Seeds Efficient Hitch Hikers



Dave Rushworth


Just returned from a walk to have a look at the effect of water run-off after recent heavy rain. Waterfalls are running after a few dry years. Rivers are full and dams overflowing. Most water is brown and carrying away tons of valuable soil to silt the waterways. We are thankful for the rain but the excess run off is an ominous sign of poor infiltration. Good plant cover - and particularly grass cover - would hold much of the rain and prevent soil particles from being carried away.

Better water infiltration would replenish underground supplies which would seep into waterways throughout the year. Water life and fish populations would thrive in clear, stable water conditions. With deep, perennial pools there would be less requirement for dams, which silt rapidly. Many older folk can remember the deep, clear, perennial rivers of the lowveld with ‘tiger fish' and other species in abundance.

Our major rivers are now seasonal, filled with sand and hippo struggle to submerge in muddy shallows or crowd in isolated pools. Tiger fish are no longer able to migrate upstream. There is a definite correlation between floods and droughts. The more water that runs off the less there is to replenish supplies and the sooner drought conditions are manifested.

The graph for rainfall fluctuates around a fairly constant mean while the graph for drought conditions steadily rises. Most drought conditions are manmade. Compare a healthy piece of veld with a paved parking lot and you get the picture. North and south of the equator, desertification is Africa's greatest downfall.

Grass Seeds

While musing over veld condition I pick grass seeds from my socks. This is a sure sign of degraded grassland. The best (high succession) grasses generally have rounded seeds that don't stick to socks while the poorer grasses have burrs or spikes. I recollect feeling the ‘prick' of ‘spear grass' while walking and removed the uncomfortable ‘seeds' immediately. The burrs went un-noticed until my return - the same with some ‘black-jacks' and a few ‘sticky' seeds.

Those species with a ‘narrow tolerance' - of specific soil conditions - don't wish to be carried into unsuitable conditions and so make themselves felt to be discarded close by. Other species with a ‘wide tolerance' of growing conditions stick on without causing discomfort and can be carried great distances. Many plant species are inter-continental ‘hitch-hikers' on unsuspecting hosts.

Designed For Habitat

Methods of seed dispersal are extremely varied and designed to interact with climate and surrounding communities. Some seeds are contained within hard shelled capsules that are carried by flowing water or ocean currents.

Others are protected, while immature, by poison or bitter fruits which become palatable when the seed is ready for dispersal. Certain hard coated seeds pass through animal digestive tracts where they are softened by stomach acids before growing in a pile of rich manure.

By observing dispersal methods one can usually work out the normal habitat preferences and community relationships of plants. ‘Khaki-bos' and other similar plants with ‘springy' stems, when dry, normally require passing mammals to bend the stems and flick the seeds nearby from their little ‘pepper-pot' capsules. These plants have a relationship with large mammals. Edible fruit, similarly, have a relationship with birds and mammals. Fluffy, parachute-type seeds are adapted to, normally, open and windy areas.

They may use insects but are more often animal independent. Pods or fruit with ‘wings' are similarly adapted to wind dispersal, usually late in the season, when they are ‘ripe' and have fallen or been blown off. The ‘tumble weed' type designs are also adapted to wind dispersal. Edible fruit and pods normally have seeds adapted for distant dispersal through animal digestive systems. If they want to prevent this treatment they may be distasteful or sour so they are spat out after a short while before being swallowed.

Certain seeds require charring in occasional fires to release them from their hard covering. There are many plants with intricate dispersal methods involving specialised animal feeding processes and manipulations. All the burr-type seed pods are obviously designed for a relationship with hair-covered animals to which they can cling. Others have a sticky covering by which they adhere to animals with which they come into contact. Many species are able to disperse without any inter-relationships with climate or community.

An example are the explosive pods of certain plants that shoot the seeds just far enough to be free from competition for light from the adult canopy. Your time in the veld can be enhanced by observing the plant adaptations and their apparent relationships within their communities. Learn from them and choose wisely your own optimum ‘habitat and relationships' for personal development, success and contentment. Happiness is not a ‘noun' for which you can search - it is a ‘verb' which results from contentment.



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