GRASSLAND ECOLOGY

WORLD GRASSLANDS

NORTH AMERICAN GRASSLANDS REFLECT WEATHER PATTERNS

PRECIPITATION IS IMPORTANT

DIFFERENTGRASSLANDSWITHDIFFERENTPRECIPITATION

GRASSLAND NET PRIMARY PRODUCTION (NPP) DEPENDS ON MOISTURE

SOIL TYPES CAN BE IMPORTANT WHY?

SEASONALITY OF MOISTURE ALSO IMPORTANT

SEASONALITY LEADS TO DIFFERENT GRASS PHOTOSYNTHETIC PATHWAYS

NOT JUST WATER, MOISTUREAFFECTS NITROGEN AVAILABILITY

PRODUCTION AT BISON RANGE IS NITROGEN LIMITED Schmitz (1992) found that N - fertilization increased plant production more than water supplementation. Plant production depends on soil N availability (resin bags) at microsites. NITROGEN DEVIATION FROM CONTROL (mg/bag) BIOMASS DEVIATION FROM CONTROL (g-dry/cage) r = 0.64, N = 21, P < 0.002

GRASSLAND: LAND OF COMMON DISTURBANCE

ANNUAL VARIATION IN MOISTURE (great)

DRYNESS AND LIGHTNING

HERBIVORY

HERBIVORY CAN BE GREAT IN GRASSLANDS

BISON RANGE HERBIVORES 2.5 g/m g/m 2 Each unit of consumption = 1.25 – 1.67 units eaten (Pre-Columbian on Great Plains no more than 5 g/m 2 ) WHY?

TREATMENT PLANT BIOMASS (g/m 2 ) ADDED WATER NATURAL PRECIPITATION TRADITIONAL VIEW OF GRASSHOPPERS * * * *

GRASSHOPPERS AND THE NITROGEN CYCLE Drought Year (grasshoppers decrease plants by 43% - P < 0.03) Normal Precipitation Year (grasshoppers do not decrease plants - P < 0.5) LITTER POOL 2.2 g/m 2 LITTER POOL 1.7g/m 2 AVAILABLE SOIL NUTRIENT POOL 1.0 g/m 2 AVAILABLE SOIL NUTRIENT POOL 1.7 g/m g/m g/m g/m 2 FAST CYCLE 35% SLOW CYCLE 65% FAST CYCLE 50% SLOW CYCLE 50% 0.5 g/m g/m g/m 2 PLANTS (0.9 g/m 2 ) frass & carcasses PLANTS (1.5 g/m 2 ) frass & carcasses

TREATMENT PLANT – GROWING SEASON NITROGEN (mg/g of rexyn) A NITROGEN PERSPECTIVE FOR GRASSHOPPERS * * * * * * * *

DENIZENS OF THE SOIL DRIVE NUTRIENT DYNAMICS Change with plant spp. Change with herbivory Change with fire Change with drought Different microbes = different dynamics

VERY COMPLEX DYNAMICS

HUMAN DISTURBANCE (fire suppression, overgrazing, exotics)

NATIONAL BISON RANGE, OUR LABORATORY

MEASURING PRIMARY PRODUCTION CLIPPING TO MEASURE BIOMASS -- Must separate current year’s growth from past (how?) Why dry the vegetation? Timing, plot size, number of plots? SPECTRAL CHARACTERISTICS OF LIGHT REFLECTANCE – Why does vegetation look green? What wavelengths do chlorophyll absorb? Radiometer measures ratio of infrared to red (why?). What do you have to control for? How do you calibrate measures to biomass? Remote sensing (plane and satellite). Timing, area measured (height), number of areas?

MEASURING SPECIES COMPOSITION (bare ground) TOE POINT AND POINT FRAME – Incidence. What is missing? Timing and how many points? CLIPPING – Same issues as biomass measures. What does this consider? REMOTE SENSING – Different species absorb slightly different wavelengths. Calibration and sensitivity. Timing and how many points?

MEASURING HERBIVORY PLANT PERSPECTIVE (exclosures) – Measure primary production with and without herbivores. How large an area and how many areas? How to ensure adequate matching of exclosures and outside areas? Does the exclosure affect plant production? PLANT PERSPECTIVE (measure damage) – Absolute measure or index? How to calibrate to make it an absolute measure? What might you fail to consider? ANIMAL PERSPECTIVE (compute consumption) – How many herbivores and how much does each eat? Precision? What might you fail to consider? ANIMAL PERSPECTIVE (estimate abundance) – Index of abundance

MEASURING ABIOTIC FACTORS SOIL TYPES – Organic matter, sand, clay. SOIL MOISTURE AND COMPACTION – Conductance or actual moisture? Force to penetrate? Timing and number of sites? TEMPERATURE AND WIND – Why important? Timing? NUTRIENTS – Measure in soil? Problem? Capture from plants? Problem? Which nutrients? Timing?

MISCELLANEOUS SEED BANK – See what germinates. Problem? Flotation methods. Problem? SOIL MICROBES – Why important? Measure activity (in situ vs. in vitro)? Identify participants (molecular techniques)? CRYPTOPHYTES – Why important? Incidence and activity? FIRE AND DROUGHT – How to measure (frequency and intensity)?

TOUR OF BISON RANGE Purpose: To see what is there to help you in designing the two class projects.

FIRST PROJECT Problem: Compare two adjacent sites, one with cattle and the other without. Goal: Learn methods. Assess sampling intensity necessary to be confident in primary production, species composition and abiotic measures. Product: Single group presentation, including statistical analysis. Value: How much to sample at each site in the second exercise?

SECOND PROJECT Problem: Assess what might determine the presence of different plant communities at different sites. Goal: Learn about what creates different grasslands. How to sample to address a comparative community ecology study. Apply more advanced statistics. Product: Two group presentations (including statistical analysis). Can different communities be identified? How do communities differ? Value: Learn about comparative ecology and why plant communities may differ.