Requirement of vegetation gaps for seedling establishment of two unpalatable grasses in a native grassland of central Argentina

Abstract The objective was to determine the effects of root and shoot competition on seedling establishment of the unpalatable grasses Stipa gynerioides and S. tenuissima in a native grassland of central Argentina dominated by the palatable grass S. clarazii. Seeds of the two unpalatable species were sown in natural occurring microsites with shoot and root competition from the palatable species, and in artificially created microsites without either shoot competition or shoot and root competition. In addition, fresh seeds of the unpalatable species were subjected to daily alternating temperatures under laboratory and field conditions to determine the effect on seed dormancy and germination. Seedling establishment of S. gynerioides and S. tenuissima occurred only in microsites without shoot and root competition. Also, the fluctuation of temperature near the soil surface in these microsites reduced dormancy and promoted rapid germination in both species. Our results support the hypothesis that, in swards dominated by palatable grasses, vegetation gaps of low competitive pressure favour seedling establishment of unpalatable grasses. It is suggested that the creation of these gaps by overgrazing can be an important mechanism in the process of species replacement in native grasslands.     

Seedling emergence and survival in contrasting soil microsites in Patagonian Monte shrubland

Abstract. The potential of two perennial species (Larrea divaricata and Stipa tenuis) to colonize different soil microsites was analyzed in the Patagonian Monte shrubland. We hypothesize that the short-lived grass S. tenuis is more able to colonize the soil of microsites beneath vegetation patches where N-fertility is higher than those in bare soil, while the long-lived shrub L. divaricata colonizes different soil microsites irrespective of their N fertility. A greenhouse experiment was carried out to evaluate the emergence and survival of both species in different soil microsites at different water, inorganic N and seed densities. In all cases soil microsites were seed limited since the addition of viable seeds increased seedling emergence. Both species showed, however, different abilities to emerge and survive in different soil microsites. Microsites of bare soil were more favourable for seedling emergence and survival of L. divaricata than those beneath vegetation patches, independent of their water status. This ability of L. divaricata can not be explained on the basis of increased water or N availability, but probably because of lower salt content of bare soil. The addition of inorganic N reduced the survival of L. divaricata in both microsites but increased individual plant performance. The emergence and survival of S. tenuis was not different in both types of soil microsites but the addition of inorganic N increased seedling emergence and plant biomass. According to these results, emergence and plant performance of S. tenuis may be promoted during humid years by increased concentration of inorganic N. Since N mineralization occurs at a higher rate in soil microsites beneath vegetation patches than in those of bare soil, higher plant performance and probably establishment of S. tenuis is to be expected. These results are consistent with an existing conceptual model of plant dynamics under various grazing intensities in the Patagonian Monte shrubland based on previous field observations.     

The effects of gap disturbance on the seedling emergence,survival and growth of two different native species in Inner Mongolia

A field study was conducted to investigate the effects of gap disturbance on the seedling establishment process of two native species. Seeds of Agropyron cristatum and Stipa krylovii were reseeded to artificially created gaps in a degraded steppe in North China. There were seven treatments: shoot gaps and root gaps (10 cm, 20 cm and 40 cm in diameters), no gaps (control). Shoot gaps were formed by removing above ground vegetation and below ground biomass without restricting the re-growth of neighbor roots back into the gap. The root gaps were accomplished by using polyvinyl chloride pipes sunk in the soil of shoot gaps to exclude neighboring roots. Seedling emergence, survival and growth performance after 90 days of growing were recorded for both species. Gap significantly increased soil moisture, especially for root gaps. Emergence increased significantly for both species as gap size increased. Seedling emergence and survivorship of both species were greater in gaps than in controls. However, the gap size showed a significantly negative effect on Agropyron cristatum's survivorship. Growth performance of Agropyron cristatum and Stipa krylovii differ in their response to gap disturbance. Gap had positive effects on seedling growth (including seedling height, dry weight, and numbers of tillers and leaves) of Stipa krylovii, but had negative effects on seedling growth of Agropyron cristatum. The two species have significantly different responses to gap disturbance. All results suggest that Stipa krylovii is a gap-enhanced species, and Agropyron cristatum is not. Predation by insects may be one of the key reasons to explain the stand dominance in this grassland.     

Natural Establishment of Specialist Plant Species after Topsoil Removal and Soil Perturbation in Degraded Calcareous Sandy Grassland

Specialist plant species in calcareous sandy grasslands are threatened by acidification and high nutrient levels in the topsoil. We investigated whether topsoil removal and soil perturbation in degraded sandy grasslands could lead to establishment of specialist species belonging to the threatened xeric sand calcareous grassland habitat. Restoration actions performed in 2006 resulted in increased soil pH and reduced nitrogen availability. We found early colonisztion of the perennial key species Koeleria glauca after both deep perturbation and topsoil removal, and high seedling establishment in topsoil removal plots 5 and 6 years following the restoration treatment (2011–2012). After topsoil removal, overall vegetation composition in 2012 had developed toward the undegraded community, with target species accounting for 20% of the community after topsoil removal, compared to 30% in the undegraded vegetation, and less than 1% in untreated controls. Deep perturbation led to 7% target species, while there were almost no effects of shallow perturbation 6 years following treatment. These results demonstrate that topsoil removal can promote colonization of target species of calcareous sandy grassland and highlights the importance of considering the regeneration niche for target species when implementing restoration measures .     

Rooting depth,water availability,and vegetation cover along an aridity gradient in Patagonia

Above-and belowground biomass distribution, isotopic composition of soil and xylem water, and carbon isotope ratios were studied along an aridity gradient in Patagonia (44–45°S). Sites, ranging from those with Nothofagus forest with high annual rainfall (770 mm) to Nothofagus scrub (520 mm), Festuca (290 mm) and Stipa (160 mm) grasslands and into desert vegetation (125 mm), were chosen to test whether rooting depth compensates for low rainfall. Along this gradient, both mean above-and belowground biomass and leaf area index decreased, but average carbon isotope ratios of sun leaves remained constant (at-27), indicating no major differences in the ratio of assimilation to stomatal conductance at the time of leaf growth. The depth of the soil horizon that contained 90% of the root biomass was similar for forests and grasslands (about 0.80–0.50 m), but was shallower in the desert (0.30 m). In all habitats, roots reached water-saturated soils or ground water at 2–3 m depth. The depth profile of oxygen and hydrogen isotope ratios of soil water corresponded inversely to volumetric soil water contents and showed distinct patterns throughout the soil profile due to evaporation, water uptake and rainfall events of the past year. The isotope ratios of soil water indicated that high soil moisture at 2–3 m soil depth had originated from rainy periods earlier in the season or even from past rainy seasons. Hydrogen and oxygen isotope ratios of xylem water revealed that all plants used water from recent rain events in the topsoil and not from water-saturated soils at greater depth. However, this study cannot explain the vegetation zonation along the transect on the basis of water supply to the existing plant cover. Although water was accessible to roots in deeper soil layers in all habitats, as demonstrated by high soil moisture, earlier rain events were not fully utilized by the current plant cover during summer drought. The role of seedling establishment in determining species composition and vegetation type, and the indirect effect of seedling establishment on the use of water by fully developed plant cover, are discussed in relation to climate change and vegetation modelling.     

Effects of adult neighbour and gap size on seedling emergence and early growth of <Emphasis Type="Italic">Bromus inermis</Emphasis> Leyss

A field study was conducted to determine the effects of neighbour root exclusion and gap size on the seedling emergence and early growth of Bromus inermis. Seeds of B. inermis were added to artificially created gaps in an improved shortgrass steppe in northern China. Neighbour root exclusion was accomplished using PVC tubes sunk in the soil of gaps. Emergence and survival of seedlings were greater in all gaps than in the control (0-cm diameter), but better growth performance (height of seedling, leaves, tillers and dry weight per seedling) was observed only in large gaps (20- and 40-cm diameter) with neighbour root present and gaps without neighbour root presence. Seedling growth performance was improved by reducing root and shoot competition. Neighbour root exclusion provided a favourable environment for seedling establishment. Differences between gaps in light levels and topsoil temperature can explain the patterns of germination. These results confirm that B. inermis is a gap-enhanced species. Our study strongly suggests that asymmetric competition by adult neighbour plants negatively influences the establishment of B. inermis.     

Gap formation, microsite variation and the conifer seedling occurrence in a subalpine old-growth forest, central Japan

To evaluate the effects of canopy gaps and forest floor microsites (soil, fallen logs, root-mounds, buttresses and stumps) on regeneration of subalpine forests, the gap regeneration and seedling occurrence of conifers (Abies mariesii, Abies veitchii, Picea jezoensis var. hondoensis and Tsuga diversifolia) were studied in two stands of a subalpine old-growth forest, central Japan. The percentage of gap area to total surveyed area was 11.2–11.3% in the stands. Gap regeneration was not common for P. jezoensis var. hondoensis and T. diversifolia. In contrast, gap regeneration by advanced regeneration was relatively common for Abies. Seedling occurrence of P. jezoensis var. hondoensis and T. diversifolia was restricted on elevated surfaces such as stumps and root-mounds, while Abies seedlings could occur on soil as well as on elevated surfaces. Rotten stumps were the most favorable microsites for conifer seedling occurrence, which covered small area in the forest floor. Although canopy gaps were not always favorable for seedling occurrence, all conifer seedlings were larger under canopy gaps than under closed canopy. Canopy gaps and forest floor microsites clearly affected seedling occurrence and growth of conifers. This suggests that regeneration of conifers is related to the difference of growth advantage under canopy gaps and favorable microsites for seedling occurrence.     

Ungulate and topographic control of nitrogen: phosphorus stoichiometry in a temperate grassland; soils, plants and mineralization rates

Although the link between the nitrogen (N): phosphorus (P) stoichiometry of biota and availability has received considerable attention in aquatic systems, there has been relatively little effort to compare the elemental composition of biota and supply in terrestrial habitats. In this study, I explored the effects of a prominent topo-edaphic gradient, from dry hilltop to wet slope-base, and native ungulates on N and P of soils, plants, and rates of in situ net mineralization in grasslands of Yellowstone National Park. Nitrogen and P measurements were made May–September, 2000, in paired, grazed and 38–42 year fenced, ungrazed grassland at five topographically variable sites. Similar to findings from other grassland ecosystems, several site factors associated with organic activity, including soil moisture, C, and plant biomass, covaried with soil N concentration and/or net N mineralization. Soil P concentration and net P mineralization, however, were unrelated to those factors. Instead, net P mineralization was negatively related to soil pH, which is known to control the form of inorganic P and its availability, and soil P was uncorrelated with any soil or plant variable measured in the study. Because of being influenced by different soil properties, N and P net mineralization were unrelated among grasslands. Furthermore, supply and plant N:P ratios were uncorrelated in this grassland system. Based on critical N:P ratios reflecting nutritional limitation of plants, Yellowstone grassland vegetation ranged from being N limited to N-P co-limited. Grazers increased N-P co-limitation by enhancing plant N concentrations and the soil pH gradient across grassland sites regulated plant nutritional limitation by affecting plant-available P. These findings showed how ungulates and a landscape factor, i.e. soil pH, determined plant nutrient status among YNP grasslands differently by influencing plant N concentration versus plant P concentration, respectively.     

Effects of position, understorey vegetation and coarse woody debris on tree regeneration in two environmentally contrasting forests of north-western Patagonia: a manipulative approach

Aim To investigate the differential effects of position within gaps, coarse woody debris and understorey cover on tree seedling survival in canopy gaps in two old‐growth Nothofagus pumilio (Poepp. & Endl.) Krasser forests and the response of this species to gaps in two forests located at opposite extremes of a steep rainfall gradient. Location Nahuel Huapi National Park, at 41° S in north‐western Patagonia, Argentina. Methods In both study sites, seedlings were transplanted to experimental plots in gaps in three different positions, with two types of substrate (coarse woody debris or forest floor), and with and without removal of understorey vegetation. Survival of seedlings was monitored during two growing seasons. Soil moisture and direct solar radiation were measured once in mid‐summer. Seedling aerial biomass was estimated at the end of the experiment. Results Mid‐summer soil water potential was lowest in the centre of gaps, in plots where the understorey had been removed, and highest at the northern edges of gaps. Direct incoming radiation was highest in gap centres and southern edges, and lowest at northern edges. Seedling mortality was highest in gap centres, in both sites. Coarse woody debris had a positive effect on seedling survival during summer in the mesic forest and during winter in the xeric forest. The removal of understorey cover had negative effects in gap centres during summer. Seedling final aerial biomass was positively affected by understorey removal and by soil substrate in both sites. In the dry forest gaps, seedling growth was highest in northern edges, whereas it was highest in gap centres in the mesic forest. Overall growth was positively related to survival in the xeric forest, and negatively related in the mesic forest. Main conclusions Survival and growth were facilitated by the shade of gap‐surrounding trees only in the xeric forest. Understorey vegetation of both forests facilitated seedling survival in exposed microsites but competed with seedling growth. Nurse logs were an important substrate for seedling establishment in both forests; however, causes of this pattern differed between forests. Water availability positively controls seedling survival and growth in the xeric forest while in the mesic forest, survival and growth are differentially controlled by water and light availability, respectively. These two contrasting old‐growth forests, separated by a relatively short distance along a steep rainfall gradient, had different yet unexpected microenvironmental controls on N. pumilio seedling survival and growth. These results underscore the importance of defining microscale limiting factors of tree recruitment in the context of large‐scale spatial variation in resources.     

Effects of soil mulches and conditioners on seedling emergence and survival of Astragalus nigricans Barneby in an arid steppe rangeland

Soil mulches and conditioners have been shown to improve soil moisture conservation, infiltration, and seed germination and survival, but their interactive effects with sporadic rainfall and the existing vegetation have rarely been considered. In an experimental field study, we assessed the effects of soil additives (sawdust and hydrogel) and mulches (river sand and plant debris) on seedling emergence and survival of Astragalus nigricans Barneby, in the rangelands of Mashhad, northeast Iran. We also assessed any effects on soil moisture and temperature several days after rain in July 2017 and May 2018 and weed composition, density, and diversity. The most successful treatment was hydrogel, associated with earlier seedling emergence for A. nigricans, greater seedling survival, and biomass production. Sawdust and sand treatments were useful for root proliferation and seedling emergence in the spring of the first season, but they led to high seedling mortality under drought. Debris of Artemisia khorasanica shoots was the most efficient and consistent treatment for soil moisture conservation and temperature stability in both years, but its possible allelopathic effects led to high seedling mortality and a long delay (41 days) on seedling emergence. Plant debris also negatively affected the density, richness, and diversity of nontarget plant species. Despite differences among different rainfall events, mulch treatments have an important role in regenerating degraded rangelands.     

The role of a mound-building ecosystem engineer for a grassland butterfly

Both land use intensification and abandonment within grasslands lead to a homogenisation of vegetation structure. Therefore, specially structured microsites such as vegetation gaps with bare ground play an important role for species conservation within grasslands. Vegetation gaps are crucial for the establishment of low-competitive plant species and offer special microclimatic conditions essential for the development of the immature stages of many invertebrate species. The influence of small-scale soil disturbance in the form of mounds created by ecosystem engineers such as ants or moles on biodiversity is therefore of special scientific concern. The effects of mound-building species on plant species diversity have been extensively studied. However, knowledge on the significance of these species for the conservation of other animals is rare. In this study we analyse the importance of mounds created by the European mole (Talpa europaea) as an oviposition habitat for the small copper (Lycaena phlaeas) within Central European mesotrophic grasslands. Our study showed that host plants occurring at molehills were preferred for oviposition. Oviposition sites were characterised by an open vegetation structure with a high proportion of bare ground (with a mean coverage of about 50 %), a low cover of herbs and low-growing vegetation (mean height: 4.5 cm). Our study clearly illustrates the importance of small-scale soil disturbance for immature stages of L. phlaeas and the conservation of this species within mesotrophic grasslands. Mound-building ecosystem engineers, such as T. europaea, act as important substitutes for missing dynamics within mesotrophic grasslands by diversifying vegetation structure and creating small patches of bare soil.     

云南南涧干热退化山地人工植被恢复初期生物量及土壤环境动态

 研究了云南南涧干热河谷退化山地人工恢复植被初期阶段(3～5年)主要植物群落的地上生物量和恢复植被后土壤水分及养分的相关动态。结果表明,几种外来植物的适应性强,早期生长迅速并能很快郁闭。人工群落生物量都高于当地次生的坡柳灌草丛。引进种的地上生物量和总平均生长量分别是坡柳的3～16倍和5～20倍,其生长速度也高于乡土树种云南松。雨季人工植被下土壤含水量比光坡地增加约100％,表土层则增加2倍以上。但在旱季,林地土壤含水量与光坡地相近甚至低于光坡地。植被的恢复使土壤养分朝着良性循环转变。土壤有机质、速效钾含量提高,全氮含量稍有降低但不明显,速效磷含量降低,pH值有所下降。这些变化主要发生在土壤表层,人工植被及其土壤生态系统的恢复仍处于不稳定状态。     

Controls of fine root dynamics across a gradient of gap sizes in a pine woodland

Controls of fine dynamics were investigated in a Pinus palustris Mill. (longleaf pine) woodland subjected to two understory vegetation treatments (control versus removed) and four overstory treatments (no gap control, and canopy gaps of three sizes with constant total gap area per stand). Fine root (<2 mm diameter) dynamics were measured over 11 months using ingrowth cores (all treatments) and minirhizotrons (understory removed in no gap control and large gap treatments only). At the fine (microsite) spatial scale, pine and non-pine root mass production responded negatively to each other (P=0.033). Each life form was significantly (P< or =0.028) related to nearby overstory density, and pine root production compensated for reductions in non-pine roots if understory vegetation was removed. Soil moisture and NO(3) mineralization rate were negatively related to pine root mass production (ingrowth cores; P<0.001 and P=0.052) and positively related to pine root length production, mortality and turnover (minirhizotrons; P from <0.001 to 0.078). Temperature variance was negatively related to pine root lifespan P<0.001) and positively related to pine root turnover (P=0.003). At the ecosystem scale, pattern of overstory disturbance (gap size and number) had no significant effect on non-pine, pine, or total root production. However, the presence of gaps (versus the no-gap control) increased non-pine root mass production (ANOVA, P=0.055) in natural understory conditions, and reduced pine root mass production (P=0.035) where the understory was removed. Ecosystem-wide pine root length production, mortality and turnover were positively related to weekly soil temperature (P< or =0.02). In natural systems, fine root dynamics are highly variable and strongly affected by biotic factors. Roots quickly close belowground gaps because one life form (pine or non-pine) compensates for the absence of the other. When understory vegetation is removed, however, pine roots respond to the local abiotic environment, particularly moisture and NO(3).     

Effects of fire history and N and P fertilization on seedling biomass,Specific Leaf Area,and root:shoot ratios in a South African savannah

Fire exerts clear direct effects on savannah vegetation dynamics, but the indirect effects of fire, for example via changes in soil fertility, are less clear. In fire-dominated nutrient-poor savannahs, there is little evidence that fire affects plant-available nutrients, but plant performance on soils with contrasting fire histories has not been investigated. A bioassay experiment was conducted in Kruger National Park, South Africa, to test for effects of long-term fire manipulation on the ability of soils to influence tree growth. Combretum hereroense, a common savannah species, was used as a phytometer species in an experiment that combined fire history with N and P fertilization treatments. The results suggested no effect of fire history on a number of seedling traits after seven months of growth. Root mass and shoot:root ratios responded to P addition, with seedlings exhibiting lower allocation to root tissue under elevated P, particularly in the presence of N, suggesting some N and P co-limitation. Overall, it is concluded that there is little evidence that fire degrades or alters soil chemistry in a way that is likely to influence vegetation structure and dynamics in nutrient-poor savannah ecosystems.     

Smoke and heat: influence on seedling emergence from the germinable soil seed bank of mesic grassland in South Africa

We examined if germination and seedling emergence of species from the soil seed bank of mesic grassland in South Africa differed in their response to smoke or heat treatments alone or combined. Soil seed bank samples taken from 0 to 5 cm depth of the topsoil were treated with smoke-water solution, heat and heat + smoke-water combined and subsequent emergence of seedlings monitored over 90 days. In total, 790 individuals from 11 different plant families representing 37 graminoid (Poaceae) and non-graminoid species of flowering plants were identified. The most abundant plant families that emerged were Poaceae followed by Asteraceae. Grasses contributed 18% of the germinable seed bank, while non-grass (forbs and trees) species contributed >80%. The most abundant grass species that emerged was Themeda triandra and the most common forb species was Centella asiatica. Compared to the control, smoke-water (SW) and/or smoke-water + heat (H + SW) treatment resulted in a 1.6-fold increase in mean number of seedling emergence. SW and H + SW treatment of soil seed bank also resulted in fourfold to fivefold greater biomass production. These results suggest that emergence of some smoke-responsive perennial grasses (e.g. Themeda triandra) from the soil seed bank can be enhanced using smoke techniques. Moreover, plant-derived smoke could potentially have a significant role in the restoration of degraded grasslands in South Africa and elsewhere.     

Experimental manipulation of water levels in two French riverine grassland soils

In this experimental study, we simulated the effects of different river flooding regimes on soil nutrient availability, decomposition and plant production in floodplain grasslands. This was done to investigate the influences of soil water contents on nutrient cycling. Water levels were manipulated in mesocosms with intact soil turfs from two French floodplain grasslands. Three water levels were established: a `wet' (water level at the soil surface), an `intermediate' (water level at –20 cm) and a `dry' treatment (water level at –120 cm). With increasing soil moisture, soil pH became more neutral, while redox-potential and oxygen concentration decreased. The `dry' treatment showed much lower values for process rates in soil and vegetation than the `intermediate' and `wet' treatments. Regressions showed that soil C-evolution and N-mineralization were positively related to soil moisture content. Not all mineralized N was available for plant uptake in the wet treatment, as a considerable part was denitrified here. Denitrification was especially high as soil water contents increased to levels above field capacity, where redox-potentials sharply dropped. Further, soil P availability was higher under wet conditions. In the `dry' treatment, soil water content was close to the wilting point and plant production was low. In the `intermediate' treatment, plant production was most likely limited by nitrogen. The `wet' treatment did not result in a further increase in plant production. Dam construction and river bed degradation can result in lower river levels and summer drought on floodplains. This experimental study suggests that summer drought on floodplain soils reduces decomposition of soil organic matter, nutrient availability, denitrification, plant production and nutrient uptake. This can affect the capacity of floodplains to remove or retain nutrients from river water in a negative way.     

Antecedent Conditions Influence Soil Respiration Differences in Shrub and Grass Patches

Quantifying the response of soil respiration to past environmental conditions is critical for predicting how future climate and vegetation change will impact ecosystem carbon balance. Increased shrub dominance in semiarid grasslands has potentially large effects on soil carbon cycling. The goal of this study was to characterize the effect of antecedent moisture and temperature conditions on soil respiration in a grassland now dominated by shrubs. Continuous measurements of soil respiration, soil temperature, and soil moisture were made over the entire summer of 2005 within distinct vegetation microsites in this shrubland community—under grasses, shrubs, and in open spaces. We analyzed these data within a Bayesian framework that allowed us to evaluate the time-scale over which antecedent conditions influence soil respiration. The addition of antecedent conditions explained an additional 16% of the variation in soil respiration. High soil moisture during the preceding month increased respiration rates in both the grass and shrub microsites. However, the time period over which antecedent soil moisture influenced the temperature sensitivity of soil respiration was shorter in the shrub compared to the grass microsites (1 vs. 2 weeks, respectively). The depth of moisture was important; for example, for respiration under shrubs, near-surface moisture was more influential on the day of the respiration measurement but subsurface moisture was more influential on the antecedent time scale. Although more mechanistic studies are required, this study is the first to reveal that shrub encroachment changes the time scales over which soil moisture and temperature affect soil respiration.     

Litter accumulation alters the abiotic environment and drives community successional changes in two fenced grasslands in Inner Mongolia

Fencing is an effective and practical method for restoring degraded grasslands in northern China. However, little is known about the role of excess litter accumulation due to long‐term fencing in regulating abiotic environment and driving changes in community structure and function. We conducted a three‐year field experiment in two fenced grasslands in Inner Mongolia, and monitored light quantity, soil temperature, and soil moisture continuously, and determined community height, community aboveground net primary productivity (ANPP), and the relative dominance of different plant functional groups. Litter accumulation reduced light quantity and soil temperature but increased soil moisture. The regulating effects of litter accumulation on soil temperature and soil moisture fluctuated temporally and gradually weakened over the growing season. Litter accumulation also altered community vertical structure and function by increasing community height and ANPP. The increase in soil moisture increased the relative dominance of rhizome grasses but suppressed bunch grasses, thereby shifting bunch grass grasslands to rhizome grass grasslands. Our findings provide a potential mechanism for community succession in the context of litter accumulation in fenced grasslands and indicate that the vegetation and ecosystem services of degraded grasslands are improved after appropriate fencing.     

Native remnants can be sources of plants and topsoil to restore dry and wet cerrado grasslands

Neotropical grasslands have undergone intensive degradation by land conversion or biological invasion, but their restoration is still challenging. Here, we integrated two approaches to (1) assess the resilience of pristine dry and wet cerrado grasslands after removal of plants and topsoil and (2) evaluate the effectiveness of different treatments based on the material extracted from pristine grasslands to restore degraded dry and wet grasslands after pine invasion. We used old‐growth cerrado grasslands in southeastern Brazil as donor ecosystems and assessed their resilience after the removal of all plants and the upper 5‐cm soil layer. To restore both wet and dry grasslands, we tested topsoil translocation, plant transplantation, direct seeding, topsoil translocation + direct seeding, and needle layer removal. Both wet and dry grasslands were resilient to plants and topsoil removal, as evidenced by their fast recovery. The major mechanisms promoting resilience were seed germination in the wet grasslands and resprouting from underground organs in the dry grasslands. Transplantation was the most successful treatment to restore vegetation cover, species richness, and composition in both wet and dry grasslands, especially for herbaceous species. Restoration of the herbaceous layer of cerrado grasslands can be successful using natural ecosystems as donor sites without impairing their resilience in the studied scale. Improving the resilience of degraded dry and wet cerrado grasslands depends on reestablishing the condition to seed germination in the wet grasslands and reintroducing species with the ability to resprout after disturbance in the dry grasslands, attributes that explained the quick recovery of the donor ecosystems.     

东灵山地区辽东栎幼苗的建立和空间分布

研究树木实生苗的建立对森林生态系统的保育和恢复具有重要意义,在北京东灵山地区调查了辽东栎(Quercus liaotungensis)实生和萌生幼苗在几种典型的植被类型中的空间分布以及辽东栎一年生实生幼苗在1个林窗梯度上的建立。选择几种典型的植被类型,研究辽东栎实生幼苗和萌生幼苗在森林中的空间分布。结果显示,在不同植被类型中辽东栎实生和萌生幼苗的密度存在空间差异,实生苗密度随幼苗年龄增大逐渐降低,种群的更新主要依靠萌生苗完成。在1个落叶阔叶林中选择1个林窗,在不同梯度(即林窗中间、林窗和树冠连接处,以及树冠下)上,播种辽东栎坚果,第二年秋季调查实生幼苗的2个生长指标和出苗率。结果显示,林窗对一年生实生幼苗的生长高度有影响。幼苗高度在林窗中比在树冠下大;林窗对辽东栎幼苗最长叶片长度和幼苗的出苗率没有影响。说明辽东栎实生幼苗的良好生长需要阳光比较充足的生境条件。本项研究结果建议,对辽东栎种群的更新,应该适当择伐一些较大个体,使森林形成一些林窗或林中空地,以利于辽东栎实生幼苗的建立,这样才能使辽东栎种群通过实生苗进行更好的自然更新。