Silvicultural and phytosanitary researches in thinned chestnut coppices at different elevations in Sila (Calabria)

Abstract

The results of mensurational and phytosanitary researches ten years after thinning trials in chestnut coppices (Castanea sativa Miller) in Sila, are reported.. Eight experimental areas, four located at an average elevation of 1200 m a.s.l. aged 20 yrs and four located on average at 1050 m a.s.l. aged 13 yrs, were compared. Three sub-plots were installed in each area and mensurational and phytosanitary surveys were carried out in 1997 (before and after thinning trials) and ten years later (2007) on 30 stools per sub-plot to assess bio-ecological, structural and compositional status of the standing crops. At each elevation, the experimental protocol included the following theses: thesis T (control: release of the standing crop and removal of dried up stems on the ground, only); thesis A (light thinning: removal of the dominated storey, on average 30% of coppice shoots, poorly shaped, both withered and green); thesis B (moderate thinning: removal from the dominated up to the dominant storey = 43% of the shoots, both dried up and green); thesis C (heavy thinning: removal = 62% of coppice shoots, both withered and green). Results highlighted the significance of thinnings in the cultivation of chestnut coppices. As for silviculture and growth pattern, the surveying ten years later showed the following outcomes: reduction of shoots mortality, according to the thinning intensity from A to C (by comparing the number of dried up coppice shoots surveyed in the control theses); a higher number of coppice shoots in the commercial category “average stems” in the thinned plots; the higher percentage increment in dbh, basal area and volume in the sub-plots undergoing thinning A and C at the elevation of 1050 m and, in general, with thesis C at both elevations; the complete recovery of canopy cover even in the sub-plots heavily thinned. As for the phytosanitary aspects, the research has been oriented on the chestnut blight caused by Cryphonectria parasitica, due to the lack of symptomatology of “ink disease” in the sub-plots, even though present on the same territory. The hypovirulence is predominant and steady with time for the high presence of healing and healed cankers. Among the factors of coppice shoots mortality, blight plays a minor role here. The disease spreads regardless of thinnings and silviculture can operate therefore independently to get a wide range of assortments, from poles to timber. Basically, thinning release has to ensure the predominance and steady presence of hypovirulence in the chestnut stands. In this way, foci for the natural spreading of hypovirulent strains are being created and preserved. This seem to be a basic tool to ensure a phytosanitary equilibrium between the parasite and the host in chestnut coppices, which still represent an important economic resource in Calabria as well as in several other Italian regions.