This paper reviews aspects of the functional ecology of naturally established tree seedlings in the boreal forests of North America with an emphasis on the relationship between light availability and the growth and survival of shade tolerant conifers up to pole size. Shade tolerant conifer species such as firs and spruces tend to have a lower specific leaf mass, photosynthetic rate at saturation, live crown ratio, STAR (shoot silhouette area to total needle surface area ratio), and root to shoot ratio than the shade intolerant pines. The inability of intolerant species such as the pines and aspen to survive in shade appears to be mainly the result of characteristics at the shoot, crown, and whole-tree levels and not at the leaf level. Although firs and spruces frequently coexist in shaded understories, they do not have identical growth patterns and crown architectures. We propose a simple framework based on the maximum height that different tree species can sustain in shade, which may help managers determine the timing of partial or complete harvests. Consideration of these functional aspects of regeneration is important to the understanding of boreal forest dynamics and can be useful to forest managers seeking to develop or assess novel silvicultural systems.Résumé : Cet article passe en revue les aspects de l'écologie fonctionnelle des semis établis naturellement dans les forêts boréales de l'Amérique du Nord, avec une emphase sur la relation entre la disponibilité de la lumière et la survie et la croissance de conifères tolérants à l'ombre jusqu'au stade perchis. Les conifères tolérants à l'ombre comme les sapins et les épinettes tendent à avoir une masse foliaire spécifique, un taux de photosynthèse au point de saturation, des rapports de cime vivante, des indices STAR (rapport de la surface de la silhouette de la pousse par rapport à la surface foliaire totale) et des rapports racines/pousse inférieurs en comparaison avec les pins intolérants à l'ombre. L'incapacité à survivre à l'ombre des espèces intolérantes comme les pins et le peuplier faux-tremble semble résulter principalement des caractéristiques au niveau de la pousse, de la cime et de l'arbre entier et non pas au niveau foliaire. Même si les sapins et les épinettes coexistent fréquemment dans des sous-bois ombragés, leurs patrons de croissance et leurs architectures de cime diffèrent. Les auteurs proposent un cadre conceptuel basé sur la hauteur maximale que les différentes espèces peuvent atteindre à l'ombre et qui pourrait aider les aménagistes à décider du moment où procéder à une récolte partielle ou totale. La prise en compte de ces aspects fonctionnels de la régénération est importante pour la compréhension de la dynamique des forêts boréales et peut être utile aux aménagistes forestiers cherchant à développer ou évaluer des systèmes sylvicoles innovateurs.[Traduit par la Rédaction] Review / Synthèse 823

The synthesis and structural characterization of three-coordinate iron(II) and cobalt(II) complexes supported by new N-phosphinoamidinate ligands is reported, along with the successful application of these complexes as precatalysts for the challenging room-temperature hydrosilylation of carbonyl compounds to afford alcohols upon workup. Under the rigorous screening conditions employed (0.015 mol % Fe) for the reduction of acetophenone, the well-defined iron(II) amido precatalyst 2b, featuring bulky N-2,6-diisopropylphenyl and di-tert-butylphosphino moieties within the N-phosphinoamidinate ligand, exhibited exceptional catalytic performance. Further experimentation revealed that the yield achieved in the hydrosilylation of acetophenone employing 2b was unaltered when conducting reactions in the absence of light, in the presence of excess mercury, or under solvent-free conditions. Notably, precatalyst 2b was found to exhibit the broadest substrate scope reported to date for such room-temperature iron-catalyzed carbonyl hydrosilylations en route to alcohols, enabling the chemoselective reduction of structurally diverse aldehydes and ketones, as well as for the first time esters, at remarkably low loadings (0.01−1.0 mol % Fe) and using only 1 equiv of phenylsilane reductant.

A new (N-phosphinoamidinate)manganese complex is shown to be a useful pre-catalyst for the hydrosilative reduction of carbonyl compounds, and in most cases at room temperature. The Mn-catalyzed reduction of tertiary amides to tertiary amines, with a useful scope, is demonstrated for the first time by use of this catalyst, and is competitive with the most effective transition-metal catalysts known for such transformations. Ketones, aldehydes, and esters were also successfully reduced under mild conditions by using this new Mn catalyst.

The first examples of stoichiometric dehydrogenative B-H/C(sp )-H benzylic borylation reactions, which are of relevance to catalytic methylarene (di)borylation, are reported. These unusual transformations involving a (κ -P,N)Pt(η -benzyl) complex, and either pinacolborane or catecholborane, proceed cleanly at room temperature. Density functional calculations suggest that borylation occurs via successive σ-bond metathesis steps, whereby a Pt -H intermediate engages in C(sp )-H bond activation-induced dehydrogenation.

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