Seedling Bank Research Articles

Forest seedling community response to understorey filtering by tree ferns

AbstractQuestionsLarge pteridophytes frequently co‐occur with conifers and angiosperms in the understorey of temperate broad‐leaved podocarp forests but interactions between them are poorly understood. We evaluated the impact of tree ferns on the regeneration niche of vascular woody species to determine whether tree ferns function as biotic filters and influence seedling occurrence. We asked the following questions: (i) do understorey tree ferns influence the woody seedling bank, and (ii) which potential mechanisms drive any such influence?LocationAuckland and Waikato regions, northern New Zealand.MethodsWe measured woody seedlings in 164 1‐m2 plots in northern New Zealand temperate broad‐leaved podocarp forest and used multivariate analyses and modelling to assess the relative contributions of abiotic and biotic effects on community composition and seedling abundance. We manipulated the environments beneath 160 tree fern individuals by removing fronds and/or macro‐litter in a balanced factorial design, and recorded the response of the seedling community over 1 year. We then assessed the relative influences of shading and litter depth on the seedling community response.ResultsDistance to the nearest tree fern was the best predictor of understorey seedling abundance; seedling abundance decreased beneath tree ferns. There was no strong evidence, however, that tree ferns influence seedling community composition; although the palm Rhopalostylis sapida, was consistently present away from tree fern micro‐sites. Removal of tree fern shading and macro‐litter both influenced the local seedling community; conifers responded positively, and most consistently to frond removal. Frond‐shading and deep litter reduced seedling species richness and seedling abundance.ConclusionsTree ferns influence the woody seedling bank in temperate broad‐leaved podocarp forest through increased shading and macro‐litter accumulation, both of which reduce the abundance of angiosperm and conifer seedlings. A tree fern‐dominated understorey is likely to reduce conifer establishment and may limit direct competition among woody plants by reducing densities and regeneration opportunities immediately beneath tree fern canopies.

Forest recovery in set-aside windthrow is facilitated by fast growth of advance regeneration

Key messageThe disturbance of a research plot by a windstorm allowed us to study the role of the seedling bank in the regeneration processes. The released advance regeneration dominated among the saplings; taller individuals retained their position until the end of the study. Pioneer species occurred sporadically. Seven years after the disturbance, the windthrow was covered by a dense thicket of young trees.ContextThe dominant role played by advance regeneration in natural regeneration processes after intense wind disturbances is still a matter of dispute.AimsWe took advantage of a windstorm in one of our research plots to study the role of the seedling bank released by the disturbance in the regeneration processes.MethodsWe collected data in 70 plots, recording the survivorship of seedlings, annual height growth, and signs of browsing. The height ranking was analyzed with Kendall’s concordance coefficient, and the height growth rates were compared using Dunn’s test.ResultsThe density of seedlings increased from 6.7/m2 in 2008 to 8.1/m2 in 2010 and then decreased to 1.2/m2 in 2015. The density of saplings increased continuously from 0.14 to 1.9/m2. The highest size differentiation occurred in sycamore maple; the individuals which were taller before the windstorm retained their position until the year 2015. The only species that was recruited mainly from germinants was European hornbeam.ConclusionThe advance regeneration released by the windstorm played a major role in the regeneration process, while pioneer species occurred only sporadically. Seven years after the disturbance, the windthrow was already covered by a dense thicket of young trees.

IMPACT OF SEEDLING REMOVAL ON NATURAL REGENERATION IN THE SOUTHERN ATLANTIC FOREST REMNANT

ABSTRACT The use of a forest seedling bank has been recommended as an alternative to increase species richness in forest nurseries, as well as to produce seedlings of species that are diffi cult to propagate, especially those that belong to the late secondary and climax successional groups, which are not as commercially available. However, little is known about the impact of this method on forest dynamics. Thus, the present study aimed to examine the resilience and dynamics of a seedling bank in a remnant of a subtropical seasonal forest belonging to the Atlantic Forest Biome when subjected to different intensities of seedling removal. The experiment was conducted in a random block design in a factorial scheme (5 × 4), with treatments composed of fi ve intensities of removal of individuals from the seedling bank and the four seasons. The treatments were distributed into 18 blocks and the experimental units were composed of 1 m × 2.5 m plots. The resilience of the seedling community was assessed by examining effects of the fi ve removal intensities. The dynamics between the evaluation periods within each treatment were verifi ed by comparing the number of species and seedlings present before the treatments with those in the other evaluation periods. After one year, we found that tree-shrub vegetation had a partial capacity for restoration after withdrawal of individuals from the seedling bank. Our results show that the impact on the regeneration community can absorb the effects of up to 25% seedling removal. The technique of seedling transplantation may be recommended for species that have abundant regeneration, such as Actinostemon concolor, Eugenia rostrifolia, Trichilia claussenii and Nectandra megapotamica.

Regeneration dynamics in the laurel forest: changes in species richness and composition

Abstract: The recovery and survival of the Macaronesian laurel forest depends on its regeneration strategies. After years of long-term monitoring, both sexual and asexual regeneration appear to be equally important. However, the mechanisms for each are just beginning to be understood. In order to contribute to the understanding of the laurel forest sexual regeneration, we analyzed the species composition of the seedling bank every two weeks over three years in the laurel forest of Anaga (Tenerife, Canary Islands). We compared the species compositions of the seedling bank with the canopy, and analyzed changes in their diversity over this period in different forest stands. We found that species diversity (evenness) is different among plots regardless of the stand. In some cases, plot diversity remained constant over time, while others showed some variations, which were little related to climatic conditions (temperature and precipitation). We also found no relationship between the seedling bank and canopy composition, with shade-intolerant species being more abundant in the former. Although climatic conditions remained constant during the period and other environmental conditions did not vary either, some changes were found in the seedling bank species composition. These were related to the increased degree of conservation of the laurel forest of Anaga (by closing unpaved roads, limiting access, and the abandonment of agriculture) that had negatively affected the density of shade-intolerant species. We suggest that such conservation measures should be maintained and extended to other areas where agriculture has been recently abandoned to allow the potential establishment of laurel forest and late successional species.

Variable seed behavior increases recruitment success of a hardwood tree, Zelkova serrata, in spatially heterogeneous forest environments

Abstract Variable seed behavior (e.g., seed heteromorphism) plays an important role in enhancing plant fitness by spreading risk in spatially and temporally changing environments. This adaptation is common in herbs but rare in trees. Zelkova serrata, one of the most important commercial tree species in Japan, has two types of seeds: shoot seeds that disperse via a seed-bearing shoot and single seeds that disseminate after separating from shoots. To evaluate whether the seeds of Z. serrata show heteromorphism, we compared several inherent ecological properties (e.g., seed mass, degree of seed dormancy, and dispersal ability) between the two seed types and assessed the effects of variable seed behavior on recruitment success in forest environments. The degree of seed dormancy did not differ between the two seed types. Seed mass increased with a delayed seed dispersal time but did not differ between the two types at any time. Seed dispersal ability was greater in shoot seeds than in single seeds. These inherent seed behaviors suggest that the two types of seeds do not reflect seed heteromorphism. The results, however, indicate that shoot seeds dispersed larger seeds over much greater distances than did single seeds, particularly at later seed dispersal times, whereas a greater number of single seeds were disseminated near adults. To evaluate the effects of variable seed dispersal ability on seedling establishment in forest environments, we measured seedling performance at different distances (≤27.5 m) from adults isolated from one another in the forest understory. Seedling density, survival, and growth did not vary with distance from adults (i.e., there was little negative distance-dependent seedling mortality), which suggests that single seeds can contribute to persistent seedling banks near conspecific adults. To evaluate the advantages of long-distance dispersal of shoot seeds for recruitment on disturbed sites (i.e., gaps), we compared the occurrence and relative abundance of Z. serrata among 1100 plots with different slopes; steep slopes are closely associated with gap creation (e.g., landslides). The occurrence and relative abundance of Z. serrata increased with slope inclination, which suggests that shoot seeds may enhance recruitment success in disturbed sites along steep slopes, thereby generating Z. serrata-dominated forests. This suggests that the variability in seed behavior of Z. serrata may enhance recruitment success in spatially heterogeneous forest environments. Knowledge of the unique reproductive behaviors and the wide range of habitats suitable for this species is important for forest managers when making sustainable timber production plans for Z. serrata.

Chronosequence-based population structure and natural regeneration of Haloxylon ammodendron plantation in the southern edge of the Gurbantunggut Desert, Northwestern China

In the Gurbantunggut Desert of Northwestern China, we surveyed the population structure and regeneration characteristics of six Haloxylon ammodendron plantations based on chronosequencing. The results showed that the age class of an individual H. ammodendron plant from youngest to oldest showed growth potential under the present environment. The optimal termination stage of H. ammodendron occurred at 20 years of age, which was accompanied by a regeneration phase at 17 years. The H. ammodendron plantations started to regenerate after 7 years. The maximal height and basal stem diameter of a grade III seedling reached 1.2 m and 1.9 cm in a 17-year-old plantation. In a 33-year-old plantation, the transformation rate of the seedling from grade I to grade III increased up to 92.3%. Although the seedling bank was plentiful in the plantations, the replenishment of the canopy was not continuous and timely. Therefore, measures to further the stability and sustainability of H. ammodendron plantation were necessary.

Do understorey or overstorey traits drive tree encroachment on a drained raised bog?

One of the most important threats to peatland ecosystems is drainage, resulting in encroachment of woody species. Our main aim was to check which features - overstorey or understorey vegetation - are more important for shaping the seedling bank of pioneer trees colonising peatlands (Pinus sylvestris and Betula pubescens). We hypothesised that tree stand parameters will be more important predictors of natural regeneration density than understorey vegetation parameters, and the former will be negatively correlated with species diversity and richness and also with functional richness and functional dispersion, which indicate a high level of habitat filtering. The study was conducted in the 'Zielone Bagna' nature reserve (NW Poland). We assessed the structure of tree stands and natural regeneration (of B.pubescens and P.sylvestris) and vegetation species composition. Random forest and DCA were applied to assess relationships between variables studied. Understorey vegetation traits affected tree seedling density (up to 0.5-m height) more than tree stand traits. Density of older seedlings depended more on tree stand traits. We did not find statistically significant relationships between natural regeneration densities and functional diversity components, except for functional richness, which was positively correlated with density of the youngest tree seedlings. Seedling densities were higher in plots with lower functional dispersion and functional divergence, which indicated that habitat filtering is more important than competition. Presence of an abundant seedling bank is crucial for the process of woody species encroachment on drained peatlands, thus its dynamics should be monitored in protected areas.

Efeito de borda ou da exploração? Demografia e estado de conservação de Euterpe edulis Martius em área protegida de floresta atlântica de terras baixas (RJ)

Intrinsecamente, a palmeira-juçara (Euterpe edulis Martius) desperta grande interesse por sua beleza e papel-chave em comunidades de fragmentos de Floresta Atlântica, porque é explorada como recurso alimentício por uma vasta assembleia de vertebrados. O objetivo do estudo foi investigar o estado de conservação de Euterpe edulis na Reserva Biológica União (Rio das Ostras, RJ) através do estudo de sua demografia, bem como responder às seguintes questões: A população sofre efeito de borda? A escala de observação influencia sua detecção? Variáveis da estrutura da vegetação (cobertura herbácea, do dossel e sub-bosque) foram mensuradas para caracterização dos ambientes e a fim de relacioná-las com a abundância e diâmetro dos indivíduos. Os resultados indicaram que a população de palmeira-juçara estudada não sofre efeito de borda. As variáveis da estrutura da vegetação não apresentaram relação com a abundância e diâmetro dos indivíduos nos distintos estágios de vida. Todavia, a estrutura da população estudada não indica potencial para regeneração natural (localmente) da espécie (distribuição em J invertido), porque não há banco de plântulas formado. A baixa densidade e agregação, além da ausência de um banco de plântulas, junto ao diâmetro médio observado para adultos (14 cm), sugerem que a população foi drasticamente suprimida no passado.

<b>Ferns influence on the woody species seedling bank in semi-deciduous forest, Southern Brazil

Different species of plants can act as environmental filters affecting the composition, structure and spatial distribution of seeds and seedlings of forest species. This study aimed to examine whether the presence of the fern stratum acts as a biotic environmental filter on the woody species seedling bank in a semi-deciduous forest remnant (Atlantic biome), Southern Brazil. Two experiments were developed in areas with ferns (F) and ferns-free (NF): a) richness and abundance of woody seedling bank were determined in 10 plots (25 m 2 ) in each area; b) seedlings abundance of Actinostemon concolor (Spreng.) Mull. Arg., Aspidosperma polyneuron Mull. Arg., Euterpe edulis Mart., Guarea kunthiana A. Juss. and Inga marginata Kunth were monitored for a year in three areas F, NF and an area with ferns whose fronds were cut (CF). In this experiment, it was used five plots (4 m 2 ) in each area. The abundance of seedlings (considering all species) was higher in F areas and ferns positively and negatively affected the abundance of A. polyneuron and G. kunthiana , respectively. It is possible to conclude that ferns worked as a selective environmental filter for some woody species.

Life history ofAdenostemma brasilianum(Pers.) Cass. (Eupatorieae, Asteraceae): A psychophilous herbaceous species of the Brazilian Atlantic Forest understory1

Abstract Adenostemma brasilianum is an herbaceous asteracean pollinated by male Ithomiinae butterflies. These insects feed on the nectar, which contains pyrrolizidine alkaloids, and depend on these compounds for their defense and reproduction. The life history of this species was described from seedlings to the death of adult plants. In addition, we analyzed its reproductive phenology and identified herbivores. The study was conducted in southeastern Brazil, in a semideciduous seasonal forest fragment. Fifty plants with up to two pairs of well-defined leaves were monitored, on which we observed buds, flowers, dispersed diaspores, and herbivores. We labeled 140 capitula in the bud stage and monitored them from anthesis of the first flowers to diaspore dispersal. Adenostemma brasilianum is biennial and monocarpic, and establishes a seedling bank within about 9 months (from February to October, in the first year of life). Plant mortality resulting from physical damage was high (46%) at the beginning of the r...

Negative canopy–understorey interaction shapes the sapling bank of Fagus crenata in a cool-temperate, conifer–hardwood mixed forest

Negative density-dependence (NDD) is a major mechanism for shaping forest communities. However, its influence on species coexistence in conifer–hardwood mixed forests remains unclear. We aimed to determine whether NDD influences establishment of the seedling and/or sapling bank of Fagus crenata in an evergreen, coniferous Cryptomeria japonica-dominated stand, focusing on canopy structure (openness, distance from mature plants and species composition). For F. crenata trees, we analysed the spatial pattern using the pair-correlation function g(r) to test for NDD and spatial correspondence to canopy structure in two study plots established in a cool-temperate, old-growth conifer–hardwood mixed forest in western Japan. We also analysed the height growth of offspring and understorey light condition with respect to canopy structure. We detected evidence of NDD among neighbours during the transition of seedlings (age ≤ 4 years) to saplings (age > 4 years, stem length 4 years) was elevated under the canopy of C. japonica, which was lighter than under that of F. crenata. Our results suggest that F. crenata recruitment was affected by NDD at the seedling-to-sapling transition under the conspecifics and allowed for the formation of the sapling bank under C. japonica canopies beyond the drip lines of conspecifics.

Seedling establishment in a masting desert shrub parallels the pattern for forest trees

The masting phenomenon along with its accompanying suite of seedling adaptive traits has been well studied in forest trees but has rarely been examined in desert shrubs. Blackbrush (Coleogyne ramosissima) is a regionally dominant North American desert shrub whose seeds are produced in mast events and scatter-hoarded by rodents. We followed the fate of seedlings in intact stands vs. small-scale disturbances at four contrasting sites for nine growing seasons following emergence after a mast year. The primary cause of first-year mortality was post-emergence cache excavation and seedling predation, with contrasting impacts at sites with different heteromyid rodent seed predators. Long-term establishment patterns were strongly affected by rodent activity in the weeks following emergence. Survivorship curves generally showed decreased mortality risk with age but differed among sites even after the first year. There were no detectable effects of inter-annual precipitation variability or site climatic differences on survival. Intraspecific competition from conspecific adults had strong impacts on survival and growth, both of which were higher on small-scale disturbances, but similar in openings and under shrub crowns in intact stands. This suggests that adult plants preempted soil resources in the interspaces. Aside from effects on seedling predation, there was little evidence for facilitation or interference beneath adult plant crowns. Plants in intact stands were still small and clearly juvenile after nine years, showing that blackbrush forms cohorts of suppressed plants similar to the seedling banks of closed forests. Seedling banks function in the absence of a persistent seed bank in replacement after adult plant death (gap formation), which is temporally uncoupled from masting and associated recruitment events. This study demonstrates that the seedling establishment syndrome associated with masting has evolved in desert shrublands as well as in forests.

Vegetative propagation through stem cuttings and air layering in Salacia malabarica Gamble, Bull. - an endemic climber of Southern Western Ghats

Salacia malabarica (Celastraceae), an important endemic climber of the southern Western Ghats is found very poor seedling bank in this natural habitats. This will lead to the untimely endangerment of the species in near future. The present study is therefore, aimed to develop and standardize the clonal propagation techniques through stem cuttings and air layering methods with the aid of auxins. The highest rooting of 90% was achieved with the use of NAA-1000 ppm from tender stem cuttings of 10-12 years old plant and air layering success was also found to be 80% by the use of NAA-1000 ppm from the same age of plants used for stem rooting.

Unfavourable microsites, competing vegetation and browsing restrict post-disturbance tree regeneration on extreme sites in the Northern Calcareous Alps

Changing natural disturbance regimes threaten forest functions in the Northern Calcareous Alps, with steep, sun-exposed sites on shallow soils at particular risk due to inhibited recovery. Natural tree regeneration after severe disturbances may fail due to extreme microclimate, dense layers of competing understorey vegetation and herbivory. In order to gain insight into regeneration patterns and dynamics, chronosequences of disturbed forest sites were selected along a longitudinal section of the Austrian Northern Calcareous Alps. Regeneration densities of trees, cover of competing vegetation and microsite characteristics were recorded on a total of 19 disturbed sites and in the respective adjacent forest stands. Although high densities of germinants and small seedlings (≤0.1 m) were recorded in the forest stands, recruitment establishment (trees >0.1 m) frequently failed on both disturbed sites and adjacent stands. In fact, half of the disturbed sites were found to be without sufficient regeneration and no significant increase of regeneration density was detected with time since disturbance. Overall, regeneration densities reflect a very critical situation along the disturbance chronosequence. Even if seedling banks are composed of individuals smaller than 0.1 m, seedling mortality is high. General linear mixed models revealed positive effects of convex microsites and thick organic layers on Picea abies (L.) Karst. establishment, while dense litter and grass cover impaired spruce regeneration. Regeneration of other tree species was scarce. The results corroborate the urgent need for establishing seedling banks of larger individuals (>0.1 m) and for reducing ungulate browsing. They also underline the need for comprehensive long-term studies to better understand the dynamic processes, driving resilience of disturbed sites.

Seedling survival patterns in Macaronesian laurel forest: a long-term study in Tenerife (Canary Islands)

Seedling dynamics of the Macaronesian laurel forest have been monitored for the first time in a long-term study to determine whether the survival of the seedling community is affected by slope aspect and forest structure. More than 4000 seedlings were monitored monthly from 2000 to 2003 in well-preserved laurel forest stands on Tenerife, Canary Islands. Trees and seedling bank species composition differed between windward and leeward slopes. On both slopes, differences in species composition between the canopy and the seedling bank suggest future shifts in canopy species composition towards a more advanced successional stage. Surprisingly, seedling survival was higher on the drier leeward than on the wetter windward slope. This seems to be related to environmental and structural differences of the forest stand between slope aspects (e.g. larger trees, higher canopy cover and tree density and lower light penetration in windward plots). Analysed species have long-lived seedling banks with survival rates of 12 per cent and 5 per cent in the long term (12 years) for leeward and windward slopes, respectively, with significant differences among species. This result reflects the high regeneration potential of the forest in well-preserved stands, indicating that no management interventions are required to ensure the regeneration of this endemic forest.

Large sample area and size are needed for forest soil seed bank studies to ensure low discrepancy with standing vegetation.

A large number of small-sized samples invariably shows that woody species are absent from forest soil seed banks, leading to a large discrepancy with the seedling bank on the forest floor. We ask: 1) Does this conventional sampling strategy limit the detection of seeds of woody species? 2) Are large sample areas and sample sizes needed for higher recovery of seeds of woody species? We collected 100 samples that were 10 cm (length) ×10 cm (width) ×10 cm (depth), referred to as larger number of small-sized samples (LNSS) in a 1 ha forest plot, and placed them to germinate in a greenhouse, and collected 30 samples that were 1 m×1 m×10 cm, referred to as small number of large-sized samples (SNLS) and placed them (10 each) in a nearby secondary forest, shrub land and grass land. Only 15.7% of woody plant species of the forest stand were detected by the 100 LNSS, contrasting with 22.9%, 37.3% and 20.5% woody plant species being detected by SNLS in the secondary forest, shrub land and grassland, respectively. The increased number of species vs. sampled areas confirmed power-law relationships for forest stand, the LNSS and SNLS at all three recipient sites. Our results, although based on one forest, indicate that conventional LNSS did not yield a high percentage of detection for woody species, but SNLS strategy yielded a higher percentage of detection for woody species in the seed bank if samples were exposed to a better field germination environment. A 4 m2 minimum sample area derived from power equations is larger than the sampled area in most studies in the literature. Increased sample size also is needed to obtain an increased sample area if the number of samples is to remain relatively low.

Quantifying targets to manage invasion risk: light gradients dominate the early regeneration niche of naturalized and pre-commercial Miscanthus populations

Prospective bioenergy crops have caused concern about their invasive potential because they often share characteristics with known invasive species. Studies that examine the factors that limit regeneration of these crop species will be crucial for identifying vulnerable habitats and devising management strategies to reduce the likelihood of escape from cultivation. Using a response surface design, we investigated the influence of light availability, soil moisture, and litter cover on recruitment and establishment of a potential biofuel cultivar of Miscanthus as well as an invasive congener. Responses were similar for the two plant types. Light availability had a strong influence on seedling success at both stages, though light limitation prevented establishment only at the lowest light level. Although variation in recruitment rates was low within plant types, establishment varied extensively in response to different light conditions. Low variation in Miscanthus seedling recruitment that led to establishment of a seedling bank under a range of light intensities may facilitate a “sit and wait” situation that raises the likelihood of successful escapes. Therefore, management efforts that restrict seed movement and increase light competition for seedlings will be important for lowering invasion risk. As deliberate introductions of bioenergy crops increase, ecological studies that quantify conditions required for successful escapes will be key to helping agronomists and managers mitigate the risk of unintended invasions.

Mecanismos de regeneração natural em remanescente de Floresta Ombrófila Mista, RS, Brasil

Neste estudo, objetivou-se caracterizar os mecanismos de regeneração natural em um remanescente de Floresta Ombrófila Mista. O trabalho foi realizado na Floresta Nacional de São Francisco de Paula, RS, Brasil, utilizando seis conglomerados de 1 ha, com 16 parcelas (20×20 m) cada, desconsiderando 10 m de bordadura. A amostragem da chuva de sementes (CS) foi realizada em 96 coletores circulares (1 m²), distribuídos no centro de cada parcela. O banco de sementes do solo (BS) foi amostrado de forma aleatória, a 3 m de cada coletor da CS, e o banco de plântulas (BP) foi amostrado em subparcelas de 2×2 m, alocadas a 4 m dos coletores, contabilizando o número de indivíduos (altura > 30 cm e diâmetro à altura do peito (DAP) < 1 cm) para cada espécie. Os mecanismos de regeneração foram avaliados quanto à composição florística e estrutura horizontal. Na CS, foram amostradas 81 espécies, 46 gêneros e 28 famílias, no BS, 103, 65 e 41 e no BP, 88, 57 e 36, respectivamente. A riqueza encontrada e abundante frutificação de espécies com dispersão zoocórica indicam a importância da chuva de sementes como mecanismo estratégico para o equilíbrio da fauna e flora no ecossistema. O banco de sementes do solo demonstra potencial para colonização imediata e restabelecimento da vegetação após perturbações e o banco de plântulas consiste na principal estratégia de regeneração de muitas espécies arbóreas que compõe a atual estrutura da floresta.

FACTORS AFFECTING THE VEGETATION SUCCESSION OF MOIST·DECIDUOUS FORESTS AT SIGIRIYA SANCTUAR~SRILANKA

This study examines the vegetation succession of moist deciduous forests at the Sigiriyasanctuary and some factors affecting for this. Thirty eight 20x20m2 experimental plotswere established in sites ranging in disturbance history from areas abandoned for onemonth after swidden farming to forests not known to have been recently disturbed. Thevegetation was enumerated while the canopy openness, soil moisture and soil temperaturewere measured. Seed rain was monitored while the soil seed bank was enumerated threetimes over a year in four month intervals. Seedling bank was also enumerated in lx2m2quadrat in each experimental plot. Seed predation was examined by keeping seeds ofChloroxylon swietenia seeds in the experimental plots and by continuous observations.Succession appears to be a process of progressive change in species dominance and lossof less shade-tolerant subordinates rather than accumulation of new colonists. Both seedrain and soil seed bank in all these young successional forests contain many agriculturalweed species but the density of seeds of climax species is negligible. Consequently, theseedling bank is very poor and contains many agricultural weed and light demandingshrub species. The soil temperature in young successional forests is higher while the soilmoisture is lower than the older successional or high forests. After 18-20 years, the treesare released and shade-out light demanding species. This results in the death of most ofthe light demanding shrubs and as a consequence, root competition is reduced and morespace is available for the establishment of new immigrant climax forest species. The seedrain, soil seed bank and the seedling bank of 20-25 year old forests contain some seeds ofclimax forest species.High forests contain many climax forest tree ,IUd shrub species but seeds a.id seedlings ofvaluable timber tree species are rare in them. High seed predation is one reason for thissituation. Seedling bank is very fragmented and mostly contains individuals of climaxforest shrub species.It seems that the studied moist deciduous forests are somewhat degraded and thevegetation succession after a large scale disturbance is a slow process. Therefore,protection and rehabilitation of these forests are vital activities for their perpetuity.

Coevolution of mast seeding in trees and extended diapause of seed predators

Many trees in forests show synchronized and intermittent reproduction, which is called “masting” or mast seeding. According to recent theoretical studies, the evolution of masting is promoted both by recruitment through the seedling bank and by seed predators. An important class of specialist seed predators (e.g., weevils and some moths) are parasitoids that oviposit on or in fruits from which the next generation emerges over the following several years. This staggered emergence is called “extended diapause”. In this paper, we study the simultaneous evolution of tree masting and extended diapause of seed predators. If a fixed fraction of diapausing larvae matures every year, the evolution of trees results in masting (intermittent reproduction with a large fluctuation in reproductive activity) or non-masting (trees reproduce every year). The transition occurs discontinuously, showing evolutionary jumping. The range of seedling survivorship for which masting evolves is broader when the ovipositing efficiency and larval survivorship of the seed predators are large. Interestingly, the conditions for the evolution of masting are broadest for an intermediate fraction of extended diapause of seed predators. When both tree masting and the extended diapause of seed predators evolve simultaneously, the evolutionary end point of the fraction of extended diapause is clearly greater than the value that most favors masting evolution. The stochasticity caused by the finiteness of the number of trees tends to promote masting evolution.