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I investigated the effects ofhabitat loss and subsequent restoration on invertebrate community structure and ecosystem functioning in a mined peat bog in the North Island, New Zealand. In an experimental trial, the impact of peat bog habitat loss and isolation on the invertebrate community associated with Sporadanthus ferrugineus (Restionaceae) was investigated. Potted S. ferrugineus plants were exposed to invertebrates at various distances up to 800 m from an intact habitat (the presumed source population) over 18 weeks. Invertebrates rapidly colonised the experimental plants, with all major Orders and trophic groups present on Sc ferrugineus within 6 weeks. However. with increasing distance away from the undisturbed habitat, there was a significant decrease in total richness and abundance of invertebrates associated with the potted plants. Additional tests showed that even a moderate degree of isolation (i.e. greater than 400 m) from the intact habitat caused an almost complete failure of 'Batrachedra' sp. to colonise its host plant, at least in the short-term, The density of eggs and larvae, and the average larval size of 'Batrachedra' sp. (Lepidoptera: Coleophoridae) colonising Si ferrugineus plants, as well as the proportion of Si ferrugineus stems damaged by 'Batrachedra' sp. herbivory, all decreased logarithmically with increasing distance from the intact habitat. Surprisingly, though, the rate of recovery of the insect-plant interaction following experimental habitat restoration was remarkably rapid (i.e. between 3Y2 and 6 years). After just 6 years there was no significant difference in insect-plant interactions between the intact peat bog sites and any of the experimentally restored sites up to 800 m away. These results suggest that the degree of isolation from undisturbed habitat has a major impact on the rate and patterns of restoration recovery in the invertebrate community and that some insect-plant interactions can recover rapidly from habitat loss with restoration management. Restoration of mined peat bogs in northern New Zealand is initiated by establishing a native vegetation cover to minimize further peat degradation. The effects of various restoration techniques on litter decomposition, microbial community activity and beetle community composition were investigated within an experimental trial, These treatments included translocation ofpeat bog habitat (direct transfer of islands), milled peat islands with no seed and milled peat islands with seed, and were compared with an unrestored mined site and an undisturbed peat bog. In all the response variables measured, the undisturbed peat bog sites had significantly higher decomposition rates and microbial respiration rates, and significantly higher abundance and species richness of beetles than any of the restoration treatments. Inaddition, the technique used to restore mined peatlands had a significant effect on the beetle community composition and litter decomposition processes. Despite a rapid initial change in the beetle community following habitat translocation, the direct transfer islands were still the most similar in beetle species composition to the undisturbed peat bog. Microbial activity and decomposition rates were higher in the direct transfer and mined peat surface after 6 months. However, even after 12 months, decomposition rates in the restored habitats were still far from reaching the levels recorded in the undisturbed peat bog. The results suggest that beetle community structure and ecosystem processes such as decomposition and microbial activity rates may be able to recover faster with certain restoration techniques, such as direct transfer of intact habitat islands. Subsequently, I examined long-term beetle community reassembly on islands that had been restored by creating raised areas ofprocessed peat with the addition of Leptospermum scoparium seed. Monitoring of different-aged restored islands representing the full range of restoration ages (up to 6 years) available at the peat mine, indicated that as the peat islands became older and the vegetation structure became more complex, the abundance, species richness and composition of the beetle community became increasingly similar to the community in the undisturbed peat bog. Despite this, distinct differences between the intact peat bog and older restored peat islands still persisted, even after 6 years, particularly at an individual species level. However, it is predicted that within 12 years the restored peat islands will share 100% ofbeetle species in common with the undisturbed peat bog. Taken together, these results indicate that restoration is effective in initiating the recovery of beetle assemblages and ecosystem processes (such as litter decomposition and microbial community activity) in cut-over peat bogs. However, it is estimated to take at least 12 years before pre-mining communities and functions are attained, and ongoing monitoring to develop an understanding of the longer-term dynamics of such ecosystems and processes is clearly required.

Diss. (sammanfattning) Umeå : Sveriges lantbruksuniv., 2007. / Härtill 3 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniversitet, 2006. / Härtill 4 uppsatser.

Made available in DSpace on 2015-04-17T14:55:20Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 4002692 bytes, checksum: 85600be9b689a4e4048b5414df434ab6 (MD5) Previous issue date: 2012-08-23 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Studies related to litter dynamics are important to comprehend decomposing deciduos material, nutrients cycling, succession patterns, ecological disturbance and environmental variables interactions in terrestrial ecosystems. In opposition to Caatinga's degradation speed, a lack of studies related to litter production dynamics is observed. Thus, this study aimed to evaluate climatic factors (rainfall and evapotranspiration) and vegetation effects over temporal and spatial dynamics of litter production in Brazilian Northeastern's semiarid. A phytosociologic survey was performed in Paraiba's Cariri in 12 sampling areas. Two 1 m2 collectors (with 0,15 m3) were placed about 50 m distant from each other in order to estimate litter monthly production between November 2009 and 2011. Litter deposition values observed in this study varied between 3430 and 4600 kg.ha-1.year-1. Litter production was significantly bigger in the second year of survey and it varied between months in both years. Intra-annual variation was positive to total litter production, showing peaks of litterfall in dry period about three or four months after the greatest rates of monthly rainfall. While reproductive structures and branches corresponded to 14% and miscellany from 3% to 5%, leaves, which represented more than 60% of the total, corresponded to the predominant part of litter. Litter production was significantly different between areas so as each of its parts. The density of plant species, vegetation height and trunk diameter at ground were responsible for 79% of annual litter production in those different areas. Results reveal that litter production in Caatinga have a spatiotemporal heterogeneity, which is related to climate and vegetation and must provide effects over substratum in edaphic microorganisms activities and, consequently, in edaphic conditions and nutrients availability. Therefore, in Caatinga, associations of spatial variations in microhabitats conditions and inter-annual variations could interfere in the offering period of floral resource, substrate nutrients availability and, possibly, in the behavior of substrate-using animals. / Apesar do reconhecimento de que a fauna seja importante na ciclagem de nutrientes, as suas relações com a decomposição da serrapilheira ainda são pouco conhecidas em ambientes semiáridos. O objetivo deste estudo foi investigar o efeito espacial e temporal das condições do habitat e dos microartrópodes do solo sobre a decomposição na Caatinga. No Cariri paraibano, entre novembro de 2009 e outubro de 2011, a taxa de decomposição foliar foi avaliada através de dois transectos com 30 bolsas de serrapilheira, com 10±0,5 g de folhas de Caesalpinia pyramidalis e Croton blanchetianus, em igual proporção, distribuídos em 12 áreas de amostragem. No transecto denominado controle, as bolsas foram preenchidas apenas com folhas, enquanto no segundo transecto, denominado fauna-reduzida, além das folhas, as bolsas de serrapilheira apresentavam cerca de 30 bolas de naftalina (~33,2 g), para avaliação do efeito da fauna sobre a decomposição. No primeiro ano, a taxa de decomposição foi menor independentemente do período de exposição, sendo decomposto cerca de 32%, 47% e 63% em 120, 240 e 360 dias, respectivamente. Enquanto, no segundo ano, a perda de massa foi de 45%, 54% e 73%, respectivamente. A taxa de decomposição correlacionou-se com a precipitação (acumulada) e a evapotranspiração (acumulada). Analisando os efeitos da fauna de microartrópodes e de cada área de amostragem sobre a taxa de decomposição, verificou-se que estes fatores tanto atuam isoladamente, quanto de forma conjunta sobre esse processo, entre os diferentes períodos de exposição (120, 240, 360 dias). A riqueza de espécies, densidade, altura da vegetação e o diâmetro do tronco à altura do solo (DTS), a serrapilheira produzida e o efeito da fauna, juntas, explicaram 91% da taxa de decomposição anual da serrapilheira, porém o DTS foi à única variável não significativa neste modelo. A precipitação e ETR tem efeito chave sobre a decomposição, pois além de atuarem sobre as perdas por lixiviação de compostos lábeis solúveis em água, estes fatores influenciam a vegetação, a produção de serrapilheira e a fauna decompositora e, portanto, desencadeiam estímulos sobre diferentes fatores, que atuam sobre o processo de decomposição. Este experimento mostrou que a decomposição de plantas pode ser influenciada por fatores bióticos em uma Floresta Tropical Seca, como a Caatinga, e que a decomposição não pode ser explicada apenas pelo clima e pela qualidade do substrato, visto que no sistema solo-serrapilheira, a vegetação e os organismos edáficos são fatores críticos na manutenção e disponibilidade de nutrientes.

Les prairies subalpines abritent de grandes populations d’herbivores sauvages et sont souvent soumises au pâturage domestique. Le but de cette thèse est d’analyser la réponse métabolique des plantes subalpines à l’herbivorie, et d’identifier les conséquences fonctionnelles sur l’écosystème via la décomposabilité des litières. Pour cela, nous avons établi un dispositif d’exclusion des herbivores sur l’alpage d’Armenaz dans le massif des Bauges, dans deux contextes de pâturage différents : extensif par des herbivores sauvages (chamois, Rupicapra rupicapra) et intensif par des herbivores domestiques (génisses, Bos taurus). Nous avons caractérisé une vingtaine d’espèces végétales par des traits fonctionnels foliaires reflétant leur métabolisme de croissance et de défense, en présence ou en absence d’herbivores, et avons estimé la décomposabilité des litières de certaines d’entre elles. Contrairement à l’hypothèse du compromis entre croissance et défense, nos résultats montrent que la présence de composés de défense (polyphénols et lignine) chez les plantes n’est pas reliée à leur stratégie d’acquisition des ressources. Dans notre étude, la réponse des plantes à l’exclusion des herbivores dépend essentiellement : (1) du contexte d’herbivorie, la réponse étant d’avantage marquée dans le contexte du pâturage intensif par les génisses qu’extensif par les chamois, (2) des espèces végétales, suggérant l’existence de différentes stratégies de défense, (3) des conditions environnementales, pouvant être le reflet d’effets d’interaction avec le traitement d’herbivorie. Parmi les réponses observées, l’exclusion des herbivores entraîne chez certaines espèces une diminution de la teneur en composés phénoliques, et plus particulièrement en flavonoïdes, pouvant refléter la relaxation de la synthèse de ces composés de résistance en absence d’herbivores. L’exclusion des chamois n’influence pas la composition chimique des litières ni leur décomposabilité. Cette dernière, parmi les composés étudiés, dépend majoritairement de sa composition en polyphénols. L’identification d’effets contrastés de différents contextes d’herbivorie sur la réponse des plantes et des fonctions écosystémiques qui en découlent nous permet d’améliorer notre compréhension du fonctionnement des prairies subalpines. Ce sont autant d’éléments pour nous aider à mieux appréhender les effets sur l’environnement d’éventuels changements démographiques des populations de grands herbivores. / Alpine grasslands are home to large populations of wild herbivores and are often exposed to additional grazing by domestic herbivores. This study aims to investigate the metabolic response of subalpine plant species to herbivory and to identify the ecosystem functional consequences via the alteration of litter decomposability. For this purpose, we set up a two-year experimental design using exclosures on the Armenaz subalpine grassland from the Bauges massif, under two mammalian herbivory regimes: intensive grazing by domestic heifers (Bos taurus) and extensive grazing by wild chamois (Rupicapra rupicapra). We measured leaf functional traits representative of growth and defense metabolisms on about twenty plant species grown in presence or absence of herbivores, and estimated litter decomposability of some of these species. Contrary to the hypothesis of a growth/defense tradeoff, our results show that the allocation of defensive compounds (polyphenols and lignin) in plants is not related to their nutrient acquisition strategy. In our study, plant responses to grazing exclusion vary according to: (1) herbivory context, plant response being more pronounced in the case of intensive grazing by heifers than extensive grazing by chamois, (2) plant species, suggesting that they rely on different defensive strategies, (3) environmental conditions, which may reflect the interactive effects with grazing treatment. One of the observed responses of plants to grazing exclusion is the decrease of their phenolic content, and more specifically flavonoids, which can be explained by the relaxation of the production of plant defenses when herbivores are no longer present. Chamois exclusion has no influence on chemical composition and decomposability of litters, the latter being best explained by its phenolic content. Revealing the contrasted effects of wild and domestic mammalian herbivores on vegetation and related soil processes allow us to improve our understanding of subalpine grasslands functioning. This should help us to better predict the effects of potential demographic variations of herbivore populations on environment.

La France compte de nombreux étangs (environ 251 000), construits le plus souvent par l’aménagement d’un barrage sur un cours d’eau de tête de bassin, dans des fonds de vallées argileux, pour la production de poissons. La Lorraine est une région riche en étangs et ces derniers sont le plus souvent localisés sur des cours d’eau temporaires dans des bassins versants agricoles et/ou forestiers. Ces cours d’eau ont un fonctionnement écologique basé sur l’intégration, par les réseaux trophiques détritiques, des ressources organiques allochtones. Or, les étangs constituent des zones lentiques biogènes : la matière organique (MO) autochtone (constituée entre autres par le plancton, les macrophytes, les fèces produits par le biote) peut modifier les équilibres – souvent fragiles – de ces écosystèmes aquatiques de tête de bassin. L’objectif de ce travail de thèse est d’étudier l’influence des étangs de barrage sur le recyclage et l’intégration de la MO allochtone et autochtone par les réseaux trophiques basaux aquatiques des cours d’eau de tête de bassin. Premièrement, ce travail a porté sur l’étude de la décomposition des litières (et des communautés associées) en amont et en aval d’étangs localisés sur des bassins soit agricoles, soit forestiers. Nos résultats mettent en exergue l’intérêt de la prise en compte de l’occupation du sol sur le bassin versant pour appréhender au mieux l’effet des étangs sur les processus de décomposition des litières. Nous montrons ainsi que l’étang de barrage entraîne une diminution de la vitesse de décomposition des litières, en lien notamment avec une diminution de la biomasse fongique, uniquement dans les cours d’eau en milieu agricole. Sur les cours d’eau forestiers, ce sont essentiellement les communautés de macroinvertébrés qui semblent influencées, et de manière plus marquée qu’en milieu agricole, avec une diminution des taxons les plus sensibles aux pollutions organiques. Puis, nous avons cherché à préciser les processus de décomposition des litières dans les cours d’eau temporaires de tête de bassin versant entravés ou non par un étang. Notre choix s’est porté sur les cours d’eau en milieu forestier afin de limiter les effets confondants liés à d’autres perturbations humaines. Dans ces conditions, nos résultats montrent que la présence d’un étang tend à augmenter la vitesse de décomposition des litières. Cela serait dû à un meilleur conditionnement des litières et également à une modification des communautés de déchiqueteurs en aval de l’étang. En revanche, l’effet de l’étang sur l’intégration des ressources allochtones par les réseaux trophiques détritiques nécessite la prise en compte des conditions hydrologiques se présentant à l’aval du barrage. Il s’agit là d’un résultat original révélant que l’impact de l’étang est plus marqué sur les communautés de déchiqueteurs et sur leur action de dégradation des litières lorsque le cours d’eau passe en régime permanent à l’aval de l’étang. Enfin, nous nous sommes intéressés à la modification des niches trophiques à partir de l’étude des signatures isotopiques des communautés de macro-invertébrés de cours d’eau entravés ou non par un étang. Nos résultats montrent que l’étang influence majoritairement les signatures isotopiques des biofilms et des matières en suspension. En lien avec cette observation, nous remarquons que les niches isotopiques des différentes guildes trophiques de macro-invertébrés sont modifiées à l’aval de l’étang. Ce résultat souligne ainsi que l’ensemble des guildes trophiques ici étudiées consomment et intègrent les ressources autochtones produites au sein même de l’étang. Pour résumer, ce travail a mis en évidence les interactions complexes entre étang et cours d’eau de tête de bassin. Il souligne de fait la nécessité de prendre en compte l’occupation du sol sur les bassins versant et le régime hydrologique du cours d’eau pour conclure sur l’effet de l’étang sur le fonctionnement écologique des cours d’eau de tête de bassin. / In France there are more than 250,000 ponds. Most often, they are dam reservoirs constructed on headwater streams in clay valleys for fish production and thus named fishponds. In Lorraine region, most of the numerous fishponds are located on temporary streams (i.e. periodically dry during summer time) in agricultural and/or forested catchments. These streams have an ecological functioning based on the integration of allochthonous organic matter (OM) resources by the basal detrital food webs. Yet, fishponds constitute biogenic lentic systems that favor autochthonous OM production (e.g. plankton, macrophytes, faeces). Consequently, fishponds could disrupt the fragile balances in these headwater stream ecosystems. The goal of my thesis was to study the effect of fishpond on the recycling and the integration of allochthonous and autochthonous OM by the aquatic food webs within headwater streams. First, we studied the litter decomposition (and the associated communities) between upstream and downstream fishponds located in agricultural or forested catchments. Our results indicate the needs to take into account the catchment land uses to grasp the fishpond effect on litter decomposition. We found that in agricultural catchments fishponds lead to a decrease of the litter breakdown rate in association with a fungal biomass decrease. In forested catchments, the macro-invertebrate assemblages are more affected than in agricultural catchments, showing a decrease of the most sensitive taxa to organic pollution. Secondly, we focused on litter processes in temporary headwater streams hampered or not by a fishpond. To this end, we worked on forest streams to exclude confounding anthropogenic effects. In this environment our results indicate that the presence of a fishpond tends to increase litter breakdown rate. It can be related with a better litter conditioning and to the shredder assemblage’s modification downstream from the fishpond. Furthermore, fishpond effect on the integration of allochthonous resources by food webs was found to be highly dependent on hydrological conditions downstream from the fishpond. This original result highlights that the impact of the fishpond seems to be greater on the shredder assemblages and on their litter breakdown activities when the stream show important hydrological modifications (i.e. become permanent downstream from the fishpond). Finally, in order to analyze the modification of trophic niches, we studied benthic macroinvertebrate isotopic signatures in streams hampered or not by a fishpond. Our results indicate that fishpond mainly influenced the isotopic signatures of biofilms and suspended OM. In line with this result, isotopic niches of the different macroinvertebrate trophic guilds are also modified downstream from the pond. Consequently we may suggest that all the studied trophic guilds consume and integrate autochthonous resources produced into the fishpond. In summary, our work highlights complex interactions between fishpond and headwater streams and underlines the needs to take into account the catchment land use and the stream hydrology before concluding on the fishpond effect on stream functioning.

O objetivo deste estudo foi verificar a associação do desenvolvimento de peso corporal da 1º inseminação até o 1º desmame com o desempenho reprodutivo, produção de leitões e taxa de descartes até o 3º parto, em 196 primíparas Landrace x Large White, usando modelos de regressão logística. O peso corporal (PC) foi medido na inseminação artificial (IA), 24h após o 1º parto e no dia do desmame. Na 1º IA, primeiro parto e desmame o PC foram em média 140.4 kg, 170.8 kg e 163.7 kg, respectivamente. O intervalo desmame-estro (IDE), o número de leitões nascidos totais no primeiro, segundo e após três partos, e a taxa de descarte até terceiro parto foram, em média 5.7 dias, 12.5, 11.8 e 36.7 leitões nascidos, e 10.2%, respectivamente. O aumento de 10 kg no ganho de peso na primeira prenhes (OR = 0.63), no peso ao 1º parto (OR = 0.63), peso ao 1º desmame (OR = 0.69) e ganho de peso entre a 1º IA e o 1º desmame (OR = 0,67) diminuiu a percentagem de primíparas com longo IDE. Os aumentos da duração da lactação e do número de leitões desmamados foram responsáveis pela, respectivamente, diminuição (OR = 0.79 por dia de lactação) e aumento (OR = 1.45 por leitão desmamado) do percentual de fêmeas com IDE longo. Primíparas com PC <159.5 kg a desmama apresentaram maior taxa de não-parto (TNP) em comparação com porcas com PC >170 kg (OR = 4.73). Porcas com <17.5 kg de ganho entre a 1º IA e o 1º desmame tiveram maior chance (OR = 4,88) de TNP do que fêmeas > 30 kg. Cada dia adicional de lactação diminuiu a TNP (OR = 0.77). As fêmeas com PC <139 kg na 1º IA apresentaram maior porcentagem de leitegadas pequenas no segundo parto (NT2P, OR = 2.00) e após três parições (OR = 3.28) em comparação com aquelas pesando ≥139 kg. Porcas com ganho de peso <25 kg durante a primeira prenhes apresentaram maior chance de NT2P (OR = 3.01), em comparação com porcas ganhando acima de 35 kg. A cada 10 kg de aumento no peso ao primeiro desmame e no ganho de peso entre a 1º IA e o 1º desmame (OR = 0.71 e 0.73, respectivamente) diminuiu a taxa de descarte total, e por razões reprodutivas (OR = 0.57 e 0.61, respectivamente). A taxa de descarte até o 3º parto aumentou em porcas com menores leitegadas a primeira parição. Os resultados mostram que atingir um peso mínimo à 1º IA é importante, mas também deve ser considerado o ganho de peso corporal adequado até o primeiro desmame para melhor desempenho reprodutivo, produtividade, e retenção de matrizes no rebanho. / The aim of this study was to verify the association of sow body weight development until 1st weaning with the reproductive performance, piglet production and culling rate until 3rd farrowing in 196 Landrace x Large White primiparous sows using logistic regression models. Body weight (BW) was measured at artificial insemination (AI), 24h after farrowing and on the weaning day. At 1st AI, 1st farrowing and 1st weaning the BW was on average 140.4 kg, 170.8 kg and 163.7 kg, respectively. The weaning-to-estrus interval (WEI), the number of piglets born at 1st, 2nd and over three parities, and culling rate until 3rd farrowing were on average 5.7 days, 12.5, 11.8 and 36.7 piglets born, and 10.2%, respectively. Each 10kg increase in weight gain in 1st pregnancy (OR= 0.63), weight at 1st farrowing (OR= 0.63), weight at 1st weaning (OR= 0.69) or weight gain from 1st AI to 1st weaning (OR= 0.67) decreased the percentage of primiparous sows with long WEI. Increasing lactation length and increasing the number of weaned piglets were responsible for respectively decreasing (OR=0.79 per day of lactation) and increasing (OR= 1.45 per piglet weaned) the percentage of sows with long WEI. Sows with <159.5 kg at weaning had higher non-farrowing rate (NFR) compared to sows with >170 kg (OR = 4.73). Sows with <17.5 kg of gain from 1st AI to 1st weaning had higher odds (OR= 4.88) of NFR than sows gaining >30 kg. Each additional lactation day decreased the NFR (OR = 0.77). Females weighing < 139 kg at 1st AI had higher percentages of small number of total born in second parity (STB2, OR= 2.00) and over three parities (OR = 3.28) compared to those weighing ≥139 kg. Sows with weight gain at 1st pregnancy <25 kg had higher odds of STB2 (OR= 3.01) compared to sows gaining >35 kg. Each 10 kg of increase in weight at 1st weaning or in weight gain from 1st AI to 1st weaning decreased the total culling rate (OR= 0.71 and 0.73, respectively) and culling by reproductive reasons (OR= 0.57 and 0.61, respectively). Culling rate until 3rd farrowing was also increased in sows with smaller first litter size. The results show that not only to reach a minimum weight at 1st AI but also to have an adequate body weight gain until 1st weaning is important for the reproductive performance, productivity and retention of sows in the herd.

La régénération naturelle du Pin pignon (Pinus pinea L.) est difficile à atteindre. Ce processus est soumis à de multiples contraintes abiotiques et biotiques et leurs interactions qui demeurent partiellement connues. Une meilleure connaissance de ces facteurs est nécessaire pour la mise au point de recommandations sylvicoles en vue de favoriser la régénération. Compte tenu de la littérature disponible, nous avons supposé que l’établissement des semis de Pin pignon est contrôlé principalement, par ordre d’importance, par : (i) la disponibilité de la lumière, (ii) la biomasse des aiguilles de la litière et enfin (iii) la concurrence avec la végétation du sous-bois. En outre, l’étude a été complétée par une caractérisation de la structure du peuplement en termes de croissance et de fructification. L’établissement des semis de Pinus pinea a été étudié in situ et sous des conditions contrôlées pour trois forêts au nord de la Tunisie (Mekna III, Ouchtata II et Bechateur). Les semis vivants ont été comptés sur 90 placettes de 500m² chacune distribuées sur les trois forêts, et mis en relation avec la lumière disponible, la biomasse de la végétation du sous-bois et la biomasse des aiguilles de litière. Une expérience complémentaire a été menée dans des pots en conditions contrôlées sous serre avec des graines des trois forêts. Trois régimes de lumière incidente ont été appliqués (3%,16% et 58%) combinés avec trois modalités de lit de germination : sol nu, sol couvert d’aiguilles de litière et sol arrosé d’extrait d’aiguilles. L’étude a montré que la limitation de la germination n’était pas directement due à la lumière, mais plutôt à la température et à l’humidité liées à leur tour à la disponibilité de la lumière. L’émergence des semis a été significativement entravée par les couches de litière imposant une barrière mécanique, tandis qu’aucun effet chimiotoxique n'a été détecté. La végétation du sous-bois ne semble pas avoir joué un rôle important dans les premiers stades d’établissement des semis de Pinus pinea sous ces conditions climatiques méditerranéennes. Les besoins en lumière des jeunes plantules augmentent au fur et à mesure de leur développement et par conséquent le type d’interaction avec la végétation du sous-bois passe de la neutralité à la compétition. Nos résultats peuvent servir comme base initiale pour affiner la sylviculture afin d’améliorer l’établissement des pins. Le plan de gestion doit inclure une scarification afin de réduire l’épaisseur des couches de litière et des éclaircies intensives pour augmenter la disponibilité de la lumière. / Natural regeneration of Pinus pinea stands in Tunisia is difficult to achieve. This process is threatened by multiple abiotic and biotic stresses and their interactions which are still not well known, whereas, the knowledge of these factors is essential for sylvicultural recommendations. Given the available literature, we hypothesized that stone pine seedling establishment is mainly controlled in order of importance by (i) light availability, (ii) amount of needle litter, and (iii) competition with understory vegetation. Furthermore, the study was completed by a characterization of stand structure in terms of growth and fructification. The seedling establishment behaviour of Pinus pinea was studied under field and controlled conditions for three forests of north Tunisia (Mekna III, Ouchtata II and Bechateur). Live seedling were counted in 90 plots (500m² each) distributed in these forests, and related to light availability, biomass of understory vegetation, and biomass of needle litter collected in eight square subplots (0.5m × 0.5m). An additional experiment was conducted under controlled conditions in pots in greenhouse with seeds of the three forests. Three light regimes were applied (3%, 16%, and 58%) of incident light, combined with three seedbed modalities: bare soil, soil covered with needle litter and soil watered with needle extract. The study showed that germination limitation was not directly related to light, but rather to temperature and humidity linked to the light regime. Seedling emergence was significantly suppressed by litter layer which imposed a mechanical barrier, whereas no chemotoxic effect was detected. The understory vegetation did not appear to play a significant role in Pinus pinea early seedling establishment in these Mediterranean climate conditions. During the subsequent development of seedlings, their light requirement increased and their interactions with understory woody vegetation moved from neutral relationship towards a competitive relationship. We use our results to propose an initial silvicultural approach to favour pine establishment. A management plan should first include scarification to reduce litter thickness and then heavy thinning to significantly increase light availability.