Interactive disturbance effects of two disparate ecosystem engineers in North American shortgrass steppe

Disturbances such as fire, grazing, and soil mixing by animals interact to shape vegetation in grassland ecosystems. Animal-generated disturbances are unique in that they arise from a suite of behaviors that are themselves subject to modification by external factors. The manner in which co-occurring animal taxa interact to alter vegetation is a function of their respective behaviors, which shape the characteristics (e.g., the magnitude or extent) of their disturbances. To determine whether prairie dogs (Cynomys ludovicianus) and harvester ants (Pogonomyrmex occidentalis) interactively alter vegetation structure and heterogeneity on the Colorado shortgrass steppe, we characterized the size, dispersion, and vegetation of prairie dog burrow mounds and ant nests (located on and off prairie dog colonies) and vegetation growing beyond mound and nest perimeters. Ants located on prairie dog colonies engineered significantly larger nests and disturbed nearly twice as much total soil area as their off-colony counterparts. Ant nests were overdispersed both on and off prairie dog colonies, while prairie dog mounds were randomly dispersed. Where harvester ants and prairie dogs co-occur, the overdispersed pattern of on-colony ant nests is in effect "overlaid" onto the random pattern of prairie dog mounds, resulting in a unique, aggregated pattern of soil disturbance. Ant nests on prairie dog colonies had significantly less vegetation and lower plant species diversity than did prairie dog mounds, while off-colony nests were similar to mounds. These results suggest that ant nests are more highly disturbed when located on prairie dog colonies. Beyond nests proper, ants did not appear to alter vegetation in a manner distinct from prairie dogs. As such, the interactive effects of prairie dogs and ants on vegetation arise mainly from the disturbance characteristics of mounds and nests proper.     

Rhombomys opimus contribution to the “fertile island” effect of tamarisk mounds in Junggar Basin

Fertile islands are created and maintained by a combination of physical and biologically mediated processes. Plants have been shown to be very important in the formation of fertile islands, and recent research indicates that the activities of burrowing animals have a significant influence on the physiochemical properties of soil that can promote the development of fertile islands. In this paper, we chose tamarisk (Tamarix spp.)??a constructive species that grows in the oasis-desert ecotone, and the great gerbil (Rhombomys opimus)??a widely distributed rodent in Central Asia to study the influence of great gerbils on soil nutrient dynamics in tamarisk mounds. Results indicate that fertile islands exist in tamarisk mounds without burrows of the great gerbil. However, the great gerbil??s burrowing activities promote the fertile island effect in tamarisk mounds: soil nutrients under shrubs with great gerbil activity were significantly higher than inter-mound areas in both surface soil and deep soil from 15 to 50?cm. Available nitrogen in mounds with rodent burrows was over twice as high as in tamarisk mounds without burrows at the same depth. The great gerbil??s burrowing activities promote the concentration of soil nutrients in the tamarisk mounds.     

Cultural monuments and nature conservation: a review of the role of kurgans in the conservation and restoration of steppe vegetation

Steppe is among the most endangered biomes of the world, especially in Eastern Europe, where more than 90 % of original steppes have been destroyed due to conversion into croplands, afforestation and other human activities. Currently, steppe vegetation is often restricted to places unsuitable for ploughing, such as ancient burial mounds called kurgans. The aim of our study was to collect and synthesise existing knowledge on kurgans by a review of research papers and grey literature. The proportion of kurgans covered by steppe vegetation increases from west to east and from lowlands to uplands. Despite their small size, kurgans act as biodiversity hotspots and harbour many red-listed species. High overall species richness and a high proportion of grassland specialists are maintained by a pronounced fine-scale environmental heterogeneity. The main factors threatening the biodiversity of kurgans are intensified agriculture and construction works. We conclude that kurgans can play a crucial role in preserving steppe vegetation, especially in intensively used agricultural landscapes in the western part of the steppe zone. Despite the vital role of kurgans in sustaining steppe vegetation, we identified serious knowledge gaps on their distribution, vegetation, flora and fauna and their potential role in steppe restoration.     

Spatial distribution of ant mounds and effects on soil physical properties in wetlands of the Sanjiang plain, China

Ants constitute a dominant element of soil mesofauna due to their biomass, abundance, richness of species and distribution within terrestrial ecosystems. They are important regulators of soil aggregate structure as they translocate large amounts of soil from the bottom to the soil surface. In doing so, they form biogenic structures (BS) made up of aggregates of different sizes and characteristics, i.e. ant mounds. These BS have varying characteristics according to the ant species and the soil where they carry their activities. Ants are considered soil engineers because of their effects on soil properties, availability of resource and flow of energy and nutrients in soil. Thus, it is important to gain information on their distribution and abundance. Relatively little is known about the spatial distribution of mounds and their role in the soil physical properties in wetlands of the Sanjiang plain, China. We conducted a survey of ant mounds and measured the density, height, and diameter and material composition of different ant mounds. The ecological characteristics of wetlands that ant mounds wide occurrence were also investigated, including soil type, hydrology characters and plant composition. Differences in soil particle composition, bulk density and soil moisture between ant mound and natural meadow were measured to assess the influences of ant mounds on soil physical properties. We also studied the effects of ant mounds on the microtopography of meadows. Ant mounds were found mainly in the transition zone between terrestrial and aquatic habitats, with wetland type, including Calamagrostis augustifolia wet meadow, C.augustifolia marsh meadow, shrubs marsh meadow and Carexmeyeriana–Carexappendiculata wetland, being a significant factor. Most of the mounds detected were inhabited by Lasius flavus Fabricius, Lasius niger Linnaeus and Formica sanguinea Latreille, which occupied 52.9%, 26.5% and 20.6% of the mounds surveyed, respectively. The density, height, diameter and mound composition were significantly different among the mounds of F. sanguinea Latreille, L. flavus Fabricius and L. niger Linnaeus. The average density and diameter of L. flavus mounds was significantly higher than those of other ant mounds. The average height of F. sanguinea mounds was highest among the mounds detected. Mound building activities changed soil particle size distribution, with the silt and clay content of mounds higher than for non-mound soil. Compared with adjacent, non-mound soil, the bulk density (0–30 cm) and water content (0–25 cm) of mound soil were significantly lower, but there were no significant differences between the mound soil of F. sanguinea Latreille and L. flavus Fabricius. The spatial distribution of ant mounds with different height and diameter also changed the micro-geomorphology of the soil surface, increasing the degree of fluctuation of the microtopography. The ant distribution characteristics and their ecological roles respond to a wide range of environmental alterations. The biogenic structures of ant and the specific environment associated with them have been defined as the “functional domain”, a sphere of influence that may significantly affect soil processes at certain spatial and temporal scales. Our results suggest that the distribution and structure of ant mounds can indicate wetland environmental changes, with mounds influencing ecosystem functions and enhancing wetland degradation.     

Ecology of a steppe-tundra gradient in interior Alaska

Abstract. Subarctic steppe is currently restricted in interior Alaska and the Yukon Territory to steep, south-facing river bluffs. Paleoecological and biogeographic evidence suggests that some steppe taxa may have been more widespread during the Full-Glacial. We examined factors controlling the distribution of steppe taxa on an elevation gradient across a steppetundra ecotone; such analyses may help define potential Full-Glacial distributions of these taxa. Multivariate analyses suggest that species can be divided into four spatially distinct groups, but individualistic species distributions create considerable overlap among these groups. The steppe-tundra ecotone comprises a broad zone of mixing between steppe taxa and drought-tolerant alpine tundra taxa, followed by an abrupt shift to alpine shrub tundra. The transition from low steppe to tundra vegetation is primarily associated with a gradient of decreasing soil temperature. The more abrupt transition from mixed steppe-tundra to alpine shrub tundra vegetation is primarily associated with changes in soil depth and soil moisture. Variation in vegetation within steppe is associated with gradients in soil phosphorus and moisture. Greenhouse experiments on drought tolerance of two steppe and two tundra taxa suggest that the individualistic distribution of species along the ecotone is partly a function of physiological differences among species. Our analyses of vegetation-environment relationships support the hypothesis that some components of the steppe community could have been more widespread during the colder Full-Glacial.     

高原鼢鼠土丘对矮嵩草草甸植被演替及土壤营养元素的作用

本文研究了矮蒿草草甸上高原酚鼠土丘的出现率及其对植被的覆盖状况,土丘高度的下降及其直径的变化,土丘植物地上生物量和土丘营养元素含量。高原鼢鼠土丘出现率为242个/只/年,合土壤干重为1023.82公斤/只/年,对植被的覆盖面积高达22.53平方米/只/年。土丘在地表滞留时间约1年,处于不同演替阶段植被区域内出现的土丘,其植物地上生物量间的差异显著。5月前,在原生植被区出现的土丘,经4个月后,土丘边缘形成环状富草区,士丘边缘至中心区形成环状贫草区,而土丘中心仍处于无草状况。在次生植被区上的土丘则无此现象。新土丘除速效钾的含量与对照区无显著差异外,速效氮、磷的含量显著地高于对照区。旧土丘土壤中的速效氮、磷、钾含量均低于新土丘,但氮、磷的含量仍高于对照区。     

Burrowing activities of kangaroo rats and patterns in plant species dominance at a shortgrass steppe-desert grassland ecotone

Abstract. Our objective was to evaluate the effects of burrowing activities by banner-tail kangaroo rats (Dipodomys spectabilis Merriam) on plant community structure and species dominance for two patch types at the ecotone between shortgrass steppe and desert grassland in New Mexico, USA. 10 mounds produced by kangaroo rats were selected in patches dominated by Bouteloua gracilis (the dominant in shortgrass steppe communities) and 10 mounds were selected in patches dominated by B. eriopoda (the dominant in Chihuahuan desert grasslands). Plant cover and density by species were sampled from three locations associated with each mound: the mound proper, the edge of the mound in the transition area, and the off-mound vegetation. Similar cover of B. eriopoda for the edges of mounds in both patch types indicates the ability of this species to respond to animal disturbances regardless of the amount of cover in the surrounding undisturbed vegetation. By contrast, cover of B. gracilis was low for all mounds and mound edges in patches dominated by this species. Much higher cover of B. eriopoda on mound edges compared to the undisturbed vegetation in B. gracilis-dominated patches indicates that kangaroo rats have important positive effects on this species. Lower cover of perennial grasses and higher cover of forbs, shrubs, and succulents on the edges of mounds in B. eriopoda-dominated patches compared to patches dominated by B. gracilis indicate the importance of surrounding vegetation to plant responses on disturbed areas. Our results show that kangaroo rats have important effects on both species dominance and composition for different patch types, and may provide a mechanism for small-scale dominance patterns at an ecotone; thus providing further support for their role as keystone species in desert grasslands.     

The effects of micro-habitats and grazing intensity on the vegetation of burial mounds in the Kazakh steppes

Background: Burial mounds (kurgans) of Eurasian steppes are man-made habitat islands that have the potential to harbour rich plant diversity due to micro-habitats associated with their topography.

Aims: We assessed whether kurgan micro-habitats harboured different species pools and functional groups from those found on the surrounding steppes. In addition, we asked if these mounds were affected by different grazing intensities from those on the surrounding vegetation.

Methods: We surveyed kurgan micro-habitats (northern and southern slopes, surrounding ditch) and adjacent steppe plains in non-grazed, moderately grazed and heavily grazed sites in northern Kazakhstan. We analysed differences in species composition of four habitats under three grazing regimes using Generalised Linear Mixed Models, PCA ordination and indicator species analysis.

Results: Kurgan micro-habitats had diverse vegetation and supported the co-existence of plant species with different environmental needs. We identified 16 steppe specialists confined to kurgan micro-habitats. Steppe vegetation was well-adapted to extensive grazing, although heavy grazing supported ruderals and a decline in steppe specialists. There was a significant interaction between grazing intensity and habitat type: heavy grazing supported ruderals and suppressed steppe specialists especially on the slopes.

Conclusions: We highlighted that kurgans play an important role as maintaining high plant diversity locally in extensive steppe plains in Central-Asia by increasing environmental heterogeneity and supporting specialist species confined to these micro-habitats.     

若尔盖退化高寒湿地土壤理化性质、酶活性及微生物群落的季节动态

以若尔盖退化高寒湿地为研究对象,连续3年(2015—2017年)于植被返青期(4—5月)、草盛期(7—8月)和枯黄期(10—11月)监测高原鼢鼠鼠丘密度、3个土层(0—10、10—20、20—30 cm)土壤理化性质、酶活性及微生物数量的季节动态,并分析土壤生物学特征与土壤环境间的季节相关性。结果表明:(1)各植被物候期,土壤pH值、容重指标均随土层加深而显著升高(P<0.05),土壤含水量、有机质、全氮、碱解氮、有效磷、速效钾、酶活性及微生物数量指标均随土层加深而显著降低(P<0.05);(2)植被物候期对高寒鼠荒地非土丘土壤养分在不同土层的垂直分配有显著影响,对0—10 cm土层土壤生物学特征含量的影响程度显著大于10—20 cm和20—30 cm土层。(3)冗余分析(RDA)表明3个植被物候期,土壤生物学特征指标与土壤理化性质指标间显著相关(P<0.05),主成分分析(PCA)表明各指标在不同土层均呈现明显的季节性分布,数量特征表现为:枯黄期>返青期>草盛期。揭示了高寒鼠荒地高原鼢鼠季节性活动对土壤理化性质、酶活性及微生物数量的影响,为今后青藏高原鼠...     

不同形成时间高原鼢鼠鼠丘土壤养分分配规律

高原鼢鼠(Myospalax baileyi)作为青藏高原唯一营地下生活的鼠类,其造丘活动不仅能影响草地群落演替的方向和进程,而且对鼠丘土壤养分含量和分配造成空间异质性。关于不同形成时期的高原鼢鼠鼠丘养分含量及在垂直高度的分配规律研究报道尚少。基于此本研究以不同形成时期的鼢鼠鼠丘为研究对象,对鼠丘土壤养分含量及空间分配规律进行探讨。结果表明:随着鼠丘形成时间的推移,土壤养分总体表现为:1年鼠丘多年鼠丘对照区;与非鼠丘区相比,随着土壤土层增加,土壤养分未呈现规律性的变化。其中,土壤全氮和速效氮含量表现为1年鼠丘3年鼠丘5年鼠丘对照区;0—10cm土壤全磷和速效磷含量变化总体表现为多年鼠丘1年鼠丘对照区,10—30cm土层1年鼠丘土壤中全磷和速效磷含量最高。土壤速效钾和有机质含量随着鼠丘形成时间推移总体表现为:1年鼠丘5年鼠丘3年鼠丘;其中在10—30cm土层,1年鼠丘速效钾和有机质含量显著高于多年鼠丘和对照区。由此可见,高原鼢鼠造丘活动能显著改变土壤养分分配格局,短期内形成养分富集的肥力岛,为鼠丘土壤种子库中种子的萌发和植被生长提供必需的养分保证。     

Influence of pocket gopher mounds on a Texas coastal prairie

Summary Effects of pocket gopher (Geomys attwateri) mound-building activity on plant community composition and soil nutrient concentrations were investigated in south Texas on both burned and unburned coastal prairie sites. Pocket gophers deposited large amounts of soil which were lower in nutrient content than randomly-collected samples. Above-ground plant biomass was greater around mounds than in random samples mainly because of increased dicots around mounds on the burned area when compared with random samples on the same area. Pocket gophers may have concentrated their activities (and therefore, mounds) in areas with higher dicot biomass on the burned area since they prefer perennial dicots as food, or the presence of mounds may have ameliorated the apparent negative effect of fire on dicots.     

Component diversity of the soil cover in the Chuya depression, Gorny Altai

The high-mountain Chuya depression (Gorny Altai) was studied in 2006–2008. New data on the diversity of soil components of the soil cover in terms of the new Russian soil classification system have been obtained. Some relations of soil components to biotic and abiotic components of high-mountain steppe terrestrial ecosystems have been revealed.     

Heuweltjies (earth mounds) in the Clanwilliam district,Cape Province,South Africa: 4000-year-old termite nests

Summary Examination of eroded and intact earth mounds in the Clanwilliam district, South Africa, indicates that they are well-established active termitaria of the harvester termite Microhodotermes viator. Unoccupied lower portions of the mounds contain ubiquitous trace-fossil evidence of earlier inhabitation by the same species. Previous studies indicating that fossorial molerats played a major role in the formation of the mounds are not supported by the observations presented here. Calcretization of the basal parts of the earth mounds has been caused by groundwater interaction with the more alkaline mound soil. ¹⁴C dating of this calcrete indicates that the earth mounds have been in existence for at least 4000 years, an order of magnitude greater than any previously recorded longevity for termitarium inhabitation.     

宁夏典型天然草地土壤团聚体稳定性及其有机碳分布特征

土壤团聚体作为土壤结构的基本单元和土壤有机碳存在的重要场所,对维系土壤质量和生态环境可持续发展具有重要作用。为探究宁夏天然草地土壤团聚体稳定性及其有机碳分布特征,以宁夏4种典型的天然草地（草甸草原、温性草原、草原化荒漠和荒漠草原）为研究对象,系统开展研究。结果表明：草甸草原、温性草原和草原化荒漠各粒级机械团聚体和水稳性团聚体含量均呈现随粒径减小而先减小后增大趋势,荒漠草原机械团聚体含量呈现随粒径减小而先减小后增大的趋势,水稳性团聚体含量呈现随粒径减小逐渐增大的趋势;且草甸草原和温性草原机械稳定性和水稳性团聚体在0-10 cm、10-20 cm和20-40 cm 3个土层均以>0.25 mm大团聚体为主,草原化荒漠和荒漠草原水稳性团聚体均以<0.25 mm的微团聚体为主。4种草地类型机械团聚体和水稳性团聚体MWD和GMD,以及各粒级土壤团聚体有机碳含量均表现为草甸草原和温性草原显著高于草原化荒漠和荒漠草原。草甸草原和温性草原在3个土层深度均以>0.25 mm的大团聚体对有机碳的贡献率最高,分别达到43.86%、59.26%、58.89%和58.02%、54.03%、57.15%;草原化荒漠和荒漠草原在3个土层深度,均以<0.25 mm的微团聚体贡献率高,分别达到了60.37%、55.86%、54.33%和75.61%、78.34%、78.74%。结果表明：草甸草原和温性草原较草原化荒漠和荒漠草原土壤团聚体稳定性更高,更有利于土壤有机碳累积。     

高寒草原土壤有机碳及土壤碳库管理指数的变化

高寒草原对高寒生态系统的稳定具有重大意义。为探明高寒草原土壤有机碳（SOC）、土壤活性有机碳（ASOC）变化,以及草地退化对土壤碳库稳定性的影响,对藏北高原正常、轻度和严重退化高寒草原表层（0-10 cm）、亚表层（10-20 cm）土壤进行了初步研究。结果表明：（1）轻度、严重退化草地各土层SOC、ASOC均呈不同程度的下降。其中,退化草地SOC的降幅均以表层最大,且各土层降幅均随草地退化加剧而下降;退化草地ASOC的降幅则均以亚表层最大,但各土层ASOC的降幅随草地退化加剧而提高。（2）正常草地、轻度和严重退化草地表层ASOC比率分别为16.8%、21.3%、16.6%,亚表层分别为21.8%、18.1%和16.0%;土壤碳库活度与ASOC比率的变化趋势完全一致。因此,轻度退化草地SOC的不稳定性主要体现在表层土壤。（3）退化草地表层、亚表层碳库管理指数（CMI）均呈显著下降,但表层降幅相对较低;与严重退化草地比,轻度退化草地不同土层CMI明显提高。（4）高寒草原环境中,正常草地、轻度和严重退化草地各土层SOC、ASOC间则均呈一定程度的负相关,表明土壤微生物对SOC、ASOC的影响和作用可能不同。     

Role of termites in the restoration of soils and plant richness on bowé in West Africa

Bowé (hardened ferricrete soils formed by erosion, drought or deforestation) are often associated with termite mounds, but little is known about these mounds and their role in the restoration of soils and plant biodiversity on bowé. This study examined termite mounds on bowé and their effects on soil depth and plant richness. Sixty-four sampling plots were laid out randomly on bowé sites with mounds and on adjacent bowé sites without mounds. The height and circumference of each mound were measured. Species inventories were made and soil depth measured in each plot. Linear mixed effects and generalised mixed effects models with Poisson error distribution were used to assess the variation in soil depth and plant species richness in mound and nonmound microsites. Two types of mounds (small vs. large) associated with different termite species were observed on bowé, with the small mounds being most common. Plots with either large or small mounds had deeper soils and higher plant richness than the adjacent plots without mounds. Conservation of termite mounds is important for restoring soils and plant richness on bowé, and termite mounds should be taken into consideration in biodiversity and soil management strategies for bowé.     

高原鼠兔挖掘活动对土壤中氮素含量的影响

本文通过测定不同类型高原鼠兔鼠丘和鼠丘下0 ～ 10 cm 土壤中总氮、铵态氮和硝态氮的含量变化,分析了高原鼠兔挖掘活动对土壤中无机氮含量的影响,并通过测定高原鼠兔鼠丘密度,计算了每只高原鼠兔对氮素循环的贡献。研究结果表明:不同类型鼠丘土壤中总氮含量无明显变化,铵态氮、硝态氮和无机氮含量处理间变化趋势为当年鼠丘>两年鼠丘> 多年鼠丘> 对照。方差分析结果表明,硝态氮含量在5 月时差异显著,当年鼠丘和两年鼠丘显著大于多年鼠丘和对照,无机氮含量在5 月和9 月表现为当年鼠丘显著高于对照。在不同月份,铵态氮含量月间变化趋势为5 ～ 8 月逐渐降低,至9 月略有增加,硝态氮和无机氮含量呈现“高- 低- 高-低- 高”的“W”变化趋势。方差分析结果显示,铵态氮、硝态氮和无机氮含量月间变化显著。不同类型鼠丘下0 ～ 10 cm 土壤中铵态氮、硝态氮和无机氮含量处理间和月份间变化趋势与鼠丘土壤中变化趋势基本一致,但硝态氮和无机氮含量在当年鼠丘中均显著高于对照,且不同月份间铵态氮、硝态氮和无机氮的含量差异显著(P
< 0.05)。每只高原鼠兔挖掘活动所形成的鼠丘土壤中的铵态氮、硝态氮和无机氮分别增加了162.6 mg/ kg、355.1 mg/kg 和497.7 mg/ kg。     

热带森林不同演替阶段蚂蚁巢穴的分布特征及其影响因素

为探明热带森林蚂蚁巢穴的分布特征及其影响因素, 采用样方法研究了西双版纳不同演替阶段热带森林定居巢穴蚂蚁的种类及其巢穴的密度、盖度和空间分布特征, 并分析了土壤理化环境与蚂蚁种类总数、巢穴密度及盖度的相关性。结果表明, 不同演替阶段热带森林蚂蚁种类总数、巢穴的密度及盖度大小顺序为: 小果野芭蕉 (Musa acuminata)群落>白背桐(Mallotus paniculatus)群落>思茅崖豆(Mellettia leptobotrya)群落, 并且热带森林的演替类型显著影响蚂蚁种类总数及巢穴密度, 而对巢穴盖度的影响未达到显著水平; 蚂蚁种类总数、巢穴密度与土壤总有机碳和水解氮显著正相关, 与土壤容重和土壤含水率显著负相关, 但所选择的土壤理化指标与巢穴盖度的相关性均未达到显著水平; 蚂蚁巢穴的空间分布呈随机分布格局。我们的数据表明, 不同演替阶段热带森林所形成的植被类型及土壤环境状况共同影响定居的蚂蚁种类总数与筑巢密度。     

Robust Prediction of Treefall Pit and Mound Sizes from Tree Size Across 10 Forest Blowdowns in Eastern North America

Treefall pits and mounds, formed when trees are uprooted by wind, influence an exceptionally broad range of phenomena in forests, having impacts on vegetation composition, soil formation, erosion, and soil respiration, among other processes. For example, treefall pits and mounds are known to have plant species composition with more pioneer species than nearby undisturbed soil; these microsites also are wetter (pits) or drier (mounds) than undisturbed soil; and have lower rates of soil respiration. Therefore, knowledge of the extent or coverage of these microsites will improve estimates of several processes as well as vegetation composition at the stand and landscape scale. Such information would be timely, given predictions of climate-change driven increases in severe weather that is the primary agent of pit and mound formation. However, to date, there have been no attempts to define a robust relationship to predict the sizes of these microsites across multiple forest types in eastern North America. Here, we summarize field measurement of the relationship between tree size and treefall pit and mound sizes, across ten catastrophic windthrow study sites. We find that for all ten sites pooled, simple ln–ln regression explains almost 54% of the variation in sizes of treefall pits (n = 1,039) and treefall mounds (n = 962) on the basis of tree diameter. This relationship spans numerous soil types, 31 tree species, and tree sizes ranging from 5 cm to greater than 105 cm diameter. Such a relationship may be coupled with information on the severity of disturbance (for example, proportion of stems uprooted) and pre-disturbance tree size structure, to provide a basis for predicting the area covered by pit and mound microsites at the landscape scale, and thereby a basis to frame expected impacts on soil formation, carbon cycling, vegetation establishment, and other ecological, edaphic, and biogeochemical processes.     

Interaction between the non-myrmecochorous herb Galium aparine and the ant Formica polyctena

Non-myrmecochorous plant species are able to colonize Formica polyctena mounds. Galium aparine has been chosen as a model to study this kind of ant-plant association. In order to understand benefits to ants and plants, we have studied removal rates of fruits by ant workers, and compared soil seed material, seedling pattern and development of plants of the nest versus forest.Ant workers remove fruits at very low rates; removal time for half of the sample of 10 seeds was on average 5 h. Removed fruits were usually lost within 20–30 cm distance of the ant route. The soil samples from the nests contained a higher number of fruits, than those from randomly chosen sites in the forest. Seeds start to germinate in late August; on the F. polyctena mounds significantly earlier than at surrounding places. The seedling density was higher within experimental quadrats located on mound sites especially in late September–early October. The highest density of seedlings was on the slope of the mound. Plants from mounds are significantly longer, have a higher number of nodes during all stages of development and a higher mortality rate than that at surrounding places.The interactions between G. aparine and F. polyctena ants are asymmetrical. In spite of higher mortality rate of seedlings on mounds, ants provide some benefits to the plant. Firstly, workers are additional dispersal agents for G. aparine fruits. Furthermore, the soil peculiarities of ant mounds are beneficial for seed germination and seedling growth. G. aparine does not provide ants with energetically valuable food like plants with elaiosome-bearing seeds. Moreover, the high density of seedlings and plants on the mounds shades the nest.