Source: South Dakota State University
Author: Kaylee Wheeler, SDSU Extension Range Field Specialist
Additional Authors: Alexander “Sandy” Smart
Understanding Plant Recovery
When defoliation occurs, regardless of how it happened (haying, hail damage, grazing, etcetera) it is essential to allow the grasses to fully recover before defoliating again. Animals should be removed until recovery occurs. Pasture recovery depends on: 1) the extent of damage, 2) the growth stage when damage occurred, and 3) the subsequent growing conditions for the remainder of the growing season.
Figure 2 depicts the effects of the extent of defoliation on plant recovery. When defoliation is severe enough that growing points and most of the leaf area are removed, it must rely entirely on energy from roots and basal buds to regrow. As a result, the plant takes longer to recover and root mass is diminished (Plant A).
Figure 3 depicts the effects of defoliation timing on biomass production in western South Dakota (Smart et al., 2012). The plots were primarily made up of cool-season midgrasses (for example, western wheatgrass, green needlegrass, prairie junegrass) and were clipped in the middle of each month for three consecutive years. These grasses were most harmed by defoliation when they were clipped in mid-June, because they were in the rapid stem elongation phase (or boot stage) and the key meristems (or growing points) were removed.
In contrast, earlier defoliation (May) was much less harmful, because the growing points remained intact and much of the growing season remained for recovery to occur. Later defoliation (July or August) also removed the growing points. However, the grasses would have all set seed by then and completed their life cycle. Thus, heavier defoliation after plants have headed out was less harmful on the following growing season’s production.
In a cool-season dominated plant community, like western South Dakota, most of the prime growing season conditions (higher precipitation, cool temperatures, and an increasing day length) occur before July 1. For producers with weather-damaged pastures from recent storms, it is likely that decent recovery can occur with proper autumn growth conditions. Thus, we wouldn’t expect a lot of regrowth in a pasture until cooler and wetter conditions arrive again in autumn. When hail damage is combined with dry conditions, regrowth may not happen until moisture returns.
However, in autumn, cool-season grasses are preparing for dormancy and bud formation of next year’s shoots. So, you should be extra careful not to overgraze in autumn and interfere with carbohydrate storage in roots, stem bases, rhizomes, and the formation of buds. In some cases, grazing should be completely avoided until the next growing season to protect pasture integrity.
Extreme and unexpected weather is a part of life for South Dakota. It is not ‘if’ it occurs, but ‘when’ it occurs. Consider the ways that your operation can adjust to be able to weather the storms.
