Plant diversity consequences of a herbivore‐driven biome switch from Grassland to Nama‐Karoo shrub steppe in South Africa

Although the relationships between species diversity and aboveground biomass (AGB) are highly debated in grassland ecosystems, it is not well understood how climatic factors influence AGB directly and indirectly via plant coverage and species diversity in large-scale grasslands along a topographic gradient. In doing so, we hypothesized that climatic factors would regulate plant coverage, species diversity and AGB due to maintaining plant metabolic and ecological processes, but the relationship of plant coverage with AGB would be stronger than species diversity due to covering physical niche space. To test the proposed hypothesis, we collected data for calculations of species richness, evenness, plant coverage and AGB across 123 grassland sites (i.e., the mean of 3 plots in each site) dominated by Leymus chinensis in northern China. We used a structural equation model for linking the direct and indirect effects of topographic slope, mean annual precipitation and temperature on AGB via plant coverage, species richness, and evenness through multiple complex pathways. We found that plant coverage increased AGB, but species evenness declined AGB better than species richness. Topographic slope influenced AGB directly but not indirectly via plant coverage and species diversity, whereas temperature and precipitation increased with increasing topographic slope. Regarding opposing mechanisms, on the one hand, precipitation increased AGB directly and indirectly via plant coverage as compared to species richness and evenness. On the other hand, temperature declined AGB indirectly via plant coverage but increased via species evenness as compared to species richness, whereas the direct effect was negligible. Our results show that niche complementarity and selection effects are jointly regulating AGB, but these processes are dependent on climatic factors. Plant coverage promoted the coexistence of species but depended greatly on precipitation and temperature. Our results highlight that precipitation and temperature are two key climatic drivers of species richness, evenness, plant coverage and AGB through complex direct and indirect pathways. Our study suggests that grasslands are sensitive to climate change, i.e., a decline in water availability and an increase in atmospheric heat. We argue that temperature and precipitation should be considered in grassland management for higher productivity in the context of both plant coverage and species diversity which underpin animals and human well-being.

Agroforestry practices (AFPs) have the potential to improve species composition and the ecological integrity of various landscapes. However, site-specific studies on the role of AFPs in enhancing plant species composition, richness, and diversity are scarce. This study aimed to determine variations in useful plant species composition and diversity across five agroforestry practices: Boundary Planting Agroforestry Practice (BAP), Multiple Woody Perennial Agroforestry Practice (MWPAP), Agrosilvopastoral Practice (ASP), Coffee Intercropped Agroforestry Practice (CIAP), and Mixed Intercropping Agroforestry Practice (MAP). A 10 × 10 m plot size was used to assess plant species composition and richness. Four plant species life forms were identified: trees, shrubs, climbers, and herbs. Variations in plant species composition and diversity among the AFPs were statistically analysed using ANOVA in R software, while correlations between plant life forms were determined using Pearson product-moment analysis. A total of 58 tree species (61.6%), 20 shrub species (21.3%), 10 climber species (10.5%), and 6 herb species (6.6%) belonging to 40 families and 72 genera were identified. Fabaceae and Euphorbiaceae were the most represented families, with 13 and 9 species, respectively. The highest mean species richness for trees (39), shrubs (19), and herbs (6) was recorded in ASP, while the highest mean climber species richness (10) was observed in CIAP. MAP exhibited the highest mean diversity for tree and herb species, whereas shrub and climber species diversity was highest in MWPAP and CIAP, respectively. Tree, shrub, climber, and herb species richness and diversity differed significantly (p < 0.001) across all AFPs. A significant positive correlation was observed between the species richness in trees, shrubs, and climbers in all practices (p < 0.05). The ASP and MAP demonstrated higher potential for supporting plant species richness and diversity, as well as a greater number of plant life forms. These two systems should be prioritized for their ecological and socio-economic benefits.   Key words: Plant life forms, agroforestry practices, useful, species diversity, species richness.

Parthenium hysterophorus is an alien annual herb that aggressively threatens biodiversity of Queen Elizabeth National Park (QENP) in Uganda. Occurrence, abundance and impact of P. hysterophorus on plant species diversity were examined. An observational inspection survey assessed the occurrence of P. hysterophorus while Quadrats sampled vegetation in P. hysterophorus invaded and uninvaded sites of Mweya Peninsula and along Kazinga Channel Track. Plant species richness, dominance, evenness and diversity of invaded and uninvaded sites were statistically different at P < 0.05. Species richness (R) and dominance (D) were higher in invaded sites (R = 58, D = 0.62) than uninvaded sites (P = 0.043; R = 39, P = 0.04; D = 0.46). Consequently, species diversity of other plants became less (1-D = 0.38) in invaded than uninvaded (P = 0.039;1-D = 0.55). Also, P. hysterophorus significantly starts to reduce species diversity and richness at very low levels of abundances, as low as (4.6%) and (7.7%), respectively, and dominates at a relatively higher level (40.2%). It was concluded that P. hysterophorus in QENP, negatively affects the plant species diversity at low levels of abundances through dominance. Key words: Parthenium hysterophorus, environmental impact, species abundance, species richness, weed spread.

The Nama Karoo biome is one of the least well-studied biomes in the semi-arid region of South Africa, and essential baseline biodiversity data for this region are lacking. The aim of the present study was to examine the influence of environmental factors on the species diversity and richness of Mountain Zebra National Park, South Africa, which includes this vital biome. Vegetation data were obtained using the step-point method. Both species richness and diversity were unaffected by slope, aspect, coarse fragments, and soil texture. Multiple linear regression analyses indicated that a combination of four variables (nitrogen, clay, and sand contents, and longitude) should be included in the optimal model for species richness, and the optimal model for species diversity also revealed four influencing variables: soil organic carbon, clay and sand contents, and longitude. Overall, both species richness and diversity could be predicted by a combination of climatic, topographic, and soil properties. The findings of this study can be used as a reference for the effects of environmental factors on plant species richness and diversity in semi-arid environments.

Keywords: Rotational grazing, full protection, continuous grazing species richness, species diversity, soil seed bank, Bayesian methods, Salsola vermiculata, seed longevity, rangeland management, Syria. Rangelands represent 70% of the semi-arid and arid Mediterranean land mass. It is a natural habitat for millions of people whose livelihood depends on animal husbandry. The revolutionary developments in the animal husbandry and veterinary medicines resulted in exponential increases in human and livestock population living on and from dry lands. To respond to population growth, urbanization and transportation means and expanded road networks, land reform and rural development policies forced nomads to adopt semi to fully sedentary lifestyles with disintegrated traditional community structures and organizational frameworks. Under these demographic changes coupled with national and international border crossing restrictions, there was an escalation in opportunistic cultivation, and excessive exploitation of the scarce and slowly renewable vegetation cover resulting in a steep decline in the primary production components of the rangeland ecosystems. In an attempt to stop and reverse the degradation process, large-scale re-vegetation programs based on transplanting and reseeding with perennial shrubs, resting and grazing management systems were devised and implemented. This study aimed to evaluate the impacts of the rehabilitation programs on the above-ground vegetation cover and soil seed bank replenishment in the Syrian rangelands. The underlying assumption of the rehabilitation program is that with a well-established perennial plant cover and proper grazing management, top soil is stabilized, soil moisture, nutrients and seed bank are replenished, organic matter is accumulated and microorganisms' activity is promoted resulting in greater abundance, species richness and diversity of annuals. To test the above hypothesis, field and controlled environment based studies were carried out with quantitative data collection and processing on plant species abundance, richness and diversity of above-ground vegetation and soil seed bank for fully protected rotationally and continuously grazed areas of 10 rangeland sites in northern Syria for three consecutive seasons. In addition to the use of frequentist statistical approaches for species diversity estimation in the studies, the Bayesian method was explored. Moreover, the crucial issues of seed quality in re-vegetation were tackled through a study on seed viability and longevity in Salsola vermiculata L., which is a highly palatable, well adapted and widely used species in the arid Mediterranean rangeland rehabilitation programs. The major findings are indicated below. Above ground vegetation cover The vegetation cover data analysis using ANOVA showed that overall plant density consistently declined from full protection to rotational and then continuous grazing in 9 out of the 10 sites studied, whereas the trends of change in species richness and diversity were not consistent. Pair-wise comparison showed that plant density, species richness and diversity were lowest for the overall plant population under rotational grazing in which plant density of perennial grasses was highest. This suggests that rotational grazing has reshaped the composition of the plant communities under the study areas by promoting the perennial grasses that are more arid rangeland adapted and ecosystem significant. Higher plant density under rotational grazing and similarity in species diversity under the three grazing treatments for perennial grasses imply that a longer period of rehabilitation and/or probably incorporating inter-seasonal rotational grazing and variation in herbivore types into the current intra-seasonal rotational grazing system will be required to cross the line of no return in plant community composition optimization through the prevalent arid Mediterranean rangelands rehabilitation programs. Soil seed bank assessment The soil seed bank data analysis using ANOVA showed no significant differences in the overall physical and germinable soil seed bank size and diversity along the grazing gradient. However, there was a significant grazing-by-site interaction for both and a significant grazing-by-year interaction for germinable seed bank size showing that the change in seed bank size is moderated by physical and environmental characteristics and human-induced disturbances. Continuous grazing treatments for some sites were located near agglomerations of people and animals, main roads and water points. Under such conditions the more disturbance-adapted ephemerons and non-palatable plants with limited constraints for seed setting dominated and this resulted in a larger soil seed bank under continuous compared to rotational and full protection grazing treatments. For the more human-induced disturbance distanced sites, the soil seed bank was at larger or similar under full and/or rotational compared to continuous grazing. Results from pair-wise comparisons showed a simultaneous decline and surge in physical and germinable soil seed bank size of annuals and those of perennials under the grazing treatments over sites. This suggests relative differences in root competition and gap exploitation characteristics among plant functional groups; these differences could be considered indicative to rangeland status and a guide to vary herbivores in order to maintain optimum plant species diversity in the target rangelands. Soil seed banks with no seeds of perennial grasses generated 208 seedlings m-2 of germinable soil seed bank under continuous grazing. This is probably due to seed setting failure resulting from overgrazing compensated by vegetative reproduction. The widely used phanerophytes in the rangeland rehabilitation program had a physical soil seed bank of 59.7 to 119 seed m-2 and a zero germinable one. This shows high complementarity between physical and germinable seed testing methods for rangeland monitoring. Similarity indices High Morisita-Horn and Sørensen similarities were recorded between the quadrat and point intercept measurements of the above ground vegetation and with each of physical and germinable soil seed banks. However, the similarity indices of the above ground vegetation measurements were higher with the germinable soil seed bank than with the physical soil seed bank. This suggests that the germinable soil seed bank is more suitable for monitoring arid Mediterranean rangeland than the physical soil seed bank. Correlation coefficients Based on the coefficients of determination (CDs), the variation in plant density and seed bank size accounted for a significant portion of the variations in spcies richness but not of the diversity indices. However, plant density and species diversity consistently and significantly declined during the season with the lowest mean annual precipitation showing the crucial role of precipitation in the dynamics of the yet active soil seed banks of the study areas. The CDs for the germinable soil seed bank size tested under optimum soil moisture with species richness were also significant throughout the grazing treatments reflecting the dependence of seed bank dynamics on soil moisture. For the physical soil seed bank (PSSB), CDs of its size with species richness were only significant under rotational grazing implying positive impacts of grazing management on soil seed bank replenishment. Morover, the CDs of PSSB richness with the diversity indices were only significant for Singletons but not for Shannon and Simpson. This is attributable to the fact that the Singleton index is more sensitive to rare species than Shannon and Simpson. The non-significant correlations between plant density and species diversity reflect a need to incorporate inter-seasonal rotational grazing and herbivore variation to the current intra-seasonal rotational grazing for greater plant community integrity. Phytogeographic analysis Using two above and two underground vegetation data collection methods, a total of 137 species, including 102 annuals and 35 perennials from 36 families of 11 chorotypes, were recorded. The number of species recorded were 56, 66, 68 and 98 from physical seed extraction, point intercept, quadrat and grow out test, respectively. These results showed the superiority of the growing out test over the three other methods. With its easiness and relative flexibility of application in terms of time and space, the grow out test seems to be the best method for arid Mediterranean rangelands monitoring and assessment of rehabilitation impacts in which the frequency of good rainy season is one out of four years. Conclusions  The rotational grazing component of the rangeland rehabilitation program resulted in a change in plant community composition shown by an increase in low proportional abundance perennial grasses with greater arid Mediterranean rangeland adaptation.  Continuous grazing reduced plant density but not richness and diversity, indicating that maximum diversity is not a sign of rangeland health and integrity. This also suggests that inter-seasonal rotational grazing and herbivore variation could probably improve the shaping effects of grazing on the arid rangeland rehabilitation programs.  Capturing more species and higher similarity indices with the above ground measurements, the simple and flexible, germinable soil seed bank test seems to be a good monitoring and evaluation method for arid Mediterranean rangelands. However, results from the tedious and less accurate physical seed extraction method could be crucial to capture the species with long seed dormancy.  Larger Bayesian estimates of diversity, smaller standard errors, lower p-values and more significance of differences in diversity between grazing treatments compared to the frequentist approaches were observed, thus indicating clear merits for the approach in estimating diversity.  The seed longevity study showed that under relatively higher seed moisture content, longevity increased suggesting that desiccation susceptibility is probably the cause of short seed longevity of Salsola vermiculata L. Moreover, drying and packaging alone increased longevity, thus providing a simple, cost-effective and environmentally friendly method for rangeland rehabilitation programs.

IntroductionScarcity 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 Shannon-Wiener’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.MethodsVegetation 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. Two-way ANOVA was used to determine if piospheric distance had an effect on species diversity, richness, and evenness using GenStat 15th edition.ResultsA 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.ConclusionsThe 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 net effect of heavy grazing and land degradation on plant diversity and richness is insufficiently understood for incorporation in national biodiversity assessments. A study was undertaken to determine the effects of heavy grazing primarily on richness of vascular plant species across the arid and semi-arid rangeland biomes of South Africa. Major grazing contrasts were systematically identified for sampling in rangelands of Succulent Karoo, Nama-Karoo, Thicket, Grassland, Kalahari dune savanna and Mopane savanna. The related parameters of species diversity, evenness and turnover were also examined and analysed at the whole site level. The study represents a new site-level comparison of earlier individual studies that also necessitated recalculation and standardization of original data, where appropriate. Impacts of heavy grazing on plant species richness were found to vary from negligible or slightly positive to distinctly negative, depending on site. The sharp reductions in richness may have been associated with special secondary conditions that can occur in arid areas. Species diversity did not track species richness well and was often dominated by species evenness patterns. Moderate to substantial turnover of species occurred, even with negligible change in species richness. Species turnover was largely associated with replacement of species, except on one site where turnover was more evenly split between its replacement and nestedness components. Heavy grazing altered species composition on all study sites, usually with reduced grazing quality and favouring annual plants. Surprisingly few of the replacement species on most of the study areas were alien or exotic. Remarkably, the magnitude of change in species richness across the limited rainfall gradient of the study often greatly exceeded changes associated with the heavy grazing levels at each site. Use of the significant non-linear relationship found between loss of plant canopy cover through grazing and the relative decline in species richness needs further exploration.

Small-scale plant species richness and evenness in semi-natural grasslands respond differently to habitat fragmentation

Understanding relationships between large herbivores and plant species diversity in dynamic riparian zones is critical to biodiversity conservation. The Nkuhlu exclosures in the Kruger National Park (KNP) provided opportunity to investigate spatial heterogeneity patterns within riparian zones, as well as how these patterns are affected by fire and herbivory. A monitoring project was initiated to answer questions about the dynamics of the herbaceous layer and was aimed at determining, (1) whether there exists meaningful variance in herbaceous plant species richness and diversity across different treatments in the ecologically sensitive sodic zone and (2) whether an increase in herbaceous biomass, an artefact of herbivory and fire exclusion, suppresses herbaceous plant species diversity and richness. Herbaceous vegetation was sampled in two 1 m2 circular sub-plots in the eastern and western corners of 81 fixed plots. The biomass of each plot was estimated with a disc pasture meter (DPM) diagonally with the plot. DPM-readings were converted to kg/ha, according to the latest conversions for the Lowveld Savanna. Species richness and biomass showed significant variance across treatments, whereas no significant variation in herbaceous species diversity was perceived. Combined treatment of fire absence and herbivore presence contributed to higher forb species richness in the sodic zone. Biomass is significantly higher in fully fenced areas where herbivores are excluded, as opposed to the open and partially fenced areas. Although no significant variation was recorded for diversity across treatments, lowest diversity was recorded in the absence of all herbivores, especially in combination with fire treatment. Therefore herbivores are essential in sustaining herbaceous plant species richness in the sodic zone, whilst no significant results were found with regard to their effect on species diversity. Although statistically non-significant, fire seems to suppress species richness.Conservation implications: This study could be used as framework to advance and develop science-based management strategies for, at least, the sodic zones of the KNP. Research in these exclosures will create better understanding of these landscapes, benefit ecosystem conservation planning of national parks and also provide valuable long-term information on key ecological processes.

Species diversity and other integral parameters of zooplankton community in the Japan, Okhotsk, Bering, Chukchi seas and adjacent Pacific waters (total area close to 7.0 . 10 6 km 2 ) are compared on the data obtained in the large-scale surveys conducted by Pacific Fish. Res. Center (TINRO) in 1984-2013. Standard Juday net with mesh size 0.186 mm and mouth area 0.1 m 2 was used for sampling. Among four seas, the Chukchi Sea takes the 1 st place by abundance (ind./m 3 ) and biomass (mg/m 3 ) of zooplankton, 2 nd by species evenness, 3 rd by mean size of organisms, and the last by species richness and diversity. The Bering Sea is the 1 st by mean size of animals, 2 nd by species richness, diversity and biomass, 3 rd by abundance, and the last by species evenness. The Okhotsk Sea takes the 2 nd place by mean size of zooplankton, the last by its abundance, and the 3 rd by other parameters. The Japan Sea is the 1 st by species richness, evenness and diversity, 2 nd by abundance, and the last by mean size of zooplankton and therefore by its biomass. Zooplankton in the Pacific waters has the lowest abundance, but its biomass is higher there in comparison with the Japan Sea. Species richness is the highest in the Pacific, but species diversity is higher there than in the Chukchi Sea and species evenness is the lowest. Mean size of zooplankton organisms in the Pacific is rather large but smaller than in the Bering Sea. In general, zooplankton abundance increases northward in accordance with nutrients supply, as well as the mean size of animals (with exclusion of the Chukchi Sea), but uniformity of the species abundance has opposite tendency (except the Chukchi Sea again). The rank in biodiversity coincides with the rank in species richness. The latter decreases from south to north (with exclusion of the Okhotsk Sea), but depends strongly on size of the surveyed area and surveyed volume of water. Some unexpected statistically significant relationships are found between the integral parameters of zooplankton and these parameters for pelagic and bottom macrofauna which have not yet any rational interpretation.

Although species richness has been hypothesized to be highest at 'intermediate' levels of disturbance, empirical studies have demonstrated that the disturbance-diversity relationship can be either negative or positive depending on productivity On the other hand, hypothesized productivity diversity relationships can be positive, negative or unimodal, as confirmed by empirical studies. However, it has remained unclear under what conditions each pattern is realized, and there is little agreement about the mechanisms that generate these diverse patterns. In this study, I present a model that synthesizes these separately developed hypotheses and shows that the interactive effects of disturbance and productivity on the competitive outcome of multispecies dynamics can result in these diverse relationships of species richness to disturbance and productivity The predicted productivity diversity relationship is unimodal but the productivity level that maximizes species richness increases with increasing disturbance. Similarly, the predicted disturbance diversity relationship is unimodal but the peak moves to higher disturbance levels with increasing productivity Further, these patterns are well explained by the opposite effects of productivity and disturbance on competitive outcome that are suggested by the change in community composition along these two environmental gradients: higher productivity favours superior competitors while higher disturbance levels favour inferior competitors.

Fire is a key driver of forest ecosystem structure and function, influencing the distributions of both plants and animals. Australia’s Black Summer wildfires of 2019–2020 burnt through over 9 M ha of land including about 7.6 M ha of temperate Eucalyptus forest over several months. This is an unprecedented scale of fire when considering the last few centuries of fire history in south-eastern Australia. This study assessed a 1983 regenerated Eucalyptus forest for plant and bird diversity in 2016, 4 years prior to the Black Summer wildfires, and again in November 2020, eleven months after the wildfires. With a range of fire severities resulting from previous fuel reduction treatments, the before and after wildfire biodiversity assessments allowed the investigation of fire severity impacts on plant and bird diversity. Species richness, Shannon’s diversity, and community composition were studied using mixed effects models and community composition was analysed using multivariate generalised linear models. The results showed that wildfire severity had no impact to plant species richness, diversity or composition. Although wildfire severity had no significant effect on plant species diversity, 33% of previously recorded plant species were not present almost a year after the wildfire, while 22% of previously unrecorded species appeared. Overall, 46 bird species were observed across all sites, with 38 species observed prior to and 28 species observed after wildfire. The bird species diversity was reduced, with a shift to a greater abundance of insectivorous birds after the wildfire. This study enhances our understanding of the impact of fire severity on plant and bird species diversity and provides valuable information for managers to refine fuel reduction practices to mitigate fire impact on biodiversity.

شاخص‏های تنوع زیستی ابزاری نیرومند برای ارزیابی پایداری نظام های کشاورزی محسوب می شوند. در این تحقیق که به منظور ارزیابی تنوع زیستی محصولات زراعی و باغی شهرستان های استان اصفهان و همچنین بررسی روابط موجود بین تنوع زیستی و عوامل اقلیمی ‏این استان صورت گرفت، سطح زیر کشت، غنای گونه ای، یکنواختی، تنوع گونه ای و تنوع آلفا و بتای محصولات زراعی و باغی محاسبه شده و مورد ارزیابی قرار گرفتند. بدین منظور، اطلاعات مربوط به سطح زیر کشت گیاهان زراعی و باغی شهرستان‏های مختلف استان اصفهان در سال زراعی 92-1391 از طریق اطلاعات سازمان جهاد کشاورزی استان و همچنین پرسشنامه‏هایی جمع‏آوری گردید. محصولات زراعی به هشت گروه غلات، حبوبات، جالیزی، سبزیجات، علوفه ای، صنعتی و دارویی و محصولات باغی به دو گروه درختان میوه معتدله و گرمسیری طبقه بندی شدند. تنوع آلفا و بتا نیز با استفاده از رابطه غنای گونه‏ای مساحت برای اقلیم‏های مختلف استان محاسبه شد. نتایج نشان داد که در گروه محصولات باغی، درختان میوه معتدله (2/76 درصد) بیشترین و در گروه محصولات زراعی غلات (36/59 درصد) و گیاهان دارویی (09/1 درصد) به ترتیب بیشترین و کمترین سطح زیر کشت را دارا هستند. شهرستان های سمیرم و برخوار و میمه به ترتیب بیشترین و کمترین سطح زیر کشت محصولات باغی را به خود اختصاص دادند. بیشترین سطح زیر کشت محصولات زراعی در شهرستان اصفهان و کمترین آن در شهرستان خوروبیابانک مشاهده شد. شهرستان-های کاشان، لنجان، و نطنز با 17 گونه گیاهی، بیشترین و آران و بیدگل با سه گونه گیاهی کمترین غنای گونه ای محصولات باغی استان را در برداشتند. بیشترین و کمترین شاخص یکنواختی محصولات باغی به ترتیب مربوط به شهرستان های اصفهان (83/0) و سمیرم (192/0) بود. شهرستان های فلاورجان، خمینی شهر، کاشان، نایین و نجف آباد دارای بیشترین شاخص یکنواختی در محصولات زراعی و شهرستان اصفهان کمترین میزان این شاخص را نشان داد. به طور میانگین بیشترین و کمترین شاخص تنوع زیستی شانون- وینر در محصولات زراعی به ترتیب مربوط به گیاهان علوفه ای (929/0) و جالیزی (442/0) بود. این شاخص برای درختان معتدله بیش از دو برابر درختان گرمسیری گزارش شد. بیشترین و کمترین میزان تنوع آلفا به ترتیب در شهرستان‏های واقع در اقلیم‏های معتدل و بیابانی گرم مشاهده شد. اقلیم بیابانی معتدل نیز بالاترین میزان تنوع بتا را شامل شد.

The present study assessed the impact of invasive alien species on plant species composition, richness, and diversity in the lower montane forest of Kilimanjaro National Park. The study area was categorized into four sites: the first three dominated by non-native species, namely Black Wattle (Acacia mearnsii), Mexican weeping pine (Pinus patula), and Eucalyptus (Eucalyptus spp.), and the fourth zone comprised natural forests. Sixty plots, each measuring 20 m × 50 m, were established at each site for vegetation sampling. A total of 168 plant species representing 135 genera and 64 families were identified and recorded from the study area. The highest plant species diversity was recorded in the natural forest with a mean plant species number of 13.8 ± 1.7, followed by Eucalyptus spp. A. mearnsii, and P. patula with 10.3 ± 1.2, 10.13 ± 1.1, and 7.33 ± 1.1, respectively. The plant species richness was significantly higher in the natural forest than in the areas invaded with non-native plant species (p < .05). Natural forest had the highest tree density of native trees with 774 ± 111 stems/ha and the lowest was observed in the P. patula site with a mean density of 12.7 ± 6.9. The reduction in plant species diversity and density in areas invaded with invasive alien species highlights the negative impact these species have on native plant communities. Sustainable forest management focusing on the protection of natural forests, the control of invasive species, and forest enrichment is highly recommended.

The mixed Cunninghamia lanceolata (Lamb.) Hook., Pinus massoniana Lamb., and hardwood forest in southeastern China is a major assemblage in natural secondary forests, and of national and international importance in terms of both timber and ecosystem services. However, over-harvesting has threatened its long-term sustainability, and there is a knowledge gap relating to the effect of harvesting on the ecosystem. After conifer species were selected for harvesting, the mixed Chinese fir, pine, and hardwood forest was changed into mixed evergreen broadleaf forest. In this context, we observed the restoration dynamics of plant communities over a period of 15 years (1996 to 2011) with different levels of harvesting intensity, including selective harvesting at low (13.0% removal of growing stock volume), medium (29.1%), high (45.8%), and extra-high (67.1%) intensities, as well as clear-cut harvesting (100.0%), with non-harvesting as the control, based on permanent sample plots established in a randomized block design in these forests in southeastern China. The impact on the richness, diversity, and evenness of plant species derived from descriptive statistical analyses was shown to initially increase, and then decrease, with an increase in harvesting intensity. The most critical impacts were on the richness, diversity, and evenness of shrub and herb species. Richness, diversity, and evenness of plant species recovered and increased under selective harvesting at low and medium intensities, while these parameters had not recovered and significantly decreased under selective harvesting at high and extra-high intensities, as well as with clear-cut harvesting. The impact on the plant community stability was derived from the stability test method of the improved Godron M. The plant community stability was closest to the point of stability (20/80) under selective harvesting at medium intensity, followed by selective harvesting at low intensity. The plant community stability was far from the point of stability (20/80) under selective harvesting at high and extra-high intensities, as well as with clear-cut harvesting. Of these treatments, clear-cut harvesting had the greatest effect with regard to reducing stability. Therefore, these results indicate that the selective harvesting at low and medium intensities is conducive to preserve or increase the species diversity and community stability. In order to prioritize promoting plant species diversity, clear-cut harvesting and selective harvesting at high and extra-high intensities should be avoided with regard to this type of forest in this region. This study sheds light on the practice of forest operation in the study region and subtropical forests with the same environment.