MadSci Network: Botany

Re: How does the light intensity of a wood affect the distribution of bluebells

Date: Tue Jul 3 21:31:34 2001
Posted By: David Hershey, Faculty, Botany, NA
Area of science: Botany
ID: 994018095.Bt

I encourage you NOT to make the assumption that English bluebell (Hyacinthoides 
non-scriptus) [formerly Scilla non-scripta, Endymion non-scripta] prefers 
shaded areas without scientific evidence. Spring bulbs start growing before the 
trees leaf out so are exposed to high light early in the season. There is also 
typically a strong interaction between light intensity and soil moisture in 
shade tolerant plants. Many species that are said to "prefer" shade will 
actually grow much better in full sun, than in shade, if there is adequate soil 
moisture. Examples are caladium and impatiens. Other species are obligate shade 
plants, such as African violet, and their leaves are damaged in full sun. 
Another thing to consider is if competing species in higher light areas 
outcompete bluebell making competition and not light the key factor in 
distribution. This appears to be the case with bluebell and bracken fern. In 
higher light, the taller bracken fern is more vigorous, grows taller sooner, 
and shades out the bluebell. In shady areas, the bracken fern grows more 
slowly, which allows the bluebell to receive adequate light before its leaves 
die back in the summer.

It is often difficult to collect good experimental data under natural 
conditions because the environment is so variable. Experimentally, it would be 
desirable to grow bluebells in containers to standardize soil conditions 
(optimal water, fertilizer, soil aeration, soil pH, lack of soil borne 
diseases). This would allow a fair comparison of growth under different light 
intensities, by using shade cloth or growth chambers. It would be best to 
exactly quantify light level with a quantum sensor (see LI-COR) measuring PAR 
(Photosynthetically Active Radiation). With natural light, it is best to 
measure the daily total of PAR in moles per square meter because instantaneous 
readings vary widely throughout the day, particularly in dappled shade. PAR is 
the best way to quantify light for photosynthesis. To do a long term growth 
study, you would need to measure weight gain, perhaps measuring just the bulb 
weight would be easiest as it could be done at the start and at the end of the 
experiment. Otherwise, you could measure total weight of leaves and flowers. 
Shorter term photosynthesis experiments would require an expensive lab system 
to measure photosynthesis of a single leaf or single plant under various PAR 
levels (see LI-COR). 


Bluebell Info Summary


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