Response of Annual and Perennial Grass Growth, Energy Reserves and Fuels Accumulation to Climatic Variation

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1 Response of Annual and Perennial Grass Growth, Energy Reserves and Fuels Accumulation to Climatic Variation Brad Schultz Extension Educator University of Nevada Cooperative Extension Winnemucca, NV

2 Types of Range Plants: Grasses Annual small roots New plants - seed production Perennial large roots Population persists primarily from annual regrowth of existing plants - not seed production Seedlings replace recent deaths - comparatively few each year Management goal is to maintain the ability of existing plants to regrow new tillers each year from buds at base of plant

3 From NDSU EB-69 Seasonal Plant Growth Consumes Stored Energy Produces and Stores Energy for Future Needs

4 Where Does Spring Growth Originate Dormant buds Root crown Axillary buds on tillers on Perennial Grasses? Over-wintering tillers May or may not be green Soil temperature of degrees. Soluble carbohydrates Lower stems Root crowns Roots

5 Photosynthesis Allows Plants to complete their biological processes and ecological function Production of carbohydrates Structural Roots Leaves Stems Flowers/Seed Forage Energy storage for future needs Respiration (survival) during dormancy Growth initiation after dormancy breaks

6 Annual Growth Cycle For Perennial Grasses Break dormancy Initiate growth from buds in the spring Energy consumptive New green leaves produce carbohydrates Winter Dormancy Respiration in root crowns, lower part of tiller and roots Growth - Vegetative tillers Culm elongation Developing seed heads - Energy storage and biomass production Fall regrowth Existing tillers Axillary buds Takes energy that must be restored for following spring Or Reproduction Summer dormancy Respiration of buds consume energy

7 Stored Enegry (Soluble Carbohydrate Reserves) Primary Role Produce new tillers from buds or growing points when dormancy breaks Secondary Role New growth only when defoliation is severe Insufficient leaf area to meet plant needs Short-term and less important than for initiation of new growth

8 Changes in Soluble Carbohydrates Thurber s Needlegrass

9 Phenological Development Spp Yr Mar Ap May Jun Jul Aug Brte ,2 3, , Pose ,4 4, ,2 3,4 5 Pssp ,2 2,3 4 4, ,2,3 4 5 Feid ,3, Heco , Year Oct- Mar (mm) AMJ (mm) Total (mm) Mean = growth initiation 4= seed set and shatter 2= floral initiation 5 = cured 3= full flower Pitt and Wikeem 1990: JRM

10 Soluble Carbohydrates and Drought Drought generally reduces growth quicker than photosynthesis Cell production and enlargement largely ends, but leaves and stems remain green Lack of additional biomass accumulation Storage of energy reserves continues End result is high CHO concentrations and total pools of soluble carbohydrates and total pools

11 Axillary Buds and Drought From: Busso et al. 1989: Annals of Bot.

12 Functional Soil Moisture Pools Upper Winter (dormant season) and spring (growing season) precipitation usually replenish, sometimes frequently Root zone where nutrient uptake largely occurs Critical for growth of plants Lower/deeper Primarily recharged by dormant season precipitation Plant maintenance/seed production as water for abundant growth declines Photosynthesis at later phenology stages

13 Elko Precipitation Frequency Inches Year= Year= Year= Year=2013 Year= Frequency Inches Year= Year= Year= Year=2013 Year= April May Water Year (Oct-March) Precip Mean 5.71 Median Mean and median from

14 Root Distribution - Perennials Perennial grasses typically shallower than sagebrush Large grasses can penetrate > 1-m deep Smaller grasses (squirreltail, Sandberg) much shallower root systems all < 1-m deep Half or more of biomass typically in surface 10 inches of biomass almost one-third in surface 4 inches Shallower for POSE and similar species Most nutrients needed for growth in this depth zone

15 Canopy Cover and Precipitation Event Size From: Huxman et al Oecologia

16 Perennial Herbaceous Yield Dubois, Idaho Y= (July-March precip) For this site, across these years, July March (mostly winter) moisture was best predictor

17 Perennial Herbaceous Yield Integrated data across three locations Burns, Oregon; DER, Utah; and Dubois, Idaho. Used a precipitation index based on median crop year Sept 1 to June 30 From: Sneva and Hyder JRM.

18 Perennial Herbaceous Yield

19 Hutchings and Stewart USDA Circular No 925. Do Consecutive Dry Years Affect Biomass Recovery?

20 Montana Mountains in a Dry Year In 2014: Oct-March precipitation was 9.6 in vs an avg of 15.6 AMJ precipitation was 2.9 inches vs mean of 4.9 inches

21 Perennial Herbaceous Production Considerable year-to-year variation in net aboveground phytomass accumulation in response to varying climate There is a good, statistically significant correlation between biomass accumulation and crop year precipitation Species richness had an even stronger correlation with biomass production Increase richness, increase probability that roots have good distribution and density throughout entire soil profile (shallow and deep moisture pools) ensuring more complete water extraction From: West and Yorks West. N. Am. Nat. (Idaho Kapukas data)

22 Biomass Prediction Equations Many developed Usually on data sets of 6-13 years May not include all of the precipitation cycles that exist total amount, distribution, event intensity, interval between events Probably don t include all of the temperature cycles that exist and interact with precipitation Accuracy within a year may be questionable, but reliability depends on intended use All have established the general relationship that as winter and growing season precipitation increase, biomass production of perennial grasses increases Amount of increase is highly variable

23 Yearly Production vs Total Biomass Herbaceous and shrub fuel components on a Wyoming sagebrush site in south-central Washington 8.5 inch precipitation zone with about 5-8% sagebrush cover Rickard et al Shrub-steppe: balance and change in a semi-arid terrestrial ecosystem

24 Annual Production on Sagebrush Sites in Northern and Central NV

25 Annual Grasses Cool season species Fall or early spring germination Fall germination/growth is excellent with about 2 inches of moisture Spring germination Height and yield both lower Dry fall and spring Height about 3 inches or less Warm and rainy fall and spring Height often exceeds 24 inches

26 Annual Grasses - Phenology Rapid phenological development (less biomass production) warmer temperatures, less precipitation and less cloud cover Less cured fuels but for a longer period Slower phenological development (more biomass) Cooler, but not cold, temperatures, average to greater precipitation and cloudy skies More cured fuels available for shorter period

27 Annual Grasses Cheatgrass can have multiple sets of inflorescences in a single growing season increases standing biomass/fuel Timing of precipitation is key Abundant, late moisture as first seeds set but plants are still alive with active buds at base of tillers Vernalization affects flowering and seed production Fall germinated plants usually have larger more productive panicles than spring germinated plants Some observation that mid and late spring germinants do not produce flowers and seed Abundant potential fuel

28 Annual Grasses Seed production (potential new plants) ranges from several pounds to about 450 pounds per acre 150,000 seeds per pound Over 99% viable at maturity Germination can begin one day after maturity, can exceed 50 % of viable seed after two days, and be nearly complete within five days Fall precipitation (less overwinter seed loss) pattern can dramatically affect population dynamics for coming year

29 Annual Grasses Annual production can vary by ten-fold, perhaps more, on any given site Yields in excess of 4,000 lbs/ac have been cited Roots generally shallow but some can reach 3 ft or deeper May complete lifecycle in weeks (dry conditions) or many months (wet and cooler years)

30 Annual Grasses Optimum density for herbage and seed yield roughly 50 plants per ft 2 At 5 to 200 plant per ft 2 dried biomass can range from 3,500 to 5,300 lbs/ac Fewer plants typically result in larger plants, especially more culms

31 Cheatgrass Production Cheatgrass produced = (April precipitation) (April mean temp) (February mean temperature) (May mean temperature) +1.5 (May precipitation) R 2 =0.99

32 Precipitation Variability

33 Decomposition Standing dead < surface litter < soil organic matter Particle size Large particles slower than small particles Plant chemistry High C:N ratio slower microbial breakdown More lignin slower decomposition

34 Standing dead Decomposition Wetting and drying cycles, and wind physical breakdown Leaching water soluble nutrients to soil Shredding and ingestion by insects, small mammals Bacterial and fungal degradation of tissues Consumption by larger mammals quickest breakdown besides fire Surface litter Soil microbes Moist soil frequency/size of ppt events important Warm temperatures

35 Decomposition Significant amount of standing dead after a wet year, let alone multiple wet years especially cheatgrass Can persist several years Snowfall is insufficient to knock the plants to the ground and/or few animals to consume the material As surface litter Slow decomposition 19-23% of cheatgrass lost after one year (Oct-Oct) at both low and high elevations (ARTR Wy community in Washington) Leads to litter build up and fuel continuity Increases risk of medusahead establishment Spring moisture pulses (amount and frequency) probably have large influence on decomposition rate Protracted moisture inputs as temperature warms, results in more rapid decomposition Cool and dry spring results in slower and shorter period of decomposition potential fuel accumulation.

36 Role of Multi-Year Events Not well documented Back to back wet years increase total biomass, especially standing biomass for cheatgrass Inter-annual variability based on temperatures and timing of precipitation Probably greater C:N ratios of litter which may prolong period of decomposition, increasing fuel loads Consecutive dry years Decrease cheatgrass production and seed development Fewer plants next wet year but typically larger; thus, rapid fuel accumulation Perennials Wet-Dry alternation Some evidence from other areas of lag affect Carry over from wet year minimizes effect of dry year probably about the number of viable buds

37 Questions?

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39 Do Not Forget the Roots Out of sight does not mean out of mind Leaf area produces structural carbohydrates used to develop roots Roots gather the nutrients and water that the leaves use to produce carbohydrates Productive plants must have roots and shoots in balance

40 Root and Shoot Balance Permanent decline in leaf area = fewer roots Fewer roots = less leaf biomass