The effects of three regeneration harvest methods on plant diversity and soil characteristics in the southern Appalachians

We evaluated the effects of three regeneration harvest methods on plant diversity and soil resource availability in mixed-hardwood ecosystems. The study area is in the Wine Spring Creek watershed on the Nantahala National Forest of the Southern Appalachian Mountains in western North Carolina. The regeneration treatments were: an irregular, two-aged shelterwood cut (2A), with 5.0 m²/ha residual basal area; a shelterwood cut (SW), with 9.0 m²/ha residual basal area; a group selection cut (GS), with 0.10–0.20 ha openings and 25% overstory removal on area basis at first entry; fourth, the control, consisted of two uncut sites (UC). Each harvest treatment was replicated three times across the landscape in similar plant community types. Within each treatment area, permanent plots were marked and inventoried for overstory, midstory, and herbaceous layer plants. In each permanent plot, we collected soil samples in winter (December–March) to reduce temporal variation due to vegetation phenological stage and rainfall events. We analyzed soil samples for extractable calcium (Ca), magnesium (Mg), potassium (K), cation exchange capacity (CEC), pH, bulk density, A-horizon depth, total carbon (C), and nitrogen (N). Species diversity of overstory, understory, and herbaceous layer species was evaluated using species richness (S), Shannon–Wiener's index of diversity (H′), and Pielou's evenness index (E). We used direct gradient analysis (non-metric multidimensional scaling, NMS) to explore the changes in vegetation–site relationships among herbaceous layer abundance, and soil characteristics and overstory basal area between pre-harvest (1994) and post-harvest (2000). Twelve minor overstory species were cut from the 2A treatments and nine species were cut from the SW treatments. Thus, it is not surprising that S and H′ were reduced in the overstory on the heavily cut sites. However, most of these species sprouted from cut stumps and were substantially more abundant in the midstory layer after harvest than before. For the midstory, we found higher S and H′ on the harvested treatments than the control; however, H′ did not differ significantly among the harvest treatments. We measured an increase in herbaceous layer H′ on the more heavily cut treatments (2A and SW) after harvest. We found an increase in average distance in the NMS ordination among sites in 2000 compared to 1994, which suggests greater herbaceous species diversity after harvest. However, we did not see a clear separation among harvest treatments in the NMS ordination.     

Ten-year response of bird communities to an operational herbicide-shelterwood treatment in a northern hardwood forest

Use of herbicides in forestry to direct successional trajectories has raised concerns over possible direct or indirect effects on non-target organisms. We studied the response of forest birds to an operational application of glyphosate and sulfometuron methyl herbicides, using a randomized block design in which half of each 8 ha block received herbicide and the other acted as a control, on shelterwood seed-cut Allegheny hardwood stands in northwestern Pennsylvania. We monitored birds using 50 m radius point counts in two pretreatment years and for 10 years post-treatment (1992-2004). Fences were erected six years after herbicide treatment in response to increased deer browsing at a subset of sites. Avian responses to herbicide treatment varied by nesting guild: we detected no response by cavity-nesters, but documented declines in the shrub-, ground- and canopy-nesting guilds. Responses were short-lived (2-4 years post-treatment), but shrub-nesters did not recover until fencing provided regenerating vegetation respite from browsing. Thus, apparent responses of birds to herbicide were confounded with deer browsing in this study. High species turnover, even within control plots, suggests that avian communities may be assessed more appropriately assessed at larger spatial scales than those used in this study (6.5-8 ha).     

Plant community responses to a gradient of site preparation intensities in pine plantations in the Coastal Plain of North Carolina

Intensively managed loblolly pine (Pinus taeda) forests are common in the southeastern United States and offer opportunities for conservation of biologic diversity. Within intensively managed landscapes, stand establishment relies on combinations of mechanical and chemical site preparation and herbaceous weed control (HWC) to manage competing vegetation and increase pine production. However, few long-term studies have described relationships between intensity of stand establishment and effects on plant communities. Therefore, we examined effects of 6 treatments that varied in intensity via combinations of mechanical (wide spacing and strip shear or narrow spacing and roller chop) and chemical (application or no application) site preparation treatments with HWC (broadcast or banded) from 1 to 8 years after site preparation on plant communities in loblolly pine plantations (n = 6) in the Coastal Plain of North Carolina, USA. All treatments resulted in abundant and diverse plant communities. Chemical site preparation had short lived (?4 year) effects on the herbaceous community but long-term effects on woody plants and pine cover. Increasing management intensity by including broadcast HWC or roller chop/narrow spacing did not additively reduce woody vegetation cover or species richness. However, broadcast HWC reduced grass, vine, and forb cover in the first year post-treatment. Average Morista community similarity values ranged from 0.69 to 0.89 among treatments and plots receiving the same chemical site preparation contained the most similar plant communities. Banded HWC can be paired with wide spacing to maximize herbaceous plant growth important for many wildlife species, particularly in the first few years after site preparation. Site preparation techniques should be tailored to local site conditions, plant communities, and management objectives.     

伞伐更新法对赫卡尼亚(Hyrcanian)森林系统中森林再生和林分结构的影响

研究伞伐更新法对赫卡尼亚森林系统中森林再生和林分结构的影响。在伊朗北部优势种为山毛榉（Fagus orientalisLipsky）的硬木林,采取伞伐更新法和非伞伐更新法方法设计实验区。结果表明,在山毛榉（F orientalis Lipsky）林中采用伞伐更新法处理,明显影响林下草本植物种的频度和密度。伞伐更新法处理后,林堇菜（Viola silvestris Lam.）、车叶草（Asperula odorata L.）、苔草（Carex spp.）和悬钩子（Rubushyrcanus Juz）的种频度明显增加。在对照区,树种的胸高直径（57.50±2.15cm）大于被处理区（50.67±1.88cm）的树种的胸高直径（50.67±1.88 cm）,但对照区和处理区的树种的高度值相似。在1995-2005年间,波斯铁木（Parrotia persica）苗木数量增加到13.2%,而山毛榉（F orientalis）和欧洲鹅耳枥（Carpinus betulus）的苗木数量却明显减少。总之,应该利用其它育林方法,如,带状择伐作业,而不是伞伐更新法培育赫卡尼亚森林中山毛榉林。     

The effect of shelterwood harvesting and site preparation on eastern red-backed salamanders in white pine stands

We studied the effects of the regeneration cut of the shelterwood system and four site preparation options on populations of eastern red-backed salamanders in 90–100-year-old white pine forests in central Ontario, Canada. We established the study in 1994 using a randomized complete block design with three replicates and five treatments: (1) no harvest, no site preparation; (2) harvest, no site preparation; (3) harvest, mechanical site preparation; (4) harvest, chemical site preparation; (5) harvest, mechanical and chemical site preparation. We applied harvest and site preparation treatments from fall 1995 to fall 1997. We collected pre-treatment data in spring and summer of 1995 and post-treatment data from 1998 to 2002. We monitored salamander abundance using a grid of 20 cover boards surveyed 10 times per year within each of the 15 treatment plots. We also quantified changes in overstory and understory cover, supply of downed woody debris, and disturbance to the forest floor. Our data suggest that shelterwood cutting and site preparation can have immediate negative effects on the abundance of red-backed salamander populations in pine forest. However, effects are relatively short lived (<5 years). Changes in abundance appeared to be related to overstory and understory cover, and forest floor disturbance.     

Vegetation response to strip cutting young hardwood stands in West Virginia

Three 21-year-old Appalachian hardwood stands were strip cut using three cutting widths (2.4-m, 3.7-m, and 4.9-m) and allowed to resprout. One year after strip cutting, we examined the vegetation response within the harvested strips relative to non-treated control areas, focusing on the sprouting ability of young hardwood stems and the herbaceous component for wildlife habitat. Results indicate the width of the strip cutting significantly affected the amount of biomass produced from stump sprouts (p = 0.042) and influenced species composition. Shade-intolerant species accounted for more of the biomass production within the wider cut strip widths, while shade-tolerant and shade-intermediate species were more prominent within the narrower cut strips. Cut strip width did not have a significant effect on the biomass of new seedlings germinating after the cuttings. Herbaceous vegetation was greater within the 4.9-m cut strips than in the control plots (p = 0.046); however, the amount of herbaceous biomass produced did not vary among months during the first growing season. Overall, our initial results suggest that strip cutting can provide benefits to wildlife and can possibly provide for additional biomass as the regrowth is harvested in the future.     

Control of bilberry vegetation by steam treatment – effects on seeded Scots pine and associated mycorrhizal fungi

In boreal forest, ground vegetation of bilberry (Vaccinium myrtillus L.) and feather mosses strongly suppress seed regeneration of Scots pine (Pinus sylvestris L.). We investigated a site preparation technique by steam treatment to control bilberry and moss vegetation after clear cutting. Sowing experiments were performed between 1993 and 1995 with Scots pine in four treatments: (1) untreated vegetation, (2) activated carbon added to the soil surface of otherwise intact ground vegetation, (3) steam treated vegetation, and (4) activated carbon added to the soil surface of steam treated vegetation. Activated carbon was added to adsorb possible phenolic compounds released from bilberry leaves and litter. Steam killed ground vegetation effectively and recolonisation of vascular plants and mosses was slow. Scots pine seedling establishment was improved by steam treatment especially when activated carbon was added to the soil surface. We interpret that activated carbon adsorbed and reduced the levels of phenolics from bilberry litter and humus, which otherwise may inhibit seed germination. Dry weight of four year old seedlings was three times higher in steam treated plots than in untreated plots. Seedling nutrient content was also strongly improved by steam treatment. We interpret the increased growth of seedlings in steam treated plots mainly as an effect of reduced resource competition from ground vegetation. Irrespective of treatment, almost all fine roots were colonised by ectomycorrhizal fungi. Using PCR-based molecular methods we were able to identify 28 taxa forming mycorrhiza on the seedlings. Steam treatment did not affect species richness and abundance of ectomycorrhizal inocculum. We conclude that steam treatment has the potential to be an efficient and environmentally acceptable method to reduce negative influence of bilberry vegetation on Scots pine seedling establishment and early growth.     

Influence of browsing damage and overstory cover on regeneration of American beech and sugar maple nine years following understory herbicide release in central Maine

Northern hardwood stands, notably those with American beech (Fagus grandifolia Ehrh), sugar maple (Acer saccharum Marsh.), and yellow birch (Betula alleghaniensis Britton), are abundant across the forested landscapes of northeastern USA and southeastern Canada. Recent studies have reported an increasing dominance of American beech in the understory and midstory of these forests. Beech is a commercially less desirable tree species due to its association with beech-bark disease, and because it commonly interferes with the regeneration of other more desirable tree species. We examined hardwood regeneration characteristics nine years after application of a 3 × 4 factorial combination of glyphosate herbicide (0.56, 1.12, and 1.68 kg ha^?1) and surfactant concentrations (0.0, 0.25, 0.5, and 1.0% v v^?1) to release sugar maple regeneration from beech-dominated understories using three stands that received shelterwood seed cutting in central Maine. Measurements nine years after treatment showed that glyphosate rate increased both absolute (AD) and relative density (RD) of sugar maple regeneration, but not its height (HT). In contrast, beech AD, RD, and HT were all significantly reduced with increasing glyphosate rate. Post-release browsing by ungulates and a high residual overstory basal area resulted in reduced sugar maple HT. Our results indicated that glyphosate herbicide applied in stands that have been recently shelterwood seed cut can significantly increase the abundance of sugar maple regeneration. However, subsequent browsing damage combined with the negative influence of the residual overstory cover can limit the longer-term benefit of understory herbicide treatments. Subsequent removal of the overstory and browsing-control measures may be needed to promote sugar maple regeneration over beech in similar northern hardwood stands.     

The role of herbicide in savanna restoration: Effects of shrub reduction treatments on the understory and overstory of a longleaf pine flatwoods

Woody plant encroachment is a threat to savanna ecosystems worldwide. By exploiting differences in the physiology and seasonality of herbaceous species and encroaching hardwoods, herbicides can be used to control woody shrubs in savannas without causing lasting harm to desirable vegetation. We applied three herbicides and one tank mix to control shrubs following removal of the slash pine (Pinus elliottii Engelm.) canopy and replanting with container-grown longleaf pine (Pinus palustris Mill.) seedlings in a mesic-wet savanna in the southeastern USA. The herbicides tested were imazapyr, sulfometuron methyl, hexazinone, and a hexazinone + sulfometuron methyl tank mix. 4 years after application, no negative effects on understory species richness, diversity, evenness, or community composition were evident in any of the herbicide treatments. Oaks (Quercus spp.), one of the dominant shrub genera on the study site, were resistant to sulfometuron methyl, and this herbicide was therefore ineffective both as a pine release treatment and for enhancing herbaceous species cover. Imazapyr was the most effective treatment overall, leading to significant improvements in longleaf pine seedling growth and also enhancing herbaceous species cover. Both hexazinone and the hexazinone + sulfometuron methyl tank mix provided some seedling growth and understory enhancement as well. In particular, the tank mix significantly increased wiregrass cover relative to the control. Shrubs resprouted quickly following a dormant-season prescribed fire in the fifth year after treatment, indicating that herbicide-related increases in herbaceous cover may be lost if an aggressive prescribed fire program is not implemented.     

Long-term effects of establishment practices on plant communities across successive rotations in a loblolly pine (Pinus taeda) plantation

Implementation of repeated, high-intensity short rotations in forest plantations raises concerns about the effects of such practices on herbaceous layer biodiversity and overall sustainability. To investigate these concerns, we conducted a comparative study of second and third rotation plant communities in a loblolly pine plantation in the Piedmont of North Carolina. The second rotation stand was established in 1960 using conventional practices and was harvested in 1981, leaving two plots in each of three blocks as “historical” plots representing the second rotation. The third rotation was planted in 1982, and a 2 × 2 factorial experiment was established within an area that had been complete-tree harvested, using two site preparation (drum-chop versus shear, pile, and disk) and two cultural (vegetation control versus no vegetation control) treatments in each of three blocks. Presence/absence data for vascular plant taxa were collected in the second rotation historical plots at year 22 and also in the third rotation treatment plots at year 18 and analyzed using non-metric multidimensional scaling (NMDS) ordination, indicator species analysis, analysis of species richness, and computation of species turnover. Results indicated overall similarities in the herbaceous layer from year 22 in the second rotation to year 18 in the third rotation, while revealing some key differences in species composition, including persistence of disturbance-responsive species associated with the vegetation control treatment in the third rotation plots. The addition of these species largely accounted for an increase in species richness from the second to the third rotation. Species composition in low intensity third rotation plots (chop, no vegetation control) most closely resembled that of the second rotation plots of similar age. In addition, differences in species composition due to soil and topographic differences within the study persisted through both rotations, while compositional effects of treatments implemented at the beginning of the third rotation diminished with time. We conclude that more intensive silvicultural practices, such as site preparation and vegetation control, reduce initial competition from woody species and thus permit the persistence of early successional species, increasing overall diversity. From the larger perspective of the entire study, the second and third rotation stands converged to similar species composition after approximately two decades post-planting despite early treatment-related differences in the third rotation. It remains to be seen whether additional harvests, rotations, and intensive practices will continue to support a functioning understory plant community in these short rotation plantation forests.     

Seeding and fertilization effects on plant cover and community recovery following wildfire in the Eastern Cascade Mountains, USA

Slope stabilization treatments are frequently applied following high severity wildfires to reduce erosion, protect water quality, and mitigate threats to human life and property. However, the effectiveness of many treatment options has not been well established. Furthermore, treatments may unintentionally inhibit natural vegetation recovery or facilitate exotic species invasion, compromising long-term ecosystem function. We evaluated the effects of seeding and fertilization treatments on plant cover and vegetation recovery following the Deer Point fire in the Eastern Cascade Mountains of Washington State, surveying vegetation for three consecutive years following fire. We applied a fertilization treatment and two seeding treatments in factorial combination on experimental plots at four sites within the fire. Natural vegetation recovered rapidly on control plots, exceeding 40% average cover the second post-fire year and 53% cover the third year. Seeding and fertilization, applied alone and together, did little to increase total plant cover in any of the three post-fire years. A seed mix containing mostly native species increased seeded species cover, but failed to increase in total plant cover, as reductions in non-seeded species cover largely offset increases in seeded species cover. The seed mix also reduced the cover and frequency of several disturbance-adapted native species and reduced tree seedling abundance by the third year after fire. Exotic species averaged less than 0.5% cover across all treatments, and were not significantly affected by any treatment. Minimal treatment effects on total plant cover suggest that seeding and fertilization did little to reduce erosion hazards. However, seeding with the species mix did interfere with natural vegetation recovery, despite the use of native species and low realized seeded species cover.     

Comparative mast seed production in unmanaged and shelterwood white pine (Pinus strobus L.) stands in central Ontario

The effect of the seed cut of the uniform shelterwood silvicultural system on white pine seed production, seed characteristics, and seed viability during 2 mast seeding events was examined in operationally harvested second growth, white pine-dominated forest stands in central Ontario. Seed traps placed along transects in unmanaged and shelterwood stands in each of 3 blocks were used to monitor seed production in 2000 and 2006 (4 and 10 years after harvesting). During these 2 mast seed years between 386,000 and 2,730,600 seed ha^?1 were produced among study stands. Total seed production expressed on a per hectare and unit pine basal area basis did not differ by harvest treatment or among blocks in either year. Variability in seed production among stands was primarily due to differences in stand structure, with seed production positively related to white pine basal area. Seed characteristics were largely similar between harvested and unmanaged stands and between seed years. Seed viability was relatively high in both years, with seed from shelterwoods germinating slightly slower than those from unmanaged stands. Seed quality, as estimated by laboratory germination performance, was higher in 2006 than 2000, likely due to improved seed development and maturation in the warmer, wetter growing season of 2006. Our results suggest that the seed cut of the uniform shelterwood system applied to second growth white pine stands is unlikely to adversely affect white pine seed production, seed quality, or potential for natural regeneration during mast seeding events.     

Plant species cover,frequency, and biomass: Early responses to clearcutting,burning, windrowing,discing, and bedding in Pinus elliottii flatwoods

Pinelands in a 49 ha naturally-regenerated, mature flatwoods forest in north Florida were clearcut harvested in the fall of 1978, site prepared by burning, shearing and piling, discing, and bedding, and planted to slash pine (Pinus elliottii) in 1979. Three vegetation surveys were conducted: one prior to harvest in the summers of 1977 and 1978, and two subsequent to planting in the summers of 1980 and 1981.Cover and frequency of all plant species encountered were assessed on permanent transects. Foliage biomass by species was assessed by destructive sampling of distinct subplots within permanent plots. The aim was to assess plant species cover, frequency, and biomass responses to the forest operations imposed.Pine was eliminated as a dominant genus by harvesting. Planted pines were a fast increasing, but not dominant, component of the vegetation at 2 years of age. Previously dominant shrubs were severely reduced — often by approximately two orders of magnitude. Indeed, woody species were severely reduced: woody cover from 151 to 12% of surface area at plantation age 2 years; woody biomass from 6223 to 521 kg/ha.Conversely, herbaceous species were substantially increased: herbaceous cover from 38 to 51% of surface area at 2 years; herbaceous biomass from 382 to 1439 kg/ha. Thus, a predominantly woody ecosystem was converted to a predominantly herbaceous one for 2 years following planting.There was little change in plant species richness as a result of forest operations. Plant diversity changes were mixed the 1st year but diversity substantially increased the 2nd year. Comparisons with a companion study (Conde et al., 1983) suggest that, while increases in diversity following maximum site preparation may lag increases following minimum site preparation, cover, frequency, and biomass diversity all converge to common values after 2 years despite disparity in treatments.     

Vegetation community responses to different establishment regimes in loblolly pine (Pinus taeda) plantations in southern MS,USA

Management treatments involving multiple herbicide applications are standard procedure on most industrial pine plantation sites in the southern USA, raising concerns about biodiversity impairment. Management decisions impact not only plant communities but also the habitat potential they create for wildlife. We tested the effects of five intensities of stand establishment treatments on vegetation communities in loblolly pine plantations (n = 4) to age 5 in the Middle Coastal Plain (MCP) of Mississippi. Measurements were species richness, diversity, coverage, and community composition. Treatments were combinations of mechanical site preparation (MSP), chemical site preparation (CSP), and herbaceous weed control (HWC) both banded or broadcast for 1 or 2 years using the same herbicide mixtures. Tree richness and diversity were reduced by increasing treatment intensity; tree coverage, which included crop and non-crop trees, was less in moderate-intensity treatments. Vine richness and coverage were less in more intensive treatments, but 2 diversity indices differed on whether vine diversity was likewise affected. Richness and coverage of forbs and graminoids was lessened by broadcast HWC, with effects mostly limited to the year of application. Plant communities differed in all 5 years, with CSP acting as the primary factor for years 2–5. Early seral communities were favored by CSP, but broadcast HWC suppressed resulting herbaceous plants. Though CSP may somewhat reduce stand-level plant diversity, it may increase overall biodiversity within plantation-dominated landscapes by creating early succession plant communities that enhance wildlife habitat.     

Establishment success of conservation tree plantations in relation to silvicultural practices in Indiana,USA

In the Central Hardwood Forest region of the United States, the variable and somewhat unpredictable establishment success of hardwood tree plantations has traditionally been attributed to competing vegetation and damage due to animal browse. We examined operational plantation establishment success (1–5 years following planting) as it relates to use of particular silvicultural practices. Silvicultural histories were obtained for 87 randomly selected plantations throughout Indiana and field data were collected from each to determine tree survival, tree vigor, and abundance of surrounding vegetation. Survival was highest at sites that were treated with herbicide prior to planting and that had been mechanically planted (as opposed to hand planted). The percentage of trees with evidence of dieback was highest on sites at which browse protection measures had been used, likely reflecting a combination of damage due to inherently high white-tailed deer (Odocoileus virginianus Zimmermann) populations at such sites and ineffectiveness of current browse protection measures. Sites planted by a professional forester and those with herbicide applied subsequent to planting had a higher percentage of trees deemed free-to-grow. Subsequent herbicide application did not reduce cover or height of competing vegetation; however, when used in conjunction with mechanical site preparation techniques, overall cover and height of herbaceous vegetation was reduced.     

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.     

Effects of elevation and postharvest disturbance on the composition of vegetation established after the clear-cut harvest of conifer plantations in southern Shikoku, Japan

Large areas of previously clear-cut conifer plantations have been recently abandoned in Japan. We investigated the vegetation in the clear-cut sites and examined the environmental factors affecting species composition of the vegetation. We set up 32 study sites, each composed of several study plots (5 × 5 m), ranging from 220 m to 1060 m a.s.l. Elevation and warmth index (cumulated thermal quantity) were the primary factors affecting the species composition, with clear-cut areas showing a smaller effect in the nonmetric multidimensional scaling (NMS) ordination. Two-way indicator species analysis (TWINSPAN) divided the 32 study sites into ten vegetation groups, clustering the sites by elevation or by postharvest disturbances (i.e., replanting or browsing of Sika deer). Deciduous trees and shrubs were significant in the vegetation cover at higher elevations, while they were less so in areas of high Sika deer populations. We also investigated the abundance of old-growth species, which are expected to regenerate where the clear-cut site is abandoned. Evergreen Quercus and Castanopsis saplings were abundant at low elevations (<600 m), suggesting that they will successfully regenerate. The sapling densities of Abies firma and Betula grossa were significantly large where a clear-cut site was adjacent to natural forest, which is expected to act as a seed source. This implies that degraded deciduous forests may establish after clear-cutting at intermediate and high elevations (>600 m) if the clear-cut site is distinct from seed sources. It is argued that the preservation of natural forests is critical for the regeneration of old-growth species.     

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.     

Effects of grazing exclusion and environmental conditions on the soil seed bank of a Mediterranean grazed oak wood pasture

Large seed banks in the soils of Mediterranean wood pastures can allow the composition of the understorey vegetation to adapt to changing conditions such as under-grazing, grazing exclusion and climate change. This three year study investigated the effect of grazing exclusion on the transient and persistent seed banks of 23 areas of a Mediterranean wood pasture of Quercus suber L., Q. ilex L. and Q. pubescens Willd. A canonical correspondence analysis was used to determine the effect of topo-climatic (elevation, aspect, slope, rainfall, temperature, tree coverage), soil (pH, soil texture, and soil nitrogen, phosphorus, lime and organic carbon content) and biodiversity (Shannon index, species richness index, and Pastoral Value) variables on the soil seed bank under grazed and ungrazed conditions. The size of the persistent seed bank increased with rainfall, grazing, and the available phosphorus content of the soil. Specific site by site grazing regimes could increase the abundance of legumes in the soil seed bank and the species richness and diversity of the understorey vegetation. These results can help guide the conservation management of this silvopastoral area.     

科尔沁沙地活沙障对土壤种子库的影响

选取科尔沁沙地不同生长年限活沙障,调查并测定了土壤种子库的种类组成、密度以及物种多样性等特征。结果表明:(1)仅有封育措施时,流动沙丘没有物种存在。建活沙障后,7年和5年样地的行间和行下物种种类比生长3年样地多,1年生植物逐年增多。(2)随沙障生长年限延长,土壤种子库中种子密度表现出逐年增多的趋势。(3)在物种多样性和相似性方面,建活沙障的样地变化趋势不明显。封育3年后的流动沙丘无物种多样性,与其他样地相比相似性系数为零。(4)建活沙障后,各样地在物种种类和种子数方面逐年增多,认为建黄柳和羊柴网格状活沙障可以达到治理沙丘的目的。