Simplified methods to inventory the current annual increment of forest standing volume

摘要

The assessment of the current annual increment of forest standing volume(CAI) is a fundamental tool to support forest management and planning. A suitableapproach to such an end is to rely on growth and yield models. However,this kind of models are often not available for many countries and/or locationsand/or species. Furthermore, they may become obsolete due to potentialchanges in the environmental and silvicultural conditions. Such shortcomingsmay be distinctively detrimental in the context of forest inventories. Severalmethods have been proposed to inventory CAI on one single occasion, i.e.,when repeated measurements of standing volume are not available. A wellknownfamily of methods, still largely exploited in Alpine and EasternEuropean countries, derives from the estimation of the percentage current annualincrement of forest standing volume by the current annual increments ofstem diameter and tree height (Δh). In this study an experimental comparisonof Δh assessment by three different approaches is presented with reference toa properly designed case study: (i) Δh is measured on felled trees; (ii) Δh is estimatedby dynamic height curve (i.e., diameter-height-age model); (iii) Δh isestimated by conventional height curve (i.e., diameter-height model). Underthe examined experimental conditions (a pure forest of silver fir on highly fertilesoils in southern Italy, aged around 60 years), both simplified approaches(ii) and (iii) have proven to underestimate height increments, with a larger underestimationby the approach based on the conventional height curve. However,the consequent error in the estimation of percentage current annual incrementof forest standing volume has proved to be quite limited (4% for theapproach based on the dynamic height curve and around 9% for the approachbased on the conventional height curve). Hence, such simplified approachesmay be rather safely considered for estimating percentage current annual incrementof forest standing volume when neither Δh is directly detectable onstanding trees nor sample trees can be felled, nor an appropriate model topredict Δh is available. The Δh estimation on the conventional height curveshould turn out to be even more suitable in the case of uneven-aged stands,where the position of the height curve remains stationary over time.