Jenkins, T. A. R.

Mayhead, G. J.

Subasinghe, S. M. C. U. P.

University of Sri Jayewardenepura: Journals & Proceedings

PREDICTION OF INDIVIDUAL TREE DIAMETERS OF Pinus nigra var.maritima (Ait.) Melville (CORSICAN PINE)S M CUP Subasinghe!, TAR Jenkins2 and G J Mayhead21Department of Forestry & Environmental Science, Univeristy of Sri Jayewardenepura2School of Agricultural and Forest Sciences, university of Wales Bangor, UKA growth model to predict the future diameter at breast height of Corsican pinetrees was constructed using easily measurable explanatory variables. For thiswork it was assumed that future growth of individual tree diameter at breastheight Cdbh, + /).t ) can be predicted as a function of current dbh (dbhl), currentage (al), age at the time prediction is required (at + /).t ), current stand density (dl)and quality of the site (s) as in the equation I.dbht+/).t = f (dbht, at, at+/).1'd., s)Repeated measurement data of permanent sample sample plots over a long periodwere obtained from the Forestry Commission in Great Britain. These plots weremaintained under two thinning types i.e. intermediate and neutral. First the datawere divided by the thinning type and each thinning type was divided by thethinning type and each thinning type was divided again as working (3/4) andvalidating (1/4) data.In order to reduce the number of variables, the time difference between thebeginning and end of the simulation period (ad;) was used for the age factor. Fourfactors i.e., top height, top height/age, total basal area/age and top height/totalbasal area were used to represent the site quality. Suitable transformations were2used for all the cadidate variables in order to obtain the best medel. R , residualdistribution, average model bias, mean absolute difference and modellingefficiency were tested for the evaluation purpose.When tested, stand density was not significant and the best site factor was thetotal basal area/age. The finally selected equations were as below.Intermediate thinning:~dbht+/).t = 1.014~db~ +O.059site +O.004aJif 2Neutral thinning:~db~+/).t = 1.050~db~ - O.059site +O.005aJif 3When there is little difference in age, adi! ~ 0 and site factor can be ignoredbecause it dies not change when age difference is zero. In such a situation,~db~+/).t == ~db~ and therefore the parameter associated with ~db~ mustnot be significantly different from one. However, this condition was not fulfilledby above models and a new set of parameters were estimated forcing thatparameter to be one. The test results for the models with new parameters indicatedthat there was no bias and the modelling efficiency was 0.99 for both thinningtypes. The validation procedure indicated that the models were adequate. Thefinal models are given in equation 4 and 5.Proceedings of the Sixth Annual Forestry and Environment Symposium 2000 EJ3of the Department of Forestry and Environmental ScienceUniversity of Sri Jayewardenepura, Sri Lanka

PREDICTION OF INDIVIDUAL TREE DIAMETERS OF Pinus nigra var. maritima (Ait.) Melville (CORSICAN PINE)

http://journals.sjp.ac.lk/index.php/fesympo/article/download/1442/615

PREDICTION OF INDIVIDUAL TREE DIAMETERS OF Pinus nigra var. maritima (Ait.) Melville (CORSICAN PINE)

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University of Sri Jayewardenepura: Journals & Proceedings