Analysis of Terrain and Stand Characteristics as a Basis for Planning Operations of Timber Harvesting and Forest Accessibility

Istraživane su terenske i sastojinske prilike gospodarskih državnih i privatnih šuma iz dostupnih prostornih podataka koje će potom omogućiti stvaranje osnovice za razredbu terena za potrebe pridobivanja drva i otvaranja šuma. S gledišta pridobivanja drva te kao gospodarski najznačajnije šume izdvojena su i prikazana četiri bioklimata: 1) bioklimat jelovih, bukovo-jelovih i smrekovih šuma, 2) bioklimat brdskih bukovih šuma, 3) bioklimat bežuljkastih šuma hrasta kitnjaka te 4) bioklimat nizinskih šuma hrasta lužnjaka i poplavnih šuma. Na tim su područjima određene ove terenske i sastojinske značajke: 1) nagib terena i stjenovitost tla (pokrivenost površine), 2) način vlaženja tla i rizik od erozije tla vodom, 3) drvna zaliha, 4) stupanj razvedenosti šumskih cesta i 5) srednja udaljenost privlačenja drva kao pokazatelj otvorenosti šuma. Provedene analize mreže šumskih cesta pokazale su da postoji statistički značajna razlika između cesta bioklimata nizinskih šuma hrasta lužnjaka i poplavnih šuma te bioklimata brežuljkastih šuma hrasta kitnjaka u odnosu na ostale bioklimate. Analize šumskih cesta po pojedinom bioklimatu treba promatrati u sklopu ostalih terenskih čimbenika, kao što su stjenovitost terena te stvarnoga rizika od erozije tla vodom, koji će svoj utjecaj, uz nagib terena, iskazati pri planiranju budućih trasa šumskih cesta. Povezivanjem značajki terena započeto je stvaranje primjenjive razredbe terena za uvjete hrvatskoga šumarstva kao važnoga logičkoga alatu pri gospodarenju šumama i planiranju radova u šumarstvu, osobito u pridobivanju drva i otvaranju šuma.

Characterization of Diameter Distribution and Prediction of Weibull Parameters Equation for Plantation-grown Eucalyptus Species

Aim: To characterization of the diameter distribution and prediction of Weibull parameters of a plantation-grown Eucalyptus species. Study design: Stratified sampling method was adopted, in which the plantation was stratified into four age series. Place and duration of study: Afaka Forest Reserve, one month. Methodology: Fifty (50) sample plots of 20 x 20 m were laid across the age series. In each of the plot, all the trees were counted and data of variable of interest was collected and processed. A separate Weibull distribution is fitted to the diameter at breast height (dbh) frequency data from each of the plot for the estimation of Weibull parameters (location, scale and shape). The data set obtained from the Weibull parameter estimate was then used to develop regression equations with the stand variables. Coefficient of Determination (R2) and Root Mean Square Error (RMSE) was used as goodness of fit test. Results: The result on the stand characteristics revealed that, the mean diameter at breast height (dbh) ranges between 13.4 – 18.2 cm across the four stands. This indicates that the species are still of pole sizes. The average site productivity of the species ranges between 24.0 m to 37 m at an index of 25 years. The mean Basal area varies between 14.13 to 26.85 m2 per ha, while the average tree total height ranges between 24.6 to 28.2 m across the four species. The result on diameter class distribution shows that most of the species fell within dbh class of 11 -20 cm class except E. cloeziana in which the highest frequency fell into 16 – 20cm dbh class. Best equation were selected for each of the Weibull parameters (α, β, ) per species based on fit statistics. The formation of straight line pattern from the plotted normal probability plots indicates the adequacy of the selected models for predicting Weibull parameters. A fluctuation pattern exists between the Weibull parameters and the stand characteristics. this may be due to variation in climatic factor, most especially fluctuations in rainfall pattern in the area at that particular period. Conclusion: The ease of fit and high value of coefficient of determination of the models in this study has re-affirmed the use of Weibull parameter in prediction of stand characteristics as been suggested by many authors in the literature.