Soil seed banks in four 22-year-old plantations in South China: Implications for restoration

To better understand the potentials of the soil seed banks in facilitating succession towards a more natural forest of native tree species, we quantified the size and composition of the soil seed banks in established plantations in South China. The seed banks were from four typical 22-year-old plantations, i.e., legume, mixed-conifer, mixed-native, and Eucalyptus overstory species. Species diversity in the seed banks was low, and the vegetation species differed from those found in the seed bank in each plantation. A total of 1211 seedlings belonging to eight species emerged in a seedling germination assay, among which Cyrtococcum patens was most abundant. All species detected were shrubs and herbs, and no viable indigenous tree seeds were found in soil samples. Size and species composition of the seed banks might be related to the overstory species compositions of the established plantations. The seed bank density in soils was highest in the mixed-conifer plantation followed by Eucalyptus, mixed-native, and legume plantations. Species richness among the seed banks of plantations was ranked as follows: Eucalyptus > mixed-conifer > mixed-native = legume. The results indicated that the soil seed banks of the current plantations are ineffective in regenerating the former communities after human disturbances. Particularly, the absence of indigenous tree species seeds in the seed banks would limit regeneration and probably contribute to arrested succession at the pioneer community stage. It would appear from these data that the soil seed banks under the current plantations should not be considered as a useful tool leading the succession to more natural stages. Introduction of target indigenous species by artificial seeding or seedling planting should be considered to accelerate forest regeneration.     

Germination characteristics and diversity of soil seed banks and above-ground vegetation in disturbed and undisturbed oak forests

The destruction of natural ecosystems is an important issue in many parts of the world. In the west of Iran, a vast area of the Zagros Mountain range is covered by typical vegetation including several rare plant species, of which many are currently considered endangered by anthropogenic activities. Despite the important role of soil seed banks to help conserve these degraded plant communities, the floristic studies in the Zagros forests have only focused on above- ground vegetation. In this study, the characteristics of soil seed banks and above-ground vegetation were examined at two forest sites： an undisturbed control （Un） and a disturbed （D） site. The objectives of this study were 1） to investigate the diversity of above-ground vegetation and soil seed banks in disturbed and undisturbed forests, 2） to examine the soil properties and the germination characteristics of the soil seed bank in disturbed and undisturbed oak forests and 3） to estimate the potential of soil seed banks in the restoration of disturbed sites. The results show that soil properties between Un and D sites were significantly different with higher values of pH, NH4-N, N~o,, CEC, OC, clay and canopy percentage in the Un site than in the D site. The Simpson diversity, Margalef richness and evenness indices differed significantly between sites, either for the soil seed banks or the above-ground vegetation. After a period of 26 weeks, the germination speed and the mean daily number of germinants were significantly different between Un and D sites. Without other conservation measures, soil seed banks alone cannot result in a full recovery after severe disturbances in the oak forests of Zagros.     

Comparison of 5th- and 14th-year Douglas-fir and understory vegetation responses to selective vegetation removal

The effects of early vegetation management on the survival and growth of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] were examined 5 and 15 years after planting in the Oregon Coast Range. Our first objective was to document the effects of vegetation species competition upon key ecosystem properties. The second objective was to document the effects of vegetation removal during early Douglas-fir stand establishment upon long-term tree growth and on biomass production by vegetation components. Seven levels of manual vegetation removal were maintained for the first 5 years after planting: 0%, 25%, 50%, 75%, and 100% shrub removal; and 100% shrub removal combined with 50% or 100% herbaceous vegetation removal. Shrub and herb removal did not affect Douglas-fir survival at year five, but treatments providing less than 75% shrub removal significantly reduced Douglas-fir survival by year 15. Removing shrubs and herbs completely (100S + 100H) during the 5 years following tree planting allowed successful tree establishment, with a 366% increase in biomass accumulation per hectare for Douglas-fir in that treatment at the end of 14 years of growth. At 15 years stand age, even with shrub removal alone, a 304% gain in tree biomass per hectare was obtained compared to no vegetation removal (NVR). By stand age 15 years, any increase in the degree of understory removal beyond 75% did not contribute significantly to additional tree survival and growth. The understory vegetation on NVR treatment plots and the herbaceous vegetation on 100% shrub removal (100S) treatment plots, contained >90% and >80% of aboveground biomass N at 5 years, respectively, indicating possible competition for soil N. Soil moisture was not different among treatments at 5 years. Complete vegetation removal (100S + 100H) for 5 years resulted in a significant increase in soil bulk density (P < 0.05), a significant decrease in total soil C (P < 0.05) and no change in total soil N in the upper 15 cm of the mineral soil. By 14 years, however, only the soil bulk density remained greater (P < 0.05) on the 100S + 100H treatment. We conclude that greater tree survival and growth occurred with at least 75% shrub removal. Our results suggest that managers may have substantial flexibility in maintaining a partial understory component suitable for ecosystem productivity, canopy cover and wildlife habitat, while maintaining forests productive for timber resources.     

香格里拉亚高山不同退化程度森林群落土壤种子库的特征研究

2006～2007年采用种子萌发法,对香格里拉亚高山不同退化森林群落的土壤种子密度、丰富度,物种组成及地上植被组成开展了调查研究。结果表明:(1)亚高山土壤种子库中共有42个种子植物,种子密度为471～891粒/m2;(2)退化林地种子库中的物种密度依次为重度退化>极度退化>中度退化>轻度退化>未退化,物种丰富度依次为轻度退化>未退化>极度退化>中度退化>重度退化;(3)多年生草本植物在5类群落中均占绝对优势,只在未退化林地中发现木本植物;(4)土壤种子库及地上植被在物种组成上具有较小的Jaccard相似系数;(5)11月份物种数量及种子密度比4月份及7月份高;(6)0～5 cm表土种子库中具有较高的物种数量及种子密度;(7)种子扩散、地上植物的无性繁殖及人工造林是恢复香格里拉亚高山退化植被的有效途径。     

Enrichment planting as a silvicultural option in the eastern Amazon: Case study of Fazenda Cauaxi

Liana-dominated forest patches constitute 15–20% of old-growth forests in the Eastern Amazon but are generally excluded from management for timber production. Here we ask if liana-dominated patches may be brought into production by clearing lianas and conducting enrichment planting (EP) of native timber species. We present growth results from 8 years of such EP trials. Rapid growth and low mortality of all species in this study suggest that EP in cleared liana patches can contribute to timber stocks in second and third harvests of managed forests. The most vigorous individuals of Parkiagigantocarpa and Schizolobium amazonicum in each enrichment site grew more than 1 cm diameter per year (rates were initially >2 cm yr⁻¹), and attained dominant canopy positions and diameters equal to those of small canopy trees in the surrounding forest within 8 years of planting (mean dbh ∼18 cm and ∼20 cm, respectively, at year 8). Limited data on Ceiba pentandra plantings indicate a similar trajectory for this species (dbh ∼40 cm in 8 years). The most vigorous Swietenia macrophylla grew at least 1 cm per year in enrichment plots (mean dbh ∼10 cm in 8 years), but take longer to attain dominant positions. Tabebuia serratifolia may take much longer to reach the canopy than other species tested (rates <1 m yr⁻¹). We attribute the excellent performance to light availability; planting in intact soil with minimal compaction and abundant organic material; and low competition rates maintained by periodic thinning of competing vegetation.     

Alternative silvicultural practices with variable retention improve bird conservation in managed South Patagonian forests

Alternative silvicultural approaches to timber management, such as regeneration treatments with different degrees of stand retention, may mitigate negative effects of clear-cutting or shelterwood cuts in forested ecosystems, including changes in old-growth forest bird communities. The aims of this work were: (a) to compare bird species richness and densities among different silvicultural designs with variable retention (dispersed and/or aggregated) and unmanaged primary forests, and (b) to assess temporal changes at community and species levels before and after treatments. A baseline avian survey was conducted prior to harvesting to evaluate canopy gap presence and forest stand site quality influences. Subsequent to harvesting, data on bird species richness and density were collected by point-count sampling during the summer season for 5 consecutive years (4 treatments × 5 years × 6 sampling points × 5 counts). Bird species richness and density (15 species and 9.2 individuals ha⁻¹) did not change significantly with forest site quality of the stands and canopy gap presence in unmanaged forests. However, both variables were significantly modified in managed forests, increasing over time to 18 species and reaching to 39 individuals ha⁻¹. Inside the aggregated retention, bird communities were more similar to unmanaged primary forests than those observed within the dispersed retention or in clear-cuts. Opting for a regeneration method with dispersed and aggregated retention has great potential for managing birds in Nothofagus pumilio forests. This method retained enough vegetation structure in a stand to permit the establishment of early successional birds (at least in dispersed retention), and to maintain the bird species of old-growth forests which could persisted in the retention aggregates.     

Structure and composition of the seed bank in monospecific and tree species-rich temperate broad-leaved forests

How tree species diversity affects ecosystem functioning is a topic of intensive research. This study compares monospecific and species-rich broad-leaved forests under similar bedrock and climate conditions for the size and composition of their seed bank. We tested the hypotheses that (i) the actual herb-layer vegetation has an only weak influence on the composition of the seed bank, (ii) the species diversity of the seed bank increases with tree-layer diversity, and (iii) tree species forming a more persistent litter layer reduce the number of germinating seeds. The number of seeds and their species composition were investigated in soil cores taken from three soil depths (0–5, 5–10 and 10–20 cm; n = 4, with each 6 sub-samples) in 9 study plots differing in tree species diversity (3 monospecific Fagus plots, 3 plots with Fagus, Fraxinus and Tilia, and 3 plots with Fagus, Fraxinus, Tilia, Carpinus and Acer). Tree species diversity had a much stronger influence on the size and composition of the seed bank than herb-layer diversity or composition, the latter revealing only a low similarity to the corresponding seed bank. The number and species diversity of emerging seedlings decreased significantly with the amount of acidifying Fagus litter, but increased with litter mass of Tilia and other trees with nutrient-rich, rapidly decomposing litter. We conclude that tree species diversity does not influence the seed bank through effects on herb-layer composition, but mostly through differential disturbance histories of the stands and litter quality effects on germination and soil chemistry. From the contrasting effects of Fagus and Tilia leaf litter, it appears that effects of tree species identity are more relevant than influences of tree species diversity itself.     

Native woody species regeneration in exotic tree plantations at Munessa-Shashemene Forest,southern Ethiopia

Regeneration of native woody species was studied in the plantations and the adjacent natural forest at Munessa-Shashemene Forest Project Area, Ethiopia. The aim of the study was to test the hypothesis that tree plantations foster regeneration of native woody species. A total of 60 plots, having 10 × 10 m area each, were studied in monoculture plantations of 4 exotic species (Cupressus lusitanica, Eucalyptus globulus, E. saligna, Pinus patula) and an adjacent natural forest. Ages of the plantations ranged between 9 and 28 years. Soil seed bank analysis was also undertaken from soil samples collected in each of the 60 plots to examine the similarity between the soil seed flora and aboveground vegetation. A total of 56 naturally regenerated woody species were recorded beneath all plantation stands with densities ranging between 2300 and 18650 individuals / ha in different stands. There was a significant difference among plantation stands with regard to understorey density (standard deviation: 4836 ± 1341). Vegetation diversity was assessed through analyses of floristic composition, species richness and abundance. Generally, seedling populations were the most abundant components of the regeneration in most of the plantation stands, forming 68 % of the total regeneration count in all stands. A total of 77 plant species represented by 44 herbs, 13 woody species, 8 grasses and 12 unidentified species were recorded in the soil seed bank from all stands. Similarity between the soil seed bank and aboveground flora was very low implying that the role of soil seed banks is negligible rather dispersal plays an important role in the process of regeneration. These results support the concept that forest plantations can foster the regeneration of native woody species, thereby increasing biological diversity, provided that there are seed sources in the vicinity of the plantations.     

Polylepis australis’ regeneration niche in relation to seed dispersal,site characteristics and livestock density

Establishment of Polylepis forests endemic to the mountains of South America may be affected by seed dispersal, site characteristics and livestock density. Polylepis australis (“tabaquillo”) grows in the high mountains of central Argentina, where we set up 76 square study plots of 900 m². To determine dispersal distance, we distributed 6 seed traps per plot in and around 20 plots. To determine the best site characteristics and livestock stoking rates, at two river basins differing in historic stocking rates, we analyzed the presence of seedlings in 56 plots and recorded topography, vegetation types and indicators of livestock activity. We also measured microsite characteristics in a sample of 32 comparable pairs of 1 m² quadrats, with and without seedlings. Maximum recorded dispersal distance of P. australis seeds was 6 m, and seedlings were found no more than 10 m from seed trees. The numbers of seedlings and seed trees were 3.5 and 4 times higher, respectively, in the basin with less livestock. At the 900 m² plot scale, a Poisson regression indicated a positive relationship between seedling number and P. australis canopy cover. At the quadrat scale (1 m²), seedlings were found in quadrats with significantly lower evidence of soil erosion than comparison quadrats without seedlings. We conclude that the main limitations to recruitment are short seed dispersal distances, lack of seed trees and extreme soil erosion. Management should therefore aim at preserving seed trees and reducing livestock density to prevent erosion.     

Effect of mangrove restoration on crab burrow density in Luoyangjiang Estuary,China

Background:Mangrove restoration seeks to restore or rebuild degraded mangrove systems.The methods of mangrove restoration include ecological projects and restoration-oriented technologies,the latter of which are designed to restore the structure,processes as well as related physical,chemical and biological characteristics of wetlands and to ensure the provision of ecosystem services.As important components of mangrove ecosystem,benthic organisms and crabs play a key role in nutrient cycling.In addition,mangrove restoration,such as vegetation restoration measures,can lead to changes in the benthic faunal communities.This study investigates whether the presence of different mangrove species,age and canopy cover of mangrove communities affect the density of crab burrows.Methods:The Luoyangjiang Estuary,in the southeast of Fujian Province,was selected as our research area.A survey,covering 14 sites,was conducted to investigate the impacts of mangrove restoration on the density of crab burrows in four rehabilitated forests with different stand ages and canopy.Results:It was found that differences in vegetation types had a large impact on crab density and that the density of crab burrows was lower on exposed beaches(non-mangrove)than under mature Kandelia candel,Aegiceras corniculatum and Avicennia marina communities.In general,the amount of leaf litter and debris on mangrove mudflats was greater than on the beaches as food sources for crabs.Two-factor analysis of variance(ANOVA)shows that changes in mangrove species and age since restoration had different effects on crab burrow density.The effect of canopy cover was highly significant on crab burrow density.Conclusions:The results suggest that in the process of mangrove restoration the combined effects of mangrove stand age,canopy cover and other factors should be taken into account.This study further supports the findings of the future scientific research and practice on mangrove restoration and management measures.     

Dominance by the introduced tree Rhamnus cathartica (common buckthorn) may limit aboveground carbon storage in Southern Wisconsin forests

Many ecosystems are now dominated by introduced species, and because dominant species drive ecosystem properties, these changes lead to increased uncertainty in estimates of carbon storage and cycling. We examined aboveground biomass in forests dominated by the introduced tree Rhamnus cathartica (common buckthorn) relative to forests dominated by native species, and measured aboveground biomass increment over a three-year period (2005-2008). Three of the four lowest biomass levels occurred in R. cathartica-dominated forests, and biomass in these forest types was stored primarily in trees 10-20 cm DBH. By contrast, forests dominated by native trees (including those with R. cathartica understories) had the six highest biomass levels, and biomass was stored primarily in trees >50 cm DBH. On average, forests dominated by R. cathartica stored half as much aboveground biomass (14.6 ± 3.3 kg/m²) as forests dominated by native tree species (28.9 ± 8.3 kg/m²). R. cathartica-dominated forests also had half the aboveground biomass increment of native-dominated forests (0.28 vs. 0.60 kg/m²/year). Although known anecdotally as a fast-growing species, R. cathartica growth rates declined with increasing size. Between 2005 and 2008, R. cathartica individuals <10 cm DBH grew faster than native species; however, R. cathartica individuals >10 cm DBH grew consistently slower than native species. Overall, our findings indicate that intrinsic size limitations on R. cathartica will lead to lower biomass stocks in forests where it acts as a canopy dominant relative to forests dominated by native tree species.     

Through droughts and hurricanes: Tree mortality,forest structure,and biomass production in a coastal swamp targeted for restoration in the Mississippi River Deltaic Plain

Coastal swamps are among the rapidly vanishing wetland habitats in Louisiana due to accelerated sea-level rise and hydrological alterations that alter the natural flooding regime. In particular, the swamp forests of Lake Maurepas, Louisiana, have degraded considerably, and research regarding their condition might suggest approaches for their restoration. We measured forest structure, species composition, tree mortality, annual aboveground net primary production (ANPP) of woody species, and aboveground biomass allocation to leaf litter and wood, and soil strength at forty study plots within the Lake Maurepas basin over 5 years to evaluate the current condition of this coastal forested wetland. Local measures of salinity and regional measures of flooding were used to predict ANPP and aboveground biomass allocation. The 5-year study period included an intense drought as well as years characterized by hurricane-induced flooding. The forty study plots could be divided into four distinct habitat clusters based on standing biomass, structural variables, and salinity. The majority of the plots were co-dominated by Taxodium distichum and Nyssa aquatica. Acer rubrum var. drummondii and Fraxinus pennsylvanica were common mid-story species throughout the western and southern parts of the study area, while Salix nigra, Morella cerifera, and Triadica sebiferum were more important at the more degraded plots in the eastern part of the basin. Annual mean soil salinity reached unprecedented level (2–5 psu) during the drought and cumulative tree mortality reached up to 85% in areas characterized by frequent saltwater intrusions. The ANPP was higher during the drought period in 2000–2001 than during subsequent years, and was dominated by T. distichum. At most sampling plots, litter production exceeded wood production annually. A negative correlation between aboveground biomass allocation to litter and flooding indicated that biomass allocation shifted from litter toward wood during wet years. Overall, the majority of the plots sampled produced less than 400 g m⁻² yr⁻¹ of aboveground biomass annually due to the interacting negative effects of saltwater intrusion and prolonged flooding with nutrient-poor water. Reintroduction of Mississippi River water to the Maurepas system has the potential to benefit these swamps greatly by restoring a greater flow of nutrients, sediments, and fresh water through the wetlands. The historically slow (i.e., multi-decadal) process of swamp deterioration was greatly sped by low salinity (i.e., 2–5 psu) saltwater intrusions during a drought in 1999–2000. The majority of the coastal swamps in the Pontchartrain Basin are deteriorating, and most of this swamp area will be lost to open water in the foreseeable future if no restoration action is taken.     

Forest vegetation responses to climate and environmental change: A case study from Changbai Mountain, NE China

The distribution of plant species has always been altered by changing climatic conditions. Nonetheless, the potential for species’ range shift responses has recently become severely limited, as exceptionally fast temperature changes coincide with a high degree of anthropogenic habitat fragmentation. This study provides rare insights into the effects current temperature increases have on pristine temperate forest ecosystems, using the forests of Changbai Mountain, NE China, as a case study. On the northern slopes of the mountain at elevations between 750 and 2100 m, the composition of trees, shrubs and herbaceous species was recorded on 60 plots in 1963 and 2006/07. Multiple linear regression (MLR) and canonical correspondence analysis (CCA) were used to establish the response of plant diversity and plant distribution patterns to environmental conditions. Climatic factors proved important in explaining the spatio-temporal trends within the vegetation. The composition of dominant trees remained mostly unchanged over the last 43 years, reflecting a very slow response of the forest canopy to environmental change. The composition of young trees, shrubs and herb species showed varied changes in the different forest types. A homogeneous species composition in the cohort of regenerating trees indicates an increased future uniformity in the mixed broadleaved and coniferous forest. The understory vegetation of high elevation birch forests was invaded by floristic elements of the lower-elevation coniferous forests. Both these trends pose potential threats to forests plant diversity. Future research investigating climate change responses in forest canopy composition needs to be based on even longer timescales, while investigations in the near future need to pay particular attention to the changes in the distribution of rare and threatened herbaceous species.     

凉风坳亚热带次生常绿阔叶林土壤种子库和种子雨的特征研究

选择四川省沐川县凉风坳亚热带次生常绿阔叶林为研究对象,在2004年5月、2004年12月和2005年5月对其林下土壤种子库、种子雨以及种子天然萌发状况等方面进行系统调查及分析研究。结果显示,种子下落前后土壤种子库储量,变动为643.2～889.2粒.m-2,物种和种子密度多年生草本物种均占优势。天然林土壤种子库Shannon-Wiener指数均在2004年5月最大,2004年12月次之,2005年5月最小;Simpson指数却和Shannon-Wiener指数H＇的变化趋势相反;Pielou均匀度指数在2004年12月有所降低,此后又升高。种子均呈明显垂直分布,其中0～2 cm土层种子数量最多,其次是枯枝落叶层,其数量随着土层加深而降低。土壤种子库年输入活力种子142.3粒.m-2,年输出活力种子268.9粒.m-2,动物取食是造成种子损失的主要原因。对照人工林土壤种子库物种和密度均低于天然林地;种子库与地上植被物种相似性系数,人工林较高,而天然次生常绿阔叶林较低。     

Effects of disturbance history and environmental factors on the diversity and productivity of understory vegetation in a cool-temperate forest in Japan

We assessed the species richness and aboveground productivity of understory plants in nine types of forest stand (116 plots in total) that had different disturbance histories that were combinations of the frequency of plantation (clear-cutting, site preparation, planting), typhoon damage, and selective cutting. We established two 1 m × 1 m quadrats to measure species richness and productivity and one 1 m × 30 m belt to measure species richness in each plot. Canopy leaf area index (LAI), soil NH₄⁺, soil C/N ratio, slope angle, and slope aspect were measured as current environmental factors affecting each plot. The variance in species richness was better explained by disturbance history (69% in quadrats; 86% in the belt) than by current environmental factors. Species richness and the Simpson index decreased as the frequency of plantation increased. In contrast, the variance in productivity was better explained by current environmental factors (82%), especially canopy LAI (45%), than by disturbance history. The relations of species presence and productivity to the explanatory variables differed among species, although there were some common responses within life forms. The effects of disturbance on species diversity remained for 20–80 years. Forest management should therefore take into account the long-term effects of disturbance history to maintain understory plant diversity.     

Herb layer vegetation of south Swedish beech and oak forests—effects of management and soil acidity during one decade

Effects of forest management and soil acidity on herb layer vegetation were studied after 10 years on 190 permanent plots in south Swedish beech (Fagus sylvatica) and oak (Quercus robur) forests. Species richness generally increased with management intensity, mainly due to establishment of ruderal species from the seed bank. Species richness of the typical forest flora was unaffected by management. Moderate management of oak stands favoured several species which are commonly found in semi-natural pastures. Classification and ordination of the data showed that the main floristic gradient within Swedish beech and oak forest vegetation is related to soil acidity. Species richness of the typical forest flora was strongly positively correlated with soil pH in beech forests, but this correlation was weaker in oak forests. The number of herbaceous plants with a broader habitat range increased with pH only in the oak forest plots. Long term changes in the forest environment, which may affect the vegetation, are the decline of grazing 150-50 years ago and soil acidification mainly caused by atmospheric pollutants during the last 50 years. In the one-decade perspective of this study, however, we did not find a general trend towards a more acid-tolerant flora. Neither could we find a general decrease of pasture species in currently ungrazed oak stands. The results indicate that most typical forest plants are well adapted to and partly depend on occurrence of canopy gaps and soil disturbance. If canopy thinning is followed by periods of canopy closure the characteristic shade tolerant flora of Swedish beech and oak forests may be able to persist as long as soil chemical limits of existence are not exceeded.     

Floristic composition and spatial distribution of germinable seeds in a spruce plantation

Introduction

The logging of several spruce plantations is planned for the next years in the Eifel National Park (Western Germany). To understand the ecological mechanisms of spontaneous forest regeneration that follows these impacts, it is crucial to investigate the species composition and functional diversity of the buried germinable seeds in those stands.

Methods

We analysed the soil seed bank by germination method and characterised germination dynamics and distribution of seedlings throughout the samples according to a sigmoid model and cumulative curves, respectively. To compare the proportions of functional and syntaxonomical groups between seed bank and aboveground vegetation, we applied the Fisher??s exact test. Additionally, we described the spatial distribution of the species in the seed bank according to semivariograms.

Results

The studied seed bank reached a density of about 5,300 seed?m^?2. Most of the species detected in the seed bank are related to open vegetation, forest fringes and early successional stages of forest regeneration. In spite of a low floristic similarity between seed bank and aboveground vegetation, the functional and syntaxonomical composition is very similar. Further studies considering the distribution of seeds in the soil and the changes of the seed bank composition during the regeneration process are required.     

Short-term response of the herbaceous layer within leave patches after harvest

Leave patches, uncut areas in a harvested forest, may conserve herbaceous layer species that decline after forest clearcutting. They may also serve to maintain source populations for the recolonization of the harvest area. The main objective of this study is to characterize the short-term response of the herbaceous layer to clearcut harvesting disturbance within and adjacent to leave patches. Four experimental 1 ha patches and two uncut references were established. Within each patch or reference, belts of five 1 m² quadrats were placed at 50 m and 5 m outside the patch, at 0 m (edge), and at 25 m, 35 m, and 50 m (centre) inside. These belts of quadrats were replicated at all four aspects (North, South, East, and West). Ground vegetation was sampled yearly for 1 year before harvest and 3 years after harvest in the experimental patches and for 2 consecutive years in the references. Some common residual species declined significantly in the clearcuts, but remained stable inside the patches in the short term (3 years after harvest). Overall species composition changed little in the patch interior and edge after harvest. Colonizing species (those that appeared in quadrats after harvest) in the patch exterior were predominantly early-seral species, whereas colonizers in the patch interior tended to be shade-tolerant forest species. Species were grouped a priori based on two habitat preferences (amounts of canopy cover and disturbed substrate). Species characteristic of a habitat with closed canopy and undisturbed substrates that decreased significantly over time in the patch exterior were negatively correlated with the amount of exposed mineral soil and open canopy. Species characteristic of a habitat with open canopy and disturbed substrates that increased significantly at the patch exterior showed a positive correlation with the amount of exposed mineral soil and open canopy. No species’ habitat preference groups declined significantly in the patch interior or edge over time. Based on species’ responses to forest operations, it appears that at least the common forest species are maintained in the short term within leave patches.     

长白山杨桦次生林采伐林隙种子库特征

研究长白山杨桦次生林不同大小采伐林隙的土壤种子库特征.结果表明:杨桦次生林非林隙林分中种子库储量远高于林隙,但多样性比林隙低;不同大小林隙内的种子库储量差异显著,其中50～100 m2大小的林隙内种子库储量最大;随林隙形成时间的延长,林隙内的种子库储量减少,但多样性有所增加;林隙内不同部位间的种子库储量变化较大,且丰富度大小同个体密度大小的变化不一致;种子库中优势种突出,水曲柳、紫椴、山槐与色木槭4个树种的种子数量占种子总量的74.3%以上;地表凋落物层对种子落入土壤有明显的阻滞作用;在林隙形成初期,种子库的组成及数量主要由腐殖质层种子库决定,但随时间的推移枯枝落叶层种子库对整个种子库的贡献越来越大;林隙内土壤种子库同地上更新幼苗相似性不大.     

Patterns in spatial extent of gap influence on understory plant communities

Gap formation in forests can have impacts on forest ecosystems beyond the physical boundary of the canopy opening. The extent of gap influence may affect responses of many components of forest ecosystems to gap formation on stand and landscape scales. In this study, spatial extent of gap influence on understory plant communities was investigated in and around 0.1 and 0.4 ha harvested canopy gaps in four young Douglas-fir (Psuedotsuga menziesii) dominated stands in western Oregon. In larger gaps, the influence of gap creation on understory plant communities in surrounding forests was minimal. The area showing evidence of gap influence extended a maximum of 2 m beyond the edge of the canopy opening, suggesting that the area affected by gap creation did not differ greatly from the area of physical canopy removal. In smaller gaps, influence of the gap did not extend to the edge of the canopy opening. In fact, the area in which understory vegetation was influenced by gap creation was smaller than the physical canopy opening. Gap influence appears to be limited to areas where ruderal or competitor species are able to replace stress-tolerator species, likely due to elimination or reduction of these species by physical disturbance or competition. The limited gap influence extent exhibited here indicates that gap creation may not have a significant effect on understory plant communities beyond the physical canopy opening. This suggests a limited effectiveness of gaps, especially smaller gaps, as a tool for management of understory plant diversity, and perhaps biodiversity in general, on a larger scale.