Abstract
The occurrence of old-growth forests is quite limited in Mediterranean islands, which have been subject to particularly pronounced human impacts. Little is known about the carbon stocks of such peculiar ecosystems compared with different stages of secondary succession. We investigated the carbon variation in aboveground woody biomass, in litter and soil, and the nitrogen variation in litter and soil, in a 100 years long secondary succession in Mediterranean ecosystems. A vineyard, three stages of plant succession (high maquis, maquis-forest, and forest-maquis), and an old growth forest were compared. Soil samples at two soil depths (0–15 and 15–30 cm), and two litter types, relatively undecomposed and partly decomposed, were collected. Carbon stock in aboveground woody biomass increased from 6 Mg ha-1 in the vineyard to 105 Mg ha-1 in old growth forest. Along the secondary succession, soil carbon considerably increased from about 33 Mg ha-1 in the vineyard to about 69 Mg ha-1 in old growth forest. Soil nitrogen has more than doubled, ranging from 4.1 Mg ha-1 in the vineyard to 8.8 Mg ha-1 in old growth forest. Both soil parameters were found to be affected by successional stage and soil depth but not by their interaction. While the C/N ratio in the soil remained relatively constant during the succession, the C/N ratio of the litter strongly decreased, probably following the progressive increase in the holm oak contribution. While carbon content in litter decreased along the succession, nitrogen content slightly increased. Overall, carbon stock in aboveground woody biomass, litter and soil increased from about 48 Mg ha-1 in the vineyard to about 198 Mg ha-1 in old growth forest. The results of this study indicate that, even in Mediterranean environments, considerable amounts of carbon may be stored through secondary succession processes up to old growth forest.
Highlights
Carbon storage in old growth forestsForests in the Mediterranean basin have been subject to millennial human exploitation, which deeply modified and simplified their composition, structure, functioning and the ability to provide ecosystem services [1,2]
We studied and compared a vineyard (VIN), three successional stages differing in time since abandonment, that is high maquis (HMA: 0–45 years), maquis-forest (MAF: 45–70 years), and forest-maquis (FOM: 70–100 years), and an old-growth forest (OGF: > 105 years) (Fig 1)
Trees were sampled at breast height because coring at ground level is more physically difficult and it is not assured to reach the pith in hardwoods like holm oak
Summary
Carbon storage in old growth forestsForests in the Mediterranean basin have been subject to millennial human exploitation, which deeply modified and simplified their composition, structure, functioning and the ability to provide ecosystem services [1,2]. The ageing without significant human impact is the necessary condition to allow a forest stand to reach an old-growth status in terms of structure, living biomass, deadwood traits and biological diversity [5]. Very few studies have been carried out in potentially old-growth Mediterranean oak forests [11,12], including Italy, where the identified OGFs, mostly beech stands, are estimated to cover about 160,000 ha [13]. They are likely to be rare, some oak OGF has been reported and investigated in the last few years [14]. Very little is known about the carbon stocks and belowground pools of these unique ecosystems
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