Forest@ (May 2012)
Tree biomass and deadwood density into aged holm oak (Sardinia) and beech coppices (Tuscany)
Abstract
Current National Forest Inventory highlight the further increase over the last two decades of coppice area under the position of mature standing crop or in the post-cultivation phase, both being developed throughout the original cultivation area. This pattern, mainly due to the unprofitable fuel wood harvesting, also involved holm oak and beech forests, some of the most diffused forest covers in Sardinia, along the Apennines and pre-Alps. The alternative management option to ageing (the pro-active way of coppice conversion into high forest) has been also practiced in the public domain, but on much smaller areas as compared with those undergoing post-cultivation phase. Aged coppices located into medium-good site classes showed a positive growth pattern resulting in a high, age-related, wood matter storage. At the meantime, regular mortality occurring since former rotation into the fully-stocked shoot populations, stocked up high deadwood amounts, this becoming an outstanding attribute of these types. Carbon storage is becoming one of the major tasks attributable to these systems within the post-cultivation phase. Purposes are here to: (i) estimate living woody and standing + lying deadwood mass densities; (ii) determine deadwood/living mass ratio; (iii) verify lying deadwood decay class; (iv) analyse diversity between two sites aged likewise but different as for geographical location and tree species. A holm oak coppice aged 55 in Sardinia and a beech coppice aged 57 in Tuscany were selected at the purpose. Both stands have been developing the post-cultivation phase since two-three times the traditional rotation and represent the maximum ages in this position. Living and standing dead woody dry mass density were determined in each site by specific allometric functions. Lying deadwood amount was assessed by a sampling design covering systematically the full test area. Three decay classes were determined according to Hunter (modified). The tree species, both shade-tolerant, showed a similar pattern as for time of wood formation and its transfer to deadwood, as well. The main difference consists only in their evergreen and deciduous habit. Auto-ecology seems to be the main driver of stand development as for carrying capacity, mortality rate and survival time into the overstocked stand structures. Leaf standing mass and leaf /thin branches ratio are two and three times higher in holm oak, consistently with its biology. Living woody mass density is made basically by stem and thick branches (88%) and varies from 322 Mg ha-1 (beech) to 225 Mg ha-1 (holm oak). Deadwood amount ranges from 28 to 25 Mg ha-1 i.e., from 9 to 11% of living woody mass. Standing deadwood is 70 to 73% of total amount. As for lying material, the intermediate decay class is prevailing: 74%, (beech) and 66% (holm oak). Both dynamics and age-related data suggest the active role these types may play in soil conservation, improvement of forest quality and carbon storage. The need of a consistent monitoring of the further post-cultivation progress is finally stressed to recognize driving forces acting, the onset of possible limiting factors and feedbacks.
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