Restoring dry Afromontane forest using bird and nurse plant effects: Direct sowing of Olea europaea ssp. cuspidata seeds

To identify the perspectives of seed sowing for reforestation of degraded dry Afromontane savanna in exclosures in northern Ethiopia, seeds of a fleshy-fruited, secondary climax tree, Olea europaea ssp. cuspidata, were placed under two pioneer shrub species (Euclea racemosa and Acacia etbaica) and in open microhabitats. Seed removal and germination rates were examined. The effects of bird ingestion, manual pulp removal and mechanical endocarp treatments on germination rates were also studied.

Pulp removal promoted seed germination, in particular in seeds without endocarp manipulation. Seed removal, presumably by rodents, was concentrated in narrow strips along linear soil conservation structures, and not different between shrubs and open microhabitats. In the absence of water stress, humus types did not have a significant effect on germination rates. Under field conditions however, germination was higher under Euclea canopies. The observed facilitative effect of Euclea shrubs on germination may be attributed to moisture retention effects, related to the deep humus layer and canopy architecture, preventing desiccation and promoting imbibition of seeds. When readily available Olea seeds are not used for seedling production, direct sowing of seeds in the humus under dense Euclea shrubs could offer a cheap complement to planting of nursery-raised seedlings for forest restoration projects in recovering Afromontane savanna.     

动物取食和扩散森林植物种实研究进展

动物取食扩散森林植物种实作为森林生态系统中植物和动物联系的-个重要方面, 不仅是联系母株与其子代幼苗的重要桥梁, 也是植物生活史中的-个重要阶段。文中综述了近年来关于动物取食森林植物种实及其与这些植物种子散布、萌发、幼苗生长和种群扩展等方面关系的研究成果。动物在取食和破坏森林植物种实的同时也将这些植物的种子扩散到-个新的生境斑块, 其消化道机械的或化学的作用提高了这些森林植物的种子萌发率和萌发进程, 促进了其早期定居和种群扩大。动物对森林植物的这种作用具有长期性, 形成特定动植物间或多物种间的协同进化。近年来, 森林生态系统受到了严重的干扰和破坏, 可能会因为干扰了森林植物种实的动物散布者而影响森林植物种群的扩展。     

Effects of seed quality and seed location on the removal of acorns and beechnuts

We examine whether different guilds of foragers remove seeds differentially according to seed quality (seed size and insect infestation) and seed location (habitat and microhabitat) in a mixed oak-beech forest. Video recordings indicated that the wood mouse (Apodemus sylvaticus) was first to encounter seeds. Foragers preferred acorns to beechnuts, large to small size and sound to infested. Nevertheless, infested seeds were removed by rodents even when sound seeds were present. Seeds that were not preferred by scatter-hoarding rodents remained longer on the ground and were more vulnerable to predation and desiccation (4% moisture loss per day). However, seeds that were removed by scatter-hoarders were moved away from their mother trees (96%) and cached individually (32%), increasing their moisture content (3% per day). Buried seeds, simulating scatter-hoarding behavior, experienced only a 17% removal after 4 months. Seed removal differences among habitats were not due to habitat attributes but to the spatial distribution of rodent-preferred microhabitats. Thus, a significant lower seed removal was observed under the tree canopy with no shrubs. However, seed removal in forest gaps with deadwood cover was not significantly different from the preferred microhabitat (under shrub cover). In pure beech forests, seed removal by rodents only occurred under Ilex aquifolium (the only perennial cover) and under woody debris. This study concludes that seed quality and seed location determine the contribution of different removers (predators vs. dispersers), their seed selection and their removal speed, leading to different seed fates which will eventually affect tree regeneration.     

Artificial Nest Predation Dynamics Along a Forest Fragmentation Gradient: A Preliminary Analysis

Abstract

Studies in eastern North America suggest that nest predation on forest songbirds increases with habitat fragmentation. However, the majority of these studies have been conducted in highly fragmented suburban/rural deciduous forest habitat, making generalization of the results difficult. The objective of this study was to examine artificial nest predation dynamics along a fragmentation gradient (farm woodlots, logged forest stands and contiguous forest) in the conifer dominated Boreal Mixedwood. Predation was significantly higher in farm woodlots (78.8% edge and 78.5% interior) than the forest interior in contiguous and logged areas (42.8% and 41.9%, respectively). Predation at logged edges (60.0%) was not significantly different from either the woodlots or the forest interiors. All land-uses showed a variety of avian and mammalian predators. Using timer nests, we determined that predation was highest immediately after sunrise, with a second peak around sunset. Census results suggest that farm woodlots have significantly more red squirrels and a very different corvid community than forested areas. Overall, fragmentation due to agriculture seems to have a far greater impact on nest predation in the Boreal Forest than does logging and is in part, due to changes in the predator community. Further work is required to confirm the relative importance of nest predators in different land-uses. Clarification of the impact that logged edges have is also required.     

Natural and human disturbances affect natural regeneration of Swietenia macrophylla: Implications for rainforest management

In this paper we document how changes in forest structure mediated by natural (hurricane) and human (logging) disturbances affect natural regeneration of Swietenia macrophylla via its effects on seed predation, germination, and early recruitment. Work was carried out in two ejidos within the Mayan zone of Quintana Roo, differing with regard to their exposure to the effect of the hurricane Dean 2008 (Naranjal Poniente; high hurricane impact) and Señor (with no evidence of hurricane effects). We experimentally set S. macrophylla seeds in both hurricane conditions and contrasting logging effects, in three treatments: (1) open access, (2) rodent and insect access and (3) rodent and insect exclusion. We measured three dependent variables: (i) number of seeds predated, (ii) number of seeds germinated and (iii) number of seedlings established. We found that the three variables measured were differentially affected by logging and hurricane Dean. Seed predation was higher in areas with hurricane effects; germination showed no differences, but early recruitment was differentially affected by the two conditions, via an increasing of herbivory and sun exposition. Both types of disturbances studied occurred periodically in Yucatan Peninsula and elsewhere in tropics, so it is necessary to implement specific actions in order to face changes in mahogany natural regeneration stocks, and supporting the future management of tropical forests.     

自然脱水过程中七叶树种子生理特性的变化

于 2003 年研究了自然脱水过程中七叶树种子生理特性的变化。结果表明:七叶树种子对脱水高度敏感,为顽拗性种子。种子成熟采收时含水量高达 60.3%,种子在室温下自然干燥 30 天后,含水量下降到 30.2%,此时种子生活力完全丧失。在脱水初期,种子发芽率有所上升,但随后种子发芽率迅速降低。随着含水量的下降,种子浸出液相对电导率上升,但当含水量在 53.7% 到 50.9%之间时,种子浸出液相对电导率出现异常升高。同时种子超氧化物歧化酶(SOD)的活性随脱水时间的延长而下降,只有种子含水量在 53.7% 到 50.9%之间时出现例外。丙二醛(MDA)含量在脱水初期缓慢上升,在含水量下降到低于 50.9%时,丙二醛(MDA)含量快速上升。可溶性糖含量随脱水时间的延长缓慢上升。当种子含水量为 47%–60%时,种子发芽率较高,说明这一含水量区间有利于种子生活力的保持。图 6 参 13。     

Seed bank analysis of tree species in two stands of the Tenerife laurel forest (Canary Islands)

We analyzed the germination from the seed bank for two laurel forest stands (Moquinal versus Aguirre) of Tenerife collected at two different seasons (summer versus winter). We incubated and monitored germination in greenhouse conditions for 1 year. A high variability in germination was found between trays. Germination was much higher in summer than in winter, especially from Moquinal seed bank. Shade tolerant species (Laurus azorica, Persea indica, Rhamnus glandulosa and Viburnum tinus) have a shorter germination delay than shade-intolerant species (Erica arborea, Erica scoparia and Myrica faya), which dominate the seed bank. The species composition of germinating seeds after one year did not reveal any differences between sites nor between, despite the high differences in number between seasons.

We compared the species composition of germinating seeds to that of the canopy (expressed as basal area). The results indicate that the winter seed bank does not significantly differ from the canopy composition in the Aguirre stand. We interpret our results to imply that the Aguirre stand is of an earlier successional stage than the Moquinal stand, because of a higher species richness in the germinated tree seeds, and compositional similarities between the winter seed bank and the canopy (both characteristic of earlier successional stages).     

Regeneration strategies in a temperate hardwood floodplain forest of the Upper Rhine: sexual versus vegetative reproduction of woody species

The regeneration mechanisms of woody species in the hardwood floodplain forest of the Upper Rhine are not well known, although they are of primary importance for future forest development. To gain a better understanding of the balance between sexual and asexual regeneration strategies and to assess the role of the seed bank in regeneration, the similarities in species composition and abundance of four fundamental compartments involved in regeneration (the seed rain, the seed bank, the recruits and the canopy) were compared in three hardwood forest stands with different flooding conditions. The results show that the floristic composition of the recruits is very similar to that of the canopy, whereas the composition of the seed bank is very dissimilar to the latter and comprises very few hardwood species. However, some species such as Fraxinus excelsior, Carpinus betulus and Acer pseudoplatanus which are very rare in the seed bank release a high number of diaspores, and seedlings of these species germinate abundantly in the field in the year following seed release. Moreover, the germinating seeds originate from the litter layer and not from the soil itself. This shows that most woody species regenerating by seed in the hardwood Rhine forest build transient seed banks and that the role of persistent seed banks for regeneration is very limited. Furthermore, it appears that many woody species have developed strategies favouring vegetative propagation for their regeneration, particularly understorey species, such as Cornus sanguinea and Prunus padus. As vegetatively grown individuals better withstand prolonged inundation in their early life stages than seedlings, species relying on vegetative regeneration strategies might be advantaged by regular and prolonged flooding of the Rhine forest over species regenerating only by seeds.     

Predispersal seed predation in Acacia macrostachya,its impact on seed viability,and germination responses to scarification and dry heat treatments

Predispersal seed predation among individual Acacia macrostachya trees over two sites in Burkina Faso was assessed. In addition, the effects of seed predation on seed viability; germination responses to scarification (mechanical, hot water at 60, 70 and 80°C, and sulphuric acid for 10, 20 and 30 min) and dry heat (at 60, 70 and 80°C for 15, 30 and 60 min each) treatments were investigated under laboratory conditions. The results indicated a large difference in predation intensity among individual trees, as well as between sites. Predispersal predation significantly decreased seed germination, particularly when the number of insect larvae per seed increased. Scarified and unscarified seeds germinated equally well, except for hot water treatments of high temperature. This indicates lack of physical dormancy and dispersed seeds can readily germinate provided that conditions for germination are conducive. Seeds exposed to dry heat treatments also germinated close to 97% under low intensity and short exposure times. This suggests that fire, under natural condition, plays a key role in triggering germination of A. macrostachya seeds.     

Acorn defenses to herbivory from insects: Implications for the joint evolution of resistance,tolerance and escape

Acorn predation by insects and its effects on seedling establishment were investigated among three co-occurring oak species (Quercus variabilis, Q. serrata and Cyclobalanopsis glauca) in a subtropical evergreen broadleaved forest, Southwest China. All oak species had high tannin concentration (over 10%) but differed in acorn mass and germination schedule. We hypothesized that the defensive traits in acorns (e.g. seed mass, tannins and germination schedule) act together to reduce damage from insect seed predators. Q. variabilis had significantly lower predation (51.2%) than either Q. serrata (71.4%) or C. glauca (73.8%). Seedling establishment decreased with increasing injury for all oak species studied. As much as 43% of insect infested acorns germinated and established as viable seedlings despite extensive acorn mortality due to insect seed predators. The larger seed mass of Q. variabilis appears to tolerate insect infestation and retain enough stored reserves for seed germination and early growth of seedlings. Autumn germination also benefited Q. variabilis and Q. serrata, allowing escape from both direct and ancillary effects of insect feeding by fast reserve shifting to immediate germination of mature acorns. Our results indicate that large seed mass, tannin and autumn germination act together to ameliorate effects of insect seed predation, and the joint evolution of resistance and tolerance (as well as escape through autumn germination) in acorns may be the selective consequences driven in part by interactions with insect seed predators.     

Distribution patterns of acorns after primary dispersion in a fragmented oak forest and their consequences on predators and dispersers

Forest fragmentation affects seed production, but little is known about how seeds are distributed in fragmented forests after primary dispersion and how this affects their interactions with other organisms. This study addressed these issues in a fragmented oak forest of Quercus laeta where four habitat types were recognized: interior and edge of patches, deforested matrix around patches, and an abandoned field. Areas and distances to the abandoned field were measured for 40 patches, and acorns were sampled in all habitats. Only samples from the interior and edge of patches had acorns, which were classified as aborted, viable, and parasitized by insects or fungi. Acorns in all these classes were regressed against patch area and distance to the abandoned field. Field experiments were also conducted to determine whether acorn removal rates varied across habitats. Aborted acorns within patches were not related to area or distance, but they decreased with increasing values of both variables at patch edges. Within patches, viable acorns were positively related to increases in area and distance, while the converse occurred for insect-damaged acorns; fungal-infested acorns were not related to patch variables in this habitat. Complex interactions between area and distance explained how acorns in these classes were distributed across patch edges. Acorn removal was higher within patches and their edges when compared to human-disturbed habitats; both mice and birds were identified as potential acorn dispersers. These results suggest that forest fragmentation affects acorn-mediated processes and that this may influence the recovery of patch connectivity in the landscape.     

色木槭和拧筋槭种子脱水耐性分析——基于含水量、发芽率和ABA含量变化的结果

通过采集不同发育阶段种子并对其进行自然干燥处理,以含水量、发芽率和ABA含量变化为指标,研究了色木槭和拧筋槭种子在自然发育和干燥过程中的脱水耐性变化.结果表明,色木槭和拧筋槭种子虽经历了成熟脱水,但种子仍不耐脱水;其发芽率和活力指数随发育进程而逐渐增加,但随自然脱水进程而逐渐降低;色木槭和拧筋槭种子最大脱水耐性分别出现在花后100 d和120 d;在整个发育过程中,两树种种子的ABA(脱落酸)含量均较低;拧筋槭种子中ABA含量在脱水过程中呈下降趋势,而色木槭种子中ABA含量在脱水过程中虽有升高但变化不显著.推测ABA含量低可能为色木槭和拧筋槭种子不耐脱水的主要原因之一.     

Germination and seedling growth of Quercus vulcanica: effects of stratification, desiccation, radicle pruning, and season of sowing

Effects of stratification, desiccation, radicle pruning, and season of sowing on Quercus vulcanica germination and growth were studied to identify optimum nursery procedures for artificial regeneration of this species. Following stratification (0, 2, 4 and 8 weeks), acorns were germinated, and acorn moisture content and germination performance were also determined at various times during desiccation. In early December unsprouted acorns were planted in containers, and in early April sprouted acorns, which had been stored in polyethylene bags at 4 °C, with radicles left intact or with radicles pruned back to 1.0 cm were planted in containers.Stratification for 2 and 4 weeks did not increase germination percentage but significantly increased germination rate. Germination percentage of the seeds dropped when the moisture content of the seeds was reduced by desiccation, and the critical minimum moisture content of the recalcitrant Q. vulcanica acorns was found to be 11–16%. Spring sowing of sprouted acorns altered the morphology the containerized seedlings and caused the formation of significantly more main roots, but resulted in significantly less shoot height and shoot dry weight. Spring-sown sprouted acorns had also a significant advantage over the fall-sown unsprouted acorns in seedling survival, and thus nursery personnel should not be concerned if acorns sprout before sowing.     

Effects of livestock exclusion on tree regeneration in church forests of Ethiopia

In Ethiopia, forests near churches, are the last remnant forest patches. These forests are currently under threat, probably due to diminishing areas of the forest itself and repeated grazing for extended periods by cattle. We assessed the effect of livestock exclusion on the regeneration of four indigenous tree species in two church forests. The four species have a high abundance and socioeconomic value, but limited regeneration in the two forests. We investigated the effect of grazing and trampling on seed germination, seedling survival, and seedling growth. Livestock grazing had a strong negative effect on germination, seedling growth and mortality. In fenced plots, more seeds germinated, seedling survival was higher and seedlings grew faster. Seed germination was higher inside the forest than in the adjacent open area for all species. Seedling survival was not different between forest interior and open fields, except for unfenced plots in the open fields where survival was lower because of the higher grazing pressure. In unfenced plots, no seedlings survived until the end of the year, indicating that grazers destroyed the seedling bank in and around the forest. The significant interaction between fencing and species on seed germination and seedling survival revealed that the magnitude of damage due to grazing can vary with species.     

Effects of fire disturbance on bird communities and species of mountain Serrano forest in central Argentina

In central Argentina, Serrano forest has a long history of fire disturbance; however, the impact of fire on avifauna remains unknown. We compared the avian–habitat relationships in forest patches with low, moderate, and high fire regimes using a community-level (species richness, abundance, ordination and guilds) and species-level (indicator species analysis) approach. In patches under each fire condition, we recorded bird community composition, richness and abundance, and different vegetation structure variables. The site under high-severity fire regime was structurally poor and had been converted from original forest to dense grassland. There, diversity of bird community was low, retaining approximately 30 % of the species present in the least impacted site. Avian assemblage was dominated by generalist and open area birds. Guilds were underrepresented, showing an important reduction of foliage granivorous, nectarivorous, omnivores, and foliage and bark insectivorous, and absence of fly-catchers. Moreover, low abundance of forest understory, midstory, and canopy species and of birds belonging to open and closed nesting guilds was detected. By contrast, under low and moderate-severity fire regimes highest bird diversity as well as highest representativeness of most guilds was observed. Forest bird species were strongly associated with low fire disturbance, whereas moderate fire disturbance was characterized by the presence of forest and generalist species. Given the critical conservation status of Serrano forest in Córdoba, Argentina, habitat restoration and protection of forest relicts could be suitable measures to promote avifauna preservation.     

Effects of group-selection opening size on the distribution and reproductive success of an early-successional shrubland bird

Group-selection is a widely used silvicultural technique, and although recent studies have compared the ecology of birds inhabiting patches of regenerating forest created by group-selection with that of birds in clearcuts, little is known about the effect of opening size and shape on the ecology of early-successional shrubland birds within stands treated with group-selection. We studied chestnut-sided warblers (Dendroica pensylvanica), which are an early-successional shrubland bird, nesting in 29 patches of regenerating (4–5 years old) northern hardwoods forest 0.15–0.69 ha in area to determine whether the ecology of this species is affected by patch size or shape. Chestnut-sided warbler density decreased with patch size, however nests were initiated earlier in larger patches. There were no relationships between patch area and number of young fledged per territory or nest predation rates. Similarly, there were no relationships between patch shape (defined as the ratio of the patch perimeter to the perimeter of a circle of the same area) and territory density, date of initiation of first nests, number of young fledged per territory, or nest predation rates. These results contrast with the results of studies of area sensitivity of mature forest and grassland birds, in which bird density is negatively related to patch area. However, later nest initiation in smaller patches suggests that smaller patches are lower quality habitat, which is consistent with the negative relationships between patch area and habitat quality reported in studies of birds nesting in patches of mature forest.     

Seed germination and seedling establishment of the monocarpic dwarf bamboo Sasa veitchii var. hirsuta

In order to determine the influences of environmental factors on seed germination and to identify the effects of germination characteristics on seedling establishment for Sasa veitchii var. hirsuta, germination experiments and a survey on current seedling dynamics were conducted in a natural habitat after mass flowering. The results of the germination experiments revealed that the seeds require a low-temperature environment for germination; those exposed to low-temperature conditions for a time similar to the length of winter (4 months of low-temperature conditions) germinated gradually, while those exposed for longer (>4 months of low-temperature conditions) germinated rapidly. These results were compatible with field observations indicating that seedlings emerged from June to October in the year after mass flowering, and they suggested this germination characteristic (i.e., variation of germination timing due to seed dormancy) may play an ecological function in spreading risk (although it may also increase the potential for seed predation). The results also revealed that stronger light and alternating temperature conditions had no effect on germination, whereas high temperatures and drying had negative effects. The outcomes of the survey on current seedling dynamics revealed that the seedling establishment ratio was high in a forest understory compared to that seen at a site where solar radiation was strong and soil water content was low. This implies that germination characteristics may promote seedling establishment in forest understory.     

赤霉素浸种对白藤种子萌发特性的影响

白藤是中国热带、南亚热带森林中重要的伴生藤本和非木质森林资源。为探究白藤种子萌发的最佳处理,采用赤霉素（GA₃）浸种对白藤种子发芽特性进行研究。结果表明：发芽率以50 mg/L的GA₃溶液浸种处理最高（91.82%）,该处理能提高白藤种子发芽率;发芽势和发芽指数均以400 mg/L GA₃溶液浸种处理最高（83.18%,16.67）,20 mg/L GA₃溶液浸种处理最低（50.65%,11.50）。建议采用GA₃溶液浸种与催芽技术相结合,以提高白藤种子发芽率、发芽势和发芽指数。     

Long-lasting effects of unplanned logging on the seed rain of mixed conifer-hardwood forests in southern South America

Understanding the effects of disturbance on seed rain is critical to predict changes in forest species composition and diversity.Logging effects on seed rain in a mixed conifer-hardwood forest complex in southern Brazil were evaluated.One year of seed rain data were collected from a large-scale observational experiment in logged and protected forests and quantity and average seed size weighted by species abundance(CWM) were compared between old-growth and logged stands 55 years after logging activities.Using these data,variations in frequency of functional groups of species in the seed rain were examined to see if they could be attributed to logging.Results show that the number of seeds per trap was highly right-skewed,ranging from 13 to 12,788 seeds per trap in one year.Seed rain was affected by logging history,with seed traps in old-growth plots receiving significantly less seeds than traps in logged plots.All species included mean seed size weighted by species abundance were significantly smaller in logged than in old-growth forests.This difference persisted after the exclusion of Arawcaria a large-seeded pioneer which was intensively logged,although the difference of seed size between the two forest classes was greatly reduced.Species abundance in the seed rain differed significantly from the established tree community,between logged and oldgrowth stands.The composition of the seed rain was much more variable than the composition of the established tree community and its points more scattered over the ordination space than the points corresponding to the protected forests.The number of collected seeds across different functional groups of species significantly differed between logged and old-growth plots.The seed rain of logged forests reflects their arrested succes sion as indicated by reduced abundance of functional groups such as pioneers,large seeded pioneers and A raucaria,as well as reduced functional diversity.S eed rain differences between logged and old-growth stands reflect the intensive logging of A.angustifolia.     

Seed production of western larch in seed-tree systems in the southern interior of British Columbia

A series of surveys and experiments were conducted on four sites to identify constraints to seed production and natural regeneration in western larch seed-tree systems in the southwestern interior of British Columbia, Canada. These surveys included pollen monitoring, a cone analysis to evaluate seed production potential, seed trapping to estimate seed rain and the installation of field germination trials to assess the effects of germination substrate and seed losses due to bird and rodent predators. Pollen shedding was found to be adequate for moderate seed production with filled seed counts ranging from 9 to 30 per cone (10–34% of all seeds/cone). No significant differences in seed yields per cone and cone characteristics were observed between uncut control stands and seed-tree stands. Seed rain was generally good in 1995, ranging from 70,000 to 4.6 million seed/ha. For the four seed-tree stands, the average filled seed percentage of the trapped seeds ranged from 9–30%. Seed rain and seed quality were much reduced in 1996. Field germination trials showed western larch seeds germinated and survived best (15–70%) on mineral soil but rodent and/or bird predation reduced germination success significantly. Germination/germinant survival on undisturbed forest floor, covered with predator exclusion screens, was intermediate.