The relationship between soil seed bank,above‐ground vegetation and disturbance intensity on old‐field successional permanent plots

Questions: How does disturbance and successional age influence richness, size and composition of the soil seed bank? What is the potential contribution of the soil seed bank to the plant community composition on sites differing in their successional age or disturbance intensity? Location: Experimental Botanical Garden of Göttingen University, central Germany. Methods: Above‐ground vegetation and soil seed bank were studied on formerly arable fields in a 36‐year‐old permanent plot study with five disturbance intensities, ranging from yearly ploughing via mowing to long‐term uninterrupted succession. We compared species compositions, seed densities and functional features of the seed bank and above‐ground vegetation by using several methods in parallel. Results: The seed bank was mainly composed of early successional species typical of strongly disturbed habitats. The difference between seed bank composition and above‐ground vegetation decreased with increasing disturbance intensity. The species of greatest quantitative importance in the seed bank was the non‐native forb Solidago canadensis. Conclusions: The ability of a plant community to regenerate from the soil seed bank dramatically decreases with increasing time since abandonment (successional age) and with decreasing disturbance intensity. The present study underlines that plant species typical of grasslands and woodlands are limited by dispersal capacity, owing to low capacity for accumulation of seeds in the soil and the fact that most species do not build up persistent seed banks. Rare and target species were almost absent from the seed bank and will, after local elimination, depend on reintroduction for continuation of their presence.     

Succession in sub‐boreal forests of West‐Central British Columbia

Abstract. Structural and compositional changes were analysed over the course of 400+ yr of post‐fire succession in the sub‐boreal forests of west‐central British Columbia. Using a chronosequence of 57 stands ranging from 11 to 438 yr in age, we examined changes in forest structure and composition with complementary PCA and DCA ordination techniques. To determine stand ages and timing of tree recruitment, approximately 1800 trees were aged. Most early successional forests were dominated by Pinus contorta, which established rapidly following fire. Abies lasiocarpa and Picea glauca × engel‐mannii were also able to establish quickly, but continued to establish throughout the sere. Few Pinus contorta survived beyond 200 yr, resulting in major changes in forest structure. In some stands P. contorta never established, which led to considerable variation among stands less than 200 yr old. The oldest forests converged on dominance by Abies lasiocarpa. Vascular plant diversity decreased during succession whereas canopy structure became more complex as gap dynamics developed. Although these sub‐boreal forests contain few tree species, successional changes were pronounced, with structure changing more than composition across the chronosequence.     

Seed banks of temperate deciduous forests during secondary succession

Question: (i) How does former land use and land use intensity affect seed bank development during post‐agricultural succession? (ii) How does time since the last clear‐cut change seed bank composition during post‐clear‐cut succession? Methods: One data set was compiled per succession type using the following selection criteria: (i) the data set included a successional series, (ii) plots were located in mesotrophic forest plant communities and (iii) vegetation data were available. The post‐agricultural succession data set comprised 76 recent forest plots (eight studies); the post‐clear‐cut succession data set comprised 218 ancient forest plots (three studies). Each data set was analysed separately using either linear mixed models or generalized linear models, controlling for both environmental heterogeneity and variation between study locations. Results: In the post‐agricultural succession data set, land use and time significantly affected nearly all the studied seed bank characteristics. Seed banks on former arable land recovered poorly even after 150 year of restored forest cover, whereas moderate land use intensities (grasslands, heathlands) yielded more rapid seed bank recovery. Time was a significant determinant of all but two soil seed bank characteristics during post‐clear‐cut succession. Seed banks in managed ancient forest differed strongly in their characteristics compared to primary forest seed banks. Conclusions: Forest seed banks bear the marks of former land use and/or forest management and continue to do so for at least 150 years. Nevertheless, time since the last major disturbance, being either former land use or clear‐cutting, remains a significant determinant of the seed bank.     

Long‐term seed bank dynamics in a temperate forest under conversion from coppice‐with‐standards to high forest management

Questions: How do changes in forest management, i.e. in disturbance type and frequency, influence species diversity, abundance and composition of the seed bank? How does the relationship between seed bank and vegetation change? What are the implications for seed bank dynamics? Location: An ancient Quercus petraea — Carpinus betulus forest in conversion from coppice‐with‐standards to regular Quercus high forest near Montargis, France. Methods: Seed bank and vegetation were sampled in six replicated stand types, forming a chronosequence along the conversion pathway. The stand types represented mid‐successional stages of stands in transition from coppice‐with‐standards (to high forest (16 plots) and early‐ and mid‐successional high forest stands (32 plots). Results: Seed bank density and species richness decreased with time since last disturbance. Adjusting for seed density effects obscured species richness differences between stand types, but species of later seres were nested subsets of earlier seres, implying concomitant shifts in species richness and composition with time since disturbance. Later seres were characterized by species with low seed weight and high seed longevity. Seed banks of early seres were more similar to vegetation than to later seres. Conclusions: Abandonment of the coppice‐with‐standards regime altered the seed bank characteristics, as well as its relationship with vegetation. Longer management cycles under high forest yield impoverished seed banks. For their persistence, seed bank species will increasingly rely on management of permanently open areas in the forest landscape. Thus, revegetation at the beginning of new high‐forest cycles may increasingly depend on inflow from seed sources.     

Multiple successional pathways of boreal forest stands in central Canada

Predicting forest composition change through time is a key challenge in forest management. While multiple successional pathways are theorized for boreal forests, empirical evidence is lacking, largely because succession has been inferred from chronosequence and dendrochronological methods. We tested the hypotheses that stands of compositionally similar overstory may follow multiple successional pathways depending on time since last stand‐replacing fire (TSF), edaphic conditions, and presence of intermediate disturbances. We used repeated measurements from combining sequential aerial photography and ground surveys for 361 boreal stands in central Canada. Stands were measured in 8–15 yr intervals over a ~ 60 yr period, covering a wide range of initial stand conditions. Multinomial logistic regression was used to analyze stand type transitions. With increasing TSF, stands dominated by shade‐intolerant Pinus banksiana, Populus sp., and Betula papyrifera demonstrated multiple pathways to stands dominated by shade‐tolerant Picea sp., Abies balsamea, and Thuja occidentalis. Their pathways seemed largely explained by neighborhood effects. Succession of stands dominated by shade‐tolerant species, with an exception of stands dominated by Picea sp., was not related to TSF, but rather dependent on edaphic conditions and presence of intermediate disturbances. Varying edaphic conditions caused divergent pathways with resource limited sites being dominated by nutrient‐poor tolerant species, and richer sites permitting invasion of early successional species and promoting species mixtures during succession. Intermediate disturbances promoted deciduous persistence and species diversity in A. balsamea and mixed‐conifer stands, but no evidence was detected to support “disturbance accelerated succession”. Our results demonstrate that in the prolonged absence of stand‐replacing disturbance boreal forest stands undergo multiple succession pathways. These pathways are regulated by neighborhood effects, resource availability, and presence of intermediate disturbance, but the relative importance of these regulators depends on initial stand type. The observed divergence of successional pathways supports the resource‐ratio hypothesis of plant succession.     

Disturbance of suburban Fagus forests by recreational activities: Effects on soil characteristics,above‐ground vegetation and seed bank

Questions: How does recreational disturbance (human trampling) affect soil characteristics, the performance of the understorey vegetation, and the density and species composition of the soil seed bank in Fagus sylvatica forests? Location: Suburban forests near Basel, northwestern Switzerland. Methods: We compared various soil characteristics and the performance of the understorey vegetation in six beech forest areas frequently disturbed by recreational activities with those in six undisturbed control areas, in spring 2003. In the same forest areas, the soil seed bank was investigated using the seedling emergence method. Samples were obtained from soil cores in January 2003. Results: We found substantial changes in soil compaction, above‐ground vegetation and in the soil seed bank due to recreational activities. In frequently visited areas, soil compaction was enhanced which caused a decrease in cover, height and species richness of both herb and shrub layers. Compared with control areas, the number of trampling‐tolerant species of the seed bank was significantly higher in disturbed areas, and total species richness tended to be higher in disturbed than in control areas. Furthermore, the similarity in species composition between the above‐ground vegetation and seed bank was significant lower in disturbed than in control areas. Conclusions: The intensive use of suburban forests for recreational activities, mainly picnicking, affects the vegetation of natural beech forests. Our study indicates that a restoration of degraded forest areas from the soil seed bank would result in a substantial change of the vegetation composition.     

Understorey vegetation development in North Finnish Picea forests after disturbance: re‐analysis of Sirén's data

Abstract. Sirén (1955) studied understorey species composition, tree stand properties and humus‐layer thickness in 64 unlogged forest stands on topographically and pedologically comparable sites. The stands were of even age (6 – 300 yr), stocked with the first or second tree generation after wildfire. The view of Sirén and several authors after him, that the vegetation of old‐growth boreal Picea forests is homogeneous on a broad scale, was examined by applying, in parallel, the partial variants of two ordination methods (DCA and PCA) to Sirén's vegetation data. Two main vegetation gradients were found: a major gradient running from recently burnt plots with prominence of pioneer species to plots with stand age > 100 yr, a well stocked tree layer and a thick humus layer, dominance of feather‐mosses and ample occurrence of shade‐tolerant as well as light‐preferring vascular plant species, and a second gradient along which first‐ and second‐generation plots segregate. The more prominent element of Betula trees in first‐ than in second‐generation stands < 100 yr contributed to the latter. A minor third gradient related to humus‐layer thickness was recovered by partial DCA only. The main vegetation gradient reappeared in separate ordinations of data from 47 mature forest stands (> 100 yr), but without being correlated with forest age. Variation among mature‐forest stands in the importance of pioneer species is considered mainly to be brought about by fine‐scale disturbance processes such as tree uprooting. Increasing importance of factors operating on within‐stand scales [development of a varied gap structure and stronger gradients in tree influence (radiation at ground level), soil moisture, soil depth and nutrient availability] with time is also reflected in the second and third mature‐forest ordination axes. Possible implications of the results for conservation of biological diversity and monitoring of changes in boreal forests are discussed.     

Stability in the patterns of long‐term development and growth of the Canadian spruce–moss forest

Aim The spruce–moss forest is the main forest ecosystem of the North American boreal forest. We used stand structure and fire data to examine the long‐term development and growth of the spruce–moss ecosystem. We evaluate the stability of the forest with time and the conditions needed for the continuing regeneration, growth and re‐establishment of black spruce (Picea mariana) trees. Location The study area occurs in Québec, Canada, and extends from 70°00′ to 72°00′ W and 47°30′ to 56°00′ N. Methods A spatial inventory of spruce–moss forest stands was performed along 34 transects. Nineteen spruce–moss forests were selected. A 500 m² quadrat at each site was used for radiocarbon and tree‐ring dating of time since last fire (TSLF). Size structure and tree regeneration in each stand were described based on diameter distribution of the dominant and co‐dominant tree species [black spruce and balsam fir (Abies balsamea)]. Results The TSLF of the studied forests ranges from 118 to 4870 cal. yr bp . Forests < 325 cal. yr bp are dominated by trees of the first post‐fire cohort and are not yet at equilibrium, whereas older forests show a reverse‐J diameter distribution typical of mature, old‐growth stands. The younger forests display faster height and radial growth‐rate patterns than the older forests, due to factors associated with long‐term forest development. Each of the stands examined established after severe fires that consumed all the soil organic material. Main conclusions Spruce–moss forests are able to self‐regenerate after fires that consume the organic layer, thus allowing seed regeneration at the soil surface. In the absence of fire the forests can remain in an equilibrium state. Once the forests mature, tree productivity eventually levels off and becomes stable. Further proof of the enduring stability of these forests, in between fire periods, lies in the ages of the stands. Stands with a TSLF of 325–4870 cal. yr bp all exhibited the same stand structure, tree growth rates and species characteristics. In the absence of fire, the spruce–moss forests are able to maintain themselves for thousands of years with no apparent degradation or change in forest type.     

Restoration of the understorey layer of recent forest bordering ancient forest

Abstract. Recently established forests are commonly characterized by an impoverished understorey. Restoration is mostly based on spontaneous secondary succession, but little is known about the time period needed to achieve a community species pool with species composition equal to that of ancient forests. Vegetation in transects of 197 plots in 13 recent forest stands contiguous to the Meerdaalwoud ancient forest complex was surveyed. The recent forest stands ranged in age from 36 to 132 yr. The community species pool was described with an ecological, functional and phytosociological approach and based on groups derived from a CCA. Differences in community species pool between age classes of recent forest stands were analysed. During establishment of a new forest competitive species, forest edge species and species with high Ellenberg values for light and nitrogen and a more persistent seed bank will dominate the understorey. After 90 yr of succession the cover by these species decreases and reaches equal values to ancient forest after ca. 105 yr. A large number of forest species will be able to colonize the forest in less than 90 yr. Some typical forest species, however, have very low colonization rates and still have low cover in recent forest more than 105 yr old, so that complete restoration of the understorey requires a time period of over a century. Anthropogenic introduction of forest plant species may reduce the time required for ancient forest vegetation equality.     

Persistent and pervasive compositional shifts of western boreal forest plots in Canada

Species compositional shifts have important consequences to biodiversity and ecosystem function and services to humanity. In boreal forests, compositional shifts from late‐successional conifers to early‐successional conifers and deciduous broadleaves have been postulated based on increased fire frequency associated with climate change truncating stand age‐dependent succession. However, little is known about how climate change has affected forest composition in the background between successive catastrophic fires in boreal forests. Using 1797 permanent sample plots from western boreal forests of Canada measured from 1958 to 2013, we show that after accounting for stand age‐dependent succession, the relative abundances of early‐successional deciduous broadleaves and early‐successional conifers have increased at the expense of late‐successional conifers with climate change. These background compositional shifts are persistent temporally, consistent across all forest stand ages and pervasive spatially across the region. Rising atmospheric CO₂ promoted early‐successional conifers and deciduous broadleaves, and warming increased early‐successional conifers at the expense of late‐successional conifers, but compositional shifts were not associated with climate moisture index. Our results emphasize the importance of climate change on background compositional shifts in the boreal forest and suggest further compositional shifts as rising CO₂ and warming will continue in the 21st century.     

Influence of land use history on seed banks in European temperate forest ecosystems: a review

This study summarises European research on seed banks in temperate forest systems and analyses for differences in seed bank composition between geographically scattered forests with a different land use history. Special attention is given to seed bank characteristics of ancient forest species. Results of Detrended Correspondence Analysis suggest that historical land use is a key factor in determining the seed bank composition. Particularly seed banks of forests on former heathland sites differ from seed banks of ancient forest due to a high contribution of early successional species. The effect of former land use decreases after 50 yr, due to seed senescence. Total seed density decreases with recent forest age. Seed bank composition of eastern European forests is different from northern or western European forests, a difference which is mainly caused by species with a higher Ellenberg indicator value for continentality, temperature and reaction. In general, ancient forest species are poorly represented. Only a limited number is mentioned to have a persistent seed bank, and their densities are relatively low, which means that restoration of typical ancient forest vegetation can not rely on the seed bank. However, there is still a considerable lack of knowledge concerning seed bank and germination characteristics of forest species.     

Soil seed bank and driftline composition along a successional gradient on a temperate salt marsh

Abstract. This study focuses on the relationship between vegetation succession and soil seed bank composition on the Schiermonnikoog (The Netherlands) salt marsh over 100 yr. The importance of driftline material in seed dispersal and the relationship with succession is also investigated. The results indicate that the majority of species have a transient or short‐term seed persistent bank. Seeds of most species are able to float over the salt marsh and become concentrated in the driftline higher up the marsh. After plants have established a seed bank forms, which disappears when vegetation is replaced by later‐successional species. Exceptions are Spergularia mar‐itima, which is still present in the seed bank of late successional stages, and Juncus gerardi and Glaux maritima, which appear in the seed bank of early successional stages, but are absent in the vegetation. Based on the results of this study constraints and possibilities for salt‐marsh restoration by de‐embankment are discussed.     

Short‐term effect of selection cutting in boreal balsam fir forest on cerambycid and scolytid beetles

The ecology and management of boreal forest ecosystems are drawing greater attention worldwide as their importance is being increasingly recognized for carbon sequestration or for harbouring the world's largest remaining intact forests. Selection cuts have been introduced as a more socially acceptable silvicultural method to improve the maintenance of habitat structure and functions as they mimic aspects of boreal forest succession dynamics. Many studies have shown that selection cutting helps maintaining arthropod communities in mature forests, but few have examined the increased risks of damage by bark‐ and wood‐boring insects in boreal forests of eastern North America. We used multidirectional flight‐interception traps to quantify the response of these beetles to 25 and 40% selection cutting in a balsam fir–white birch forest of Québec, Canada. The abundance and species number of both cerambycid and scolytid beetles were 5–6 times larger in selectively cut stands than in controls the year following treatments. Analyses revealed that bark‐ and wood‐boring beetles’ response was mostly associated with increased canopy openness in selectively cut stands (and sun‐exposed locations within them) and residual tree injuries caused by harvesting operations. These conditions attracted beetles such as Trypodendron lineatum (Scolytinae) and Rhagium inquisitor (Cerambycidae), two species known for their ability to attack weakened, dying and dead hosts. Most species were more abundant in selection cuts, except for Evodinus m. monticola (Cerambycidae) whose abundance was strongly reduced after treatment. Some beetles can have detrimental effects on residual trees and thus could reduce timber value, but most species found in treated stands do not represent a high risk for healthy trees. Thus, selection cuts do not seem favourable to the establishment of tree‐killing beetles. However, as they were found more active/abundant after selection cutting, it would be wise to further study their population dynamics over mid‐ and long‐term periods, along with the ecological and economic implications associated with this silvicultural treatment.     

Temporal variation in the influence of forest succession on caterpillar communities: A long‐term study in a tropical dry forest

Forest succession can influence herbivore communities through changes in host availability, plant quality, microclimate, canopy structure complexity and predator abundance. It is not well known, however, if such influence is constant across years. Caterpillars have been reported to be particularly susceptible to changes in plant community composition across forest succession, as most species are specialists and rely on the presence of their hosts. Nevertheless, in the case of tropical dry forests, plant species have less defined successional boundaries than tropical wet forests, and hence herbivore communities should be able to persist across different successional stages. To test this prediction, caterpillar communities were surveyed during eight consecutive years in a tropical dry forest in four replicated successional stages in Chamela, Jalisco and Mexico. Lepidopteran species richness and diversity were equivalent in mature forests and early successional stages, but a distinctive caterpillar community was found for the recently abandoned pastures. Species composition tended to converge among all four successional stages during the span of eight years. Overall, our results highlight the importance of both primary and secondary forest for the conservation of caterpillar biodiversity at a landscape level. We also highlight the relevance of long‐term studies when assessing the influence of forest succession to account for across year variation in species interactions and climatic factors. Abstract in French is available with online material.     

Changes in forest understorey vegetation in Norway related to long‐term soil acidification and climatic change

Question: Does the understorey vegetation of Norwegian boreal forests change in relation to broad‐scale, long‐term changes? Location: Norway. Methods: Permanently marked 1‐m² vegetation plots from 17 monitoring reference areas in forests dominated by Picea abies (11 areas, 620 plots) and Betula spp. (six areas, 300 plots) were analysed twice, at the start in 1988–1997 and 5 yr later (1993–2002). Species subplot frequency data were analysed separately for each area by univariate and multivariate statistical methods; 5‐yr changes in single species abundances, species number per plot and species composition were tested. Results: Two distinct patterns of change were found: 1. Abundance of several vascular plant species decreased in SE Norwegian Picea forests, most noticeably of species with a preference for richer soils, such as Oxalis acetosella. 2. Abundance of many bryophyte species as well as bryophyte species number per plot increased in forests of both types over most of Norway. Conclusions: The pattern of vascular plant changes is probably a time‐delayed response of long‐lived, mainly clonal, populations to acidified soils resulting from deposition of long‐distance airborne pollutants. The pattern bryophyte changes, with reference to the close link between climatic conditions for growth and abundance changes for Hylocomium splendens established in previous demographic studies, is related to climatic conditions favourable for bryophyte growth. We conclude that many forest understorey plants are sensitive indicators of environmental change, and that the concept used for intensive monitoring of Norwegian forests enables early detection of changes in vegetation brought about by broad‐scale, regional, impact factors.     

西双版纳热带森林土壤种子库与地上植被的关系

通过实验研究探讨了西双版纳几类热带森林的土壤种子库与地上植被的关系．结果表明,在森林演替的初期,土壤种子库与地上植被共有的种类和种子储量较多,随着林龄的增大,外来种子的比例逐渐增加,到季节雨林阶段,土壤种子库中的种子大部分为来自群落外的先锋种类．这些种子在郁闭的林冠下很难萌发,一旦森林受到干扰出现林窗或空旷地,这些潜在的种源将迅速萌发,参与植被的恢复或演替     

Disturbance regimes,gap‐demanding trees and seed mass related to tree height in warm temperate rain forests worldwide

For tropical lowland rain forests, Denslow (1987) hypothesized that in areas with large‐scale disturbances tree species with a high demand for light make up a larger proportion of the flora; results of tests have been inconsistent. There has been no test for warm temperate rain forests (WTRFs), but they offer a promising testing ground because they differ widely in the extent of disturbance. WTRF is dominated by microphylls sensu Raunkiaer and has a simpler structure and range of physiognomy than tropical or subtropical rain forests. It occurs in six parts of the world: eastern Asia, New Zealand, Chile, South Africa, SE Australia and the Azores. On the Azores it has been mostly destroyed, so we studied instead the subtropical montane rain forest (STMRF) on the Canary Islands which also represents a relict of the kind of WTRF that once stretched across southern Eurasia. We sought to find whether in these six regions the proportion of tree species needing canopy gaps for establishment reflects the frequency and/or extent of canopy disturbance by wind, landslide, volcanic eruptions (lava flow and ash fall), flood or fire. We used standard floras and ecological accounts to draw up lists of core tree species commonly reaching 5 m height. We excluded species which are very rare, very localized in distribution, or confined to special habitats, e.g. coastal forests or rocky sites. We used published accounts and our own experience to classify species into three groups: (1) needing canopy gaps for establishment; (2) needing either light shade throughout or a canopy gap relatively soon (a few months or years) after establishment; and (3) variously more shade‐tolerant. Group 1 species were divided according the kind of canopy opening needed: tree‐fall gap, landslide, lava flow, flood or fire. Only some of the significant differences in proportion of Group 1 species were consistent with differences in the extent of disturbance; even in some of those cases other factors seem likely to have had a major determining influence during evolution. We also sought to determine whether the species that are at least ‘short‐term persistent’ in the soil seed bank (lasting 2–4 years) are all species needing canopy gaps for establishment. The answer was negative; large numbers of seeds of some shade‐tolerants accumulate in the soil, and these species are able to benefit from soil disturbance in deep shade. We found a significant and strong positive relationship in Japan between mean seed mass and mature tree height, a weak positive relationship in New Zealand and no relationship in any of the other four regions. When comparing the seed mass values of Group 1 and Group 3 species we obtained different answers depending on whether or not we confined ourselves to taxonomically controlled contrasts. In only two of the four regions with an appreciable number of species in Group 1 is the mean seed mass of such species significantly lower than that of Group 3 species when taxonomic relatedness is ignored.     

Secondary Succession and Indigenous Management in Semideciduous Forest Fallows of the Amazon Basin1

To the discussion on secondary succession in tropical forests, we bring data on three under‐addressed issues: understory as well as overstory changes, continuous as opposed to phase changes, and integration of forest succession with indigenous fallow management and plant uses. Changes in vegetation structure and species composition were analyzed in secondary forests following swidden agriculture in a semideciduous forest of Bolivian lowlands. Twenty‐eight fallows, stratified by four successional stages (early = 1–5 yr, intermediate = 6–10 yr, advanced = 12–20 yr, and older = 22–36 yr), and ten stands of mature forests were sampled. The overstory (plants ≥5 cm diameter at breast height [DBH]) was sampled using a 20 × 50 m plot and the understory (plants <5 cm DBH) in three nested 2 × 5 m subplots. Semistructured interviews provided information on fallow management. Canopy height, basal area, and liana density of the overstory increased with secondary forest age. The early stage had the lowest species density and diversity in the overstory, but the highest diversity in the understory. Species composition and abundance differentiated mature forests and early successional stage from other successional stages; however, species showed individualistic responses across the temporal gradient. A total of 123 of 280 species were useful with edible, medicinal, and construction plants being the most abundant for both over‐ and understories. Most of Los Gwarayo preferred mature forests for making new swidden, while fallows were valuable for crops, useful species, and regenerating timber species.     

General and specific responses of understory vegetation to cervid herbivory across a range of boreal forests

Understanding the responses of ecological communities to perturbation is a key challenge within contemporary ecology research. In this study we seek to separate specific community responses from general community responses of plant communities to exclusion of large cervid herbivores. Cervid herbivory and forestry are the main drivers of vegetation structure and diversity in boreal forests. While many studies focus on the impact of cervids on trees, a high proportion of the biodiversity and ecosystem services in boreal forests is found in the field layer. However, experimental approaches investigating the influence of herbivory on understory vegetation are highly localised. In this study we use a regional‐scale design with 51 sites in four boreal forest regions of Norway, to investigate the influence of cervid herbivory on the physical and ecological structure of field layer vegetation. Our study sites cover a range of forest types differing in productivity, management and dominant cervid species, allowing us to identify generic responses and those that are specific to particular conditions. We found that the height of the field layer and the abundances of individual species were most susceptible to change following short‐term cervid exclusion across different forest types and cervid species. Total vegetation density and vascular plant diversity did not respond to cervid exclusion on the same time scale. We also found that the field‐layer vegetation in clear‐cut forests used by moose was more susceptible to change following cervid exclusion than mature forests used by red deer, but no strong evidence that the response of vegetation to herbivore exclusion varied with productivity. Our study suggests that the parameters that respond to cervid exclusion are consistent across forest types, but that the responsiveness of different forest types is idiosyncratic and hard to predict.     

Soil seed banks in dry Afromontane forests of Ethiopia

Abstract. The soil seed bank was investigated in four dry Afromontane forests of Ethiopia. At least 167 plant species were identified in the 0–9 cm soil layer with total densities ranging between 12 300 and 24 000 seeds/m². Herbs were represented with the largest numbers of species and seeds in the seed bank, while the contribution of tree species was generally low. The overall vertical distribution of seeds was similar at all sites with the highest densities occurring in the upper three cm of soil and gradually decreasing densities with increasing depth. Relatively high densities also occurred in the litter layer. There were large differences in depth distribution between species, suggesting differences in seed longevity. A large number of species in dry Afromontane forests evidently store quantities of seeds in the soil and this is in contrast to the situation in most tropical rain forests, dry lowland forests and savannas, where both the number of seeds and the number of species are relatively small. It is possible that the strongly seasonal and unpredictable climate of this region may have selected for high levels of dormancy, and that herb regeneration is associated with small scale disturbance. The fact that most of the dominant tree species do not accumulate seeds in the soil suggests that their regeneration from seed would be unlikely if mature individuals disappeared. Most tree species have relatively large seeds and poor long-distance dispersal; this implies that restoration of Afromontane forests after destruction would be difficult. Since there is a diverse seed bank of the ground flora, this component of the vegetation would have a better chance of reestablishing. However, because most cleared forest land is used for agricultural crop production, it is probable that the seed bank will be depleted in only a few years. Therefore, the future of the Afromontane forest flora seems to depend on the successful conservation of the few fragments of remaining natural forest.