Soil, biomass, and management of semi-natural vegetation – Part II. Factors controlling species diversity

Using a wide range of conditions and plant community types, species diversity was investigated in relation to edaphic and non-edaphic site conditions, management, and biomass characteristics. Both standing biomass and aboveground production were investigated, and their effects compared. Three taxonomic assemblages were studied: (1) vascular plants only, (2) bryophytes also included, (3) terrestrial lichens included as well. Using a multivariate approach, both species richness and evenness could best be explained when only vascular plants were considered, emphasizing the role of taxonomic restrictions. The models best explaining species richness merely required abiotic conditions. This supports recent theories emphasizing the importance of an environmental regulation of the pool of (adapted) species from which the actual species are recruited. Explanatory soil properties were moisture and pH (both unimodal), and the soil available N:P ratio. Plots with large perimeter:area ratios had significantly more species than those with low ratios, indicating the importance of consistency in quadrat shape. Hump-shaped species richness relationships could be identified for both standing biomass and productivity, but they explained only a small part of the variation and were apparent only if soil and management effects were not accounted for. Unimodality (and notably the decreasing phase) was most pronounced when using maximum standing biomass, suggesting that the key factor is competition for light. At intermediate levels of standing biomass, the positive effects of habitat productivity and the negative effects of standing biomass itself are in balance, and high species numbers may be expected. When soil or management variables were allowed in the models, hump-shaped biomass relationships were no longer confirmed, suggesting that such relationships may arise from the covariation of biomass with other factors. Management explained a much larger part of the variation than the hump-shaped biomass relationship, suggesting that mowing and hay removal (both showing independent positive effects) regulate species richness in ways other than solely through the control of maximum standing biomass. Significantly higher evenness values were obtained at sites with low maximum biomass values, but only for the vascular plants. In addition, species evenness was positively related to the frequency of mowing. The numbers of both rare and endangered species were strongly curtailed by high standing biomass values, suggesting that these species are more susceptible to competitive exclusion than others. Through direct as well as indirect effects, management is confirmed to be beneficial not only for general species richness, but also for the occurrence of rare and endangered species.     

Modelling biomass of mountainous grasslands by including a species composition map

High mountain grasslands offer multiple goods and services to society but are severely threatened by improper land use practices such as abandonment or rapid intensification. In order to reduce abandonment and strengthen the common extensive agricultural practice a sustainable land use management of high mountain grasslands is needed. A spatially detailed yield assessment helps to identify possible meadows or, on the contrary, areas with a low carrying capacity in a region, making it easier to manage these sites. Such assessments are rarely available for remote and inaccessible areas. Remotely sensed vegetation indices are able to provide valuable information on grassland properties. These indices tend, however, to saturate for high biomass. This affects their applicability to assessments of high-yield grasslands.The main aim of this study was to model a spatially explicit grassland yield map and to test whether saturation issues can be tackled by consideration of plant species composition in the modelling process. The high mountain grassland of the subalpine belt (1800 – 2500 m a.s.l.) in the Kazbegi region, Greater Caucasus, Georgia, was chosen as test site for its strong species composition and yield gradients.We first modelled the species composition of the grassland described as metrically scaled gradients in the form of ordination axes by random forest regression. We then derived vegetation indices from Rapid Eye imagery, and topographic variables from a digital elevation model, which we used together with the multispectral bands as predictive variables. For comparison, we performed two yield models, one excluding the species composition maps and one including the species composition map as predictors. Moreover, we performed a third individual model, with species composition as predictors and a split dataset, to produce the final yield map.Three main grassland types were found in the vegetation analysis: Hordeum violaceum-meadows, Gentianella caucasea-grassland and Astragalus captiosus-grassland. The three random forest regression models for the ordination axes explained 64%, 33% and 46% of the variance in species composition. Independent validation of modelled ordination scores against a validation data set resulted in an R² of 0.64, 0.32 and 0.46 for the first, second and third axes, respectively. The model based on species composition resulted in a R² = 0.55, whereas the benchmark model showed weaker relationships between yield and the multispectral reflectance, vegetation indices, and topographical parameters (R² = 0.42). The final random forest yield model used to derive the yield map resulted in 62% variance explained and an R² = 0.64 between predicted and observed biomass. The results further indicate that high yields are generally difficult to predict with both models.The benefit of including a species composition map as a predictor variable for grassland yield lies in the preservation of ecologically meaningful features, especially the occurrence of high yielding vegetation type of Hordeum violaceum meadows is depicted accurately in the map. Even though we used a gradient based design, sharp boundaries or immediate changes in productivity were visible, especially in small structures such as arable fields or roads (Fig. 6b), making it a valuable tool for sustainable land use management. The saturation effect however, was mitigated by using species composition as predictor variables but is still present at high yields.     

中国主要苜蓿品种的产量性状及其多样性研究

对28个4龄苜蓿品种单株产量性状及其相关性和变异进行了研究．结果表明,品种间单株干物质产量及各产量性状存在显著差异,其中单株干物质产量最高和较高的分别是新疆大叶(452．8g·株^-1)和甘农3号(373．0g·株^-1);叶片最宽和最长者均为新疆大叶和甘农3号;单株枝条数增加最多是第3茬,3茬单株枝条数最高和较高的品种是新牧1号、图牧2号、肇东和北疆;苜蓿株高生长高峰期在第1茬,生长最快的品种为甘农3号和新疆大叶．相关分析表明,单株干物质产量与株高及枝条数等构成因素之间存在显著或极显著相关,其中1、3茬株高及3茬单株枝条数等性状相关最好,呈显著相关的品种达19～22个,且相关系数亦最高．产量性状变异分析表明,品种内变异大于品种间变异,前者占总变异的76．0％～93．8％,而后者仅占6．1％～24．0％．各性状变异程度表现依次为3茬单株枝条数>单株干物质产量>1茬单株枝条数>2茬单株枝条数>春季株高>3茬株高>2茬株高>叶宽>现蕾期株高>叶长>1茬株高．     

Allometric equations to predict the total aboveground biomass of tree species in a planted forest in Egypt

The aim of this study is to estimate the total above‐ground biomass (TAGB), stem height (H), diameter at breast height (dbh) and basal area of five tree species (ages 7‐8 years) irrigated by municipal sewage water in the Egyptian‐Chinese friendship forest, Sadat City, Egypt. From the biomass data that obtained through destructive sampling, models for predicting aboveground biomass were developed. The highest values for stem density and height were estimated for Eucalyptus citriodora, while the lowest value for density was obtained for Dalbergia sissoo and stem height for Khaya senegalensis. The highest values for basal area and dbh were obtained for Casuarina spp., while the lowest values were recorded for Dalbergia sissoo. Eucalyptus camaldulensis had the highest stand stem biomass and TAGB (55.5, 83.9 t DW ha^‐1, respectively). In addition, Casuarina spp. had the highest leafy branches biomass (32.5 t DW ha^‐1) while Dalbergia sissoo had the lowest values for all tree components. All the generated allometric equations had high correlation coefficients at high probability levels. Moreover, the results revealed that not only the dbh data can be used as independent variable for biomass determination, but also stem height and size index are recommended for biomass estimation (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Relationships between culture density and the composition of three floating aquatic macrophytes

Eichhornia crassipes (Mart.) Solms, Pistia stratiotes (L.), and Lemna minor (L.) were cultured at four different densities each and analyzed for cell-wall fraction, crude protein, total available carbohydrate and ash. Cell-wall fraction increased and crude protein content decreased as density increased in Eichhornia and Pistia cultures. The cell-wall and crude protein content of Lemna did not change with increasing culture density. Differences in the trends of cell-wall and crude protein content of the three plants at increasing culture densities appear to be related to differences in growth form. There was no difference in the total available carbohydrate or ash content of the three species at different culture densities.     

Spatial distributions of biomass and carbon density in natural grasslands of Hebei,China

分析不同草地类型生物量与碳密度空间分布特征及其影响因素, 揭示草地植物碳库的变化规律, 对于了解我国草地生态系统碳汇具有重要意义。2011-2013年以河北省天然草地为研究对象, 调查了不同草地类型的地上活体生物量、凋落物生物量和根系生物量以及各组分的碳密度。结果表明: 温性草原、温性草甸、温性山地草甸、低地盐化草甸、暖性草丛和暖性灌草丛6种草地类型的总生物量差异显著, 其中低地盐化草甸总生物量最高, 为2 770.2 g·m ^-2, 而温性草原最低, 为747.6 g·m ^-2, 前者约为后者的3.7倍; 地上活体生物量最大的是低地盐化草甸, 其次是暖性灌草丛和温性山地草甸, 最小的是温性草原, 分别为285.0、235.1、203.1和110.6 g·m ^-2; 凋落物生物量也是低地盐化草甸最大, 其次是温性山地草甸和温性草甸, 分别为584.0、187.9和91.0 g·m ^-2。6种草地类型的根系生物量均大于地上生物量, 是地上生物量的1.9-4.3倍, 不同草地类型根冠比的平均值为3.1; 低地盐化草甸的根系生物量最高, 为1901.3 g·m ^-2, 温性草原的根系生物量最低, 只有低地盐化草甸的1/3。在各类草地生物量碳密度方面, 低地盐化草甸的地上活体碳密度、凋落物碳密度与根系碳密度均为最大, 分别为132.7、81.2和705.9 g C·m ^-2。草地地上生物量、凋落物生物量和根系生物量以及总生物量均随海拔的升高先减少而后增加(p < 0.05); 草地生态系统总生物量和根系生物量随大于10 ℃积温的增加先降低而后升高(p < 0.01)。该研究中暖性灌草丛多分布在石质山区, 土层很薄, 植物地上生物量和根系生物量都比土层较厚的草甸草原低。可见, 在较大区域比较不同草地类型生物量时, 应综合考虑气候、土壤、地理等因素。     

河北省天然草地生物量和碳密度空间分布格局

分析不同草地类型生物量与碳密度空间分布特征及其影响因素, 揭示草地植物碳库的变化规律, 对于了解我国草地生态系统碳汇具有重要意义。2011-2013年以河北省天然草地为研究对象, 调查了不同草地类型的地上活体生物量、凋落物生物量和根系生物量以及各组分的碳密度。结果表明: 温性草原、温性草甸、温性山地草甸、低地盐化草甸、暖性草丛和暖性灌草丛6种草地类型的总生物量差异显著, 其中低地盐化草甸总生物量最高, 为2 770.2 g·m ^-2, 而温性草原最低, 为747.6 g·m ^-2, 前者约为后者的3.7倍; 地上活体生物量最大的是低地盐化草甸, 其次是暖性灌草丛和温性山地草甸, 最小的是温性草原, 分别为285.0、235.1、203.1和110.6 g·m ^-2; 凋落物生物量也是低地盐化草甸最大, 其次是温性山地草甸和温性草甸, 分别为584.0、187.9和91.0 g·m ^-2。6种草地类型的根系生物量均大于地上生物量, 是地上生物量的1.9-4.3倍, 不同草地类型根冠比的平均值为3.1; 低地盐化草甸的根系生物量最高, 为1901.3 g·m ^-2, 温性草原的根系生物量最低, 只有低地盐化草甸的1/3。在各类草地生物量碳密度方面, 低地盐化草甸的地上活体碳密度、凋落物碳密度与根系碳密度均为最大, 分别为132.7、81.2和705.9 g C·m ^-2。草地地上生物量、凋落物生物量和根系生物量以及总生物量均随海拔的升高先减少而后增加(p < 0.05); 草地生态系统总生物量和根系生物量随大于10 ℃积温的增加先降低而后升高(p < 0.01)。该研究中暖性灌草丛多分布在石质山区, 土层很薄, 植物地上生物量和根系生物量都比土层较厚的草甸草原低。可见, 在较大区域比较不同草地类型生物量时, 应综合考虑气候、土壤、地理等因素。     

Biology and ecology of theDusmoecetes Jeannel (Col. Curculionidae) species complex on Marion Island

Summary TheDusmoecetes species complex on sub-Antarctic Marion Island comprises two species. The larger species,D. similis (C.O. Waterhouse), feeds on angiosperms as adults and detritus as larvae, whereas the smaller species,D. marioni Jeannel feeds on bryophytes in all stages.D. similis has seven larval instars and a generation time of one year or longer.D. marioni has between five and seven larval instars, depending on the plant community it inhabits, and a generation time of one year or less. Immatures ofD. similis have a theoretical null point of development of -0.62°C and aQ ₁₀ of 3.57. In both species there are overlapping generations in the field, although in the case ofD. similis there is a distinct seasonal emergence of adults starting in September. Mean standing crop of larvae on the coastal plain is approximately 5.5 kg (dry mass)·ha^-1, but can be as high as 11.85 kg (dry mass)·ha^-1 inAzorella selago dominated communities. This study indicates that both species are important herbivores and/or detritivores on Marion Island.     

Effects of grass-encroachment on vegetation and soil in Dutch dry dune grasslands

The encroachment of tall grass species in open dune vegetation, as observed in the Dutch dry dune area, is considered unfavourable for nature conservation. The effects of grass-encroachment on the vegetation and the availability of light and its relation to nutrients were investigated through a comparative study of grass-dominated and open dune grassland plots at ten locations along the Dutch coast.Grass-dominated plots have a low species diversity and number of species, especially of mosses and lichens. This is associated with a high biomass and a low availability of light at soil surface. In addition, nutrient availability seems to be important. Root biomass and the amounts of both ectorganic and endorganic matter are significantly higher in grass-dominated plots, which may account for the higher nutrient uptake in the vegetation.It is likely that a grass-dominated system can maintain and consolidate itself because of the better competition for light and nutrients. The relevance of these results for restoration management is briefly discussed.     

Correlations of phytoplankton standing crop,species diversity and dominance with physical-chemical data in a coastal salt pond

A set of environmental variables from a coastal salt pond were regressed in a stepwise fashion against the following dependent variables: phytoplankton standing crop, species diversity and dominance. Multiple variable interaction, as measured by multiple correlation coefficients yielded higher values than the coefficients obtained by regressing individual environmental variables against the dependent variables. The seasonal variation in the dependent variables could, therefore, be explained to a greater extent by the effects of multiple variables rather than single limiting factors.Financial support was supplied by a fellowship from the Jessie Smith Noyes Foundation to the senior author.     

Effects of restoration with cattle grazing on plant species composition and richness of semi-natural grasslands

Restoration of semi-natural grasslands by cattle grazing is among the most practical options for reversing the decline of northern European floristic diversity, but no studies on this subject are available. In this work the success of restoration of abandoned, privately owned mesic semi-natural grasslands by farmers receiving support from the EU agri-environmental support scheme was studied in southwestern Finland. Three kinds of grasslands were compared: old (continuously cattle grazed), new (cattle grazing restarted 3–8 years ago) and abandoned pastures (grazing terminated >10 years ago). Plant species composition of the three pasture types was floristically different in multivariate analyses (non-metric multidimensional scaling). Total species richness, richness of grassland plants, indicator plants and rare plants were highest in old and lowest in abandoned pastures in all studied spatial scales (0.25–0.8 ha, 1 and 0.01 m²). The results were congruent with different scales and species list definitions, suggesting that species density scale (1 m²) can be used as a partial surrogate for large scale species richness. Species richness of new pastures was 20% higher on 0.25–0.8 ha, 40–50% higher on 1 m² and 30% higher on the 0.01 m² scale compared to abandoned grasslands. Rare species showed insignificant response to resumed grazing. Despite problems in management quality, this study showed promising results of restoration of abandoned grasslands by cattle grazing on private farms. However, populations of several rare grassland plants may not recover with present cattle grazing regimes. Management regulations in the agri-environmental support scheme need to be defined more precisely for successful restoration.     

Establishment and persistence of target species in newly created calcareous grasslands on former arable fields

The effects of different restoration measures and management variants on the vegetation development of newly created calcareous grasslands were studied in southern Germany from 1993 to 2002. In 1993, fresh seed-containing hay from a nature reserve with ancient calcareous grasslands was transferred onto ex-arable fields with and without topsoil removal. Nine years after start of the restoration, the standing crop was lower and the cover of bare soil was higher on topsoil-removal sites than on sites without soil removal. Topsoil removal had a positive effect on the proportion of target species (class Festuco-Brometea), because the number and cover of productive meadow species (class Molinio-Arrhenatheretea) were reduced. Persistence of hay-transfer species and the number of newly colonizing target species were highest on topsoil-removal sites. On plots with and without soil removal, species richness and the number of target species increased quickly after hay transfer and were always higher on hay-transfer plots than on plots that had not received hay in 1993. In 2002, differences induced by hay transfer were still much more pronounced than differences between management regimes. Management by mowing, however, led to higher species richness, a greater number of target species and a lower number of ruderals in comparison to no management on restoration fields without soil removal. A detrended correspondence analysis (DCA) indicated that vegetation composition of the hay-transfer plots of the restoration fields still differed from the vegetation of ancient grasslands in the nature reserve. Vegetation of an ex-arable field in the nature reserve (last ploughed in 1959) showed an intermediate successional stage. In general our results indicate that the transfer of autochthonous hay is an efficient method for the restoration of species-rich vegetation, which allows not only quick establishment but also long-term persistence of target species.     

Changes in dry matter and nutrient yields during the restoration of species-rich grasslands

Abstract. In two moderately productive grasslands that had been withdrawn from agricultural use, one on humic sandy soil and one on heavy clay, the decrease in dry matter, N-, P- and K-yields were measured for 14 and 11 years respectively, after fertilization had been stopped. The grasslands were mown twice a year. The yields and concentrations of nutrients were compared with those of already unproductive grasslands under the same growing conditions. On sandy soil, the annual dry matter yield decreased from 10.2 to 6.5 ton / ha in four years. After nine years, the dry matter (4.1 ton / ha) and K (20.5 kg / ha) yields were as low as those of the unproductive grassland. At that time yields and concentrations of N and P were still greater. The low K- concentration of 0.50 % and the lack of response upon N fertilizing indicate that the supply of K limits biomass production. On clay, during the first three years, the dry matter yield decreased from 10.2 to 5.0 ton / ha, after 6 yr the production increased again. The low N-concentration of 1.52 % after 10 yr indicates that N is likely to limit biomass production, but the low P-concentration of 0.14% indicates that P shortage can also be expected. In the lower productive grassland on sand the number of species that invaded was higher.     

Biodiversity of soil biota and plants in abandoned arable fields and grasslands under restoration management

The currently widespread abandoning of agricultural land use in Western Europe offers new opportunities for ecological restoration and nature conservation. This is illustrated for abandoned arable fields and for permanent grasslands cut for hay after the cessation of fertilizer application. Although initiated by a sudden reduction of nutrient input to the system, the changing nutrient supply from the soil is considered to be the main driving force of succession. The soil nutrient supply is affected by soil organisms, both directly (root symbionts and herbivores) and indirectly (nutrient mineralization from dead organic matter). It is argued that because of the close association of changes in species diversity with changes in the functioning of ecosystems, biodiversity has to be studied in an ecosystem ecology context.     

不同产量水平旱地冬小麦品种干物质累积和转移的差异分析

旱地小麦高产栽培中品种起着重要作用,研究不同产量水平旱地冬小麦品种干物质累积和转移的差异,对黄土高原旱区作物高产稳产有重要意义。以9个旱地冬小麦品种为材料,通过田间试验研究了不同产量水平旱地冬小麦品种的生物量、花前花后干物质累积量、干物质转移量、转移率及转移干物质对籽粒的贡献率、叶面积、SPAD值以及光合速率的差异。结果表明,不同小麦品种的生物量、花前花后干物质累积量、干物质转移量、转移率及转移干物质对籽粒的贡献率均存在明显差异。与不施肥相比,高、中、低3个产量水平小麦品种在低养分投入时,成熟期生物量分别提高29%,22%和6%,高水平时分别提高46%,39%和23%,高产品种的生物量及其对养分投入的敏感程度明显高于低产品种。不同品种的花后干物质累积量随养分投入水平提高而增加,但花前营养器官中储存物质的转移量、转移率和对籽粒的贡献率却明显随之下降。功能叶(旗叶)在灌浆期高、中、低3个产量水平品种的SPAD值在低养分投入条件下分别为20.7、17.5和13.7;高养分投入时,分别为35、26.1和16.8。高产品种西农88的光合速率为6.0μmolCO.2m-.2s-1),中产和低产品种的平均光合速率分别为4.3μmolCO.2m-.2s-1和4.0μmolCO.2m-.2s-1,高产品种功能叶(旗叶)在灌浆期能保持较高的SPAD值和光合速率,因而花后能生产较多的干物质,但其花前干物质转移量、转移率及转移干物质对籽粒的贡献率均没有明显优势。可见,花后较高的叶绿素水平、光合速率和干物质累积是旱地小麦品种高产的重要原因。选择优良品种,采取合理的栽培措施,特别是通过养分调控保持花后具较高的干物质累积量是西北旱地进一步提高冬小麦产量的重要途径。     

An integrated biogeochemical and economic analysis of bioenergy crops in the Midwestern United States

This study integrates a biophysical model with a county‐specific economic analysis of breakeven prices of bioenergy crop production to assess the biophysical and economic potential of biofuel production in the Midwestern United States. The bioenergy crops considered in this study include a genotype of Miscanthus, Miscanthus×giganteus, and the Cave‐in‐Rock breed of switchgrass (Panicum virgatum). The estimated average peak biomass yield for miscanthus in the Midwestern states ranges between 7 and 48 metric tons dry matter per hectare per year ( t DM ha^?1 yr^?1), while that for switchgrass is between 10 and 16 t DM ha^?1 yr^?1. With the exception of Minnesota and Wisconsin, where miscanthus yields are likely to be low due to cold soil temperatures, the yield of miscanthus is on average more than two times higher than yield of switchgrass. We find that the breakeven price, which includes the cost of producing the crop and the opportunity cost of land, of producing miscanthus ranges from $53 t^?1 DM in Missouri to $153 t^?1 DM in Minnesota in the low‐cost scenario. Corresponding costs for switchgrass are $88 t^?1 DM in Missouri to $144 t^?1 DM in Minnesota. In the high‐cost scenario, the lowest cost for miscanthus is $85 t^?1 DM and for switchgrass is $118 t^?1 DM, both in Missouri. These two scenarios differ in their assumptions about ease of establishing the perennial crops, nutrient requirements and harvesting costs and losses. The differences in the breakeven prices across states and across crops are mainly driven by bioenergy and row crop yields per hectare. Our results suggest that while high yields per unit of land of bioenergy crops are critical for the competitiveness of bioenergy feedstocks, the yields of the row crops they seek to displace are also an important consideration. Even high yielding crops, such as miscanthus, are likely to be economically attractive only in some locations in the Midwest given the high yields of corn and soybean in the region.