| 1. |
|
|
| 2. |
- Gauslaa, Y., et al.
(författare)
-
Growth of epiphytic old forest lichens across climatic and successional gradients
- 2007
-
Ingår i: Canadian Journal of Forest Research. - 0045-5067 .- 1208-6037. ; 37:10, s. 1832-1845
-
Tidskriftsartikel (refereegranskat)abstract
- This paper aims to assess the influence of canopy cover on lichen growth in boreal forests along a regional forest gradient. Biomass and area gain, and some acclimation traits, were assessed in the old-forest lichens Lobaria pulmonaria (L.) Hoffm., Pseudocyphellaria crocata (L.) Vain., and Usnea longissima Ach. transplanted 110days in three successional Norway spruce (Picea abies (L.) Karst.) forest stands (clearcut, young, and old forest) repeated along a rainfall gradient (continental, suboceanic, and Atlantic zones) in Scandinavia. Lichen growth peaked in Atlantic rainforests with mean dry matter (DM) gain up to 36%-38%. The alectorioid lichen U. longissima showed the widest range of growth responses and no signs of chlorophyll degradation. Its highest DM gain consistently occurred in clearcuts, whereas the DM gain was close to zero in the shadiest young forest. The two foliose lichens L. pulmonaria and P. crocata exhibited maximal growth rates in old forests, but apparently growth was limited by low light even in old forests. Their DM gain was reduced in the most sun-exposed clearcuts due to chlorophyll degradation and was relatively high under closed young canopies, suggesting a better adaptation to shade. The lichen responses show that a high frequency and dominance of young and dense fast-growing forest stands at a landscape level are not compatible with large populations of these old-forest lichens and that a lack of lichens under an industrial forestry regime may not necessarily be determined by low dispersal efficiency only. Cet article a pour but d'évaluer l'influence du couvert de la canopée sur la croissance des lichens dans les forêts boréales le long d'un gradient forestier régional. Le gain en biomasse et en superficie ainsi que certains caractères d'acclimatation ont été évalués chez les lichens des forêts âgées, Lobaria pulmonaria (L.) Hoffm., Pseudocyphellaria crocata (L.) Vain. et Usnea longissima Ach., qui ont été transplantés pendant 110 jours dans trois peuplements d'épicéa commun (Picea abies (L.) Karst.) rendus à différents stades de succession (forêt coupée à blanc, jeune et vieille forêts). L'expérience a été répétée le long d'un gradient pluvial (zones continentale, subocéanique et atlantique) en Scandinavie. La croissance des lichens a culminé dans les forêts pluviales atlantiques avec un gain moyen en matière anhydre allant jusqu'à 36%-38%. Le lichen alectorioïde U. longissima a montré la plus vaste gamme de réponses en croissance végétative et aucun signe de dégradation de la chlorophylle. Son gain maximal en matière anhydre est survenu essentiellement dans les coupes à blanc alors qu'il était presque nul dans la jeune forêt la plus ombragée. Les deux lichens foliacés, L. pulmonaria et P. crocata, montraient des taux maximum de croissance dans les vieilles forêts, mais la croissance était apparemment limitée par la faible luminosité, même dans les forêts âgées. Leur gain en matière anhydre était réduit dans la plupart des coupes à blanc exposées au soleil à cause de la dégradation de la chlorophylle alors qu'il était relativement élevé sous les jeunes canopées fermées, ce qui indique une meilleure adaptation à l'ombre. La réponse des lichens montre qu'une fréquence élevée et une forte dominance de jeunes peuplements forestiers à croissance rapide à l'échelle du paysage ne sont pas compatibles avec de grandes populations de ces lichens, typiques des forêts matures, et que le manque de lichens sous un régime forestier industriel pourrait ne pas nécessairement être dû seulement à la faible efficacité de dispersion des lichens.
|
|
| 3. |
- Kolberg, D., et al.
(författare)
-
Effect of Rhizome Fragmentation, Clover Competition, Shoot-Cutting Frequency, and Cutting Height on Quackgrass (Elymus repens)
- 2018
-
Ingår i: Weed science. - : Cambridge University Press. - 0043-1745 .- 1550-2759. ; 66:2, s. 215-225
-
Tidskriftsartikel (refereegranskat)abstract
- Quackgrass is a problematic agricultural weed in the temperate zones of the world and is difficult to control without herbicides or intensive tillage. However, it may be possible to control quackgrass with less environmental impact by combining multiple low-intensity control methods. A pot experiment was conducted in July to October 2012 and repeated in June to September 2013 to investigate the effect of rhizome fragmentation, competition from white clover, shoot-cutting frequency, and cutting height on quackgrass. Rhizome fragmentation was expected to result in more, but weaker, quackgrass shoots that would be more vulnerable to shoot cutting and competition. However, by 20 d past planting, rhizome fragmentation did not change the total number of quackgrass shoots per pot, because an increase in main shoots was offset by a decrease in tiller numbers. Rhizome fragmentation did not reduce quackgrass biomass acquisition during the experimental period. Although rhizome fragmentation did reduce total fructan content, it did not enhance the effect of clover competition, shoot-cutting frequency, or shoot-cutting height. Clover competition by itself reduced quackgrass shoot numbers by 72%, rhizome biomass by 81%, and belowground fructan concentration by 10 percentage points, compared with no competition. The more frequently quackgrass shoots were cut, the less biomass quackgrass acquired, and a high shoot-cutting frequency (each time quackgrass reached 2 leaves) resulted in a lower belowground fructan concentration than a low shoot-cutting frequency (at 8 leaves). However, in pots without competition, a higher shoot-cutting frequency resulted in more quackgrass shoots. A lower shoot-cutting height (25 mm) had more impact when shoot cutting was more frequent. In conclusion, rhizome fragmentation did not reduce the number of quackgrass shoots or rhizome biomass, but competition from white clover, a high shoot-cutting frequency, and a low shoot-cutting height strongly suppressed quackgrass biomass and fructan acquisition.
|
|
