Submitted to: Journal of Environmental Horticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2001
Publication Date: N/A
Interpretive Summary: Few alder and birch species are commonly cultivated. Alders are thought to be well adapted to flooding but sensitive to drought, while most common birches are better adapted to drought but more sensitive to flooding. Many alders and birches have ornamental merit, but are rarely cultivated. To learn more about their adaptation and landscape use, we tested 8 uncommon alder and birch species for response to flooding and drought. Our goal was to evaluate photosynthesis, leaf surface area, and overall health in relation to the birch variety, 'Whitespire Sr.' Control plants were watered daily, while pots of flooded plants were immersed. No water was given to the drought-treated species showing the least daily water loss, with the amounts of water added to the other plants adjusted for that loss. After 3 drought cycles that caused wilting and decreased photosynthesis, Alnus hirsuta was least affected among alders. Although drought reduced photosynthesis in all birches, Betula uber was affected least. Flooding for 7 days had no effect on alder photosynthesis, but reduced it in all birches except B. davurica. After 21 days of flooding, B. albosinensis and costata were killed, and A. maritima was the only alder not to show reduced photosynthesis. While our results generally confirm that most alders are adapted to wet sites and most birches to drier sites, drought responses varied among alders and flooding responses varied among birches, potentially useful variation for selecting more adaptable landscape trees. Evaluations should be done to confirm our results under field conditions, which can help guide horticulturists and nursery professionals in choosing more stress-tolerant alders and birches.
Technical Abstract: The selection of birches (Betula) and alders (Alnus) for landscape use can be guided by knowledge of their responses to moisture extremes in the root zone. Our objective was to evaluate the photosynthetic response, leaf surface area, and overall health of 8 birch and alder taxa in relation to the common birch cultivar, 'Whitespire Sr.' when subjected to drought and flooding in containers. Control plants were irrigated daily, while pots o flooded plants were immersed. All water was withheld from the drought- treated taxon that showed the least evapotranspiration each day, with the amounts of water added to the other plants adjusted for that lost through evapotranspiration. After 3 drought cycles that induced wilting and a reduction in photosynthetic rate, A. hirsuta showed the smallest decrease in leaf surface area among alders. Although drought reduced photosynthesis in all the birches, B. uber retained the highest photosynthetic rate among them. Flooding for 7 days had no influence on photosynthetic rates of any alder, but reduced photosynthesis in all birches except B. davurica. After 21 days of flooding, B. albosinensis and costata were killed, and A. maritima was the only alder not to show reduced photosynthesis. While our data generally support the notion that most alders are adapted to wet sites and most birches to drier sites, we found that responses to drought varied among alders and responses to flooding varied among birches, presenting potentially useful variation for selecting more adaptable landscape trees. Additional evaluations should be done to confirm our results under field conditions.