Spring Grazing Cuts Native Range Yield

Article Abstract
Cathie Erichsen Arychuk, P.Ag.
Bison Production Specialist
AAFRD, Fairview

Summary

Spring is a critical time for growth and food production in plants on native rangelands.  Spring grazing management will enhance long term forage production on these pastures.

Spring Grazing Cuts Native Range Yield

 Early spring grazing often damages native rangelands.  Spring is a critical time for range plants.  Plants require food for maintenance and growth.  They make their food by photosynthesis, a process that converts energy from the sun into simple sugars the plant can use.  Photosynthesis occurs in the green leaves and stems of the plant, so the size of the plant and the amount of green leaf determines how much food it produces.

Perennial plants store part of the food made each year for future use.  Native grasses store food reserves in the stem bases and roots.  These reserves feed the plants when they are not making food.  As much as 75% of the plant's reserve is used to produce 10% of the new leaf growth in the spring.  Food reserves are lowest when the shoot is half grown.  Grazing at this time is very hard on the plant.  Once the plant is larger, and actively growing, it begins storing food again and tolerates more grazing. 

 The plant stops using its stored food reserves and begins to store energy when it is about half grown.  If the plant is grazed lightly now, enough leaf area remains to produce food for the plant.  By the time the plant is 90% grown (flowering) it has stored half the energy it needs.  When it is full grown (ripe seeds) it has stored nearly all the food reserves required.  These reserves continue to accumulate slowly while the leaves remain green.  Then reserves slowly decline during dormancy.

 Removing leaves any time during the growing season reduces the amount of food made and stored by the plant, damaging its ability to regrow next year.  Fortunately native grasses have adapted to survive some summer grazing.  About 55% of the green leaf can be removed from half-grown native grasses without reducing the future growth of the plant.  The exact amount will vary with grass species.

When is it safe to start grazing native range?  Allow mixed prairie species like needle and thread, blue grama grass, and western wheatgrass 3 to 4" of leaf growth before grazing.  Rough fescue pastures should be left until the leaves are 8" long.  A rule of thumb is that when the buffalo bean is blooming, mixed prairie range is ready to graze.  When the shooting star flowers, rough fescue pastures are ready to graze.

Deferred grazing, where native pastures are not grazed during the critical spring period helps to maintain healthier, more productive plants, and better range condition.  This allows higher stocking rates.  Agriculture Canada research suggests that for every day of delayed grazing in the spring, you will get an additional two to three days of grazing at the end of the season.

To help get through this early spring period, seeded tame pastures come in handy.  Grasses like crested wheat grass, intermediate wheatgrass, and bromegrass grow earlier than the native grasses do, and are more tolerant of grazing in the spring.  Use these pastures in early spring, allowing the native range to rest.  If you have no tame pastures,  a careful deferred rotational grazing system on native pastures can reduce spring damage.