Étude des gelées tardives en relation avec les problèmes de reboisement

-Forking is a frequent flaw in beech which can adversely affect the formation of high quality logs. Even though the hypothesis that late frosts increase forking is widely accepted by forest managers, it remains to be proved and quantified experimentally. Damage caused by a late frost on 15 May 1995 to young beech trees in an experimental site at Lyons-La-Forêt (France) and the consequences on the development of forking were analysed. The beech trees were 17 years old with heights between 1.5 and 9 m. Of all the plantation densities tested only the lowest density (625/ha) showed various and severe frost damage. Three levels of immediate damage to the growing terminal shoot were observed, with increasing intensity from: (1) no trace of frost damage, (2) reddened leaves and (3) frost-nipped shoots. The intensity of visible damage to the terminal shoot appeared to be very dependent on the height of the plant which justified our original experimental approach, based on an evaluation of the damage for each individual. Almost all of the beech trees less than 4 m high suffered frost damage and all those taller than 7 m were unaffected. Three-year-old forks due to frost which occured in May 1995 were recorded at the end of 1997 using an objective definition based on dendrometric and age criteria. The worst frost damage resulted in a significant increase in the risk of fork emergence (71.7% of the plants were forked). With a risk related to forking in the presence of frost-nipped shoots equal to 2.15 and a fraction of the attributed risk of 0.36 it was concluded that the late frost observed played a significant role in the degradation of the shape of the beech affected by frost and the overall quality of the stand.forks / Fagus silvatica / frost damage / relative risk / attributive fraction of risk / plantation Résumé -Les dégâts de gel tardif sur la pousse terminale : un facteur de risque d'apparition de fourches chez le hêtre (Fagus sylvatica L.). La fourchaison est un défaut fréquent du hêtre qui peut nuire à la formation d'une grume de qualité. L'hypothèse d'un effet des gelées tardives contribuant à aggraver la fourchaison, bien que largement admise par les gestionnaires forestiers, restait pourtant à démontrer et à quantifier dans un cadre expéri-mental. Les dégâts occasionnés par la gelée tardive du 15 mai 1995 sur de jeunes plants de hêtre du dispositif expérimental de Lyons-La-Forêt (France) et leurs conséquences sur la mise en place de fourches ont été analysés. Les hêtres étaient alors âgés de 17 ans et de hauteur comprise entre 1,5 et 9 m. Parmi toutes les densités de plantation testées seule la plus faible (625/ha) présentait un impact fort et diversifié du gel. Trois niveaux d'intensité croissante de dégâts immédiats sur la pousse terminale en élongation ont pu être distingués : (1) aucune trace de gel, (2) feuilles roussies (3) pousse gelée. L'intensité des dégâts visibles sur la pousse terminale est apparue très dépendante de la hauteur du plant justifiant notre approche expérimentale originale ce...

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Frost damage on the terminal shoot as a risk factor of fork incidence on common beech (Fagus sylvatica L.)

Ningre

Colin

2007

“…But cover provided by understorey also has a positive effect beyond browsing pressure. The understorey reduces the risk of spring frosts which affect fir more than spruce [1,3,50] and protects seedlings from over-exposure to sun and uprooting when soil is washed away during strong rains, two important causes of fir mortality [56]. In addition, by creating shade, understorey limits the development of herbaceous species such as Festuca altissima that may hinder fir establishment through allelopathic processes [5].…”

Section: How Fir May Be Replaced By Spruce or Notmentioning

confidence: 99%

Consequences of increased deer browsing winter on silver fir and spruce regeneration in the Southern Vosges mountains: Implications for forest management

Heuzé¹,

Schnitzler²,

Klein

2005

-Forest and wildlife management practices in the Vosges have changed rapidly during the last 200 years, modifying interactions between animals and plants, especially deer and silver fir. In order to assess the impact of browsing on fir regeneration, we compared two sets of similar forests which differed primarily in terms of deer population dynamics and history. On slopes with southern exposures, many fir seedlings did not reach heights above 30 cm and spruce developed; this was related to browsing intensity. Spruce expansion was also facilitated by its presence in nearby mature stands, and was not related to a particularly high level of browsing. Of the six site characteristics taken into consideration, only the presence of foliage from the understorey above seedlings was found to benefit fir by limiting spruce development and reducing browsing intensity. Results are discussed in light of current and proposed management practices for silver fir-beech forests and their wildlife.silver fir-beech forest / regeneration / browsing / deer / management Résumé -Conséquences de l'augmentation de l'abroutissement hivernal par les cerfs et chevreuils sur la régénération du sapin et de l'épicéa dans les Vosges du Sud. Implications pour la gestion forestière. Les récents changements de gestion forestière et faunistique ont profondément modifié les interactions entre la flore et la faune, notamment entre les cervidés et le sapin. Pour évaluer l'impact de l'abroutissement sur la régénération du sapin, nous avons comparé deux ensembles de forêts sur la base de conditions environnementales similaires mais à différents degrés de colonisation par les cervidés. Les résultats montrent que les sapins des versants exposés sud subissent une pression d'abroutissement forte et poussent difficilement au-delà de 30 cm, alors que l'épicéa est particulièrement abondant. L'expansion de l'épicéa au détriment du sapin abrouti est également facilitée par sa présence parmi les arbres matures, mais ici sans relation avec un abroutissement particulièrement fort du sapin. Un seul facteur parmi les sept étudiés joue en faveur du sapin : la présence d'une strate arbustive, qui limite le développement de l'épicéa et réduit l'abroutissement du sapin. Les résultats sont discutés en relation avec la gestion actuelle des hêtraie-sapinières vosgiennes et de leur faune, et des propositions sont émises pour une gestion qui intègre davantage la présence des animaux.hêtraie-sapinière / régénération / abroutissement / cervidés / gestion

“…The extent of damage due to late frost depends on the species, the provenance, the lowest temperature reached and the phenological stage of the plant when frost occurred [4,29]. Day and Pearce [14] reported that oak is more sensitive to late frost than ash and beech.…”

mentioning

confidence: 99%

“…B) On the GU established at the end of the previous growing season: a subterminal bud (STB-pGU) (4) and a lateral bud (LB-pGU) (5).…”

mentioning

confidence: 99%

Impact of late frost on height growth in young sessile oak regenerations

Chaar

Colin

1999

-The damage due to late frost during the 1995 and 1996 growing seasons was analysed in sessile oak seedlings in a natural regeneration. The seedlings were 5 years old at the beginning of the 1995 growing season. In 1995, frost occurred after the complete elongation of the growth unit (GU) of the stem which was produced during the first period of elongation. In 1996, frost occurred during the elongation period of the first GU. Damage intensity was observed visually and ranged from simple necroses of the leaf or the terminal bud of the new GU to the total loss of the GU. Damage intensity appeared to depend on the growing season and the bud phenological stage when frost occurred but not on the initial dimensions (height and collar diameter) of the seedling. Damage was higher when the seedling was at the shoot elongation stage (1996 growing season) and lower when the seedling was in apparent rest (1995 growing season). The consequences of frost damage on growth were greater in the 1996 growing season. The bud resting period after the first period of elongation and before regrowth was shorter in 1996. Regrowth occurred from either a bud from the damaged GU or a bud from the GU grown during the previous growing season. In the latter case, the GU was sometimes longer than the GU from an axillary bud of the damaged GU. The second elongation period was shorter in 1996 than in 1995 and led to a relatively small GU. The intensity of frost damage, which had an effect on the length of the GUs produced during the second period of elongation, had no subsequent effect on the length of those produced during the third elongation period.