The Ecology of Carbon Forestry in NZ

How many hectares of new forest would be needed per year to limit global warming to 1.5°C

24 million hectares of new forest per year until 2030 would lead to ¼ of atmospheric CO2 drawdown needed to limit warming to 1.5°C

How is the carbon content in trees measured

Take species specific measurements of diameter, height increments on living wild or plantation trees, then take measurements of cross-section wood density after oven-drying. These measurements mostly include aboveground biomass. 50% of biomass is assumed to be carbon

How does carbon trading in Emission Trading Schemes (ETS) work

Emitters purchase credits and one credit offsets 1 tonne of unavoidable CO2 emitted, Owners of eligible (a forest is eligible if it is new and meets area, density, and species criteria) forests sell credits to ETS (price based on amount of carbon absorbed),

How does ETS incentivise reforestation

When the value of carbon credits is high, there is a financial incentive to plant trees which leads to excess carbon credits available thus taking pressure off of emitters

How does carbon storage compare between permanent and harvested forests

Carbon storage is much lower in harvested forests than in naturally regenerating forests

Trade-offs of rapid sequestration (harvested forests) and prolonged sequestration (naturally regenerating forests)

A permanent forest will earn more units as long as the carbon stock is increasing (it will stop earning units when the forest reaches “maturity” growth=decay). Harvested forests earn fewer units for carbon sequestration but they can do it continually if it is harvested

Carbon in existing forests is not EST eligible but…

Biodiversity values could incentivise protection/restoration, herbivore removal/control significantly improves sequestration rates

Benefits of silvopastoralism

Silvopasture in Columbian cattle ranches has reduced fertilizer/pesticide use, increasing soil productivity & carrying capacity (increased milk yield). 1.5 million tonne reduction in greenhouse gas emissions, captured 1.1 million tonnes of CO2 by planting, avoided emitting 0.4 million tonnes of CO2 by protecting natural forest

How do wetlands and grasslands store carbon

Perennial grassland species have deep roots, soil carbon stock>above ground carbon, in fire prone environments, grassland soils are a more reliable long-term carbon sink than forests

What issues do wetlands pose in terms of greenhouse gas emissions

Wetlands are the largest natural source of methane globally, because of degradation of organic matter under anaerobic conditions favor mehtan-producing microbes

What happens to methane and stored carbon when a wetland is drained

The methane output is reduced but stored carbon is released

Why is soil carbon hard to measure

highly variably in space (varies with depth, soil type, affected by land management, irrigation, stock rate, cropping etc.), highly variably in time (temp and moisture availability affect rate of plant growth and microbial decomposition)

Pros and cons of native forests

Pros — natural regeneration eligible for ETS, biodiversity, culture, aesthetics, additional economic value (recreation, honey, wild food), fire risk is medium to low, extended life as a carbon sink

Cons — Low C sequestration rate in short term

Pros and cons of exotic forests

Pros — high carbon sequestration rate in short term, Source of wilding conifers, additional economic value (recreation, hunting)

Cons — fire risk medium to high, short life as a carbon sink, poor biodiversity outcomes if monoculture, harvesting methods can be environmentally damaging

Pros and cons of a hybrid forest

Pros — Additional economic value (recreation, honey, wild food), high carbon sequestration rate in short term, extended life as a carbon sink

Cons — Transition to mature native forest depends on location, climate, and management

Unsure — Can improve biodiversity co-benefits (depends on where it is and what it replaced), fire risk variable/unknown

Pros and cons of wetlands and grasslands

Pros — Additional economic value (grazing, recreation, wild food), fire risk medium to low, extended life as a carbon sink

Cons — Not currently ETS eligible, soil carbon hard to measure

Unsure — Carbon sequestration rate variable/unknown, can maximise “biodiversity” co-benefits