Tree Regeneration In Forests Research Articles

A rare case of natural regeneration in butternut, a threatened forest tree, is parent and space limited

The genetic consequences of natural in situ recovery for rare or threatened species are not as well understood as the impact of population bottlenecks, fragmentation and admixture, particularly the mechanisms by which genetic diversity is lost or preserved as populations recover. Here we examine how mating patterns, dispersal and ecologically constrained regeneration influences genetic diversity and kinship in a naturally regenerating population of a threatened temperate forest tree, Juglans cinerea L. (butternut). Butternut regeneration is now rare throughout the native range due to the butternut canker, a lethal fungal disease from Asia, and land use changes. In this study of one of the only known regenerating patches large enough for kinship and parentage analysis, we used 12 microsatellite markers, direct and inferred parentage analyses and Bayesian clustering of 152 trees to show that natural regeneration at this site resulted in loss of allele richness due to a small number of parents, most of which are spatially proximal to the regenerants. Of the 116 potential parents tested, one contributed 20.8 % and the top four contributed 71.1 % of the gametes in 36 regenerants. Parent-parent and parent-offspring distances revealed limited pollen and seed dispersal (<100 m). Regenerants were highly related and spatially clustered in sibling groups. Proximity to the regenerating patch was the most significant factor in parental success. Our results suggest that in situ regeneration of forest trees with limited propagule dispersal and specific site requirements may be insufficient to preserve native genetic diversity in protected areas with few suitable sites.

Vegetation composition and structure of woody plant communities along urban interstate corridors in Louisville, KY, U.S.A.

Urban forests adjacent to interstate corridors are understudied ecosystems across cities. Despite their small area, these forests may be strategically located to provide large ecosystem services due to their ability to act as a barrier against air pollutants and noise as well as to provide flood control. The woody vegetation composition and structure of forests adjacent to urban interstates is an important determinant of their ability to provide these services. However, these forest communities may be particularly susceptible to the introduction of exotic invasive species via the interstate and the surrounding city that can potentially alter current and future forest composition. The purpose of this study was to investigate the distribution of native and exotic woody vegetation and tree regeneration in forests along three interstate corridors in Louisville, KY, and to determine potential factors (e.g., traffic density) that are correlated with patterns in the woody vegetation community. We found the most important determinants of vegetation composition along these interstate corridors were the distance from the city center and the presence of an exotic invasive shrub, Amur honeysuckle (Lonicera maackii). Compared with forested plots within 10 km of the city center, plots further from the city center had 81% lower stem density of Amur honeysuckle, 96% higher tree seedling regeneration, and 51% greater woody plant species richness. The primarily native species composition of adult trees in forests alongside urban interstates in Louisville and the regeneration of native tree species provide optimism that these forests can maintain native species while experiencing multiple impacts from the interstate as well as from the surrounding city, emphasizing their important potential for maintaining natural forest functions across the urban landscape.

Effect of nitrogen availability on forest understorey cover and its consequences for tree regeneration in the Austrian limestone Alps

The impact of airborne nitrogen on tree regeneration has attracted increasing interest as deposition loads are by far exceeding natural amounts. Eutrophication may have both direct and indirect effects on the regeneration of forest trees. Here, we focus on potential indirect effects, mediated by nitrogen-dependent patterns in forest understoreys. Using data from a long-term monitoring site in a montane forest ecosystem of the Northern Limestone Alps, we first evaluated correlations between understorey cover of herbs and graminoids and nitrogen availability, as indicated by soil C/N ratios. Then, recruitment and growth rates of the four major tree species of this system (Acer pseudplatanus, Fraxinus excelsior, Fagus sylvatica and Picea abies) were related to understorey cover by means of linear and generalized linear mixed models, taking covariates (soil pH value, radiation, microrelief properties) and spatially varied seed input into account. Nitrogen availability is positively related to graminoid and herb cover. Herb cover had a negative effect on A. pseudoplatanus recruitment, while graminoids had a positive effect on F. sylvatica. Browsing damage on juvenile trees was reduced when graminoid cover was higher We conclude that under specific abiotic and biotic conditions, like on steep, erosion prone slopes, or under high levels of herbivore pressure, understorey vegetation may facilitate tree seedlings rather than compete with them. This highlights the complexity of the factors controlling tree regeneration and the difficulty to predict the net effects of the excess deposition of airborne nitrogen.

Temporal and spatial variation of flowering among Pinus nigra Arn. clones under changing climatic conditions

Until recently, the most important factors affecting the economics and genetics of the seed crop from seed orchards were considered to be the timing and duration of flowering, variation in fertility and the total number of clones used to establish the seed orchards. Change in climatic conditions however is an emerging factor that could prove crucial regarding the timing of flowering and synchronization among clones and thus, the quality and quantity of seed production. The temporal and spatial variation in flowering phenology and the duration of flowering were studied in consecutive years in a Pinus nigra Arn. seed orchard. Sixty plus trees representing the distribution of the species in Northern Greece were used to establish the seed orchard, and nineteen ramets per clone were planted in a honeycomb experimental design in order to avoid kinship. Temporal variation among clones, as well as spatial variation among ramets within clones growing at different sites of the orchard were recorded, for initiation and duration of male and female flowering. The majority of clones were synchronized in dates of flowering during the year with weather conditions close to the long-term climatic conditions, except for a limited number of clones that were precocious or late flowering. The pronounced variability in climatic conditions over the 2 years strongly affected the flowering and synchronization among clones, resulting in almost complete asynchrony during the xerothermic year, which was characterized by a prolonged mean monthly temperature increase of 2.3 °C and a water deficit of 53% in a 7-month-period (November to May). These results suggest that one of the effects of a warmer and drier climate may be the lack of flowering synchronization, as pollen shedding might be completed before female conelets reach the phase of receptivity. The restriction of male parentage to a limited number of clones severely violates the panmixia assumption and could result in fertilization failure. The projected climate change for the Mediterranean region could potentially prove detrimental for fertility and flowering synchronization of forest trees, having consequences on the quantity and genetic diversity of the seed crop in seed orchards, and the natural regeneration of forest trees in forest ecosystems due to the reduced percentage of sound seed.

Invasive Shrubs and Forest Tree Regeneration

Invasive shrubs are having important effects on forests in the United States. Over 100 species were found that have actual or potential effects on forest structure and function. The number of invasive shrub species in each state is correlated with both latitude and state population. The majority of these shrubs have attractive fruits that are widely distributed by birds and other animals. Their reproduction is also helped by evergreen or extended-deciduous leaf habits and by the ability to reproduce vegetatively in a majority of these invasive species. In addition to suppressing native tree reproduction, invasive shrubs have many other effects on forest function; however, information is not yet available in either of these categories for a substantial number of invasive shrubs. Because most of these species can resprout, physical control is of limited effectiveness, while herbicides are much more successful. Only limited research has been conducted on both fire and biological control. Despite these negative effects on forests, more than three quarters of these shrubs are still distributed in the United States, and many are unrecognized as invasive in many states. Substantial legislative, regulatory, and research efforts are therefore needed to limit the deleterious effects of invasive shrubs on U.S. forests.

Effects of pasture management on the natural regeneration of neotropical trees

Summary Natural regeneration of forest trees in grazed pastures could potentially contribute to the conservation of tree diversity within the fragmented and agricultural landscapes that dominate much of the tropics. To understand this potential, we evaluated the effects of several widely used pasture management practices on tree regeneration in pastures in a tropical dry forest (subhumid) region of central Nicaragua. Species richness, density, diversity and composition of seedlings, saplings and adult trees were compared in 46 pastures under different management conditions. The management conditions included three different types of grasses (Brachiaria spp., Cynodon spp. and naturalized pastures) and two categories of fire history (recently burnt and not recently burnt). Thirty‐seven of the 85 tree species present in the pastures were regenerated under the current management conditions. The remaining 48 species may have had reduced natural regeneration because of limitations in either germination, dispersal, establishment or growth, as well as because of negative effects of pasture management practices. The richness, density and species composition of tree seedlings within pastures were explained by grass species composition, the density and richness of adult trees, cattle management and the distance of the pasture to forest. In contrast, no clear effect of fire history was found. Synthesis and applications. Current management practices allow the regeneration of almost half of the tree species in grazed pastures. However, to enhance the regeneration of species that show limited regeneration, management strategies, such as the retention of adult trees, protection of saplings and seedlings from weeding and grazing and use of enrichment plantings, may be necessary. These changes in pasture management would help contribute to the long‐term conservation of tree diversity within agricultural landscapes across the tropics.

Tree Regeneration and Sapling Damage of Pedunculate Oak Quercus robur in a Grazed Forest in Galicia, NW Spain: A Comparison of Continuous and Rotational Grazing Systems

Forest grazing has been recognised as being a useful tool in fire-risk reduction, in addition to having the potential to preserve or enhance forest biodiversity if managed correctly. Concern for natural regeneration of forest trees in Europe has also prompted interest in the effects of large herbivores on seedling and sapling growth and mortality. An investigation was carried out into sapling damage and density of natural regeneration of oak (Quercus robur) in a mature, pony-grazed, Pinus radiata forest in Galicia, NW Spain under two different grazing regimes (continuous and rotational). In all treatments significantly more oak seedlings and saplings were recorded in areas of grass sward than areas dominated by taller ground flora species. Damage to oak saplings was assessed from the form (height and canopy) relative to stem diameter. The height and average canopy diameter of similar-aged saplings were found to be significantly greater in ungrazed (control) than both continuous and rotationally grazed treatments. Height and canopy diameters of similar-aged oak were not significantly different between the two grazing treatments. Significant differences were observed in tree form, with unbrowsed saplings having the greatest height to canopy width ratio and those in the continuously browsed plots having the smallest. An obvious decrease in the goodness of fit (R2) of regression analyses were found in continuously grazed areas compared to rotational and control plots for both height and canopy data. The differences in damage observed were not significantly different enough to suggest one method of grazing over the other as being better for minimising sapling damage. Management requirements are more likely to dictate grazing regime. Overall, stock density is likely to have a more significant effect on damage than stocking system.

Modeling the interacting effects of browsing and shading on mountain forest tree regeneration ( Picea abies)

Although ungulate herbivory influences forest dynamics over a variety of spatial and temporal scales, relatively few models have been developed for investigating browsing effects on tree regeneration processes. We describe a new, mechanistic model (HUNGER) that modifies a well-established mathematical formulation for plant nutrient transport and conversion processes to simulate sapling response to ungulate browsing and light availability. The HUNGER model simulates primary production, height and diameter growth, dry matter allocation, and population dynamics of tree saplings at the scale of small (e.g. 0.001 ha) regeneration patches. The model was applied to Picea abies saplings in mountain forests of eastern Switzerland after calibration based on data for sapling height growth, radial growth, and biomass components under varying light conditions. Independent data were used to test the ability of the model to represent sapling responses to browsing. The model slightly over-predicted sapling height, while no significant differences were found between simulated and observed basal diameter, total biomass or leaf biomass. Model experiments were conducted to explore the interactive effects of winter browsing intensity and relative light availability upon sapling net growth. Simulated shading effects were gradual until approximately 40% relative light availability (if browsing pressure was low) or 60% relative light availability (if browsing pressure was high). Below these values, the model simulates sharp declines in net growth rate. Model results suggest nonlinear responses to browsing and light availability, and the existence of light intensity thresholds for forest regeneration that should be relevant for management activities affecting deer density and crown cover.

Wildlife habitat analysis – a multidimensional habitat management model

In intensively cultivated landscapes, the effects of land use – changing habitat quality and habitat availability - on wildlife populations are of major importance for wildlife management. Populations of some species reach high densities, grow rapidly, and can therefore cause damage to tree regeneration in forests; chamois (Rupicapra rupicapra) is an example. Other species, like capercaillie (Tetrao urogallus), suffer from substantial habitat loss resulting in a population decline. Consequently, the number of individuals and the quality of habitat are of crucial relevance for the development of wildlife management concepts. It is critical to know, which areas provide suitable habitat conditions for a species, and what quantity and quality of habitat is required to achieve a certain population size. In order to evaluate habitat quality and to link wildlife research to practical habitat management, an integrated habitat management model has been designed. The model is based on a multi-dimensional habitat analysis which employs different methodological levels, which were defined according to different spatial scales. On a country scale (level 1), the wildlife ecological landscape type (WELT) is introduced. For this study the federal state of Baden-Wuerttemberg is divided into units which represent distinct regions with similar landscape ecological habitat conditions for wildlife species. On an eco-regional scale (level 2), the landscape ecological habitat potential (LEHP) was developed. It is based on the evaluation of species-related landscape parameters within an exemplary eco-region and provides information about the potential habitat available to a population. On two local scales (level 3: forest district, level 4: forest stand), a habitat structure analysis was conducted, which serves as a foundation for habitat improvement and the monitoring of habitat conditions. The three methodological elements WELT, LEHP and habitat structure analysis were integrated into a habitat management model. The model uses chamois and capercaillie as examples, but can be equally applied to other species and wildlife management regimes.

Influence of ivy (Hedera helix L.) on the growth of downy oak (Quercus pubescens s.l.) in the Monte Carcaci Nature Reserve (central-western Sicily)

Les lianes sont communément considérées comme des espèces nuisibles aux arbres forestiers et aux processus dynamiques des forêts. En effet, elles peuvent entrer en compétition avec d’autres espèces ligneuses et avoir des influences négatives sur la régénération des arbres, leur croissance voire leur fécondité. Toutefois, quelques études rapportent que le lierre peut avoir aussi une action de coopération avec des effets positifs sur les espèces hôtes. Au cours des dernières décennies, dans un taillis âgé dans la Réserve Naturelle de Monte Carcaci (Sicile centro-occidentale, Italie), un fort développement du lierre (Hedera helix L.) a été observé au détriment des chênes blancs (Quercus pubescens s. l.) hôtes, lesquels montraient parfois des symptômes évidents de dépérissement. Une analyse de la biomasse aérienne et des cernes de croissance a donc été effectuée dans le but de clarifier la nature des interactions entre le lierre et les chênes hôtes. Les résultats ont montré que, après une phase d’influence positive du lierre sur la croissance des chênes, une phase de compétition active s’établit, se matérialisant par la réduction progressive de la vitalité des arbres porteurs. Sur cette base, un suivi de l’évolution forestière serait souhaitable afin de mieux comprendre le rôle des lianes au sein de l’écosystème et de définir les lignes guide les plus appropriés de l’aménagement forestier futur.

Growth of ponderosa pine seedlings as affected by air pollution

The effect of air pollution on seedling survival and competitive ability is important to natural and artificial regeneration of forest trees. Although biochemical and physiological processes are sensitive indicators of pollution stress, the cumulative effects of air pollutants on seedling vigor and competitive ability may be assessed directly from whole-plant growth characteristics such as diameter, height, and photosynthetic area. A few studies that have examined intraspecific variation in seedling response to air pollution indicate that genotypic differences are important in assessing potential effects of air pollution on forest regeneration. Here, we studied the effects of acid rain (no-rain, pH 5.1 rain, pH 3.0 rain) and ozone (filtered, ambient, twice-ambient) in the field on height, diameter, volume, the height:diameter ratio, maximum needle length, and time to reach maximum needle length in seedlings of three families of ponderosa pine ( Pinus ponderosa Dougl. ex Laws). Seedling diameter, height, volume, and height:diameter ratio related significantly to their pre-treatment values. Twice-ambient ozone decreased seedling diameter compared with ozone-filtered air. A significant family-by-ozone interaction was detected for seedling height, as the height of only one of the three families was decreased by twice-ambient ozone compared with the ambient level. Seedling diameter was larger and the height:diameter ratio was smaller under pH 3.0 rain compared to either the no-rain or the pH 5.1-rain treatment. This suggests greater seedling vigor, perhaps due to a foliar fertilization effect of the pH 3.0 rain.

Effect of increasing numbers of deer on bird populations in Wytham Woods, central England

In Wytham Woods, the numbers of deer have increased markedly in recent years and they have had a major impact on the woodland vegetation, both the herb layer and the shrub layer (including the lower branches of trees); they also seriously affect the regeneration of forest trees and the regrowth of coppice. Over the same period, a number of woodland bird species have declined in numbers. The large declines seem to have occurred mainly in those species which nest in low vegetation, especially bramble ( Rubus fruticosus ). Bramble is an important element of the deer diet and its decline in the woods seems likely to be largely due to deer although canopy closure may also have reduced its abundance. Hence the declines in some bird species may be brought about by the increase in deer numbers. The relevance of this suggestion to other woods is discussed.

Huftiere und Verjüngung im Gebirgswald: eine Geschichte mit vielen Variablen und noch mehr Interaktionen | Ungulates and Tree Regeneration in Mountain Forests: an Issue with many Variables and even more Interactions

After excessive cutting in Swiss mountain forests and extirpation of most of the wildlife during the past centuries, efficient forestry and hunting laws allowed a wide regeneration of the forests and a rapid increase of ungulate populations in the present century. As a consequence, the impacts of ungulates on the vegetation became obvious. Regeneration of forest trees, however, is influenced not only by ungulates, but by a number of physical site factors and biotic impacts. As these impacts and their interactions vary extensively, regeneration is neither spatially nor temporally constant. Most of the presently used tree-regeneration methods, however, assume constant conditions, which renders a proper evaluation of tree regeneration in mountain forests and the role of ungulates impossible. Furthermore, the effect of this variation on forest development and forest functions is unknown with regard to the long term. While society requires a multipurpose mountain forest, structured at a small scale, wild ungulates use their habitat at a larger scale. This often leads to conflicts. Consequently,solutions including different scales are necessary. A lack of knowledge will, therefore, have to be met by research making data available to the practice as well as through coordinated investigations and experiments.

Reducing predation of conifer seeds by clear-cutting Rubus fruticosus agg. in two montane forest stands

Natural regeneration of forest trees is negatively affected by dense ground cover of brambles ( Rubus fruticosus agg.) in montane forests in southwestern Germany. Seed predation by rodents is one potential factor which may reduce establishment of tree seedlings in these sites. In winter and early spring seed predation of two conifers ( Abies alba Mill., Picea abies (L.) H. Karsten) was studied in bramble patches and in adjacent cleared plots (6 m × 6 m, respectively) in two montane Abies-Picea stands. Losses of seeds from experimental dishes were higher under bramble vegetation than in the cleared plots in both forest stands in winter. Seed predation was consistently lower for Abies than for Picea. The results were similar in early spring. Predation was reduced after adding conifer litter into the dishes. Rodents were responsible for the seed losses, and rodent abundance was lower in the experimental clearings. The results are discussed with respect to natural succession on clearings and its practical relevance in forestry, i.e. clear-cutting of bramble patches as a measure to reduce seed predation by rodents.

Tree Regeneration and Species Diversity Following Conventional and Uniform Spacing Methods of Selective Cutting in a Subtropical Humid Forest Reserve1

ABSTRACTThere are a variety of ways to diminish the negative impacts of forest management for timber on biodiversity. A pilot project using a uniform spacing method of selective cutting was recently implemented in the 5340 ha Guarani Reserve, Misiones, Argentina, to design adequate management schemes for the subtropical forests of the region. Uniform spacing involves moderate timber harvesting and careful selection of remnant trees. In this article we compare tree regeneration in forests experimentally cut by diameter limit and uniform spacing methods. Seedlings of five size classes from 10 cm to 3 m in height were sampled using rectangular nested plots. Three years after cutting, an average of 54,330 and 22,270 seedling/ha (all height classes combined) of commercial and non‐commercial species were found in the forest cut by uniform spacing and by minimum diameter, respectively. In an adjacent uncut forest there were 34,900 seedlings/ha, and in another forest cut by minimum diameters 30 years ago there were 50,000 seedlings/ha, The forest cut by uniform spacing had the highest number of commercial seedlings/ha, with three times as many as the forest cut by minimum diameter three years ago and twice as many as the forest treated by minimum diameters 30 years ago. The forest cut by uniform spacing and the forest treated by minimum diameters 30 years ago had the highest diversity of understory plants other than trees, as well as heterogeneous canopy cover, while the other two forests had a predominance of bamboo in the understory and more open canopy conditions. Although lack of site replication limits interpretation of the results, these early findings suggest that the uniform spacing method can be an ecologically sound forest management option for the region.

Functional Leaf Phenotypes for Shaded and Open Environments of a Dominant Dwarf Bamboo (Sasa senanensis) in Northern Japan

Dense patches of evergreen dwarf bamboo species (1-3 m), such as Sasa senanensis, often prevent forest tree regeneration, and they suppress competing grassland species in Japan. We hypothesized that its evergreen habit contributes to the dominance of S. senanensis through carbon gain during the phenological gaps of spring and late fall under the improved irradiance and moisture conditions in a deciduous forest. We monitored the seasonal patterns of gas exchange in S. senanensis growing in the forest understory and in the open. The timing of greatest carbon gain in shade leaves was during early spring and late fall under a leafless forest canopy compared with that of late spring and early summer for open-grown leaves. Compared to understory S. senanensis, those grown in the open attained high photosynthesis and chlorophyll (Chl) a/b but lower area-based total chlorophyll, specific leaf area, and leaf nitrogen. In understory plants, these leaf characters and lightfleck responses indicated that they retain...

Nitrate assimilation of raspberry and pin cherry in a recent clearcut

An experimental study conducted in a recently clear-cut hardwood forest was used to determine the reduction of nitrate in the leaves of Rubus idaeus L. and Prunus pensylvanica L.F., early successional species and shrub competitors of forest tree regeneration. A factorial experimental design was chosen and the main factors were the shrub competitors and the replicates (blocks). The nitrate reductase enzyme assay was chosen as a physiological marker since it is substrate induced and it is the first key enzyme implicated in the assimilation of nitrate. Results show that for 2 consecutive years, pin cherry had extremely low enzymatic activity in their leaves (0.80 and 0.70 μmol NO2/(g dry wt.∙h)), whereas raspberry always had high values (2.52 and 2.32 μmol NO2/(g dry wt.∙h)). The induction of the enzyme with 800 kg/ha N–P–K fertilizer showed that only raspberry responded to the treatment. These findings could explain the differing peaks of dominance of these early succession species, especially in relation with the changing nitrification rate found in disturbed hardwood forest ecosystems. Pin cherry, a successional shrub reaching maximum abundance following raspberry, clearly does not acquire the large quantities of nitrogen that it does by the uptake of the nitrate form. Nitrogen assimilation of the NH4+ form predominantly would allow pin cherry to short-circuit nitrification by reducing the substrate for nitrification, thus rendering soil conditions less favourable for raspberry and leading to its successional replacement by pin cherry. Key words: disturbed forest ecosystem, nitrate reductase activity, Prunus pensylvanica L.F., Rubus idaeus L.

Modeling of Wave Regeneration in Subalpine Abies Forests: Population Dynamics with Spatial Structure

The wave regeneration of forest trees is studied theoretically in model populations with a lattice structure, in which each lattice point corresponds to stand containing a cohort of trees. It is assumed that the tree height at each site increases at a constant rate and that trees die in unit time if they are taller than their windward neighbors, with the height difference greater than a critical value. Starting from a random initial distribution, the spatial pattern becomes a saw—toothed shape, and moves at a constant rate downwind without changing its shape. In addition to this basic model, four models are also examined in which both the absolute height (or age) and the height difference between neighbors affect the tree mortality. Two rules (AND and OR rules) produce very irregular final patterns that are not saw toothed, but the other two (SUM and PRODUCT rules) often generate patterns that are close to saw toothed and more regular than those produced by the basic model. Both periodic boundary conditions and fixed height boundary conditions are examined. Two—dimensional models tend to produce more regular wave regenerating patterns than one—dimensional models.

Dynamic modeling of wave regeneration (Shimagare) in subalpine Abies forests

In a previous paper, we studied the wave regeneration of forest trees in model populations with one-dimensional lattice structures, by assuming that the tree height increases at a constant rate and that a tree dies in unit time if it is sufficiently taller than its windward neighbor. Starting from random initial distribution, the spatial pattern becomes of a saw-toothed shape, moving at a constant rate. In this paper, the model is extended in several directions: first, as the range of wind-shielding effect of trees increases, the speed of the final wave regenerating pattern increases. Second, a two-dimensional model is demonstrated to generate the patterns with dieback zones spaced more regularly than in those generated by a one-dimensional model. The effect of habitat heterogeneity is also studied. Third, the effect of disturbance in the form of additional stochastic mortality is studied. Finally the biological implication of these results to wave regeneration in forests is discussed.

Riverine forest in the Jubba Valley: A vegetation analysis and comments on forest conservation

BIOGEOGHAPH/A — vol. XIV — 1988 (Pubb/ioato fl 31 clicembre 1990) The Biogeography of Somalia Riverine forest in the Jubba Valley: A vegetation analysis and comments on forest conservation JANE MADGV/ICK Somalia RE.S‘€fl7‘Cl.7 Project, Ecology and COIZS€I‘1JcZl‘Zi07Z Uzm‘, UI2z&#39;1Jer5z&#39;ty College London WC1E 6BT, UK SUMMARY Detailed vegetation surveys were carried out in two riverine forest areas in the Jubba Valley, southern Somalia. Results of an ordination and classification suggest that the forests can be split into several soil/ hydrological types with characteristic species. Variation in composition within the forests is strongly relat— ed to distance from the river edge. There was evidence of regeneration of forest trees and shrubs through- out the study areas although several tree species were extremely scarce. The forests share many common elements with those of the Tana river in Kenya and are most similar to the more mature levee forests. Changes in river flow caused by the proposed dam at Baardheere are likely to cause gradual changes in the composition and structure of floodplain forests. Greater impacts on the forest are likely as a result of agricultural settlement in the valley. It is recommended that Shoonto and Barako Madow forests should be protected from any further degradation since they are the largest and most intact forests left in the Jubba floodplain. INTRODUCTION Most of the remaining forests in East Africa are small and fragmented and few are effectively conserved. Recently, there has been an acceleration in the loss of tropical moist forest along perennial rivers as a result of water resource development and the spread of agriculture (Andrews et al. 1975, Hughes 1984). Although the local knowledge of natural resources in these riverine areas is great, agricultural projects and foreign-aided development schemes usually fail to consider or make use of this knowledge. Assessment of the agricultural suitability of the floodplain areas is therefore rarely com- plemented by an assessment of the local and national values of natural eco- systems. Detailed studies of floodplain ecology are needed to predict the likely effects of destroying floodplain habitats, provide guidelines for sustain- able agricultural use and point to the benefits of conserving scarce natural resources. There is a great diversity of forest types along river courses in Africa, depending on the local physical and climatic conditions (Hughes in press). Here, I assess the current status and composition of the least-known and northernmost floodplain forests in the East African lowlands, those of the Jubba Valley, Somalia. Little attention has been paid to the floristic composi- tion of these forests. Italian foresters visited the Middle and Lower Jubba in 67