Chapter 5 Plant Growth and Development Rangeland

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Ecology and Management of Annual Rangelands, Figure 5 2 True grasses left sedges middle and rushes right. Table 5 1 Numerical stage of maturity used,to predict crude protein crude fiber. phosphorus and calcium content of annual,grasses filaree and bur clover George et al. Figure 5 3 Perennial herbaceous plants,include grasses and forbs and woody plants. include shrubs and trees,Life Cycles,Phenology is the progression of periodic plant.
life cycle events and is influenced by seasonal,and inter annual variations in weather. Examples of life cycle events include,germination seedling emergence flowering and. seed set A list of phenological stages normally,includes vegetative flowering and dormancy. stages for perennials Table 5 1 is a list of 12,phenological stages or stages of maturity that. have been used to study seasonal changes in,forage quality of annual grasses George and.
Ecology and Management of Annual Rangelands, Each year annual plants germinate become with tillers stolons and rhizomes Short lived. established and progress through vegetative and perennials last 3 5 years whereas properly. reproductive stages Figure 5 4 During the managed long lived perennials can survive much. winter when moisture is adequate but longer Woody perennials can live for decades. temperatures are low photosynthesis and plant or even centuries In temperate regions many. growth are slow With the arrival of spring perennial plants enter dormancy to survive. photosynthesis and plant growth rates increase freezing winter temperatures In Mediterranean. As soil moisture is depleted plants begin to dry regions where there is a pronounced summer dry. and die becoming litter Variation in seasonal season and mild winter temperatures perennial. temperatures and precipitation influence the grasses and forbs may enter a dry season. seasonality of plant growth dormancy regrowing with the fall rains Much. of the aboveground biomass of perennial grasses,and forbs die as the cold or dry season. approaches The remainder of the aboveground,and near surface portions of these plants enter a. dormant phase until the cold or dry season is,over During cold dormancy winter moisture. is stored in the soil during rainy periods and,snow melt As spring approaches and.
temperatures increase these plants use this soil,moisture to begin growth These perennial plants. will remain vegetative for several weeks but will,eventually flower and develop seeds As the. growing season progresses seed is set and,eventually dispersed With cooling. temperatures the plants begin to enter dormancy,and much of the aboveground biomass dies. Most perennial grasses and forbs in the western,U S follow this winter dormancy life cycle.
Seed Banks,When thinking about seed banks in California s. annual rangelands it is important to make a,distinction between short term i e transient. seed banks and long term i e persistent seed, Figure 5 4 Annual and perennial plant life banks Transient seed banks refer to the seeds. that spend a short time in the soil usually the,time between their production and dispersal in. Perennial plants live for more than one year and late spring and their subsequent germination. re grow each year Figure 5 4 Therefore you with the onset of fall rain In contrast persistent. will be managing the same plant year after year seed banks refer to seeds that remain in the soil. Perennials reproduce from seed or vegetatively for multiple years in fact some seeds can. Ecology and Management of Annual Rangelands, remain viable in the soil for many decades The described below in the Germination section.
degree of difference between the species Seed longevity may explain the dominance of. composition of the aboveground grassland legumes in persistent seed banks in grasslands. community and the community hidden Hull 1973 compared germination rates for a. underground in the seed bank can be quite number of North American rangeland species. striking and varies among species and grassland that had been stored in unheated sheds for 14 to. types 41 years Seeds of legumes retained their,viability longer and had much higher rates of. Although the relative contribution of different germination than any of the grass and forb. grassland species to transient and persistent seed species tested regardless of length of storage. banks can vary widely there are some general, trends Grasses although they are often the Spatial variation in the longevity of soil seed. dominant component of transient seed banks are banks can depend on the frequency of soil. much less likely to contribute to persistent seed disturbance and the formation of gaps in both. banks The seed of many grass species plant canopy and litter layers Germination. germinates in the year of its production and cueing represents the capacity of a seed to detect. rarely survives more than a year or two in the a potential opening for establishment and may. soil Young et al 1981 Even when focusing involve a number of physical cues such as light. specifically on transient seed banks the relative quality or soil temperature fluctuations For. contribution of annual and perennial grasses to example Rice 1985 reported that diurnal. these short lived seed banks can be very temperature variation among three types of. different A study of a mixed annual and microsites in annual grassland under grass litter. perennial Stipa sp grassland in the Central bare soil and gopher mounds significantly. Valley of California found that even in areas affected rates of dormancy release in broad. dominated by perennial grass cover there were leaved filaree Erodium botrys Microsite. essentially no perennial seeds in the soil seed variation in soil temperature germination cues in. bank In contrast annual grasses had a well this hard seeded forb might have a strong. developed transient seed bank even in areas influence on seed bank depletion and longevity. where they were a very minor component by affecting the loss rate due to germination. aboveground Major and Pyott 1966 Compared, to grasses forbs have a tendency to produce a Germination. more persistent seed bank A five year study in a Seed germination Figure 5 5 initiates a series. California annual grassland indicated that seed of changes that ultimately lead to a mature plant. carry over rates a measure of seed bank and reproduction of the species Favorable. persistence were more than 10 times greater for temperature and moisture are essential for. forb species than annual grasses Young et al successful development of the seedling during. 1981 Among forbs legumes frequently have the first critical stages of growth Rapid. the greatest rates of seed carryover and thus can germination and growth results in high demand. often form very long lived persistent seed for light moisture nutrients and other plant. banks Seed coat impermeability to water hard growth requirements. seed is a form of persistent seed dormancy that,Fully developed seeds contain an embryo and. is widespread in legumes and is further,food reserves wrapped in a seed coat Under.
Ecology and Management of Annual Rangelands,Figure 5 5 For an. animation of the germination,process select Germination. Process after selecting the,link to How Grass Grows. Ervin et al 2004, favorable conditions the seed begins to exhausted At this stage photosynthesis provides. germinate and the embryonic tissues resume the energy needed for continued growth and the. growth developing towards a seedling Some seedling now requires a continuous supply of. plants produce varying numbers of seeds that water nutrients and light When a seed. lack embryos these are called empty seeds germinates the new seedling leaf grows toward. which never germinate light This is called phototropism. While water is required temperature oxygen Oxygen is required for respiration during. and light quality may also influence germination Oxygen is found in soil pore. germination Mature seeds are often extremely spaces However if a seed is buried too deeply. dry and need to take in significant amounts of within the soil or the soil is waterlogged the. water relative to the seed dry weight before seed can be oxygen starved Some seeds have. cellular metabolism and growth can resume The impermeable seed coats that prevent oxygen. uptake of water by seeds is called imbibition from entering the seed causing a type of. which leads to the swelling and the breaking of physical dormancy that is broken when the seed. the seed coat When seeds are formed most coat is worn away enough to allow gas exchange. plants store a food reserve with the seed such as and water uptake from the environment Hard. starch proteins or oils This food reserve seed produced by some legumes such as rose. provides nourishment to the growing embryo clover can allow seed to survive in the soil for. When the seed imbibes water hydrolytic more than 20 years Temperature also influences. enzymes are activated which break down these germination Seeds from different species and. stored food resources into metabolically useful even seeds from the same plant typically can. chemicals After the seedling emerges from the germinate over a wide range of temperatures. seed coat and starts growing roots and leaves Seeds often have a temperature range within. the seedling s food reserves are typically which they will germinate and they will not do. Ecology and Management of Annual Rangelands, so above or below this range Many seeds While there is no single attribute that influences.
germinate at temperatures slightly above room seedling vigor and establishment seed size and. temperature 60 75 F 16 24 C while others weight rapid germination seed age high levels. germinate just above freezing or germinate only of biochemical and physiological activity and. in response to alternating warm and cool rate of root and shoot growth are all potential. temperatures Some seeds germinate when the indicators of seedling vigor Rapid root growth. soil is cool 28 40 F 2 4 C while others is fundamental to establishment and. germinate when the soil is warm 76 90 F 24 32 development of annual rangeland plants. C Individual plants and species may gain an,advantage over competitors if they are able to. Some seeds require exposure to cold maintain both rapid root and top growth In. temperatures vernalization to break dormancy California annual grasses frequently exhibit. Seeds in a dormant state will not germinate even greater root growth rates than native perennial. if conditions are favorable Some seeds will only grasses Aanderud et al 2003 This is one of. germinate following hot weather and others the reasons why native perennial grass. must be exposed to high temperatures during a establishment is so difficult in California s. forest fire which cracks the seed coat annual rangelands. Germination in many seeds especially small, seeds is regulated by light Many seeds Seasonal growth rates. including species found in forest settings will Growth rates in the annual rangelands following. not germinate until an opening in the canopy germination can be rapid if temperatures are. allows sufficient light for seedling growth Some warm but can be slow with cold temperatures. seeds need to pass through an animal s digestive Table 5 2 Figure 5 6 The average. tract to weaken the seed coat to allow the germination date at the UC Sierra Foothill. seedling to emerge Research and Extension Center UC SFREC in. Yuba County California is October 20 and the,Variability in the germination rate exists. average standing crop on December 1 is 347 lbs,between and within species Seed size has been. acre 389 kg ha or less than 12 percent of peak,shown to be a critical factor for promoting.
standing crop in May During the winter,seedling vigor for some plants For some. growth is slow such that the average standing,legumes and other forbs seed coat hardness or. crop at UC SFREC on March 1 is only about,impermeability often retards germination but. 700 lbs acre 784 kg ha which is less than 25,spreads germination over years which is a. percent of average standing crop of 2984,survival advantage for the species In general.
lbs acre 3342 kg ha on May 1 Thus daily,germination is reduced with increasing seed age. growth rates typically average about 5, Seedling Establishment lbs acre day 5 6 kg ha day from October 20 to. March 1 During rapid spring growth the,With emergence of the radical during. germination seedling establishment begins and average growth rate is about 37 lbs acre day. may not be considered successful until an 41 4 kg ha day resulting in an average standing. adequate root system and leaf area has crop on May 1 of 2942 lbs acre 3295 kg ha. On average little production occurs during May,developed to sustain growth McKell 1972. at UC SFREC resulting in only small differences,Ecology and Management of Annual Rangelands.
Table 5 2 Thirty one years of monthly standing crop estimates lbs a for annual rangeland at the. University of California Sierra Foothill Research and Information Center. Germinating, Growing Residue Standing Crop lbs acre Peak Standing Crop. lbs a Date Dec 1 Jan 1 Feb 1 Mar 1 Apr 1 May 1 lbs a Date of Mean. 1979 80 10 20 500 1300 1670 56,1980 81 11 30 350 1385 2560 85. 1981 82 9 24 550 1357 2770 92,1982 83 9 17 800 2142 4630 154. Chapter 5 Plant Growth and Development Melvin George and Kevin Rice Introduction The annual plants that dominate the annual grasslands and the understory of the oak woodlands have different life cycles from perennials which dominate most of the world s rangelands Focusing on California s annual dominated rangelands in the Coast Range and the foothills of the Sierra Nevada Mountains

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