Above- and below-ground biomass accumulation, production, and distribution of sweetgum and loblolly pine grown with irrigation and fertilization.

Abstract: Increased forest productivity has been obtained by improving resource availability through water and nutrient amendments. However, more stress-tolerant species that have robust site requirements do not respond consistently to irrigation. An important factor contributing to robust site requirements may be the distribution of biomass belowground, yet available information is limited. We examined the accumulation and distribution of above- and below-ground biomass in sweetgum (Liqrridambar sfyrac$lua L.) and loblolly pine (Pinus taeda L.) stands receiving irrigation and fertilization. Mean annual aboveground production after 4 years ranged from 2.4 to 5.1 ~g.ha-'.year' for sweetgum and from 5.0 to 6.9 ~g.ha-l.year-l for pine. Sweetgum responded positively to irrigation and fertilization with an additive response to irrigation + fertilization. Pine only responded to fertilization. Sweetgum root mass fraction (RME)in creased with fertilization at 2 years and decreased with fertilization at 4 years. There were no detectable treatment differences in loblolly pine RMF. Development explained from 67% to 98% of variation in shoot versus root allometry for ephemeral and perennial tissues, fertilization explained no more than 5% of the variation in for either species, and irrigation did not explain any. We conclude that shifts in allocation from roots to shoots do not explain nutrient-induced growth stimulations

Restauration des forêts de montagne dans le Massif Central en France

International audienceChanging economic, environmental, and social conditions have challenged foresters to modify their silvicultural practices. Forests in the Massif Central begin the twenty-first century with new management strategies, including restoring diversity and transforming existing stands and plantations into diversified stands that are storm- and pest-resistant and probably more adapted to face climate change consequences (e.g., drought occurrence), using environmentally friendly soil preparation and weed control, and taking advantage of natural processes to favor mixtures of species. Experience to date suggests that more research should be devoted to fundamental exploration of four areas: competition between trees and ground vegetation, changes of biodiversity in relation to the main environmental variables, especially light level, ecology and uses of exotic species, and natural dynamics of forest stands in diverse contexts

Cold hardiness and transplant response of Juglans nigra seedlings subjected to alternative storage regimes

$\bullet$ Effects of overwinter storage regimes on seedling cold hardiness and physiological vigor are relatively unexplored, particularly for temperate deciduous forest tree species. $\bullet$ We evaluated influence of storage duration (0, 66, 119, or 175 d) on electrolyte leakage of stem and root collar tissues following exposure to a series of freeze-test temperatures in black walnut (Juglans nigra L.) seedlings sampled from cold (3 °C) or freezer (–2 °C) storage. Seedlings were subsequently transplanted into a controlled growth chamber environment for two months. $\bullet$ Regardless of storage temperature, mean LT$_{50}$ was lowest for seedlings stored for 66 d ($\leq$ –34 °C) and increased dramatically after 119 d ($\geq$ –13 °C). $\bullet$ Root collar tissue had lower LT$_{50}$ than stem tissue after 119 d for cold-stored seedlings, reflecting importance of evaluative tissue type. Days to bud break shortened with increasing storage duration up to 119 d and stabilized thereafter for both storage regimes. Root growth potential was maximized after 119 d of storage, and subsequently declined for cold-stored seedlings. Height growth increased following storage, regardless of duration. $\bullet$ To promote stress resistance and transplant growth response, we recommend that black walnut seedlings from this genetic source be outplanted after approximately 66–119 d of storage.Endurcissement au froid et réponse des semis de Juglans nigra transplantés après exposition à différentes modalités de stockage. $\bullet$ Les effets de différentes modalités de stockage hivernal sur la résistance au froid des semis et sur leur vigueur physiologique ont été relativement inexplorés, en particulier pour les arbres forestiers décidus tempérés. $\bullet$ Nous avons évalué l'influence de la durée de stockage (0, 66, 119 ou 175 jours) sur la perte d'électrolyte de la tige et des tissus du collet racinaire exposés à une série de tests (témoin 4 %C, –10 °C, –20 °C, –40 °C) de température de congélation de semis de noyer noir (Juglans nigra L.), après stockage au froid (3 °C) ou au gel (–2 °C). Les semis étaient ensuite transplantés dans une chambre climatisée pour une durée de deux mois. Indépendamment de la température de stockage, la moyenne de LT50 (température létale correspondant à un endommagement de 50 % des plants) a été plus basse pour les semis stockés pendant 66 jours ($\leq$ –34 °C) et s'est accrue de façon spectaculaire après 119 jours ($\geq$ –13 °C). $\bullet$ Les tissus du collet racinaire avaient un plus bas LT50 que les tissus de la tige, après 119 jours pour les semis stockés au froid, reflétant l'importance du type de tissu pour l'évaluation. Le nombre de jours jusqu'au débourrement a été raccourci avec l'accroissement de la durée de stockage jusqu'à 119 jours et s'est stabilisé par la suite pour les deux modalités de stockage. Le potentiel de croissance racinaire a été maximisé après 119 jours de stockage et a décliné par la suite, pour les semis stockés au froid. La croissance en hauteur s'est accrue à la suite du stockage, indépendamment de sa durée. $\bullet$ Pour promouvoir une résistance élevée au stress et une forte reprise de croissance des semis transplantés, nous recommandons que les semis de noyer noir de cette source génétique soient plantés après approximativement 66 à 119 jours de stockage