Native Species Composition and Diversity of Valuable Woody Plants Regeneration during Fallow Period in Kamwatta, Moruca, Guyana

An intelligent method of shifting cultivation to regenerate vegetation after a long fallow period is critical information for restoration strategies. The literature review identified that the assessment of woody plant species on abandoned farmland has never been done before in Kamwatta, Moruca Region 1. In addition, more information should be available in indigenous communities and at the national level, including more documentation of the utilization of natural resources by the Warrau community. This study assessed the valuable woody plant species that grew during the fallow periods. Nine farmlands were randomly selected along a 100 m transect, each with varying fallow periods. In order to collect information on the age of farm abandonment, the researcher employed a mixed-methods approach. First, we found how long each farm had been fallow by administering a semi-structured questionnaire. Then, we conducted a flora survey to gain information on the variety and abundance of valuable plants using the age of farm abandonment as a dependent variable. The data analysis included the number of valuable woody trees with a diameter of >10 cm, seedlings and saplings with a diameter of <10 cm, the location of identified trees, and the uses of identified tree species. Microsoft Excel was used to code and analyze the questionnaire, while QGIS, Shannon’s Index of Diversity, and Simple Linear Regression were used to analyze the inventory data. The results showed that the respondents listed 38 valuable woody species, and 79% occurred in the studied area. The field verification revealed that the dominant family in the area was Mimosaceae. Species abundance increased with fallow up to 10 years before declining in the latter years. Plant diversity and abundance had a weak relationship with the age of abandoned farmlands for woody trees, while the seedlings and saplings showed no relationship.

Survival of Seedlings of Native Woody Species in the Rehabilitation of Gold Mined-Site within a Three Years Old Acacia mangium Willd Plantation of St. Elizabeth-Mahdia, Guyana

Active restoration is a critical component of biodiversity conservation for degraded tropical forest ecosystems caused by artisanal gold mining, and the success of restoration is dependent on native species selection. However, significant knowledge gaps exist regarding when and where to plant trees. This article reports on a revegetation trial undertaken in St Elizabeth, Mahdia, Guyana, to assess the survival and RGR (Relative Growth Rate) of three native woody trees and shrubs planted within three years old Acacia mangium Willd trees pruned and unpruned blocks. ANOVA (Analysis of Variance) for a completely randomized block design with four blocks, two pruned and two unpruned, within A. mangium plots. Biochar treatment was added to the plants during transplanting. Thirty-six (36) wildlings of Humiria balsamifera (Aublet.) (Tauroniro), Goupia glabra Aublet (Kabukalli), and Vismia guianensis (Aublet.) Choisy (Bloodwood) were collected and raised in a tree nursery for two weeks. The native plants were transplanted 3 m apart, survival observations and each seedling’s initial height and diameter were measured and recorded. After the experiment, 13% of seedlings from a population of 720 had died, with the highest mortality being experienced at the 92 days of the experiment (t ≤ 122 days). While the overall survival rates were high, emphasizing the importance of field trials on native and exotic species in different environments is essential to fill the knowledge gaps on suitable species for restoration in degraded areas with other land use histories.

Native Expanding <i>Merremia boisiana</i>Is Not More Allelopathic than Its Non-Expanding Congener <i>M. vitifolia</i>in the Expanded Range in Hainan

Exotic invaders may possess novel biochemical weapons that native plants do not have, and these novel biochemical weapons may be more allelopathic than those from native plants to other native competitors. During range expansion, native species also encounter many new plant competitors. Thus, allelochemicals from native expanding species may also be more novel and allelopathic than those from non-expanding species to other plant competitors in the expanded range. We test this hypothesis using the native expanding Merremia boisiana and its non-expanding congener M. vitifolia in year 2012 inthe expanded range inHainan. In petridish bioassays, we found that aqueous extracts of M. boisiana leaves were often less inhibitory or more stimulatory to seed germination and seedling growth of five vegetable species than those of M. vitifolia leaves. In pot culture, we also found that aqueous leaf extracts of the two congeners could both inhibit the growth of a naturally co-occurring plant Paederia scanden, but their effects did not differ from each other. These results indicate that while allelopathy may contribute to the competitive ability of M. boisiana, it may not act as a novel weapon explaining its success in the expanded range in Hainan.

Spatial dynamic patterns of saltmarsh vegetation in southern Hangzhou Bay:Exotic and native species

A saltmarsh has developed rapidly on the mudflat of Andong Shoal,in southern Hangzhou Bay,over the last decade since embankment.The saltmarsh vegetation changes are driven by both sediment dynamic conditions and the competition between the exotic species Spartina alterniflora(S.alterniflora) and the native species Scirpus mariqueter(S.mariqueter).This study attempted to investigate large-scale spatial variations in the exotic and native species,by analyzing and interpreting a time series(2016-2018) of high-resolution(less than 1 m) remote sensing images.The total area of the saltmarsh increased at a rate of 1.07 km^2/year,due to the accretion of the whole tidal flat.The spatial patterns revealed a new bimodal pattern for S.alterniflora invasion.S.alterniflora expanded over the upper to middle saltmarsh at a rate of1.68 km2/year.However,the S.alterniflora patches at the seaward edge expanded at a negative rate of-0.005 km^2/year,indicating a different pattern in competition:S.alterniflora had more advantages in the upper saltmarsh,while S.mariqueter had more advantages in the pioneer zone with low elevation.Consequently,S.alterniflora mainly established new habitats by invading S.mariqueter in the middle saltmarsh,but S.mariqueter occupied the bare mudflat for tradeoff.Our results aindicated that the interspecific competition result between S.alterniflora and S.mariqueter depended on elevation,and low elevation might create a favorable environment for S.mariqueter to win the competition with exotic species.This finding could be applied to future invasive species control and saltmarsh management.

Relationships between native tree species and soil properties in the indigenous forest fragments of the Eastern Arc Mountains of the Taita Hills, Kenya

The relationship between soil properties and spatial distribution of native woody species was studied in three Taita Hills forest fragments which, although degraded, are ranked among 34 biodiversity hotspots of the world due to their high biodiversity of both plant and animal species. This relationship was assessed by using Spearman correlation and principal component analyses （PCA）. The results of these analyses should be useful in instituting forest restoration programs that are crucial for the forests. Both the soil and vegetation studied were sampled from 17 subplots in the natural forest fragments of Ngangao （120 ha）, Chawia （86 ha） and Mbololo （185 ha）. The soil variables measured were： pH, texture, soil nutrients of C, N, Ca, P, K, Mg and Na. In total 36 native tree species from 13 families were identified from the three forest fragments. Ordination results show that axis 1 accounted for 35% and axis 2 for 25% of the total variation in species composition, indicating that the structure of vegetation is related to two major environmental gradients. The correlation analyses of species and soil properties showed that Na and clay particles were the most important determinants of species distribution; pH and soil variables such as C, N, Ca and P also played minor roles. Unexpectedly, some species （e.g. Psychotria petitii） showed positive relationships with Na attributed to possible substitution for K. Relationships with P were both positive （e.g. Craibia zimmermannii） and negative （e.g. Albizia gummifera） with some species, attributable to pH levels. An ANOVA for soil variables showed that there were differences in the Ca content in Mbololo （due to the parent material） and P in Ngangao where a special relationship was observed between some of the species. The presence of gaps accounted for the distribution of seedlings but not for the saplings, whose distribution responded more to factors similar to those to which mature trees respond. Soil-species relationships that were established may be utilized along with soil analyses when choosing native species for restoration.

Pre-sowing treatments for improved germination and growth of two rare native species of Bangladesh

Pre-sowing treatments are expected to increase seed germination.This evaluates response to pre-sowing treatments and the growth performance of two native and rare tree species,Garuga pinnata Roxb.and Vitex glabrata R.Br.The hard seed coats were treated by rubbing with sand paper,nail clipping,and immersion in water and acid（H_2SO_4）.Results indicate that G.pinnata showed a 90% germination rate and 30% germination energy when seed coats were nicked with a nail clipper.Rubbing with sand paper was the best pre-sowing treatment for V.glabrata,resulting a 80% germination rate and 30% germination energy.G.pinnata and V.glabrata seedlings from seeds soaked 24h in water resulted in maximum heights and collar diameters.These were significantly higher（at p〈0.05） than those of other treatments.The results indicate that scarification or nicking of seeds may have some negative impacts on seedling growth.Therefore,it is difficult to recommend a pre-sowing treatment of seeds for achieving both maximum germination and good early seedling growth.

Responses of Native Tree Species to Soil Water Stress in a Tropical Forest on Limestone,Vietnam

Forests over limestone in the tropics have received little attention and limestone forests in Vietnam have been overlooked to an even greater extent in terms of tree physiology. In Ba Be National Park, Vietnam, soil water availability in limestone forests seems to be the most limiting factor in the dry season. Therefore, in order to enhance the preliminary knowledge of choosing native tree species for enrichment planting in the restoration zone, characteristics of the 20 native tree species to soil water stress were investigated in a limestone forest. One-ha plot each consisting of twenty-five 20 m × 20 m plots was established in undisturbed forests. All trees ≥ 10 cm DBH were measured in 20 m × 20 m plots, while twenty-five 5 m × 5 m subplots were established in order to sample the regeneration of tree species with a DBH < 10 cm. The Scholander apparatus and freezing point osmometry were used in order to measure the leaf water potential (Ψw) and leaf osmotic potential (Ψπ) of the 20 native tree species, respectively in this study. 61 species belonging to 34 families of all trees with a DBH ≥ 10 cm were recorded in one ha, while 31 species representing 18 families of trees < 10 cm DBH were identified in 625 m2. The 20 species’ leaf water and osmotic potential values revealed significant differences among species. The maximum leaf water potential was not affected by any anticipated sources of variation, while the minimum water potential, however, showed significant variation to soil water stress. The results in the study area emphasized the importance of water factors in influencing tree species distribution;it could be concluded that native species with wide water potential ranges would be better able to withstand water changes and might be thus good candidates for reforestation (enrichment planting) in limestone areas.

Natural durability of wood of ten native species from northeastern Mexico

Thorn scrub vegetation in Mexico is distributed over 50 million ha, where native tree species are the source of forage, timber, firewood and charcoal. Research describing wood durability of species from this vegetation type has not been fully determined, nor classified according to international standards. Thus, the aim of this study was to determine and classify the natural durability of ten woody species. Their natural durability was determined according to the European Pre-Norm 807, the loss of dynamic modulus of elasticity （MOEdyo） （MPa） was determined and wood mass loss （g） after being exposed to Trametes versicolor and Coniophora puteana fungi. Wood durability was classified accord- ing to the European Norm 350-1. Highly significant differences （p 〈 0.001） were found between the durability of woody species. The more durable species with lower MOEdyn lost were Condalia hooked （57.5% ± 0.6%）, Havardia pallens （58.2% ± 0.4%） and Acacia schaffneri （58.9% ±6.3%）. Species with lower mass loss after exposed to Coniophora puteana were Ebenopsis ebano （6.3% ±1.9%）, Condalia hooked （8.6% ±2.3%） and Cordia boissieri （11.8% ±2.3%）. E. ebano （7.1% ±2.4%）, Condalia hooked （8.2% ± 2.5%） and Cordia boissieri （11.5% ± 3.1%） showed the lower mass lost after exposed to T. versicolor. According to European Norm 350-1, three woody species were classified as very durable and durable species.

Studies on Tracheary Element of Several Native Cycad Species in Australia and Two American Plants

Cycas angulata, Cycas armstrongii and Cycas conferta that are native species of Australia were collected in Darwin city of tropical region, Zamia erosa and angiosperm Guaiacum officinale of Zygophyllaceae which are introduced collected in the Darwin Botanic Gardens, and were carried out light microscope and electron microscope observed research to tracheary element and parenchyma tissue cells of leaflet, rachis and stem. The results showed that there are more vessel elements in their xylems;the length of vessel element of Cycadaceae with Zamiaceae are not obvious difference, the length of vessel element of angiosperm Guaiacum officinale is shorter, but their diameter is smaller, we thought that the characteristics which the length of vessel element is longer and the diameter is bigger are more evolutionary, because thus vessel, their number which interconnected points of possessed perforations’ end walls of vessel element is fewer, and the passageway space is larger so that the conduction speed and quantity are faster and more in unit length range and unit time. These vessels are annular vessels, spiral vessels, scalariform vessels, reticular vessels, pitted vessels and scalariform-pitted vessels, etc. In the transverse section, the vessel elements of Cycadaceae and Zamiaceae are circular, polygonous, more similar to vessel characteristics of leaf and stem of some angiosperms;however, the number of circular vessel of Guaiacum officinale is more, about occupy 35%, others are polygonous. The diameter of vessel is that annular vessel, spiral vessel is least, scalariform vessel or scalariform-reticular vessel is medium, reticular vessel and pitted vessel are the biggest, the characteristic is same as angiosperm. In Cycas conferta, etc. plants often can see several large perforations in the end walls, some species are several big scalariform or pitted perforations formed multiple perforation plates, in many vessel element lateral walls, there are some perforations formed a horizontal transport avenue of aqueous solution. The scale of diameter of Cycas vessel element is similar to that of Zamia, but the diameter of more vessel elements of Cycas angulata and Cycas conferta is bigger than the latter, and is bigger than that of Guaiacum officinale, although Cycas plants are more primitive than Zamia plants, and Guaiacum officinale is more evolutionary, but the scale of vessel diameter of Cycas plants is similar to Zamia or bigger than the latter, even larger than Guaiacum officinale, these showed that cycads have evolutionary and more developed characteristics in aqueous solution transport system. In Guaiacum officinale, more vessel element has been not seen the ridges in the different directions of side walls which can make vessel has more mechanical supportability, but some possessed the ridges;however, more vessel elements are twist shape and can twist together each other, thus the state can increase their mechanical supportability, and their synergy with fiber elements which is longer with a twist shape, therefore their capability of xylem conduction and the combine mechanical support capability with mechanical tissue are also stronger. In the respect of observed parenchyma tissue, any parenchyma tissue cells are without perforation, all cell walls are smoothed and like a membrane. Aimed at only one or two people pointed the query about Jeffery’s method, some scholars have made comparative researches, their research used as following methods: 1) The fresh materials were cut sections 1 - 2 mm thick by hand (the query person provided and thought right method), were examined with SEM. 2) The materials were treated by Jeffrey’s Fluid and observed with SEM and so on. The results showed that the pit membrane, the remnants in the perforation and the structural characteristics of perforations were not different;and the results of our comparative research in past time and this research all justified that Jeffrey’s method is reliable and reasonable. Meanwhile, our research results showed that only vessel element can form perforation, in other all parenchyma tissue cells cannot form perforation are also proved that the perforations of vessel element are naturally inherited character. Analyzed from the structural characteristics, although they distributed so far apart from each other, they are a well and unified taxonomy system;we thought that Australia’ most species or all species of Cycadaceae came from Asia, and it is impossible from Africa, because the latter only has one more evolutionary species and lack of fossil of Cycadaceae, these species of Cycadaceae are the descendants of ancestor species;America possessed more genera of Zamiaceae, this family is mutual with Africa and Australia, we thought that these genera of Zamiaceae in Australia and America came from Pangea before continental drift in Jurassic Period, this family is also maybe one of the proofs to Australia drifted from Pangea to present position after Jurassic Period. The characteristics of tracheary element of several different genera of cycads and angiosperm further showed that more primary species or taxon, their more tissue characteristics are not also more primary, because of the need to adapt the environment, they are also constantly evolving. The research is important significant and theory reference to understand cycads evolutionary aqueous solution transport system, and understand the ecological adaptation mechanism which why present cycads of 3 families in world major distributed in tropical or subtropical regions, even many drought and barren areas.

Improvement of Native Pasture Productivity through Introduction of Various Types of Palatable Species on Dry Lands in Timor

This research was aimed to evaluate the productivity of native pasture in Timor Island by introducing various palatable species.The study was carried out on native pasture in Tuatuka,Timor Island for seven months.The study was performed by using randomized block design(RBD)with eight treatments(S0:no introduction,S1:Cynodon dactilon,S2:Dicanthium aristatum,S3:C.plectotachyus,S4:Brachiaria decumbens,S5:Desmanthus virgatus,S6:Macroptilium atropurpureum,S7:Clitoria ternatea)with four replications.Procedures on this study include trial plots preparation,tillers preparation for each species,introduction of species in trial plots,maintenance and observation of the productivity.Variables observed were forage production(fresh and dry matter(DM)in ton/ha),nutrient content(%)and stock capacity(animal unit(AU)/ha).Data were analyzed for variance based on RBD and followed by Duncan’s test.Analysis of variance showed that introduction of species had a very significant effect(p<0.01)on all observed variables.The introduction of M.atropurpureum produced the highest fresh forage(2.1 t/ha)and DM production(0.69 t/ha).M.atropurpureum also had the highest DM content(43.61%),nitrogen free extract(52.52%)and stock capacity(1.06 AU/ha).The highest crude protein and crude fiber content were found in D.virgatus(4.31%and 36.62%).The highest extract ether was observed in D.aristatum(1.48%).No introduction had the lowest productivity,but demonstrated the highest ash content.The introduction of palatable species increased the productivity of native pasture in Timor and M.atropupureum was the best introduced species.

The non-native species to the intercontinental regions of Asia (on an example Trans-Baikal territory)

This article is devoted to the study of the composition, diversity and distribution of non-native plant elements to the intercontinental regions of Asia on an example Trans-Baikal territory. The number of non-native plants in the Trans-Baikal areas is determined by the degree of urbanization, favorable climate and the availability of skidding ways proximal to their vicinity.

Weed Species Composition in Paddy Field of Usur Town,Bade Local Government,Yobe State,Nigeria

Farmers are eager to know the various types of weeds in paddy fields.This will help in choosing the best weed management practice for effective weed control as well as reducing rice yield losses.The objectives of the study are to identify the weeds species affecting the rice field,to assess the composition of weeds species,to classify the weed species into different families,genera,species,common names,Hausa names,lifecycles,life forms,native/exotic species,propagation and uses,and to determine the dominant weed species.Random vegetation surveys were conducted.Weeds observed were photographed,and prepared as herbarium specimens.Standard key manuals and checklists were utilized for weed identification and later organized using the Angiosperm Phylogeny Group(APG)classification system.A total number of 72 plants species distributed within 16 families and 50 genera were inventoried.The annuals(66.67%)were the dominant weed followed by perennials(33.33%)while biennials were the least.The broad leaves were the dominant weed(44.61%)identified followed by Poaceae(27.7%)and Sedges(11.11%).Results obtained from this study could be useful in choosing the best management practice and in making a decision on the choice of herbicides and directing research towards improved weed control measures.

混交比例对桉树-乡土树种混交林优势树种叶片资源获取性状的影响

桉树-乡土树种混交林在提高林分生产力和生态系统功能等方面具有较大潜力。该研究以南亚热带4种桉树-乡土树种混交林(桉树与乡土树种混交比例分别为5׃5、6׃4、7׃3、8׃2)和桉树纯林为研究对象,研究了3种优势乡土树种华润楠(Machilus chinensis)、阴香(Cinnamomum burmannii)、灰木莲(Manglietia glauca)和速生树种尾叶桉(Eucalyptus urophylla)的叶片生理、结构和化学性状在不同比例混交林中的差异。结果表明,4优势造林树种的叶片性状存在明显的种间差异,其中灰木莲的比叶面积(SLA)、光合磷利用效率(PPUE)、单位质量叶片最大光合速率(A_(mass))和蒸腾速率(T_(mass))以及叶片养分含量最高,说明灰木莲采取资源获取型的生态策略;尾叶桉的SLA、A_(mass)、T_(mass)及叶片养分含量最低,但具有最高的PPUE,说明尾叶桉兼顾了资源获取型和保守型的物种特征。灰木莲与尾叶桉在SLA、A_(mass)、T_(mass)、PPUE、叶片氮含量和氮磷比等叶片性状上几乎没有任何重叠,说明灰木莲与尾叶桉之间的叶片资源利用高度互补,可能是与尾叶桉混交的理想树种。物种水平上,灰木莲叶片氮含量、华润楠叶片磷含量以及干季时阴香叶片A_(mass)和PPUE随乡土树种混交比例增加有增加的趋势,但总体上树种混交比例对于4造林树种的叶片结构、化学和生理性状的影响不大;林分水平上,桉树-乡土树种混交林的比叶面积、光合能力以及叶片氮磷比显著高于尾叶桉纯林,说明桉树与乡土树种混交能够提高林分整体的光捕获和光合能力,但同时也加剧了植物生长的磷限制。因此,建议在未来南亚热带桉树人工林的构建与改造中,应优先挑选与桉树资源利用互补并能够优化混交林磷素循环利用的乡土树种。

海南热带海岸海防林植被恢复的探索与实践

文章分析了海南岛热带海岸存在植被生态退化问题,针对主要的退化问题钛锆砂矿废弃地的植被退化和单一树种的人工木麻黄海防林的缺陷,提出了分三步走恢复海岸海防林植被的学术思路,即恢复和巩固木麻黄海防林;建立引入乡土树种的混交林型海防林;促进混交林演替成具地带性植被特征的天然林型海防林。按照这个思路开展了近20年的海岸植被生态恢复的实证研究和应用实践,验证了其可行性,实现了初步构建乡土林型的海防林植被,达到了研究构想预期的效果。研究成果为海南岛以及华南沿海热带海岸的海防林生态恢复提供了可借鉴的范例。

广西盾翅藤不同地理种源生长情况调查及南宁市引种表现初探

为探究盾翅藤在广西的种质资源分布概况、原生地概况,并探究不同种源引种至南宁市后的生长表现,实地走访调查广西6个盾翅藤地理种源(靖西、龙州、崇左、大新、大化、平果),记录并测定各种源伴生植物及土壤性质,而后将各种源引种至南宁市进行繁殖、栽培,对比各种源植株生长及食用产量。结果表明:盾翅藤主要伴生植物有23科31种,以桑科(Moraceae)为主,灌木、藤本植物居多;平果种源原生地土壤碳、氮含量最高,分别达69.00和4.62 g/kg;大化种源全磷含量最高,达3.18 g/kg;崇左种源土壤肥力较差,地理分布上越靠北土壤养分含量越高。不同种源盾翅藤引种至南宁市后植株枝条数量差异显著,而枝条总长度、食用产量则差异不显著,以龙州种源生长最好,3项指标分别达21.10个、5.13 m和90.12 g;其次是东部、北部种源,西部种源生长最差。相关性分析表明,土壤养分含量部分指标与植株生长指标之间相关关系显著或极显著,原生地土壤尚未对盾翅藤本身性质造成较大影响。隶属度分析表明,龙州种源引种至南宁市后生长表现最佳,最适宜南宁市推广种植;平果种源次之,靖西、崇左种源不推荐在南宁市引种栽培。

城市建设中节约型园林植物群落存在问题和建议

在杭州选取城市中心区域较为典型的具有节约型园林特征的8个公园,对其植物群落开展调查发现,多数公园森林覆盖率超过了50%,乔木树种的覆盖率占比依旧不高,不透水面积占比同样差异巨大;不同公园之间乔木树种覆盖率、草坪覆盖率差异巨大,乔木树种、植物种类差异不同,乡土树种数量尚可;植物群落树种的丰富度差异并不明显。对于这些现状和问题,提出了提升园林景观的绿量、提高植物群落的丰富度、增加园林群落的郁闭度、增加抗旱树种的引入、提高立体绿化的比例、提高乡土植物的比例等建议。

乡土树种在中原地区城市园林绿化中的应用

我国中原地区夏季高温湿热,冬季寒冷干燥,这种气候环境对园林绿化中树种的适应能力要求较强,在选择园林绿化乡土树种配置时,既要确保其适合中原地区的自然环境,又要兼顾其品种的多样化与和谐性。该文通过对乡土树种在中原地区园林绿化应用中的重要作用进行分析研究,旨在为美丽、和谐城市建设提供参考。

4种乡土树种幼苗对酸铝胁迫的响应差异分析

【目的】酸铝毒害是南方人工林培育中常见的生产性问题。本文旨在探究乡土树种对酸铝胁迫的抗性差异,为人工林高效栽培提供参考。【方法】本试验以红锥、荷木、樟树、火力楠4种南方主要乡土造林树种为研究对象,在人工控制环境条件下,通过水培法,分析了不同酸铝处理下,各树种幼苗生长生理方面的变化。【结果】在pH 5.0、无铝添加处理下,供试树种幼苗均遭受到了酸胁迫伤害,幼苗存活率下降,叶绿素含量、净光合速率(Pn)、水分利用效率(WUE)、气孔导度(Gs)降低,蒸腾速率(Tr)、丙二醛(MDA)含量升高,POD、SOD活性增大。在pH 5.0+0.5~1.5 mmol·L^(-1)硫酸铝复合胁迫下,随着铝添加浓度增加,幼苗存活率减小,叶绿素含量、Pn、WUE、Ci降低,MDA含量增大,Gs先下降后上升,POD、SOD活性先增大后减小的趋势。通过主成分分析评价,在无铝添加的酸胁迫下,以荷木的抗性最强,其次为火力楠、樟树、红锥,而在酸铝复合胁迫下,供试4个树种的抗性表现为:火力楠>荷木>红锥>樟树。【结论】相较樟树、红锥,火力楠、荷木抗酸铝毒害能力较强。

Biodiversity and Invasibility: Distribution Patterns of Invasive Plant Species in the Himalayas, Nepal

Invasive plant species are exerting a serious threat to biological diversity in many regions of the world. To understand plant invasions this study aims to test which of the two plant invasiveness hypotheses; ‘low native diversity' vs. ‘high native diversity', is supported by the regional distribution patterns of invasive plant species in the Himalayas,Nepal. This study is based on data retrieved from published literatures and herbarium specimens. The relationship between invasive plant species distribution patterns and that of native plant species is elucidated by scatter plots, as well as by generalized linear models. The native plant species and invasive plant species have similar distribution patterns and the maximum number of invasive plant species is found in the same altitudinal range where the highest richness for native tree species is found. There is a clear trend of higher invasive plant richness in regions where native tree species richness is relatively high.Consequently, the native plant richness is highest in the central phytogeographic region, followed by the eastern and the western regions, respectively. The invasive plant species also follows a similar trend.Additionally, the invasive plant species richness was positively correlated with anthropogenic factors such as human population density and the number of visiting tourists. This study supports the hypothesis that ‘high native diversity' supports or facilitates invasive plant species. Further, it indicates that nativeand invasive plant species may require similar natural conditions, but that the invasive plant species seem more dependent and influenced by anthropogenic disturbance factors.