RNR 433 midterm exam

what is biogeochemical cycling?

exchange of nutrients within an ecosystem

what are the two main sources for carbon in the carbon cycle?

fossil fuel and industry (biggest source) and land use change (replacing forests with agricultural fields) (smaller source)

what are the main sinks for carbon in the carbon cycle?

atmospheric (largest sink), land and ocean sinks (half n half)

ocean sink = ocean acidification

the earth radiates what type of radiation?

infra-red (long wavelength, lower energy)

the sun radiates what type of radition?

ultraviolet and visible (short wavelength, high energy)

greenhouse gases absorb what?

absorb infra-red radiation

list the type of forests from most biomass to least

tropical forests (most)

boreal (middle)

temperate and subtropical (least but tied with boreal)

how large of an area is occupied by boreal forests?

where are boreal forests found?

Russia, Canada, China, Japan,

what type of climate are typical of boreal forests?

what are the main characteristics of boreal forests?

-low tree diversity (mostly coniferous (spruce) and broadleaf deciduous trees (birch and aspen))

-relatively low productivity

-lots of variation

-rich in nonvascular plants (ferns and mosses and bryophytes) which contribute 20-50% of aboveground NPP

-high spatial heterogeneity (harsh changes in forest composition affected by fire, soil temperature and soil moisture, and microclimate)

describe the composition of boreal forests from north to south

(north most) forested tundra, open coniferous (lichen woodlands), closed coniferous, mixed coniferous broadleaf (south most)

how does the amount of carbon stored in boreal forests compare to carbon stored in other forests?

boreal forests have the most carbon stored

why is there so much carbon in boreal forests?

climate creates soil conditions that promote organic matter accumulation and that litter input decomposes slowly (esp moss)

what types of soils are found in boreal forests?

gelisols (permafrost at or near surface), histosols, and spodosols (upland, well-drained)

cold, saturated soils —> recalcitrant litter —> slow decomposition —> organic matter accumulation

what % of ecosystem carbon is belowground for boreal forests?

40-90%

is the boreal region a net carbon sink or source

sink! (very important)

what are the models of fire succession processes?

“self replacement” - the canopy is replaced by the same species post fire (og stand is replaced by itself)

“species-dominance relay” - canopy is replaced by the fastest growing species

“species replacement” - canopy is replaced by most sturdy and fire-resistant species (depends on fire interval and fire severity)

what do successional processes depend on in boreal forests?

fire interval and fire severity = fire regime along with feedbacks from plants and environment

what disturbances affect boreal forests?

fire, insects and pathogens, permafrost thaw (physically alters the lanscape and creates a deeper active soil layer), and human impacts (logging, mining, oil and gas, humans can act as vectors for invasives (larger impacts in Canada and Eurasia))

how large of an area is occupied by temperate forests?

27% of total forested land on Earth

(15 million hectares)

where are temperate forests found?

Eastern North America, South America, Europe, Asia/China, and Australia-New Zealand

-30-60 degrees North and South (80% is in the Northern hemisphere)

what climate is characterized by temperate forests?

cold winter season, 4-6 month growing season (seasonality which changes due to temps)

temp: 5-20 degrees C (mean annual temp) temps drop below freezing and plants go dormant

precipitation: 50-200 cm (20-79 in)

what important subcategories fall into temperate forests?

-temperate broadleaf and mixed forests

-subtropical mixed-evergreen temperate forest (conifer dominated, tropical affinity (wet, warm)

-temperate rainforest (always coastal climates, has more aboveground carbon per hectare than any other forest type)

-temperate coniferous forest (low productivity, montane, snowpack dominated hydrology)

how much carbon is stored in temperate forests, aboveground and below ground?

aboveground: ~2/3 (high in temperate rainforests)

belowground: ~1/3 of total

temperate forests contribute to ~17% of global net primary productivity

what is the flux of carbon from the atmosphere into temperate forests?

-soil organic carbon is the largest pool

what disturbances affect temperate forests?

-deforestation (cleared for agriculture and grazing) and other human activities like invasive species introduction

-wind

-fire

-ice

-severe storms

-disease

-insects

-acid rain and nitrogen deposition

what is net primary productivity?

photosynthesis - respiration

rank the forest types based on their carbon sink “strength”?

1. tropical rainforest

2. temperate forest

3. boreal forest

how big of an area is occupied by tropical forests?

-45% of total forested area

~6% of earth’s land surface

where are tropical forests located?

along the equator (between 23 N and 23 S)

-South America, Central America, Africa, SE Asia (Indonesia, Malaysia, India)

what climate is characterized by tropical forests?

-never below freezing, 20-25 C (68-77F)(mean average temps)

-more than 80in of rain annually (180-250cm)

what are the subcategories of tropical forests?

-(evergreen) tropical moist rainforest

-tropical dry forest

-tropical mountain systems (coniferous)

-swamp/flooded rainforest

-cloud forests

how much carbon do tropical forests contain?

~50% of all terrestrial carbon storage

-25-40% of total soil carbon is in the tropics

-over 200 million tons of carbon can be sequestered by tropical soils

what disturbance processes effect tropical forests?

Deforestation, habitat loss, anthropogenic climate change, droughts, heatwaves, hurricanes, fire, agricultural expansion

what are the 3 kinds of energy that water in soils has?

-osmotic potential

-gravitational potential

-matric potential

what are the three size classes of soil particles?

how many elements are essential for plant growth, survival and reproduction?

17

what are macronutrients and micronutrients?

hydrogen, carbon and oxygen account for how much of the mass of a plant?

96%

C and O are

where do plants get carbon. oxygen, and hydrogen?

atmospheric CO2 (carbon and oxygen)

H2O (hydrogen and oxygen)

what are other essential nutrients for plant growth?

nitrogen, phosphorus and potassium

to pass through plant cell membranes, nutrients have to be….

in ionic form (cations or anions)

cations: attach to clay and humus particles which are negatively charged

anions: mostly in the soil water solution, not attached to soil particles

what are 2 things that create cation exchange capacity?

cation exchange capacity declines with _____ pH

lower

what is leaching? where does it occur at a faster rate?

the loss of nutrients, occurs at a higher rate with greater precipitation

when soils are acidic, what nutrients are they lacking?

nitrogen, phosphorous, potassium and sulfur

when soils are alkaline, what nutrients are they lacking?

iron, manganese, boron, copper and zinc

P availability is a function of what?

parent material

overall, nutrient availability in soils is affected by what?

-parent material

-soil texture (clay and humus content)

-soil age (older soils have less nutrient content)

-pH

-leaching (climate dependent)

how does atmospheric nitrogen become bioavailable to plants?

nitrogen-fixing bacteria and archaea (living in legume root nodules or just living in the soil)

-some lichen and other plants like Alder trees

-ammonium is converted first to nitrite and then to nitrate by nitrifying bacteria (nitrification)

-nitrate is taken up by plants

mor soils result from slow, fungal-dominated decomposition under acidic conditions which lead to what?

nutrient immobilization and accumulation of matted plant residues

mull soils form in biologically active environments with significant soil fauna, like earthworms which do what?

efficiently break down the litter into well-humified organic matter, creating a fertile, well-mixed soil

in Boreal forests, what types of soils are found?

spodosols, histosols (peatlands), and gelisols (permafrost soils)

in Temperate forests, what types of soils are found?

Spodosols, Alfisols, Ultisols, Entisols, and Inceptisols

in Tropical forests, what soil types are found?

Oxisols and Ultisols (highly weathered and nutrient poor)

-important role of leaching because there’s so much precipitation and rapid decomposition