Gap-phase dynamics and coexistence of a long-lived pioneer and shade-tolerant tree species in the canopy of an old-growth coastal temperate rain forest of Chiloé Island, Chile

Aim A major question with regard to the ecology of temperate rain forests in south‐central Chile is how pioneer and shade‐tolerant tree species coexist in old‐growth forests. We explored the correspondence between tree regeneration dynamics and life‐history traits to explain the coexistence of these two functional types in stands apparently representing a non‐equilibrium mixture. Location This study was conducted in northern Chiloé Island, Chile (41.6° S, 73.9° W) in a temperate coastal rain forest with no evidence of stand disruption by human impact. Methods We assessed stand structure by sampling all stems within two 50 × 20 m and four 5 × 100 m plots. A 600‐m long transect, with 20 uniformly spaced sampling points, was used to quantify seedling and sapling densities, obtain increment cores, and randomly select 10 tree‐fall gaps. We used tree‐ring analysis to assess establishment periods and to relate the influences of disturbances to the regeneration dynamics of the main canopy species. Results Canopy emergent tree species were the long‐lived pioneer Eucryphia cordifolia and the shade‐tolerant Aextoxicon punctatum. Shade‐tolerant species such as Laureliopsis philippiana and several species of Myrtaceae occupied the main canopy. The stem diameter distribution for E. cordifolia was distinctly unimodal, while for A. punctatum it was multi‐modal, with all age classes represented. Myrtaceae accounted for most of the small trees. Most tree seedlings and saplings occurred beneath canopy gaps. Based on tree‐ring counts, the largest individuals of A. punctatum and E. cordifolia had minimum ages estimated to be > 350 years and > 286 years, respectively. Shade‐tolerant Myrtaceae species and L. philippiana had shorter life spans (< 200 years). Most growth releases, regardless of tree species, were moderate and have occurred continuously since 1750. Main conclusions We suggest that this coastal forest has remained largely free of stand‐disrupting disturbances for at least 450 years, without substantial changes in canopy composition. Release patterns are consistent with this hypothesis and suggest that the disturbance regime is dominated by individual tree‐fall gaps, with sporadic multiple tree falls. Long life spans, maximum height and differences in shade tolerance provide a basis for understanding the long‐term coexistence of pioneer and shade‐tolerant tree species in this coastal, old‐growth rain forest, despite the rarity of major disturbances.     

Effects of Light Gaps and Litter Removal on the Seedling Performance of Six African Timber Species1

Valuable timber tree species frequently show poor regeneration after selective logging in tropical forests. Small size of logging gaps, lack of soil disturbance, and limited seed availability have each been blamed for observed regeneration failures. We investigated seed germination and seedling performance using a split‐plot factorial design involving light availability and litter removal for six Central African timber tree species, hypothesizing that canopy gaps and litter removal would improve seedling establishment, and that less shade‐tolerant species would show stronger responses to both factors. Contrary to our expectations, significantly more germinants established on intact litter than on exposed mineral soil 3 mo after seeding. After 18 mo, seedling survival, height and diameter growth, leaf area, and rooting depth were all much higher in gap plots than in the understory for all species, with the exception of Gilbertiodendron dewevrei, a highly shade‐tolerant species whose survival was higher in the understory. Leaf production was negatively influenced by litter removal in the least shade‐tolerant species, Nauclea diderrichii, with weak or positive effects in other species. G. dewevrei, while displaying a low‐light threshold for growth, exhibited a surprisingly high growth response to increasing light comparable to more shade‐intolerant species, a response that may help explain its local competitive dominance in the region. Due to the rapid closure of small gaps, we suggest that shade‐intolerant species such as N. diderrichii, Khaya anthotheca, and Entandrophragma utile might benefit from more intensive silvicultural practices that create larger canopy gaps.     

Small gap dynamics in the southern boreal forest of eastern Canada: Do canopy gaps influence stand development?

Question: To what extent do small‐scale disturbances in the forest canopy, created by natural disturbance agents, affect stand development? Doubts exist as to whether small canopy openings have any real effect on the understory tree recruitment, especially in boreal forests. Location: Conifer and mixed stands in the Gaspesian region in eastern Québec. The main natural disturbance agents are recurring outbreaks of Choristoneura fumiferana (eastern spruce budworm) and winds. Methods: Linear transects in 27 sites were used to describe the gap (< 0.1 ha) regime parameters, including gap fraction, gap size and change in disturbance severity through time. Three stand types were distinguished, based on a gradient of abundance of tree host species for the eastern spruce budworm. The impact of gaps was evaluated on the basis of changes in the number, the period of recruitment, and the composition of tree saplings present within gap areas. Changes were measured along the gap size gradient, and according to the pattern of recent budworm epidemics. Results: The gap fraction is highly variable (18%‐64%) and is on average relatively high (42%). Gap sizes have a positively skewed distribution. In most cases the growth rate among gap filling saplings increased sufficiently to date disturbance events. The composition and the structure of understory trees were affected by gap formation. The number of shade‐intolerant tree species did increase during or following periods of particularly severe canopy disturbances. However, the establishment or survival of shade intolerant species was not restricted to larger gaps or more intensely disturbed periods. Conclusions: In sub‐boreal forests of Eastern Canada, small scale disturbances in the tree canopy influence stand regeneration dynamics, but not to the extent that parameters such as sapling composition and recruitment patterns depend on gap regime characteristics.     

Seed rain of fleshy and dry propagules in different habitats in the temperate rainforests of Chiloé Island,Chile

In temperate rainforests on Chiloé Island in southern Chile (42°S), most canopy trees bear fleshy, avian‐dispersed propagules, whereas emergent tree species have dry, wind‐borne propagules. In the present study, the following hypothesis was tested: regardless of species, fleshy propagules are deposited in greater numbers in canopy gaps and in forest margins and hence have a more heterogeneous seed shadow than wind‐dispersed propagules. To test this hypothesis, the seed rains of these two types of propagules were compared in the following forest habitats: (i) tree‐fall gaps (edges and centre); (ii) forest margins with adjacent pastures; and (iii) under closed canopy (forest interior). Seed collectors (30‐cm diameter) were placed in two (15 and 100 ha) remnant forest patches (n = 60–100 seed collectors per patch) distributed in the four habitats. Seeds were retrieved monthly from each collector during two reproductive seasons (1996, 1997). In both years, the seed rain was numerically dominated by two species with dry propagules (Laureliopsis philippiana and Nothofagus nitida) and three species with fleshy fruits (Drimys winteri, Amomyrtus luma, and Amomyrtus meli). The seed shadows of the two species with dry, wind‐dispersed seeds differed markedly. Seeds of L. philippiana were deposited predominantly in canopy openings, whereas N. nitida seeds fell almost entirely in the forest interior. The fleshy‐fruited species, Drimys and Amomyrtus spp., had similar seed deposition patterns in the various habitats studied, but the between‐year differences in seed rain were greater in Drimys winteri than in Amomyrtus spp. Although no more than 10% of fleshy‐fruited propagules reached the margins of the patch, approximately 7% of these were carried there by birds. Every year, canopy gaps (pooling data from edges and centres) concentrated approximately 60% of the total seed rain of both propagule types in both forest patches. Forest margins received less than 20% of the total seed rain, which was largely dominated by fleshy‐fruited species. Seed shadows were a species‐specific attribute rather than a trait associated with propagule type and dispersal mode.     

Chance versus determinism in canopy gap regeneration in coastal scarp forest in South Africa

Question: Is tree regeneration in canopy gaps characterized by chance or predictable establishment. Location: Coastal scarp forests, Umzimvubu district, Eastern Cape Province, South Africa. Methods: Estimation of richness of gap‐filling species across canopy gaps of different size. Data are compared with regeneration under the canopy. Probability of self‐replacement of gap forming species is calculated. Results: Forest area under natural gap phase was 7.8%, caused mostly by windthrow (54%). The abundance and average size of gaps (87.8 m²) suggests that species diversity may be maintained by gap dynamics. However, only four of 53 gap‐filler species displayed gap size specialization and these were pioneer species. An additional 13 species were more common in larger gaps but there was no gradient in composition of gap‐filler species across gap size (p= 0.61). Probabilities of self‐replacement in a gap were low (< 0.3) and common canopy species were equally abundant in gaps and the understorey. Species composition in gaps showed no pattern of variation, i.e. was unpredictable, which suggests absence of a successional sequence within tree‐fall gaps. There was also only a slight increase in species richness in gaps at intermediate levels of disturbance. Conclusions: Coastal scarp forest appears not to comprise tightly co‐evolved, niche‐differentiated tree species. Unpredictable species composition in gaps may be a chance effect of recruitment limitation of species from the species pool. Chance establishment slows competitive exclusion and may maintain tree diversity in these forests. These data suggest that current levels (≤ 3 gaps per ha) of selective tree harvesting may not cause a reduction in species richness in this forest.     

The potential of small exclosures in assisting regeneration of coffee shade trees in South‐Western Ethiopian coffee forests

Ethiopian Afromontane moist forests where coffee grows as understorey shrub are traditionally managed by the local communities for coffee production through thinning of the shade tree canopy and slashing of competing undergrowth. This management practice has a negative impact on the coffee shrubs, because the removal of shade tree saplings and seedlings reduces the succession potential of the shade tree canopy, which threatens the very existence of the shade coffee production system. We assessed the functionality of small exclosures to initiate coffee shade tree canopy restoration through natural regeneration. Our results show that small exclosures have a strong restoration potential for the coffee shade trees preferred by farmers (Albizia schimperiana, A. gummifera and Millettia ferruginea), as evidenced from their seedling abundance, survival and growth. The regeneration of late‐successional tree species of the moist Afromontane forest was not successful in the small exclosures, most probably due to the low abundance or absence of adult trees as seed sources for regeneration. Therefore, temporary establishment of small exclosures in degraded coffee forest fragments where shade trees are getting old or dying is recommended for sustainable shade coffee production.     

The pristine rain forest? Remnants of historical human impacts on current tree species composition and diversity

Abstract Aim Tropical rain forests are often regarded as pristine and undisturbed by humans. In Central Africa, community‐wide disturbances by natural causes are rare and therefore current theory predicts that natural gap phase dynamics structure tree species composition and diversity. However, the dominant tree species in many African forests recruit poorly, despite the presence of gaps. To explain this, we studied the disturbance history of a species‐rich and structurally complex rain forest. Location Lowland rain forest in Southern Cameroon. Methods We identified the recruitment conditions of trees in different diameter classes in 16 ha of species‐rich and structurally complex ‘old growth’ rain forest. For the identification of recruitment preference we used independent data on the species composition along a disturbance gradient, ranging from shifting cultivation fields (representing large‐scale disturbance), to canopy gaps and old growth forest. Results In nine of sixteen 1‐ha forest plots the older trees preferred shifting cultivation fields for recruitment while younger trees preferred gaps and closed forest conditions. This indicates that these nine sites once experienced large‐scale disturbances. Three lines of evidence suggest that historical agricultural use is the most likely disturbance factor: (1) size of disturbed and undisturbed patches, (2) distribution of charcoal and (3) historical accounts of human population densities. Main conclusions Present‐day tree species composition of a structurally complex and species‐rich Central African rain forest still echoes historical disturbances, most probably caused by human land use between three to four centuries ago. Human impact on African rain forest is therefore, contrary to common belief, an issue not of the last decades only. Insights in historical use will help to get a more balanced view of the ‘pristine rain forest’, acknowledging that the dualism between ‘old growth’ and ‘secondary’ forest may be less clear than previously thought.     

Cordia millenii: on the risk of local extinction?

Selective logging of valuable tropical timber trees is a conservation concern because it threatens the long-term sustainability of forests. However, there is insufficient information regarding the postlogging recovery of harvested species. Here, I assessed the seed dispersal patterns, recruitment and abundance of Cordia millenii , a valuable timber tree in two Ugandan tropical rain forests that have been subjected to varying disturbance regimes. The aim was to determine the vulnerability of Cordia in these forests. The rate of seed dispersal was lower in the heavily disturbed Mabira Forest compared with the less disturbed Budongo Forest. Frugivores in Mabira were small-bodied individuals that spat seeds beneath fruiting trees, whereas 90% of the fruit in Budongo was consumed by large-bodied chimpanzees that disperse seeds over long distances. Juveniles of Cordia were not found in the closed forest, although they were found in forest gaps in Budongo but not Mabira. Mature tree density was higher in Budongo compared with Mabira. Lack of effective seed dispersal coupled with the inability of seedlings of Cordia to establish under closed canopy account for the arrested recruitment in Mabira. Enrichment planting in felling gaps is necessary to avoid local extinction of Cordia in forests without large vertebrates.     

Comparative demography of three coexisting Acer species in gaps and under closed canopy

Questions: 1. Is there a trade‐off between gap dependency and shade tolerance in each of the life‐history stages of three closely related, coexisting species, Acer amoenum (Aa), A. mono (Am) and A. rufinerve (Ar)? 2. If not, what differences in life‐history traits contribute to the coexistence of these non‐pioneer species? Location: Ogawa Forest Reserve, a remnant (98 ha), species‐rich, temperate deciduous forest in central Japan (36°56’ N, 140°35’ E, 600 ‐ 660 m a.s.l.). Methods: We estimated the demographic parameters (survival, growth rate and fecundity) by stage of each species growing in gaps and under closed canopy through observations of a 6‐ha permanent plot over 12 years. Population dynamics were analysed with stage‐based matrix models including gap dynamics. Results : All of the species showed high seedling and sapling survival rates under closed canopies. However, demographic parameters for each growth stage in gaps and under closed canopies revealed inter‐specific differences and ontogenetic shifts. The trade‐off between survival in the shade and growth in gaps was detected only at the small sapling stage (height < 30 cm), and Ar had the highest growth rate both in the shade and in the gaps at most life stages. Conclusions: Inter‐specific differences and ontogenetic shifts in light requirements with life‐form differences may contribute to the coexistence of the Acer species in old‐growth forests, with Aa considered a long‐lived sub‐canopy tree, Am a long‐lived canopy tree, and Ar a short‐lived,‘gap‐phase’ sub‐canopy tree.     

Effect of Tree‐Fall Gaps on Fruit‐Feeding Nymphalid Butterfly Assemblages in a Peruvian Rain Forest

One of the main natural disturbances that affects the structure of rain forests is treefalls, frequently resulting in gaps. Tree‐fall gaps can bring drastic changes in environmental conditions compared with the undisturbed understory. We investigated the effect of tree‐fall gaps on fruit‐feeding butterfly (Nymphalidae) species assemblages in an undisturbed lowland rain forest in southeastern Peru. We used fruit‐baited traps suspended 2 m above ground in 15 tree‐fall gaps ranging in area from 100 to 1000 m² and in adjacent undisturbed understory. Our data support the hypothesis that tree‐fall gap and understory habitats are utilized by different butterfly species assemblages. There were morphological differences between gap and understory species, where the understory species had a larger wing area to thoracic volume. Vegetation structure and composition were important factors affecting the butterfly assemblages. Most of the butterfly species showed an avoidance of vines and a strong association with the presence of trees and shrubs in gaps. There were also differences among gap assemblages that increased with gap size. Some of the species that were associated with gaps have been considered as canopy species. Other gap species in the present study, however, are known to feed on fruits and/or use host plants mainly, or only, occurring in gaps, implicating that the gap assemblage is a mix of canopy species and those unique to gaps. This indicates that, in an undisturbed Amazon forest, tree‐fall gaps may contribute to maintain species diversity by creating a mosaic of specific habitats and resources that favors different butterfly assemblages.     

Tree Regeneration in Church Forests of Ethiopia: Effects of Microsites and Management

Tree regeneration is severely hampered in the fragmented afromontane forests of northern Ethiopia. We explored how trees regenerate in remnant forests along the gradient from open field, forest edge to closed sites and canopy gaps inside the forest. We investigated the effects of seed sowing, litter removal, and weeding on the regeneration success along this gradient. Regeneration success was investigated for four indigenous tree species, and measured in terms of seedling establishment, growth, and survival. Species performed differently according to site conditions. Within the forest, local canopy openings facilitated seed germination ( Ekebergia ), seedling growth (all species except Olea ), or survival ( Ekebergia and Olea ), suggesting that all species benefited from local high light conditions in the forest. Outside the forest, germination (all species) and growth rates ( Juniperus and Olea ) were lower in the open field, most probably due to water stress in the dry season. Outer edge conditions favored growth for three of the four species. Natural seed germination was, however, zero at any site for Juniperus and Olea and low for Ekebergia and Prunus in the open field. Soil scarification influenced germination positively, while weeding did not have a positive effect. These results suggest that simple measures may improve seedling establishment, and that, for some species, forest edges are particularly useful for growth and survival after succesful establishment. Together with erecting fences, needed to protect seedlings against grazing, seed sowing, planting seedling, and soil scarification may contribute to maintain and restore church forests in the fragmented landscapes of northern Ethiopia.     

Spatial and Temporal Variation of Seed Rain in the Canopy and on the Ground of a Tropical Cloud Forest

Spatial and temporal patterns of seed rain impact plant fitness, genetic and demographic structure of plant populations, and species' interactions. Because plants are sessile, they rely on biotic and abiotic dispersal agents to move their seeds. The relative importance of these dispersal agents may shift throughout the year. In tropical forests, seed dispersal of epiphytes constitutes a major but hitherto unknown portion of seed rain ecology. For the first time, we report on patterns of seed rain for both epiphytic and terrestrial plants across an entire year in a Neotropical montane forest. To examine seed rain, we placed traps in the canopy and on the ground. We analyzed seed dispersal syndrome (bird, mammal, wind) and plant habit (epiphyte, liana, shrub, small tree, large tree) across all seasons of the year (dry, misty, wet). We found that the community of species collected in canopy traps was significantly different from the community in ground traps. Epiphytes were the most common plant habit found in canopy traps, while large trees were most common in ground traps. Species with bird‐dispersed seeds dominated all traps. Species richness was significantly higher during the dry season in ground traps, but did not vary across seasons in canopy traps. Our results highlight the distinct seed rain found in the canopy and on the ground and underscore the importance of frugivores for dispersing both arboreal and terrestrial plants in tropical ecosystems.     

Seed Availability as a Limiting Factor in Forest Recovery Processes in Costa Rica

Abandoned pastures and secondary forests are increasingly prominent features of tropical landscapes. Forest regrowth on abandoned pastures is generally slow and virtually limited to regeneration from seeds from external sources, since agricultural activities alter site conditions. We hypothesize that seed availability is a major limiting factor in forest recovery on abandoned pastures. This hypothesis was tested by studying the seed bank, seed rain, and seed predation in a small pasture (1 ha) situated in a forest‐pasture mosaic in northwestern Costa Rica. The tree seed density in the pasture seed bank was much lower (21/m²) than the density in the seed bank of a neighboring secondary forest (402/m²). Within a period of five weeks, 23 tree seeds entered the pasture by seed rain. This number is low compared to densities found in closed forests but higher than densities reported in other studies where virtually no seeds were found beyond 20 m from the forest edge. Possibly the small size of the pasture with seed sources nearby and the small‐scale landscape mosaic enhance seed dispersal. Predation limits the seed density in pastures, with 42% of the woody species consumed by predators. The low seed density in the seed bank, and hampered recruitment combined with significant losses, pose severe restrictions to forest recovery on abandoned pastures. Moderate land use, and small sized clearings with seed sources nearby may increase the pace of recovery. Nevertheless, forest establishment may still take a considerable time. Thus, enlarging the available pool of species may be a worthwhile management strategy.     

Differences in tree community among secondary deciduous oak forests in rural and residential areas in the Hokuriku District of Japan

Tree communities of secondary deciduous oak forests were surveyed in 13 forests (two in residential and 11 in rural areas) in the warm temperate Hokuriku District of Japan to understand the effects of fragmentation, location (residential or rural), and logging history. The rural forest logged most recently, where diameter at breast height was smallest, had a distinct canopy tree (>12 m) community due to an increase of trees from wind-dispersed seeds. The rural forest with gaps and the two residential forests also had different canopy tree communities from the other rural forests. In contrast, the tree community in the shrub layer (≤6 m) was not influenced by logging history and the existence of gaps but by location only. This was caused by an increase in evergreen trees (consequently causing poor light conditions on the forest floor) and a decrease in trees from wind-dispersed seeds in the residential forests. Among the rural forest patches, no negative effects of forest size and isolation on density of tree individuals were detected for any seed dispersal mode. This may be because many forest patches were arranged at distances of 10–50 m from neighboring patches in rural areas, which enables tree species with low dispersal ability to disperse their seeds to neighboring forests. However, as found in the residential forests, long-term abandonment and extensive fragmentation may gradually reduce tree diversity through loss of tree species with shade intolerance and low seed dispersal ability.     

Treefall gaps required for establishment,but not survival,of invasive Rubus phoenicolasius in deciduous forest,Maryland, USA

Although plant invasions are often associated with disturbance, localized disturbances can promote invasion either by: (i) creating sites where individuals establish; or (ii) enabling an invader to colonize the entire stand. The former is expected when both establishment and survival to reproductive age require disturbed conditions, whereas the latter should occur in systems when either establishment or survival are limited to disturbed sites. We investigated the role of localized disturbance, specifically treefalls, in the invasion of the Asian Rubus phoenicolasius in a deciduous forest in Maryland, USA. We investigated the density and demography of R. phoenicolasius in treefall gaps of various sizes, but identical age to non‐gap areas, using Classification and Regression Tree (CART) analyses to identify the most important predictors. To explore how the demography of established individuals responds to disturbed versus undisturbed conditions, we carried out a garden experiment with three different levels of shade (5, 12 and 22% full sun). We found vegetative and sexual reproduction, and seedling establishment, to be limited to large gaps in an old stand, but not in a stand in an earlier age of succession. However, in the garden experiment, established plants were able to survive and grow under all shade treatments. These findings indicate that R. phoenicolasius requires disturbances such as treefalls to establish in forests, but established plants will survive canopy closure, leading to stand‐wide invasion. Managers should be able to prevent invasion, however, by inspecting large gaps for new recruits every 3 years.     

Interspecific synchrony of seed rain shapes rodent‐mediated indirect seed–seed interactions of sympatric tree species in a subtropical forest

Animal‐mediated indirect interactions play a significant role in maintaining the biodiversity of plant communities. Less known is whether interspecific synchrony of seed rain can alter the indirect interactions of sympatric tree species. We assessed the seed dispersal success by tracking the fates of 21 600 tagged seeds from six paired sympatric tree species in both monospecific and mixed plots across 4 successive years in a subtropical forest. We found that apparent mutualism was associated with the interspecific synchrony of seed rain both seasonally and yearly, whereas apparent competition or apparent predation was associated with interspecific asynchrony of seed rain either seasonally or yearly. We did not find consistent associations of indirect interactions with seed traits. Our study suggests that the interspecific synchrony of seed rain plays a key role in the formation of animal‐mediated indirect interactions, which, in turn, may alter the seasonal or yearly seed rain schedules of sympatric tree species.     

Leaf structure of Syzygium spp. (Myrtaceae) in relation to site affinity within a tropical rain forest

This study examined four species of Syzygium (S. firmum, S. makul, S. operculatum, S. rubicundum) Myrtaceae, a tree genus that dominates the canopy of rain forests of south‐west Sri Lanka. Syzygium spp. occupy differing habitats with relation to succession and forest topography. We examined differences in leaf morphology and physiology in response to amount of shade, an important environmental variable affecting Syzygium distribution within the forest. To study change in leaf structure and physiology, environmental shelters were constructed simulating forest shade that differed in quality, quantity and duration. Seedlings were exposed to: (i) 0% shade (full sun, FS), red : far red (R : FR) ratio 1.27; (ii) 65% shade (large opening, LO) with direct sunlight similar to the centre of a large canopy opening, R : FR ratio 1.27; (iii) 82% shade (small opening, SO) with direct sunlight similar to the centre of a small canopy opening, R : FR ratio 1.27; (iv) 58% uniform light shade (LS) with a quality similar to the outside edge of a large canopy opening, R : FR ratio 1.05; (v) 85% uniform medium shade (MS) with a quality similar to the inside forest edge of a large canopy opening, R : FR ratio 0.97; (vi) 99% uniform deep shade (DS) similar to that of the forest understorey, R : FR ratio 0.23. The shelters were constructed in a large open area at the field station of the Sinharaja World Heritage site, Sri Lanka. Seedlings of each species were grown for two years in their respective shade treatments before physiological, morphological and anatomical measurements were made on leaves. Variation in leaf structure and physiology between the species was associated with differences in shade‐tolerance and water‐use. All species increased in photosynthesis rates and dimensions in leaf structure (leaf blade and cuticle thickness, stomatal density, thickness of upper and lower epidermis, and thickness of palisade mesophyll) with decrease in shade. In contrast, stomatal conductivity was highest in the DS (99% shade) treatment. Leaves of Syzygium firmum were thickest and largest in area. S. firmum also had highest photosynthesis in the SO (82% shade) treatment. S. firmum was the most shade‐tolerant of all species: it grows well in low shade and its leaf structure suggests it to be the most conservative in water‐use of the Syzygium spp. In the forest S. firmum can persist in the forest shade as established seedlings, but grows best within canopy openings of late‐seral rain forest. Leaves of S. operculatum were thinnest but had highest stomatal densities of the four species. S. operculatum is considered shade‐intolerant, with a leaf structure suggesting it to be prone to desiccation, and by implication susceptible to drought. S. operculatum is found along streams within early seral rain forest habitat, often originating on stream banks after land clearance for cultivation. In the FS (0% shade) treatment, S. rubicundun had highest photosynthesis rates and greatest number of leaves but smallest leaf area of the Syzygium species. S. rubicundum is more shade‐intolerant but more efficient in water‐use than S. operculatum. S. rubicundum is a mid‐seral canopy tree of the midslope stands that are thought to have originated after catastrophic windthrows or swidden cultivation. The leaf physiology and structure of S. makul suggests it to be both moderately shade‐tolerant and conservative in water‐use. It is the most widely distributed Syzygium species across the topography of late‐seral rain forest. We suggest forest disturbance and hydrology are important environmental factors that influence distribution of Syzygium species across the topography. Results from this study contribute to a body of knowledge suggesting that canopy tree species of rain forests in south‐west Sri Lanka have discrete affinities to topography and differences in successional status, and that adaptations in leaf structure and physiology are indicative of such phenomena. © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 141 , 365–377.     

Long‐term tree fern dynamics linked to disturbance and shade tolerance

Question: Do New Zealand tree ferns have recognizable shade tolerance niches? Location: Lowland temperate rain forest of New Zealand (41°20′S, 174°58′E). Methods: Growth, death and recruitment of five tree fern species were estimated from a 38‐year record of stem heights, collected within a 2.25‐ha block of forest, and electron transport rates (ETR) of photosystem II of fronds were measured. Results: Two species of Cyathea were comparatively common (603 and 351 stems in total) and two were comparatively rare (155 and 17 stems in total) on the site. The common species had lower rates of growth, recruitment and mortality than the rare species, had skewed age distributions typical of shade‐tolerant species and were probably recruited soon after a catastrophic earthquake in 1855. The two rare species were failing to recruit under closed forests; their age distributions indicated that all had regenerated long after the earthquake. ETR were higher for faster‐growing than for the shade‐tolerant species. A tree fern that regenerates vegetatively from aerial buds, Dicksonia squarrosa, was common on the site (361 stems in total). Its age distribution suggested it was relatively shade tolerant, but its mortality and recruitment rates were much higher than those of the two shade‐tolerating Cyathea species, suggesting that this multi‐stemmed species functions differently from the monopodial Cyathea species. Conclusions: New Zealand Cyathea tree ferns occupy distinct niches along a shade tolerance spectrum and their relative abundances are strongly influenced by disturbance history. The study provides evidence that tree fern species differ strongly in their responses to canopy disturbance and are not ecologically equivalent.     

Seed transfer among bird-dispersed trees and its consequences for post-dispersal seed fate

We investigated seed transfer, i.e. the seed movement away from a source canopy to areas beneath heterospecific canopies, among the ornithochorous tree species Taxus baccata, Ilex aquifolium and Crataegus monogyna in temperate secondary forests in NW Spain, by analysing the composition of multispecific seed rain beneath the canopy of each species, at four sites and for 2 years. To evaluate the consequences on seed fate, we estimated predation by rodents in manipulated seed rains, representing variable levels of relative proportion and total density for combinations of a preferred species paired with a less-preferred species. Seed rain under Taxus canopies was dominated by Taxus seeds, which occurred in low proportion under heterospecific canopies. Ilex seeds dominated the areas under Ilex but accounted for 20–40% of seeds under heterospecific trees. Crataegus seeds were not dominant in any of the microhabitats. The probability of being deposited beneath a heterospecific canopy was much higher for Ilex and Crataegus than for Taxus. The effects of seed rain composition on post-dispersal seed predation were species-specific. Taxus seeds experienced lower predation when occurring in a background of seeds dominated by heterospecific, Ilex or Crataegus, seeds. Crataegus seeds escaped predation more successfully in high-density patches, independently of seed clump composition. Predation on Ilex seeds was independent to both the density and the composition of seed clump. Seed transfer among heterospecific tree species may contribute to shape the template of propagule abundances from which forest will develop, by generating seed combinations favourable to escape from predation.     

Canopy disturbance and gap partitioning promote the persistence of a pioneer tree population in a near‐climax temperate forest of the Qinling Mountains,China

An unresolved question of temperate forests is how pioneer tree species persist in mature forests. In order to understand the responsible mechanisms, we investigated a near‐climax mixed temperate forest dominated by Betula albosinensis in the Qinling Mountains of China. Through establishing four 50 m × 50 m plots, we examined the canopy disturbance characteristics and its effects on tree recruitments. We further test the intra‐ and interspecific effects on the recruitment of B. albosinensis. The obtained data demonstrated canopy disturbance was frequent but most small‐sized. The canopy gaps are caused mainly by adult B. albosinensis by snapping. The regeneration of coexistent tree species shows a distinct preference for gap size. B. albosinensis were clumped at the juvenile stage and small scales. B. albosinensis juveniles were positively associated with B. utilis juveniles and negatively associated with the conspecific and B. utilis large trees. In addition, B. albosinensis juveniles showed negative associations with contemporary other tree species. Our results suggested that canopy disturbance caused by canopy trees and gap partitioning among the coexistent tree species are important for the persistence of the mixed forest. As a main gapmaker, B. albosinensis appear to develop a self‐perpetuating life‐history trait and allow them to persist.