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On ash: a 12-year population ecological study of Fraxinus excelsior L., with special reference to some of its inter-specific interactions, in the deciduous woodland of the outer archipelago of Stockholm
Stockholm University, Faculty of Science, Department of Botany.
1992 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Fruiting in ash was irregular over the years. Years with abundant fruit production occurred as well as more or less barren years. The resource status of the trees had no decisive influence. The probability of female trees to fruit neither decreased in the year following a fruit set, nor increased at weather conditions favourable to resource accumulation. Instead, the ultimate cause of the irregularity is interpreted as an adaptation to increase seed survival, by satiation of the seed predators in times of large seed crops. A large proportion of the seeds were infested by larvae of the monophagous seed eating moth Pseudargyrotoza conwagana, and the percentage emerging seedlings increased with increasing size of the total seed crop. Empty fruits produced in the preceding year enhanced the satiating effect of large seed crops,since the moth distributed its eggs to the same extent in the empty fruits as in fruits containing a seed. Date of leafing the preceding year was the proximate cause determining whether individual trees fruited or not. This relationship, which is hypothesized to be regulated by growth hormones, is significant in synchronizing fruit set of the trees. Regeneration in ash involved persistent juveniles. The survival of the juveniles was very high (35% of the germinated seedlings were alive after 10 years), but under a closed canopy their growth and development were slow. From the second growth season onwards they produced on average 1.2 leaf pairs and an annual height increment of < 8 mm. When a gap was opened out by a tree-fall, the juveniles were in the place, and growth increased rapidly. This behaviour was one of the explanations of the fact that ash replaced alder (Alnus glutinosa) during succession. But, ashes also grew up to the canopy stratum without a gap in the strict sense, in the interspace formed in the intersection between two or several intact alder crowns. The ashes exceeded the alders a few meters in height, and by overtopping, ashes actually killed alders.

Place, publisher, year, edition, pages
Stockholm: Stockholm University, 1992. , p. 32
National Category
Botany
Identifiers
URN: urn:nbn:se:su:diva-152990ISBN: 91-7153-050-9 (print)OAI: oai:DiVA.org:su-152990DiVA, id: diva2:1182711
Note

Härtill 5 uppsatser

Available from: 2018-02-14 Created: 2018-02-14 Last updated: 2018-02-14Bibliographically approved

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