Assessing site form as an indicator of site quality in even-aged Pinus radiata D. Don stands in north-western Spain

Abstract

& Key message Site form and site index have shown similar precision for estimating site quality in even-aged Pinus radiata D. Don stands in northwestern Spain. Additionally, SF presents the advantage that it does not require stand age information and can therefore be used in a wider set of situations in the forestry practice. & Context Estimation of site quality is essential for characterizing, monitoring and predicting forest resources. Site index (i.e. the dominant height of the stand at a reference age) is ordinarily used to estimate site quality; however, this index is only useful for even-aged stands of known age. By contrast, SF is age-independent as it uses the dominant height of the stand at a reference dominant diameter. & Aims The aim of this study was to compare the performance of SF and SI for site quality estimation in even-aged P. radiata stands. & Methods Dynamic equations derived with the Generalized Algebraic Difference Approach (GADA) from the Hossfeld IV base model were fitted to predict site quality with both SI and SF. SF predictions were compared with SI regarding variability within the same plot and consistency in site quality predictions, using the observed maximum mean annual volume increment (MAI) as a direct measure of site quality.

Evaluation of the Site Form as a Site Productive Indicator in Temperate Uneven-Aged Multispecies Forests in Durango, Mexico

“…Likewise, Fu et al [ 12 ] used ADA to test the SF MH-MD in two natural uneven-aged forests of Larix Olgensis Henry and Quercus Mongolica Fisch in northeastern China, which showed correlation coefficients of 0.55 and 0.79. On the other hand, Molina-Valero et al [ 13 ] reported a correlation of 0.71 in Pinus radiata D. Don even-aged stands in the north of Spain using GADA to test the SF MH-MD . Therefore, the effectiveness of the SF may vary based on the model used and the type of forest evaluated.…”

“…In addition to this, the SF has also been called the site productivity index [ 11 ]. It has been successfully used as an indicator of productivity in uneven-aged stands [ 12 ] and has delivered meaningful results in even-aged forests [ 13 ]. Nonetheless, the main feature of SF is its capacity to describe site quality in uneven-aged multispecies forests [ 14 ].…”

“…The assessment of the usefulness of the SF as a measure of productivity has been carried out through different methods. For instance, the SF as the average H at a specific reference D (SF H-D ) [ 10 ], as the expected mean H (MH) at a reference mean D (MD) (SF MH-MD ) [ 12 , 13 ], and as the tree height (h) at a reference diameter at breast height (dbh) estimated using a specific h-dbh model for a given site plot (SF h-dbh ) [ 14 ]. Nevertheless, there is no documentation about their comparison, and the results therefore may vary despite being based on the same assumption.…”

Modeling Above-Ground Carbon Dynamics under Different Silvicultural Treatments on the McDonald–Dunn Research Forest

“…Site index measures stand productivity based on the height of dominant or co-dominant trees at a given reference age, usually 50 years, and is often expressed in feet or meters [24,25]. Dominant or co-dominant trees are used to assess site productivity because it is assumed that their height growth has not been impacted by stand density [26]. Site index is theorized to be a function of topographic variables, such as aspect and elevation, together with soil characteristics, such as soil type and fertility, and climatic variables, such as annual precipitation and maximum summer temperatures [27].…”

Exploring new frontiers in forecasting forest growth, yield and wood property variation

“…In any projection-based approach to predicting future yield, a quantitative understanding of site quality, or the inherent potential of a site to support forest growth, is an essential component of the modelling system. Molina-Valero et al (2019) tackled the problem by considering the potential of the lesser-used "Site Form" (SF) as compared to much more widely utilised estimates of "Site Index" (SI). They showed that the two methods gave comparable overall accuracy and, given that SF does not require information on stand age, further research considering this lesser-used approach seems worthwhile.…”