Losses of seeds of temperate trees to soil fungi: effects of habitat and host ecology

Evidence suggests that impacts of fungal pathogens on tree recruitment tend to be greater in the forest understory than in openings, and that shade-tolerant trees are less vulnerable than shade-intolerant species. To investigate the role that harmful soil fungi may have in reducing regeneration of temperate trees, we applied fungicide to buried seeds of matched pairs of species differing in their relative shade tolerance and/or successional status (Acer negundo versus Acer saccharum, Prunus virginiana versus Prunus serotina, and Pinus strobus versus Tsuga canadensis), in three habitats that differed in their degree of openness (old field, forest gap, and forest understory). Our results indicated that soil fungi reduced germination of A. negundo, P. virginiana, P. serotina. and T. canadensis, and reduced viability of ungerminated seeds of P. strobus; no significant effects of fungi on seeds of A. saccharum were detected. However, we found seeds were not less likely to survive following burial in forest understory than in gaps. As well, results for only one species pair (A. negundo versus A. saccharum) were consistent with the prediction that shade-intolerant or successional species should be more susceptible to fungal attack than mature forest species. These results contrast with other studies of temperate and especially tropical forest trees.     

Differential predation on mangrove propagules in open and closed canopy forest habitats

Amounts of seed predation by grapsid crabs (Brachyura: Grapsidae) on two species of mangroves (Aegiceras corniculatum and Avicennia marina) were compared among different habitats in an Australian mangrove forest. For Avicennia, comparisons were between canopy gaps and the adjacent forest understory for six, mid intertidal, gaps of different sizes. For Aegiceras the comparisons were among canopy gaps in the high intertidal; open, accreting mud/sand banks where mangroves were colonizing in the low intertidal; and in the forest understory in both the high and low intertidal zones. These were repeated in the high salinity (35\%) downstream portion and the low salinity (0–5\%) upstream portion of a tidal river.Predation on Avicennia was significantly higher in the understory than in adjacent canopy gaps. Within a canopy opening, predation was greatest in the smallest gaps and lowest in the largest gaps. Predation on Aegiceras was greater in the high intertidal compared to the low intertidal, but no differences were found between river mouth and upstream locations. In the high intertidal zone of the forest, there were no differences in predation between canopy gap or forest understory sites for Aegiceras. In the low intertidal zone, however, significant differences in amount of predation were found between habitats. More Aegiceras propagules were consumed in the understory than on adjacent accreting sandbanks.Frequency of tidal inundation, which in turn affects the amount of time available to forage, is hypothesized to account for differences in predation between low and high intertidal forests and between small and large canopy gaps. Our results also suggest that shade intolerance in these two species may actually reflect an escape from predators, successful when the seeds are dispersed into open areas such as canopy gaps or mud banks.     

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.     

格氏栲天然林林窗和林下种子散布及幼苗更新研究

以格氏栲(Castanopsis kawakamii)天然林为研究对象,探讨了林窗和林下格氏栲种子雨、种子库的分布特征及幼苗更新状况。结果表明:林窗种子雨总量和完好种子密度高于林下,未成熟种子比例低于林下;林窗和林下种子雨高峰期掉落数量分别占种子雨总量的77.13%和74.5%;林窗种子库储量低于林下,种子库中以全食或捡拾种子比例最高,其中种子库储量垂直分布表现为枯落物层(约占2/3)>腐殖质层(0～5 cm)(约占1/3)>心土层(5～10 cm)(小于1%),以格氏栲种子占绝对优势;格氏栲从种子到幼苗的转化率低,林窗中格氏栲完好种子密度与幼苗密度均高于林下。林窗微生境提高了种子散布过程中格氏栲成熟种子的密度和比例,有利于促进格氏栲的幼苗更新,表明林窗在格氏栲种群恢复过程中扮演着重要角色。     

Seed predation patterns favor the regeneration of dominant species in forest gaps compared with the understory in an oak-pine mixed forest

Recent studies have demonstrated the higher likelihood of regeneration in forest gaps compared with the understory for the dominant species in pine-oak mixed forest. Here, we tested whether rodent seed predation or dispersal was beneficial for gap regeneration. We tracked the seed predation and dispersal of Quercus aliena var. acuteserrata and Pinus armandii using coded plastic tags in the forest understory close to gaps. Our results demonstrated that the proportions of initial buried seeds of both species were significantly more abundant in the forest understory compared with gaps. After seed caching, however, significantly lower proportions of the seeds of both species survived in the forest understory compared with gaps during the 30-day observation period. The final survival proportions of the seeds cached in the forest understory were lower than those cached in the gaps the next spring, which indicated that small rodents rarely retrieved scatter-hoarded seeds from forest gaps. Our findings suggest that rodent seed predation patterns contribute to the regeneration of the dominant species in gaps compared with the understory in a pine-oak mixed forest. In the study area, reforestation usually involves planting seedlings but direct sowing in forest gaps may be an alternative means of accelerating forest recovery and successional processes.     

Potential causes of arrested succession in Kibale National Park, Uganda: growth and mortality of seedlings

Recent studies suggest that regeneration following large-scale disturbance in Kibale National Park, Uganda, is slow or possibly arrested. Here, data is provided on the growth and mortality of seedlings in the forest understory, treefall gaps, and in large gaps that suggest that this pattern of arrested succession can be attributed partially to the fact that this East African community lacks aggressive colonizing tree species. Growth and mortality rates were contrasted for seedlings of six tree species planted in the understory, small gaps, and large gaps for 36 months. Data suggest that species are adapted to gaps of particular sizes. For example, Uvariopsis congensis grew faster in the understory than in small gaps, whereas Warburgia ugandensis had the lowest mortality rate and highest growth rate in large gaps. Seedlings (n=170) of 15 species were transplanted to assess the response of the tree community to large gap conditions. The limited survival of seedlings in large gaps relative to the understory suggests that only a small proportion of the tree community in this forest regenerates best in gaps larger than those created by the collapse of a single tree. These findings differ from a number of studies conducted in other geographical regions, and suggests that tree communities differ with respect to the proportion of tree species adapted to gaps of particular sizes. This may relate to variation among regions in their history of disturbance and thus frequency of gap formation, size of gaps, and the duration of periods of release. Such variation could imply the existence of a corresponding pattern among tropical forests of differential vulnerability to human disturbance, which tends to create many large gaps.     

辽东栎林内不同小生境下幼树植冠构型分析

以黄土高原黄龙山林区辽东栎林内3个小生境（林下、林隙、林缘）下辽东栎天然更新幼树为研究对象,采用典型抽样法对辽东栎幼树侧枝、叶片和树冠的空间分布状况以及生物量分配状况进行调查分析,探讨微生境与幼树植冠构型特征的关系,明确辽东栎幼树对不同小生境的适应策略,为栎林经营和林分结构优化提供理论依据。结果显示：（1）3种生境下辽东栎幼树构型发生了可塑性变化,林下幼树树冠层次比较单一,林隙与林缘的幼树树冠层次更加丰富。（2）由林下至林缘,幼树的树高、枝下高呈逐渐减小的趋势,而地径变化趋势与之相反;幼树的冠幅、树冠面积、树冠率呈先增加后减小的趋势,并且林下与林隙、林缘的差异显著;幼树的总体分枝率、逐步分枝率、枝径比呈先增加后减小的趋势。（3）3种生境下,幼树的一级枝的枝长、直径与倾角随着树高的增加而呈减小的趋势,但3种生境的差异不显著;林下一级枝主要分布在冠层中上部,而林隙与林缘一级枝主要分布在冠层中下、中上部。（4）由林下至林缘幼树叶长、叶宽、单叶面积和比叶面积逐渐降低,而单株叶数、叶总面积、叶面积指数呈先增大后减小趋势;与其他2种生境相比林下叶片分布趋于冠层上部。（5）幼树地上部分生物量中林下主干生物量占83%,枝和叶生物量只占17%;而林隙与林缘虽然各部位生物量有所差异但比例基本一致,其中主干占66%左右,枝和叶生物量占34%左右。研究表明,林隙生境下幼树的构型优于林缘和林下生境,在今后栎林的经营中,可以通过适当间伐来增加林隙数量,为森林更新和结构的优化提供有利条件。     

When sex is not enough: ecological correlates of resprouting capacity in congeneric tropical forest shrubs

In moist tropical forests resprouting may be an important component of life history, contributing to asexual reproduction through the clonal spread of individuals derived from shoot fragments. However, in contrast to other ecosystems where resprouting is common, the ecological correlates of resprouting capacity in tropical forests remain largely unexplored. In this study we characterized shade tolerance, resprouting capacity and sexual reproductive success of eight co-occurring Piper species from lowland forests of Panama. In field experiments we found that shade-tolerant Piper species had a higher capacity to regenerate from excised or pinned stem fragments than light-demanding species in both gap and understory light conditions. In contrast, shade-tolerant species had lower recruitment probabilities from seeds, as a consequence of lower initial seed viability, and lower seedling emergence rates. All Piper species needed gap conditions for successful seedling establishment. Of 8,000 seeds sown in the understory only 0.2% emerged. In gaps, seed germination of light-demanding species was between 10 and 50%, whereas for shade-tolerant species it was 0.5–9.8%. We propose that the capacity to reproduce asexually from resprouts could be adaptive for shade-tolerant species that are constantly exposed to damage from falling litter in the understory. Resprouting may allow Piper populations to persist and spread despite the high rate of pre-dispersal seed predation and low seed emergence rates. Across Piper species, we detected a trade-off between resprouting capacity and the annual viable seed production per plant but not with annual seed mass produced per plant. This suggests that species differences in sexual reproductive success may not necessarily result from differential resource allocation. Instead we suggest that low sexual reproductive success in the understory may in part reflect reduced genetic diversity in populations undergoing clonal growth, resulting in self-fertilization and in-breeding depression.     

Seed Dispersal by Kerama Deer (Cervus nippon keramae) on Aka Island,the Ryukyu Archipelago,Japan1

Endozoochorous seed dispersal by kerama deer (Cervus nippon keramae) was investigated at four sites on Aka Island, the Ryukyu Archipelago, Japan. Kerama deer feces contained seeds of 35 plant species. Most of the germinated seeds were small (1.3 ± 0.18 mm) and had a hard coat, comparable to the germinated seeds in several other studies of endozoochorous seed dispersal by herbivores. Both the numbers and species compositions of seeds differed among the four sites, reflecting differences in the food available to kerama deer among habitats. Although many graminoid seeds were found in the two open habitats (Sites A and B) and in the adjoining forest habitat (Site C), woody plant seeds dispersed endozoochorously by birds and mammals were dominant in the forest (Site D), away from the marsh. Although a majority of the graminoid species was growing in open habitats such as the marsh and open fields, few were growing in the forest. Therefore, the kerama deer spread many open‐habitat graminoid seeds to the open and forest habitats. If a high density of kerama deer persists for a long time and gaps in forests are created by browsing kerama deer or by other means, graminoid species may spread substantially on Aka Island. Therefore, it is possible that seed dispersal by forest deer contributes to the expansion of grasslands.     

Habitat fragmentation changes the adaptive value of seed mass for the establishment of a tropical canopy tree

To cope with the limiting light conditions in the rain forest understory, many tropical tree species have evolved large seeds that provide the emerging seedlings with nutritional reserves. Habitat fragmentation might change the adaptive value of seed size by modifying the biotic and physical conditions of the forest understory. We experimentally assessed the potential of fragmentation to alter how seed mass affects seedling survival, vigor, and attack by natural enemies of the tropical tree Nectandra ambigens. Seeds from different mother trees (families) were individually weighed and sown in experimental sites established in continuous forest and in forest fragments. Seedling survival, vigor, and damage by herbivores and pathogens were recorded periodically. While seedlings derived from larger seeds had higher survival rates in both habitats, seedling survival and vigor were significantly greater in forest fragments, and the seedlings also suffered fewer attacks by natural enemies. We found genetic variance for seed mass among families with a heritability value (h²) of 0.66, and we found evidence for selection on seed size. Average seed size differed between dead and living seedlings in three sites. In one fragment, seed size was selectively neutral in relation to survival. Overall, selection for seed size promoted survival and thus appears to affect the distribution of this trait. The maintenance of genetic variance could be related to the stochastic nature of the formation of light gaps. Our results highlight the importance of evaluating the adaptive value of traits susceptible to environmental changes for conservation purposes.     

An experimental test of density- and distant-dependent recruitment of mahogany (Swietenia macrophylla) in southeastern Amazonia

According to the Janzen–Connell model, high mortality of seeds and seedlings in proximity to conspecific adults can help maintain species diversity in tropical forests. Using a natural population of big-leaf mahogany (Swietenia macrophylla King), we tested the model’s mechanism by examining seed predation and juvenile recruitment in the forest understory and in treefall gaps in the vicinity of both isolated and clumped adults. We used tethered seeds placed in three types of exclosure plots: (1) complete access to seeds, (2) semi-access (access by small-sized seed predators) and (3) no access (all mammals excluded). Exclosure treatments were applied within the understory (both near and far from adults) and in gaps at eight fruiting adults in the late dry season (2001) and scored ten months later. Significantly more seeds were removed in canopy gaps near clumped adults than at isolated adults; otherwise, none of the treatment factors significantly influenced seed predation. In contrast, understory juvenile recruitment was significantly enhanced by distance from adults and was twice as high at isolated than clumped adults, providing novel support for the Janzen–Connell mechanism. No-access exclosures protected significantly more seeds than semi- and full-access exclosures, implicating small mammals in seed losses. Across the eight trees, juvenile recruitment in the no-access exclosures decreased significantly with conspecific adult densities, implicating non-mammalian density-responsive factor(s) in mortality following germination; likely a known specialist invertebrate herbivore. When all treatments were combined, conspecific adult basal area and total DBH explained 72 and 90% of variation in overall juvenile recruitment, respectively. Collectively, these results indicate that Janzen–Connell effects can operate in S. macrophylla, especially during the seed-to-seedling transition, and will likely reduce recruitment in areas of high conspecific densities. They also suggest that further research into the causes of density-dependence in tropical trees should investigate mortality agents following germination.     

Diversity patterns of ground beetles and understory vegetation in mature,secondary, and plantation forest regions of temperate northern China

Plantation and secondary forests form increasingly important components of the global forest cover, but our current knowledge about their potential contribution to biodiversity conservation is limited. We surveyed understory plant and carabid species assemblages at three distinct regions in temperate northeastern China, dominated by mature forest (Changbaishan Nature Reserve, sampled in 2011 and 2012), secondary forest (Dongling Mountain, sampled in 2011 and 2012), and forest plantation habitats (Bashang Plateau, sampled in 2006 and 2007), respectively. The α‐diversity of both taxonomic groups was highest in plantation forests of the Bashang Plateau. Beetle α‐diversity was lowest, but plant and beetle species turnover peaked in the secondary forests of Dongling Mountain, while habitats in the Changbaishan Nature Reserve showed the lowest turnover rates for both taxa. Changbaishan Nature Reserve harbored the highest proportion of forest specialists. Our results suggest that in temperate regions of northern China, the protected larch plantation forest established over extensive areas might play a considerable role in maintaining a high biodiversity in relation to understory herbaceous plant species and carabid assemblages, which can be seen as indicators of forest disturbance. The high proportion of phytophagous carabids and the rarity of forest specialists reflect the relatively homogenous, immature status of the forest ecosystems on the Bashang Plateau. China's last remaining large old‐growth forests like the ones on Changbaishan represent stable, mature ecosystems which require particular conservation attention.     

Effects of overstory and understory vegetation on the understory light environment in mixed boreal forests

Abstract. The percentage of above-canopy Photosynthetic Photon Flux Density (%PPFD) was measured at 0, 50 and 100 cm above the forest floor and above the main understory vegetation in stands of (1) pure Betula papyrifera (White birch), (2) pure Populus tremuloides (Trembling aspen), (3) mixed broad-leaf-conifer, (4) shade-tolerant conifer and (5) pure Pinus banksiana (Jack pine) occurring on both clay and till soil types. %PPFD was measured instantaneously under overcast sky conditions (nine locations within each of 29 stands) and continuously for a full day under clear sky conditions (five locations within each of eight stands). The percentage cover of the understory layer was estimated at the same locations as light measurements. Mean %PPFD varied from 2% at the forest floor under Populus forests to 15% above the understory vegetation cover under Betula forests. Percent PPFD above the understory vegetation cover was significantly higher under shade intolerant tree species such as Populus, Betula and Pinus than under shade tolerant conifers. No significant differences were found in %PPFD above the understory vegetation cover under similar tree species between clay and till soil types. The coefficient of variation in %PPFD measured in the nine locations within each stand was significantly lower under deciduous dominated forests (mean of 19%) than under coniferous dominated forests (mean of 40%). %PPFD measured at the forest floor was positively correlated with %PPFD measured above the understory vegetation and negatively correlated with cumulative total percent cover of the understory vegetation (R² = 0.852). The proportion of sunflecks above 250 and 500 mmol m^–2 s^–1 was much lower and %PPFD in shade much higher under Populus and Betula forests than under the other forests. Differences in the mean, variability and nature of the light environment found among forest and soil types are discussed in relation to their possible influences on tree succession.     

Postdispersal Fruit and Seed Removal by the Crab Gecarcinus lateralis in a Coastal Forest in Veracruz,Mexico1

In the coastal semideciduous forest of La Mancha, Veracruz (Mexico), we evaluated the removal of fallen fruits and seeds of different species by the land crab Gecarcinus lateralis under different environmental conditions (age soil of forest stand, topography, and cover). Crabs removed 67 percent of the propagules in the experiments (3106 of a total of 4608), and seeds were removed in greater quantities (61.1%) than fruits (38.9%). Fruits of Maclura tinctoria (Moraceae) and Ehretia tinifolia (Boraginacea) and seeds of E. tinifolia were the most affected species. Crabs removed higher quantities of fruits in old‐soil forest and in the understory than in young‐soil forest and gaps. In experiments with seeds, only for the older forest, the crabs removed more seeds in slopes and peaks than in valleys and in the understory than gaps, whereas in the young‐soil forest, the differences were not significant. Our results suggest that G. lateralis, like Gecarcoidea natalis and Gecarcinus quadratus, is an efficient propagule predator and can exert pressure in the establishment of plant species, but in La Mancha, this also depends on site conditions and identity of the species.     

Forests are not immune to plant invasions: phenotypic plasticity and local adaptation allow <Emphasis Type="Italic">Prunella vulgaris</Emphasis> to colonize a temperate evergreen rainforest

In the South American temperate evergreen rainforest (Valdivian forest), invasive plants are mainly restricted to open sites, being rare in the shaded understory. This is consistent with the notion of closed-canopy forests as communities relatively resistant to plant invasions. However, alien plants able to develop shade tolerance could be a threat to this unique forest. Phenotypic plasticity and local adaptation are two mechanisms enhancing invasiveness. Phenotypic plasticity can promote local adaptation by facilitating the establishment and persistence of invasive species in novel environments. We investigated the role of these processes in the recent colonization of Valdivian forest understory by the perennial alien herb Prunella vulgaris from nearby populations in open sites. Using reciprocal transplants, we found local adaptation between populations. Field data showed that the shade environment selected for taller plants and greater specific leaf areas. We found population differentiation and within-population genetic variation in both mean values and reaction norms to light variation of several ecophysiological traits in common gardens from seeds collected in sun and shade populations. The colonization of the forest resulted in a reduction of plastic responses to light variation, which is consistent with the occurrence of genetic assimilation and suggests that P. vulgaris individuals adapted to the shade have reduced probabilities to return to open sites. All results taken together confirm the potential for rapid evolution of shade tolerance in P. vulgaris and suggest that this alien species may pose a threat to the native understory flora of Valdivian forest.     

Effects of Habitat, Cattle Grazing and Selective Logging on Seedling Survival and Growth in Dry Forests of Central Brazil

We studied the effect of forest gaps and cattle grazing on survival and growth of seedlings of seven native tree species, planted in dry forest fragments with different intensities of past logging in Central Brazil. Seedling survival after 12 mo ranged from 35 to 77 percent among species. Survival of most species was similar in gaps and understory in minimally disturbed forest remnants, but was lower in the gaps of more heavily logged forests. In contrast, growth was much higher in gaps than in understory in minimally disturbed forests, but for most species was similar in gaps and understory in more heavily logged forests. We did not detect an effect of cattle on seedling survival. Seedlings of the most commonly logged species show a high potential to survive and grow when planted in logged forests.     

Habitat use and seed removal by invasive rats (Rattus rattus) in disturbed and undisturbed rain forest,Puerto Rico

Despite frequent occurrences of invasive rats (Rattus spp.) on islands, their known effects on forests are limited. Where invasive rats have been studied, they generally have significant negative impacts on native plants, birds, and other animals. This study aimed to determine invasive rat distribution and effects on native plant populations via short‐term seed removal trials in tropical rain forest habitats in the Luquillo Experimental Forest, Puerto Rico. To address the first objective, we used tracking tunnels (inked and baited cards inside tunnels enabling animal visitors’ footprints to be identified) placed on the ground and in the lower canopy within disturbed (treefall gaps, hurricane plots, stream edges) and undisturbed (continuous forest) habitats. We found that rats are present in all habitats tested. Secondly, we compared seed removal of four native tree species (Guarea guidonia, Buchenavia capitata, Tetragastris balsamifera, and Prestoea acuminata) between vertebrate‐excluded and free‐access treatments in the same disturbed and undisturbed habitats. Trail cameras were used to identify animals responsible for seed contact and removal. Black rats (Rattus rattus) were responsible for 65.1% of the interactions with seeds, of which 28.6% were confirmed seed removals. Two plant species had significantly more seeds removed in disturbed (gaps) than undisturbed forest. Prestoea acuminata had the lowest seed removal (9% in 10 days), whereas all other species had >30% removal. Black rats are likely influencing fates of seeds on the forest floor, and possibly forest community composition, through dispersal or predation. Further understanding of rat–plant interactions may be useful for formulating conservation strategies.     

Changes in riparian forest composition along a sedimentation rate gradient

Riparian forests are highly valued for maintaining water quality through the retention of sediments and nutrients. They also provide some of the most diverse and species-rich habitats in the world. What is largely unknown, however, is how sediment deposition affects plant community composition in these forests. The objective of this study was to examine changes in plant community composition across a gradient of increasing rates of sedimentation in riparian forests in the southeastern Coastal Plain, USA. Seventeen plots were established within riparian forests receiving between 0 and 5.5 cm year⁻¹ of sediment deposits. Species density and biomass estimates were collected annually from 2002 to 2006 for overstory and mid-story plant species within each plot. Percent cover and nested frequency of understory plant species were determined annually during 2004–2006. Measures of community composition in the understory, mid-story, and overstory layers of forests were compared to changes in environmental factors associated with increased sedimentation. In the understory, annual, exotic, and upland species had higher importance values in plots receiving high sediment deposition. The densities of shade-intolerant and N-fixing species in the mid-story also increased with increasing sedimentation rates. Increased overstory mortality was associated with high sedimentation rates, though increases in understory light levels in these gaps were not the main driver of understory species changes. Edaphic factors, such as soil texture, moisture, and temperature, were significantly correlated to species composition in all three forest layers, suggesting that changes in soil physical structure due to sedimentation may drive community-level changes in these forests.     

Seeds and seedlings of two neotropical montane understory shrubs respond differently to anthropogenic edges and treefall gaps

Edges resulting from forest clear-cutting and treefall gaps can affect plant populations and consequently the distribution of species across landscapes. These two types of disturbance might interact to exacerbate or ameliorate “edge effects”, a rarely tested possibility. We focused on the effects of distance from forest edge (0–10, 30–40, 60–70, and 190–200 m) and habitat within forest fragments (treefall gaps and intact forest) on the early stages of development of Palicourea gibbosa and Faramea affinis, two common shrubs of montane forests in southwest Colombia. Seed germination and seedling growth did not change with distance from forest edge. Within forest fragments, however, seed germination and seedling growth were higher in treefall gaps than in intact forest understory for both species. In contrast, seed predation was influenced by distance from forest edge and in P gibbosa it depended on habitat. Seed predation was highest in the forest interior (190–200 m from forest edge) and in P. gibbosa this was true only in treefall gap habitats. These results suggest that animal mediated processes such as post-dispersal seed predation are more likely than physiological processes to be affected by anthropogenic edges. Our results provide some evidence that treefall gaps may interact with “edge effects”, however, they are inconclusive as to whether they exacerbate or ameliorate them. Received: 31 August 1998 / Accepted: 18 February 1999     

Effects of the Physical Environment and Primate Gut Passage on the Early Establishment of Ampelocera hottlei Standley in Rain Forest Fragments

The regeneration of many tropical trees is threatened by forest fragmentation because it produces major physical, biological and ecological changes that limit seed germination and seedling establishment. We analyzed the regenerative potential of an old growth forest tree species—Ampelocera hottlei (Ulmaceae)—in three contrasting habitats located in the Lacandona rain forest, southeastern Mexico: continuous forest, fragments occupied by black howler monkeys (Alouatta pigra) and fragments unoccupied by howlers. We tested if germination of A. hottlei seeds among habitats was affected by understory temperature, light incidence and ingestion by A. pigra. We compared seedling survival and relative growth rate in height (RGR_H) for 20 d among habitats and between ingested and control seeds (from mature fruits). Germination was higher in continuous forest than in fragments (occupied or not), with higher germination rates for ingested seeds in fragments. Temperature and light incidence were lower in continuous forest than in fragments. Germination decreased with increasing temperature and light incidence with this relationship being significantly higher for ingested seeds. Seedling survival was higher in continuous forest than in fragments, whereas RGR_H did not differ among habitats. In addition, survival and RGR_H were higher in seedlings originating from ingested seeds. Overall, our results suggest that the populations of A. hottlei can be limited in fragments where changes in the understory physical environment and the extirpation of A. pigra will likely have deleterious consequences for the regeneration of A. hottlei and possibly for other tree species, ultimately affecting forest composition and structure. Abstract in Spanish is available at http://www.blackwell‐synergy.com/loi/btp .