Dispersal and recruitment dynamics in the fleshy‐fruited Persoonia lanceolata (Proteaceae)

Question: What is the role of dispersal, persistent soil seed banks and seedling recruitment in population persistence of fleshy‐fruited obligate seeding plant species in fire‐prone habitats? Location: Southeastern Australia. Methods: We used a long‐term study of a shrubby, fleshy‐fruited Persoonia species (Proteaceae) to examine (1) seed removal from beneath the canopy of adult plants; (2) seedling recruitment after fire; (3) the magnitude and location of the residual soil seed bank; and (4) the implications for fire management of obligate seeding species. We used demographic sampling techniques combined with Generalised Linear Modelling and regression to quantify population changes over time. Results: Most of the mature fruits (90%) on the ground below the canopy of plants were removed by Wallabia bicolor (Swamp wallaby) with 88% of seeds extracted from W. bicolor scats viable and dormant. Wallabies play an important role in moving seeds away from parent plants. Their role in occasional long distance dispersal events remains unknown. We detected almost no seed predation in situ under canopies (< 1%). Seedling recruitment was cued to fire, with post‐fire seedling densities 6‐7 times pre‐fire adult densities. After fire, a residual soil seed bank was present, as many seeds (77‐100%) remained dormant and viable at a soil depth where successful future seedling emergence is possible (0‐5 cm). Seedling survival was high (> 80%) with most mortality within 2 years of emergence. Plant growth averaged 17 cm per year. The primary juvenile period of plants was 7–8 years, within the period of likely return fire intervals in the study area. We predicted that the study population increased some five‐fold after the wildfire at the site. Conclusions: Residual soil seed banks are important, especially in species with long primary juvenile periods, to buffer the populations against the impact of a second fire occurring before the seed bank is replenished.     

Seed bank patterns in Restionaceae and Epacridaceae after wildfire in kwongan in southwestern Australia

Abstract. Post-fire seed germination, seedling mortality and seed banks were investigated in scrub-heath (kwongan) in SW Australia. Study species included herbaceous and woody, obligate seeders and resprouters in two non-bradysporous but significant plant families (Restionaceae and Epacridaceae). In all species, seedlings were recruited only in the first autumn-spring after fire and occurred in similar densities as the estimated germinable annual seed input. Seedlings were absent from unburnt vegetation. Although most species retained some residual seeds after fire, tests (excised embryo culture) indicated that a negligible number of seeds were germinable. Regardless of fire response or species, there appeared to be a large loss of seeds each year and in most cases, only a small proportion of the annual seed production was used in post-fire recovery of plants. Based on seedling: parent ratios, all species had the capacity to reconstitute parent densities from germinants in the first year after fire, but high seedling mortality and no further recruitment resulted in less seedlings than replacements for four resprouter Restionaceae and three Epacridaceae (all obligate seeders) at the end of the third year after fire.     

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.     

Bet‐hedging and germination in the Australian arid zone shrub Acacia ligulata

The diaspore of the Australian arid zone shrub Acacia ligulata is dispersed by birds and ants. To investigate the benefits of providing a dispersal structure attractive to both groups, we compared the germination response and viability of seeds eaten by birds, handled by ants or collected from trees to simulated precursors of germination: scarification, fire and rainfall were simulated. Seed germination and viability were related to the degree of preheating disturbance to the seed coat. Heating increased the germinability of seeds not scarified or eaten by birds. In the absence of heating, ingestion by birds increased germinability. Heating increased the mortality of seeds. Our results suggest that ingestion of seeds by birds may break seed dormancy and hence enable some seeds to germinate soon after dispersal. Alternatively, seeds not eaten by birds are likely to remain dormant until sufficiently scarified by soil or stimulated by fire. Consequently, in areas such as the Simpson Desert, A. ligulata may be able to use a range of seedling establishment ‘windows’ provided by monsoon rains, post‐fire environments and unseasonal winter rains, and also spread the risk of unsuccessful seedling establishment by retaining dormant seeds in the seedbank.     

Seed dynamics of resprouting shrubs in grassy woodlands: Seed rain,predators and seed loss constrain recruitment potential

Abstract Measuring the fate of seeds between seed production and seedling establishment is critical in understanding mechanisms of recruitment limitation of plants. We examined seed fates to better understand the recruitment dynamics of four resprouting shrubs from two families (Fabaceae and Epacridaceae) in temperate grassy woodlands. We tested whether: (i) pre‐dispersal seed predation affected seed rain; (ii) post‐dispersal seed predation limited seed bank accumulation; (iii) the size of the seed bank was related to seed size; and (iv) viable seeds accumulated in the soil after seed rain. There was a distinct difference in seed production per plant between plant families with the legumes producing significantly more seeds per individual than the epacrids. Seed viability ranged from 43% to 81% and all viable had seed or fruit coat dormancy broken by heat or scarification. Pre‐dispersal predation by Lepidopteran larvae removed a large proportion of seed from the legume seed rain but not the epacrids. Four species of ants (Notoncus ectatomoides, Pheidole sp., Rhytidoponera tasmaniensis and Iridomyrmex purpureus) were major post‐dispersal seed removers. Overall, a greater percentage of Hardenbergia (38%) and Pultenaea (59%) seeds were removed than the fleshy fruits of Lissanthe (14%) or Melichrus (0%). Seed bank sizes were small (<15 seeds m^?2) relative to the seed rain and no significant accumulation of seed in the soil was detected. Lack of accumulation was attributed to seed predation as seed decay was considered unlikely and no seed germination was observed in our study sites. Our study suggests that seed predation is a key factor contributing to seed‐limited recruitment in grassy woodland shrubs by reducing the number of seeds stored in the soil.     

Fire and flood: Soil‐stored seed bank and germination ecology in the endangered Carrington Falls Grevillea (Grevillea rivularis,Proteaceae)

Abstract Seed germination is dependent on the interaction between the dormancy state of a seed and the presence of favourable environmental conditions. Thus, the spectacular pulse of seedling recruitment in many Australian vegetation communities following disturbances such as fire can be attributed to changes in microsite conditions and/or the dormancy‐breaking effect of the disturbance on accumulated seed banks. Grevillea rivularis is a threatened species endemic to the area immediately above Carrington Falls in the NSW Southern Highlands. Most of the population is confined to the riparian vegetation zone in woodland and heath, and is therefore subject to periodic disturbance from fire and flood. For this species, a pulse of seedling recruitment has been recorded after fire, flood and mechanical soil disturbance. The aims of this study were to examine the density and vertical distribution of the soil‐stored seed bank and to investigate the role of heat and scarification as cues for germination of fresh and soil‐stored seed. There was a large seed bank under the canopies of established individuals (194 ± 73 seeds m^?2) and most seeds were found in the 0–2 cm and leaf‐litter layers of the soil profile. The germination response of soil‐stored and fresh seed was examined using a hierarchical series of laboratory experiments. Seeds of G. rivularis showed marked dormancy polymorphism. Thirty‐six percent of soil‐stored seed germinated without treatment, whereas no untreated fresh seeds germinated. Scarification or heating caused significant germination of dormant soil‐stored seed, but only scarification resulted in germination of dormant fresh seeds. These results highlight important differences in the dormancy state of soil‐stored and fresh seed. Thus, being a riparian species in a fire‐prone environment, the dormancy mechanisms in seeds of G. rivularis suit this species to disturbance by both fire and flood.     

Savanna fires increase rates and distances of seed dispersal by ants

Myrmecochory (seed dispersal by ants) is a prominent dispersal mechanism in many environments, and can play a key role in local vegetation dynamics. Here we investigate its interaction with another key process in vegetation dynamics—fire. We examine ant dispersal of seeds immediately before and after experimental burning in an Australian tropical savanna, one of the world’s most fire-prone ecosystems. Specifically, our study addressed the effects of burning on: (1) the composition of ants removing seeds, (2) number of seed removals, and (3) distance of seed dispersal. Fire led to higher rates of seed removal post-fire when compared with unburnt habitat, and markedly altered dispersal distance, with mean dispersal distance increasing more than twofold (from 1.6 to 3.8 m), and many distance dispersal events greater than the pre-fire maximum (7.55 m) being recorded. These changes were due primarily to longer foraging ranges of species of Iridomyrmex, most likely in response to the simplification of their foraging landscape. The significance of enhanced seed-removal rates and distance dispersal for seedling establishment is unclear because the benefits to plants in having their seeds dispersed by ants in northern Australia are poorly known. However, an enhanced removal rate would enhance any benefit of reduced predation by rodents. Similarly, the broader range of dispersal distances would appear to benefit plants in terms of reduced parent–offspring conflict and sibling competition, and the location of favourable seedling microsites. Given the high frequency of fire in Australian tropical savannas, enhanced benefits of seed dispersal by ants would apply for much of the year.     

The role of Rhytidoponera metallica (Hymenoptera,Formicidae) in facilitating post‐fire seed germination of three ant‐dispersed legume species

The fire avoidance hypothesis proposes that a benefit of seed dispersal by ants (myrmecochory) is to protect seeds from being killed during fire and to facilitate post‐fire germination of seeds that require heat shock to break their physical dormancy. The aim of this study was to quantify the effect of fire and seed burial by a predominant seed‐dispersing ant, Rhytidoponera metallica (subfamily: Ectatomminae) on germination levels of three ant‐dispersed legume species (Pultenaea daphnoides, Acacia myrtifolia and Acacia pycnantha). Experimental burial of seeds within aluminium cans at a site prior to being burnt and at an adjacent unburnt site showed that fire increased germination levels, particularly for seeds buried at 1‐ and 2‐cm deep and that overall, germination levels differed among the three plant species. To quantify seed burial depths and post‐fire germination levels facilitated by R. metallica ants, seeds were fed to colonies prior to fire at the burnt and unburnt sites. Of the seeds buried within nests that were recovered, between 45% and 75% occurred within the upper 6 cm of the soil profile, although unexpectedly, greater percentages of seeds were recovered from the upper 0–2 cm of nests in the unburnt site compared with nests in the burnt site. Germination levels of buried seeds associated with R. metallica nests ranged from 21.2% to 29.5% in the burnt site compared with 3.1–14.8% in the unburnt site. While increased seed germination levels were associated with R. metallica nests following fire, most seeds were buried at depths below those where optimal temperatures for breaking seed dormancy occurred during the fire. We suggest that R. metallica ants may provide fire avoidance benefits to myrmecochorous seeds by burying them at a range of depths within a potential germination zone defined by intra‐ and inter‐fire variation in levels of soil heating.     

Population dynamics of the shrub Acacia suaveolens (Sm.) Willd.: Survivorship throughout the life cycle,a synthesis

Survivorship in Acacia suaveolens was assessed through seedling and adult stages. Moisture stress was found to be the critical factor limiting early seedling survival. Both seedling and adult populations were characterized by periods of low mortality interspersed with pulses of high mortality. A composite survivorship curve for A. suaveolens based on nine sites predicts that some 20–25 years after afire, established plants should disappear from the above-ground flora if another fire does not occur. Fecundity and survivorship data were used to estimate the flux of seed in the soil over time in a hypothetical A. suaveolens population. From this it was predicted that, following establishment of plants after a fire, the seed-bank would rapidly reach a maximum after 6 years and thereafter slowly decline, until after 60 years there would be only as many seeds as there were original parental plants. The situation would vary with predispersal seed predation, seed predation on the soil surface, seed dispersal by ants to ‘unsafe sites’ and the size of the initial seed-bank prior to establishment. Only after a very long inter-fire period would A. suaveolens be eliminated from a site. Elimination of the species is also possible under very frequent fires. A 2–5 year fire-free period is needed for plants to reach maturity and another 6 years are needed to maximize seed input into the soil seed-bank. In addition, seedling recruitment following cool burns is low to non-existent as dormancy is not broken for most seeds in the soil during such burns.     

Edge Effects Act Differentially on Multiple Early Regeneration Stages of a Shade‐tolerant Tree Tapirira mexicana

Forest fragmentation is pervasive in tropical landscapes, and one pathway by which fragmentation may negatively impact populations is via edge effects. Early life‐stages are particularly important for species regeneration as they act as bottlenecks, but how edge effects may act differentially on different life‐stages is unknown. This study evaluated edge effects on multiple early life‐stages of a currently common animal‐dispersed, shade‐tolerant tree Tapirira mexicana (Anacardiaceae). The study was conducted in tropical premontane wet forest fragments in a highly deforested region of Costa Rica. The stages assessed were pre‐dispersal predation, primary dispersal, post‐dispersal predation, secondary dispersal, ex situ germination, in situ seed longevity, first and second year seedling abundance, second year seedling survivorship, and basal diameter growth. Results showed that impacts of edge effects were not equal across stages, but were limited to specific stages and times. One stage which may act as a bottleneck for species regeneration was pre‐dispersal predation. Over 60 percent of the seeds were predated by larvae, and predation was higher near the edge than interior habitat. Seeds lost viability within 10 d in the forest. Germination to first year seedling stage was also lower near edges, but such effect was eliminated within a year after that. Primary dispersal, seedling survivorship, and growth were not affected by proximity to edges, and both secondary dispersal and post‐dispersal predation were rare. This study demonstrates that current population abundance may not guarantee future species persistence and the importance of considering multiple life‐stages for a comprehensive assessment of forest fragmentation effects on species regeneration.     

蚁对植物种子的传播作用

许多种子植物依靠动物传播种子 ,称为动物传播。根据动物类群的不同 ,可分为哺乳类传播 ,鸟传播 ,鱼传播 ,蚁传播等。鸟传播和蚁传播的研究近年取得了很大的进展 ,但国内在这方面研究较缺乏 ,作者已就鸟传播作了综述报道 ,现将蚁传播的研究综述报道如下。1　蚁与植物的相互关系蚁类属膜翅目 (Ｈｙｍｅｎｏｐｔｅｒａ) ,蚁科 (Ｆｏｒｍｉｃｉ ｄａｅ) ,典型的社会性昆虫。多数蚁类是肉食性的 ,以小动物或更小的蚁类为食 ,但也有很多蚁类是植物食性的。在大多数生态系统中均有蚁类分布 ,而且蚁类数量众多 ,在森林生态系统中每 1ｈａ可达 6～10…     

Seed bank dynamics of the desert cactus Opuntia rastrera in two habitats from the Chihuahuan Desert

In desert environments the main input to the seed bank of many succulents is the seed rain through zoochory while high levels of granivory by rodents, birds and ants are the main cause of subsequent losses. In the patchy environment of arid lands the characteristics of both processes may vary between habitats causing differences in the recruitment of new genets. To test this hypothesis we used populations of the desert cactus Opuntia rastrera which has different recruitment rates in the two adjacent habitats where it grows. In Opuntia-dominated scrublands (nopaleras, density ca. 4,000 plants/ha) 1 seedling out of 7,000,000 seeds establish, whereas in grasslands (density ca. 100 plants/ha) this ratio is 1:20,000. From 1996 until 1998 the seed rain, seed removal by granivores and seed abundance in the soil were monitored in both habitats. Results showed striking differences in the dynamics of the seed bank of both habitats. Seed rain was 8.5 times bigger in nopaleras than in grasslands. In nopaleras most seeds were removed by rodents while the quantities of seeds removed by rodents, birds and ants in grasslands were similar. One year after dispersal (the time necessary to break seed dormancy) only 6% of original nopalera seeds and 12% of grassland seeds remained. After germination trials only 1% (ca. 15,000 seeds/ha) and 2% (ca. 2,500 seeds/ha) respectively were viable. These differences in the effective seed bank (6 times bigger in nopaleras) can not explain the differences in genet recruitment (which is several orders of magnitude bigger in grasslands). Apparently the between habitat difference in nurse plant availability and in rodent density (which inflict a strong hervibory upon seedlings) can explain the differences in genet recruitment. It is speculated that this between habitat difference in genet recruitment suggests that the species evolved in less extreme environments (e.g. grasslands) than desert scrublands which, in turn, are colonised due to the singular ability of O. rastrera for vegetative propagation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Seed dispersal by ants in the semi-arid Caatinga of North-East Brazil

BACKGROUND AND AIMS: Myrmecochory is a conspicuous feature of several sclerophyll ecosystems around the world but it has received little attention in the semi-arid areas of South America. This study addresses the importance of seed dispersal by ants in a 2500-km(2) area of the Caatinga ecosystem (north-east Brazil) and investigates ant-derived benefits to the plant through myrmecochory. METHODS: Seed manipulation and dispersal by ants was investigated during a 3-year period in the Xingó region. Both plant and ant assemblages involved in seed dispersal were described and ant behaviour was characterized. True myrmecochorous seeds of seven Euphorbiaceae species (i.e. elaiosome-bearing seeds) were used in experiments designed to: (1) quantify the rates of seed cleaning/removal and the influence of both seed size and elaiosome presence on seed removal; (2) identify the fate of seeds dispersed by ants; and (3) document the benefits of seed dispersal by ants in terms of seed germination and seedling growth. KEY RESULTS: Seed dispersal by ants involved one-quarter of the woody flora inhabiting the Xingó region, but true myrmecochory was restricted to 12.8 % of the woody plant species. Myrmecochorous seeds manipulated by ants faced high levels of seed removal (38-84 %) and 83 % of removed seeds were discarded on ant nests. Moreover, seed removal positively correlated with the presence of elaiosome, and elaiosome removal increased germination success by at least 30 %. Finally, some Euphorbiaceae species presented both increased germination and seedling growth on ant-nest soils. CONCLUSIONS: Myrmecochory is a relevant seed dispersal mode in the Caatinga ecosystem, and is particularly frequent among Euphorbiaceae trees and shrubs. The fact that seeds reach micro-sites suitable for establishment (ant nests) supports the directed dispersal hypothesis as a possible force favouring myrmecochory in this ecosystem. Ecosystems with a high frequency of myrmecochorous plants appear not to be restricted to regions of nutrient-impoverished soil or to fire-prone regions.     

Establishment of chasmogamous and cleistogamous seedlings of an ant-dispersed UNDERSTORY HERB,CALATHEA MICANS (Marantaceae)

This study compares the establishment success of cleistogamous (CL, obligately selfed) and chasmogamous (CH, potentially outcrossed) seeds of the neotropical understory herb, Calathea micans (Marantaceae). In this species, CH and CL seeds are morphologically identical and are both dispersed by ants. I measured dispersal distances and analyzed seedling recruitment and seedling size for ant-planted CH and CL seeds, a protocol made possible by the fact that the seed coat of C. micans can be indelibly marked and remains attached to the base of the seedling for a few months. Seeds were taken by ants from experimental depots placed in natural conditions. In a second experiment, I planted CH and CL seeds in gap and understory sites to determine the effects of seed type and light on germination percentage, date of emergence, and seed and seedling survivorship. Ant-planted CH and CL seedlings did not differ in dispersal distance. CH and CL seeds did not differ significantly in recruitment probability and seedling size in either experiment. However, for the ant-planted seedlings, CH recruitment was higher in the understory than in the gap, while CL recruitment was uniform across light environments. In conclusion, I found a difference in the establishment success of CH and CL seeds in this understory herb, only after dispersal by ants in field conditions.     

Linking seed dispersal,germination and seedling recruitment in the invasive species <Emphasis Type="Italic">Berberis darwinii</Emphasis> (Darwin’s barberry)

Seedling recruitment is a multi-phased process involving seed production, dispersal, germination, seedling establishment and subsequent survival. Understanding the factors that determine success at each stage of this process is of particular interest to scientists and managers seeking to understand how invasive species spread and persist, and identify critical stages for management. To understand the factors and processes influencing recruitment of the invasive species Berberis darwinii Hook. (Darwin’s barberry), temporal and spatial patterns of seed dispersal, germination and seedling establishment were examined. Seed dispersal from a large source population was measured over two fruiting seasons, and subsequent patterns of seedling emergence and survival within each cohort were measured. Seed longevity was tested under both natural and artificial conditions. Seeds were widely dispersed by birds, up to 450 m from the source population. Dispersal was essential to seedling establishment, as few seedlings survived beneath the parent canopy. Seeds were relatively short-lived in the soil under both field and glasshouse conditions, with few surviving for more than 1 year. Patterns of newly emerged seedlings largely reflected patterns of seed rain, but seedling survival was significantly affected by distance from source population, seedling density and light environment. These results suggest that recruitment of B. darwinii is dependent on dispersal of seeds to favourable microsites. Management priorities should include the removal of fruiting plants, and seedling control in highlight areas.     

A spatially explicit analysis of seedling recruitment in the terrestrial orchid Orchis purpurea

Seed dispersal and the subsequent recruitment of new individuals into a population are important processes affecting the population dynamics, genetic diversity and spatial genetic structure of plant populations. Spatial patterns of seedling recruitment were investigated in two populations of the terrestrial orchid Orchis purpurea using both univariate and bivariate point pattern analysis, parentage analysis and seed germination experiments. Both adults and recruits showed a clustered spatial distribution with cluster radii of c. 4-5 m. The parentage analysis resulted in offspring-dispersal distances that were slightly larger than distances obtained from the point pattern analyses. The suitability of microsites for germination differed among sites, with strong constraints in one site and almost no constraints in the other. These results provide a clear and coherent picture of recruitment patterns in a tuberous, perennial orchid. Seed dispersal is limited to a few metres from the mother plant, whereas the availability of suitable germination conditions may vary strongly from one site to the next. Because of a time lag of 3-4 yr between seed dispersal and actual recruitment, and irregular flowering and fruiting patterns of adult plants, interpretation of recruitment patterns using point patterns analyses ideally should take into account the demographic properties of orchid populations.     

生物土壤结皮对种子萌发和幼苗建植的影响研究进展

生物土壤结皮（BSC）在陆地生态系统中具有重要的生态地位,尤其是旱地生态系统中,BSC占据了种子植物之间的广阔地面。因此,BSC的发展必然影响种子植物更新过程与植被空间格局;但其作用方式、影响程度等因相关研究涉及多气候要素、土壤类型、BSC组成物种和种子植物物种的差异及其不同组合,导致目前的研究结论存在广泛争议。研究综合论述了BSC改变地表微形态对种子传播过程的影响;BSC改变土壤特性（物理、化学、生物学）对种子萌发和幼苗存活与建植等关键环节的影响;并结合种子形态特征及种子萌发、幼苗建植的性状等,综合分析了BSC对种子传播、种子萌发与幼苗建植等更新过程的潜在影响机理;探讨了目前研究矛盾性结论产生的原因。总体来说,深入研究并全面揭示BSC对种子植物更新过程的影响,应加强学科交叉,将分子生物学、植物生理学、生物化学等微观研究,与遥感、野外生态因子过程监测、控制实验等宏观、中观研究结合,从机理到过程方面动态研究BSC对种子植物更新过程的影响,并引入水文模型、气候模型、种群动态模型等模型预测方法,研究气候变化、各类干扰频发的情景下,BSC对种子传播、萌发及幼苗建植过程的潜在影响,以期促进对BSC与种子植物间相互关系的研究,加深对干旱脆弱生态系统植被发展规律的认识。     

Multiple stages of tree seedling recruitment are altered in tropical forests degraded by selective logging

Tropical forest degradation is a global environmental issue. In degraded forests, seedling recruitment of canopy trees is vital for forest regeneration and recovery. We investigated how selective logging, a pervasive driver of tropical forest degradation, impacts canopy tree seedling recruitment, focusing on an endemic dipterocarp Dryobalanops lanceolata in Sabah, Borneo. During a mast‐fruiting event in intensively logged and nearby unlogged forest, we examined four stages of the seedling recruitment process: seed production, seed predation, and negative density‐dependent germination and seedling survival. Our results suggest that each stage of the seedling recruitment process is altered in logged forest. The seed crop of D. lanceolata trees in logged forest was one‐third smaller than that produced by trees in unlogged forest. The functional role of vertebrates in seed predation increased in logged forest while that of non‐vertebrates declined. Seeds in logged forest were less likely to germinate than those in unlogged forest. Germination increased with local‐scale conspecific seed density in unlogged forest, but seedling survival tended to decline. However, both germination and seedling survival increased with local‐scale conspecific seed density in logged forest. Notably, seed crop size, germination, and seedling survival tended to increase for larger trees in both unlogged and logged forests, suggesting that sustainable timber extraction and silvicultural practices designed to minimize damage to the residual stand are important to prevent seedling recruitment failure. Overall, these impacts sustained by several aspects of seedling recruitment in a mast‐fruiting year suggest that intensive selective logging may affect long‐term population dynamics of D. lanceolata. It is necessary to establish if other dipterocarp species, many of which are threatened by the timber trade, are similarly affected in tropical forests degraded by intensive selective logging.     

干扰对动物传播森林植物种子有效性影响的研究进展

干扰在森林生态系统中普遍存在,并影响森林的更新和演替.动物传播种子是种子更新的必经阶段,其对森林干扰的响应在一定程度上能够预测未来的森林群落组成和结构变化,对于明确森林演替方向具有重要意义.本文论述了森林干扰对动物传播种子有效性(包括动物传播种子的数量和质量)影响研究的生态学意义,全面揭示了自然干扰(火干扰、林窗干扰等)和人为干扰(生境破碎化、狩猎、采伐等)对动物传播种子数量、传播距离以及传播后幼苗更新影响的研究进展,指出干扰通过影响动物种群动态,进而造成动物传播种子数量发生了改变,动物传播种子的距离对干扰的响应基本表现出轻微负相关;干扰对传播后幼苗更新的影响结果因干扰类型的不同而复杂多变,干扰迹地环境因子的变化也影响着传播后的种子萌发和幼苗更新.干扰对动物传播种子有效性影响研究中存在的问题,主要表现为火干扰迹地恢复过程、增益性的干扰(如抚育、间伐、林窗)等对种子传播有效性影响研究的匮乏,以及忽略了温带森林内的干扰对动物传播种子的影响等.今后,应开展干扰对种子传播有效性的长期研究;对于干扰多发地带的森林,应高度重视增益性干扰影响动物传播植物种子的研究.     

Seed predation limits post-fire recruitment in the waratah (<Emphasis Type="Italic">Telopea speciosissima</Emphasis>)

Seed predation may reduce recruitment in populations that are limited by the availability of seeds rather than microsites. Fires increase the availability of both seeds and microsites, but in plants that lack a soil- or canopy-stored seed bank, post-fire recruitment is often delayed compared to the majority of species. Pyrogenic flowering species, such as Telopea speciosissima, release their non-dormant seeds more than 1 year after fire, by which time seed predation and the availability of microsites may differ from that experienced by plants recruiting soon after fire. I assessed the role of post-dispersal seed predation in limiting seedling establishment after fire in T. speciosissima, in southeastern Australia. Using a seed-planting experiment, I manipulated vertebrate access to seeds and the combined cover of litter and vegetation within experimental microsites in the 2 years of natural seed fall after a fire. Losses to vertebrate and invertebrate seed predators were rapid and substantial, with 50% of seeds consumed after 2 months in exposed locations and after 5 months when vertebrates were excluded. After 7 months, only 6% of seeds or seedlings survived, even where vertebrates were excluded. Removing litter and vegetation increased the likelihood of seed predation by vertebrates, but had little influence on losses due to invertebrates. Microsites with high-density vegetation and litter cover were more likely to have seed survival or germination than microsites with low-density cover. Recruitment in pyrogenic flowering species may depend upon the release of seeds into locations where dense cover may allow them to escape from vertebrate predators. Even here, conditions suitable for germination must occur soon after seed release for seeds to escape from invertebrate predators. Seed production will also affect recruitment after any one fire, while the ability of some juvenile and most adult plants to resprout after fire buffers populations against rapid declines when there is little successful recruitment.