Effects of natural forest conversion and plantation tree species composition on soil macrofauna communities in Northeast China mountains

As primary and secondary forests are being replaced by plantations across the globe,the soil macrofauna community structure is also affected,but little is known about the impact of mixed culture plantations compared with monocultures on the soil macrofauna.To determine the impact of forest conversion on soil macrofauna,we surveyed the soil macrofauna in two broad-leaved and three coniferous monoculture stands and four coniferous-broadleaved mixed stands,and in adjacent reserved secondary stands as a reference.Soil macro fauna community composition was significant affected by forest type,season and their interaction(P<0.05).The abundance,taxa richness and diversity of soil macro fauna changed to different degrees depending on the plantation type.Broadleaved monoculture stands and secondary stands had similar macrofauna abundance and taxa richness,but values were lower in coniferous stands than in secondary stands.The Shannon index for macrofauna in coniferous stands was also the lowest,but the Pielou index did not differ between forest types.The negative effects of the conifer monoculture on soil macro fauna were not present in the mixed stands with broad-leaved trees.Forest conversion impacted soil properties;soil moisture,NO_(3)^(-),and pH were significant drivers of soil macrofauna community structure.The impact of forest conversion on soil macrofauna was closely dependent on tree species composition and diversity.The macro fauna community structure in the broadleaved and the mixed stands were relatively similar to that in the natural forest,and thus recommended for forest conversion in the study area.

Species composition and influencing factors of understory woody species in Robinia pseudoacacia plantations on the Loess Plateau

Black locust(Robinia pseudoacacia L.)plantations have contributed significantly to soil and water conservation and ecological reconstruction on China’s Loess Plateau.Understanding the impact of stand and environment on species composition of understory woody plants will improve the stability of existing black locust plantations.Ten stands were selected in second-generation black locust plantations in tableland and gully areas of the Loess Plateau.The number of understory tree species in the tablelands was significantly lower than in the gully stands.Regenerated black locust(19.76%)and Rubus corchorifolius L.f.(64.85%)were the most abundant understory tree and shrub species,respectively,in the tableland stands;Broussonetia papyrifera(L.)L’Hér.ex Vent.(6.77%)and Acanthopanax senticosus(Rupr.Maxim.)Harms.(37.22%)were most abundant in the gully stands.Species richness(S),Shannon diversity(H),and evenness index(J)of the understory plants were significantly lower in the tableland stands than in the gully stands.More diverse understory species and community structures occurred in the gully stands.Differences in species diversity among landform positions may be attributed to differences in soil moisture.In addition,77.57%of the variation in understory species composition was explained,among which shrub and herb coverage,stand age,leaf area index,slope and total soil phosphorus in the 10-20 cm layer were the main factors.Soil organic carbon and total potassium significantly impacted S,H and J.Considering the environmental conditions and the biological characteristics of the plants investigated,R.corchorifolius should be given priority in the development of tableland stands,while B.papyrifera and Celtis sinensis Pers.should form mixed forests with black locust in gully stands.This management could promote biodiversity and stability of the existing black locust plantations but also optimize regional landscape patterns.

Species Composition and Diversity of Fagus longipetiolata in Leigong Mountain, Guizhou Province

[Objectives]To understand the species composition and diversity of Fagus longipetiolata community.[Methods]The F.longipetiolata community in Guizhou Province was investigated by typical plot method.[Results]There were 107 species of vascular plants belonging to 79 genera and 51 families in Leigong Mountain F.longipetiolata community,including 3 species of pteridophytes belonging to 3 genera and 3 families,104 species of spermatophytes belonging to 76 genera and 48 families,including 3 species of gymnosperms belonging to 3 genera and 3 families,and 101 species of angiosperms belonging to 73 genera and 45 families.The types of Leigong Mountain F.longipetiolata community were divided into 7 formations,and the top 10 important species of each formation were Fagaceae,followed by Lauraceae and Ericaceae.The change trend of tree layer richness index was formation I>formation IV>formation VI>formation III>formation VII>formation II>formation V;the dominance index was formation I>formation IV>formation V>formation VI>formation VII>formation III>formation II;H diversity index was formation V>formation II>formation I>formation III>formation VII>formation VI>formation IV;the evenness index is formation II>formation III>formation VI>formation VII>formation IV>formation I>formation V;the total diversity index of the community,formation I(3.67)was the highest,formation V(2.74)was the lowest,manifested as formation I>formation III>formation VI>formation II>formation IV>formation VII>formation V.[Conclusions]The community stability is closely related to its species composition,and the background species is the basis for the survival of the community;the existence of rare species can further enhance the community diversity index and enhance the community stability.

Species composition and diversity of Euphausiacea in the East China Sea

Based on the data of four seasonal oceanographic censuses in the East China Sea （23°30＇-33°00＇N, 118°30＇-128°00＇E） in 1997-2000, the species composition and the diversity of Euphausiacea were discussed as well as their relations with environmental variables. Results showed that there were totally 23 different species of Euphausiacea, in which 16 occurred in spring and autumn respectively; 15 were present in summer and only 10 were observed in winter. According to the calculated alternation fraction （R）, the species composition showed a clear seasonal alternation with the changes of seasons. Moreover, the environmental variables had different impacts on the distribution of Euphausiacea in different seasons. The distribution in summer was not significantly related to water temperature and salinity. However, the surface salinity was a major determinant of the distribution in spring. In autumn, both surface and bottom temperatures were influencing factors. The distribution in winter depended on salinity at the surface and 10 m depth as well as the temperature at 10 m depth. Regarding to the seasonal variation of species composition, the variations in spring, summer and autumn were not so significant as those in winter. Except in summer, the species number changed with synchronous water temperature and salinity, as a result of the presence of warm currents in the East China Sea and the habitability of the dominant species. Since Euphausiacea tend to agglomerate, the distribution of different species was uneven, which was the major reason for the low diversity of Euphausiacea in the East China Sea.

Species composition and diversity of pelagic fishes based on a longline fishery catch in the North Pacific Ocean

Evaluation of spatial-temporal variability of species composition and diversity in oceanic ecosystems is not easy because it is usually difficult to obtain sufficient data quantifying such variability.In this study,we examined pelagic species diversity indicators,species richness,Shannon-Wiener index of diversity and Hurlbert's species evenness,for fish assemblages from two areas(north and south) in the North Pacific Ocean(2°±12°N,178°E±165°W) during May±July 2008.The assemblages were based on data collected by an onboard scientific observer during a commercial longline fishing trip.The species richness and Shannon-Wiener diversity index of fish assemblages in the northern area were slightly higher than those in the southern area,although these differences were not significant(t test,P.0.05).Non-parametric multidimensional scaling and analysis of similarities indicated that there were significant differences in fish assemblages between the two areas(P,0.01).

Studies on the species composition and biodiversity of free-living marine nematodes in the southern Huanghai Sea

Free-living marine nematodes were sampled and studied at a grid of 22 stations （from 32°29.35′ to 37°0.56′N, 122°0.37′ to 125°1.16′ E） in the southern Huanghai Sea in January 2003. Nematode abundance varied from 50.5 to 127.2 ind./cm^2 [（83.1 ±24.7） ind./cm^2] at different stations, 80.1% of the total nematodes were in the surface layer （0-2 cm） of sediments. Two hundred and twenty-three species or taxa of marine nematodes belonging to 145 genera, 32 families and four orders were identified and first recorded in the Huanghai Sea. The common dominant species were Dorylaimopsis rabalaisi, Terschellingia longicaudata, Sphaerolaimus bolticus, Metalinhomoeus longiseta, Quadricoma scanica, Prochromadorella sp., Paramonohystera riemanni, Marylynnia sp. 1, Vasostoma spircaum, Halalaimus spp., Pierrickia sp. 1 and Promonhystera faber. Nematode diversity was correlated with sediment granularity. Pearson correlation analysis showed that Shannon-Wiener index had highly significant positive correlation with a sand content and negative correlation with a silt-clay content （P〈0.01）; species richness index （d） had significant positive correlation with the sand content and negative correlation with the silt-clay content （P〈0.05）. The diversity of the southern Huanghai Sea was lower than that in the center of Bohai Sea, but the dominance was higher.

Spatial structure and species composition of soil seed banks in moving sand dune systems of northeast China

Soil seed banks can provide a mechanistic for understanding the recruitment dynamics and can inform conservation management of ecosystems. To investigate the contribution of soil seed banks to vegetation restoration in moving sand dune systems, we compared seed structure and species similarity between soil seed banks and standing vegetation among moving sand dunes, ecotones and dune slacks in northeast China. Average seed density in dune slacks was greater than in ecotones or moving sand dunes. Seed density in the soil layer of 0-10 cm was greater than at 10-20 cm both in the moving sand dunes and the eco- tones, but seed densities were similar at depths of 10-20 and 20-30 cm in moving sand dunes. Moreover, the spatial autocorrelation of seed density on moving sand dunes was weak but was strong on the ecotones and dune slacks. The species in the soil seed bank of moving sand dune systems were nearly all annuals, and the low similarity was mainly due to the lack of perennial species that were common in standing vegetation. Consequently, vegetation restoration cannot mainly rely on the soil seed banks in the movingsand dunes and more attention should be paid to protection of the dune slacks because they are the main source of seed disperse and seedling recruitment in moving sand dune systems.

SPECIES COMPOSITION, HORIZONTAL DISTRIBUTION AND SEASONAL SUCCESSION OF PHYTOPLANKTON IN THE CHANNEL FROM DONGTING LAKE TO THE CHANGJIANG RIVER, CHINA

The species composition, horizontal distribution and seasonal succession of the phytoplankton at five sampling stations in the channel between Dongting Lake and the Changjiang River, China were studied from May 1995 to December 1997. A total of 416 taxa were observed; diatoms comprised the most diverse taxonomic group representing 58.2 % of the total species. The β-mesotrophic indicators were 92 taxa or 22 % of the total, the α-mesotrophic or α,β-eutrophic indicators decreased distinctly to 20 taxa or 4.8 % of the total. The species number and composition of various phyla were approximately similar at Stations 1, 2, 3 and 4, but at Station 5 the number of species was the minimum and the ratio of diatoms to total phytoplankton in the number of species was the highest. In seasonal succession of the phytoplankton species, the number was the highest in May and June, lower in December, January, March and July in the channel. The dominant species were different in different months. The ratio of diatoms species number to blue green algae and green algae species number diminished gradually from winter to summer and autumn, and then increased gradually from autumn to winter and early spring in the annual cycle. Margalef, Simpson and Shannon-Weaver diversity indices changed in different months, their values were higher in winter, lower in summer. Nygaard’s diatoms quotients were lower in winter, then in spring and autumn, higher in summer. These results indicated that the water quality was the best in winter, better in spring and autumn than in summer. The relationship between the structure of the phytoplankton community and the water environmental quality was discussed.

Ecology and Species Composition of Fresh Water Snails in Amassoma Community and Niger Delta University Campuses, Bayelsa State, Nigeria

The knowledge about the population dynamics of freshwater snail intermediate host and their roles in disease transmission is little known in Bayelsa State. This study investigated the species composition of fresh water snail intermediate host in Amassoma community and the Niger Delta University Campuses during August 2019-October 2019 across five locations (Main campus Hostel, E.T.F Building, Ogboebi-Ama, Efeke-Ama, Ogbopina). Snails were collected from the water bodies with the aid of a scooping net and hand picking. The morphological identification of the snail intermediate host followed standard procedures. From the result, five hundred and seventy-one freshwater snails belonging to four genera and five species were recorded. The presence of Lymnae and Bulinus in the locations highlights foci for fascioliasis and schistosomiasis. The presence of Melanoides spp. is novel in Bayelsa State. The public health implications of these snails have called for timely control intervention.

Species composition,structure,regeneration and management status of Jorgo-Wato Forest in west Wollega,Ethiopia

Species composition,structure,regeneration,and management status of Jorgo-Wato Forest(JWF)was studied.Number of individuals,diameter at breast height(dbh)and height of woody species(dbh≥2.5 cm)were counted and measured in each plot.Group discussions with local farmers residing around JWF were carried out to understand the management of the JWF.Forest structural attributes were computed using descriptive statistics;correlation was used to assess relationships between the structural variables.A total of 4313 individuals(dbh≥2.5 cm)with a density of 1477 ha-1 were recorded,the number of species and individuals decreasing with increasing dbh classes.Species with the highest Importance Value Index(IVI)were Pouteria adolfifriedericii(37.7),Syzygium guineense subsp.afromontanum(23.6),Dracaena afromontana(20.5),Chionanthus mildbraedii(15.9),and Croton macrostachyus(12.3).Overall distribution of woody plants across size classes exhibited a reverse J-pattern,suggesting a healthy population structure and good regeneration.Nevertheless,some species were not represented in smaller diameter classes,including juvenile phases,which indicate a lack of regeneration.For these species,monitoring and enrichment planting would be necessary,along with curbing illegal cutting and coffee farming in the natural forest.Management interventions in the JWF need to consider livelihood options and to respect the rights of local communities.

Species Composition and Gear Characteristics of the Macrobrachium Fishery of the Cross River Estuary,Nigeria

The Cross River Estuary,Nigeria,is an important shrimping area for artisanal fishermen of the coastal communities.The multi-species Macrobrachium fishery is exploited with three main gears,namely beach seine,push net and trap.Studies on species composition of this fishery recorded thirteen shrimp species,one swimming crab (Callinectes amnicola) and two fish species (Eleotris sp.and Pellonula leonensis).The shrimp species identified included Macrobrachium macrobrachion (83.39% and 55.69% by number and weight,respectively),M.vollenhovenii (9.66% and 37.18%),M.equidens (3.8% and 2.87%),juveniles-sub-adults of Penaeus notialis (1.11% and 1.3%),M.dux,M.felicinum,Palaemonetes africanus,Palaemon maculatus,Palaemon elegans,Desmocaris sp.,Leander sp.,Nematopalaemon hastatus and Alpheus pontederiae.While the selectivity index for trap was 0.25,beach seine and push net had a lower index of 0.063.The results present the first comprehensive and representative report for the Estuary shrimp fishery and will assist in the management of the biodiversity of this ecosystem.

A fuzzy distinguishability on species composition similarities of pelagic fishes in different years in the southern Taiwan Strait

A fuzzy mathematical method is used to discriminate the similarities of pelagic fishes land- ed in the 9180 hauls by 10 light-seine information vessels in the southern Fujian waters from 1989 to 1998. The results indicate that the dominant species of the communities had an obvious alternation and the fuzzy adjacency of annual species composition varied between 0. 659 and 0. 923 with an average value of 0. 791. The fuzzy clustering analysis indicates that the annual fuzzy adjacency in general remains good although the species composition of the pelagic fishes has changed to a certain degree since 1992. This paper concludes that the community structure of pelagic fishes in the southern Taiwan Strait remains rel- atively stable and the state of fish stocks shows a good potentiality for a larger utilization.

Species Composition and Diversity Analysis of Lava Flow in Different Periods in Wudalianchi Nature Reserve,China

The species composition and succession discipline after eruption of volcanoes in Wudalianchi Nature Reserve, China, including new volcanoes, such as Huoshao and Laohei Mountains, and old volcanoes, such as East Jiaodebu, Wohu and North Gelaqiu Mountains, in different historical periods were investigated by adopting the concept of space as a substitute for time. The species composition, community characteristics and diversity analysis in the remains of volcanic lava flow at various stages were analyzed. The results showed that 192 types of vascular plants that belonged to 50 families and 126 genera in the survey areas existed in the restoration process of primary succession. At the same time, the agglomeration process of plant community succession and the diversity of dominant community were investigated, and the changes in plant diversity at different succession stages were calculated using Margalef, Simpson, Shannon–Wiener, Pielou, Jaccard and Cody indices.

Species Composition and Protection of Fish Eggs and Larvae in Spawning Ground of Liaodong Bay

[Objective] The paper was to explore the species composition, number distribution and seasonal dynamics of fish eggs and larvae in Liaodong Bay in 2008. The protection and exploitation status of spawning ground in Liaodong Bay was analyzed, and the corresponding protection measures were put forward. [Methods] The species composition of fish eggs and larvae in spawning ground of Liaodong Bay was investigated by horizontal trawling associated with vertical trawling with zooplankton net in May, July, September and October in 2008. [Result] It was found that 7 724 eggs and 229 larvae of fishes belonging to 32 taxa were collected, in which 29 taxa were identified as species, belonging to 9 genera, 21 families and 28 orders, 2 taxa were identified to only family level, and one failed to be identified. The main spawning groups were Cynoglossus joyneri, Engraulis japonicus, Johnius belengerii, Larimichthys polyactis, Konosirus punctatus, Sardinella zunasi, and Scomberomorus niphonius, and the main spawning ground was found in northern waters and Changxing Island waters in Liaodao Bay. There was slightly less spawning species in 2008 compared with 1998, especially the number of fish eggs and larvae decreased greatly. [Conclusion] The effective measures for protection of spawning grounds in Liaodong Bay are suggested, including control of fishing intensity, development of artificial reefs, establishment of germplasm resources reserves, and standardization of compensation standards for marine ecological damage.

Polypore funga and species diversity in tropical forest ecosystems of Africa,America and Asia,and a comparison with temperate and boreal regions of the Northern Hemisphere

Polypores play a cru cial role in energy recycling and forest regeneration in forest ecosystems.The majority of them are wood degraders;some are forest pathogens and others are ectomycorrhizal symbionts.The basidiocarps provide food and shelter for many organisms,mostly invertebrates,but also some vertebrates,as well as food and medicine for humans.Despite extensive research on the species diversity and phylogenetic relationships of polypores in recent years,there remains a lack of comprehensive understanding of their distribution patterns and species composition at the large scale.Checklists of polypores from the tropical zone,including tropical Africa,tropical America,and tropical Asia,were analyzed for species diversity,distribution patterns,major taxa,and nutritional modes.A total of 1,902 polypore species was found in the three regions,representing 8 orders,46families,and 250 genera of Agaricomycetes.The orders Polyporales(especially the family Polyporaceae)and Hymenochaetales(especially the family Hymenochaetaceae)had the most prolific taxa,with their species accounting for 93.4%of the total polypores listed.Each of 1,565(or 82.3%)of the total 1,902 species were found in only one of the three regions studied,and we treat them temporarily as"regional endemic species".Only 141species were shared among all three regions,accounting for a mere 7.4%.Tropical Africa and tropical America had the greatest number of shared species and the highest S?rensen similarity index(SC)value.Tropical forests had a higher species richness compared with temperate to boreal forests of the Northern Hemisphere,and in addition,also a higher proportion of white rot polypores compared to brown rot and ectomycorrhizal species.This study outlines the distribution patterns and species diversity of polypores in the world,shedding light on their ecological significance in diverse ecosystems.

Effects of Vegetation Cover, Grazing and Season on Herbage Species Composition and Biomass: A Case Study of Yabello Rangeland, Southern Ethiopia

The Yabello rangeland is a semi-arid area in Borana, Ethiopia that is facing great degradation challenges. Increasing infestation of vegetation cover, over grazing and high seasonal variation have significantly affected the herbage composition and biomass in the Yabello rangeland. This study focused on assessing the effect of vegetation cover, grazing and season on both herbage composition and biomass in the Yabello rangeland. An experiment was conducted using randomized plots of 1m×1m. Sites were selected based on vegetation cover type and grazing variation, and seasonal impacts were also assessed. Data on herbage composition, height and mass with respect to those parameters were analyzed using SAS statistical software version 9.1(SAS Institute, 2001) and Microsoft Excel. A total of 26 grass species were recorded and Chloris roxburghiana Chrysopogon aucheri and Chrysopogon aucheri grass species showed the highest average single species cover height and biomass production, for all the sites among all parameters. As a result, those grass species are highly recommended for the rehabilitation of degraded rangeland in the study area. This study also showed that vegetation cover type grazing and seasonal variation were the key factors in determining herbage species composition, height and biomass production. Finally, we recommended that sustainable management which controls bush vegetation cover and balances grazing levels is essential for sustainable herbage production and biodiversity conservation in the area.

Regeneration and utilization of nutrients during collapse of a Mesodinium rubrum red tide and its influence on phytoplankton species composition

High-biomass red tides occur frequently in some semi-enclosed bays of Hong Kong where ambient nutrients are not high enough to support such a high phytoplankton biomass. These high-biomass red tides release massive inorganic nutrients into local waters during their collapse. We hypothesized that the massive inorganic nutrients released from the collapse of red tides would fuel growth of other phytoplankton species. This could influence phytoplankton species composition. We tested the hypothesis using a red tide event caused by Mesodinium rubrum(M. rubrum) in a semi-enclosed bay, Port Shelter. The red tide patch had a cell density as high as 5.0×10~5 cells L^(-1), and high chlorophyll a(63.71 μg L^(-1)). Ambient inorganic nutrients(nitrate:NO_3^-, ammonium: NH_4^+, phosphate: PO_4^(3-), silicate: SiO_4^(3-)) were low both in the red tide patch and the non-red-tide patch(clear waters outside the red tide patch). Nutrient addition experiments were conducted by adding all the inorganic nutrients to water samples from the two patches followed by incubation for 9 days. The results showed that the addition of inorganic nutrients did not sustain high M. rubrum cell density, which collapsed after day 1, and did not drive M. rubrum in the non-red-tide patch sample to the same high-cell density in the red tide patch sample. This confirmed that nutrients were not the driving factor for the formation of this red tide event, or for its collapse. The death of M. rubrum after day 1 released high concentrations of NO_3^-,PO_4^(3-), SiO_4^(3-), NH_4^+, and urea. Bacterial abundance and heterotrophic activity increased, reaching the highest on day 3 or 4, and decreased as cell density of M. rubrum declined. The released nutrients stimulated growth of diatoms, such as Chaetoceros affinis var. circinalis, Thalassiothrix frauenfeldii, and Nitzschia sp., particularly with additions of SiO_4^(3-) treatments, and other species. These results demonstrated that initiation of M. rubrum red tides in the bay was not directly driven by nutrients.However, the massive inorganic nutrients released from the collapse of the red tide could induce a second bloom in low-ambient nutrient water, influencing phytoplankton species composition.

Plant species composition and diversity depending on piospheres and seasonality in the southern rangelands of Kenya

Introduction:Scarcity of water in the rangelands of Kenya has led to the introduction of piospheres.Previous research has however produced contrasting results on the effects of piospheres and seasonality on ShannonWiener’s diversity index,and therefore,this information is still deficient.In this study,the impact of these piospheres on plant species composition,diversity,and richness was assessed.Methods:Vegetation sampling was done during both the long rains(April)and the dry season(August).Three piosphere types(dam,trough,and a seasonal river)were studied using 0.25 m2 quadrats to sample vegetation at intervals of 20 m along 100-m transects.Four 100-m transects were used per piosphere(north,east,south,and west directions).Shannon-Wiener’s diversity index was used to determine species richness and composition.Twoway ANOVA was used to determine if piospheric distance had an effect on species diversity,richness,and evenness using GenStat 15th edition.Results:A total of 22 grasses and 29 forbs were recorded in the study area.The most abundant grasses near the piospheres were Eragrostis tenuifolia(12.9%)and Cynodon dactylon(10.6%).E.tenuifolia is an increaser species and was therefore most abundant in areas of severe grazing while C.dactylon has been known to be tolerant to grazing.The most abundant forbs were Crotalaria brevidens(37.5%).The Shannon-Wiener diversity index significantly increased(F=25.07,P=0.001)with distance from the three piospheres owing to the high grazing intensity near the piospheres and was significantly different between piospheres,being higher(F=10.05,P=0.001)at 20 m from the river(1.2±0.1)compared to a similar distance from the dam(0.9±0.1)and the trough(0.8±0.2).This was probably because the trough was smaller in size compared to the other piospheres,thereby concentrating more grazing animals per unit area and causing a greater impact on plant species.Conclusions:The study demonstrated that species diversity,richness,and evenness were low near the piospheres due to heavy grazing.Similarly,the lowest species diversity,richness,and evenness were recorded near the trough compared to the dam and the river.This study therefore recommends that range reseeding and rest period be done to rehabilitate degraded areas and facilitate plant regeneration.Larger piospheres should also be used to minimize animal impact per unit area.

The influence of cultivation frequency on weed species composition and diversity in flood recession farming in the Okavango Delta, Botswana

Introduction:Flood recession farming,locally known as molapo farming,is an important livelihood activity for the subsistence farming community around the Okavango Delta.The study was aimed at investigating the influence of cultivation frequency on non-crop species composition.It was carried out in the peripheral settlements of Shorobe,Makalamabedi and Lake Ngami.Methods:Vegetation sampling was conducted from March to April 2016 in 36 fields of varying historical cultivation frequencies.The cultivation frequencies were 5,10 and 15 years with an uncropped control site.Sampling was done in 1-m^(2) quadrats placed 10 m apart along a line transect.Shannon’s diversity and equitability indices were used to compare diversity for each cultivation frequency within and across the study sites.The Kruskal–Wallis test was used to investigate significant differences in diversity between cultivation frequencies.Rank of abundance was used to determine the association of weeds with the cultivation frequencies.Results:Cultivation frequency did not influence species diversity(p>0.05)at either Lake Ngami or Shorobe.Species evenness was significantly different(p<0.05)between the cultivation frequencies at Shorobe,but not at either Makalamabedi or Lake Ngami.There was a significant difference(p<0.05)in diversity indexes across the four cultivation frequencies.The 5-year frequency recorded the highest median score(Md=1.352)while the 15-year frequency recorded the lowest median score(Md=1.035).Corchorus tridens was the most abundant noncrop species at the 5-and 15-year frequencies.Cynodon dactylon was most abundant in the 10-year frequency while Cyperus esculentus was most abundant in uncropped fields.Conclusions:Cultivation frequency influenced weed species diversity and composition in flood recession farming.Flood recession farming fields were dominated by common weed species which are also troublesome in dryland arable farming.Uncropped sites were composed of wetland species that tolerate some dry periods or seasonal flood plains.

Species composition and quantitative variation of zooplankton in the Great Wall Bay and its adjacent waters，Antarctica

A preliminary identification has been made of 35 species of the zooplankton in the Great Wall Bay and its adjacent waters,Antarctica. The dominant species in the investigated area are Calanus propinquus, Calanoides acutus, Metrdia gerlachei and the larvae of antarctic krill.The results indicated that the zooplankton in the investigated waters were simple in species number, which conforms to the general pattern of the distribution of the zooplankton in antarctic waters.The total biomass and number of individuals of the zooplankton in the investigated waters showed obvious seasonal variation. In summer there were Calaninioides acutus and the larvae of antarctic krill; in winter there were Metrdia gerlacher, Calanus propinquus, Oithon similis, O. frigda and the larvae of antarctic krill. The quantity of Copepoda occupied a considerable proportion in each month. The water temperature is an important factor in controling the biomass of zooplankton.