Journal of the Oklahoma Native Plant Society, Volume 2, Number 1, December 2002


82 Oklahoma Native Plant Record 
Volume 2, Number 1, December 2002 

Editorial 

Water, Soil, and Plant Diversity in Oklahoma 
Sheila Strawn 

In 1963 John Shed and William Penfound 
did a study on legume distribution. They found a 
general relationship between soils and vegetation 
types. Sand deposits generally became forests 
while limestone and clay deposits generally 
became prairie (Proc. Okla. Acad. Sci. 44:2-6). 
But soil-to-plant relationships are not always that 
simple. Tropographic effects such as slope and 
solar and wind exposure as well as precipitation 
rates can override the characteristics of the 
various soils making it difficult to determine 
specific soil types based on vegetation. 

In 1964 Dr. Paul Buck wrote "Relationships 
of the Woody Vegetation of the Wichita 
Mountains Wildlife Refuge to Geological 
Formations and Soil Types (Ecology 45:2). He 
had found that when it rains, soil type and 
topographic features, together, control the 
movement of water. Granite formations at the 
Refuge erode to make a cobbly soil at the foot of 
the mountains that drains quickly, making it 
difficult for some plants to become established. 
Different amounts and patterns of precipitation 
can also interact with soil type producing 
gradients of moisture availability for plants with 
different moisture requirements. Some species 
can live only at certain positions across the 
moisture gradient. Others are more tolerant of 
variable moisture availability. Sugar Maple is 
able to dominate some of the more mesic, cobbly 
patches near streams, while Black-jack Oak 
dominates the less mesic, cobbly upland patches 
in this newly formed soil. 

In places like the Carolinas bountiful 
precipitation on limestone soils can actually make 
soil very poor in nutrients. Organic acids from the 
abundant vegetation react with calcium, sodium, 
and magnesium ions in the soil The abundant 
rainfall then leaches them from the soil and 
washes them into the groundwater below the 
reach of roots. However, this is not usually the 
case in Oklahoma. Oklahoma actually loses more 
water to evaporation than it gets in precipitation. 
Rivers and groundwater from the Rocky 
Mountains make up the difference. Here, 

precipitation is not sufficient to leach all the 
minerals from our limestone soils. Dense stands 
of forbs and grasses grow in the Tallgrass Prairie 
Preserve where these mineral-rich formations are 
not leached by excess precipitation.  

Southwest of the Refuge the precipitation 
rate is so low that much of the water evaporates 
before it gets very deep into the soil. In those 
soils, the calcium ions accumulate at the lowest 
level of water penetration, sometimes, just inches 
from the surface and form a calcium carbonate. 
Known as "caliche", this layer restricts root 
growth, so fewer species grow on caliche. 
Gypswn, mostly calcium sulfate, was formed long 
ago in a similar manner when the seawater 
evaporated from the plains. In Oklahoma 
Mesquite and mixed grass are associated with 
“gyp soil”. 

Soil and water relations alone do not explain 
why plants grow where they do in Oklahoma. 
Other variables like humus, micro-organisms, 
nematodes, grazing animals, fire, ice, windstorms, 
and human influence all work on a smaller scale 
and are responsible for much of the physical 
heterogeneity and resultant biodiversity. This 
small-scale heterogeneity is what actually 
accounts for our having more species than other 
continental United States, except California, 
Florida, and Texas. 

Ironically, plant diversity in Oklahoma has 
been woefully understudied. With the promise of 
improved medical treatments based on genetic 
engineering, we need to know where species are 
in Oklahoma that might be beneficial. We are, 
therefore, obliged to preserve as much of our 
diversity as we can. But we will need to save it on 
the landscape level, because it is our diverse 
landscape that supports our diverse biota. Indeed, 
researching and preservmg Oklahoma's 
landscape-to-species relationships is worth 
researching and preserving twice as much 
elsewhere. 

ONPS 
Strawn, S.
https://doi.org/10.22488/okstate.17.100015