Woody Species Alpha‐diversity and Species Abundance Distributions in an African Semi‐deciduous Tropical Rain Forest

Understanding plant species diversity patterns and distributions is critical for conserving and sustainably managing tropical rain forests of high conservation value. We analyzed the alpha‐diversity, species abundance distributions, and relative ecological importance of woody species in the Budongo Forest, a remnant forest of the Albertine Rift in Uganda. In 32 0.5‐ha plots, we recorded 269 species in 171 genera and 51 families with stems of ≥2.0 cm in diameter at breast height (dbh). There were 53 more species with stems of ≥2.0 cm dbh than with stems of ≥10 cm dbh, of which 33 were treelets and 20 were multi‐stemmed shrubs. For both minimum stem diameter cut‐offs (i.e., ≥2 cm dbh vs. ≥10 cm dbh), the Fabaceae, Euphorbiaceae, Ulmaceae, and Meliaceae families and the species Cynometra alexandri, Lasiodiscus mildbraedii, and Celtis mildbraedii had the highest relative ecological importance. The relative ecological importance of some species and families changed greatly with the minimum stem diameter measured. Alpha‐diversity, species richness, and species abundance distributions varied across historical management practice types, forest community types, and as a function of minimum stem diameter. Species richness and Shannon–Weiner diversity index were greater for species with stems of ≥2.0 cm dbh than of ≥10 cm dbh. The decrease in species evenness with an increasing number of plots was accompanied by an increase in species richness for trees of both minimum diameters. This forest is characterized by a small number of abundant species and a relatively large proportion of infrequent species, many of which are sparsely distributed and with restricted habitats. We recommend lowering the minimum stem diameter measured for woody species diversity studies in tropical forests from 10 cm dbh to 2 cm dbh to include a larger proportion of the species pool.     

The Importance of Large-Diameter Trees to Forest Structural Heterogeneity

Large-diameter trees dominate the structure, dynamics and function of many temperate and tropical forests. However, their attendant contributions to forest heterogeneity are rarely addressed. We established the Wind River Forest Dynamics Plot, a 25.6 ha permanent plot within which we tagged and mapped all 30,973 woody stems ≥1 cm dbh, all 1,966 snags ≥10 cm dbh, and all shrub patches ≥2 m². Basal area of the 26 woody species was 62.18 m²/ha, of which 61.60 m²/ha was trees and 0.58 m²/ha was tall shrubs. Large-diameter trees (≥100 cm dbh) comprised 1.5% of stems, 31.8% of basal area, and 17.6% of the heterogeneity of basal area, with basal area dominated by Tsuga heterophylla and Pseudotsuga menziesii. Small-diameter subpopulations of Pseudotsuga menziesii, Tsuga heterophylla and Thuja plicata, as well as all tree species combined, exhibited significant aggregation relative to the null model of complete spatial randomness (CSR) up to 9 m (P≤0.001). Patterns of large-diameter trees were either not different from CSR (Tsuga heterophylla), or exhibited slight aggregation (Pseudotsuga menziesii and Thuja plicata). Significant spatial repulsion between large-diameter and small-diameter Tsuga heterophylla suggests that large-diameter Tsuga heterophylla function as organizers of tree demography over decadal timescales through competitive interactions. Comparison among two forest dynamics plots suggests that forest structural diversity responds to intermediate-scale environmental heterogeneity and disturbances, similar to hypotheses about patterns of species richness, and richness- ecosystem function. Large mapped plots with detailed within-plot environmental spatial covariates will be required to test these hypotheses.     

The spatial relationship between post‐crop remaining trees and the establishment of saplings in Pinus sylvestris stands in Spain

Question: What is the spatial relationship between remaining trees and the establishment and development of recruited saplings? Location: The Pinus sylvestris forest Pinar de Valsaín, in the Sistema mountain range (central Spain). Methods: Three 0.5 ha plots have been analysed. The saplings were located in a 2 m x 2 m grid, characterizing their spatial pattern through a nested ANO VA. The spatial pattern of stems was analysed using the L(d) function. To analyse the spatial relationship between stems belonging to different cohorts, the intertype L_rs(d) function was used. Finally a new function K_rx(d) is presented as a method to analyse the relationship between the spatial distribution of stems and the sapling density (a sampled continuous variable). Results: The mother trees show cluster pattern at scales of ca. 12 m ‐ 22 m, leading to a spatial pattern at 14 m–16 m for the saplings during the regeneration period. At the beginning of the shelter phase, saplings less than 1.30 m in height show spatial repulsion from the old crop at distances above 10 m, whereas taller saplings show repulsion at shorter distances, due to the suppression of sapling development near the mother trees. At the end of the regeneration period, saplings < 1.30 m appear under the last remaining mother tree canopies. Conclusions: In the stands analysed, located at the southern limit of Pinus sylvestris distribution, this species behaves as half‐shade tolerant. This study shows that the K_rx(d) function might be widely applied to analyse the relationship between patterns that occur at different scales or between a point pattern and a continuous variable, being a useful tool for analysing some forest processes.     

桥山林区麻栎种群不同发育阶段空间格局及关联性

为探究麻栎种群不同发育阶段的空间分布特征及关联性,以黄土高原南部桥山林区麻栎天然次生林为研究对象,用L(r)函数对麻栎种群不同发育阶段空间分布特征及关联性进行分析。结果表明:(1)样地内麻栎种群各发育阶段数量结构均为不规则倒"J"型,种群结构稳定,能实现持续更新。(2)麻栎种群总体的空间分布特征受生境异质性影响较大,纯林样地中,种群在0—10 m尺度上表现为高强度聚集分布,5—35 m尺度表现为低强度聚集;混交林样地中,0—5 m尺度上表现为高强度聚集分布,5—35 m尺度上则表现为低强度聚集分布。(3)随着种群的发育及尺度的增大,麻栎种群空间聚集强度减弱,纯林样地内,麻栎幼苗在0—6 m的小尺度表现为聚集分布,6—12 m尺度上表现为随机分布;幼树在各尺度上均表现为聚集分布;中龄树与成龄树在各尺度上均表现为随机分布。混交林样地中,仅幼苗在0—6 m尺度上表现为聚集分布,其余各阶段在各尺度下均趋于随机分布。(4)种群不同发育阶段不同尺度空间关联性不同,纯林样地中,幼苗与幼树在1—2 m小尺度上呈负相关,幼树与中龄树在8 m尺度呈正相关,其余各生长阶段之间在任意尺度上均无关联性;混交林样地中,幼树与中龄树在2—12 m尺度上表现为正相关,其余各生长阶段之间在各尺度上均无关联。在未来的森林经营中,应对不同发育阶段、不同生境的种群进行不同抚育措施,促进种群良性发育。     

Efficiency of inventory plot patterns for the estimation of woody vegetation recruit density in a tropical dense forest in Bénin

This study assessed the effectiveness of plot patterns for estimating recruit density of woody species in the dense forest of Lama Reserve (Bénin). The experimental design consisted of thirty 0.04 ha plots randomly settled in the forest and each subdivided into four hundred 1‐m² quadrats. Within each quadrat, recruits (dbh ≤10 cm) were counted and saplings (h ≥ 2 m and 2 cm ≤ dbh < 7 cm) and young trees (h ≥ 2 m and 7 cm ≤ dbh < 10 cm) were measured in dbh. In each 0.04 ha plot, seven different plot shapes and sizes were considered by grouping adjacent 1‐m² quadrats. Relationship between mean square error of the estimation of the density of recruitments and the plot sizes was modelled using the Smith law. Results obtained showed an average value of density of recruitments of 10.7 plants/m² with Green index value of 0.01. Shape and size of plots highly influenced the estimation of the density of recruitments. Rectangular plots of length/width = 2 and size of 72 m² (12 m × 6 m) were most efficient for the estimation of the density of recruitments in tropical dense forest with standard error of 0.79 plants/m².     

Spatial distribution patterns of two predominant emergent trees in a tropical rainforest in Sarawak,Malaysia

Spatial distribution patterns of two emergent tropical rainforest tree species (Dryobalanops aromatica & D. lanceolata) were examined in where they were dominant (17–20% of total basal area of canopy trees) in Sarawak, East Malaysia. Newly established seedlings (< 2 years old) were restricted to areas < 40 m from mother trees for both species, suggesting a limited seed dispersal. Seedling (< 1 cm in dbh) density was highest around conspecific adults ( 30 cm in dbh). Negative spatial patterns were observed between larger juveniles (1–5 cm in dbh) and conspecific adults for both species; the most dense populations of sapling (1–5 cm in dbh) and poles (5–30 cm in dbh) were found at a distance of 15–20 m from the nearest conspecific adult. Seedlings of both species were distributed randomly with respect to light conditions evaluated by a forest floor diffuse site factor and a canopy closure index. Saplings of both species, and poles of D. lanceolata, were distributed under more open conditions than expected from spatially random distributions, and from average light conditions of all species of the same size classes. Possible mechanisms for the observed distribution patterns and intermediate canopy dominance of Dryobalanops were discussed from the viewpoints of gap-dynamics and distance-dependent mortality.     

Beyond the tropics: forest structure in a temperate forest mapped plot

Question: How do the diversity, size structure, and spatial pattern of woody species in a temperate (Mediterranean climate) forest compare to temperate and tropical forests? Location: Mixed evergreen coastal forest in the Santa Cruz Mountains, California, USA. Methods: We mapped, tagged, identified, and measured all woody stems (≥1 cm diameter) in a 6‐ha forest plot, following Center for Tropical Forest Science protocols. We compared patterns to those found in 14 tropical and 12 temperate forest plots. Results: The forest is dominated by Douglas‐fir (Pseudotsuga menziesii) and three species of Fagaceae (Quercus agrifolia, Q. parvula var. shrevei, and Lithocarpus densiflorus), and includes 31 woody species and 8180 individuals. Much of the diversity was in small‐diameter shrubs, treelets, and vines that have not been included in most other temperate forest plots because stems <5‐cm diameter had been excluded from study. The density of woody stems (1363 stems ha^?1) was lower than that in all but one tropical plot. The density of large trees (diameter ≥30 cm) and basal area were higher than in any tropical plot. Stem density and basal area were similar to most other temperate plots, but were less than in low‐diversity conifer forests. Rare species were strongly aggregated, with the degree of aggregation decreasing with abundance so that the most common species were significantly more regular than random. Conclusions: The patterns raise questions about differences in structure and dynamics between tropical and temperate forests; these need to be confirmed with additional temperate zone mapped plots that include small‐diameter individuals.     

湖南省阳明山山顶苔藓矮林优势种空间分布格局

山顶苔藓矮林是亚热带山地常绿阔叶林区在极端气候与环境条件下发育的一种群落变型,通过研究优势植物的分布格局与规模,可以有效地指导植被保护与管理活动。在湖南阳明山国家级自然保护区的山顶苔藓矮林区设置3个样地,应用相邻格子法对优势种云锦杜鹃(Rhododendron fortunei)进行每木调查,在不同取样尺度(面积)上采用方差/均值比率法(v/m)、负二项参数(k)、丛生指数(I)、平均拥挤度(m~*)、聚块性指数(m~*/m)、聚集指数(C_a)和格林指数(GI)等聚集强度指数对云锦杜鹃种群分布格局进行分析。结果表明:阳明山山顶苔藓矮林优势种云锦杜鹃种群在北、南、东三个方位上的空间分布格局总体上为聚集分布,随着取样尺度的增大,聚集格局强度和规模依次减弱;而山顶苔藓矮林优势种群不同年龄阶段的空间分布特征为随着种群年龄的增大,其空间分布格局呈聚集强向聚集弱、以至于向随机分布发展;阳明山山顶苔藓矮林优势种群及其分布格局形成的主要原因是云锦杜鹃种群本身的种子繁殖及传播方式和类营养繁殖等生物学特性及方位、坡向等环境因子影响所致。     

Clonality in the Endangered <Emphasis Type="Italic">Ambrosia pumila</Emphasis> (Asteraceae) Inferred from RAPD Markers; Implications for Conservation and Management

Clonal plants have the ability to spread and survive over long periods of time by vegetative growth. For endangered species, the occurrence of clonality can have significant impacts on levels of genetic diversity, population structure, recruitment, and the implementation of appropriate conservation strategies. Here we␣examine clone structure in three populations of Ambrosia pumila (Nutt.) Gray (Asteraceae), a federally endangered clonal species from southern California. Ambrosia pumila is a perennial herbaceous species spreading from a rhizome, and is frequently found in dense patches of several hundred stems in a few square meters. The primary habitat for this species is upper terraces of rivers and drainages in areas that have been heavily impacted by anthropogenic disturbances and changing flood regimes. RAPD markers were employed to document the number and distribution of clones within multiple 0.25 m² plots from each of three populations. Thirty-one multi-locus genotypes were identified from the 201 stems sampled. The spatial distribution of clones was limited with no genotypes shared between plots or populations. Mean clone size was estimated at 9.10 ramets per genet. Genets in most plots were intermingled, conforming to a guerrilla growth form. The maximum genet spread was 0.59 m suggesting that genets can be larger than the sampled 0.25 m² plots. Spatial autocorrelation analysis found a lack of spatial genetic structure at short distances and significant structure at large distances within populations. Due to the occurrence of multiple genets within each population, the limited spread of genets, and a localized genetic structure, conservation activities should focus on the maintenance of multiple populations throughout the species range.     

基于无人机的昆明海口林场宽地坝林区植物群落建群种格局研究

建群种是植物群落优势层中的主要物种,对群落环境有显著控制作用。空间格局是植物种群的基本特征之一,探讨建群种的空间格局是理解生物与生境之间关系和认识群落生态过程的有效途径。空间格局特征包括种群空间关联性及其空间分布型。利用无人机技术,获取昆明海口林场半湿润常绿阔叶林和落叶栎类林的多光谱遥感影像,采用ArcGIS Pro软件进行遥感影像分类并提取滇青冈(Cyclobalanopsis glaucoides)、光叶石栎(Lithocarpus mairei)、滇石栎(L.dealbatus)、栓皮栎(Quercus variabilis)、槲栎(Q.aliena)植株树冠中心点空间坐标。在Programita Febrero 2014软件中进点格局分析。结果表明:各物种10m以下呈均匀分布或随机,随尺度增加,渐渐表现为聚集分布。光叶石栎种群和滇石栎种群空间关联性表现为负相关。     

天山云杉种群空间格局与动态

天山云杉(Picea schrenkiana)林是天山林区的重要针叶林。研究调查了两块分别代表天山云杉不同演替阶段的标准地,应用Ripley’s K系数法研究了天山云杉种群空间格局与动态。结果表明：天山云杉是聚集型种群,天山云杉活立木、枯死木、天山桦(Betula tianschanica Rupr．)和天山柳(Salix tianschanica Rgl．)的空间格局均为聚集型;天山云杉枯死木的聚集强度大于天山云杉活立木的聚集强度;天山桦和天山柳的聚集强度大于天山云杉枯死木的聚集强度;天山桦和天山柳的空间格局随种群所处的演替阶段不同而不同,增长型种群在所有尺度上其空间格局都为聚集型,在大于70m尺度上表现为均匀格局,而天山云杉成熟林中的天山桦和天山柳只在小尺度(0～40m)上表现为聚集。随着天山云杉的生长,其聚集强度逐渐减小,聚集半径不断增大。从50a以下天山云杉到50～100a的天山云杉其聚集强度急速减小,这有利于天山云杉幼树获得足够的资源,是天山云杉幼树的一种生存策略或适应机制。150a以上天山云杉的聚集强度增加,这是由于天山云杉生长到150a左右时开始出现成熟后死亡,形成林窗有利于天山云杉林的更新。研究还对Ripley’s K系数法和频次检验法进行了比较,Ripley’s K系数法能够分析各种尺度下的种群空间格局,且不受样方大小的影响,结果清楚、直观。     

Tree species diversity and forest structure in relation to microtopography in a tropical freshwater swamp forest in French Guiana

Diversity of tree association and forest structure were analysed in relation to microtopography and flooding intensity in a tropical freshwater swamp forest in the Sinnamary river basin, French Guiana. A 530-m-long vegetation transect was established through a hummock-hollow terrain. Nine 10 m× 50 m sample plots, perpendicular to the main transect, were located so that each was as microtopographically uniform as possible. Trees with dbh (diameter at 1.3 m) 10 cm were censused in all plots and trees with 2 cm dbh < 10 cm in three plots. Sixty tree species belonging to 39 genera and 30 families were recorded. The study area was divided into low and high sites according to microtopography and flooding intensity. According to the Czekanowski similarity matrix, the tree association in low, most frequently flooded, sites differed from that in the high sites under intermediate or low flooding intensity. The low sites had higher stand density and lower species richness than the high sites. Trees with dbh 10 cm in low sites were small and stand basal area (SBA) was about the same in low (69.6 m² ha^–1) and high (64.3 m² ha^–1) sites. The low areas were dominated by Pterocarpus officinalis (38% of stems with dbh 10 cm and 36% of SBA) and Malouetia tamaquarina (26 and 15%). Diospyros guianensis (13.4% of stems with dbh 10 cm and 6.1% of SBA), a Caraipa sp. (14.0 and 7.9%), Lecythis corrugata (6.6 and 3.5%) and emergent Caryocar microcarpum (0.9 and 13.9%) were abundant in high sites. Nodulated legume trees, P. officinalis, Hydrochorea corymbosa and Inga disticha, comprised 44% of stems in the low sites. The abundant nodulation suggests that symbiotic dinitrogen fixation may be an adaptation to N-depleted waterlogged soils. Other adaptive responses were litter accumulation between the buttresses of P. officinalis, which formed hummocks above surface water, and clonal growth habit of M. tamaquarina, which resulted in formation of monospecific groves in low sites.     

Diversity,structure and dynamics of a gallery forest in central Brazil

The structure and dynamics of approximately 64 ha of undisturbed gallery forest were studied over six years. Trees from 31 cm gbh (c. 10 cm dbh) were measured every three years from 1985. They were in 151 (10×20 m) permanent plots in the Gama forest in the Federal District of Brazil. Natural regeneration (individuals under 31 cm gbh) was measured in subplots (of 2×2 m, 5×5 m and 10×10 m) within the 200 m² plots. The total tree flora (gbh31 cm) consisted of 93 species, 81 genera and 44 families in 1985. The Leguminosae, Myrtaceae and Rubiaceae were the families richest in number of species. Most individuals and species were under 45 cm diameter and 20 m high while the maximum diameter per species ranged from 30 to 95 cm. The density structure of trees and natural regeneration was similar, in which the densities of c. 80% of the species represented less than 1% of the total density. The periodic mean annual diameter increment for trees from 10 cm dbh, was c. 0.25 cm/year. Variability was high with coefficients of variation c. 100% or more. The Gama community may maintain tree diversity and structure in undisturbed conditions. Regeneration of c. 80% of the species was found in the establishing phase (poles); the diameter structure was typical of native forests with the number of individuals decreasing with increasing size classes and showing little change over the six years; recruitment compensated for the mortality of most of the abundant species. The soils in Gama gallery forest were dystrophic with high aluminium content. Multivariate analysis suggested the stream, natural gaps and edges as the main causes of floristic differentiation at the community level.     

The cupule-carpel theory. A defence

Background: Spatial patterns within forests reflect their formative processes. In Kamchatka, the dominant stone birch (Betula ermanii) forest exists in a primeval state. Betula species can reproduce via clonally produced ramets, leading to a clustered distribution of stems, or from seed on open ground, although subsequent mortality may obscure initial establishment patterns.

Methods: Spatial patterns of all trees and regenerating stems in a fully mapped 0.25 ha plot were analysed using the g(r) function and the pattern of trees modelled using a Matérn cluster process. Mark correlation analysis was used to detect patterns in stem sizes.

Results: Clustering of trees at scales up to 3 m occurred, with model parameters indicating a density of 180 clusters ha^?1, each containing on average three stems >1 cm diameter at breast height (DBH) within a 1.6 m radius. Stem size compensation was detected, with nearby trees smaller than expected by chance. Regenerating stems were strongly clustered at scales below 3.5 m and from 5–8 m, and were aggregated around small trees (<10 cm DBH) but not large trees (≥10 cm DBH), or in gaps.

Conclusions: These patterns are consistent with clonal reproduction followed by competition as the processes determining spatial structure in old-growth stone birch forests.     

Population structure and spatial patterns for trees in a temperate old-growth evergreen broad-leaved forest in Japan

The population structure and spatial pattern of major tree species in a warm-temperate old-growth evergreen broad-leaved forest in the Tatera Forest Reserve of Japan were investigated. All stems 5 cm in diameter at breast height (DBH) were mapped on a 4 ha plot and analyses were made of population structure and the spatial distribution and spatial association of stems in different vertical layers for nine species. This was done in the context of scale dependency. The plot was located on a very gentle slope and 17.1% of its canopy layer was in gaps. It contained 45 woody plant species and 4570 living stems with a basal area of 63.9 m² ha^–1. Castanopsis cuspidata var. sieboldii, the most dominant species for the basal area, had the maximum DBH among the species present, fewer smaller stems and a lower coefficient of statistical skewness of the DBH distribution. The second most dominant species, Dystilium racemosum, had the highest stem density (410 ha^–1), more abundant smaller stems and a relatively higher coefficient of skewness. Most stems in different vertical layers showed a weakly aggregated distribution with loose colonies as basic units. Gap dependency for the occurrence of stems under the canopy layer was weak. Maximum slope degree of the plot also weakly affected the occurrence of stems. Spatial associations varied among intra- and interspecific cohorts in the different layers and spatial scales examined, and positive associations among cohorts were found more frequently as the scales examined became larger. This tendency suggests that key factors forming observed spatial associations might vary with the spatial scales.     

Community dynamics of Ogawa Forest Reserve,a species rich deciduous forest,central Japan

Forest community dynamics were studied for 4 years in a 6 ha permanent plot of species rich, old-growth, temperate deciduous forest in Ogawa Forest Reserve, central Japan. The gap formation rate, recruitment, mortality, gain and loss rate in basal area during 4 years were 42 m2 ha^–1 yr^–1, 1.74% yr^–1, 1.19% yr^–1, 1.12% yr^–1 and 0.88% yr^–1, respectively. The turnover time calculated from them ranged from 58 to 240 years. Both the mortality and mortality factors were size dependent; trees in middle size class had smallest mortality, and the proportion of the trees killed by disturbances increased with size. Gap creations were concentrated in a particular year, suggesting a large heterogeneity in time. Spatial distribution of recruited trees were biassed to the old gaps (older than 4 years), especially that of the species with Bell-shaped dbh distribution (shade intolerant) strongly associated with the gaps. Recruitment in tree stems and the loss of basal area, thus had the larger variability than mortality of stems and this forest, and the species with L-shaped dbh distribution seemed to going to increase the importance in the future if the present trend continues to be held. The turnover time of population is positively correlated with the maximum dbh size of the species, indicating the slow change of the population of large sized species.     

Spatial patterns of trees in natural forests of East-Central Europe

The analysis of spatial patterns is one of the ways to estimate the role of competition among trees in forest dynamics. Three hypotheses concerning distribution patterns in old-growth stands were tested: (1) fine-scale spatial patterns of trees are regular; (2) patterns do not differ significantly from a random distribution, and (3) spatial patterns at larger scales are clumped because of site heterogeneity. Old-growth forest stands in Poland and the Czech Republic were analysed with a modified Ripley K function, using distribution maps of tree stems. Fine-scale spatial patterns (with distances among trees not exceeding 15 m) were usually intermediate between random and regular. Trends towards a regular distribution occurred more often among dead than among live individuals. No significant relationships between tree species were found at smaller scales; however, at larger scales (distances from 15–25 m) negative associations between some species were found. This reflects site heterogeneity rather than any direct influence of one tree species upon another.     

木林子大样地两个木姜子属物种空间分布格局及关联性

该文以湖北木林子国家级自然保护区15 hm2大样地同属物种[木姜子(Litsea pungens)和黄丹木姜子(L. elongata)]为研究对象,通过成对相关函数和不同零模型(完全空间随机模型、异质泊松模型和先决条件模型)的方法分析两个物种的空间分布格局、种内和种间空间关联性,从同属物种的空间分布格局角度探讨群落的构建机制。结果表明:(1)种群空间分布格局研究中,两个种的空间分布格局大致为聚集分布。基于CSR零模型,木姜子和不同径级(幼树、小树、中树和成年树)的聚集尺度分别为0~114 m、0~103 m、0~56 m、0~34 m和0~16 m,黄丹木姜子和不同径级的聚集尺度分别为0~150 m、0~150 m、0~59 m、0~56m和0~14 m;基于HP零模型,木姜子整体的空间分布格局聚集尺度为0~23 m,其中幼树、小树和中树均在0~22 m呈现聚集分布,成年树仅在0~3 m尺度上表现为聚集分布,黄丹木姜子整体的空间分布格局聚集尺度为0~36 m、140~150 m,各径级的聚集尺度分别为0~35 m、0~35 m、0~12 m和0~6 m。(2)种内关联性研究中,木姜子和黄丹木姜子不同径级个体种内关联在小尺度上基本呈现正关联,随着尺度的增大变为微弱的无关联或负关联。(3)种间关联研究中,木姜子对黄丹木姜子和黄丹木姜子对木姜子的空间关系大致相同。总体上,两物种之间均体现为在30 m尺度内对另外一个物种呈现正关联,40~68 m尺度内呈现负关联;不同径级之间都表现为无关联,偶尔出现正关联或负关联。研究认为,种群空间分布格局基本上为聚集分布,其主要受到生境异质性和扩散限制的影响,木林子大样地中木姜子和黄丹木姜子空间分布格局存在相似性,而不同的生境偏好可能是导致两同属物种共存的原因。     

Spatial genetic structure of Simarouba amara Aubl. (Simaroubaceae), a dioecious, animal-dispersed Neotropical tree, on Barro Colorado Island, Panama

Simarouba amara (Simaroubaceae) is a vertebrate-dispersed, insect-pollinated Neotropical tree found in lowland moist forest from upper Mesoamerica to the Amazon basin. We assessed the spatial genetic structure of S. amara within the 50-ha Forest Dynamics Plot on Barro Colorado Island in the Republic of Panama. A total of 300 individuals were genotyped using five microsatellite loci, representing 100 individuals with a dbh>or=10 cm, 100 individuals of 1-10 cm dbh, and 100 individuals of <1 cm dbh. The 200 individuals in the two larger size classes were also genotyped with 155 AFLP loci. Spatial autocorrelation analysis using Moran's Index detected significant genotypic association at the smallest distance classes for 1-10 cm dbh (0-20 m) and >10 cm dbh (0-40 m) size categories. Significant spatial autocorrelations were detected over larger scales (0-140 m) in <1 cm dbh individuals. The relatively weak genetic structure of S. amara, in comparison to other recent studies, may be explained by pollen and seed dispersal over the 50 ha plot, overlapping seed shadows, and postrecruitment mortality.     

Regeneration of Rhizophora mucronata (Lamk.) in degraded mangrove forest: Lessons from point pattern analyses of local tree interactions

Spatial structural patterns emerging from local tree interactions influence growth, mortality and regeneration processes in forest ecosystems, and decoding them enhance the understanding of ecological mechanisms affecting forest regeneration. Point-Patterns analysis was applied for the very first time to mangrove ecology to explore the spatial structure of Rhizophora mucronata regeneration in a disturbed mangrove forest; and the pattern of associations of juvenile–adult trees. R. mucronata trees were mapped in plots of 50 m × 10 m located at the seaward, central and landward edge along 50 m wide transect in the forest, and the mapped patterns were analysed with pair correlation and mark-connection functions. The population density of R. mucronata differed along the tidal gradient with the highest density in the central region, and the least near the shoreline. The study revealed that short distance propagule dispersal, resulting in the establishment of juveniles in closed distance to the mother trees, might not be the driving force for distribution of this species. The spatial structural pattern of R. mucronata population along tidal gradient showed a characteristic spatial aggregation at small scale, but randomly distributed as the distances become larger. There was a distinct spatial segregation between recruits and adult trees, and hence spatially independent. Though, adult–adult trees associations did not show a clear spatial segregation pattern; the recruit–recruit species associations exhibited significant clustering in space. Although habitat heterogeneity might be responsible for the local scale aggregation in this population, the effect of plant–plant conspecific interactions is more probable to inform the long-term structure and dynamics of the population of R. mucronata, and ditto for the entire forest.