In a second step, two different systems of models were fitted to estimate the canopy variables defining the vertical distributions; the first system related these variables to stand variables obtained in a field inventory, and the second system related the canopy variables to airborne laser scanning metrics. The models of each system were fitted simultaneously to compensate the effects of the inherent cross-model correlation between the canopy variables. Heteroscedasticity was also analyzed, but no correction in the fitting process was necessary. The estimated canopy fuel load profiles from field variables explained 84% and 86% of the variation in canopy fuel load for maritime pine and radiata pine respectively; whereas the estimated canopy fuel load profiles from ALS metrics explained 52% and 49% of the variation for the same species. The proposed models can be used to assess the effectiveness of different forest management alternatives for reducing crown fire hazardSIFunding was provided by projects DIABOLO (H2020 GA 633464) and GEPRIF (RTA 2014-00011-c06-04). The funders did not participate in designing the study, data collection and analysis, decision to publish or preparation of the manuscript. We are grateful to the Galician Government and European Social Fund (Official Journal of Galicia – DOG n° 52, 17/03/2014, p. 11343, exp: POS-A/2013/049) for financing the postdoctoral research stays of Dr Eduardo González-Ferreiro at different institutions. Copyright of LiDAR data, Instituto Geográfico Nacional-Xunta de Galici

Modelling the vertical distribution of canopy fuel load using national forest inventory and low-density airbone laser scanning data

The fuel complex variables canopy bulk density and canopy base height are often used to predict crown fire initiation and spread. Direct measurement of these variables is impractical, and they are usually estimated indirectly by modelling. Recent advances in predicting crown fire behaviour require accurate estimates of the complete vertical distribution of canopy fuels. The objectives of the present study were to model the vertical profile of available canopy fuel in pine stands by using data from the Spanish national forest inventory plus lowdensity airborne laser scanning (ALS) metrics. In a first step, the vertical distribution of the canopy fuel load was modelled using the Weibull probability density function. In a second step, two different systems of models were fitted to estimate the canopy variables defining the vertical distributions; the first system related these variables to stand variables obtained in a field inventory, and the second system related the canopy variables to airborne laser scanning metrics. The models of each system were fitted simultaneously to compensate the effects of the inherent cross-model correlation between the canopy variables. Heteroscedasticity was also analyzed, but no correction in the fitting process was necessary. The estimated canopy fuel load profiles from field variables explained 84% and 86% of the variation in canopy fuel load for maritime pine and radiata pine respectively; whereas the estimated canopy fuel load profiles from ALS metrics explained 52% and 49% of the variation for the same species. The proposed models can be used to assess the effectiveness of different forest management alternatives for reducing crown fire hazardWe are grateful to the Galician Government and European Social Fund (Official Journal of Galicia—DOG n° 52, 17/03/2014, p. 11343, exp: POS-A/2013/049) for financing the postdoctoral research stays of Dr Eduardo González-Ferreiro at different institutions. Copyright of LiDAR data, Instituto Geográfico Nacional-Xunta de GaliciaS

Estimación de la distribución vertical de combustibles finos del dosel de copas en masas de Pinus sylvestris empleando datos LiDAR de baja densidad

[ES] La altura de la base de la copa, la carga de combustible disponible y la densidad aparente son características estructurales del dosel de copas utilizadas para predecir la actividad de fuego de copas. La medición directa en campo de estas variables es impráctica y por tanto sus valores se estiman habitualmente mediante el empleo de modelos predictivos. Avances en la modelización del comportamiento del fuego hacen que sea de gran interés explorar la posibilidad de estimar de forma precisa y a escala de paisaje la distribución vertical de los combustibles en el dosel de copas. En este sentido, este estudio pretende analizar el potencial de los datos obtenidos de sensores LiDAR (Light Detection and Ranging) aerotransportados para modelizar dicha distribución vertical en masas de pino silvestre en Galicia. Para ello se usaron datos del vuelo LiDAR del PNOA (Plan Nacional de Ortofotografía Aérea) con una densidad de 0,5 primeros retornos m–2 y datos de campo procedentes del Cuarto Inventario Forestal Nacional (IFN4). En un primer paso, la distribución vertical fue caracterizada empleando la función de densidad de probabilidad de Weibull para, en un segundo paso, ajustar un sistema de ecuaciones que relacionan las variables del dosel con métricas derivadas de los datos LiDAR. Las ecuaciones se ajustaron simultáneamente para corregir los posibles problemas de correlación entre errores. Las distribuciones verticales finalmente estimadas explicaron el 41% de la variabilidad observada en las parcelas de estudio. El sistema de ecuaciones propuesto puede ser usado también para evaluar la efectividad de diferentes alternativas de gestión del combustible para reducir el riesgo de fuego de copa en rodales de pino silvestre[EN] Canopy fuel load, canopy bulk density and canopy base height are structural variables used to predict crown fire initiation and spread. Direct measurement of these variables is not functional, and they are usually estimated indirectly by modelling. Advances in fire behaviour modelling require accurate and landscape scale estimates of the complete vertical distribution of canopy fuels. The goal of the present study is to model the vertical profile of available canopy fuels in Scots pine stands by using data from the Spanish national forest inventory and low-density LiDAR data (0.5 first returns m–2) provided by Spanish PNOA project (Plan Nacional de Ortofotografía Aérea). In a first step, the vertical distribution of the canopy fuel load was modelled using the Weibull probability density function. In a second step, a system of models was fitted to relate the canopy variables to Lidar-derived metrics. Models were fitted simultaneously to compensate the effects of the inherent cross-model correlation between errors. Heteroscedasticity was also analyzed, but correction in the fitting process was not necessary. The estimated canopy fuel load profiles from LiDAR-derived metrics explained 41% of the variation in canopy fuel load in the analysed plots. The proposed models can be used to assess the effectiveness of different forest management alternatives for reducing crown fire hazardS