Event Title

Initial Response of Saplings and Stump Sprouts to Experimental Canopy Gap Formation in a Northern Hardwood Forest

Event Website

http://www.nafew2009.org/

Start Date

23-6-2009 9:40 AM

End Date

23-6-2009 10:00 AM

Description

The response of forest regeneration to canopy gap formation plays a key role in forest stand dynamics and future species composition of mesic forests. Results from controlled, replicated experiments, however, are limited. We measured light environment and extension growth for saplings and stump sprouts in and around experimentally harvested canopy gaps two years after formation to evaluate the initial response of shade tolerant sugar maple (Acer saccharum) versus mid-tolerant bitternut hickory (Carya cordiformis) and white ash (Fraxinus americana). Gap areas (projected) ranged from 9 to 443 m≤ and were chosen to represent the typical range found in old-growth forests of the Great Lakes region. No saplings (>0.5 cm dbh) were browsed by deer, but because of heavy browsing on stump sprouts, analysis of extension growth on sprouts was restricted to a subset of plots fenced to exclude deer. Surprisingly, sugar maple saplings attained higher extension growth rates across all light conditions than the two mid-tolerant species (18.2 vs. 13.0 cm, respectively; p = 0.004). Sugar maple sapling extension growth varied significantly as a function of pre-treatment growth rate and gap area (p < 0.001). Extension growth of mid-tolerant saplings was not significantly correlated with any measured variable. However, stump sprouts grew two to five times faster than saplings (p < 0.001), and unlike the trend among saplings, mid-tolerants grew faster than sugar maple (100.1 vs. 67.8 cm, respectively). Our results indicate that sugar maple saplings respond to canopy gap formation more quickly than midtolerant associates and that stump sprouts outgrew saplings considerably. In addition, the importance of stump sprouting to gap regeneration increased significantly in larger gaps because of harvest damage to saplings. However, saplings have an advantage of greater initial height, so future competitive status may depend on changes in relative growth rates over the next few decades.

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Jun 23rd, 9:40 AM Jun 23rd, 10:00 AM

Initial Response of Saplings and Stump Sprouts to Experimental Canopy Gap Formation in a Northern Hardwood Forest

The response of forest regeneration to canopy gap formation plays a key role in forest stand dynamics and future species composition of mesic forests. Results from controlled, replicated experiments, however, are limited. We measured light environment and extension growth for saplings and stump sprouts in and around experimentally harvested canopy gaps two years after formation to evaluate the initial response of shade tolerant sugar maple (Acer saccharum) versus mid-tolerant bitternut hickory (Carya cordiformis) and white ash (Fraxinus americana). Gap areas (projected) ranged from 9 to 443 m≤ and were chosen to represent the typical range found in old-growth forests of the Great Lakes region. No saplings (>0.5 cm dbh) were browsed by deer, but because of heavy browsing on stump sprouts, analysis of extension growth on sprouts was restricted to a subset of plots fenced to exclude deer. Surprisingly, sugar maple saplings attained higher extension growth rates across all light conditions than the two mid-tolerant species (18.2 vs. 13.0 cm, respectively; p = 0.004). Sugar maple sapling extension growth varied significantly as a function of pre-treatment growth rate and gap area (p < 0.001). Extension growth of mid-tolerant saplings was not significantly correlated with any measured variable. However, stump sprouts grew two to five times faster than saplings (p < 0.001), and unlike the trend among saplings, mid-tolerants grew faster than sugar maple (100.1 vs. 67.8 cm, respectively). Our results indicate that sugar maple saplings respond to canopy gap formation more quickly than midtolerant associates and that stump sprouts outgrew saplings considerably. In addition, the importance of stump sprouting to gap regeneration increased significantly in larger gaps because of harvest damage to saplings. However, saplings have an advantage of greater initial height, so future competitive status may depend on changes in relative growth rates over the next few decades.

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