Effet des facteurs physiques de l'environnement sur les premiers stades de la régénération naturelle du sapin pectiné (Abies alba Mill) dans certaines stations du Jura

Abstract

Résumé — Les premières phases de la régénération du sapin ont été analysées en étudiant la germination et le comportement des semis dans des expériences menées à la fois au champ en environnement naturel et au laboratoire en conditions contrôlées. Pour atteindre ces objectifs, le vaste domaine karstique du Jura a constitué un milieu modèle de choix parce que des stations forestières typiques sont observées côte-à-côte, avec des niveaux de régénération, soit très élevés, soit très bas. L'absence de géotropisme à la germination détermine à la fois la morphologie «en crosse» observée sur les semis naturels et le comportement ultérieur des semis. Les radicules qui rampent sur le substrat sans s'y implanter, rendent les semis très sensibles aux agents physiques, parmi lesquels les orages et les ensoleillements printaniers sont les plus efficaces pour entraîner des lésions et la dessiccation des semis. Le bilan de la régénération apparaît significativement modulé par l'humidité relative et la température de l'air, l'ensoleillement pendant le mois qui suit la germination, puis par le pédoclimat pendant les mois chauds qui agissent sur les semis mal enracinés. In vitro, il est démontré que l'humidité de l'air constitue le facteur qui détermine la survie des semis (premiers stades de développement) et que l'humidité du sol constitue le facteur qui détermine le développe-ment racinaire et la résistance des plantules à des stress hydriques. régénération naturelle / Abies alba / enracinement des semis 1 stress hydrique 1 humidité de l'air 1 pédoclimat 1 Jura Summary — Effect of physical environmental factors on the initial stages of the natural regeneration of fir (Abies alba) at some sites in the Jura. The early stages of fir regeneration were analysed in order to study the germination and the seedling behaviour in the field and in the greenhouse. The large karstic area of the Jura offers typical forest sites with high regeneration levels adjacent to those with low regeneration levels (fig 1). The lack of geotropism which is observed on seed germination induces the "grip" morphology of natural seedlings and their subsequent behaviour. The primary root extends over the substrate without penetrating it, and so appears to be susceptible to physical factors such as rain storms and insolation which damage and dry out the seedlings (tables IV and V). The regeneration balance was found to be significantly influenced by air humidity, air temperature and insolation during the first month following germination and later by the soil environment during the hot periods which could result in elimination of superficially rooted seedlings (fig 2). Laboratory measurements (fig 3) showed that air humidity was the determinant factor in seedling survival and soil humidity the parameter influencing root growth and resistance to moisture stress. natural regeneration / Abies alba / seedling rooting / moisture stress / air humidity / soil en-

Improving the estimation of landscape scale seed dispersal by integrating seedling recruitment

“…Silver fir is mainly found in mountainous regions characterized by their high humidity (Rolland et al 1999). Tan and Bruckert (1992) confirmed this trend by showing that soil and atmospheric humidity were the two limiting variables conditioning regeneration survival. At high elevations, the limiting factor is most probably frost (Balcar and Kacálek 2008).…”

The influence of the spatial pattern of trees on forest floor vegetation and silver fir (Abies alba Mill.) regeneration in uneven-aged forests

“…The same conclusion may be drawn from the findings of Š imak (1951), Duchafour and Millischer (1954), Mayer (1960), Korpel' and Vinš (1965), Jaworski (1973) and Schrempf (1978). Here, it is also worth noting that the soil moisture and ectohumus depth acknowledged by some authors to be crucial for successful fir regeneration (Calaone and Giannini, 1971;Grunda, 1972;Tan and Bruckert, 1992;Končer, 1992) could not be restricting factors in the stands sampled for this study. In particular, patches occupied by less hygrophilous and moder/mor humus-indicative plant species exhibited more abundant fir regeneration (Fig.…”

Changes in landscape structure in the northwestern Alps over the last 7000 years: lessons from soil charcoal

“…Currently these forests have disappeared and individuals of Abies are scattered in the abundant P. sylvestris forests. The process causing these changes could result from climatic conditions in the late Holocene being drier than they are at present; Abies is less adapted to drought than P. sylvestris (Aussenac 1980;Tan & Bruckert 1992;Guicherd 1994). However, the Pinus cembra treeline has also been lowered, and P. cembra is better adapted to dry conditions than P. sylvestris (Hättenschwiller & Körner 1995).…”