Restoring Aristida stricta to Pinus palustris Ecosystems on the Atlantic Coastal Plain, U.S.A.

Aristida stricta (wiregrass), a perennial bunchgrass, quickly accumulates dead leaves, which along with the shed needles of Pinus palustris (longleaf pine) provide the fuel for frequent surface fires. Thus, historically, wiregrass played a key role in many longleaf communities where it significantly influenced the natural fire regime and thereby the composition of the plant community. Reestablishment of wiregrass is, therefore, critical to restoring the native understory of Atlantic Coastal Plain longleaf pine ecosystems. This study measured the effects of different site preparations and fertilizer application on the survival and growth of wiregrass seedlings. Two-month–old seedlings were underplanted in existing longleaf pine stands on dry Lakeland soils at the Savannah River Site in South Carolina. Survival was acceptable at 51% after four years, although reduced owing to drought and small seedling size. Survival and growth could both be increased by using older seedlings with an initial height of at least 6 cm. Wiregrass leaves grew quite rapidly and attained an average length of 48 cm in four years on control plots. Basal area growth rate was greater than expected, averaging 40% on control treatments and 55% on cultivated and fertilized plots. If growth rates during the first four seasons continue, wiregrass will attain mature size on cultivated and fertilized plots at six years, while non-fertilized control plots will take eight years. A planting density of one seedling per m² is recommended to provide sufficient wiregrass foliar cover to influence fire regimes in a reasonable length of time (i.e., 5–7 years).     

Aristida beyrichiana (Wiregrass) Establishment and Recruitment: Implications for Restoration

Restoration of the longleaf pine ecosystems of the southeastern United States has focused interest on the regeneration and establishment of Aristida sp. (wiregrass) as a means to reestablish ecological function and structure of the ecosystem. This study examined dispersal distance from planted adults and canopy cover and density effects on establishment and reproduction. In 1994 wiregrass plugs were planted in two densities (500 seedlings/100 m² and 49 seedlings/100 m²) and three canopy‐thinning treatments (25 m² basal area/ha, 16 m² basal area/ha, and 8 m² basal area/ha) were implemented in a 20‐year‐old longleaf plantation in southwestern Georgia. Due to the intense site preparation and the density of pines planted, virtually no understory vegetation was present. The site was burned in June 1995, which promoted seed production of the planted wiregrass. Results indicate that the 8 m² basal area/ha treatment results in larger plants that in turn produce a greater number of seedling recruits. No seedling recruitment occurred in control plots. Dispersal distances of up to 594 cm were recorded. Natural seedling recruitment occurred at low‐density transplanting (5 plants/10 m²), denoting that high‐density planting similar to natural density (5 plants/m²) is not required for successful establishment or reproduction. However, overstory thinning in dense pine plantations is required for reproduction and increases the survival of individual plants due to changes in the environmental conditions at the forest floor.     

Burning Influences on Wiregrass (Aristida beyrichiana) Restoration Plantings: Natural Seedling Recruitment and Survival

Regeneration and expansion of Aristida beyrichiana and Aristida stricta (wiregrass) populations in remaining fire‐maintained Pinus palustris (longleaf pine) stands of the southeastern United States has become an objective of land managers. Although growing‐season fire is required for successful wiregrass seed production, studies examining naturally occurring wiregrass seedling dynamics are few. This study investigates how seedling survivorship is affected by season of burn, seedling size, time since germination, and proximity to adult plants. Restoration at this research site was begun in 1992 with the planting of containerized longleaf pine and wiregrass seedlings. Study plots were established in November 1997 after a growing‐season prescribed fire (June 1996) that resulted in successful seed production and seedling recruitment. Burn treatment plots included (1) no burn (control), (2) fire in the dormant season of the first year after germination (March 1998), (3) fire in the growing season of the first year after germination (August 1998), and (4) fire in the growing season of the second year after germination (July 1999). Seedling mortality increased with growing season burning and close proximity to planted adults. Natural seedling recruitment continued into the second year after initial seed‐drop in all plots, which verifies that wiregrass seed banking occurs for a minimum of 2 years after seed drop. Where wiregrass management objectives include population expansion, seedling recruits should be allowed 1 to 2 years post‐germination without growing season fire for successful establishment.     

Experimental test for facilitation of seedling recruitment by the dominant bunchgrass in a fire-maintained savanna

Facilitative interactions between neighboring plants can influence community composition, especially in locations where environmental stress is a factor limiting competitive effects. The longleaf pine savanna of the southeastern United States is a threatened and diverse system where seedling recruitment success and understory species richness levels are regulated by the availability of moist microsites. We hypothesized that the dominant bunch grass species (Aristida stricta Michx.) would facilitate moist seedling microsites through shading, but that the effect would depend on stress gradients. Here, we examined the environmental properties modified by the presence of wiregrass and tested the importance of increased shade as a potential facilitative mechanism promoting seedling recruitment across spatial and temporal stress gradients. We showed that environmental gradients, season, and experimental water manipulation influence seedling success. Environmental properties were modified by wiregrass proximity in a manner that could facilitate seedling success, but we showed that shade alone does not provide a facilitative benefit to seedlings in this system.     

The regeneration niche of the grey mangrove (Avicennia marina): effects of salinity,light and sediment factors on establishment,growth and survival in the field

Field observations of seedlings and saplings of Avicennia marina showed patterns that correlated with salinity, light and sediment. Models that account for these observations were subsequently tested in a series of field experiments. Establishment varied within an estuary under controlled conditions but was not related to salinity or sediment type. Seedling survival was uniform over 3 years regardless of position in estuary and sediment type. Seedling densities and survival under canopies or in canopy gaps were not significantly different. However, seedling growth and density of saplings were greater in canopy gaps. Experiments involving manipulations of canopies showed no differences in seedling survival under canopies or in light gaps, but addition of slow-release fertilizer enhanced growth and survival in canopy gaps and under canopies. Long-term comparison of areas denuded of a canopy and with sediment disturbance showed enhanced establishment and survival when compared with areas with canopy gaps but with undisturbed sediments. Overall there appears to be no restriction to establishment of propagules within mangrove stands other than the supply of propagules and tidal or wave action. In contrast, recruitment to the sapling stage appears to be restricted by light and sediment resources. We suggest that propagules need to establish in a regeneration niche for seedling recruitment to the sapling stage. This differs from the view that seedlings in the under-storey are analogous to a seed pool in the soil.     

Longleaf and loblolly pine seedlings respond differently to soil compaction,water content,and fertilization

Aims

Longleaf pine (Pinus palustris Mill.) is being restored across the U.S. South for a multitude of ecological and economic reasons, but our understanding of longleaf pine’s response to soil physical conditions is poor. On the contrary, our understanding of loblolly pine (Pinus taeda L.) root and shoot growth response to soil conditions is well established.

Methods

We performed a comparative greenhouse study which modeled root length density, total seedling biomass, and the ratio of aboveground:belowground mass as functions of volumetric water content, bulk density and soil fertility (fertilized or not).

Results

Root length density was about 35 % greater in longleaf pine seedlings compared to loblolly pine seedlings, and was reasonably well modeled (R ²?=?0.54) for longleaf pine by bulk density (linear), volumetric water content (quadratic), soil fertility, and the interactions of bulk density, volumetric water content, species, and soil fertility. The aboveground:belowground mass ratio (ABR) increased at both extremes of water content.

Conclusions

This research indicates that young longleaf pine seedling root systems respond more negatively to extremes of soil physical conditions than loblolly pine, and compacted or dry loamy soils should be ameliorated in addition to normal competition control, especially on soils degraded by past management.     

地上竞争与地下竞争对科尔沁沙地榆树幼苗生长的影响

榆树疏林草原对科尔沁沙地植被恢复和景观保护有着重要意义.本文采用双因素两水平控制试验,从幼苗生物量、地下/地上生物量、茎高、根茎比、叶片数等方面,研究了草-树地上、地下竞争对科尔沁沙地榆树幼苗生长的影响.结果表明:对于1年生榆树幼苗,单株平均生物量表现为无竞争＞地上竞争＞全竞争＞地下竞争;地下/地上生物量表现为地下竞争＞全竞争＞无竞争＞地上竞争;幼苗高度表现为地上竞争＞无竞争＞全竞争＞地下竞争;根茎比表现为地下竞争＞全竞争＞无竞争＞地上竞争;叶片数表现为地上竞争＞无竞争＞地下竞争＞全竞争.地下竞争对1年生榆树幼苗生长影响显著,而地上竞争对榆树幼苗生长无显著影响.地上竞争与地下竞争对2年生榆树幼苗生长的影响均不显著.科尔沁沙地草本植物对榆树幼苗生长的影响主要通过地下竞争的方式实现,但地下竞争并没有改变榆树幼苗的资源分配方式.随榆树幼苗龄级的增长,草本植物竞争作用的影响逐渐减弱.     

Facilitation and competition influence succession in a subtropical old field

The effects of neighboring vegetation and soil fertility on the establishment, survival and growth of tree species were studied in a subtropical old-field area in south Brazil. Seed damage, germination and seedling establishment of four tree species plus growth and survival of two transplanted tree species were monitored under factorial combinations of the following treatments: (1) pioneer vegetation (presence and absence); (2) soil fertility (addition of NPK and control). Facilitation was the main process affecting plant performance. The presence of pioneer vegetation significantly improved germination, establishment, growth and survival of most study species. Around 90% of sown seeds were damaged and the removal of pioneer vegetation significantly increased seed damage for all species studied, decreased germination in three out of four species, and decreased establishment in one species. Moreover a significantly higher seedling growth rate of Inga virescens was found after the first year of the experiment in plots where vegetation was present. The presence of vegetation significantly increased seedling survival of I. virescens by protecting seedlings from leaf loss due to winter frosts. Competition was detected by the second year when a higher growth of transplanted seedlings of the species Araucaria angustifolia occurred in plots where vegetation was present and fertilizer were applied. A lower growth rate was detected in plots where vegetation was present but fertilizer was not applied. These results indicate a balance between competition for soil nutrients and protection by neighbor vegetation. Damage of seedlings by leaf cutter ants was an important barrier for plant survival. Damage occurred in 80% of the A. angustifolia seedlings and 58% of these damaged seedlings died. The presence of neighboring vegetation tended to protect seedlings from ant damage. Although competition occurred, facilitation seems to be the main process driving early successional changes in this subtropical old field. This was mainly due to the improvement of local microclimatic conditions and protection against herbivores by neighboring vegetation. Facilitation occurred during establishment and growth phases in a subtropical area that is considered a productive, low stress environment. Our results indicate that facilitation may be more frequent in productive environments than previously thought.     

山地落叶阔叶林优势树种米心水青冈幼苗的定居

在郁闭的林冠下、模拟林窗和林间空旷地3种光照环境中,研究了施肥和未施肥的米心水青冈幼苗生存和生长发育过程．结果表明,幼苗在林下的发育受到光照不足的严重抑制,生长在林下的幼苗比生长在林窗和空旷地幼苗死亡快,死亡率高,幼苗在郁闭林下能够生存的时间不超过12周．施肥处理的幼苗比对照的幼苗死亡快,死亡率高．幼苗死亡很可能与土壤中的病原生物有关．虽然由林下光照强度增加到模拟林窗的光照强度后,幼苗发育有明显改善,但幼苗在模拟林窗环境和空旷地的生长没有显著差异．结果说明,米心水青冈新出土的幼苗在郁闭林冠下易受伤害,更新立苗阶段需要有比较好的光照条件,肥沃土壤可能也无助于改善郁闭林冠下幼苗的定居．     

Survival and growth responses of Myricaria laxiflora seedlings to summer flooding

Myricaria laxiflora, an endangered shrub species distributed along the banks of the Yangtze River in the Three Gorges area, is completely submerged from June to October every year. It is generally assumed that summer flooding has a strong impact on the survival and growth of seedlings. We designed an outdoor randomized block experiment on the responses of seedling survival and growth to different flooding depth and flooding duration treatments during the flood season in the Three Gorges area. Seedling survival rate, aboveground biomass, belowground biomass, total biomass, root depth, length of primary branch and the number of primary and secondary branches were examined.M. laxiflora was found to acclimate to summer flooding by becoming dormant and losing biomass. Seedlings of M. laxiflora ceased growing during the summer flooding season, regardless of the flooding depth and flooding duration they were subjected to. The number of primary and secondary branches, aboveground biomass and total biomass of seedlings was reduced with prolonged flooding. The length of primary branches and aboveground biomass were more sensitive to flooding than other measured parameters and differed significantly between the onset and the end of flooding.In each flooding treatment most seedlings of M. laxiflora survived a flooding period of 2 months and recovered rapidly after the flooding was terminated in September. After 3 months of recovery, aboveground biomass, total biomass and the number of the primary branches increased significantly. Furthermore, seedling survival and growth in the flooding treatments were not significantly different from the controls both during the summer flooding stage and in the recovery stage. All of these results suggest that summer flooding does not affect seedling survival and growth in this species. On the contrary, flooding released seedlings from the stress of drought during summer and facilitated seedling establishment. M. laxiflora appears to cope adaptively with the flooding cycle by going into a state of dormancy during the flood season.     

The Initial Phase of a Longleaf Pine‐Wiregrass Savanna Restoration: Species Establishment and Community Responses

The significant loss of the longleaf pine‐wiregrass ecosystem in the southeastern United States has serious implications for biodiversity and ecosystem functioning. In response to this loss, we have initiated a long‐term and landscape‐scale restoration experiment at the 80,125 ha (310 mi²) Department of Energy Savannah River Site (SRS) located near Aiken, South Carolina. Aristida beyrichiana (wiregrass), an important and dominant grass (i.e., a “matrix” species) of the longleaf pine savanna understory, and 31 other herbaceous “non‐matrix” species were planted at six locations throughout SRS in 2002 and 2003. Of the 36,056 transplanted seedlings, 75% were still alive in June 2004, while mean 1–2 year survival across all planted species was 48%. Lespedeza hirta (hairy lespedeza) exhibited the greatest overall survival per 3 × 3 m cell at 95%, whereas Schizachyrium spp. (little bluestem) exhibited the greatest mean cover among individual species at 5.9%. Wiregrass survival and cover were significantly reduced when planted with non‐matrix species. Aggregate cover of all planted species in restored cells averaged 25.9% in 2006. High rates of survival and growth of the planted species resulted in greater species richness (SR), diversity, and vegetative cover in restored cells. Results suggest that the loss of the longleaf pine‐wiregrass ecosystem may be ameliorated through restoration efforts and illustrate the positive impact of restoration plantings on biodiversity and vegetative cover.     

Mowing and fertilizer effects on seedling establishment in a successional old field

Aims We used a 10-year field experiment that consisted of mowing and fertilizer treatments to evaluate the role of niche limitation in seedling establishment of species from different functional groups and of varying local abundance in an old field undergoing succession.Methods Seedlings of nine different species were planted into a successional field subjected to mowing and fertilizer treatments for 10 years that resulted in different plant communities and resource availability. Species representative of the factorial combination of three functional groups (C 4 grasses, C₃ grasses and legumes) and three abundance categories (abundant, present, or absent in the old field) were planted in four treatments resulting from the factorial combination of annual spring mowing (mowed and unmowed) and fertilizer application (annually fertilized and unfertilized). Survivorship, relative growth rate (RGR) and biomass were measured to determine the role of niche limitation on recruitment and growth.Important findings Mowing increased the establishment success of seedlings. Fertilization had little influence on seedling performance and survivorship. C₃ grasses had the highest survivorship, while C₄ grasses and legumes had equivalent RGRs, but higher than C₃ grasses. By contrast, survivorship of legumes was unrelated to mowing or fertilizer, suggesting that establishment of this functional group was dependent on other, unmeasured conditions or processes. Species already present, but at low abundance, performed better than locally abundant or absent species. Propagule limitation may restrict the arrival of a species. However, recruitment and establishment was subject to niche limitation, which varied among species, functional groups and whether a species is already resident at the site and its abundance. Thus, species interactions restrict establishment during old-field succession, supporting the niche limitation hypothesis.     

Aboveground environment type, soil nutrient content and arbuscular mycorrhizal fungi explain establishment success of Centaurea jacea on ex-arable land and in late-successional grasslands

We studied the relative importance of the aboveground and belowground environment for survival and growth of emerged seedlings of Centaurea jacea to better understand the general difficulty of establishing late-successional species at restoration sites on ex-arable land. Potted seedlings growing on soil from six late-successional grasslands and from six ex-arable (restoration) sites were reciprocally exchanged, and survival and relative growth rate of the seedlings monitored. In addition, we assessed aboveground herbivory and colonization of roots by arbuscular myccorhizal fungi of all plants, as well as nutrient availability, and microbial biomass and community composition using PLFA techniques in all twelve soils. Seedling survival was higher in restoration habitat and soil than in grassland habitat and soil, but growth did not differ between the aboveground and belowground environment types. Shoot growth rate was initially correlated with soil nutrient content, and later in the experiment with mycorrhizal colonization levels. Our results indicate that arbuscular mycorhizal fungi may be important for the successful establishment of C. jacea and that abiotic soil factors, like K availability and N:P ratio, can promote mycorrhizal colonization. Hence, the belowground environment should be considered when selecting sites for restoring species-rich grasslands.     

去叶对水曲柳和落叶松苗木当年生长及细根动态的影响

叶片被取食会导致树木生长发育和生理代谢发生显著的变化。目前对细根动态如何对叶片损失做出响应的了解仍然有限。以生物量分配和高生长策略不同的水曲柳(Fraxinus mandschurica)和落叶松(Larix gmelinii)苗木为研究对象, 进行了不同强度的人为去叶处理(叶面积去除0% (对照)、40%和80%), 采用微根管技术对细根(直径≤2 mm)生产和死亡的季节动态进行了定量观测, 同期测定了地上部分(苗高和地径)的生长。结果表明: 1)去叶降低了两树种苗高(统计上均不显著)和地径的生长, 但是对苗高生长的影响小于地径。随着去叶强度的提高, 苗木地上生长受到的影响加大, 生长季末期水曲柳苗高比对照降低3.3%-12.1%, 地径降低5.7%-23.1%; 而落叶松苗高和地径降低相对较少(< 12%)。2)去叶显著地减少了水曲柳和落叶松细根现存量(p< 0.001), 其相对增长量((去叶后现存量高峰-去叶当日现存量)/去叶当日现存量)随着去叶强度的加大而降低。3)与对照相比, 去叶后两树种细根生产量显著减少(p< 0.05), 而细根死亡量在不同处理间没有显著差异。综合来看, 去叶对水曲柳地上部分(特别是地径)生长影响较大, 而对落叶松地下部分(主要是新根)生长影响较大。研究结果为理解冠层碳供应对根系动态影响的种间差异及其机制提供了必要的理论依据。     

THE RELATIVE ROLES OF ABIOTIC AND BIOTIC FACTORS IN SEEDLING DEMOGRAPHY OF ARROYO WILLOW (SALIX LASIOLEPIS: SALICACEAE)

The abiotic and biotic factors causing mortality of Salix lasiolepis (Salicaceae) seedlings were studied along a seasonally flowing stream in northern Arizona. Mortality of first-year seedlings approached or equaled 100% for the four cohorts observed. Water-addition experiments demonstrated that lack of soil surface moisture was the primary cause of mortality for seedlings through their first 2 years with > 75% of seedlings dying in the first month of growth in unwatered plots. Biotic factors, including herbivory and inter- and intraspecific competition were evaluated, but played a minor role in the dynamics of seedling populations during this study. Shade conditions between sites were inferred to influence growth and survival, and experiments verified the effect of shade in decreasing seedling size. Smaller seedlings were shown experimentally to have a greater likelihood of dying during the winter. The probability of survival between years increased with seedling age, and seedlings that survived three growing seasons were likely to join the population of mature, reproductive plants. Studies of seedling survivorship through the establishment phase have seldom reported mortality levels as extreme as those reported here.     

Effects of Planting Depth,Sediment Grain Size,and Nutrients on Ruppia maritima and Potamogeton perfoliatus Seedling Emergence and Growth

Protocols are now available for seed harvest, storage and germination of several mesohaline and polyhaline species; however, low seedling survival rates point to the need for an increased understanding of factors affecting seedling establishment. Depth of seed burial in sediments and initial seedling growth rates are shown to be limiting factors for photosynthetic competency of Ruppia maritima and Potamogeton perfoliatus. Seedling emergence is inversely proportional to planting depth on sediments ranging in grain size from coarse sands (850 μm) to silt (63 μm). Less than 6% of the seeds of either species emerged when buried to a depth of 3 cm in test sediments. Germination was greatest for seeds placed on the surface of sediments; however, these seedlings were subject to displacement because of the weak and fragile roots produced during early growth. Fine sediments may be more favorable for R. maritima seedling establishment, because seedling emergence and height decreased with increasing sediment grain size. Potamogeton perfoliatus seedlings seem to be more tolerant of a wider range of sediment grain sizes than R. maritima as indicated by the lack of an effect of sediment grain size on P. perfoliatus seed emergence, seedling height, and biomass. Increasing nutrients stimulated seedlings of both species; however, even at the highest concentrations tested, growth, as determined by shoot elongation and leaf and root formation, slowed within 7–10 days. This suggests factors other than mineral nutrients and light limit growth or that growth shifts from aboveground biomass production to belowground vegetative spread.     

常绿阔叶林林冠环境对栲幼苗建成的影响

植物幼苗建成阶段是决定种群自然更新的关键生活史阶段。研究林冠环境对常绿阔叶林优势种幼苗建成阶段的影响对该类森林的恢复和管理具有重要意义。2014-2016年, 该研究在重庆市缙云山国家级自然保护区的常绿阔叶林的不同林冠环境(大林窗: >150 m ², 中林窗: 100-150 m ², 小林窗: 50-100 m ², 对照: 林下)下进行栲(Castanopsis fargesii)种子野外播种实验, 并对栲幼苗命运和生长情况进行了3年的持续监测。结果表明: (1)栲幼苗出土时间从7月持续到12月, 出苗时间较长, 大林窗对幼苗出土具有延迟作用; (2)栲种子野外平均萌发率为(62.8 ± 2.0)%, 第3个生长季(2016年)末幼苗平均存活率为(65.1 ± 2.2)%, 枯萎是栲幼苗死亡的主要原因; (3)林冠环境对栲种子萌发率及第1个生长季(2014年)末的幼苗存活率无显著影响, 对第2个(2015年)和第3个生长季末的幼苗存活率具有显著影响; (4)林冠环境在第1个生长季对幼苗生长无明显影响, 但在第2个和第3个生长季具有显著影响, 大、中林窗中幼苗总生物量、株高、基径、根长和叶片数显著高于林下, 比叶面积显著低于林下; (5) 3个生长季内, 4类林冠条件下栲幼苗的叶质量比和茎质量比升高, 根质量比和根冠比降低, 并且从第2个生长季开始大林窗中栲幼苗的叶质量比显著高于林下, 根质量比和根冠比显著低于林下。栲幼苗早期的存活和生长依赖种子储存的能量, 受林冠条件影响较弱, 后期则依赖光合作用, 受林冠条件影响较强, 从整个幼苗建成过程看, 大、中林窗更有利于栲幼苗定居。     

How do deer affect tree seedlings on a dwarf bamboo-dominated forest floor?

A field experiment was conducted in Mt. Ôdaigahara, west-central Japan, to reveal the effects of two herbivores, Sika deer (Cervus nippon) and mice (Apodemus spp.), on the seedlings of five cohorts of three tree species, Abies homolepis, Fraxinus lanuginosa f. serrata and Fagus crenata. The forest floor of the study site was covered with dwarf bamboo, Sasa nipponica, which would also affect the seedlings. Eight combinations of three treatments were set: exclusion of deer, exclusion of mice and removal of dwarf bamboo. Deer were expected to affect the seedlings not only negatively by foraging but also positively by browsing dwarf bamboo that overshadows seedlings. The survival of these cohorts was analyzed by survival analysis and the differences in their survival between the treatments were investigated. The results of the experiment showed that: (1) exclusion of deer increased the aboveground biomass of dwarf bamboo and made it more difficult for seedlings to survive under the regenerated dwarf bamboo stand, and (2) deer negatively affected the seedlings, but they had positive, indirect effects in some cohorts by decreasing the aboveground biomass of dwarf bamboo. However, such effects were not detected in some cohorts which were affected excessively by deer or dwarf bamboo. No clear results on the effect of mice on seedlings were obtained. We conclude that a positive, indirect effect of deer on seedling survivorship would be observable when the magnitude of a positive, indirect effect caused by decreasing dwarf bamboo is larger than that of a negative, direct effect of deer.     

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.     

Fire,canopy cover and seedling dynamics in Mediterranean shrubland of northeastern Spain

Abstract. Seedling establishment and survival of the main woody species of early-successional shrubland in northeastern Spain were studied from 1992 to 1995 with emphasis on the importance of vegetation cover (existence of open areas and the situation beneath the plant canopy) and microhabitat (occurrence of stones, litter and bare soil). In the absence of fire, vegetation cover (measured at a scale of 30cm × 30 cm) was not correlated with seedling emergence of most species, nor with growth and survival of seedlings up to one year old. Seedlings older than one year showed a similar pattern: their density was not significantly different in both kinds of habitats. The emergence of seedlings was mainly associated with the presence of mature plants – which can provide seeds – and with the absence of unsuitable microhabitats (large stones, deep litter and bare soil). In April 1994 a wildfire burned the study area. This enabled a study of the pattern of post-fire establishment. After the wildfire, seedling emergence of several species increased and most species produced seedlings with higher survival and growth rates than in the period before the fire. Pre-fire cover, however, did not show significant effects on post-fire seedling dynamics in most cases.