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Consequence of the use of Non-Linear function in this study, which is believed to be in harmonic with the characteristics of tree stand, twelve trees were selected which represents different location over an area planted with Populus nigra trees ,and after data analysis of variable values , three mathematical equations were obtains which link the yield per area ,a dependent variable and age ,mean height of stand quadratic mean diameter as the independent variable , in order to obtain yield table of revocable densities for Populus nigra , selecting the best model , different measures of precision , such as , coefficient of determination, standard error of estimate and residual analysis test, so following regressions selected : Y= 4.1356 G1.12355 R2= 0.9796 S.E=1.8 Y= 0.12788H2.27 R2= 0.913 S.E=3.54 Y= -0.64168+0.34744A2+0.063183Dq2.4 R2= 0.9674 S.E=2.29 Since there are good values of precision measures , so we will be able to use equations to prepare yield table at different densities of Populus nigra stands in Nineveh, depending on mean height or basal area per hectare or for age and quadratic mean. Nineveh.

Many mathematical function were used to estimate tapering degree of Populus nigra main stem tree in Zakho . 35 sample obtained thought stand classification and according to there density using strata randomized sampling method . Each sample area was 0.01 hectare .To record all changes that affect longitudinal and diametrical growth , one tree was chosen from each sample area , and all tree morphological dimension were recorded , in addition to distance between the trees . The chosen trees were felled and cuted into different parts at one meter length from ground level to 4 cm stem diameter . By using simple linear regression , four mathematical Models were established. In order to find the best fit model for these four Models , coefficient of determination, standard error of estimate were used and the following model give the best result d0 = b0+b1 cw (b2 (-b3hi) ) R2=0.87 S.E%=0.6369 By using above model , tapering tables was prepared for Populus nigra trees grown in Zakho at different stand density . By using this table a desired management decision can be chosen which can be suitable for the harvesting plan.