Tree Distribution Patterns Research Articles

Comparison ofT-Square, Point Centered Quarter, andN-Tree Sampling Methods inPittosporum undulatumInvaded Woodlands

Tree density is an important parameter affecting ecosystems functions and management decisions, while tree distribution patterns affect sampling design.Pittosporum undulatumstands in the Azores are being targeted with a biomass valorization program, for which efficient tree density estimators are required. We comparedT-Square sampling, Point Centered Quarter Method (PCQM), andN-tree sampling with benchmark quadrat (QD) sampling in six 900 m2plots established atP. undulatumstands in São Miguel Island. A total of 15 estimators were tested using a data resampling approach. The estimated density range (344–5056 trees/ha) was found to agree with previous studies using PCQM only. Although with a tendency to underestimate tree density (in comparison with QD), overall,T-Square sampling appeared to be the most accurate and precise method, followed by PCQM. Tree distribution pattern was found to be slightly aggregated in 4 of the 6 stands. Considering (1) the low level of bias and high precision, (2) the consistency among three estimators, (3) the possibility of use with aggregated patterns, and (4) the possibility of obtaining a larger number of independent tree parameter estimates, we recommend the use ofT-Square sampling inP. undulatumstands within the framework of a biomass valorization program.

Tree Species Composition and Distribution Pattern in a Myristica Swamp of Northern Kerala, India

Knema Phytosociological studies have been carried out in a Myristica swamp in Northern Kerala to reveal the composition and distribution pattern of different tree species. On the basis of IVI, the family Myristicaceae was dominant and the association is attenuata - Myristica malabarica -Holigarna arnottiana type. The species like Gymnacranthera canarica and Myristica fatua var. magnifica, which are believed to be the essential elements of Myristica swamps, are totally absent here. A total 403 individuals (gbh > 10.1 cm) were recorded with a basal area of 34.25 m2 ha-1 in 0.5 ha. area. Total number of species recorded was 28, which represent 21families in which Myristicaceae represents 48.18% of total IVI. Among two dominant species, Myristica malabarica prefer swampy area hence their number of individual shows decreasing trend when we move from the swamp while the second dominant species Knema attenuata showing a reverse trend and was completely absent in the first five quadrats where soil water content is too high. Species specific eco-physiological studies are required to understand the reasons for change in the distribution pattern of these dominant species.

Farmland tree species diversity and spatial distribution pattern in semi-arid East Shewa, Ethiopia

Information on tree species occurring in farming systems in semi-arid agroecologies is critical for sustainable land management, biodiversity conservation and informing food security interventions. The aim of the study was to characterize the species composition, diversity, structure and spatial distribution patterns of trees in the semi-arid East Shewa Zone of Oromia, Ethiopia. A survey of 172 land parcels with a total area of 76.09 ha, and belonging to 100 randomly selected farm households was conducted in 5 semi-arid sites in East Shewa. A total of 77 tree species belonging to 32 families were identified, and the Fabaceae were the dominant group. Trees were distributed differently in the four identified land uses (homesteads, line plantings, in crop lands and woodlots). Tree diversity was the highest in line plantings and the lowest in woodlots with the Shannon diversity index of 3.1 and 1.8, respectively. The majority (70%) of the species were native, whereas the remaining 30% were exotic. The average number of tree species per parcel was 4.7 ranging from treeless condition to 36 tree species in an exceptional farm condition. The height and diameter at breast height of the 6066 recorded individuals (2 m and above) ranged from 2 to 25 m and from 1 to 86 cm, respectively. The species Acacia tortilis, Eucalyptus camaldulensis and Acacia senegal were the three dominant species in the system. Correlation analysis revealed that land-holding size had significant positive relationships with tree species abundance and basal area, but not with species richness. Interventions are suggested for increasing the currently very low tree cover through planting and managing natural regeneration for improved farming system resilience in the face of climate change.

Effects of wind and tree density on forest fire patterns in a mixed-tree species forest

ABSTRACTIt is well known that global climate change causes an increase in forest fire frequency and severity. Thus, understanding fire dynamics is necessary to comprehend the mitigation of the negative effects of forest fires. Our objective was to inform how fire spreads in a simulated two-species forest with varying wind strengths. The forest in this study was comprised of two different tree species with varying probabilities of transferring fire that was randomly distributed in space at densities (Ctot) ranging from 0.0 (low) to 1.0 (high). We studied the distribution pattern of burnt trees by using local rules of the two-dimensional model. This model incorporated wind blowing from south to north with strength (Pw) ranging from 0.0 (low) to 1.0 (high). Simulation results showed that when Ctot > 0.45 the fire covered the entire forest, but when Ctot ≤ 0.45 the fire did not spread. The wind effect on the variation of the amount of the burnt tree was maximized at the critical density and dramatically decreased with increasing Ctot. Additionally, we found that the term of Ctot and Pw plays an important role in determining the distribution.

Predicting vegetation type through physiological and environmental interactions with leaf traits: evergreen and deciduous forests in an earth system modeling framework.

Earth system models are incorporating plant trait diversity into their land components to better predict vegetation dynamics in a changing climate. However, extant plant trait distributions will not allow extrapolations to novel community assemblages in future climates, which will require a mechanistic understanding of the trade-offs that determine trait diversity. In this study, we show how physiological trade-offs involving leaf mass per unit area (LMA), leaf lifespan, leaf nitrogen, and leaf respiration may explain the distribution patterns of evergreen and deciduous trees in the temperate and boreal zones based on (1) an evolutionary analysis of a simple mathematical model and (2) simulation experiments of an individual-based dynamic vegetation model (i.e., LM3-PPA). The evolutionary analysis shows that these leaf traits set up a trade-off between carbon- and nitrogen-use efficiency at the scale of individual trees and therefore determine competitively dominant leaf strategies. As soil nitrogen availability increases, the dominant leaf strategy switches from one that is high in nitrogen-use efficiency to one that is high in carbon-use efficiency or, equivalently, from high-LMA/long-lived leaves (i.e., evergreen) to low-LMA/short-lived leaves (i.e., deciduous). In a region of intermediate soil nitrogen availability, the dominant leaf strategy may be either deciduous or evergreen depending on the initial conditions of plant trait abundance (i.e., founder controlled) due to feedbacks of leaf traits on soil nitrogen mineralization through litter quality. Simulated successional patterns by LM3-PPA from the leaf physiological trade-offs are consistent with observed successional dynamics of evergreen and deciduous forests at three sites spanning the temperate to boreal zones.

Influence of the exclusion distance among trees on gap fraction and foliage clumping index of forest plantations

A hypergeometric model is proposed explicitly instead of two previous stochastic models (the Poisson model and Neyman-A model) to describe the topological relationship of trees and the influence of the exclusion distance on gap fraction and clumping index of forest plantation canopies. Gap fraction (GF) and clumping index (CI) play key roles in plant light interception, and therefore they have strong impacts on plant growth and canopy radiative transfer processes. Trees are usually assumed to be randomly distributed in natural forests in many previous studies. However, few studies have shown how trees are distributed in forest plantations and how these distribution patterns affect GF and CI in these forests. In this paper, a simple and general distance factor defined as relative allowable shortest distance between centers of two adjacent crowns divided by the mean diameter of the crowns (RASD) is proposed to describe quantitatively the degree of mutual exclusion among trees in forest plantations of various tree distribution patterns. A hypergeometric model is proposed instead of two previous stochastic tree distribution models (the Poisson model and Neyman-A model) to describe the topological relationship of trees and the influences of the exclusion distance on the GF and CI of the forest plantation canopies. The results show that: (1) the hypergeometric model is more suitable than the Poisson model and Neyman-A model for describing the topological relationship of trees in forest plantations; (2) the exclusion distance has strong impacts on GF and CI: there are significant differences between the results of the hypergeometric model and the Poisson model. Larger RASD causes lower GF and larger CI. The simulations are verified by field measurements in four forest plantation stands. Similarly, impacts of RASD on GF and CI are also found for other two crown shapes (prolate and oblate ellipsoids).

Seedling growth responses to phosphorus reflect adult distribution patterns of tropical trees.

Soils influence tropical forest composition at regional scales. In Panama, data on tree communities and underlying soils indicate that species frequently show distributional associations to soil phosphorus. To understand how these associations arise, we combined a pot experiment to measure seedling responses of 15 pioneer species to phosphorus addition with an analysis of the phylogenetic structure of phosphorus associations of the entire tree community. Growth responses of pioneers to phosphorus addition revealed a clear tradeoff: species from high-phosphorus sites grew fastest in the phosphorus-addition treatment, while species from low-phosphorus sites grew fastest in the low-phosphorus treatment. Traits associated with growth performance remain unclear: biomass allocation, phosphatase activity and phosphorus-use efficiency did not correlate with phosphorus associations; however, phosphatase activity was most strongly down-regulated in response to phosphorus addition in species from high-phosphorus sites. Phylogenetic analysis indicated that pioneers occur more frequently in clades where phosphorus associations are overdispersed as compared with the overall tree community, suggesting that selection on phosphorus acquisition and use may be strongest for pioneer species with high phosphorus demand. Our results show that phosphorus-dependent growth rates provide an additional explanation for the regional distribution of tree species in Panama, and possibly elsewhere.

Distribution of juveniles of tree species along a canopy closure gradient in a tropical cloud forest of the Venezuelan Andes

Abstract: Cloud forests represent a minor portion of the world forests, though outstanding in terms of biodiversity, endemisms, and environmental services provided. Understanding the factors that drive the regeneration and species composition of these forests, and in particular how light availability affects the patterns of juvenile tree distribution in the understory, is critical for conservation and restoration programs. In this study, we determined the range-size and overlap of the abundance distribution of juveniles for 20 tree species in an Andean tropical cloud forest in Venezuela along a gradient of percentage canopy openness (%CO) used as a surrogate of light availability. The observed distribution of %CO was then compared with a bounded null model of community structure in order to test light partitioning as a driver of tree species’ coexistence. We measured %CO using hemispherical photography and the abundance and size of juvenile trees in 280 plots of 1-m radius spread over a 32 ha forest area. The distribution of sites was skewed towards the lower end of the %CO gradient (0.5 to 12.8%), while species abundance sharply diminished at both ends of the gradient. Nevertheless, 15 out of 20 species had a non-random distribution in relation to %CO, with many species concentrated near the lower side of the gradient. The observed pattern of species’ overlap was within the 95% confidence limits for the average overlap expected under the bounded null model. These patterns indicate that low canopy openness is the rule in this forest, in spite of the scattered tree-fall gaps, and suggest that light partitioning does not determine the tree community structure at the juvenile stage. High redundancy in light requirements among juveniles of tree species may have a positive effect on species coexistence in cloud forests, thus maintaining a high species diversity. However, other factors such as recruitment limitation and differential growth/carbon-gain among species at the juvenile stage along the light gradient could contribute to the high diversity of these ecosystems.

Mixing of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) enhances structural heterogeneity, and the effect increases with water availability

The mixing of tree species with complementary ecological traits may modify forest functioning regarding productivity, stability, or resilience against disturbances. This may be achieved by a higher heterogeneity in stand structure which is often addressed but rarely quantified. Here, we use 32 triplets of mature and fully stocked monocultures and mixed stands of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) located along a productivity and water availability gradient through Europe to examine how mixing modifies the stand structure in terms of stand density, horizontal tree distribution pattern, vertical stand structure, size distribution pattern, and variation in tree morphology. We further analyze how site conditions modify these aspects of stand structure. For this typical mixture of a light demanding and shade tolerant species we show that (i) mixing significantly increases many aspects of structural heterogeneity compared with monocultures, (ii) mixing effects such as an increase of stand density and diversification of vertical structure and tree morphology are caused by species identity (additive effects) but also by species interactions (multiplicative effects), and (iii) superior heterogeneity of mixed stands over monocultures can increase from dry to moist sites. We discuss the implications for analyzing the productivity, for modelling and for the management of mixed species stands.

Spatial patterns of tree species distribution in New Guinea primary and secondary lowland rain forest

AbstractQuestionsHow do spatial patterns of tree distribution and species co‐occurrence differ between primary and secondary tropical rain forests? What signatures of ecological processes might be discerned by comparing the spatial patterns of trees between primary and secondary forest plots?LocationTropical rain forest vegetation, lowlands of Papua New Guinea.MethodsAll trees over 5 cm DBH were surveyed in two non‐replicated 1‐ha plots situated in primary and secondary forest. Grid location, DBH, height and species identity were recorded for all surveyed trees. Analysis of the spatial pattern and the autocorrelation of tree sizes and identities were used to assess the structure of the forest found within the plots. Functions combining Ripley's K and the individual species–area relationship were applied to study the spatial distribution of trees and species diversity.ResultsThe spatial distribution of common species, and all stems collectively, was aggregated in the secondary forest plot but not different from random in the primary forest plot. Diameter and height were also strongly spatially auto‐correlated in the secondary forest plot but not in the primary forest plot. Conspecific aggregations were more common in the secondary forest plot. Finally, the secondary forest plot was characterized by the presence of diversity‐repelling species and lower diversity than the primary forest plot, where diversity‐accumulating species were present.ConclusionsWe attribute the weaker autocorrelation of tree size in the primary forest to the development of size hierarchies throughout the course of stand aging. The conspecific aggregation and low local diversity within the secondary forest plot are likely caused by dispersal limitation during a brief period of establishment after disturbance. The higher local diversity of the primary forest can be explained by the reduction of species aggregation through increased mortality of conspecifics. This is caused by strong intraspecific competition, supporting the spatial segregation hypothesis (interspecific spatial segregation).

Measuring diversity of tree distribution patterns in natural forests

Patterns of tree distribution are an important part of forest structure and directly affect the health and stability of forest ecosystems. Maintaining and preserving forest structural diversity has often been considered the best way to protect biodiversity. One method measuring the diversity of tree distribution patterns was discussed in this paper in order to provide a theoretical basis for the expression of forest structure diversity. The key to the study of distribution pattern diversity is to select the appropriate biodiversity measuring method and index which has a distributed attribute. In this paper, we put forward a method to express tree distribution pattern diversity which counted the distributions frequency of uniform angle index and Voronoi polygon side, and calculate uniform angle index diversity and Voronoi polygon side distribution diversity by the Simpson index, respectively. The distribution pattern diversity of three long-term monitoring Pinus koreansis broad-leaved forest plots (area = 100 m × 100 m) in northeastern China was analyzed by this method. The results showed that both of the distribution of uniform angle index and the Voronoi polygon side were close to the normal distribution. The frequency of randomly distributed trees was the maximum and more than 55% in the uniform angle index distribution; the type of Voronoi polygon side was great than 10 and over 50% of the trees had 5–6 closest neighboring trees. The result of using the Simpson index to analyze tree distribution pattern diversity showed that the tree distribution pattern diversity was higher in the cluster ·研究报告· 第 3期 惠刚盈等: 林木分布格局多样性测度方法: 以阔叶红松林为例 281 distribution stand than the random distribution stand. We also found that Simpson index values were different when different distribution pattern diversity methods were used, and the uniform angle distribution diversity was significantly lower than that of the Voronoi polygon side distribution diversity, which mainly due to the different quantity grade of each index. Therefore, study on the diversity of forest distribution pattern should choose distribution pattern indices with distribution attribute. The uniform angle index distribution and Voronoi polygon side distribution used in this paper had this attribute, however, different indices reflected different aspects of distribution pattern, so the same pattern analysis method should be used in the analysis and comparison of distribution pattern diversity of different forest stands.

Assessing Impact of Physiographic Factors on Spatial Distribution Patterns of Oak Trees in Iran

Spatial pattern is a key attribute of forest ecosystems. Spatial distribution pattern of woody plants, especially trees, has gained many interest by plant ecologists which leads to introducing a large number of different methods for quantifying spatial patterns. The purpose of the present study was the investigation of effects physiographic factors on spatial distribution patterns of oak trees (Quercus brantii var. persica) in western forests of Iran. So, based on systematic-random sampling methods with 400 m × 700 m dimensions, 82 plots (1000 m2) were selected and measured. In each plot, distance of two nearest neighbors to central of plot and physiographic factors including of altitude, slope gradient and aspect were measured. Hopkins, Hinez, Eberhart and C indexes were used to analyze the spatial distribution pattern. All indexes showed a clumped pattern for oak trees in study area without considering effects of physiographic factors. The results of this study showed that in different physiographic condition changes spatial distribution pattern of oak trees. So, physiographic factors have a key role in the determination of spatial distribution pattern.

Density-dependent effects in Picea schrenkiana forests in Tianshan Mountains

The density-dependence hypothesis is one of the most important mechanisms proposed to explain species coexistence in natural forest communities. Picea schrenkiana is the single dominant species of the forest communities in Tianshan Mountains, which plays a very important role in temperate forests of China. We used reexamined data with a five-year interval on an 8-ha P. schrenkiana forest dynamics plot to illustrate the dynamics of species composition. Pointpattern analysis was conducted to reveal the spatial structure of P. schrenkiana individuals of different ages, and the effects of the density-dependence hypothesis on different ages of P. schrenkiana was discussed. The results were as follows: (1) Woody plants with DBH ≥ 1 cm were 11,835 trees in 2009 and 11,050 in 2014. The mortality rate was 8.82%, the recruitment rate was 2.19%, and the net decrease was 6.63%; (2) Young and medium trees of P. schrenkiana presented an aggregation distribution across a scale of 0–40 m, and the aggregation intensity decreased as the scale increased. Mature trees presented a random distribution on scales of 0 m ≤ r ≤ 2 m and r = 4 m, and an aggregation distribution on other scales with a low density. (3) Using a “case-control” design method and eliminating habitat heterogeneity, the distribution of young and medium trees were taken as examples of case. The distribution pattern of mature trees was used as a comparison and represented habitat heterogeneity, and was compared with that of young and medium trees. Young and medium trees of P. schrenkiana were observed to present ·研究报告· 第 3 期 王慧杰等: 天山雪岭云杉森林群落的密度制约效应 253 more considerable gathering than was observed for mature trees on scales of 0–40 m, and density decreased while the diameter class increased. These results indicate that the density-dependence hypothesis has an influence on distribution patterns of different age classes. This study reveals that P. schrenkiana was affected by habitat heterogeneity and presented a significant aggregation effect. The spatial pattern of P. schrenkiana is revealed to be affected by the density-dependence hypothesis after eliminating the effects of habitat heterogeneity. The results of this paper support the Janzen-Connell hypothesis.

Comparing tree seedling composition and distribution patterns under different sampling intensities in the 24 ha Gutianshan forest dynamics plot

Comparing tree seedling composition and distribution patterns under different sampling intensities in the 24 ha Gutianshan forest dynamics plot

Characterization of the structure, dynamics, and productivity of mixed-species stands: review and perspectives

The growth and yield of mixed-species stands has become an important topic of research since there are certain advantages of this type of forest as regards functions and services. However, the concepts and methods used to characterize mixed stands need to be understood, as well as harmonized and standardized. In this review we have compiled a set of measures, indices, and methods at stand level to characterize the structure, dynamics, and productivity of mixed stands, and we discuss the pros and cons of their application in growth and yield studies. Parameters for the characterization of mixed stand structure such as stand density, species composition, horizontal (intermingling) and vertical tree distribution pattern, tree size distribution, and age composition are described, detailing the potential as well as the constraints of these parameters for understanding resource capture, use, and efficiency in mixed stands. Furthermore, a set of stand-level parameters was evaluated to characterize the dynamics of mixed stands, e.g. height growth and space partitioning, self- and alien-thinning, and growth partitioning among trees. The deviations and changes in the behaviour of the analysed parameters in comparison with pure stand conditions due to inter-specific interactions are of particular interest. As regards stand productivity, we reviewed site productivity indices, the growth–density relationship in mixed stands as well as methods to compare productivity in mixed versus monospecific stands. Finally, we discuss the main problems associated with the methodology such as up-scaling from tree to stand level as well as the relevance of standardized measures and methods for improving forest growth and yield research in mixed stands. The main challenges are also outlined, especially the need for qualitatively sound data.

Spatial Distribution Patterns in the Very Rare and Species-Rich Picea chihuahuana Tree Community (Mexico).

The very rare Mexican Picea chihuahuana tree community covers an area of no more than 300 ha in the Sierra Madre Occidental. This special tree community has been the subject of several studies aimed at learning more about the genetic structure and ecology of the species and the potential effects of climate change. The spatial distribution of trees is a result of many ecological processes and can affect the degree of competition between neighbouring trees, tree density, variability in size and distribution, regeneration, survival, growth, mortality, crown formation and the biological diversity within forest communities. Numerous scale-dependent measures have been established in order to describe spatial forest structure. The overall aim of most of these studies has been to obtain data to help design preservation and conservation strategies. In this study, we examined the spatial distribution pattern of trees in the P. chihuahuana tree community in 12 localities, in relation to i) tree stand density, ii) diameter distribution (vertical structure), iii) tree species diversity, iv) geographical latitude and v) tree dominance at a fine scale (in 0.25 ha plots), with the aim of obtaining a better understanding of the complex ecosystem processes and biological diversity. Because of the strongly mixed nature of this tree community, which often produces low population densities of each tree species and random tree fall gaps caused by tree death, we expect aggregated patterns in individual Picea chihuahuana trees and in the P. chihuahuana tree community, repulsive Picea patterns to other tree species and repulsive patterns of young to adult trees. Each location was represented by one plot of 50 x 50 m (0.25 ha) established in the centre of the tree community. The findings demonstrate that the hypothesis of aggregated tree pattern is not applicable to the mean pattern measured by Clark-Evans index, Uniform Angle index and Mean Directional index of the uneven-aged P. chihuahuana trees and P. chihuahuana tree community and but to specific spatial scales measured by the univariate L-function. The spatial distribution pattern of P. chihuahuana trees was found to be independent of patches of other tree species measured by the bivariate L-function. The spatial distribution was not significantly related to tree density, diameter distribution or tree species diversity. The index of Clark and Evans decreased significantly from the southern to northern plots containing all tree species. Self-thinning due to intra and inter-specific competition-induced mortality is probably the main cause of the decrease in aggregation intensity during the course of population development in this tree community. We recommend the use of larger sampling plots (> 0.25 ha) in uneven-aged and species-rich forest ecosystems to detect less obvious, but important, relationships between spatial tree pattern and functioning and diversity in these forests.

Spatial distribution of trees on light taiga plots before selective thinning

Since 2009 the School of Agroecology and Business, Institute of Plant and Agricultural Sciences of the Mongolian University of Life Sciences in Darkhan has established research plots in two research areas in the Selenge aimag. The establishment was conducted in close cooperation with development organisations (FAO, GIZ) and the University of Goettingen. The purpose of the research initiative is to combine capacity development and monitoring of forest structure in the mountain forest steppe zone and taiga zone. Here we report results on the horizontal spatial structure of forest stands. We analysed the spatial distribution of trees on birch and larch plots of the research area «Altansumber» before a selective thinning took place on some plots in 2009. The research area is situated in the mountain forest steppe zone. The forests belong to the light taiga. The selected stands approach a chronosequence. The results showed that the tree distributions were mainly irregular («clumped»).Random spatial tree distribution occurred especially in the medium-aged birch stand. We found no indication of regular tree distributions in any of the plots. We assume that the disturbance regime and successional processes are the driving factors leading to the specific tree distribution pattern on the plots. Due to different regeneration strategies and life span of the dominating species the birch stands and the larch stands seem to differ slightly concerning the chronological occurrence of clumped and random spatial tree distribution. We finally conclude that a better control of the disturbance regime would not only support an undisturbed forest succession to riper forest stands but also result in less forest stands with irregular spatial distribution. This may also have implications on forest productivity.Mongolian Journal of Agricultural Sciences Vol.15(2) 2015; 91-99

Urbanization effects on spatial-temporal differentiation of tree communities in high-density residential areas

The changing mode of urban development through time can bring a varied landscape mosaic accompanied by spatial-temporal differentiation of urban vegetation. Hong Kong as an ultra-compact city generates intense interactions between trees and urban fabric to highlight urbanization effects on tree communities. The study areas cover public housing estates which accommodate about half of the 7.26 million population. Thirteen site factors related to estate, landform and habitat traits were measured or computed as surrogate urbanization effects. Species composition and diversity of tree communities in 102 estates were assessed by field surveys, including four estate groups: older or newer ones situated respectively in urban core or new towns. They contain 48,823 trees belonging to 232 species with heavy exotic representation. Total tree density and native tree density in newer estates were significantly higher than older ones. Differences in species richness and diversity and native species richness between older and newer estates were not significant, expressing to a certain extent the floristic-homogenization phenomenon. Multi-response Permutation Procedures (MRPP) results showed significant difference in species composition between older and newer estates, which could be explained by variations in development age, density, town plan and pre-urbanization land cover. Nonmetric Multidimensional Scaling (NMDS) results found tree distribution patterns in four estate groups strongly associated with estate area, open space area, estate population, estate age, Shannon index (H′) at planting strip and tree pit, and tree site quality index. Urban-forest management could be improved by adopting more native species and providing high-quality and spacious planting sites to accommodate more and larger trees. The research methods and findings could be used by policy makers and planners in similar large and developing cities to evaluate, design, maintain and enhance urban biodiversity.

Analyzing the Distribution Patterns of Nutmeg (Myristica spp.) in Busama Forest Area Using Quadrat Size Technique

Trees in natural forests are scattered across and along altitudinal gradients. The mode of dispersion varies within a natural forest and is influenced by natural translocation phenomena of biotic and abiotic factors acting on the environment. It is understood that dispersion in a natural forest can be in random, uniformed or clumped and assumed to be in random at a certain degree. This study was carried out in Busama forest area in a permanent sampling plot to describe the distribution pattern of trees within the forest area with Myristica spp. used because of its dominance within the forest. The index of dispersion technique was used to assess and analyze the distribution patterns of Myristica spp. where quadrat sizes are increased from 1m2 to 2,500m2 using Microsoft EXCEL to generate subplots within the PSP and f – test was used to test the significance of the departure or closeness of the distribution to randomness at F0.01 ≥ 1.36 (at 1% level of significance). It was found that as the quadrat size increase the distribution pattern of Myristica spp. becomes random and also the population density increases but it is predicted that it will become random but in clumps (F0.01 ≥ 1.36), as the quadrat size increased to about 200m² and above, there is a significant departure from the randomness of closeness. However, the distribution pattern of Myristica species in this case is general and can be applied to other tree species in other locales.

Effects of microtopography on spatial point pattern of forest stands on the semi-arid Loess Plateau, China

Microtopography may affect the distribution of forests through its effect on rain redistribution and soil water distribution on the semi-arid Loess Plateau, China. In this study, we investigated the characteristics of microtopography on two shady slopes (slope A, 5 hm2, uniform slope; slope B, 5 hm2, microtopography slope) and surveyed the height, the diameter at breast height and the location (x, y coordinates) of all selected individual trees (Robinia pseudoacacia Linn., Pyrus betulifolia Bunge, Populus hopeiensis Hu & Chow, Armeniaca sibirica Lam., Populus simonii Carr. and Ulmus pumila Linn.) on slope A and slope B in the watersheds of Wuqi county, Shaanxi province. Subsequently, the effects of microtopography on the spatial pattern of forest stands were analyzed using Ripley’s K(r) function. The results showed that: (1) The maximal aggregation radiuses of the tree species on the uniform slope (slope A) were larger than 40 m, whereas those of the tree species on the microtopography slope (slope B) were smaller than 30 m. (2) On slope B, the spatial association of R. pseudoacacia with P. betulifolia, A. sibirica, P. simonii and U. pumila varied from being strongly negative to positive at microtopography scales. The spatial association of Populus hopeiensis Hu & Chow with U. pumila also varied from being strongly negative to positive at microtopography scales. However, there was no spatial association between P. betulifolia and P. hopeiensis, P. betulifolia and A. sibirica, P. betulifolia and P. simonii, P. betulifolia and U. pumila, P. hopeiensis and A. sibirica, P. hopeiensis and P. simonii, A. sibirica and P. simonii, A. sibirica and U. pumila, and P. simonii and U. pumila. On slope A, the spatial association between tree species were strongly negative. The results suggest that microtopography may shape tree distribution patterns on the semi-arid Loess Plateau.