Stratégies villageoises pour la gestion des paysages forestiers du Menabe Central, Madagascar

Introduction In order to reduce deforestation, the current attitude of conservation programmes and forest politics does no longer ban the local populations from the forests, because such measures present negative consequences for the communities. Today's tendency is to focus on a multifunctional planning of the forest landscape that combines the conservation of biodiversity with the long-run improvement of local livelihood. Following this global trend, Madagascar – biodiversity hotspot of international importance – has been passing through a process of devolution of the renewable resources management rights to local communities since 1995. Because of a too strong human pressure, the Malagasy forests have been drastically reducing; the conversion of forest soils into cultivated lands is the major cause of deforestation. In Madagascar, cultivation is the main activity in rural areas, and 73.5% of rural population is still living below the poverty line. Research background In the Central Menabe region, west coast of Madagascar, the annual loss of forest cover (dry dense forest) is about 1%. Numerous researches were carried out on the forests or on the man-forest interface in Central Menabe, but studies focusing on interdisciplinary questions at a regional level are rare. A forest landscape research that considers villages, cultivated fields, secondary vegetations and natural forests is therefore necessary to propose regional forest landscape management recommendations. Such a research project aiming at providing scientific information for a sustainable, multifunctional and participative forest landscape management was launched in 2005 in this region; the present PhD thesis integrates with this research project. Objectives, methods and results The PhD thesis aims at setting up a scientific basis for a sustainable management of forest soils, non timber forest products (NTFPs) and forest services. This management tries to answer, in a participative way, the local populations' needs and expectations while decreasing the pressure on biodiversity. The research methodology comes from social (questionnaires, surveys, participant's observations, scoring exercises) and natural sciences (inventories and descriptions of the cleared surfaces, NTFPs' inventories). The analyses were done mainly by means of non parametrical tests, and calculations of averages, standard deviations and frequencies. The following paragraphs present the PhD thesis's specific objectives and the obtained results. To analyze the socio-economic role and ecological impact of cultivation in the Central Menabe rural system Rice and slash and burn cultivation products are the objects of a bit less than the half of rural commercial transactions. Rice is the product the most marketed, but its supply is judged insufficient. The slash and burn cultivation contributes intensively to the rural households' alimentary and financial safety, but the commercial interest in its products remains weak. The surfaces of the clearings for cultivation vary between 0 and 2 ha, but it is difficult to estimate the frequency of the different types of vegetation that are cleared. Nevertheless, clearings for rice cultivation (cultivation principally done on irrigated plots) are less frequent than the ones for slash and burn cultivation. To analyze the socio-economic role and potentialities of the small and big livestock, and to assess the environmental impact of the big livestock Dependently on the breeders' ethnicity, zebus represent a social (enhancing of the breeder's social prestige) or an economical (products' utilisation or sale) value, always slightly lucrative. The small livestock's products contribute more intensively to the households' budgets, because the majority of the breeders sell these products for emergency or precise needs. The use of fire to renew pasture lands accentuates the deforestation, and the overgrazing present during the dry season creates local ecological instabilities. To analyze the NTFPs' socio-economic potentialities and to assess the harvests' environmental impact Amongst the four studied NTFPs, tenrec (Tenrec ecaudatus) is the one economically the most promising. For tenrec as for both tubers, traditional harvests do not represent a threat for the upholding of the species; however, the destructive harvest of wild honey perils the long-run survival of the bees' specie. To analyze the possibilities and political choices concerning the biodiversity conservation payments PES (payments for environmental services) programmes proposing payments in kind would be suitable, on some conditions, to protect biodiversity and to reduce poverty in Central Menabe. These conditions are i) to establish a PES contract with villages that are aware of biodiversity conservation and other economical potentialities, and ii) to focus the PES's goal on deforestation decrease and not on its full cessation. To synthesise, on a regional level, the socio-economic role and ecological impact of the main villager land uses, and to analyze the potentialities and the constraints of an optimisation of the forest landscape traditional use Socio-economically, cultivation and small livestock represent the main activities that insure the rural households' alimentary and financial safety. Ecologically, clearings for cultivation and big livestock's pastures are the activities generating the most destructive environmental impacts. Globally, the optimisation of cultivation techniques, the chicken breeding development and the improvement of the pasture management present big potentials to optimise the rural livelihood while decreasing the pressure on biodiversity. More detailed recommendations are presented in the chapter 7. Global synthesis and conclusion The recommendations are divided into three categories: some only act on biodiversity conservation, others have an exclusive effect on livelihood improvement, and some contribute to the both goals. This highlights the necessity to consider both the relation between biodiversity conservation and livelihood improvement, and other alternatives that are particular either to biodiversity conservation or to livelihood improvement.

Dead wood in managed forests: how much and how much is enough?

Rita Bütler Sauvain

The aims of this research were twofold: to develop an efficient method for the quantification of large spruce snags (standing dying and dead trees), and to establish snag target values for sustainable forest management. We answer the two basic questions: how much dead wood is currently available in managed forests? And how much dead wood is enough for biodiversity conservation? It is widely accepted that modern forest management has to be sustainable. One generally recognised criterion of sustainability is the maintenance of biodiversity. Since this concept encompasses a large range of scales and features (landscapes, ecosystems, species and genes; components, processes, functions, etc.), biodiversity indicators have been identified for measurement and monitoring purposes. "Dead wood" has been recognised as a key indicator for biodiversity in forest ecosystems. Verifying and assessing progress towards biodiversity maintenance or restoration hence requires the measurement of different kinds of dead wood. Yet cost-efficient and rapid methods are still lacking. That is why we developed in this thesis an efficient method for the quantification of large spruce snags. Being based on infrared Aerial Photos and a Geographic Information System (GIS), it is called the AP-GIS-method. It enables mapping of snags and calculation of the spatial snag-density, i.e. the number of snags per hectare, and can be used to answer the question: How much dead wood is in managed forests? Beside techniques to assess dead-wood quantities, forest managers need quantitative target values, i.e. guidelines in order to know how much dead wood should be maintained in managed forests for biodiversity conservation. Natural forests may be used as reference systems to define such targets. However, since dead-wood amounts in natural forests may be extremely high, up to 30% of dead trunks, the retention of such amounts in managed forests would hardly be compatible with economic objectives. Another possibility for defining guidelines is the translation of the habitat requirements of deadwood- dependent species into management targets. The Three-toed woodpecker Picoides tridactylus has previously been recognised as a potential indicator species of features characteristic for forests with natural dynamics (especially old-growth). Although ecological studies had demonstrated its need of dying and dead trees for foraging, nesting and drumming, the required density of such trees has never been quantified. In this thesis, we analysed the dependence on dead wood for both European subspecies, the Alpine Picoides tridactylus alpinus and the northern P. tr. tridactylus. The study was conducted in sub-Alpine spruce forests in Switzerland and boreal forests in central Sweden. In both countries, we found a significant non-linear response of the probability of woodpecker presence to different amounts of dead trees, and identified critical ecological thresholds for the local presence of this species. Clearly, the Three-toed woodpecker depends on relatively high amounts of dying and dead trees. In Switzerland, the road network density negatively affected the presence of this woodpecker species, since a high road density facilitates forest management intensification and the removal of diseased and dead trees. Based on our results, and since several other links with biodiversity have previously been demonstrated, we suggest that Three-toed woodpeckers be considered indicators of dead wood and habitat quality. This species has therefore been used in this thesis to find an answer to the question: How much dead wood is enough in managed forests? In order to ascertain dead-tree targets, we developed a bioenergetic model for Threetoed woodpeckers, enabling estimation of snag amounts required by this species to satisfy its energy needs. By comparing modelling results with the previously identified critical dead-wood thresholds, we were able to derive reliable targets, since both approaches resulted in similar critical values. We recommend, for both boreal and sub-Alpine spruce forests, aiming for 5% of the standing tree basal area, or volume to be dead. Such snag-retention levels, to be applied over an area of about 100 ha, correspond in sub-Alpine forests to a basal area of ≥ 1.6 m2 ha-1, or a volume of ≥ 18 m3 ha-1, or a minimum of 14 snags with a diameter ≥ 21 cm per hectare. Considered as a pragmatic way to stimulate forest managers' interest in dead wood maintenance or restoration, we analysed the potential usefulness of Three-toed woodpeckers as natural agents against bark beetles. By defining three scenarios for different levels of woodpecker effectiveness, we compared the numbers of bark beetles consumed with those caught in pheromone traps used in forestry. We demonstrate that woodpeckers catch 2-19 times more bark beetles than traps do. This result is true for both cases, when one woodpecker is compared with one trap, and when the whole Swiss woodpecker population is compared to all traps installed in Swiss forests.

EPFL2003

Subalpine Pasture-Woodlands in a Changing Climate

Konstantin Svetlozarov Gavazov

Climate change in temperate mountain systems and associated increase in temperature and decrease in precipitation are expected to have strong implications for vegetation productivity, species diversity and carbon turnover in subalpine grasslands. Little is known, however, about the interaction between the effects of climate change and those of local land use management and possible changes in landscape structure. Pasture woodlands in the Swiss Jura Mountains are a traditional landscape, resulting from a long-lived sustainable use of grasslands and woodlands, and as such provide a suite of important ecosystem services to human society. These range from carbon sequestration and biodiversity preservation, to provision of timber and forage for livestock, and last but not least an aesthetic value, much appreciated by tourism. In this thesis various aspects of ecosystem functioning have been studied, investigating the combined effects of experimental climate change and land use on structurally different wooded pastures. An altitudinal gradient method has been used to simulate future climate change conditions, by imposing warmer and drier climate on subalpine turfs transplanted at lower elevation. The resulting gradient in mean annual temperature and precipitation – ranging from cold and wet in the subalpine zone, to warm and dry in the colline zone – has allowed for the detection of tipping points and altered states of ecosystem functioning in response to the treatments. The method employed provided also the possibility for a direct comparison of three land use types: unwooded pastures, sparsely wooded pastures, and densely wooded pastures (the result of pasture management intensity), in their response to climate perturbation. During the four years of experimental work, a series of observations have been made at the plot scale (square metre) in terms of plant performance and biogeochemical cycles, as well as at the landscape scale (hectare) in terms of forage production. A general threshold level for ecosystem resistance to experimental climate change was detected between the moderate IPCC scenario (+2 K mean annual temperature; -20 % annual precipitation) and the intensive IPCC scenario (+4 K mean annual temperature; -40 % annual precipitation). A concomitant gradient in ecosystem response to climate change was observed across the three land use types. The intensively managed unwooded pasture type was consistently more affected by the experimental treatment and rarely exhibited signs of resistance, especially under the intense climate change scenario. A drastic loss of plant species diversity, reduction of herbaceous biomass, impaired litter decomposition and soil microbial metabolic activity have all contributed to the altered state of ecosystem functioning. In contrast, the two extensively managed wooded pasture types showed considerable resistance to climate perturbation in terms of both above and belowground ecosystem processes. The reported inter-annual variation in herbaceous diversity and biomass production within these land use types demonstrated their resilience (recovery) potential too. Using a modelling approach for upscaling these results to the heterogeneous landscape of pasture woodlands in the Swiss Jura Mountains, has proven that extensively used wooded pastures could grant sustainable ecosystem services in terms of forage provision for cattle under climate change. Considering that the two experimental climate change intensities implemented this study are the projected ‘best’ and ‘worst’ case scenarios for the coming decades, the reported resistance of wooded pastures to climate change has to be embraced, and sustainable land use set as a goal in high altitude mountain pastures.

EPFL2013

Theoretical and Experimental Studies of Dendritic Metacommunities

Francesco Carrara

The present thesis deals with the understanding of the origins and the mechanisms of maintenance of biodiversity in natural landscapes, in particular by identifying key processes that define large-scale patterns of abundance and diversity. Biological communities often occur in spatially structured habitats where connectivity directly affects dispersal and metacommunity processes. Recent theoretical work suggests that dispersal constrained by the connectivity of specific habitat structures affects diversity patterns and species interactions. This is particularly relevant in dendritic networks epitomized by fluvial ecological corridors. This thesis addresses whether connectivity alone can explain observed features of biodiversity and selectively promote different components of community composition in river-like landscapes, such as local species richness or the among-community similarity. The relevance of this thesis lies in the major ecological challenges posed by the topic, and its fundamental importance to conservation biology. The studies pursued herein are also deemed relevant because of the influence of the spatial connectivity and dispersal on population dynamics and of the relevance of biodiversity to ecosystem functioning. Mechanisms of species coexistence were investigated with a blend of theoretical tools (broadly related to statistical mechanics and the theory of stochastic processes) and experimental work using laboratory microbial communities. The research tools ranged from aspects of modern coexistence theory in a local perspective to the recent concept of the metacommunity in spatial ecology, within a unified framework. The study of biodiversity in riverine ecosystems guided by observational data has been addressed by combining theoretical metacommunity models with laboratory experiments. The results are diverse. First, they show experimentally that connectivity per se shapes key components of biodiversity in metacommunities. Local dispersal in isotropic lattice landscapes homogenizes local species richness and leads to pronounced spatial persistence. By contrast, dispersal along dendritic landscapes leads to higher variability in local diversity and among-community composition. Although headwaters exhibit relatively lower species richness, they are crucial for the maintenance of regional biodiversity. By suitably arranging patch sizes within river-like networks the effect of local habitat capacity (i.e., the patch size) and dendritic connectivity on biodiversity can be experimentally disentangled in aquatic microcosm metacommunities. It is shown in this thesis that species coexistence and community assembly depend on intricate, non-trivial interactions of local community capacity and network positioning. Furthermore, an interaction of spatial arrangement of habitat capacity and dispersal along river-like networks also affects a key ecosystem descriptor, namely regional evenness. High regional evenness in community composition is found only in landscapes preserving geomorphological scaling properties of patch sizes. In riverine environments some of the rarer species sustained regionally more abundant populations and were better able to track their own niche requirements compared to landscapes with homogeneous patch size or landscapes with spatially uncorrelated patch size. All the experimental results were supported and extended by a theoretical analysis where the above mechanisms have been generalized. This thesis provides the first direct experimental evidence that spatially constrained dendritic connectivity is a key factor for community composition and population persistence in riverine landscapes. As such, this thesis assesses a longstanding issue in spatial community ecology. It offers unique insights into the ecological forces structuring natural communities in a key ecosytem, and demonstrates principles that can be further tested in theoretical metacommunity models possibly to be extended to real riverine ecosystems. Taken together, the analyses show how the structure of ecological networks interacts with the spatial environmental matrix in determining biodiversity patterns and the functioning of biological communities. The analyses also suggest that altering the natural linkage between dendritic connectivity and patch size strongly affects community properties at multiple scales. The first part of this thesis (chapters 2 and 3) addresses key aspects of biodiversity-ecosystem functioning research where the combination of theory-guided experiments and theoretical investigations shows how a stochastic implementation of population dynamics proves fundamental for key community properties such as species persistence and community stability. The diversity-productivity and diversity-stability relationships are explored. Both experimental findings and the results of a stochastic model fitted to the experimental interaction matrix, suggest the emergence of strong stabilizing forces when species from different functional groups interact in the same environment, increasing species coexistence and community biomass production. The last part (chapter 6) provides a synthesis of this thesis work, in that it aims at unifying aspects from niche-theory, usually adopted in spatially implicit models, with those characteristic of a spatially explicit context from a typical real-life mountainous regions. It is dedicated to the possible explanation for a macroecological pattern routinely observed from organisms in different domains of life, that is, the mid-elevational peak in local species richness. Guided by empirical observations on diversity of macroinvertebrates in Swiss river basins, a theoretical ansatz is provided which is deemed to capture the essential geomorphological drivers and controls relating species-fitness to altitude. A set of overarching conclusions and perspectives for future research are discussed in the concluding chapter.

EPFL2013

Subalpine Pasture-Woodlands in a Changing Climate

Konstantin Svetlozarov Gavazov

EPFL2013

Theoretical and Experimental Studies of Dendritic Metacommunities

Francesco Carrara

EPFL2013

Dead wood in managed forests: how much and how much is enough?

Rita Bütler Sauvain

EPFL2003