Predation on Pinus sylvestris seeds and juvenile seedlings in Swedish boreal forest in relation to stand disturbance by logging

Authors


Ove Nystrand (fax +46 90 78 66 12; e-mail Ove.Nystrand@svek.slu.se).

Summary

1. Forest management involving live tree retention and natural regeneration after cutting is currently increasing in boreal areas. This calls for further analysis of the optimal conditions for seedling establishment from seed following stand disturbances due to logging.

2. We studied post-dispersal predation on seeds and juvenile seedlings of Pinus sylvestris over 3 years in 32 north Swedish boreal forest stands with different levels of stand disturbance by logging. The aims were to identify the most important predator species and to quantify the damage inflicted upon seeds and seedlings in relation to disturbance.

3. In most stands and years, seed predation resulted in < 20% seed mortality, although occasionally it reached 60%. Predation on juvenile seedlings ranged from 5% to 100%, with > 70% mortality in 10 cases and < 30% in 44 cases (of a total of 79 observations).

4. The most important seed predators were the carabids Pterostichus oblongopunctatus and Calathus micropterus, and seed predation was correlated with the number of seed-eating carabids caught in pitfall traps. Microtine rodents caused high damage levels only on a single occasion.

5. Logging affected both catches of carabids and seed predation levels, but the relationship between tree stand density and predation was not linear and, generally, seed predation decreased in the order shelterwood > unlogged forest > clear-cut.

6. The most important predator on juvenile seedlings was the slug Arion subfuscus, which attacked seedlings during the first weeks after germination. Pitfall trap catches of Hylobius abietis, which commonly damage planted (1–3-year-old) conifer seedlings, were not related to the levels of seedling predation.

7. Seedling predation was negatively related to stand disturbance, with the highest predation levels by slugs in unlogged forests and the lowest in clear-cuts. Seedling predation was higher in wet than in dry summers, probably because slugs are moisture-limited.

8. There was a large between-site variation in both seed and seedling predation, but predation was not strongly related to forest site types. The fact that predation was strongly affected by logging operations indicates that there may be opportunities to reduce damage through modification of the silvicultural practices.

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