The decline of cypress forests: can a natural experiment be used as a tool to design partial cutting regimes for the regeneration of cypress forests?

AMOROSO, MARIANO; LARSON, BRUCE

Shizuoka, Japón

Workshop; Workshop of "uneven-aged silviculture" in Shizuoka - Feasibility of Silviculture for Complex Stand Structures: Designing Stand Structures for Sustainability and Multiple Objectives.; 2008

International Union of Forest Research Organizations

The forests of Austrocedrus chilensis (cordilleran cypress) in Argentina suffer mortality from what is locally known as ‘‘Mal del Cipres”. This spatially erratic process of overstory mortality, referred by several authors as a forest decline, has been going on for the past 60 years. At the stand level, it usually appears as aggregations of varying sizes as well as disaggregated. Symptoms at the tree level often include a decline in radial growth, loss of foliage and vigour followed by death. The highly variable mortality rates results in a natural experiment that allows the comparison of overstory mortality with regeneration rate. This comparison should then make it possible to estimate the regeneration success which would follow after different levels of partial cutting. We collected data to study the stand development patterns in declining stands. We used 8 plots in 4 cypress dominated stands where we reconstructed mortality and regeneration for the past 60 years.  The data was then separated both temporally and spatially to develop measures of mortality and regeneration rates.  Regeneration rate was considered for A. chilensis, Nothofagus dombeyi, and the combination of both species.  In this way regeneration success could be expressed for either species alone or the stand as a whole depending on management objectives. The results of this analysis were then used to consider three scenarios: I. partial cutting without decline; II. partial cutting with decline; III. decline with no partial cutting.  Current management practices follow scenario III (decline with only salvage cutting).  Regeneration is highly variable depending on the degree of decline related mortality.  Use of partial cutting allows the purposeful direction of the regeneration process.  Examples are given on how the regeneration of a future stand might have been different with purposeful management. Cypress decline means that these stands will become unevenage. Management prescriptions can be designed by understanding the factors that control the species composition of the future unevenage stands (e.g. cutting levels and silvic characteristics of the species).