Root:shoot ratio in developing seedlings: How seedlings change their allocation in response to seed mass and ambient nutrient supply

Root:shoot (R:S) biomass partitioning is one of the keys to the plants' ability to compensate for limiting resources in the environment and thus to survive and succeed in competition. In adult plants, it can vary in response to many factors, such as nutrient availability in the soil or reserves in the roots from the previous season. The question remains whether, at the interspecific level, reserves in seeds can affect seedlings' R:S ratio in a similar way. Proper allocation to resource‐acquiring organs is enormously important for seedlings and is likely to determine their survival and further success. Therefore, we investigated the effect of seed mass on seedling R:S biomass partitioning and its interaction with nutrient supply in the substrate. We measured seedling biomass partitioning under two different nutrient treatments after 2, 4, 6, and 12 weeks for seventeen species differing in seed mass and covering. We used phylogenetically informed analysis to determine the independent influence of seed mass on seedling biomass partitioning. We found consistently lower R:S ratios in seedlings with higher seed mass. Expectedly, R:S was also lower with higher substrate nutrient supply, but substrate nutrient supply had a bigger effect on R:S ratio for species with higher seed mass. These findings point to the importance of seed reserves for the usage of soil resources. Generally, R:S ratio decreased over time and, similarly to the effect of substrate nutrients, R:S ratio decreased faster for large‐seeded species. We show that the seed mass determines the allocation patterns into new resource‐acquiring organs during seedling development. Large‐seeded species are more flexible in soil nutrient use. It is likely that faster development of shoots provides large‐seeded species with the key advantage in asymmetric above‐ground competition, and that this could constitute one of the selective factors for optimum seed mass.     

Seedling dynamics at elevation limits: Complex interactions beyond seed and microsite limitations

? Premise of the study: Limited availability of seeds and microsites are important constraints for seedling emergence and survival. However, little is known about population-level feedbacks between seed and microsite limitation and how these relationships vary in contrasting conditions. Focusing on Armeria caespitosa, a high-mountain endemic, we asked whether seedling establishment was simultaneously limited by seed and microsite availability, whether the balance between seed and microsite limitations varied with contrasting environments, and whether seed and microsite limitations interacted with each other. ? Methods: We studied seedling emergence and survival at the edges of the elevation range of A. caespitosa in central Spain over 4 years. We used mixed linear models and structural equation modeling. ? Key results: Our results showed that A. caespitosa recruits similar numbers of new seedlings per plot in contrasting environments. Seedling emergence and survival in A. caespitosa were both limited by seed and microsite availability. Habitat suitability (the surrogate of microsite limitation) varied between populations and indirectly affected fertility (the surrogate of seed limitation). ? Conclusions: Seedling emergence and survival are both seed and microsite limited, there are interactions between seed and microsite limitations, and both factors, which control seedling establishment, and their interconnections, vary among local populations.     

Multivariate path analysis of the relationships between seedling regeneration and environmental factors beneath a dwarf bamboo understory

Seedling emergence and establishment are fragile processes that determine the direction and structure of forest succession and regeneration. However, seedling emergence and establishment are easily affected by biotic and abiotic (environmental) factors. A dense and expanding understory of dwarf bamboo is one such important factor that can seriously hinder the seedling regeneration. We conducted a field experiment to investigate the emergence and establishment of canopy tree seedlings under artificially controlled densities of dwarf bamboo. We found that understory dwarf bamboo obstructed seedling emergence but reduced the death of seedlings. Although understory dwarf bamboo reduced the median retention time of seedlings, dense bamboo increased the mean survival time of seedlings. Our results suggest that understory dwarf bamboo has multiple selectivities for tree seedling emergence and establishment: high‐density dwarf bamboo was beneficial to evergreen species but lower‐density of bamboo was conducive to the survival of deciduous species, it means the dwarf bamboo potentially alters successional trajectories of forest communities. Path analysis revealed that the most important factors affecting tree seedling emergence and death were the abundance of seeds in the seed bank and the density of emerged seedlings, and that the soil temperature promoted seedling emergence but increased seedling death, the thickness of litter limited seedling emergence, and the leaf area index of the bamboo canopy limited seedling death. The present study suggests that dwarf bamboo can directly alter the microenvironment, significantly reducing light levels and soil temperature but increasing the thickness of litter and soil humus, thereby indirectly impacting the regeneration of tree seedlings. Our results indicate that various factors affected seedling emergence, and there were complex indirect relationships among these factors. In general, biological factors had a stronger influence on tree seedling regeneration than environmental factors.     

Restoration of Araucaria Forest: The Role of Perches, Pioneer Vegetation, and Soil Fertility

The Araucaria forest is Brazil's highly threatened subtropical forest ecosystem that has been disappearing in recent decades. Restoration programs involving this forest type are scarce, and there is a lack of scientific information on how ecological processes such as competition, facilitation, and seed dispersal influence natural forest restoration. This work aims to investigate how use of perches to attract seed dispersers and the influence of pioneer vegetation and soil fertilization could affect the colonization of woody species in a degraded area. An experiment was conducted in an abandoned field where the natural establishment of seeds and seedlings of woody species was monitored under factorial combinations of the following treatments: (1) pioneer vegetation (presence and absence); (2) soil fertility (addition of NPK and control); and (3) perches (presence and absence). Seed and seedling abundance, seed and seedling species richness, and seedling mortality were recorded monthly during 12 months. Seed abundance and species richness were significantly greater in places with perches than in control plots. These results were consistent over the year and more pronounced when the surrounding forest produced a higher amount of fruit. Species richness and abundance of seedlings were significantly greater in places with perches than in control plots, and in places with vegetation than without. Soil fertility did not influence seedling establishment. Facilitation and seed dispersal are important factors affecting the colonization of woody species in this subtropical area. Nutrient availability neither regulates the facilitation process nor influences species replacement during the early stages of Araucaria forest succession.     

Seed bed treatment effects on vegetation and seedling establishment in a New Zealand pasture one year after seeding with native woody species

Summary Efforts to re‐establish indigenous forests in pastoral New Zealand have increased as the value of native biodiversity has been realized. Direct seeding of woody species is preferable to transplanting, as labour and material costs are less. However, the success rate of direct seeding in pasture has been variable due to intense competition from adventive species. We initiated an experiment in pasture plots adjacent to a forest fragment where seed bed treatments (increasing in degree of disturbance from herbicide application to turf removal and topsoil removal) in combination with mulch treatments (wood chip shavings with and without forest floor organic material) were seeded with a mixture of New Zealand lowland forest species. The objective of the study was to determine if early successional plant communities, and ultimately seedling establishment, differed as a result of seed bed preparation after 1 year. Coprosma robusta (Karamu) and Kunzea ericoides (Kanuka) seedlings established on plots in significant numbers: both species were most abundant on topsoil‐removed plots where bare substrate was greatest and plant cover least. Both seed bed treatments and mulching treatments led to measurable differences in overall composition of early successional plant communities. However, absence of plant cover and low soil fertility (both associated with the topsoil‐removed treatment) were the most important factors in seedling success.     

Effects of vegetation canopy and climate on seedling establishment in Mediterranean shrubland

Abstract. Question: Does the influence of plant canopy on seedling establishment interact with climate conditions, and particularly, do intensified drought conditions, enhance a positive effect of the vegetation canopy on seedlings in Mediterranean‐type ecosystems. Location: Mediterranean shrubland near Barcelona, Spain at 210 m a.s.l. Methods: Over the course of four years we recorded seedling emergence and survival in open areas and below vegetation under control, drier and warmer experimental climatic conditions. Results: Seedling emergence is more sensitive to climate conditions than later stages of growth. When considering the whole set of species, the total number of established seedlings at the end of the experiment was lower in the drought and warming stands than in control ones, and vegetation canopy increased the number of these seedlings in the drought stands. Drought reduced seedling emergence but not warming, while the interaction between climate treatments and vegetation canopy was not significant. Seedling survival was lower in the warming treatment than in the control. Under drought conditions, vegetation canopy increased seedling emergence of the dominant Globularia alypum. In control stands, vegetation canopy reduced their survival. Vegetation canopy increased the survival of the dominant Erica multiflora in warming stands, and it reduced the survival of G alypum in drought stands. No significant effects of drought and warming were observed in the seed rain of these two species. Conclusions: The balance of the facilitation‐competition interactions between vegetation canopy and seedling establishment in Mediterranean‐type ecosystems determined by water availability, and drought conditions enhance the positive effect of vegetation canopy. This interaction is species‐specific and shows important between‐year variability.     

Seed mass and seedling establishment after fire in Ku‐ring‐gai Chase National Park,Sydney, Australia

Abstract Relationships between seed mass and several aspects of plant regeneration ecology were investigated in a post‐fire environment in Ku‐ring‐gai Chase National Park near Sydney, Australia. We found a significant positive relationship between seed mass and time to seedling emergence (P < 0.001) and a strong negative relationship between seed mass and time between emergence and production of the first true leaf (P < 0.001). Surprisingly, we found no relationship between seed mass and seedling establishment (P = 0.21). It seems most likely that this lack of relationship is a result of the many stochastic factors affecting seedling establishment during any given recruitment episode at any given site. A cause of mortality was assigned to 56% of the 781 seedlings that died during the present study. There was no relationship between cause of death and seed mass (P = 0.28). Of the seedlings for which the cause of death was known, 57% were killed by herbivory and 21% were killed by drought. Seedling–seedling competition affected only one species.     

Shifts in seed size across experimental nitrogen enrichment and plant density gradients

We tested the hypotheses that increased soil resource availability selects for larger seeded plants by: (1) increasing community seed density and seedling competition, (2) increasing light competition, which favours larger seeded species if their additional seed resources are allocated to shoots. We also tested the hypothesis that plants respond to increased nutrient availability by producing larger seeds. In a controlled environment experiment, we grew monocultures of five species of co-occurring annual plant species at two N addition rates and measured seed size and the number of seeds produced. In a second experiment, we sowed seed of the five species together, manipulated nitrogen (N) addition rate and community seed density and measured species performance. In the first experiment, elevated N addition increased seed size, but only in larger seeded species. In the second experiment, high N addition increased community seed production. However, contrary to our hypothesis small seeded species were selected under high seed density, possibly because they germinated and grew more rapidly thus enabling them to pre-empt limiting resources. Larger seeded species were favoured by high N addition, as hypothesised. However, our data suggest that this was due to their seed reserves boosting survival below the denser canopies of fertile conditions rather than via competitive advantages. Our results point to a largely overlooked role of recruitment in determining community response to fertilisation. Although our results may not generalise to all plant communities they suggest that seed traits play a role in community response to both the direct effect of N addition and the stimulation of seed density caused by increased productivity. These results are also consistent with the view that the advantage of large seed size is not a competitive one, but greater survival in the face of environmental hazards.     

Effects of nutrient loading and extreme rainfall events on coastal tallgrass prairies: invasion intensity, vegetation responses, and carbon and nitrogen distribution

Soil fertility and precipitation are major factors regulating transitions from grasslands to forests. Biotic regulation may influence the effects of these abiotic drivers. In this study, we examined the effects of extreme rainfall events, anthropogenic nutrient loading and insect herbivory on the ability of Chinese tallow tree ( Sapium sebiferum ) to invade coastal prairie to determine how these factors may influence woody invasion of a grassland. We manipulated soil fertility (NPK addition) and simulated variation in frequency of extreme rainfall events in a three growing season, full factorial field experiment. Adding water to or pumping water out of plots simulated increased and decreased rainfall frequencies. We added Sapium seeds and seedlings to each plot and manipulated insect herbivory on transplanted Sapium seedlings with insecticide. We measured soil moisture, Sapium performance, vegetation mass, and carbon and nitrogen in vegetation and soils (0–10 cm deep, 10–20 cm deep). Fertilization increased Sapium invasion intensity by increasing seedling survival, height growth and biomass. Insect damage was low and insect suppression had little effect in all conditions. Recruitment of Sapium from seed was very low and independent of treatments. Vegetation mass was increased by fertilization in both rainfall treatments but not in the ambient moisture treatment. The amount of carbon and nitrogen in plants was increased by fertilization, especially in modified moisture plots. Soil carbon and nitrogen were independent of all treatments. These results suggest that coastal tallgrass prairies are more likely to be impacted by nutrient loading, in terms of invasion severity and nutrient cycling, than by changes in the frequency of extreme rainfall events.     

Nutrient stoichiometry and land use rather than species richness determine plant functional diversity

Plant functional traits reflect individual and community ecological strategies. They allow the detection of directional changes in community dynamics and ecosystemic processes, being an additional tool to assess biodiversity than species richness. Analysis of functional patterns in plant communities provides mechanistic insight into biodiversity alterations due to anthropogenic activity. Although studies have consi‐dered of either anthropogenic management or nutrient availability on functional traits in temperate grasslands, studies combining effects of both drivers are scarce. Here, we assessed the impacts of management intensity (fertilization, mowing, grazing), nutrient stoichiometry (C, N, P, K), and vegetation composition on community‐weighted means (CWMs) and functional diversity (Rao's Q) from seven plant traits in 150 grasslands in three regions in Germany, using data of 6 years. Land use and nutrient stoichiometry accounted for larger proportions of model variance of CWM and Rao's Q than species richness and productivity. Grazing affected all analyzed trait groups; fertilization and mowing only impacted generative traits. Grazing was clearly associated with nutrient retention strategies, that is, investing in durable structures and production of fewer, less variable seed. Phenological variability was increased. Fertilization and mowing decreased seed number/mass variability, indicating competition‐related effects. Impacts of nutrient stoichiometry on trait syndromes varied. Nutrient limitation (large N:P, C:N ratios) promoted species with conservative strategies, that is, investment in durable plant structures rather than fast growth, fewer seed, and delayed flowering onset. In contrast to seed mass, leaf‐economics variability was reduced under P shortage. Species diversity was positively associated with the variability of generative traits. Synthesis. Here, land use, nutrient availability, species richness, and plant functional strategies have been shown to interact complexly, driving community composition, and vegetation responses to management intensity. We suggest that deeper understanding of underlying mechanisms shaping community assembly and biodiversity will require analyzing all these parameters.     

Species richness and evenness respond in a different manner to propagule density in developing prairie microcosm communities

Diversity has two basic components: richness, or number of species in a given area, and evenness, or how relative abundance or biomass is distributed among species. Previously, we found that richness and evenness can be negatively related across plant communities and that evenness can account for more variation in Shannon’s diversity index (H′) than richness, which suggests that relationships among diversity components can be complex. Non-positive relationships between evenness and richness could arise due to the effects of migration rate or local species interactions, and relationships could vary depending on how these two processes structure local communities. Here we test whether diversity components are equally or differentially affected over time by changes in seed density (and associated effects on established plant density and competition) in greenhouse communities during the very early stages of community establishment. In our greenhouse experiment, we seeded prairie microcosms filled with bare field soil at three densities with draws from a mix of 22 grass and forb species to test if increased competition intensity or seedling density would affect the relationships among diversity components during early community establishment. Increased seed density treatments caused diversity components to respond in a different manner and to have different relationships with time. Richness increased linearly with seed density early in the experiment when seedling emergence was high, but was unrelated to density later in the experiment. Evenness decreased log-linearly with seed densities on all sampling dates due to a greater dominance by Rudbeckia hirta with higher densities. Early in the experiment, diversity indices weakly reflected differences in richness, but later, after the competitive effects of Rudbeckia hirta became more intense, diversity indices more strongly reflected differences in evenness. This suggests that species evenness and diversity indices do not always positively covary with richness. Based on these results, we suggest that evenness and richness can be influenced by different processes, with richness being more influenced by the number of emerging seedlings and evenness more by species interactions like competition. These results suggest that both diversity components should be measured in plant diversity studies whenever it is possible.     

Protecting direct seeded grasses from herbicide application: can new extruded pellet formulations be used in restoring natural plant communities?

Restoration of native plant communities through direct seeding often experience low seedling establishment success rates, partly due to competition with invasive weed species. To improve seeding success, herbicides can be applied to control weed competition, however, this can have negative impacts on the seeded species. Activated carbon (AC) can be incorporated into newly developed seed enhancement technologies to adsorb herbicides and increase seedling tolerance. This study expands upon research completed to date, by developing new formulations of extruded pellets containing AC, aiming to provide increased protection to seeded species and increase herbicide selectivity. We tested six extruded pellet formulations, which included two pellet formula variations, and three quantities of AC, to examine the impact on emergence (without herbicide) and mortality (with herbicide) of Lolium rigidum Gaudin (annual ryegrass). Extruded pellet formulations containing a superabsorbent polymer (3%) and AC (10%) did not impede emergence (79%), in the absence of herbicide, similar to the non‐pelleted seeds (81%). This extruded pellet formulation increased seedling tolerance to Simazine (a pre‐emergent, soil applied herbicide) application, with mortality reduced from 96% in non‐pelleted seeds, and 77% in pellets containing no AC, to 22% in pellets containing AC. The results from this study demonstrate that AC extruded pelleting can be used as a restoration seeding technology by protecting seeds from the negative effects of pre‐emergent herbicide applications. Field evaluations with native seeds will mark an important step forward to ensure seed enhancement technology options, such as AC extruded pelleting, are available for restoring natural plant communities in restoration programs.     

Life History Traits of Lianas During Tropical Forest Succession

Tropical secondary forests form an important part of the landscape. Understanding functional traits of species that colonize at different points in succession can provide insight into community assembly. Although studies on functional traits during forest succession have focused on trees, lianas (woody vines) also contribute strongly to forest biomass, species richness, and dynamics. We examined life history traits of lianas in a forest chronosequence in Costa Rica to determine which traits vary consistently over succession. We conducted 0.1 ha vegetation inventories in 30 sites. To examine the establishment of young individuals, we only included small lianas (0.5–1.5 cm diameter at 1.3 m height). For each species, we identified seed size, dispersal mode, climbing mode, and whether or not the seedling is self‐supporting. We found a strong axis of variation determined by seed size and seedling growth habit, with early successional communities dominated by small‐seeded species with abiotic dispersal and climbing seedlings, while large‐seeded, animal‐dispersed species with free‐standing seedlings increased in abundance with stand age. Contrary to previous research and theory, we found a decrease in the abundance of stem twiners and no decrease in the abundance of tendril‐climbers during succession. Seed size appears to be a better indicator of liana successional stage than climbing mode. Liana life history traits change predictably over succession, particularly traits related to seedling establishment. Identifying whether these trait differences persist into the growth strategies of mature lianas is an important research goal, with potential ramifications for understanding the impact of lianas during tropical forest succession.     

Old-field seedling responses to insecticide,seed addition,and competition

The controls of seedling emergence and survival determine the potential distribution of adult plants and, thereby, plant community structure. Seed availability, competition from established neighbors, and seedling predation may all limit seedling recruitment. In this field experiment, we followed the emergence and survival of seedlings of three perennial forbs, Achillea millefolium, Hypericum perforatum, and Monarda fistulosa, in old-fields in southeastern Michigan, USA. As adults, all three have aromatic foliage that may deter herbivory, but seedlings may be more susceptible than adults. To establish the relative importance of potential controls on seedling numbers, we manipulated seed availability through seed additions, the influence of competitors by neighbor-removals, and the influence of insect herbivores with insecticide in a fully factorial field experiment. Seed addition and insecticide never affected seedling emergence for any species. Competition from established neighbors controlled seedling emergence for all three species and decreased Achillea survival. Insecticide significantly increased Monarda seedling survival in competition plots, significantly increased Hypericum survival in open plots, and had no effect on Achillea. Notably, insecticide increased survival of the native Monarda fistulosa more than the two introduced species. While neighbors strongly reduced emergence and survival of all three species, herbivores acted on a species-specific basis. These results suggest the differential effects of insects may contribute more to the seedling species composition and abundance patterns than the less-selective influence of competition.     

Establishment of tree seedlings in the understory of restoration plantations: natural regeneration and enrichment plantings

Little is known about the potential of restoration plantations to provide appropriate understory conditions to support the establishment of seeds arriving from neighboring native forests. In this article, we investigated how seedling establishment is affected in the understory of restoration sites of different ages and assessed some of the potential environmental factors controlling this ecological process. We first compared the density and richness of native tree seedlings among 10‐, 22‐, and 55‐year‐old restoration plantations within the Atlantic Forest region of southeastern Brazil. Then, we undertook a seed addition experiment in each study site, during the wet season, and compared seedling emergence, survival, and biomass on local versus old‐growth forest soil (transferred from a reference ecosystem), in order to test whether local substrate could hamper seedling establishment. As expected, the oldest restoration site had higher density and richness of spontaneously regenerating seedlings. However, seedling establishment was less successful both in the oldest restoration planting and using substrate transferred from a reference ecosystem, where emergence and survival were lower, but surviving seedlings grew better. We attribute these results to lower light availability for seedlings in the understory of the oldest site and speculate that higher incidence of pathogens on old‐growth forest soil may have increased seedling mortality. We conclude that the understory of young restoration plantations provides suitable microsite conditions at the early establishment phases for the spontaneous regeneration or enrichment planting of native trees.     

Spatial patterns of tree seedling establishment and their relationship to environmental variables in a cold-temperate deciduous forest of eastern North America

Patterns of seedling recruitment may have persistent effects on population and community processes. Assuming seed availability is not limiting, the environmental sieve (i.e., the suite of factors influencing seed germination and seedling emergence and survival) determines how many seedlings establish and, most importantly, where they do so. In this study, we identify the spatial structure of some resources and abiotic conditions known to be significant for tree seedling emergence and survival and determine how these environmental factors influence the establishment of Fagus grandifolia, Acer saccharum, Fraxinus americana, and Ostrya virginiana in a deciduous forest of southern Québec (Canada). We expect an increase from Fagus, through Acer and Fraxinus, to Ostrya in the control of environmental variables on seedling emergence and survival, because of differences in the seed size of these species. Density of newly-emerged seedlings of all four species showed positive spatial autocorrelation at distances of up to ca. 10 m. Environmental variables were also structured at the same spatial scale, except for soil moisture. Acer seedling emergence pattern was positively correlated to photosynthetic photon flux density (PPFD), and the pattern of Fraxinus to soil N and moisture. Seedling survival was not spatially autocorrelated for any of the four species, although it was positively density-dependent in Acer and Fagus. In only Ostrya was seedling survival correlated (positively) to one of the environmental variables studied, i.e., PPFD. Overall, environmental variables were spatially less heterogeneous than seedling emergence and survival. Either seed availability was not saturating or factors not considered here, such as competition and predation (the intensity of which often varies with resources and/or abiotic conditions), modified the influence that the physical environment had on patterns of seedling establishment. Our prediction of a greater environmental control on seedling emergence and survival in small-seed species was not totally confirmed.     

Small vertebrate granivores reduce seedling emergence in native tallgrass prairie restoration

High seed cost and low rates of establishment make tallgrass prairie restorations challenging and expensive endeavors. Typical seedling emergence rates in prairie restorations are approximately 10% and the causes of seed mortality are poorly understood. In this study, we examined the impact of small vertebrate granivores on prairie restoration by comparison of seedling emergence in open (sham) versus closed exclosures at three newly restored sites. To assess other causes of seed loss, we also tracked seed fates at one prairie restoration site. We coated seeds of four prairie species with fluorescent dye, placed them under closed exclosures, and monitored their fate (emerging seedling, partially germinated, nongerminated/viable, and nongerminated/nonviable) over a 5‐month period. On average, 9.6 more seedlings/m² emerged in the closed than the opened exclosures, suggesting that small vertebrate granivores reduce seedling emergence in prairie restoration. Granivores influenced the composition of the emerging community but did not preferentially consume large‐seeded species. In the seed‐tracking experiment, we found that greater than 70% of seeds were lost within 30 days of sowing, that seed recovery and viability both decreased with time in soil, and that seed fates differed between species. Collectively, our results indicate that small vertebrate granivores are an important cause of seed loss in prairie restoration, but unidentified belowground (e.g. fungal decomposition, invertebrate predation) and environmental (wind, rain) factors account for a greater proportion of total seed loss. Until these causes of seed loss are better understood, high seed costs will persist and continue to impede prairie restoration.     

Effects of increased N and P availability on biomass allocation and root carbohydrate reserves differ between N‐fixing and non‐N‐fixing savanna tree seedlings

In mixed tree‐grass ecosystems, tree recruitment is limited by demographic bottlenecks to seedling establishment arising from inter‐ and intra‐life‐form competition, and disturbances such as fire. Enhanced nutrient availability resulting from anthropogenic nitrogen (N) and phosphorus (P) deposition can alter the nature of these bottlenecks by changing seedling growth and biomass allocation patterns, and lead to longer‐term shifts in tree community composition if different plant functional groups respond differently to increased nutrient availability. However, the extent to which tree functional types characteristic of savannas differ in their responses to increased N and P availability remains unclear. We quantified differences in above‐ and belowground biomass, and root carbohydrate contents in seedlings of multiple N‐fixing and non‐N‐fixing tree species characteristic of Indian savanna and dry forest ecosystems in response to experimental N and P additions. These parameters are known to influence the ability of plants to compete, as well as survive and recover from fires. N‐fixers in our study were co‐limited by N and P availability, while non‐N‐fixers were N limited. Although both functional groups increased biomass production following fertilization, non‐N‐fixers were more responsive and showed greater relative increases in biomass with fertilization than N‐fixers. N‐fixers had greater baseline investment in belowground resources and root carbohydrate stocks, and while fertilization reduced root:shoot ratios in both functional groups, root carbohydrate content only reduced with fertilization in non‐N‐fixers. Our results indicate that, even within a given system, plants belonging to different functional groups can be limited by, and respond differentially to, different nutrients, suggesting that long‐term consequences of nutrient deposition are likely to vary across savannas contingent on the relative amounts of N and P being deposited in sites.     

Resilience of Mediterranean shrubland to a severe drought episode: the role of seed bank and seedling emergence

Extreme climate events, such as severe drought episodes, may induce changes in vegetation if they induce species‐specific adult mortality and changes in the seedling recruitment pattern. In 2005 a severe drought occurred in Doñana National Park (south Spain) causing extensive shrubland mortality. Over the following years we monitored the soil seed bank and seedling emergence via a gradient of canopy dieback induced by the drought episode. The canopy dieback corresponded to an increase in emergence of seedlings of woody species in 2007, probably because of the reduced competition induced by canopy loss. The soil seed bank of woody species sampled in 2008 was less abundant on plots with a higher proportion of dead vegetation, probably because of depletion of the seed bank as a result of the increased germination in the previous year and also as a result of a reduction in seed supply in these sites. Accordingly, in 2009 we detected reduced emergence of woody species on plots that had suffered the greatest shrub mortality. We failed to find any significant changes in patterns of the soil seed bank and seedling emergence of short‐lived herbaceous species, indicating greater resilience in these types of species. This study highlights the resilience of Mediterranean shrublands to climate fluctuations at one extreme of the variability characteristic of these ecosystems. An increase in the frequency of severe drought episodes – increasingly probable under the new climate conditions – does have the potential, however, to induce changes in vegetation, especially in woody communities that need more time to replenish their seed banks.     

Effects of surface disturbance and light level on seedling emergence in a Japanese secondary deciduous forest

Abstract. The effects of soil surface disturbance and light level on seedling emergence were examined by creating experimental conditions differing in soil surface treatment and light level in a temperate deciduous broadleaved secondary forest in central Japan. The results of MANOVA showed that soil surface disturbance exerted a favourable influence upon the seedling emergence of many species. Effect of soil disturbance on total density and number of emerged species was greater than that of a high light level. The interaction between soil surface disturbance and light level revealed significant positive effects for seedling emergence, especially for small‐seeded species. The relationship between the percentage of emerged seedlings and seed weight was significantly negative in the soil‐surface disturbed and high light level condition, suggesting that minute‐seeded species largely depend on both factors for seedling emergence. Both soil surface disturbance and high light level had a positive effect on the number of emerged species, suggesting that these factors contributed to species richness at the stage of seedling emergence.