The results of the present study show that there were significant differences in basal area, browsed plant density, shrub density and species diversity across the three strata in Gonarezhou National Park. The structural and compositional differences across the three strata in Gonarezhou National Park were possibly related to herbivory, fires, human activities, droughts, geology and soil differences (Tafangenyasha, 1997a, 1998; Gandiwa and Kativu, 2009; Gandiwa et al., 2011a, b). Repeated fires and elephant browsing are known to stress normal growth and affect the health of the woodland and may top-kill woodyvegetation (Bond, 2008; Ryan and Williams, 2011; Asner and Levick, 2012). Furthermore, elephant populations in Gonarezhou National Park have over the years continued to increase, from ~3100 in 1969 to ~9100 in 2009 (Dunham et al., 2010). This increase may also have been influenced by the recent non-culling of elephants in the park since the last elephant cull in Gonarezhou National Park was conducted in 1993. Tsetse fly (Glossina spp.) (Diptera: Glossinidae) eradication teams cleared riparian woodlands from parts of the major river systems, i.e. Save, Runde and Mwenezi, in Gonarezhou National Park, also negatively influencing the woodyvegetation (Gandiwa and Kativu, 2009).
Fully protected areas such as national parks are often assumed to be the best way to conserve biodiversity (Banda et al., 2006; Gaston et al., 2008). Interestingly, the present study results also revealed that Save-Runde Junction IBA which occurs inside a protected area had a higher species richness (59) and species diversity (H′ = 3.28) compared to Manjinji Pan IBA which had a species richness of 43 and a species diversity of 2.90. Similarly, Save-Runde Junction IBA had a higher number of bird species of special concern than Manjinji Pan IBA (Table 1). The lower woody plant species richness and diversity in Manjinji Pan IBA could be attributed to its relatively smaller area and isolation as compared to Save-Runde IBA (Fig. 1) and to the likely loss of woody plant species within the IBA. Loss of woody species in Manjinji Pan IBA could have resulted from targeted extraction of certain plant species for construction or firewood. Human influence has undoubtedly influenced the woodyvegetationstructure and composition of several terrestrial ecosystems (Luoga et al., 2002; Gaugris and Van Rooyen, 2010). The present study results are consistent with those of Higgins et al. (1999) who also recorded lower species richness in woody communities occurring in communal land as compared to protected private game reserves in South African semi-aridsavanna. In Save- Runde Junction IBA, the higher species richness and species diversity of woody plants could be a result of low current woody species extraction due to strict law enforcement inside Gonarezhou National Park (Gandiwa et al., 2013).
Some general observations were made by Furley et al. (2008) in a study conducted in Zimbabwe on the results of frequent burning: (1) Vegetationstructure is strongly affected, lowering the proportions of trees to shrubs and herbaceous plants and reducing ground cover; irregular fire behaviour leads to patchiness; ground layer plants change from perennials to a dominance of annuals. (2) Tree height decreases inversely with fire frequency; total above-ground biomass is severely reduced. (3) Tree and woody shrub density remains fairly constant through seedling recruitment and resprouting, though numbers of individual species may be affected. The ability of stems that are killed in fire to resprout is a key life-history trait that promotes the persistence of trees in savanna. In a study conducted by Russell-Smith et al. (2003) in Eucalyptus dominated open forest and woodland in Northern Australia, significant changes were observed between burned and unburned treatments specifically in the development of a denser midstorey in both open-forest and woodland unburned treatments.
Chapter 3 - Soil seed banks and aboveground vegeation
A continuous grass layer with a discontinuous layer of trees and shrubs are typical features of semi-arid savannas (Van de Koppel and Prins, 1998; Van Langevelde et al., 2003). The balance between trees and grasses, however, is often highly disturbed due to heavy grazing and poor management (Pugnaire and Lazzaro, 2000; Van Auken, 2000). The disappearance of good fodder grasses and browse species are serious challenges, threatening the livelihoods of millions of people in semi-aid savannas worldwide (Oba et al., 2000; Harris, 2010). Grazing is often regarded as the most important factor responsible for large structural changes in savanna ecosystems. Increasing the grazing pressure beyond a certain threshold, often leads to irreversible effects. At high grazing pressures, the perennial grasses disappear and are replaced by annual herbs, which could trigger a vegetation collapse; once the herbaceous vegetation collapses, it is extremely difficult to return to the grassland state, even if the grazing pressure is greatly reduced (Rietkerk et al., 1996; Van de Koppel et al., 1997). However, the return of species that disappeared from the aboveground vegetation under extensive, or “heavy” grazing can be facilitated by the soil seed banks (Baker, 1989; Leck et al., 1989; de Villiers et al., 2003), as the soil seed bank forms a pool of propagules for the regeneration of the native vegetation after disturbance, stimulating recovery of the vegetation (Thompson and Grime, 1979; Leck et al., 1989). In this study, we tested whether the availability of seeds in the soil could “kick start” the recovery of the vegetation and accelerate the transition from a degraded state to a vegetation with a perennial grass cover.
Table 1. Summary of statistical analyses results of the study variables in Save, Runde and Mwenezi riparian vegetation in Gonarezhou National Park, Zimbabwe. Notes: Values across columns not sharing the same
superscript letters are significantly (LSD; P < 0.05) different.
Discriminant analysis results of nine woodyvegetation variables showed that Root 1 explained about 73% (eigenvalue = 0.81) whereas Root 2 explained about 27% (eigenvalue = 0.30) in woodyvegetationstructure and composition in the sample plots across the three strata in Gonarezhou. Root 1 was negatively correlated to taller woody plants, high density of fire damaged plants and low density of browsed plants, and positively correlated to high numbers of stems per plant, low tree density, high shrub density and high woodyvegetation species diversity. Root 2 was negatively correlated to high basal area and high tree density, and positively correlated to high woodyvegetation species diversity. Mwenezi riparian stratum was generally negatively correlated to both Roots 1 and 2 whereas Runde riparian stratum was positively correlated to Root 1 and negatively correlated to Root 2. Lastly, Save riparian stratum was positively correlated to both Roots 1 and 2 (Fig. 1). Overall, there were significant differences in distances between Mwenezi and Save riparian strata (P = 0.020) and between Mwenezi and Runde riparian strata (P = 0.001). In contrast, there was no significant difference in distances between Save and Runde riparian strata (P = 0.112).
Research results indicate that the crops which take longer to mature, normally attain better yields as compared to those which take fewer days [24,25]. The accessions took a range of 75 - 94 days to mature. The accessions varied in the number of days to maturity. This is because, a plant which takes longer time to mature, grows bigger in size and can hold heavier produce. According to [22,26] variation of in a parameter among different accessions can be attributed to their inherent genes. Other researchers reported a similar range of the number of days to maturity  who reported 82 - 89 days to mature. The results were however not comparable to those of other researchers, for example [20,22], who reported 53 - 62 days and 47 – 50 days to maturity respectively.
Post-fi re dynamics of the woodyvegetation of a savanna forest (Cerradão) in the Cerrado-Amazon transition zone
Acta bot. bras. 29(3): 408-416. 2015.
composition and structure of the woodyvegetation of this habitat and killed trees, with smaller individuals being more affected. The results only partially corroborate the hypothesis tested, however, given the occurrence of an increase in the basal area in the burned plots. In this sense, Tachigali vulgaris appears to be a key savanna forest species for the recuperation of biomass following wildfire disturbance, given the significant investment in biomass of the individuals surviving this disruption. It is nevertheless important to note that this species has a short life cycle (Franczak et al. 2011), and that this “recuperation” of biomass may be no more than a short-term effect, reinforcing the need for further monitoring of the study plots in order to better evaluate the medium- to long-term response. Overall, the results indicated that frequent burn-off of the savanna forest would result in marked modification of the species composition and structure of its woodyvegetation, which may be undetectable from biomass estimates alone, at least over the time scale analyzed during the present study.
Soil quality indices (SQIs) are often management driven and attempt to describe key relationships between above- and below-ground parameters. In terrestrial systems, indices that were initially devel- oped and modiﬁed for agroecosystems have been applied to non-agricultural systems in increasing number. We develop an SQI in arid and semi-arid ecosystems of the Western US impacted by differ- ent types of geologic mineralization using the relationship between vegetation community parameters and soil abiotic and biotic properties. We analyze these relations in soils associated with three different mineralization types: podiform chromite, Cu/Mo porphyry, and acid-sulfate gold vein systems at four different sites in California and Nevada. Soil samples were collected from undisturbed soils in both min- eralized and nearby unmineralized substrates as well as from waste rock and tailings. Aboveground net primary productivity (ANPP), canopy cover and shrub density were measured for the vegetative com- munities. Minimum data sets were developed based on correlations between the soil and vegetation parameters, reﬁned using principal components analysis, scored using non-linear functions, and com- bined into an overall SQI. The indices are comprised of one or two microbial parameters and three to six abiotic parameters, the latter consisting of nutrients and metals. Given the preliminary development of this approach, the parameters and combinations to arrive at an SQI for a given site cannot at this time be correlated or compared with that of another site. This SQI approach provides a means of quantify- ing disturbed ecosystem recovery resulting from mining, and could be applied to other disturbances in a way that readily distills the information for potential use by land managers. However, severely dis- turbed areas with little to no aboveground biomass, such as unreclaimed tailings, have likely crossed an ecological threshold that precludes the use of this type of monitoring tool.
Several object-based features can be calculated and extracted in eCognition and applied during the classification procedure. In this study, various features were extracted, including vegetation indices (VIs), principal component analysis (PCA) (Taylor, 1977), and gray-level co-occurrence matrix (GLCM) (Haralick et al., 1973). VIs and PCA are widely used for the retrieval of vegetationstructure as well as land cover classification (Hurni et al., 2013). We have selected the following VIs (Table 1): The Normalized Difference Vegetation Index (NDVI), Green Normalized Difference Vegetation Index (gNDVI), Enhanced Vegetation index (EVI2), Soil-adjusted Vegetation Index (SAVI), and Modified Soil-adjusted Vegetation index (MSAVI). NDVI was selected to separate mangroves from other non-vegetated areas. To address the limitations of NDVI that is affected by soil brightness (Carlson and Ripley, 1997) and saturates in high biomass areas (Huete et al., 2002; Wang et al., 2002), EVI2 was calculated as it shows greater sensitivity to vegetation and reduces atmospheric effects on vegetation index values (Huete et al., 2002). SAVI (Haboudane et al., 2004) was computed as a corrective index on soil brightness for areas with low vegetation cover and exposed soil surface. The brightness algorithm was calculated to represent the reflectance intensity of bare rocks and soils among other features sharing similar spectral radiance (Kauth and Thomas, 1976; Schönert et al., 2014).
The study area is between 6°29'43.0'' and 6°38'24.1'' North and 2°22'02'' and 2°34'13.4'' East. The soils are hydromorphic and settled on alluvial material (clay and sandy clay) and clayey sediments of the Continental Terminal (Volkoff, 1976; Willaine and Volkoff, 1976). The hydrographical network consists of two parallel watercourses: Ouémé in the East and Sô in the West. The two watercourses, interconnected by arms, play the role of tributary, or distributary depending on the period (of flood or recession). They are bordered by vast flooding areas. Between Ouémé and Sô, the vast plain receives most of its water during flood periods. The climate is subequatorial and characterized by two rainy seasons from March to July and from September to October and two dry seasons from November to February and August. The annual rainfall averages are 1124 mm in Adjohoun, 1296 mm in Porto-Novo and 1251 mm in Cotonou from 1960 to 2009. The minimum and maximum temperature averages are 24.4 and 30.2°C. The vegetation is composed of a mosaic of swampy formations, flooding forest, a few islands of mangrove planted, and low meadows and aquatic vegetation. Agriculture is the major activity and occupies nearly 60% of land (Anonyme, 2002).
We found strong evidence of competition among woody plants within a 2.5–5.0 m radius neighborhood depending on the species of the focal plant, with a community- scale neighborhood of 3.0 m. At this scale, our results indicate a decrease in growth rates with increasing neighbor size and decreasing distance to neighbors. Basal stem size of neighbors better predicted RGR of focal plants compared to height and crown area metrics. This finding strongly points to belowground competition for water as the likely mechanism generating competitive suppression of growth rates, as has been sug- gested by other studies of woody plant spatial patterns in the region (Franz et al. 2011, 2012). Studies of compe- tition among trees in forests generally show increased performance of models utilizing crown area to describe tree size, reflective of size- asymmetric competition for light typical in wetter systems (e.g., von Oheimb et al. 2011, Fraver et al. 2014). Water limitations and drought seasonality characteristic of tropical savannas shift the primary limiting factor to belowground resources. Thus, it follows that morphological characteristics reflective of below- ground resource capture are linked with variation in savanna plant growth rates. The spatial extent of com- petition we detected may reflect species- specific average lateral range of primary root biomass, though we lack root distribution data to test this directly.
livestock forage. As in most pastoral zones, woody taxa resources play an important role in the nourishment of livestock and meeting the needs of the human communi- ties that tend to those livestock . However, these re- sources have been progressively degraded over the last 40 years, driven by droughts, such as the large drought of the 1970s, and multiple forms of human activity. This degradation has been found to be associated with the loss of certain taxa as well as the expansion of others . Simultaneously, the average density of woody taxa in the Ferlo zone has clearly diminished over the course of the last several decades  with consequences for the quality of soil through increased erosion. Facing this situation, strategies are much needed to rehabilitate these degraded ecosystems. One such strategy is a rotational grazing approach promoted by the Senegales government to fa- cilitate the regeneration of vegetation during years in which climate conditions allow for growth and re-estab- lishment . The government has also promoted efforts to plant trees across the southern border of the Sahara desert, a pan-African project known as the Green Wall Initiative, to prevent the southwards encroachment of the desert. All of these projects have been developed with the aim of improving natural resource stocks, but have little evidence of success. In order for these strategies to work, it will be necessary to put in place a system of sustainable management that emphasizes the protection of woody taxa on fragile and vulnerable soils. This sus- tainable management requires familiarity with the precise ecological conditions under which these taxa perform best. This study aims to document the conditions under which the structural diversity of woody taxa changes in the Ferlo zone in order to facilitate more appropriate ma- nagement strategies.
This set of recommendations is based on a comprehensive analysis of current goat production and marketing and key constraints in six districts of southernZimbabwe. These recommendations do not necessarily comprise the entire evolutionary process in goat development, but present the ‘fi rst steps’ of development towards improved goat production and marketing. These options therefore need to be revised within the respective local contexts and implemented in a holistic approach, engaging different interest groups, and taking into account farmers’ interests/objectives, limitations and existing initiatives. Most of the recommendations apply to both types of farmers, those with few goats who focus on building and maintaining fl ocks, as well as those with larger fl ocks who can successfully commercialize. The farmers with fewer goats will however need extra support and perhaps also a different approach to implementing the recommendations. The key fi ndings of this report indicate that resource-poor farmers have the potential to improve goat production and increase offtake levels, making use of locally adapted resources (genetic and natural). However, high goat mortality is the most limiting factor. This is due to a number of causal factors that include inadequate disease control, dry season feed shortages and poor nutrition, inappropriate housing and little efforts in improving the local breeds.
station in April 2005). The frequency of flows higher than this particular event is 1·9% over the 1990–2005 period (annual flood = 120 m 3 s −1 ). The elevations of measured flood marks in the embanked study reach were confirmed by
an automatic water monitoring level fitted with a pressure sensor (model CTD-Diver).
Number and sizes of pioneer units. Within the active floodplain, in both the embanked and unconstrained study reaches, distinct landform units were identified: a main low flow channel, secondary channels, unvegetated bars, bars occupied solely by herbaceous species and units occupied by a mixture of herbaceous and pioneer ligneous species such as willow, alder and/or poplar. Our study focuses on the last one of these identified landform units, which are referred to in this paper interchangeably as ‘pioneer vegetation units’ or ‘pioneer patches’. The pioneer vegetation units or pioneer patches are considered to be islands (‘pioneer islands’) where they (1) form a discrete patch of ligneous vegetation occupied mainly by willow and poplar and (2) are surrounded entirely by water and/or unvegetated bar surfaces (Osterkamp, 1998; Ward et al., 2000). These islands correspond well to phase II island types described by Edwards et al. (1999) along the River Tagliamento, a similar gravel bed river located in northeastern Italy.
Evidence from the species of relatively fire-tolerant savanna trees seems at first sight to be somewhat less valuable than that from the forest species. It appears, however, that certain species of savanna trees e .g Isoberlinia species are normally found on site unfavorable for farming whereas other species e.g. Daniellia oliveri and Hymenocadia acida occur commonly in farmed areas; in addition certain species especially Parkia biglobosa and Vitellaria paradoxa are deliberately encouraged by farmers. It is therefore possible to deduce the intensity of farming from the composition and also the structure of savanna. Areas which on other grounds are known to be derived savanna usually show by their composition that farming and other anthropogenic activities has been heavy (Keay, 1959, Essien and Aniama, 2014).
Acknowledgements. The authors acknowledge the E-OBS dataset from the EU-FP6 project ENSEMBLES (http://ensembles-eu. metoffice.com, last access: 31 March 2017) and the data providers in the ECA & D project (http://www.ecad.eu, last ac- cess: 31 March 2017). The authors also wish to acknowledge the ASTER GDEM data product, courtesy of the NASA Land Pro- cesses Distributed Active Archive Center (LP DAAC), USGS Earth Resources Observation and Science (EROS) Center, Sioux Falls, South Dakota (https://lpdaac.usgs.gov/data_access/data_pool, last access: 15 June 2017). We are grateful to ICNF for sharing the inventory database performed in 2010 in continental Portugal. We also thank Cristina Catita, Ana Russo and Patrícia Páscoa for the advice and helpful comments as well as Ana Bastos for the elabo- ration of the satellite datasets of the vegetation index NDWI and Miguel Nogueira for the insights on model sensitivity analysis. We are very grateful to Eric Font for the useful insights on soil properties. Inês Gomes Marques and research activities were sup- ported by the Portuguese National Foundation for Science and Technology (FCT) through the PIEZAGRO project (PTDC/AAG- REC/7046/2014). This publication was also supported by FCT – project UID/GEO/50019/2019 – Instituto Dom Luiz. The authors further thank the reviewers and editor for helpful comments and suggestions on an earlier version of the paper.
Agriculture in arid and semi-arid lands of Kenya is depends on seasonal characteristics of rainfall. This study seeks to distinguish components of regional climate variability, especially El Niño Southern Oscillation events and their impact on the growing season normalized difference vegetation index (NDVI). Datasets used were: 1) rainfall (1961-2003) and 2) NDVI (1981-2003). Results indicate that climate variability is per- sistent in the arid and semi-arid lands of Kenya and continues to affect vegetation condition and conse- quently crop production. Correlation calculations between seasonal NDVI and rainfall shows that the Octo- ber-December (OND) growing season is more reliable than March-May (MAM) season. Results show that observed biomass trends are not solely explained by rainfall variability but also changes in land cover and land use. Results show that El Niño and La Niña events in southeast Kenya vary in magnitude, both in time and space as is their impact on vegetation; and that variation in El Niño intensity is higher than during La Niña events. It is suggested that farmers should be encouraged to increase use of farm input in their agricul- tural enterprises during the OND season; particularly when above normal rains are forecast. The close rela- tionship between rainfall and NDVI yield ground for improvement in the prediction of local level rainfall. Effective dissemination of this information to stakeholders will go along way to ameliorate the suffering of many households and enable government to plan ahead of a worse season. This would greatly reduce the vulnerability of livelihoods to climate related disasters by improving their management.
The European settlers also introduced many exotic plant species which have become naturalised in Central Otago (Hubbard and Wilson, 1988). This, and the degradation caused by grazing and burning, has given rise to an induced vegetation, dominated by exotic species, which today bears little resemblance to that of pre-European times. Some improvement of the pastoral productivity of the region was achieved with the advent of aerial topdressing and a reduction in the rabbit population in the 1950s (O’Connor, 1986), although this period also saw the spread of weed species (Morgan, 1989). Over this century, rabbits populations in Central Otago have resurged repeatedly despite eradication efforts, and although irrigation has allowed vegetation improvement in some areas, there is otherwise little evidence of the reversal of the degradation.
filter can be parameterized to extract objects (in our case crown canopies) from their surroundings and from larger objects. The feature termed “mean” was used - the objects have grayscale values depending on their distinctiveness - which was rescaled between 0 and 100, resulting in a quantita- tive estimate of the areas covered by canopies. Each image was visually screened and images domi- nated by obvious mis-estimations (strong under- or overestimation) were discarded. The final values represent the subpixel woody coverage, with 100 being fully covered and 0 free of any green leaved woodyvegetation. The advantage of this weighted method over a binary tree/no tree classification is that a sub-pixel coverage (i.e. small crowns and edge pixels) receives a lower weight, thus pre- venting overestimation (Extended Data Figs 2,3). Moreover, using such weighting emphasizes larg- er canopies, which makes the product more robust against a rapidly changing (fire, field clearing, etc.) bush layer, which receives a lower weight. Burned areas were manually clipped to keep only high quality training images. In total, 219 images were kept. The accuracy of the method was cali- brated and tested with field data (144 plots) from Senegal. The squared field plots are small (50 x 50 m) and include canopies of all size classes thereby being well suited to validate the VHR prod- uct.