Primerjava različnih regresijskih modelov za napovedovanje debelinskega priraščanja jelke

We present seven alternative statistical models for modelling tree diameter increment with data from permanent sampling plots. In addition to the polynomial regression model, we present a regression model with added random noise, a mixed linear model, regression with natural splines, and three models with limited dependent variables: truncated regression, tobit regression and grouped data regression. The models may be used when dealing with truncated or censored variables, biased estimation of the increment due to censoring and rounding down, or when having multilevel data. The parametrization of the models was done using 21,013 fir trees on 4,405 plots in the period 1990–2014 in uneven-aged Dinaric fir-beech forests. All models showed a similar effect of tree diameter, stand basal area, basal area of larger trees, diameter structure diversity, altitude and slope. There were only minor differences in the regression coefficients and fit measures. The highest increment predictions were given by the tobit model. The mixed model fit the data best and, compared to the other models, predicted a slower decrease in the growth of large-diameter trees after growth culmination.

Evaluating the Accuracy of Remote Dendrometers in Tree Diameter Measurements at Breast Height

An accurate tree diameter (DBH) measurement is a significant component of forest inventory. This study assessed the reliability of remote dendrometers to measure tree DBH. We compared direct caliper measurements (reference measurements) to the remote measurements collected from a laser caliper and a smartphone at 0.5 m, 1 m, and 1.5 m distances from each tree within three forest types (pine, oak, and poplar forests). In general, all remote dendrometers underestimated the mean diameter compared to direct caliper measurements, regardless of forest types and distances. We observed that the mean deviation of direct caliper measurement and smartphone measurement at 1.5 m within a pine forest and oak forest were the lowest (0.3 cm and 0.36 cm, respectively). The deviations between direct caliper measurements and smartphone measurements at a 0.5 m distance, across forest types, were noticeably larger compared to others. An ANOVA test was used to determine whether significant deviations existed between caliper measurements and remote measurements at a specific distance, and among three different forest types. We rejected the null hypothesis, which suggested that there were no statistically significant differences (p<0.05) between tree DBH measurements obtained from the direct caliper measurements and indirect measurements (smartphone and laser caliper) captured at a distance. Then, a post-hoc test was performed to examine which set of estimated deviations was different from the reference data. The results suggested that indirect tree DBH measurements using the smartphone app at 1 m and 1.5 m in certain forest types (pine and oak) were not significantly different from direct tree DBH measurements. Also, our test results mostly indicated no significant difference within each forest, except for measurements using the smartphone app at 0.5 m across all forest types when the smartphone measurements were compared to laser caliper measurements. Although forest characteristics and measurement distance may play an important role in remote tree DBH measurement accuracy, the smartphone app may be used as a practical alternative to direct measurement in measuring the DBH of a tree, which may be a positive development for forestry due to the increased use of smartphones and the availability of a free measure app.

Gum Arabic Production and Population Status of Senegalia senegal (L.) Britton in Dryland Forests in South Omo Zone, Ethiopia

Senegalia senegal (L.) Britton is a multi-purpose dryland tree species that produces gum arabic, a commercially valuable product. However, this resource is underused in Ethiopian dryland areas. The aim of this study was to evaluate the population status and potential gum yield of S. senegal growing in natural stands in South Omo Zone, Ethiopia. Forty-five sample plots, each measuring 20 × 20 m, were established at 500 m intervals along transects, with 1 m2 subplots located within the main plots to determine regeneration. S. senegal trees with a diameter at breast height of between 2 and 12 cm were most prevalent. Forty-two tree species were associated with S. senegal, of which 16 were gum- and resin-producing species. S. senegal was positively associated with Vachellia tortilis, Senegalia mellifera, Vachellia nilotica, Commiphora edulis, and Dobera glabra. Senegalia senegal comprised approximately 35% of regenerating trees. The maximum gum arabic yield obtained was 3948 g tree−1. Linear models of dendrometric variables indicated that gum arabic yield is better predicted by tree diameter than by height. Despite the limitations of this pioneer survey, the population status and yield potential suggest that gum arabic could be sustainably produced and commercialized in natural stands of S. senegal in the studied dryland areas, providing local communities with supplementary seasonal incomes.

Tracheid dimensions of Norway spruce in uneven-aged stands

Tracheid length and width patterns from pith to bark at a height of 0.6 m in uneven-aged Norway spruce (<i>Picea abies</i> L. (H.) Karst) trees were addressed. The identification of the main factors and a comparison with even-aged stands were also pursued. 96 trees were sampled from experimental stands in Southern Finland. The material encompassed the variation in tracheid properties from early years to silvicultural maturity, i.e. from corewood to outerwood up to a cambial age of 111 years. Data from 39 Norway spruce trees from even-aged stands we utilized for comparison. Models fitted to the data indicated that annual ring widths did not influence mean tracheid dimensions but the latewood proportion showed a significant influence on tracheid dimensions. Tracheids in uneven-aged stands were slightly wider and longer at the base of the stem with a similar tree diameter, cambial age, and annual ring number.

Is there tree senescence? The fecundity evidence

Despite its importance for forest regeneration, food webs, and human economies, changes in tree fecundity with tree size and age remain largely unknown. The allometric increase with tree diameter assumed in ecological models would substantially overestimate seed contributions from large trees if fecundity eventually declines with size. Current estimates are dominated by overrepresentation of small trees in regression models. We combined global fecundity data, including a substantial representation of large trees. We compared size–fecundity relationships against traditional allometric scaling with diameter and two models based on crown architecture. All allometric models fail to describe the declining rate of increase in fecundity with diameter found for 80% of 597 species in our analysis. The strong evidence of declining fecundity, beyond what can be explained by crown architectural change, is consistent with physiological decline. A downward revision of projected fecundity of large trees can improve the next generation of forest dynamic models.

Symmetric and Asymmetric Diffusions through Age-Varying Mixed-Species Stand Parameters

(1) Background: This paper deals with unevenly aged, whole-stand models from mixed-effect parameters diffusion processes and Voronoi diagram points of view and concentrates on the mixed-species stands in Lithuania. We focus on the Voronoi diagram of potentially available areas to tree positions as the measure of the competition effect of individual trees and the tree diameter at breast height to relate their evolution through time. (2) Methods: We consider a bivariate hybrid mixed-effect parameters stochastic differential equation for the parameterization of the diameter and available polygon area at age to ensure a proper description of the link between them during the age (time) span of a forest stand. In this study, the Voronoi diagram was used as a mathematical tool for the quantitative characterization of inter-tree competition. (3) Results: The newly derived model considers bivariate correlated observations, tree diameter, and polygon area arising from a particular stand and enables defining equations for calculating diameter, polygon-area, and stand-density predictions and forecasts. (4) Conclusions: From a statistical point of view, the newly developed models produced acceptable statistical measures of predictions and forecasts. All the results were implemented in the Maple computer algebra system.

POTENSI TEGAKAN DAN PRODUKSI BUAH PENAGE (Calophyllum inophyllum) DI PESISIR PANTAI PULAU DATOK KECAMATAN SUKADANA

Abstrak Tanaman penage (Calophyllum inophyllum) tumbuh secara alami di pantai Pulau Datok Kecamatan Sukadana Kabupaten Kayong Utara diameter yang sudah besar dengan diameter lebih dari 30 cm). Tujuan penelitian untuk mengkaji potensi tegakan dan produksi buah penage (C. inophyllum) di pesisir pantai Pulau Datok Kabupaten Kayong Utara dan mengetahui korelasi antara diameter dan luas tajuk terhadap produksi buah. Penelitian ini dilakukan di pantai Pulau Datok Kecamatan Sukadana Kabupaten Kayong Utara Provinsi Kalimantan Barat, menggunakan metode survei dengan teknik pengambilan data dilakukan secara sensus. Data yang dikumpulkan berupa tinggi total (m), tinggi bebas cabang (m), diameter setinggi dada dari permukaan tanah, tinggi tajuk (m), diameter tajuk (m), luas tajuk (m2). Hasil penelitian menunjukan pohon penage yang terdapat di pantai Pulau Datok Desa Sutera Kecamatan Sukadana, ditemukan sebanyak 70 dengan ukuran tinggi 8,1 -14 m, dan volume sebesar 47,72 m3.Produksi buah pohon penage yang terdapat di pantai Pulau Datok sebanyak ± 31,14 kg/pohon. Luas tajuk pohon penage di pesisir pantai Pulau Datok sebesar 647,26 m2 atau rata-rata luas 9,25 m2/pohon. Ukuran luas tajuk dan diameter pohon berkorelasi dengan produksi buah dimana semakin besar ukuran tajuk dan diameter pohon, maka produksi buah semakin besar. Kata kunci : penage, jumlah pohon, luas tajuk dan produksi buah. AbstractPenage (Calophyllum inophyllum) plants grow naturally on the coast of Pulau Datok, Sukadana District, Kayong Utara Regency, which has a large diameter of more than 30 cm. The research objective was to assess the stand potential and production of penage fruit (C. inophyllum) on the coast of Pulau Datok, Kayong Utara Regency and to determine the correlation between diameter and crown area on fruit production. This research was conducted on the coast of Pulau Datok, Sukadana District, Kayong Utara Regency, using a survey method with the data collection technique carried out by census. Data collected in the form of total height (m), branch-free height (m), diameter at breast height from ground level, crown height (m), crown diameter (m), crown area (m2). The results showed that there were 70 penage trees found on the coast of Pulau Datok, Sutera Village, Sukadana District, with a height of 8,1-14 m, and volume is 47,72 m³. The fruit production of penage trees on Datok Island is ± 31,14 kg / tree. Penage tree crown area on the coast of Datok Island is 647,26 m2 or an average area of 9,25 m2/tree. The size of crown area and tree diameter correlated with fruit production where greater the crown size and tree diameter, Fruit production is getting biger. Keywords: penage, number of trees, crown area and fruit production