Assessment of the Carbon Stock in Pine Plantations in Southern Spain through ALS Data and K-Nearest Neighbor Algorithm Based Models

Abstract

Accurate estimation of forest biomass to enable the mapping of forest C stocks over large areas is of considerable interest nowadays. Airborne laser scanning (ALS) systems bring a new perspective to forest inventories and subsequent biomass estimation. The objective of this research was to combine growth models used to update old inventory data to a reference year, low-density ALS data, and k-nearest neighbor (kNN) algorithm Random Forest to conduct biomass inventories aimed at estimating the C sequestration capacity in large Pinus plantations. We obtained a C stock in biomass (W t -S) of 12.57 Mg·ha −1 , ranging significantly from 19.93 Mg·ha −1 for P. halepensis to 49.05 Mg·ha −1 for P. nigra, and a soil organic C stock of the composite soil samples (0-40 cm) ranging from 20.41 Mg·ha −1 in P. sylvestris to 37.32 Mg·ha −1 in P. halepensis. When generalizing these data to the whole area, we obtained an overall C-stock value of 48.01 MgC·ha −1 , ranging from 23.96 MgC·ha −1 for P. halepensis to 58.09 MgC·ha −1 for P. nigra. Considering the mean value of the on-site C stock, the study area sustains 1,289,604 Mg per hectare (corresponding to 4,732,869 Mg CO 2 ), with a net increase of 4.79 Mg·ha −1 ·year −1 . Such C cartography can help forest managers to improve forest silviculture with regard to C sequestration and, thus, climate change mitigation.In addition to biomass, C is also stored in litter and forest soils. In fact, soils are the largest reservoir of terrestrial C, for both organic and inorganic forms [6]. Soil organic carbon (SOC) can be stored in soils for thousands of years under, suitable conditions, and is a vital component of plant nutrient cycles [7]. Forest management aimed at increasing stand growth has been shown to be effective in increasing the C sequestration capacity [8,9]. Thinning treatments improve health and tree vigor, increasing forest productivity [10], while the soil C content shows a slight decrease in the first stages, recovering its level and increasing once the canopy is restored [11].Accurate estimation of forest biomass to produce spatially explicit mapping of forest C stocks over large study areas is of considerable interest nowadays [12]. In this regard, the field-based inventory is the most common method for evaluating the dendrometric characteristics and stand dynamics of forests. These classic forest inventories have a high demand for labor, are expensive, and require lots of field plots to obtain full inventory data for large areas on the ground [13,14]. Thus, with the advances in remote sensing techniques, these traditional methods are being replaced or supplemented with Light Detection and Ranging (LiDAR) techniques, which provide stand data over large areas, optimizing time and costs. LiDAR technology brings a new perspective to forest inventories by directly providing three-dimensional information on the entire surface [12].LiDAR (Laser Imaging Detection and Ranging) systems from an airborne platform (airborne laser scanning, ALS) are equipped with a scanning device th...

Improving WRF-Fire Wildfire Simulation Accuracy Using SAR and Time Series of Satellite-Based Vegetation Indices

“…AGB values of the woody vegetation fuel type from the CCI biomass product [39] were similar to those reported in studies conducted in Mediterranean forests in Spain [57,58] and Northern Israel [32]. These values are much higher than the AGB values of the 13 fuel-type model that was developed for the Mediterranean climate of California [26,28] and that is used in the Israeli operational WRF-Fire forecasting system.…”

Carbon Sequestration in Carob (Ceratonia siliqua L.) Plantations under the EU Afforestation Program in Southern Spain Using Low-Density Aerial Laser Scanning (ALS) Data

“…The final maps of C stocks (biomass and SOC) are crucial for the assessment of land-use changes and greenhouse gas emission balances. However, few studies have mapped C stocks at Mediterranean forest plantations on agricultural lands in Europe (see, [33]) from LiDAR data. The development of C prediction models would be based on regional equations, opening many alternatives to ALS data to estimate the C stock in Mediterranean forest plantations at affordable costs and with good accuracy.…”

“…In the last decade, the use of airborne laser scanning (ALS) data has provided high-precision dasometric information on forest stands, improving above-ground biomass (AGB) [30]. Many studies have provided methodologies to integrate tree allometric models with LiDAR data to estimate the C stock of forest plantations [23,[31][32][33]. However, despite these recent contributions, there is still a gap in the knowledge about the estimation of biomass accumulation and carbon sequestration at a species-specific scale for afforestation activities in Mediterranean environments.…”

Carbon Sequestration in Resin-Tapped Slash Pine (Pinus elliottii Engelm.) Subtropical Plantations

“…Over the past years, several carbon sequestration estimates have been performed in pine forests growing in temperate, boreal, and Mediterranean Zones. Most of them were carried out based on models built up from biomass allometric regression equations or modeling predictions that might rely on previous local forest information such as inventories data [2,4,6,7,[22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] and laser-scanning-based approaches [40,41].…”