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What drives grassland-forest boundaries? Assessing fire and frost effects on tree seedling survival and architecture
  • Monique Botha,
  • Sally Archibald,
  • Michelle Greve
Monique Botha
University of Pretoria
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Sally Archibald
University of the Witwatersrand
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Michelle Greve
University of Pretoria
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Abstract

1. Fire and frost represent two major hurdles for the persistence of trees in open grassy biomes and have both been proposed as drivers of grassland-forest boundaries in Africa. 2. We assess the response of young tree seedlings, which represent a vulnerable stage in tree recruitment, to traumatic fire and frost disturbances. 3. In a greenhouse experiment, we investigated how seedling traits predicted survival and resprouting ability in response to fire vs frost; we characterised survival strategies of seedlings in response to the two disturbances, and we documented how the architecture of surviving seedlings is affected by fire vs frost injury. 4. Survival rates were similar under both treatments. However, different species displayed different levels of sensitivity to fire and frost. Seedling survival was higher for older seedlings and seedlings with more basal leaves. Survivors of a fire event lost more biomass than the survivors of a frost event. However, the architecture of recovered fire and frost treated seedlings were mostly similar. Seedlings that recovered from fire and frost treatments were often shorter than those that had not been exposed to any disturbance, with multiple thin branches, which may increase vulnerability to the next frost or fire event. 5. Synthesis. Fire caused more severe aboveground damage compared to frost, suggesting that trees in these open grassland systems may be subjected to a seedling release bottleneck maintained by fire. However, the woody species composition will almost certainly be influenced by phenomena that affect the timing and frequency of seedling exposure to damage, as mortality was found to be dependent on seedling age. Therefore, changes in fire regime and climate (esp. changes that bring about less frost and reduced fire intensity and frequency) are likely to result in changes in the composition and the structure of the woody components of these systems.

Peer review status:ACCEPTED

01 Jun 2020Submitted to Ecology and Evolution
04 Jun 2020Submission Checks Completed
04 Jun 2020Assigned to Editor
08 Jun 2020Reviewer(s) Assigned
26 Jun 2020Review(s) Completed, Editorial Evaluation Pending
30 Jun 2020Editorial Decision: Revise Minor
28 Jul 20201st Revision Received
29 Jul 2020Submission Checks Completed
29 Jul 2020Assigned to Editor
29 Jul 2020Review(s) Completed, Editorial Evaluation Pending
10 Aug 2020Editorial Decision: Accept