Woody species composition,diversity and structure of riparian forests of four watercourses types in Burkina Faso

Riparian forests are classified as endangered ecosystems in general,particularly in sahelian countries like Burkina Faso because of human-induced alterations and civil engineering works.The modification of this important habitat is continuing,with little attention being paid to the ecological or human consequences of these changes.The objective of this study is to describe the variation of woody species diversity and dynamic in riparian forests on different type of watercourse banks along phytogeographical gradient in Burkina Faso.All woody species were systematically measured in 90 sample plots with sides of 50 m × 20 m.Density,dominance,frequency and species and family importance values were computed to characterize the species composition.Different diver-sity indices were calculated to examine the heterogeneity of riparian forests.A total of 196 species representing 139 genera and 51 families were recorded in the overall riparian forests.The species richness of individuals with dbh ≥ 5cm increased significantly from the North to the South along the phytogeographical gradient and varied significantly between the different types of riparian forests.Similarity in tree species composition between riparian forests was low,which indicates high beta diversity and reflects differences in habitat conditions and topography.The structural characteristics varied significantly along the phyto-geographical gradient and between the different types of riparian forests.The diameter class distribution of trees in all riparian forests showed a reverse ＂J＂ shaped curve except riparian forest of stream indicating vegetation dominated by juvenile individuals.Considering the ecological importance of riparian forest,there is a need to delineate and classify them along watercourses throughout the country.

Success of three soil restoration techniques on seedling survival and growth of three plant species in the Sahel of Burkina Faso(West Africa)

In the Sahel of Africa, where 90 % of the population depends on natural resources for their liveli- hood, a large part of the soils are structurally unstable, prone to crusting and hard setting, and have low water holding capacity, which hamper vegetation establishment. The effect of soil restoration techniques on survival and growth of seedlings of Acacia nilotica, Acacia tortilis and Jatropha curcas was tested in completely barren, degraded land in a Sahelian ecosystem in Burkina Faso. A total of 522 seedlings （174 plants of each plant species） were planted in a randomized complete block design with three replicates combining three soil preparation techniques： half-moon, zai＂ and standard plantation. Survival and growth rates evaluated over 20 months were significantly higher using the half-moon technique compared with the other two techniques. Survival rates of plant species planted using half-moon technique were 62.5, 28.57 and 10.71% for A. nilotica, A. tortilis and J. curcas respec- tively, but in za＇i and standard planting, seedling survival was zero. The low survival rate of J. curcas using the half-moon technique may indicate that J. curcas is unsuit- able for barren and degraded land, whereas A. nilotica and A. tortilis appear to be promising tree species for rehabil- itation of degraded land.

Aboveground biomass allometric equations and distribution of carbon stocks of the African oak(Afzelia africana Sm.)in Burkina Faso

The significant role of tropical forest ecosystems in the global carbon budget has increased the need for accurate estimates of tropical forest biomass.The lack of large-scale biomass allometric equations hampers the understanding of the spatial distribution of tree biomass and carbon stocks and their influencing factors in West Africa.This study aimed to develop allometric equations to estimate aboveground biomass of African oak(Afzelia africana Sm.)in Burkina Faso and to analyze factors affecting the variability of tree biomass and carbon storage.Sixty individual trees were destructively sampled in four protected areas along two climatic zones.In each climatic zone,log–log models were tested and fitted to each aboveground biomass component and to the total aboveground biomass.Carbon content in tree aboveground components was evaluated using the ash method.All validated equations showed good fit and performance with high explained variance.Allometric equations differed between the Sudano-sahelian zone and the Sudanian zone,except for leaf biomass equations.Both biomass allocation and carbon content varied significantly between tree components but not between climatic zones.Carbon content in tree components followed the patterns of biomass allocation with branches accounting for the highest proportion.In the two climatic zones,carbon contents were 50.18–52.62%for leaves,54.78–54.94%for stems and 54.96–55.99%for branches.Dry biomass ranged from 509.05 to 765.56 kg tree^-1 at site level and from 620.21 to 624.48 kg tree^-1 along climatic zones.Carbon content varied from 53.90%in the Sudano-sahelian zone to 54.39%in the Sudanian zone.This study indicated that climate does not influence aboveground biomass production and carbon sequestration of Afzelia africana along the Sudanosahelian and the Sudanian climatic zones of Burkina Faso.Future studies on climate–growth relationships should contribute to better understanding climate effects on biomass production and carbon storage.

A comparison of Guibourtia copallifera Benn. stands in South West Burkina Faso-community structure and regeneration

Shifting agriculture, fire, and over exploitation of wood and copal resin are the major causes of Guibourtia copallifera Benn. vulner- ability in the south-west of Burkina Faso. Conservation of endangered species requires a thorough understanding of the dynamics of small populations. In the present study, we investigated the diversity and the dynamics of G copallifera communities in two different types of land use history, a protected area （stated forest of Como6-Leraba） and an unprotected area （the woodlands of Toumi and Timba）. A total of 17 rectangular plots （50 m × 20 m） were sampled in both protected and unprotected areas. All woody species were systematically identified, measured and classified into diameter and height classes. In the two different types of land use, the dynamics of G. copallifera＇s communities were good, and the diversities were similar and low with high β diversity.

Impact of disturbance from roadworks on Pteleopsis suberosa regeneration in roadside environments in Burkina Faso, West Africa

The seedling population structure of Pteleopsis suberosa and their regeneration mechanisms were investigated in four roadside environments （graded, adjacent, intermediate and ungraded areas） along paved and unpaved roads in West Africa. A total of 203 quadrats of 2 m × 5 m in size were surveyed and placed along transects parallel to the roads. Within each quadrat, the total number of seedlings and the number of living shoots per seedling base were recorded. Regeneration mechanisms were determined by assessing basal and aerial sprouts and excavating the root systems below ground level. The results show that the total seedling density and the densities of single- and multi-stemmed individuals varied significantly （p 〈 0.05） among the four roadside environments. However, all seedlings were produced asexually; root suckers were predominant （98%） compared to water sprout （1%） and coppices （less than 1%）. This study demonstrates that an intermediate level of soil disturbance from grading along paved and unpaved roads may stimulate P. suberosa regeneration by root suck- ering. Road type （paved and unpaved） did not affect seedling density, but was a highly significant variable in relation to the coppicing ability of P. suberosa populations in roadside sites. In conclusion, P. suberosa is a disturbance-tolerant species which can proliferate mainly by root suckering after roadwork disturbance.

Relationships between soil seed banks and above-ground vegetation along a disturbance gradient in the W National Park trans-boundary biosphere reserve,West Africa

Aims Vegetation succession depends on the availability of suitable prop-agules in the soils,thus knowledge of soil seed banks is essential for formulating effective strategies for restoring the vegetation of degraded sites.The W National Park,the only trans-boundary bio-sphere reserve in West Africa,is being extensively fragmented and degraded in recent decades.The aims of this study were to assess the reserve’s soil seed banks,their relationships with standing veg-etation and bundle of disturbances and their potential significance for vegetation restoration.Methods The size and composition of the above-ground species vegetation were assessed in nine plots of 1 ha each representing a range of habitats with differing disturbance severity(low,intermediate and high).A total of 702 soil samples were taken from three layers(0-3,3-6 and 6-9 cm)and soil seed bank was analyzed using the seed-ling emergence technique.Important Findings Generally,seeds of non-woody taxa dominated in samples from all soil depths and habitats of all disturbance severities.The mean soil seed density was 17.8,24.4 and 26.3 seeds/dm^(3) in samples from the least,intermediate and most disturbed sites,respectively,and highest in the upper soil layers in all cases.The results indi-cate that there is limited potential for restoring woody vegetation solely from soil seed banks,and that woody species in the region rely more on recently shed seeds trapped in the standing dead biomass and litter on the ground than soil seed banks for regen-eration.Thus,human intervention is needed to accelerate forest recovery,mainly through alleviating anthropogenic impacts on the ecosystem(for instance,avoiding destruction of new seeds by intense fire),and site manipulation to improve environmen-tal conditions for seedling establishment and growth.Other ways of restoring forests than through the soil seed bank(e.g.sowing seeds collected elsewhere,and planting tree seedlings)could also be relevant.