Lecture 12: Temporal Dynamics in Terrestrial Ecosystems

What is Gross Primary Production (GPP)?

The total amount of carbon captured through photosynthesis.

What is Net Ecosystem Production (NEP)?

NEP is calculated as GPP minus respiration; it indicates if carbon is accumulating in the ecosystem.

What happens to NEP in spring and fall?

NEP is positive in spring (carbon accumulating) and negative in fall (due to leaf fall and tree barrenness).

What is a disturbance in terrestrial ecosystems?

A discrete event that removes organic matter such as plant biomass or soil.

What does disturbance intensity refer to?

The amount of energy released per unit of time/area during a disturbance.

What is primary succession?

Ecosystem development starting from bare parent material after a major disturbance.

What is secondary succession?

Ecosystem recovery starting from existing soil and seed banks after a disturbance.

What characterizes late successional species?

They are typically slow-growing, have large seeds, long lifespans, and adapt to low resource availability.

What effect does herbivory have on early successional species?

Herbivory can speed up succession by removing fast-growing early colonizers.

What is facilitation in ecosystem succession?

The process where the presence of one species benefits another species, enhancing growth.

What life history traits are expected in primary colonizers?

Fast growing, low stress tolerance, and small seed sizes for easier dispersal.

What is the trade-off between growth rate and stress tolerance in plants?

Faster growth rates often result in lower stress tolerance, while slower growth allows for higher stress tolerance.

How does NPP reflect succession in forest ecosystems?

NPP peaks mid-succession due to increased species replacement and nitrogen inputs, then declines.

What happens to carbon pools over the course of primary succession?

Carbon pools increase and then eventually level off as the ecosystem reaches a steady state.

What factors drive species replacement in ecosystems?

Variations in species traits and interactions such as facilitation and competition.

What is albedo in the context of successional changes after a fire?

Albedo is the measure of reflectivity; it decreases after a fire (burnt land absorbs more light) and increases as vegetation regrows.

What are the main differences in starting NPP between primary and secondary succession?

Primary succession starts with very low NPP due to a barren substrate; secondary succession begins with moderate NPP due to existing soils.

What defines a disturbance regime's frequency?

The interval at which disturbances occur.

How do carbon fluxes change during mid-succession?

During mid-succession, carbon fluxes (NPP, GPP, respiration) peak before declining.

What typically occurs to soil carbon pools during secondary succession?

Soil carbon pools recover quickly due to existing carbon from previous conditions.

How does decomposition change as slower-growing species dominate late in succession?

Decomposition decreases and slows down since longer-lived species dominate.

What is the significance of having a seed bank in an ecosystem?

A seed bank allows for quicker recovery and growth after disturbances, especially in secondary succession.

What does the timing of peak NPP indicate in primary succession?

It indicates that it takes a long time to reach peak NPP due to the development of a climax community.

How does microbial activity affect nutrient retention over succession?

Microbial activity helps with nutrient cycling and the retention of nutrients in the soil.

What role does water/energy balance play after disturbance?

It affects runoff and transpiration, decreasing runoff as the ecosystem recovers.

Define ecological succession.

Directional change in ecosystem structure and functioning characterized by species replacement over time.

What is the impact of soil temperature on microbial activity in spring?

Soil takes longer to warm than air, which affects microbial activation.

What is 'NPP'?

Net Primary Production; the difference between photosynthesis and respiration in an ecosystem.

Explain the concept of steady state in ecosystems.

A condition where there are no directional changes in ecosystem structure.

What is the significance of cation exchange capacity (CEC) in soil?

CEC indicates the soil's ability to retain nutrients, which increases as carbon accumulates.

How do disturbances influence plant and soil carbon pools?

Disturbances typically decrease plant and soil carbon pools, which then gradually recover.

What do late successional species tend to do in terms of resource availability?

Late successional species are adapted to low resource availability and often dominate these conditions.

What is the role of small seeds in primary succession?

Small seeds are better for dispersal and can establish in barren areas; they often have faster growth rates.

Why do larger seeds dominate in later stages of succession?

Larger seeds have greater longevity and better survival in stable, resource-poor environments.

Explain the domino effect in Glacier Bay, Alaska.

A sequence of species replacements observed after glacial retreat, where each species alters conditions favoring the next.

What changes in respiration can occur during succession?

Respiration initially increases with biomass but stabilizes earlier in secondary succession.

What distinguishes early successional species from late successional species?

Early successional species produce many short-lived seeds and are more appealing to herbivores.

How does secondary succession affect nutrient recycling compared to primary succession?

Nutrient recycling is greater in secondary succession due to the presence of existing soil organic matter.

What happens to carbon and nutrient flow over time in ecosystems?

Carbon and nutrient flow change as ecosystems develop, with mid-succession peaking in productivity.

What mechanisms can accelerate succession?

Herbivory, facilitation, and nutrient contributions from pioneer species can help accelerate succession.