Thesis (MSc)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Nyungwe Forest in the South West of Rwanda is surrounded by a dense human population (350 people/km') which depends on subsistence agriculture and livestock. Previous reports on the Forest have shown that its survival is threatened by illegal use of its resources. Participatory rural appraisal was conducted in five Communes next to the Forest to study the community's perceptions, uses and interests with respect to access and management of the Forest. Respondents perceived the Forest as a source of 18 categories of products of which only 14 were said to be of value for the respondents'livelihoods. Land, timber and minerals (gold) were the priority resources preferred by more than 55% of the respondents. Other important resources included fodder/pastures, wooden goods, fuelwood and poles. Fourteen different species were most preferred for timber, 16 for poles, 45 for medicinal materials and six for wooden goods. However, the majority of these species were preferred for multiple uses as timber, poles and medicines. A forest resource assessment was carried out to identify the stock of the preferred tree species. Not all woody resources mentioned as being preferred were available, with some tree species not found at all in the Forest. In order to identify tree species that can be used sustainably, different criteria including abundance (density), dominance, diameter size-class distribution and regeneration, were used in combination. Of the 12 tree species recorded in the Forest and most preferred for timber, only three species were present in sufficient abundance and sizes to allow sustainable utilisation. Of the 12 pole species identified, six were not vulnerable to exploitation, and of the preferred medicinal tree species only five were considered to fit into this category. Low resource availability and the need to address the interests of adjacent communities necessitated management options which enable access to some resources and benefits the communities as well as conservation measures to protect the biodiversity. A range of joint forest management options is discussed in order to assess the feasibility of a collaborative approach in the management of Nyungwe Forest. Some recommendations are made with respect to access to resources, the use of substitutes and areas for future research. / AFRIKAANSE OPSOMMING: Nyungwe Bos in die suidweste van Rwanda word omring deur 'n digte bevolking van 350 mense/km- wat van bestaanslandbou en lewende hawe afhanklik is. Vorige verslae het aangedui dat die voortbestaan van die Bos bedreig word deur die onwettige gebruik van sy hulpbronne. 'n Evaluering is in vyf gemeenskappe (Communes) langs die Bos gedoen om die gemeenskap se persepsies oor, gebruike van en belangstelling in die toegang tot die Bos, sowel as die bestuur daarvan te bestudeer. Die mense van hierdie plattelandse gebied is by die evaluering betrek. Respondente sien die Bos as 'n bron van produkte wat in 18 kategorieë ingedeel kan word, maar waarvan slegs 14 kategorieë van waarde is vir die respondente om 'n bestaan te kan maak. Meer as 55% van die respondente het grond, hout en minerale (goud) as die belangrikste hulpbronne aangedui. Ander belangrike hulpbronne sluit in veevoer of weivelde, houtartikels, brandhout en pale. Die respondente het 14 verskillende houtspesies verkies as timmerhout, 16 vir pale, 45 vir medisinale gebruike, en ses vir houtartikels. Die meerderheid van hierdie spesies is egter verkies vir veelvuldige gebruike soos timmerhout, pale en medisyne. 'n Evaluering van die hulpbronne in die bos is uitgevoer om te bepaal hoeveel bome van die gunstelingspesies daar in die bos is. Nie al die houthulpbronne wat deur die respondente verkies is, was beskikbaar nie, en sommige boomspesies is glad nie in die Bos gevind nie. Ten einde boomspesies te identifiseer wat vir lewensmiddele gebuik kan word, is 'n kombinasie van verskillende kriteria gebruik, insluitende die hoeveelheid bome (digtheid), dominansie, die verspreiding van die verskillende klasse deursneegroottes, en regenerasie. Van die 12 boomspesies in die Bos wat na aanleiding van hierdie evaluering opgeteken is en wat voorheen as gunstelingspesies vir timmerhout aangedui is, is daar slegs drie wat volop en groot genoeg is om vir lewensmiddele gebruik te word. Van die 12 spesies wat vir pale geïdentifiseer is, is ses teen oorontginning bestand, en van die gunsteling medisinale boomspesies val slegs vyf in laasgenoemde kategorie. Lae hulpbronbeskikbaarheid en die behoefte om die aangrensende gemeenskappe se belange aan te spreek, het bestuuropsies genoodsaak wat toegang tot sommige hulpbronne moontlik maak en wat die gemeenskappe bevoordeel, sowel as bewaringsmaatreëls ten einde die biodiversiteit te beskerm. 'n Verskeidenheid gesamentlike bosbestuuropsies is bespreek ten einde die uitvoerbaarheid van 'n benadering van samewerking in die bestuur van die Nyungwe Bos te ondersoek. Enkele aanbevelings is gemaak wat betref toegang tot hulpbronne, die gebruik van plaasvervangers, en studiegebiede vir verdere navorsing.

L’indice de surface foliaire (Leaf Area Index, LAI), défini comme la moitié de la surface foliaire par unité de surface de sol, est un paramètre clé du cycle écologique de la Terre, et sa précision d'acquisition a toujours la nécessité et la possibilité d'amélioration. La technologie du scanner laser actif offre une possibilité d'obtention cohérente du LAI à plusieurs échelles, car le scanner laser terrestre et le scanner laser aéroporté fonctionnent sur le même mécanisme physique. Cependant, les informations tridimensionnelles du scanner laser ne sont pas complètement explorées dans les méthodes actuelles et les théories traditionnelles ont besoin d'adaptation. Dans cette thèse, le modèle de distribution de longueur de trajet est introduit pour corriger l'effet d’agrégation, et il est appliqué aux données du scanner laser terrestre et du scanner laser aéroporté. La méthode d'obtention de la distribution de longueur de trajet de différentes plates-formes est étudiée et le modèle de récupération cohérent est établi. Cette méthode permet d’améliorer la mesure du LAI des arbres individuels dans les zones urbaines et la cartographie LAI dans les forêts naturelles, et ses résultats sont cohérents à différentes échelles. Le modèle devrait faciliter la détermination cohérente de l'indice de surface foliaire des forêts à l'aide de données au sol et aéroportées. / Leaf Area Index (LAI), defined as one half of the total leaf area per unit ground surface area, is a key parameter of vegetation structure for modeling Earth's ecological cycle and its acquisition accuracy always has the need and opportunity for improvement. Active laser scanning provides an opportunity for consistent LAI retrieval at multiple scales because terrestrial laser scanning (TLS) and airborne laser scanning (ALS) have the similar physical mechanism. However, the three-dimensional information of laser scanning is not fully explored in current methods and the traditional theories require adaptation. In this thesis, the path length distribution model is proposed to model the clumping effect, and it is applied to the TLS and ALS data. The method of obtaining the path length distribution of different platforms is studied, and the consistent retrieval model is established. This method is found to improve the individual tree measurement in urban areas and LAI mapping in natural forest, and its results at consistent at different scales. The model is expected to facilitate the consistent retrieval of the forest leaf area index using ground and airborne data.