Isolating the role of soil resources,defoliation, and interspecific competition on early establishment of the late successional bunchgrass Festuca campestris

Native grasslands are valued for biodiversity and supporting dormant season grazing, but are prone to invasion. In western Canada, revegetation of Festuca campestris grasslands may be hindered by Poa pratensis, an invasive grass. To determine the competitive interaction of these species during establishment, two greenhouse experiments were conducted where F. campestris seedlings were planted in monocultures or mixtures with P. pratensis. The first experiment used equal‐aged (3‐month old) seedlings of both species, while the second experiment used unequal‐aged seedlings (4‐month‐old F. campestris and 2‐month‐old P. pratensis). Seedling performance was measured in response to manipulations of water and nitrogen, defoliation, and plant neighbor. While water and nitrogen reduced the biomass and vegetative reproduction (tillering) of F. campestris, exposure to P. pratensis most strongly limited the growth of F. campestris seedlings regardless of other treatments. More frequent and consistent decreases in F. campestris due to P. pratensis were observed in older F. campestris seedlings than younger seedlings. Defoliation also reduced the growth of F. campestris, and the added presence of P. pratensis during defoliation further enhanced these reductions in younger, equal‐aged bunchgrass seedlings. Overall, these results suggest that when restoring native F. campestris grasslands, early establishment may be improved by reducing the negative impacts of P. pratensis, and avoiding severe defoliation.     

Using phenological niche separation to improve management in a Northern Glaciated Plains grassland

Many of the remaining patches of untilled (native) prairie in the Northern Glaciated Plains of North America are heavily invaded by the cool‐season grasses, Bromus inermis and Poa pratensis. However, the native vegetation in these patches contains many warm‐season species. This difference in phenology can be used to benefit restoration. We conducted an experiment to examine the efficacy of restoration treatments (mowing and prescribed fire) applied early in the growing season for consecutive years to decrease cool‐season invasive plant biomass without impacting the native warm‐season species. Our treatments were successful at significantly decreasing invasive cool‐season plant biomass and increasing native warm‐season plant biomass. No differences between treatments (mowing and prescribed fire) were found. Results suggest that incorporating differences in phenology between target and nontarget species into management may increase restoration success.     

不同生态恢复措施对草地样带食物消费的影响——以锡林郭勒盟为例

生态工程的实施对区域居民生产生活产生了重要影响。以锡林郭勒草地样带为例,利用2017年8月—2018年7月农牧户食物跟踪调查数据、农牧户问卷调查数据、生态恢复措施数据,结合土地利用数据和社会经济数据等,重点分析了不同生态恢复措施对锡林郭勒草地样带农牧户食物消费的影响。研究结果显示:(1)锡林郭勒草地样带生态恢复措施沿样带自北向南实施力度逐渐变弱,草地恢复措施由以草畜平衡、休牧和禁牧为主向休牧和围栏封育为主转变,草地恢复措施中对人类活动的限制也随之由弱变强;(2)沿草地样带自北向南居民食物消费形成了三种模式,在食物消费数量和消费结构上呈显出由牧区特征向农区特征的转变,即人均食物消费量沿样带递减,食物消费由肉蛋奶和蔬菜水果为主向粮食和蔬菜水果为主转变;(3)食物消费模式受到草地供给、收入及其结构、文化习俗和职业分布等生态、经济和社会多方面因素的影响。研究为实现区域生态、经济和社会的协调发展相关政策的制定提供参考。     

北方风沙区生态修复的科学原理、工程实践和恢复效果

北方风沙区位于欧亚草原的东部,是我国生态环境最为脆弱的地区之一,其在北方生态安全屏障和丝绸之路经济带建设中具有十分重要的战略地位。在国家一系列生态保育工程的支持下,该地区的生态环境得到明显改善。但是,由于受人类活动和全球气候变化的影响,该地区仍然面临着严峻的环境压力。在中国科学院科技服务网络计划(STS计划)等项目支持下,开展了北方风沙区土地沙化成因及退化土地空间分布研究,集成了北方风沙区重点脆弱区生态恢复的理论和技术体系,以内蒙古中部的阴山北麓地区、内蒙古浑善达克沙地和蒙辽交界的科尔沁沙地为重点研究区域,进行了高效人工草地建植、天然草地恢复和管理、沙化草地治理等相关工程技术的示范,开展生态恢复模式的效果跟踪监测和生态效益评估,确定生态恢复技术和模式的技术参数和指标,明确不同集成技术与模式在北方风沙区的适用区域和范围,为技术模式的推广应用提供科学依据。通过上述研究,可以为中央和地方政府制定生态系统管理和退化生态系统恢复政策、建立我国北方生态安全屏障提供决策依据,为生态修复产业提供技术指南,为相关研究提供全面系统的基础数据支撑。     

Invasive alien plants and environmental remediation: a new paradigm for sustainable restoration ecology

This article explores some fundamental aspects of ecological restoration dynamics when an ecosystem is exposed to and altered by environmental disturbances like invasive alien plants and metals/particulates. These dynamics are assessed in socioeconomic and phytoremediation terms with respect to the perspective of emerging nations (e.g. an Indo‐Burma global biodiversity hotspot). In this short report, we discussed the positive ecological uses of invasive alien plants in remediation/restoration of the contaminated environment. Therefore, the impacts of invasive alien plants on the ecosystem are analyzed as prerequisite for remediation/restoration efforts. The utility of an integrated approach is proposed as a promising option to help restore or sustain the socioecological systems from diverse disturbances.     

外来植物入侵对土壤生物多样性和生态系统过程的影响

随着科学家对生态系统地下部分的重视,评价外来植物入侵对土壤生态系统的影响成为当前入侵生态学领域的研究热点之一。本文综述了外来植物入侵对土壤微生物、土壤动物以及土壤碳、氮循环动态影响的研究,并探讨了其影响机制。已有的研究表明,植物入侵对土壤生物多样性及相关生态系统过程的影响均存在不一致的格局,影响机制也是复杂多样的。外来植物与土著植物凋落物的质与量、根系特征、物候等多种生理生态特性的差异可能是形成格局多样性和影响机制复杂性的最主要原因。今后,加强多尺度和多生态系统的比较研究、机制性研究、生物多样性和生态系统过程的整合性研究及土壤生态系统对植物入侵的反馈研究是评价外来植物入侵对土壤生态系统影响的发展趋势。     

生态恢复和经济发展悖论中毒害草的地位及悖论解决途径

探讨了毒害草存在的生态价值、利用价值及毒害草防治的弊端。认为过度放牧是畜牧业陷入困境的主要原因,毒害草的繁衍只是草原退化的直接反映,防除缺乏依据。现有的防治措施存在各种弊端,对环境和生物多样性保护不利;并指出毒害草可以覆盖地面、减少水土流失,对草原生态系统的保护和恢复有利,故认为毒害草的大量繁衍是草原生态系统与放牧系统协同进化的结果,是草原生态系统发展的防御机制,具有极大生态价值。同时提出草原生态系统可持续发展要从人的生存和经济发展着眼,要改变现有生活模式,发展多种经营,实行跨区域经济补偿;要控制人口数量,对现有人口要实现城镇化。     

Resilience and restoration of tropical and subtropical grasslands,savannas, and grassy woodlands

Despite growing recognition of the conservation values of grassy biomes, our understanding of how to maintain and restore biodiverse tropical grasslands (including savannas and open‐canopy grassy woodlands) remains limited. To incorporate grasslands into large‐scale restoration efforts, we synthesised existing ecological knowledge of tropical grassland resilience and approaches to plant community restoration. Tropical grassland plant communities are resilient to, and often dependent on, the endogenous disturbances with which they evolved – frequent fires and native megafaunal herbivory. In stark contrast, tropical grasslands are extremely vulnerable to human‐caused exogenous disturbances, particularly those that alter soils and destroy belowground biomass (e.g. tillage agriculture, surface mining); tropical grassland restoration after severe soil disturbances is expensive and rarely achieves management targets. Where grasslands have been degraded by altered disturbance regimes (e.g. fire exclusion), exotic plant invasions, or afforestation, restoration efforts can recreate vegetation structure (i.e. historical tree density and herbaceous ground cover), but species‐diverse plant communities, including endemic species, are slow to recover. Complicating plant‐community restoration efforts, many tropical grassland species, particularly those that invest in underground storage organs, are difficult to propagate and re‐establish. To guide restoration decisions, we draw on the old‐growth grassland concept, the novel ecosystem concept, and theory regarding tree cover along resource gradients in savannas to propose a conceptual framework that classifies tropical grasslands into three broad ecosystem states. These states are: (1) old‐growth grasslands (i.e. ancient, biodiverse grassy ecosystems), where management should focus on the maintenance of disturbance regimes; (2) hybrid grasslands, where restoration should emphasise a return towards the old‐growth state; and (3) novel ecosystems, where the magnitude of environmental change (i.e. a shift to an alternative ecosystem state) or the socioecological context preclude a return to historical conditions.     

气温上升对草地土壤微生物群落结构的影响

在 2 0世纪内 ,全球气温已经上升了 0 .6℃ ,并预计到本世纪末仍将上升 1.4～ 5 .8℃。全球气候变暖对生态系统的潜在影响 ,生态系统对气温上升的反馈已成为国际生态学界的研究热点 ,而且所研究的系统也已经从过去简化的模拟系统到复杂的真实生态系统。但是 ,现有对真实生态系统的研究大部分集中在地上植物群落和土壤气体交换等领域 ,对在土壤有机碳分解和保护中起决定作用的土壤微生物研究较少。为此 ,在美国大平原地区进行人工提高气温 (上升 1.8℃ ) ,来研究土壤微生物对气温上升的反应。结果表明 :增温对土壤微生物的总生物量没有显著效应 ,但可以提高微生物的 C∶ N比。另外 ,磷脂肪酸分析发现 ,气温上升显著降低土壤微生物量中的细菌比重 ,提高真菌的份额 ,从而显著提高了群落中真菌与细菌的比值。而且 ,通过对土壤微生物底物利用方式和磷脂肪酸特征的主成份分析 ,发现增温导致了土壤微生物群落结构的转变。可见 ,气温上升可能是通过提高土壤微生物中真菌的优势 ,而导致群落结构的变化。该变化将可以提高微生物对土壤有机碳的利用效率 ,并利于土壤有机碳的保护     

Long‐term effects of prairie restoration on plant community structure and native population dynamics

The key to restoring degraded grassland habitats is identifying feasible and effective techniques to reduce the negative impacts of exotic species and promote self‐sustaining native populations. It is often difficult to extend monitoring of restoration efforts to evaluate long‐term success, but doing so is essential to understanding how initial outcomes change over time. To assess how initial treatment effects persist, we revisited degraded patches of Pacific Northwest prairie habitat 6 years after experimental restoration efforts ceased. We evaluated plant community composition to determine the lasting effects of supplemental native seeding and disturbance treatments (burning, mowing, and herbicide to reduce exotic species). We tracked the persistence of seeded species and measured spread of their populations to evaluate suitability of species for restoration and the ability of the habitat to support native plant populations. We found that plots that received supplemental seeding continued to exhibit higher richness of native species than those left unseeded, and that both seeding and disturbance treatments could positively influence native species abundance over the long term. The initially observed effects of disturbance treatments on reducing exotic grass abundance had diminished, highlighting the importance of long‐term monitoring and ongoing control of exotic species. Nevertheless, these treatments significantly influenced the population trajectories of 4 out of 8 seeded native species. There was evidence of spatial advance of most seeded species. Results from extended monitoring confirm that dispersal limitation of native species and difficulties maintaining the reduction of exotic grasses continue to be major barriers to success in restoration of invaded grasslands.     

Demography of Bouteloua gracilis in a mixed prairie: analysis of genets and individuals

1 We analysed a data set containing the locations and sizes of individual plants from five 1-m² permanent quadrats that had been mapped annually from 1934 to 1972. We digitized each map and used geographical information software to evaluate annual recruitment and mortality, age structure, survivorship and longevity of genets and individuals of Bouteloua gracilis .
2 Ninety-one per cent of the years between 1938 and 1972 had at least one seedling recruited. An average of 10.3 genets died annually, although the variability among years was high (CV = 70%). The number of seedlings recruited each year was significantly correlated with the number of genets dying. Most genets died before age 10 and the average life span was 3.7 years, although some genets were much longer lived (> 38 years).
3 The average number of individuals per genet was 1.3. Excluding seedlings, 56% of the genets were represented by a single individual. The annual number of individuals in the 5 m² ranged from 29 to 278. Average mortality of individuals was 25.8 per year and the variability among years was high (CV = 91%).
4 The plant community appeared to be relatively stable and openings created by mortality were recolonized by recruitment. Climatic variability did not have a large influence on demography.     

Reducing Competitive Suppression of a Rare Annual Forb by Restoring Native California Perennial Grasslands

Populations of the rare annual forb Amsinckia grandiflora may be declining because of competitive suppression by exotic annual grasses, and may perform better in a matrix of native perennial bunchgrasses. We conducted a field competition experiment in which Amsinckia seedlings were transplanted into forty 0.64‐m² experimental plots of exotic annual grassland or restored perennial grassland. The perennial grassland plots were restored using mature 3 cm‐diameter plants of the native perennial bunchgrass Poa secunda planted in three densities. The exotic annual grassland plots were established in four densities through manual removal of existing plants. Both grass types reduced soil water potential with increasing biomass, but this reduction was not significantly different between grass types. Both grass types significantly reduced the production of Amsinckia inflorescences. At low and intermediate densities (dry biomass per unit area of 20–80 g/m²), the exotic annual grasses reduced Amsinckia inflorescence number to a greater extent than did Poa, although at high densities (>90 g/m²) both grass types reduced the number of Amsinckia inflorescences to the same extent. The response of Amsinckia inflorescence number to Poa biomass was linear, whereas the same response to the annual grass biomass is logarithmic, and appeared to be related to graminoid cover. This may be because of the different growth forms exhibited by the two grass types. Results of this research suggest that restored native perennial grasslands at intermediate densities have a high habitat value for the potential establishment of the native annual A. grandiflora.     

Festuca campestris density and defoliation regulate abundance of the rhizomatous grass Poa pratensis in a fallow field

Invasion by the rhizomatous grass Kentucky bluegrass (Poa pratensis) is a global phenomenon, including into foothills rough fescue (Festuca campestris) grasslands of southwestern Alberta, Canada. In order to better understand the competitive relationships between these species, we conducted a fallow field study where rough fescue bunchgrass tussocks were transplanted at one of three planting densities (15, 30, or 45 cm spacing), and then subject to various treatments in a factorial design, including one‐time intensive summer defoliation and seeding of bluegrass into adjacent bare soil. Rough fescue plants exhibited marked intraspecific competition, as high planting densities increased tussock mortality, while decreasing plant tiller counts and relative inflorescence production, together with plant and tiller‐specific mass. However, high densities of the bunchgrass also reduced the cover and biomass of encroaching bluegrass, coincidental with reduced resource (soil moisture and light) availability in mid‐summer. Although summer defoliation increased rough fescue tiller counts, this disturbance reduced plant and tiller mass, and also increased Kentucky bluegrass. We conclude that while high densities of nondefoliated stands of rough fescue may increase resistance to bluegrass encroachment, a reduction in either fescue plant density or vigor via defoliation can increase the risk of bluegrass invasion within northern temperate grassland.     

伊犁河谷春秋草场草地生态调查及其恢复对策

针对新疆伊犁河谷春秋草场严重退化的现状,通过对退化草场、围栏封育并实施灌溉的草场、单纯围栏的草场和灌溉但不封牧草场样方的对比调查,从地表植物的生物量、植物种类、优质牧草所占比例和草地植物多样性指数等的变化规律和特征方面,探讨了伊犁河谷地区春秋草场退化的原因和恢复措施。结果表明:适当灌溉后草地生物量为1540.5g.m-2,远高于不灌溉的草地(生物量为188.13g.m-2),表明干旱是本区草地植被生长一个重要制约因素;而仅改变草地的水分条件,在超载率达123%的大环境下,草场中优质牧草的比例由封育的62.38%下降到未封育的2.08%。因此,适度放牧并辅以灌溉措施是本区天然草场恢复的2个必要条件。     

Efficacy and non-target effects of herbicides in foothills grassland restoration are short-lived

Questions

Selective herbicides are frequently used in ecological restoration to control invasive non-native forbs and recover plant communities. However, the long-term efficacy of this practice, its non-target effects on native plants, and its role in facilitating secondary invasions are not well understood. Similarly, little is known about the extent to which herbicide drift may affect native plant communities.

Location

Foothills grasslands of Montana, USA.

Methods

We conducted a 6-year experiment to investigate changes in the abundance of a target invasive plant, knapweed (Centaurea stoebe subsp. micranthos) and plant community structure in response to the herbicides Tordon® (picloram) and Milestone® (aminopyralid), applied at a recommended rate and a diluted rate that simulated drift.

Results

Knapweed cover and the richness of native and non-native forb species declined in the first 3 years in response to treatment at recommended rates, but not drift rates. Secondary invasion by non-native monocots was significant but weak. The cover of native forbs and the cover and richness of native monocots did not differ among treatments but changed significantly with the year. Surprisingly, 6 years after treatments, there were no differences among treatments in the cover of the target invasive plant or community structure.

Conclusions

Our results demonstrate that the efficacy and non-target effects of herbicides in grassland restoration can be short-lived and idiosyncratic because of year effects. Restoration of knapweed invasions might require other active interventions, such as seeding or repeated spraying. Our study supports previous calls for long-term monitoring of herbicides application in ecological restoration.     

Assessment of interaction between sheep and poorly palatable grass: a key tool for grassland management and restoration

Invasion of poorly palatable grasses due to abandonment or improper grazing management decreases pastures feeding value and biodiversity. With the aim to control their spread, we assessed the relationship between sheep foraging behavior and changes in aboveground phytomass, leaf traits, and chemical features of the tall grass Brachypodium rupestre and evaluated the effects of a B. rupestre-based diet on epithelium keratinization of rumen. Our results demonstrated that sheep became less selective throughout the experimental trials and B. rupestre decreased its aboveground phytomass. Some leaf traits showed significant changes (LDMC, LA, and ADL were higher in ungrazed areas; leaf nitrogen content was higher in the grazed ones). In addition, we detected an increase of the degree of epithelium keratinization of sheep. Thus high grazing pressure can be used to control the spread of B. rupestre, but negative effects on animal welfare due to the increase of rumen keratinization might be expected.     

Ecosystem Level Impacts of Invasive Acacia saligna in the South African Fynbos

Recent efforts to clear invasive plants from the fynbos of South Africa forces managers to think about how N₂‐fixing invasives have altered ecosystem processes and the implications of these changes for community development. This study investigated the changes in nitrogen (N) cycling regimes in fynbos with the invasion of Acacia saligna, the effects of clear‐cutting acacia stands on soil microclimate and N cycling, and how altered N resources affected the growth of a weedy grass species. Litterfall, litter quality, soil nutrient pools, and ion exchange resin (IER)‐available soil N were measured in uninvaded fynbos, intact acacia, and cleared acacia stands. In addition, a bioassay experiment was used to ascertain whether the changes in soil nutrient availability associated with acacia would enhance the success of a weedy grass species. Acacia plots had greater amounts of litterfall, which had higher concentrations of N. This led to larger quantities of organic matter, total N, and IER‐available N in the soil. Clearing acacia stands caused changes in soil moisture and temperature, but did not result in differences in IER‐available N. The alteration of N availability by acacias was shown to increase growth rates of the weedy grass Ehrharta calycina, suggesting that secondary invasions by nitrophilous weedy species may occur after clearing N₂‐fixing alien species in the fynbos. It is suggested that managers use controlled burns, the addition of mulch, and the addition of fynbos seed after clearing to lower the levels of available N in the soil and initiate the return of native vegetation.