SUNConferences, New Frontiers in Forecasting Forests 2018

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SITE FORM AS INDICATOR OF SITE PRODUCTIVITY FOR EVEN-AGED STANDS: A CASE STUDY FOR PINUS RADIATA D. DON STANDS IN NORTH-WESTERN SPAIN
César Pérez-Cruzado, Juan Alberto Molina-Valero, Ulises Diéguez-Aranda, Juan Gabriel Álvarez-González, Fernando Castedo-Dorado

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Date: 2018-09-27 11:25 AM – 11:50 AM
Last modified: 2018-05-11

Abstract


Reliable estimates of site productivity are the basis for many ecological and forest management studies. Due to the difficulties of direct estimating site productivity, correlated indicators are used in practical applications, being those derived from estimates of stand height at a given age the most common (Skovsgaard and Vanclay, 2008). These indicators are known as site-index (SI) and has been considered as one of the most suitable indicators of site productivity for the management of even-aged stands (Rayner and Turner, 1987; Rayner, 1992). Nevertheless, the use of SI is confined to even-aged stands of known age, variable that is expensive to obtain in large-scale forest assessments and usually lacks from most National Forest Inventories (Moreno-Fernández et al, 2018). The site-form (SF) is an alternative index to SI derived from estimates of stand height at a given stand diameter (Vanckay and Herny, 1988, Vanclay, 1992, 1994), and has the advantage of being independent of age. In spite of the potential of SF to be applied for even-aged stands, the practical application of SF is mostly restricted to uneven-aged stands.

In this paper we developed models for SI and SF, and compare the performance of SF for characterizing the site productivity of even-aged monocultures of Pinus radiata D.Don plantations in north-western Spain.

The data used corresponds to a set of 158 permanent plots established between 1995-2003 in pure Pinus radiata D.Don stands in north-western Spain. These plots were re-measured between 2 and 5 times, and corresponds to sites without interventions in the studied period. More details about the data used can be found in Castedo-Dorado et al. (2007). The models shown in Table 1 were fitted to the data after comparing several base models, by using the nested iterative procedure described in Cieszewski and Bailey (2000) to obtain both the global and site specific parameters. The reference age and dominant diameter were set in both cases to 30 (years and cm, respectively).

The fitted models were used to estimate the values of SI and SF for every inventory in each plot, as well as the mean value per plot as the correspondent for the site-specific parameters of each plot. Then the values of SI and SF were standardized to 1 by using the maximum value of SI or SF across all plots, and the standard deviation of the SI and SF values computed for each plot. Correspondence in the ranked classification of the studied plots by SI and SF was tested with the Spearman’s test.  Similarities in the uncertainties in the determination of SI and SF for each plot were compared by correlation analysis between the SI and SF estimates for each plot.

Both models showed a good performance over the trajectories observed for each plot. It can be seen a more sloppy trend in the evolution of H0 for site-form models than for site-index, which is related with the ontogenetic phase of the studied stands. A Spearman’s rank correlation coefficient of 0.652 (p<2.2e-16) was observed for the values of SI and SF, which is a greater value than the observed by Fu et al. (2018) for natural uneven-aged forests. No significant differences were seen among the variability of the predicted SI and SF values for the two methodologies, tested by the Pearson’s correlation (ρ=0.672; p<2.2e-16). This shows a similar level of uncertainty in the determination of the index for both methodologies from a single assessment. Standardised values of SI and SF showed both a significant linear relationship with basal area increment for each plot, as previously observed by Vanclay (1988), which indicates that both indexes correlates with site productivity. The correlation of SF with other measured of site productivity was already seen in previous studies for natural stands (Vanclay and Herny, 1988).

Site-form and site-index models were developed for even-aged monocultures of Pinus radiata D.Don in north-western Spain. Site-form has seen to provide consistent estimates of site productivity for even-aged stands, with identical performance than site-index when stand productivity is expressed as the basal area growth. Both techniques showed comparable variability within plot estimates of the indices. This methodology can be used for large-scale monitoring exercises in areas with even-aged stands, when the direct determination of stand age is either not possible or impractical.


Keywords


stand model, age-independent model, compatibility

References


Castedo-Dorado, F., Diéguez-Aranda, U., Álvarez-González, J.G., 2007. A growth model for Pinus radiata D. Don stands in north-western Spain. Annals of Forest Science, 64, pp.453-465.

Cieszewski, C., Bailey, R.L.,  2000. Generalized Algebraic Difference Approach: Theory based derivation of dynamic site equations with polymorphism and variable asymptotes. Forest Science, 46 pp.116-126.

Fu, L., Lei, X., Sharma, R.P., Li, H., Zhu, G., Hong, L., You, L., Duan, G., Guo, H., Lei, Y.,  Li, Y., Tang, S., 2018. Comparing height–age and height–diameter modelling approaches for estimating site productivity of natural uneven-aged forests. Forestry, 00 pp.1-15.

Moreno-Fernándeza, D., Álvarez-González, J.G., Rodríguez-Soalleiro, R., Pasalodos-Tato, M., Cañellas, I., Montes, F., Díaz-Varela, E., Sánchez-González, M., Crecente-Campo, F., Álvarez-Álvarez, P., Barrio-Anta, M., Pérez-Cruzado, C., 2018. National-scale assessment of forest site productivity in Spain. Forest Ecology and Management. 417, pp.197-207.

Skovsgaard, J.P., Vanclay, J.K., 2008. Forest site productivity: a review of the evolution of dendrometric concepts for even-aged stands. Forestry, 81(1), pp.13-31.

Rayner, M.E., 1992. Evaluation of six site classifications for modelling timber yield of regrowth karri (Eucalyptus diversicolor F. Muell.). Forest Ecology and Management, 54, pp.315-336.

Rayner, M.E., Turner, B.J., 1990. Growth and yield modelling of Australian eucalypt forests II. Future trends. Australian Forestry, 53, pp.238-247.

Vanclay, J.K., 1988. A stand growth model for cypress pine. In: Leech, J.W., McMurtrie, R.E., West, P.W., Spencer, R.D, and Spencer, B.M., (Editors), Modelling Trees, Stands and Forests. Proceedings, Agugust 1985, University of Melbourne, School of Forestry, 5 pp.310-332.

Vanclay, J.K., 1992 Assessing site productivity in tropical moist forests. Forest Ecology and Management, 54, pp.257-287.

Vanclay, J.K., 1994. Modelling Forest Growth and Yield: Applications to Mixed Tropical Forests. CAB International, Wallingford.

Vanclay, J.K., Henry, N.B., 1988. Assessing site productivity of indigenous cypress pine forest in southern Queensland. Commonwealth Forestry Review, 67, pp.53-64.

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