川西亚高山森林不同恢复途径物种组成和群落结构动态变化

川西亚高山森林作为西南林区主体,是长江上游的生态屏障,该区域植被恢复方式主要为人工恢复和自然恢复,比较不同恢复方式下森林的物种组成和群落结构动态变化,对于川西亚高山森林恢复与重建有重要的意义,可以为制定合理的森林管理策略提供科学依据。基于茂县山地生态系统定位研究站不同恢复模式形成的的华山松人工林、油松人工林和自然恢复的次生林野外调查数据,分析了2005-2020年乔、灌、草三个层次的群落结构特征和多样性。结果表明:(1)不同恢复途径下,乔木层物种数都呈现增加趋势,华山松人工林、油松人工林、自然恢复的次生林乔木层物种数分别增加了11种、7种、8种;(2)华山松人工林中华山松重要值从48.06%降低到31.1%,乡土阔叶树种四川蜡瓣花进入乔木层,2020年重要值增大至21.62%,油松人工林中油松重要值逐渐降低,从43.59%降至29.76%;自然恢复的次生林中,乡土树种锐齿槲栎逐渐成为第一优势种,2020年重要值增至19.9%。(3) 华山松人工林、油松人工林和自然恢复的次生林中,温带区系成分分别占总属数的71.43%,80.77%和84%,温带区系特征明显。(4)华山松人工林和油松人工林乔木层径级结构均为偏正态分布;而自然恢复的次生林径级分布呈倒"J"形,以小径级个体为主。(5)不同林型的乔木层高度在15年间呈现增加的趋势,具体表现为油松人工林>华山松人工林>自然恢复的次生林。(6)乔木层Shannon-wiener指数和 Simpson指数均表现为自然恢复的次生林显著大于两个人工林,丰富度指数和均匀度指数表现为油松人工林最大;灌木层4个多样性指数均表现为油松人工林最大;草本层的丰富度指数、Shannon-wiener 指数和 Simpson 指数均表现为油松人工林较大,均匀度指数没有显著差异。结论:人工林恢复速度大于自然恢复的次生林,但自然恢复的次生林更新能力更强,且更有利于多样性的保存。两个人工林逐渐由常绿针叶林演替为以常绿针叶树为主的针阔混交林,自然恢复的次生林演替为以常绿阔叶树为主的针阔混交林。     

Molecular identification and allopatric divergence of the white pine species in China based on the cytoplasmic DNA variation

Molecular identification of plant species may be highly related to the geographic isolation and speciation stages among species. In this study, we examined these possibilities in a group of white pines in China. We sampled 449 individuals from 60 natural populations of seven species from sect. Quinquefoliae subsect. Strobus. We sequenced four chloroplast DNA regions (around 3100 bp in length) and two mitochondrial DNAs (around 1000 bp in length). We identified 21 chlorotypes and 10 mitotypes. Both chlorotypes and mitotypes recovered from four species with long disjunction and restricted distributions in northern or northwestern China, Pinus sibirica, Pinus koraiensis, Pinus wallichiana and Pinus pumila are species-specific, suggesting that these cytoplasmic DNAs can distinguish them from the close relatives. Allopatric isolations should have contributed greatly to their genetic divergences. However, both chlorotypes and mitotypes recovered for Pinus dabeshanensis and Pinus fenzeliana distributed in southeastern and southern China are shared or closely related to those found in the widely distributed Pinus armandii. These two species may have diverged or derived from P. armandii recently. All of our findings together suggest that the discrimination power of the molecular identifications based on the cytoplasmic DNA barcodes may show variable discriminability depending on geographic isolation and speciation stages among the sampled species.     

Establishment of the evergreen broad-leaved tree species Castanopsis cuspidata in an abandoned secondary forest in western Japan

Recently, populations of Castanopsis cuspidata have often expanded into secondary forests in western Japan. To determine the establishment processes of this species, we analyzed its spatial distribution in a secondary forest dominated by Quercus variabilis and Quercus serrata that is located adjacent to a stand dominated by C. cuspidata. Saplings, defined as ≥30 cm stem length (SL) and <5 cm diameter at breast height (DBH), were abundant and their size distribution was inversely J-shaped, indicating continuous recruitment. Although seedlings (SL < 30 cm) and small saplings (30 ≤ SL < 50 cm) of C. cuspidata were aggregated near flowering trees of this species, some were found ≥40 m from the nearest adults, suggesting that there is animal-aided dispersal of acorns. The distribution of larger-sized individuals (≥100 cm SL) of C. cuspidata was unrelated to distance from the nearest flowering C. cuspidata or dominant Quercus species (≥5 cm DBH), but was associated with dead Pinus densiflora trees, which were abundant at the site. Thus, the establishment of C. cuspidata in this forest is controlled mainly by two factors, viz. patterns of acorn dispersal by animals, and forest disturbance regime (i.e., deaths of pine trees).     

Variation in soil respiration under the tree canopy in a temperate mixed forest,central China,under different soil water conditions

The forest canopy cover can directly and indirectly affect soil conditions and hence soil carbon emission through soil respiration. Little is known, however, on the effects of canopy cover on soil respiration under the canopy of different tree species and soil water conditions. We have examined the variation in soil respiration at different soil water conditions (dry <10 %, wet >20 %, v/v) under different tree canopy covers in comparison with the canopy interspace in a temperate coniferous (Pinus armandii Franch) and broadleaved (Quercus aliena var. acuteserrata) mixed forest in central China. The results show that soil respiration measured under tree canopy cover varied with canopy size and soil water content. Soil respiration under small-sized canopies of P. armandii (PS) was higher than that under large-sized (PL) canopies, but the difference was only significant under the dry soil condition. However, soil respiration under large-sized canopies of Q. aliena (QL) was significantly greater than that under small-sized (QS) canopies under both dry and wet soil conditions. The difference in soil respiration between differently sized canopies of Q. aliena (33.5–35.8 %) was significantly greater than that between differently sized canopies of P. armandii (2.4–8.1 %). Differences in soil respiration between inter-plant gaps and under QS canopies in both the dry and wet soil conditions were significant. Significant increases in soil respiration (9.7–32.2 %) during the transition from dry to wet conditions were found regardless of canopy size, but the increase of soil respiration was significantly lower under P. armandii canopies (9.7–17.7 %) than under Q. aliena canopies (25.9–31.5 %). Our findings that the canopy cover of different tree species influences soil respiration under different soil moisture conditions could provide useful information for parameterizing and/or calibrating carbon flux models, especially for spatially explicit carbon models.     

五台山林线过渡带华北落叶松格局过程和尺度分析

林线过渡带作为气候变化的预警区,有很重要的研究意义,林线过渡带中人工林的生存与发展对自然保护区景观生态系统影响显著。选取五台山林线内占绝对分布优势的华北落叶松为研究对象。设置50m×50m样地,随机选取5个10m×10m样方进行群落物种信息收集,对乔木的胸径和位置信息进行调查,利用点格局方法和CSR(完全空间随机模型)、HP(空间异质性过程模型)、RL(随机标签模型)对华北落叶松的活立木和枯立木的格局过程进行0—25m尺度上的分析,结果发现:活的华北落叶松平均胸径在11.54cm,死的华北落叶松平均胸径是8.27cm,这个对于30年以上华北落叶松来说胸径值偏小,其生长慢的特点是和林线这个生境特点相适应的。华北落叶松枯立木的聚块很大,在0—15m上都是聚集分布;活立木聚块小出现在0—3m、和21m上。空间异质性过程模型模拟的格局与活立木实际格局差异检验不显著,说明空间异质性可以很好解释活立木格局的成因。随机标签模型模拟结果表明现有活立木和枯立木只在21m附近出现负相关,主要是负密度制约效应是导致的华北落叶松死亡的主要原因,而且对幼苗到幼树的影响最大。同时推测灌木和华北落叶松幼苗和幼树的种间相关作用与其死亡也有一定关系。     

海南岛热带天然针叶林附生维管植物多样性和分布

作为热带林中一个重要的特征性组分, 附生维管植物对于维持热带森林的物种多样性及其生态系统功能均具有重要作用。该文首次系统地报道了热带天然针叶林中的附生维管植物多样性和分布特征。以海南岛霸王岭国家级自然保护区保存完好的热带天然针叶林(我国唯一较大面积分布的南亚松(Pinus latteri)天然林)中的附生维管植物为研究对象, 通过样带调查(共设置12个10 m × 50 m的样带, 记录每个样带内胸径(DBH) ≥ 5 cm树木上附生维管植物的物种名称、株数及附生高度), 分析附生维管植物的物种多样性和空间分布特征。结果表明: 1)热带针叶林0.6 hm ²面积内共有附生维管植物769株, 分属于7科17属27种, 附生兰科植物和萝摩科植物为优势类群; 2)附生维管植物在水平方向上呈现出聚集分布; 3)附生维管植物在垂直方向上, 在中等高度层次(10-20 m)分布最多, 在下层(0-5 m)也有较多的分布; 4)少数附生维管植物对南亚松表现出一定的选择性, 如华南马尾杉(Phlegmariurus fordii)、玫瑰毛兰(Eria rosea)、眼树莲(Dischidia chinensis)和铁草鞋(Hoya pottsii)等; 5)附生维管植物的物种丰富度及多度与宿主胸径均存在显著的正相关关系。     

How to map forest structure from aircraft,one tree at a time

Forest structure is strongly related to forest ecology, and it is a key parameter to understand ecosystem processes and services. Airborne laser scanning (ALS) is becoming an important tool in environmental mapping. It is increasingly common to collect ALS data at high enough point density to recognize individual tree crowns (ITCs) allowing analyses to move beyond classical stand‐level approaches. In this study, an effective and simple method to map ITCs, and their stem diameter and aboveground biomass (AGB) is presented. ALS data were used to delineate ITCs and to extract ITCs’ height and crown diameter; then, using newly developed allometries, the ITCs’ diameter at breast height (DBH) and AGB were predicted. Gini coefficient of DBHs was also predicted and mapped aggregating ITCs predictions. Two datasets from spruce dominated temperate forests were considered: one was used to develop the allometric models, while the second was used to validate the methodology. The proposed approach provides accurate predictions of individual DBH and AGB (R² = .85 and .78, respectively) and of tree size distributions. The proposed method had a higher generalization ability compared to a standard area‐based method, in particular for the prediction of the Gini coefficient of DBHs. The delineation method used detected more than 50% of the trees with DBH >10 cm. The detection rate was particularly low for trees with DBH below 10 cm, but they represent a small amount of the total biomass. The Gini coefficient of the DBH distribution was predicted at plot level with R² = .46. The approach described in this work, easy applicable in different forested areas, is an important development of the traditional area‐based remote sensing tools and can be applied for more detailed analysis of forest ecology and dynamics.     

Variations in leaf morphological and chemical traits in response to life stages,plant functional types,and habitat types in an old-growth temperate forest

Intraspecific leaf trait variations are becoming a topic of interest for many ecologists because individual-based traits are essentially the drivers of variations at the community level. Six coexisting major tree species in an old-growth temperate forest, Northeast China (i.e., Abies nephrolepis, Pinus koraiensis, Acer mono, Fraxinus mandshurica, Tilia amurensis, and Ulmus laciniata) were sampled, and three habitat types (i.e., Hab I: high soil organic carbon with a moderate slope; Hab II: low soil organic carbon with a gentle slope; and Hab III: low soil organic carbon with a strong slope) were used in the plot. We performed a two-way ANOVA to compare the specific leaf area (SLA), leaf dry matter content (LDMC), leaf nitrogen content (LNC), leaf phosphorus content (LPC), and leaf carbon content (LCC) between saplings (1 < DBH ≤ 5 cm) and adults (DBH ≥ 10 cm) and between habitat types within species. We simultaneously evaluated the effects of life stage, plant functional type, and habitat type on the six leaf traits. Our results showed that life stage and habitat type had varied influences on the leaf traits of the six species. Life stage was an important determinant for all leaf traits. Plant functional type was included in the best models for SLA, LNC, and LCC. Habitat type had a greater influence on LDMC than SLA. Meanwhile, habitat type had a greater influence on LNC and LPC than LCC. The correlation between leaf traits with local environmental factors varied across different plant functional types and life stages. We suggest conducting individual-based analyses of leaf trait variations according to plant functional type and life stage to understand the plant life strategies along an environmental gradient may improve understanding of the forest dynamics in an old-growth temperate forest.     

云冷杉天然次生林死木分布格局及空间关联性

为揭示天然次生林群落演替规律,以吉林省汪清林业局金沟岭林场的云冷杉天然次生林为对象,采用相邻网格法调查样地(100 m×100 m)内每株林木(DBH≥1 cm)的基本特征及坐标位置,研究死木的分布格局及空间关联性。结果表明: 死木的径级分布呈左偏单峰山状分布,其中枯倒木呈多峰山状分布;各树种的死木株数与该树种的总株数没有必然联系;树种死木株数与树种混交度之间存在显著负指数关系;死木主要在0～8 m尺度上呈聚集分布,随着尺度的增大,逐渐转变为随机分布或均匀分布,以随机分布为主;中(10 cm≤DBH＜20 cm)、小径级(1 cm≤DBH＜10 cm)死木在8 m以下的小尺度上的聚集分布是造成死木总体在小尺度上呈聚集分布的主要原因。不同径级死木与不同径级活立木的空间关联性差异较大,死木与幼树(1 cm≤DBH＜5 cm)的关系较为明显,尤其是大径级死木与幼树在2～25 m尺度上呈显著正关联性;死木与小树(5 cm≤DBH＜15 cm)没有明显的关联性;中、小径级死木与中树(15 cm≤DBH＜25 cm)在0～3 m尺度上呈正关联性,与大树(DBH≥25 cm)分别在9、11～14 m以及15、42～45 m尺度上呈负关联性。树种在生物学特性、径级分布和空间布局上的差异影响着死木的株数和径级分布;混交程度低的树种可能出现较多的死木;死木空间分布格局随林木径级和研究尺度的大小产生变化;死木与活立木的空间关联性在不同径级和不同尺度上呈现出明显差异。     

Ecological and biogeographical analyses of Mediterranean forests of northern Morocco

Mediterranean forests in northern Morocco have been studied. Tree species composition and abundance were investigated in 84 forest sites, distributed throughout the sandstone formation of the Tangier region. The relative abundance of 15 tree and arborescent shrub species was related, by ordination analysis, to altitude, disturbance by fire, and soil fertility. High-elevation forests were dominated by Cedrus atlantica, Quercus pyrenaica and Pinus pinaster. Sacred forests (protected as holy burial places) had a distinct stand structure, and were considered as refuges, for maintaining biodiversity at landscape scale. The evergreen oak Quercus suber and the semideciduous Quercus canariensis co-dominated the lowland forests. The mean basal area of the studied forests was 34 m² ha^–1. The mean trunk size (dbh) for Q. suber was 24 cm and for Q. canariensis 36.5 cm; in both cases there were indications of declining regeneration at population level. A comparative biogeographical analysis with the equivalent region in southern Spain (separated by the Strait of Gibraltar; 14 km wide), indicated a possible biodiversity loss in the Moroccan forests.     

Ecological characteristics of Abies georgei population at timberline on the north-facing slope of Baima Snow Mountain, Southwest China

Abies georgei is one of the endemic trees at timberline on Qinghai-Tibetan Plateau, but little research has been done about its timberline population. One plot was set up at timberline above 4400 m on the north-facing slope of Baima Snow Mountain in Southwest China, covering an area of 0.8 hm2. Height, DBH (diameter at breast high) or root-collar diameter of seedlings and saplings, and position were recorded for each individual. The population showed a growing trend and the number of individuals decreased with increase of DBH. The survival curve can be described by Deevy-III. The population had 2 distinct peaks of mortality: age I (seedlings, DBH = 0–5 cm) and age V-VI (DBH = 20–30 cm). The highest mortality of seedlings was due to severe climate at timberline. As the saplings grew up, the interspecific and intraspecific competition resulted in another mortality peak. Through SPPA (spatial point pattern analysis), individuals of all age-classes showed uniform, random or clumped distribution with the change of scales; however, they had mainly clumped distribution. Moreover, the relationships between individuals in different age-classes were all significantly correlated with each other. Seedlings showed the highest clumping intensity and scale.     

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.     

Scatter-hoarding rodents use different foraging strategies for seeds from different plant species

Seed predation and dispersal by scatter-hoarding rodents are key processes that determine seed survival, and thus, plant regeneration within forests. For decades, there has been much debate on the important effects of seed size (one of the most important seed traits) on rodent foraging preference. Furthermore, the possible selective forces in the evolution of seed size may be influenced by primary selectivity and how rodents treat seeds after harvesting. In this study, different-sized seeds from four species (Pinus armandii, Pinus densata, Abies sp., and Viburnum sp.) harvested by scatter-hoarding rodents were studied in an alpine forest in Southwestern China for two consecutive years. Our results showed that seed size influenced rodent foraging preferences, with bigger seeds being preferred over smaller seeds, within and across species. Rodents only removed and cached the larger seeds of P. armandii, and ate the seeds of the other three species in situ. Rodents are purely seed predators for these three species. For the cached seeds of P. armandii, significantly positive correlations were observed between seed size and dispersal distance among both primary and secondary cached seeds in 2006, but not in 2005. Our results indicate that among many coexisting species with widely different-sized seeds, scatter-hoarding rodents played important roles in the seed dispersal of the big-seeded species alone. This caching behavior could offset the limited seed dispersal of large-seeded and wingless species (P. armandii), in comparison with that of small winged seed species (P. densata and Abies sp.) and frugivore-dispersed species (Viburnum sp.).     

Differential diameter-size effects of forest management on tree species richness and community structure: implications for conservation

In this paper we tested the hypothesis that logging effects in the adult tree community reverberate upon the regeneration contingent. We examined the differences on the tree community between forest reserves and 10 year-old logged areas in the Yucatan Peninsula. We used a paired design in three independent sites to estimate the effects of logging on tree species richness, diversity, composition and structure. Analyses were conducted differentiating individuals of four diameter-size classes: 1–5, 5–10, 10–25, and >25 cm DBH. We found out that there were differential effects by size. Species richness in the smaller and larger diameter-size classes was significantly lower in logged areas. Floristic composition was also different between logged and unlogged areas, with a trend towards more secondary forest associated species and less primary forest associated species in logged areas, and a higher density of species represented by a single individual in unlogged reserves. In terms of structure, trees DBH <10 cm, lianas, and re-sprouting stumps were more abundant in logged areas. Our findings suggest that 10 years after logging, harvested areas show alterations in structure, and potentially a reduction in species richness. We suggest that to make timber extraction and forest conservation compatible at this site, it is necessary to gain a better understanding of the ecology and regeneration requirements of the less abundant species, and to assess whether current logging practices might hinder their permanence in the study area.     

六盘山典型森林伴随降水的总有机碳(TOC)通量变化特征

在六盘山香水河小流域,选择6种典型森林样地,测定了2011年生长季的大气降水、穿透水、干流、枯落物渗漏水和主根系层(0—30 cm深)土壤渗漏水的总有机碳(TOC)浓度及其相应的通量变化。结果表明,在降水转化为由穿透雨和干流组成的林下降水中,所有样地的TOC浓度都不同程度地增大;虽然林冠截持使林下降水减小,但因雨水淋洗和与林冠发生碳交换,各样地林下降水携带的生长季TOC通量(kg/hm2)(华北落叶松人工林132.28、华山松次生林106.56、油松人工林94.10、灌木林79.49、桦木林66.52、辽东栎次生林63.01)都比林外降水(53.17)不同程度地明显增大,整体看来,林冠的TOC淋出作用在针叶林很大,在阔叶林较弱。在6种森林样地的枯落物层渗漏水中,其TOC浓度彼此相差不大,平均为24.51 mg/L,高于林冠穿透水的TOC浓度;受枯落物截持部分降水及与枯落物TOC交换的影响,4个样地枯落物渗漏水的TOC通量(kg/hm2)(桦木次生林84.35、野李子灌丛129.35、辽东栎次生林79.21、油松人工林114.93)都比其林下降水TOC通量增加了,但华北落叶松人工林和华山松次生林的TOC通量分别降至90.76和104.90 kg/hm2。在测定的华北落叶松人工林和华山松次生林的主根系层(0—30 cm)土壤渗漏水中,TOC浓度均低于枯落物渗漏水;由于水量减小和与土壤发生碳交换,土壤渗漏水的TOC通量均显著低于枯落物渗漏水,两个林分样地分别降至43.04和66.33 kg/hm2。整体来看,林外降水携带的TOC输入通量在林地TOC输入中占有重要地位,林冠的TOC淋洗使其程度不同地增加TOC通量,枯落物层具有增加或减少TOC通量的作用,但主根系层土壤会显著减少TOC输出通量,所以是固定TOC的重要场所。     

关帝山寒温性云杉次生林样地树种组成、结构和空间分布

云杉次生林是关帝山的优势森林植被类型,也是华北亚高山地区寒温性常绿针叶林的代表类型.为更好地了解其物种组成、群落结构等基本特征及其潜在的生态学过程和机制,于2010年在关帝山庞泉沟国家自然保护区建立了4 hm²的云杉次生林固定监测样地(GDS样地).本文以第一次本底调查数据为基础,分析了样地树种组成、结构和空间分布.结果表明: 样地共有木本植物30种,隶属于11科22属.包括分枝的总个体数为26218(其中独立个体数为10266).植物区系组成属北温带成分;不同树种个体数、平均胸径和胸高断面积差异较大,导致群落成层分明,各层优势种明显.乔木层第一亚层树种径级结构呈双峰偏正态分布,乔木层第二亚层树种径级呈近似正态分布,灌木层树种径级呈“L”型分布.乔木优势树种青杄和华北落叶松的空间分布无论在个体数量还是聚集程度上均随径级变化而呈现不同的格局特征.相同径级的两树种,胸径(DBH)≥30 cm的华北落叶松在样地居多且聚集分布于样地中部,而DBH≥30 cm的青杄则相对较少,没有表现出空间聚集性.DBH≤10 cm的华北落叶松个体很少且散生于样地,而DBH≤10 cm的青杄大量聚集于样地中部.DBH≤10 cm的青杄在样地偏西北区域也有大量分布,而DBH≤10 cm的红桦主要分布于样地偏东南区域.灰栒子、土庄绣线菊和四川忍冬等灌木树种也表现出一定的异质性空间分布特征.树种分布格局受生境条件影响,同时与自身发育规律、更新特征及生态习性等相关.     

Common spatial patterns of trees in various tropical forests: Small trees are associated with increased diversity at small spatial scales

Tropical forests are notable for their high species diversity, even on small spatial scales, and right‐skewed species and size abundance distributions. The role of individual species as drivers of the spatial organization of diversity in these forests has been explained by several hypotheses and processes, for example, stochastic dilution, negative density dependence, or gap dynamics. These processes leave a signature in spatial distribution of small trees, particularly in the vicinity of large trees, likely having stronger effects on their neighbors. We are exploring species diversity patterns within the framework of various diversity‐generating hypotheses using individual species–area relationships. We used the data from three tropical forest plots (Wanang—Papua New Guinea, Barro Colorado Island—Panama, and Sinharaja—Sri Lanka) and included also the saplings (DBH ≥ 1 cm). Resulting cross‐size patterns of species richness and evenness reflect the dynamics of saplings affected by the distribution of large trees. When all individuals with DBH ≥1 cm are included, ~50% of all tree species from the 25‐ or 50‐ha plot can be found within 35 m radius of an individual tree. For all trees, 72%–78% of species were identified as species richness accumulators, having more species present in their surroundings than expected by null models. This pattern was driven by small trees as the analysis of DBH >10 cm trees showed much lower proportion of accumulators, 14%–65% of species identified as richness repellers and had low richness of surrounding small trees. Only 11%–26% of species had lower species evenness than was expected by null models. High proportions of species richness accumulators were probably due to gap dynamics and support Janzen–Connell hypothesis driven by competition or top‐down control by pathogens and herbivores. Observed species diversity patterns show the importance of including small tree size classes in analyses of the spatial organization of diversity.     

The role of tree sprouts in the restoration of stand structure and species diversity in tropical moist forest after slash-and-burn agriculture in Eastern Paraguay

The contribution of tree sprouts to the recovery of tropical moist forest in Eastern Paraguay after swidden agriculture was examined in 2–15 yr old forest fallows and compared with sprouting in mature forest. The proportion of stems of sprout origin, as individuals arising from stumps or lower parts of live stems ( 1 m), in the stem density declined from 59.5% (stems 1–4.9 cm DBH) and 21.0% (stems 5 cm DBH) in the young regrowth stands (2–5 yr old) to 32.9% and 19.6%, respectively in the older regrowth stands (10 and 15 yr old). Sprouts were absent in the mature forest. Out of 58 species sampled in the regrowth stands, 28 occured both as resprouts and seed regeneration, 7 were only found as resprouts, and 23 were only present as seed-established individuals. No significant relationship was found between the successional status or the growth form of species and apparent resprouting capacity. Seed-established individuals of Trema micrantha were predominant in the two and three-year old regrowth stands. In the more advanced successional stages, T. micrantha was replaced by Cecropia pachystachia and other secondary species. Species richness increased during succession. Species-abundance distribution in the successional stands followed a log series pattern, whereas the mature forest showed a log normal distribution. Floristic similarity to the mature forest, calculated with the qualitative Soerensen index, increased from 0.45 (1–4.9 cm DBH) in the young regrowth stands to 0.52 in the older regrowth stands. In the tree stratum ( 5 cm DBH), however, floristic composition approached only 0.28 in the younger regrowth stands and 0.44 in the older regrowth stands, respectively that of the mature forest.     

Small mammal assemblages in a disturbed tropical landscape at Pozuzo,Peru

Deforestation in the Peruvian pre-montane forests has increased alarmingly in recent years. Particularly, fragmentation in these forests takes place against a background of very extensive continuous forest. Until now, no studies have detailed how Peruvian small mammals responded to forest fragmentation. In this paper, we report the results of an assessment of nonvolant small mammal fauna in forest remnants (one large fragment and one small fragment) and cattle pasture in a disturbed landscape at Pozuzo, formerly a pre-montane tropical forest in central Peru. In each forest remnant, we quantify habitat parameters and identified small mammals to know if there is a relationship between forest remnant size or microhabitat structure and small mammal assemblages. In addition, we investigated the influence of habitat structure on the presence of small mammal species. We did not find any evidence that habitat structure in large fragment was greater than small fragment. Actually, both forest remnants presented habitat features typical of forests subject to higher levels of disturbance. We found that abundance of small trees (10 - 19 cm DBH) was positively associated with the presence of Marmosops noctivagus, but negatively with the presence of Oecomys bicolor. Likewise, the presence of the arboreal Rhipidomys leucodactylus was associated with the abundance of larger trees (DBH > 50 cm). We recorded 12 small mammal species in large fragment, 9 in small fragment and 3 in cattle pasture. No significant differences were found in species richness between both fragments, but marsupial abundance in the small fragment was greater than large fragment. At Pozuzo, we recorded 9 species restricted to forest habitat and 3 to forest and cattle pastures. However, it is necessary to assess more fragments to improve our knowledge about species survival in this landscape.