Re: vines and growth strategies

[Carefreeland@aol.com]

In a message dated 8/23/02 11:45:18 AM Eastern Daylight Time, adkarve@pn2.vsnl.net.in writes:

> Dan's comments

> All plants need sunlight for their photosynthesis.  They therefore strive to grow tall if they are shaded by another tree. This mechanism is called shade avoidance. The vines are an extreme example of shade avoidance mechanism.  They not only grow very fast when shaded by another plant, but make use of the shading plant itself to reach the sunlight. Another shade avoidance mechanism is found in some species in which the seeds just do not germinate if they are not exposed to direct sunlight.  This mechanism avoids shady places for the future generations. A whole group of plants, evolved in tropical rain forests, have adapted themselves to growing in the shade of tall trees.  These are the typical shade tolerators.  Most of our indoor ornamentals have been derived from such plants. We however observed another phenomenon. In some tree species, the seed falls on the ground and germinates in the shade of its own mother plant. These saplings cannot grow fast enough to grow taller than the mother tree. Therefore they become shade tolerant and just remain stunted for a few years.  During this period they accumulate food in their roots. When they have stored enough food, they cast the shade tolerance aside and become shade avoiders, growing rapidly to compete with their neighbours. 

> This is a fantastic observation. I have learned most of what I know about these plants from watching them compete over a long period of time in the same places.  I have witnessed this very phenomenon in various hardwoods locally. 
 >The Oak family is particularly adapted to the shade Vs light war of the forest. I have seen oak trees growing at 1inch per year or less for several decades in deep shade. Yet as they approach the canopy level they burst into a growth spirt that makes you question what happened.  Growing feet per year until through the canopy then spreading out dominating the area.  We had often attributed this to the tap roots reaching the permanent water table some 20 feet or more below.  There may be some of both mechanisms at work here. 
> The Oak is not always king here though in virgin forests. The hard maples such as Sugar maple can often even crowd out the oaks with another strategy. The Maples use a group assault on Oaks to crowd them out.  The Oaks fortunately are not so dominating although usually being the giant lone wolfs. You will find many other species of hardwood and other mid story trees living under the oaks in the filtered light. When the maples take over, very little else can live in their shade.        
> While our heads are turned up in the forest we must not forget that half of the competition is with the roots underground.  Where soils are shallow, the maples usually dominate by stealing every drop of moisture and sharing the dew from the moisture they transpire among themselves with their thick layered leaf canopy.  The maple roots are more shallow and form a dense sod several feet thick.
> The Oaks, although appearing to be so dominating, actually are much deeper rooted and pull up moisture from deep reserves. When they transpire and the dew collects, they share it among all of the diverse plants growing underneath them.  
 > If you doubt that Oaks nurture other plants, just look at the way the leaves appear when laying on the ground in the fall.  The deep lobes allow small patches of soil to show through. This allows other species to sprout and thrive as part of the support system for the mother tree. The curling of the leaves also allows more aeration of the usually wetter fall soils in their habitat. 
  >If you observe Maple leaves, they have the strategy of covering everything in a thick paper mulch that is best suited for moisture penetration by slow melting snow.  They trap this moisture in their thick root mats for the next dry season with less dependence on the deepness of the often shallow hillside soil. 
 > The vines have similar strategies best suited for the habitat they grow in.  Vines that take over bare areas quickly often do not thrive in the deep shade of the 3 layer canopy.  The best they can do is try to race to the tops of their hosts and choke them to death before they die themselves or live a stunted streached out life.  These are the types of vines that are becoming the biggest problem because we have cleared areas for them to thrive.  
>The giveaway is often the leaf types.  If a leaf is deeply cut or lobbed it often is better at sharing space. Broad solid leaves do not indicate a plant that shares space.
A plant with small leaves usually shares space as well.  Some plants use this combined with other strategies such as chemicals to choose what other plant can share. Take the Locust or the Walnut tree. 
 > Locust trees have small leaves but chemicals that prevent most other type plants from growing with them.  They grow as a grove and improve the sterile soil until complete.  Then the whole grove thins and dies as they allow a new crop of other more developed type trees to use the soil they improved. 

Vines grow faster than other plants because they produce a hormone called 
> gibberellic acid (GA) in larger quantities than other plants.  One can get bushy mutations of the same species with lower levels of GA. Bush bean is such a mutation derived from pole beans. One can make a bush bean plant grow into a pole bean by spraying it with GA, but if not supported by a stake, such plants topple over by their own weight. 
> A.D.Karve 

> Their are numerous complex strategies for every combination of plants. Then when we observe their interactions with the animal life they host, the strategies become more complex.   I am confident that this area of study is far from complete.  Man is just a cog in the wheel, but the only one that can influence all of the others. 
    
       Daniel Dimiduk