Thesis (M.Surg.) -- University of Adelaide, Dept. of Surgery, 1961. / [Typewritten].

In the study effect of fertilization and abandonment on growth and carbohydrate storage dynamic of Molinia caerulea were studied. During the year 2006 plants were harvested six times to cover whole vegetation season. Carbohydrate content was determinate in both basal internodes and roots. Growth parameters were compared with carbohydrate reserves.

Aromatic plants contain both volatile and non-volatile fractions and the chemical composition of these two fractions may be influenced by seasonal changes. The essential oil and solvent extracts of S. africana-caerulea, S. africana-lutea and S. lanceolata, collected at the same locality throughout the 2005 growing season, were compared in terms of essential oil composition, yields and biological activities. Mostly quantitative, rather than qualitative variationwas observed in the oil composition of each species.Major fluctuations in the composition of S. africana-caerulea oil included limonene (2–33%) and viridiflorol (2–24%). Levels of α-pinene (1–12%), myrcene (2–12%) and α-eusdesmol (trace-13%) fluctuated seasonally in the S. africana-lutea oil. In S. lanceolata, considerable changeswere noted for β-caryophyllene (1–19%), β-caryophyllene oxide (1–21%) and ledol (3–12%). The extract prepared from S. lanceolata harvested inwinterwas more active against Gram-positive bacteria. The S. africana-caerulea extract exhibited the most favourable antiplasmodial activity when harvested in winter (IC50 value: 12 μgml−1), which contrasts with the lowest anti-plasmodial activity of S. lanceolata obtained at the same period (IC50 value: 43 μgml−1). The anti-oxidant activity of the solvent extracts also displayed variation over seasons with thewinter collection of S. africana-lutea yielding the most favourable anti-oxidant activity (IC50 value: 10 μg ml−1). All the solvent extracts prepared from the winter collection exhibited the lowest toxicity (20bIC50 valuesb60 μg ml−1), while the three essential oils obtained from autumn collection were more toxic (0.03bIC50 valuesb0.4 μg ml−1).

The aim of the thesis was to conduct a literature search on cultivation and especially pollination of honeysuckle, by attempting to compare the effect of free pollination with manual self-pollination and manual cross-pollination on fruit yield and study pollinators of Lonicera cearulea L. Therefore, in 2018, pollination and bee diversity were assessed from April to May by 'Sinnaja ptica', 'Gerda' and 'Viola' varieties. The results confirmed honeysuckle insect infestation. Self-pollination and non-pollination did not reach harvest parameters as in the case of free pollination. However, there is an unspecified influence of pollinators on the efficacy of blue honeysuckle pollination since manual foreign pollination has failed to maximize yield. Blooming haskaps prefer long-tongued bees, especially bumblebees and honeybees.

Mourella caerulea, popularmente conhecida como mirim-de-chão ou bieira, e Plebeia nigriceps, comumente chamada mirim nigriceps, são meliponíneos ocorrentes no sul do Brasil, polinizadores de plantas nativas e cultivadas. M. caerulea está principalmente relacionada ao bioma Pampa e seu hábito de nidificação é subterrâneo. P. nigriceps nidifica em frestas de rochas e muros, sendo encontrada tanto no Pampa como em Mata Atlântica. O presente trabalho teve como objetivo avaliar a variabilidade populacional destas duas espécies, através de três metodologias: a morfometria geométrica de asa, perfil de hidrocarbonetos cuticulares e sequenciamento de fragmentos de genes mitocondriais. Foram coletadas operárias de 24 colônias de M. caerulea em cinco localidades de sua distribuição natural e 53 colônias de P. nigriceps em oito localidades no estado do Rio Grande do Sul. Para análise do padrão de venação da asa, foram marcados 13 marcos anatômicos na asa anterior direita de cinco a 20 operárias por colônia. A análise genética foi realizada avaliando um fragmento do gene Citocromo Oxidase I em M. caerulea, e Citocromo B em P. nigriceps. A análise morfométrica demonstrou estruturação dos grupos com separação estatisticamente significativa (<0,0001) entre as localidades de M. caerulea. As distâncias morfométricas estão correlacionadas com a distância geográfica, e coerentes com regiões fisiográficas do bioma Pampa. A análise dos perfis de hidrocarbonetos distinguiu colônias de diferentes localidades, mas suas distâncias não apresentaram correlação com as distâncias geográficas. Foram encontrados seis haplótipos, todos exclusivos, com diversidade nucleotídica de 0,01631e uma diversidade haplotípica (Hd) de 0,74. Para P. nigriceps, as análises morfométricas apresentaram diferenças significativas entre localidades e correlação com as distâncias geográficas e biomas. A análise dos perfis de hidrocarbonetos distinguiu colônias de diferentes localidades, mas suas distâncias não apresentaram correlação com as distâncias geográficas. Foram encontrados 17 haplótipos, todos exclusivos, com diversidade nucleotídica de 0,0147 e diversidade haplotípica (Hd) de 0,94. A presença de diversos haplótipos exclusivos, perfis morfométricos e de hidrocarbonetos cuticulares em populações pertencentes a diferentes biomas indicam a necessidade de uma atenção especial para estas populações no momento da definição de estratégias de conservação das espécies. Uma especial atenção às abelhas da espécie Mourella caerulea, que além de ser uma espécie representante única de um gênero monoespecífico, apresenta grandes distâncias populacionais entre os indivíduos de todas as localidades amostradas. / Mourella caerulea and Plebeia nigriceps are two stingless bees with occurrence in the South region of Brazil. The first is commonly known as mirim-de-chão or bieira and the second is known as mirim nigriceps. Both species are important pollinators of native flora and crops. M. caerulea is related to Pampa biome and place nests on the ground. P. nigriceps occurs in both Pampa biome and Atlantic Rain Forest. This thesis had the objective of to evaluate the population variability of these species through three techniques: geometric morphometrics of wing, cuticular hydrocarbons (CHC) profiles and sequencing of fragments from mitochondrial DNA genes. We collected workers from 24 colonies for M. caerulea from five localities, and 53 colonies of P. nigriceps from eight localities in Rio Grande do Sul State. For the geometric morphometrics analysis, we used 13 landmarks plotted in the right forewing of five to 20 workers per nest. The fragments of mtDNA genes used for the molecular approach were from Cytochrome Oxidase I for M. caerulea and Cytochrome B for P. nigriceps. The morphometric approach discriminated the populations of M. caerulea from different localities (<0,0001). The morphometric distances are correlated to geographic distances and go along with the physiographic regions of Pampa biome. CHC profiles differentiated the colonies of M. caerulea from different localities, but chemical distances are not in agreement with geographic distances. We found six haplotypes (all exclusives) with a nucleotide diversity of 0.01631 and a haplotype diversity (Hd) of 0.74. For P. nigriceps, morphometric analysis was significant separating localities and in accordance with the geographic distances and biomes. CHC distinguished the colonies, but there was no significant correlation between this result and the geographic distances or biomes. mtDNA revealed 17 haplotypes (all exclusives) with a nucleotide diversity of 0.0147 and a haplotype diversity (Hd) of 0.94. The discovery of different exclusives haplotypes, the morphometric and CHC profiles when comparing population belonging to different biomes indicate that we need to give a particular attention for these species at the moment of create conservation strategies for both biomes from Rio Grande do Sul. M. caerulea deserves a special concern once it is the only species of the monospecific genera, and its populations are distant between themselves.

Mourella caerulea, popularmente conhecida como mirim-de-chão ou bieira, e Plebeia nigriceps, comumente chamada mirim nigriceps, são meliponíneos ocorrentes no sul do Brasil, polinizadores de plantas nativas e cultivadas. M. caerulea está principalmente relacionada ao bioma Pampa e seu hábito de nidificação é subterrâneo. P. nigriceps nidifica em frestas de rochas e muros, sendo encontrada tanto no Pampa como em Mata Atlântica. O presente trabalho teve como objetivo avaliar a variabilidade populacional destas duas espécies, através de três metodologias: a morfometria geométrica de asa, perfil de hidrocarbonetos cuticulares e sequenciamento de fragmentos de genes mitocondriais. Foram coletadas operárias de 24 colônias de M. caerulea em cinco localidades de sua distribuição natural e 53 colônias de P. nigriceps em oito localidades no estado do Rio Grande do Sul. Para análise do padrão de venação da asa, foram marcados 13 marcos anatômicos na asa anterior direita de cinco a 20 operárias por colônia. A análise genética foi realizada avaliando um fragmento do gene Citocromo Oxidase I em M. caerulea, e Citocromo B em P. nigriceps. A análise morfométrica demonstrou estruturação dos grupos com separação estatisticamente significativa (<0,0001) entre as localidades de M. caerulea. As distâncias morfométricas estão correlacionadas com a distância geográfica, e coerentes com regiões fisiográficas do bioma Pampa. A análise dos perfis de hidrocarbonetos distinguiu colônias de diferentes localidades, mas suas distâncias não apresentaram correlação com as distâncias geográficas. Foram encontrados seis haplótipos, todos exclusivos, com diversidade nucleotídica de 0,01631e uma diversidade haplotípica (Hd) de 0,74. Para P. nigriceps, as análises morfométricas apresentaram diferenças significativas entre localidades e correlação com as distâncias geográficas e biomas. A análise dos perfis de hidrocarbonetos distinguiu colônias de diferentes localidades, mas suas distâncias não apresentaram correlação com as distâncias geográficas. Foram encontrados 17 haplótipos, todos exclusivos, com diversidade nucleotídica de 0,0147 e diversidade haplotípica (Hd) de 0,94. A presença de diversos haplótipos exclusivos, perfis morfométricos e de hidrocarbonetos cuticulares em populações pertencentes a diferentes biomas indicam a necessidade de uma atenção especial para estas populações no momento da definição de estratégias de conservação das espécies. Uma especial atenção às abelhas da espécie Mourella caerulea, que além de ser uma espécie representante única de um gênero monoespecífico, apresenta grandes distâncias populacionais entre os indivíduos de todas as localidades amostradas. / Mourella caerulea and Plebeia nigriceps are two stingless bees with occurrence in the South region of Brazil. The first is commonly known as mirim-de-chão or bieira and the second is known as mirim nigriceps. Both species are important pollinators of native flora and crops. M. caerulea is related to Pampa biome and place nests on the ground. P. nigriceps occurs in both Pampa biome and Atlantic Rain Forest. This thesis had the objective of to evaluate the population variability of these species through three techniques: geometric morphometrics of wing, cuticular hydrocarbons (CHC) profiles and sequencing of fragments from mitochondrial DNA genes. We collected workers from 24 colonies for M. caerulea from five localities, and 53 colonies of P. nigriceps from eight localities in Rio Grande do Sul State. For the geometric morphometrics analysis, we used 13 landmarks plotted in the right forewing of five to 20 workers per nest. The fragments of mtDNA genes used for the molecular approach were from Cytochrome Oxidase I for M. caerulea and Cytochrome B for P. nigriceps. The morphometric approach discriminated the populations of M. caerulea from different localities (<0,0001). The morphometric distances are correlated to geographic distances and go along with the physiographic regions of Pampa biome. CHC profiles differentiated the colonies of M. caerulea from different localities, but chemical distances are not in agreement with geographic distances. We found six haplotypes (all exclusives) with a nucleotide diversity of 0.01631 and a haplotype diversity (Hd) of 0.74. For P. nigriceps, morphometric analysis was significant separating localities and in accordance with the geographic distances and biomes. CHC distinguished the colonies, but there was no significant correlation between this result and the geographic distances or biomes. mtDNA revealed 17 haplotypes (all exclusives) with a nucleotide diversity of 0.0147 and a haplotype diversity (Hd) of 0.94. The discovery of different exclusives haplotypes, the morphometric and CHC profiles when comparing population belonging to different biomes indicate that we need to give a particular attention for these species at the moment of create conservation strategies for both biomes from Rio Grande do Sul. M. caerulea deserves a special concern once it is the only species of the monospecific genera, and its populations are distant between themselves.

Over the last millennium peatlands have accumulated significant carbon stores. Drainage for agricultural use has been widespread and has altered the functioning of these mires: shifting them towards carbon release. Recently, in recognition of the range of ecosystem services derived from these landscapes peatland restoration projects have been initiated. Carbon storage is often cited amongst the aims of these projects, especially since the inclusion of rewetting wetlands in the Kyoto Protocol. However, little is known about the effects of ditch blocking on CO2 fluxes, particularly in Molinia caerulea dominated peatlands, a species common on degraded peatlands which tolerates a range of water table depths. This thesis aims firstly to quantify CO2 fluxes from a drained Molinia caerulea dominated blanket bog and to improve understanding of the temporal and spatial controls on these fluxes and secondly, to quantify the immediate effects of ditch blocking. Closed chamber measurements of net ecosystem exchange and partitioned below-ground respiration from control-restored paired sites were collected over the growing seasons immediately pre- (2012) and post-restoration (2013/2014). These flux data were coupled with remotely sensed data quantifying vegetation phenology and structure with a fine resolution (daily/cm) over large extents (annual/catchment). Although temporal variation in water table depth was not related to CO2 fluxes, the seasonal average related to vegetation composition suggesting raising water tables may promote a change in vegetation composition within these species-poor ecosystems. The distribution of water table depths, vegetation composition and CO2 fluxes did not vary with proximity to drainage ditches despite their prominence. An empirical model suggests in a drained state these peatlands are CO2 sources, indicating carbon previously accumulated is gradually being lost. Data suggest restoration does not always significantly affect water tables and consequently CO2 fluxes in the short-term. Where shallower water tables were maintained during dry conditions photosynthesis decreased and heterotrophic respiration increased: enhancing carbon release. Research undertaken during atypical weather has been unable to determine if restoration will be able to raise water tables sufficiently to protect the existing peat store and promote the vegetation change required to reinstate CO2 sequestration in the longer-term.

Στόχος της παρούσας εργασίας αποτελεί η διερεύνηση της προσυζευκτικής συμπεριφορικής απομόνωσης στο ερμαφρόδιτο χερσαίο σαλιγκάρι Albinaria caerulea (Pulmonata, Clausiliidae), η πολυπλοκότητα της οποίας, μπορεί να αντανακλά δράση εξελικτικών μηχανισμών επιλογής συντρόφου και κατ' επέκταση ειδογενετικών διεργασιών. Η ποικιλότητα κελυφικής ποίκιλσης είναι έντονη στο είδος αυτό (δύο μορφές, λεία και γραμμωτή, που συνιστούν δυο υποείδη), αλλά δε φαίνεται να συσχετίζεται με αντίστοιχη οικολογική και γενετική διαφοροποίηση. Η συλλογή των ατόμων πραγματοποιήθηκε στη Φολέγανδρο, όπου παρατηρούνται αλλοπάτριοι πληθυσμοί αλλά και ζώνες επαφής μεταξύ των λείων και των γραμμωτών μορφών. Στο εργαστήριο πραγματοποιήθηκαν πειράματα αναπαραγωγικής συμπεριφοράς, όπου καταγράφονταν ο αριθμός κι ο τύπος (ετεροτυπικά-ομοτυπικά) των σχηματιζόμενων ζευγών, καθώς και οι αντίστοιχες ερωτοτροπικές προσπάθειες (φλερτ). Βάσει των συχνοτήτων των σχηματιζόμενων ζευγών υπολογίστηκε ο βαθμός προσυζευκτικής συμπεριφορικής απομόνωσης με τον αμερόληπτο δείκτη ΙPSI. Καταγράφηκαν επίσης και άλλες συμπεριφορικές παράμετροι (αριθμός και τύπος φλερτ, χρόνος ως το πρώτο ενεργητικό φλερτ, χρόνος από την αφύπνιση ως την έναρξη της σύζευξης, διάρκεια σύζευξης), με σκοπό την ανίχνευση λοιπών προσυζευκτικών συμπεριφορικών διαφορών μεταξύ των δυο μορφών. Τέλος, ελέγχθηκε αν τυχόν μορφομετρικές διαφορές (σχήμα/μέγεθος κελύφους) μεταξύ των δύο μορφών, χρησιμοποιούνται στις στρατηγικές επιλογής συντρόφου. Ο βαθμός προσυζευκτικής συμπεριφορικής απομόνωσης βρέθηκε μικρός, καθώς τα άτομα, ως επί το πλείστον, επέλεγαν ετεροτυπικό σύντροφο. Επίσης βρέθηκε μεγαλύτερη προσυζευκτική και συζευκτική δραστηριότητα στις ζώνες επαφής, κάτι που απορρίπτει την υπόθεση περί μηχανισμού ενίσχυσης, .καθώς εάν υπήρχε απομόνωση θα ανιχνεύονταν πρώτα σε αυτές. Όσον αφορά τις μορφομετρικές διαφορές, παρά το ότι τα άτομα διακρίνονται βάσει σχήματος και μεγέθους κελύφους, δεν φαίνεται να χρησιμοποιούν τις διαφορές αυτές στους μηχανισμούς επιλογής συντρόφου. Εντούτοις, οι διαφορές στο μέγεθος κελύφους των δυο μορφών εξομαλύνονται στις ζώνες επαφής, και επομένως δεν υπάρχει απόκλιση χαρακτήρα. Έτσι λοιπόν, ενώ δεν φαίνεται να υπάρχουν ισχυρά προσυζευκτικά φράγματα στο είδος αυτό, περισσότερο φως στις αντίστοιχες εξελικτικές διεργασίες, θα ρίξει η μελέτη μετασυζευκτικών μηχανισμών απομόνωσης, αλλά και παραμέτρων της οικολογίας και της πληθυσμιακής γενετικής τους. / The aim of this study was the investigation of premating behavioural isolation in the hermaphrodite land snail Albinaria caerulea (Pulmonata, Clausiliidae). The snails of this genus exhibit a really complicated premating behaviour, a fact that may reflect evolutionary mechanisms of mate choice, or even speciation forces acting. Shell differentiation is intense, with two patterns (smooth and ribbed) constituting two subspecies, which don’t seem to differ ecologically or genetically. The animals were collected from the island of Folegandros, where they can form contact zones –between animals with smooth and ribbed shell- or the two forms can be isolated. Mate choice experiments were conducted, with variable number of possible mates and the premating behaviour was reported (mating attempts, successful copulations, copulation duration, mating activity), between populations exhibiting the same or different ribbing pattern. To reveal other behavioural differences between the two morphs, we also reported the number and type of courtships, the time from the awakening till the beginning of copulation, the time untill the first active courtship and the duration of copulation. Finally, we examined if possible morphometric differences (shell shape and size) between the two morphs, can be used in the mate choice strategies. The unbiased isolation index IPSI, which based on mate frequencies, suggested that there aren’t strong premating barriers. The intense observed activity (copulations and courtships) in the contact zones agrees with the above results and consequently does not support the initial hypothesis of reinforcement of behavioural barriers in these sites. As far as it concerns the morphometric differences, despite the fact that the morphs are being distinguished, they don’t seem to use them as criterion in the mate choice. Nevertheless, such differences in size, seem to be eliminated in the contact zones, suggesting that there is no character displacement. In conclusion, further investigation of the reproduction of the genus in the basis of postmating isolation mechanisms, the ecology and population genetics of the genus, will reveal the possible action of evolutionary forces.

La régénération forestière, naturelle ou non, est sujette à de nombreux échecs du fait d’une compétition importante entre les espèces de sous-bois et les jeunes plants d’arbre. L’objectif de ce travail de thèse a été de comprendre les réponses du chêne sessile (Quercus petraea) et d’une poacée, tous deux en compétition dans un contexte de modification de la disponibilité des ressources. Deux espèces de poacées ont été étudiées, la molinie bleue (Molinia caerulea) et la canche cespiteuse (Deschampsia cespitosa). L’accent a été mis sur le rôle des interactions entre différentes ressources (lumière, eau et azote inorganique) sur l’évolution de la compétition (intensité/importance) entre ces espèces et les mécanismes écophysiologiques sous-jacents. Grâce à des expérimentations en conditions semi-contrôlées et à une installation in situ, nous avons pu mettre en évidence une compétition très précoce, dès les premiers mois d’interaction entre le chêne et les poacées voisines. L’abondance de lumière conduit à une compétition plus forte des poacées sur le chêne, amplifiée par l’apport d’azote. Par ailleurs, la nature et l’ampleur de ces interactions varient selon le niveau de stress abiotique appliqué et selon les organes considérés. Nos résultats montrent aussi que le chêne réagit principalement en accumulant les ressources dans son système racinaire, ressources qui sont mobilisées l’année suivante et qui peuvent avoir un arrière effet positif sur le fonctionnement du chêne en absence de stress hydrique. Enfin de la facilitation a également été observée du chêne envers la canche cespiteuse suite à un apport d’azote. Ce dernier améliore la croissance du chêne en compétition, qui pourrait augmenter sa production d’exsudats et son turn-over racinaire au bénéfice de la canche qui valoriserait cette nouvelle source d’azote. Ce travail renforce l’idée d’intégrer l’effet des interactions des différents facteurs abiotiques dans les modèles de compétitions et dans les pratiques de régénération afin d’optimiser la coexistence des espèces forestières, et ce dès la mise en concurrence des jeunes arbres avec les poacées du sous-bois. / Temperate forest ecosystems are prone to regeneration failures because of strong competition between understorey species and tree seedlings. This thesis aimed to improve our understanding of sessile oak seedlings (Quercus petraea) and poacea responses, both in competition among different levels of resource availabilities. Two poacea species were studied, Molinia caerulea and Deschampisa cespitosa. We focused on the role of the different resource combinations (light, water and inorganic nitrogen) on interaction variation (intensity and importance) between those species and underlying ecophysiological mechanisms. Our greenhouse and field experiments allowed us to infer a very early competition, from the first months of interaction between oak seedlings and poacea neighbours. High light level leads to stronger competition from poacea on oak seedlings, increased by nitrogen supply. Secondly nature and extent of these interactions depend on applied abiotic stress level and on considered organs. Thirdly Oak seedlings mainly respond by accumulating resources in coarse roots. These resources are remobilized next year and may have a positive carry-over effect on oak functioning if there is no water stress. Eventually we observed facilitation as well, from oak on D. cespitosa in fertilized environment. Nitrogen supply would foster oak seedling growth, increasing exudate production and root turn-over, to the benefit of D . cespitosa. The poacea would take up this extra nitrogen source for its own development. This study support the idea of including interaction effects of different abiotic factors in competition models. Silvicultural practices would also be enhanced by optimizing species coexistence in temperate forests as soon as tree seedlings and understorey species start to grow together.

Avec l'augmentation des sécheresses dans les forêts tempérées, la gestion sylvicole envisage de réduire la densité des peuplements adultes pour limiter le déficit hydrique. Cependant, la réduction de la canopée arborée augmente le rayonnement dans le sous-bois et permet le développement de la strate herbacée monopoliste. Nos objectifs étaient de caractériser l'évapotranspiration (ETu) de 4 herbacées monopolistes (Molinia caerulea, Calluna vulgaris, Pteridium aquilinum and Rubus sp.) et de quantifier leur impact sur la teneur en eau du sol (SWC) dans des peuplements de Quercus petraea. L’ETu des quatre herbacées cultivées en pot a été quantifiée en conditions semi-contrôlées caractérisées par deux niveaux d’éclairement relatif et 3 niveaux de SWC. In situ, le SWC, le microclimat et l’ETu de P. aquilinum et M. caerulea ont été mesurés sur 20 dispositifs dans les peuplements forestiers de Q. petraea présentant un gradient croissant de LAI. Chaque dispositif était subdivisé en 2 placettes, l’une était désherbée et l'autre enherbée. M. caerulea et C. vulgaris ont une faible régulation de leur ETu alors que P. aquilinum et Rubus sp. ont une stratégie conservatrice face au stress hydrique. SWC diminue plus rapidement quand le LAI de la strate herbacée augmente, ce qui est directement lié à l’ouverture du couvert arboré avec une valeur seuil de LAI de la strate arborée à 2-3, sous laquelle la contribution de la strate herbacée à l’évapotranspiration du peuplement pourrait compenser la diminution de celle de la strate arborée.Ces résultats montrent la nécessité de considérer la végétation du sous-bois dans la gestion sylvicole notamment lorsque la ressource hydrique est limitante. Ainsi, la réduction de la densité de la strate arborée doit être un compromis entre la réduction de la surface foliaire des arbres pour réduire l’ET, et le maintien d’une densité suffisante de la strate arborée pour limiter la croissance et l'ETu de la végétation du sous-bois. / In the context of ongoing increase of drought in temperate forests, forest managers consider the reduction of stand density to limit soil water depletion. The reduction of tree canopy density increases light below canopy and allows the development of monopolistic understorey vegetation. Our objectives were to characterize the evapotranspiration (ETu) of common understorey plants (Molinia caerulea, Calluna vulgaris, Pteridium aquilinum and Rubus sp.) and to quantify their impacts on soil water content (SWC) in mature oak stands (Quercus petraea).A first experiment was set up in a greenhouse where the 4 understorey species were potted and subjected to 2 levels of light transmittance and 3 levels of SWC. Microclimate and ETu were monitored. A second experiment was carried out on 20 plots (10 with M. caerulea and 10 with P. aquilinum) in oak stands with contrasted LAI. On each plot, two circular areas were set up, one weeded and the other untouched. SWC, microclimate and ETu were monitored.M. caerulea and C. vulgaris are more water spenders, whereas P. aquilinum and Rubus sp. are more water savers under water stress. Soil water depletion was faster with increasing understorey vegetation LAI, which was directly linked to tree canopy opening with a threshold of tree LAI of 2-3 below which the understorey contribution could offset the reduction of tree ET. The experimentations showed that the relative contribution of understory vegetation in the ecosystem water balance is significant, and depends on SWC and on the understorey species identity. These results show the necessity to consider understorey vegetation in forest management when water availability is an issue. Lower tree canopy density could increase the understorey ETu and soil water stress for trees. From a management perspective, thinning should be designed as a compromise between the reduction of tree leaf area to reduce ET, and maintaining sufficient tree canopy to restrict the growth and ETu of understorey vegetation.