Aboveground Live and Dead Biomass Distribution Using Allometric Equation in the Restored Mines of the PPC’s Western Macedonia Lignite Center

Abstract

Forests and forest plantations rank first in storing carbon and play a substantial role in climate change mitigation. Assimilated carbon is stored in the above- and belowground parts of trees, in dead wood, in litter, and in soil. The Greek power generation and supply company PPC S.A. started environmental rehabilitation projects to rehabilitate restored areas after the end of exploitation at the open-cast lignite mines of the Lignite Center of Western Macedonia in the 1980s by planting different tree species, mainly black locust. Today some of these plantations are almost 40 years old and occupy 2,200 ha in total. The dominant planted species is black locust (Robinia pseudoacacia L.), a fast-growing pioneer species, covering 95% of the planted area. Other planted species are Spartium junceum and Cupressus arizonica, covering 2.45% and 1.44%, respectively. The aim of this study was to measure and estimate the live and dead aboveground biomass distribution across the planted sites in the restored waste dumps of Amyntaio and Ptolemaida lignite mines. A total of 215 sample plots of 100 m2 each were set up through systematic sampling at a grid dimension of 500 × 500 m. In each sample plot, the tree species (dbh (cm)), tree height, and height to live crown (m) were recorded for all trees. The aboveground biomass was estimated using an exponential allometric model. The results show that in the tree-planted restored areas of the Amyntaio mine, the aboveground biomass ranges from 20.1 to 90.2 tn ha−1, and in that of the Ptolemaida mine from 11.6 to 75.8 tn ha−1. The spatial biomass distribution seems to show a trend of increase from southeast to northwest in Ptolemaida and from west to north in the Amyntaio mine. The standing dead wood ranges from 0 to 19.8 tn ha−1 for Amyntaio and 0 to 41.9 tn ha−1 for the Ptolemaida mine, and the lying dead wood from 0.5 to 19.5 ha−1 and 0.5 to 66 m3 ha−1, respectively. The overall decay degree that was classified into quality classes from 1 to 5 ranges as: 10% for decay class (1), 27% for decay class (2), 45% for decay class (3), 17% for decay class (4), and 1% for decay class (5). The black locust shows a remarkable ability to survive and grow on disturbed sites, such as the restored mines in the Lignite Center of Western Macedonia. It is very competitive compared with other planted species and has created the necessary forest environment for the natural regeneration of other more shade-tolerant and soil-demanding species, such as oaks and maples.