Locoweed is Flourishing This year

Locoweed is flourishing this year

Grass and shrub growth and grazing response This presentation is a detailed look at the structure of grass plants (and to a lesser extent shrubs), how they grow, and why this is important to range managers. In order to manage grazing on large landscapes range managers need to know how individual plants respond to grazing and climate/weather and interact with neighboring plants in that process. Grass and shrub growth and grazing response Range 101 Sarah Noelle George Ruyle

outline Variability in life forms Grass growth and development Morphology and Growth Growing points Defoliation effects Drought and Grazing Shrub growth and development

Range plant life forms Grasses Forbs Shrubs Trees Grasses, forbs, shrubs and trees are the predominant plant life forms on rangelands. Each has distinctive morphology (structure) and growth and each respond differently to drought and grazing.

Range plant life forms Grasses Annual vs. perennial Cool season vs. warm season Bunchgrass vs. sodgrass If this wasn’t enough complexity by itself, even within the grass family there is a diversity of life forms. For example, there are annual grasses, which grow from seed and complete their life cycle in one growing season. There are perennial grasses that live for many years. There are cool season grasses that begin their growth early in the spring, flower and produce seeds before hot summer weather sets in. And there are warm season grasses that begin their surge of annual growth later in the summer after the soil warms to at least 60 degrees F and summer rains begin. Grasses can be further classified according to growth stature and form. There are tall, mid and short grasses in addition to bunch grasses and sod-forming grasses. Each responds differently to grazing and drought.

blue grama

Grass growth and development Grass growth processes are directly related to plant structure and this can explain plant response to grazing Grass growth and development Morphology and Growth (Why is this important? They are the primary factors controlling plant response to grazing)   How grasses grow is directly related to how they respond to grazing, and the removal of plant tissue through grazing influences how grasses grow. To understand the process of grass growth requires knowledge of their morphology, or the study of the structure of grasses.

Grass growth A grass plant is a collection of Tillers A grass plant is really a group of individual shoots, called tillers that originate from the root crown at the base of the plant.

Grass growth A Tiller is a series of phytomers The grass tiller consists of a series of units (phytomers) each made up of a leaf blade and sheath, collar, ligule and axillary bud. Grass flowers form at the top of each reproductive tiller. Tillers in grasses are directly comparable to branches in a shrub or tree.

Grass morphology study of the structure of grasses Phytomer - basic unit of a grass plant Leaf (sheath and blade), a node, an axillary bud, and an internode A group of phytomers is a tiller A plant is a group of tillers Review phytomer (leaf blade and sheath, collar, ligule and axillary bud), tiller a series of phytomers and plant a collection of tillers

Grass growth Plant growth is concentrated in areas called meristems. In grasses, these are located at two locations: Near the soil surface at the base of the plant (buds/apical meristems) The base of leaf blades (intercalary meristems) All plants have special restricted areas of growth (growth only occurs is certain places and ways) which are established at the time of early embryo development. New growth in grasses occurs in three different ways, from two different meristems or zones of growth. New tillers grow from axillary buds at the base of the plant or at tiller nodes New leaves grow from apical meristems inside the stems Secondary zones of growth occur from intercalary meristems at the base of the internode, sheath and blade

Grass growth Intercalary meristems drive growth at leaf bases Talk about the second and least productive growth first; intercalary meristems are secondary zones of growth which occur at the base of the internode, sheath and blade. Are not responsible for production of lots of grass biomass, but are likely very responsible for improving survival when defoliation is extreme. Their presence explains why golf courses in the low deserts may mow their turf 3 or more times each week.

New tillers arise from Buds at the base of each growing During the growing season, new tillers of a grass plant are produced from buds. The timing of tiller initiation and elongation varies among species. The majority of tillers are initiated in the spring and fall. New tillers arise from the axillary buds of older tillers. New tillers usually originate at the base of the plant, (or in some grass species from axillary buds at stem nodes). Each new tiller will put down adventitious roots within a few days and are then largely independent of the mother tiller.

= Tiller recruitment

Grass growth Buds can also be produced on aerial parts of tillers In many grasses (BOER here), buds (apical meristems) can be produced at many locations along a tiller. And individual tillers--basal or aerial--can develop roots and become independent plants.

New leaves are produced by apical meristems (buds) in each tiller Once they start to grow, each new leaf unit (phytomer) develops from the apical meristem in that shoot. The apical meristem is located inside the shoot and this is where new leaves (most of the vegetative growth; forage) on a grass tiller arise. On each tiller, the youngest leaf is at the top and the oldest is at the bottom. As the tiller grows, the apical meristem may remain near the ground or become elevated when internodes elongate. The location of the apical meristem is important to how the grass responds to defoliation

Range plant growth Location of meristems depends on season Early in the growing season – close to the ground and protected Later in the growing season – elevate and are subject to removal Apical Meristem Axillary Buds

Grass growth New leaves continue to be produced as long as growing conditions are favorable, until the apical meristem becomes reproductive or is removed. Vegetative growth will continue to be produced as long as growing conditions are favorable, but not after the apical meristem becomes reproductive (starts sending up a flowering stalk) or is removed through grazing or by other means. Once a tiller starts a seed stalk or if the apical meristem is removed no new leaves will grow on that shoot. New leaves can only be produced from another basal bud producing a new shoot or tiller.

Grass growth Once the apical meristem is removed new growth must occur through the initiation and elongation of new tillers. When a grass is grazed during the growing season, the quickest new growth is from intercalary meristems but this is also the least significant amount of regrowth. New leaf growth, which can produce significant biomass, occurs from the apical meristems if they have not been grazed. If the apical meristem has been removed the plant can only produce new growth from the development of new tillers. New tiller growth is a slower process than new leaf growth on already existing tillers. This is the key to how grass plants produce growth.

Grass growth Explains importance of controlling grazing Apical meristems (from buds) drive leaf growth Majority of shoot yield is produced from these meristems Explains importance of controlling grazing

Effects of grazing depend upon: Intensity of defoliation Frequency of defoliation Season of use Growing conditions Competition 1. Intensity of defoliation refers to how much of the plant remains after defoliation, particularly relative is whether or not the apical meristem is removed.   2. Frequency of defoliation. The number of times a grass plant is defoliated over the growing season is important because it determines how long the plant has to recover between subsequent defoliations.    3. The third factor is season of use. The timing of grazing, corresponding to the growth stage of the grass influences the response of the plant. Grazing during the dormant season has the least effect because all apical meristems are at the root crown. Heavy grazing during dormancy can influence the survival of axillary buds however, which may impact production the following growing season. Grazing when the apical meristem is elevated can slow leaf recovery because regrowth is confined to new tillering. Internode elongation elevates tiller apical meristems. In grazing resistant grasses this doesn’t occur until the tiller starts to become reproductive, after which no new leaves are produced anyway. Species like Kentucky bluegrass and blue grama wait to elevate meristems while western wheatgrass culms elongate early. Sideoats grama is intermediate. Grazing during early flowering is most detrimental to subsequent production. Grazing early in the growing season can be detrimental if adequate rests are not scheduled to allow grazed plants to produce new leaves and additional tillers, but by itself, early spring grazing is not particularly detrimental to subsequent plant growth. 4. Growing conditions also influence response to defoliation. Plants withstand defoliation best when soil moisture and fertility are high. Drought or other environmental stresses will decrease the amount of new leaf and tiller production following defoliation, which can hasten plant death. If growing conditions are favorable defoliation can actually stimulate growth of axillary shoots and rapidly offset the initial loss of tissue. 5. Competition from surrounding plants is important to the recovery potential of defoliated plants. Plants can withstand clipping better and recover faster if neighboring plants are also defoliated. However, most large herbivores, such as cattle or elk, selectively graze grasses, hence; some plants will be grazed while others will remain ungrazed. Species grazed less severely, capable of growing more rapidly following defoliation, or a combination of both realizes a competitive advantage within a plant community.

Drought impacts Drought can influence grass production in two primary ways: reducing the number of active axillary buds slowing or stopping growth in developing tillers

Winter drought Influences the number of tillers that will be initiated in the spring Tiller initiation and elongation in spring is influenced by bud survival over winter

Summer drought Influences the growth on individual tillers and subsequent tiller recruitment Forage production during summer is influenced by tiller development and tiller recruitment from axillary buds during the growing season

Management Implications To condition plant communities for desired change, plants should not be defoliated during critical periods of their life cycle year after year. Because animal preferences cause heterogeneous plant use patterns, sufficient time between defoliations is needed for preferred plants to recover sufficiently to maintain themselves and reproduce.

Management Implications Adequate levels of recovery between defoliations for individual plants generally requires that they go through their rapid growth phase and elongation of the apical meristem, or even set seed and germinate, depending upon management goals. Because of the inherent variability of precipitation on rangelands, achieving adequate recovery will require adaptive management that includes variable recovery periods depending on weather, level of defoliation and timing of defoliation.

Shrub growth How shrubs grow is directly related to their response to grazing (browsing) New growth originates from meristems Apical – always terminal on the stem Removal stops new growth on that stem Lateral – what makes stems wide Axillary buds – at the nodes

Apical meristem Leaf axil (with axillary meristem)

Shrub growth Growth from buds in the canopy (sub- apical) controls production after browsing Growth from these buds is dependent on apical dominance

Management implications Because apical meristems are easily removed by browsing, shrub production can be reduced with heavy use. However, after apical meristems are removed, many shrubs can branch from axillary buds or short shoots transformed to long shoots. With moderate use growth from lateral axillary buds and apical meristems protected down in the canopy may compensate to replace grazed biomass.

Management implications Growth periods may be short, irregular and infrequent (for example jojoba experienced the majority of its growth during a 2-year study in March and May of one year) Grazing management should include periodic rest during growth periods. This needs to be adaptive because you don’t know when it will occur.

Management implications Because utilization of current year’s growth of shrugs is difficult to measure, a practical alternative is to adjust grazing based on measurements of shrub size over many years Manage for maintaining or gradually increasing shrub size, which you evaluate through a monitoring program