spatial patterns

Forest structure is a key element for assessing the ecological functions and services in forest ecosystems, which can be described and quantified using forest structural indices. This research was conducted with the aim of quantifying the structure of pure beech forests using spatial indices of forest structure in the Hyrcanian forests of Iran. For this purpose, 90 permanent sample plots of 1000m2 area in three pure beech forests (30 samples in each forest) were established based on a systematic-random grid of 150×200m and the variables of DBH, total height, species and spatial coordinates of all trees greater than 7.5cm in the sample plots were recorded. Then, the structural characteristics of the forests were quantified using O-ring statistic and indices of diameter and height differentiation, diameter and height dominance and Mingling. The results showed that the distribution patterns of trees in the pure beech forests is mainly random, the degree of diameter and height differentiation is average, the degree of species mixing is low, the top height is about 33.5m, the forests are two-storied, trees in terms of dominance indices are co- dominant and the average tree to tree distance is less than 3m. These spatial and quantitative indices of the forest structure can be used for management, planning and silvicultural interventions in the forests. Furthermore, by using these indices with permanent sample plots and assessing their changes over time, it is possible to long-term monitoring and comparing the forests.

Recently, forest decline has outburst in Zagros forests region in the west of Iran, especially in Ilam province. In this research, we selected an 83 ha infected forest area in Zarab, Ilam and the dried trees were fully investigated for variables including dbh, height, drought intensity, crown cover, origin and Cartesian coordinates. Their spatial structure, spatial patterns and spatial correlation were analyzed using variogram analysis, O-ring statistic and Mark correlation function (MCF), respectively. Results showed that the density of dried trees was 27 N/ha which is more comprised of coppice trees in small and medium diameter classes. A cluster spatial pattern of dried trees was determined up to 35 m and after that it was uniform, implying dried trees created patches with 3850 m2 surface area. Variogram analysis showed that only dbh and drought intensity of dried trees had strong spatial structure which was mapped using Kriging interpolation method of Geostatistics. Mark correlation function graph showed that adjacent dried trees were similar according to drought intensity while were not similar based on their dbh. In general, the results illustrated that all of the trees in the studied area were infected by drought with different biometric characteristics as well as at different geographical aspects. These results can be used as an instruction for sustainable management of the stands based on their spatial characteristics.

Analyzing the spatial patterns of individuals and the interaction between them are essential for understanding the spatial and temporal dynamics of plant populations. This research was conducted to study the spatial patterns and interaction of three oak species (Quercus brantii Lindl., Q. infectoria Oliv. and Q. libani Oliv.) in Baneh forests of northern Zagros region of Iran. Data collection was done using six one- hectare square sample plots which randomly selected and fully mapped. Spatial patterns and spatial association of different oak species were then analyzed using O- ring univariate and bivariate statistics, respectively. Results showed that the general spatial patterns of the trees in total and at larger scales were random, while at small scales was clumped at least up to 15 m. Spatial association analyses revealed that there was no significant inter-specific competition among the three oak species, where the spatial association was positive (attraction) at small scales (up to 5 m) or independence at larger scales. It is concluded that clustered- random pattern is due to high forest origin of the most studied stands, homogeneity of the habitat, and lack of interspecific competition among the three oak species in the study area. Whereas there is no significant interspecific competition among the three oak species, every intervention in order to enrichment and restoration of these stands should be based on keeping clustered- random spatial pattern and making individual species mixture.

Analyzing spatial patterns of individuals within life stages and spatial associations between different life stages is essential for understanding the spatial and temporal dynamics of populations. This research was conducted to study the spatial patterns and spatial association of Juniper trees (Juniperus polycarpos C. Koch) at different life stages in Juniper forests of Layen, Northeast of Iran. Data collection was done using four one- hectare square sample plots randomly selected, which fully mapped. Spatial patterns and spatial association of different life stages (juvenile, premature and mature; based on crown diameter) were then analyzed using O- ring univariate and bivariate statistics, respectively. Results showed that the general spatial patterns of the trees in total and in every life stage was clumped at least up to 25 m, while after that tends to random distribution at larger scales. Spatial association analyses revealed that there was no significant intra-specific competition among life stages namely, the spatial association was positive (attraction) or indifferent. It is concluded that clump patterns are due to heavy fruit and dispersal limitation of Juniper trees and harsh environmental condition of the study area.

Groundwater contamination with nitrate is a pervasive problem in Iran and all over the world. Groundwater nitrate pollution associated with agricultural activity is an important environmental problem in the management of this natural resource, so that this is one of the most common groundwater contaminants. Determining the concentration and its spatial variation can be useful in exploitation and management of water resources. In this research, a total number of 50 wells were selected for sampling purposes and nitrate concentrations were analyzed in the laboratory according to standard method. Measured nitrate levels were compared to World Health Organization (WHO). Although, slightly increasing or decreasing changes in nitrate concentrations were observed in some wells, however the concentrations were below the standard of WHO (50 mg/L).It seems that nitrate concentrations in plain are affected by nonpoint sources (nitrogen fertilizers) and point sources (wastewater) that will undoubtedly be most important source of nitrate pollution in the future. Spatial patterns of nitrate showed that the highest concentrations of nitrate were found in north-eastern and south-eastern. Also, no statistically significant correlations were observed between nitrate concentration and well depth.

Recently, forest decline has outburst in Zagros forests, west of Iran. Consequently, we aimed considering dried trees and their spatial patterns as well as spatial structure at Bioreh forests in Ilam province, west of Iran. For this purpose, we selected and fully inventoried a 96 ha infected forest. The interested attributes were tree species, diameter at breast height (DBH), crown diameter, origin and number of sprout in coppice trees as well as Cartesian coordinates of dried trees with drying intensity more than 50 percent. For spatial point pattern analysis and spatial structure of interested attributes, O- ring statistics and variogram analysis were used, respectively. Results showed that the density of dried trees was 10 N/ha which more comprised of coppice trees, while high frequency percentage of drying was observed in large diameter classes. The spatial pattern of dried trees was determined as cluster up to 15 m, which implied that dried trees created patches with 4500 m2 surface area. No spatial structure were found for three interested attributes (DBH, crown diameter and number of sprout) which implied that there was no similarity among infected trees. These results can be used as an instruction to manage infected stands based on their spatial characteristics.

Multi site modeling of rainfall is one of the most important issues in environmental sciences especially in watershed management. For this purpose, different statistical models have been developed which involve spatial approaches in simulation and modeling of daily rainfall values. The hidden Markov is one of the multi-site daily rainfall models which in addition to simulation of daily rainfall values, explores the spatial and temporal pattern of rainfall events. In this study, the winter (January to April) rainfall pattern of 130 rain gauges have been modeled using hidden Markov approach during a 21 years period (1990-2010). The aim of this study was finding temporal and spatial distribution of weather patterns and stochastic simulation of occurrence and amount of rainfall, simultaneously. To achieve this goal, different hidden Markov algorithms including, Viterbi decoding algorithm, Expectation-Maximization (EM) algorithm and a stochastic simulation approach with the probability transformation were applied. It is expected that extracted patterns, using hidden Markov model, are consistent with synoptic patterns and accordingly eight different weather pattern as the definite set of possible cases were recognized. The most frequent rainfall pattern extracted from hidden Markov model was the dry pattern (stable condition) in which the rainfall occurrence probability is low in most of the stations. This pattern has the maximum initial probability of 0.429 and maximum Markov transfer probability of 0.637 Besides, multi-site simulation of winter rainfall keeping the basic statistic of mean, standard deviation of total seasonal rainfall and percentile values in each station and also spatial correlation of occurrence or non-occurrence of rainfall produced reasonable result. In general this approach can be recommended for regional studies.

The spatial patterns of trees in different stages of their life provide important information related to forest regeneration and succession processes. Since competition affects forest structure, understanding competition is important when forest management aims to imitate the dynamics of natural ecosystems. For this purpose, an unmanaged control forest was selected with 26 hectares area. All Chestnut-leaved oak (Quercus castaneifolia) trees with a diameter at breast height (DBH) greater than 7.5 cm were measured, and their Cartesian coordinates were recorded. Based on their DBH, the measured trees were then divided into four classes of small timber, medium timber, large timber and extra-large timber. The univariate and bivariate O- ring statistic were used to investigate the spatial patterns and to examine the intra-specific competition, respectively. Results showed cluster spatial pattern in short distances due to heavy seed and high regeneration frequency, which was later changed to random distribution as distance increased. Moreover, interactions between diameter size classes showed that oak trees with different sizes had different positive (attraction) and negative (repulsion) interactions which occurred at different scales based on the size of trees, influenced by light-demanding, limited seed dispersal and intra-specific competition of oak trees. Since the Chestnut-leaved oak trees showed random distribution, the silvicultural interventions should thus be based on individuals and random single selection to create random spatial patterns in the stand.

One of the most visible aspects of a forest stand structure is the spatial patterns of trees. Competition affects on forest structure and its understanding is important, when the purpose of forest management is to imitate the dynamic of natural ecosystems. For this purpose, an unmanaged intact forest was selected with 26 hectares area. All Chestnut leaf Oak (Quercus castaneifolia) trees with a diameter at breast height greater than 7.5 cm were measured and their Cartesian coordinates were determined. Then the measured trees were divided into four classes based on their diameter at breast height as small timber, medium timber, large timber and extra large timber. To investigate the spatial patterns of oak trees in the region and in the each diameter size class, and to examine the intra-specific competition the univariate and bivariate Ripley’s K- function were used, respectively. Results showed that the spatial patterns of oak trees was cluster in short distances due to heavy seed and high frequency of young trees and then changed to random distribution as distance increased. Moreover, interactions between diameter size classes showed that oak trees with different sizes had different positive (attraction) and negative (repulsion) competitive effects which occur at different scales based on the size of trees, influenced by light-demanding, limited seed dispersal and intra-specific competition of oaks with various diameter sizes. Since the Chestnut leaf Oak trees showed random distribution, the silvicultural interventions should be based on individuals and random single selection to create random spatial patterns in the stand.

Forest structure is influenced by natural processes and human interventions. For proper forest management, some tools are required to study changes made at forest structure. In this study, to investigate changes made at structure of intact and natural forest of Kelardast area of Caspian Forests of Iran, three one-hectare area plots, representative of initial, optimal and decay stages of forest development, were used. After measuring distance and azimuth of each tree to the southwest corner of each sampling plot and recording some parameters such as species, diameter at breast height (dbh) and total height, three characteristics, including geographical location (Clark & Evans and uniform angle indices), mixture (Mingling index) and tree dimensions (dbh and total height differentiation indices) were studied, using a set of indices, based on nearest neighbor criteria. Results of this study showed that greatest density of trees was found at the initial stage and according to the Clark & Evans index, distribution pattern of the trees at initial and decay stages in one hand and at optimal stage at second hand was clumped and random, respectively. Furthermore, result of the uniform angle index showed that the trees arrangement within the structural groups at the three development stages was at random form. Results of Mingling index showed that mixture at initial stage was at lowest rate, compared to the other development stages. Moreover, result of dbh and total height differentiation indices showed that there were moderate-obvious and low-moderate variations for the trees at the three development stages, respectively. Regarding the intactness of the studied stands, results of these indices might be applied as a basis for similar forests and determination variation rates caused by natural processes and human interventions.