Does shade improve light interception efficiency? A comparison among seedlings from shade-tolerant and -intolerant temperate deciduous tree species

• Here, we tested two hypotheses: shading increases light interception efficiency (LIE) of broadleaved tree seedlings, and shade-tolerant species exhibit larger LIEs than do shade-intolerant ones. The impact of seedling size was taken into account to detect potential size-independent effects on LIE. LIE was defined as the ratio of mean light intercepted by leaves to light intercepted by a horizontal surface of equal area. • Seedlings from five species differing in shade tolerance (Acer saccharum, Betula alleghaniensis, A. pseudoplatanus, B. pendula, Fagus sylvatica) were grown under neutral shading nets providing 36, 16 and 4% of external irradiance. Seedlings (1- and 2-year-old) were three-dimensionally digitized, allowing calculation of LIE. • Shading induced dramatic reduction in total leaf area, which was lowest in shade-tolerant species in all irradiance regimes. Irradiance reduced LIE through increasing leaf overlap with increasing leaf area. There was very little evidence of significant size-independent plasticity of LIE. • No relationship was found between the known shade tolerance of species and LIE at equivalent size and irradiance

Sapling size influences shade tolerance ranking among southern boreal tree species

1 Traditional rankings of shade tolerance of trees make little reference to individual size. However, greater respiratory loads with increasing sapling size imply that larger individuals will be less able to tolerate shade than smaller individuals of the same species and that there may be shifts among species in shade tolerance with size. 2 We tested this hypothesis using maximum likelihood estimation to develop individual-tree-based models of the probability of mortality as a function of recent growth rate for seven species: trembling aspen, paper birch, yellow birch, mountain maple, white spruce, balsam fir and eastern white cedar. 3 Shade tolerance of small individuals, as quantified by risk of mortality at low growth, was mostly consistent with traditional shade tolerance rankings such that cedar > balsam fir > white spruce > yellow birch > mountain maple = paper birch > aspen. 4 Differences in growth-dependent mortality were greatest between species in the smallest size classes. With increasing size, a reduced tolerance to shade was observed for all species except trembling aspen and thus species tended to converge in shade tolerance with size. At a given level of radial growth larger trees, apart from aspen, had a higher probability of mortality than smaller trees. 5 Successional processes associated with shade tolerance may thus be most important in the seedling stage and decrease with ontogeny

French ichthyological records for 2018

International audienceUncommon records of fishes may evidence local or global changes in fish composition resulting from environmental change or anthropogenic activities. Significant records of uncommon marine fishes, including migrant, non-native, cryptic, rare and threatened species, collected in French waters or by French vessels in European waters, observed by scuba divers or beachgoers, are reported for the year 2018. They include first, new, rare and unusual records for the following 52 species: Hexanchus griseus, Squatina squatina, Gymnura altavela, Acipenser sturio, A. gueldenstaedtii, Dalophis imberbis, Nemichthys curvirostris, Eurypharynx pelecanoides, Maulisia mauli, M. microlepis, Sagamichthys schnakenbecki, Melanostomias bartonbeani, Astronesthes niger*, Leptostomias gladiator*, Chlorophthalmus agassizi, Magnisudis atlantica, Evermannella balbo, Regalecus glesne, Luvarus imperialis, Raniceps raninus, Fistularia cf. petimba*, Trigla lyra, Lepidotrigla dieuzeidei, Micrenophrys lilljeborgii, Howella atlantica*, Pomatomus saltatrix, Serranus cabrilla, Caranx crysos, Seriola rivoliana, Trachinotus ovatus, Lobotes surinamensis, Sarpa salpa, Chelon ramada, Pseudoscopelus altipinnis*, Trachinus draco, Parablennius pilicornis, P. ruber, Buenia affinis, B. jeffreysii, Chromogobius zebratus, Didogobius splechtnai, Gammogobius steinitzi, Gobius couchi, G. kolombatovici, Lebetus sp., Speleogobius trigloides, Thorogobius macrolepis, Vanneaugobius dollfusi, Siganus rivulatus*, Lepidocybium flavobrunneum, Hyperoglyphe sp. et Pegusa cf. nasuta, among which six, marked with an asterisk (*), represent additions to the Checklist of the marine fishes from metropolitan France and one, N. curvirostris, is a first record for the Mediterranean