Lecture 9: De and reforestation Flashcards
Lecture outline
*The global potential for forest restoration
*Co-benefits of forest restoration: Carbon sinks and biodiversity
*Reforestation projects-> carbon credits (and afforestation projects)
*Are tropical forests resilient?
How might primary and secondary forests differ?
see figure in notes
Deforestation in the tropics
*Globally, deforestation has been high
~13 million ha/yr in mid 2000s; 2010-2015- ~3 million ha/yr (FAO)
-Especially pronounced in the Tropics; Tropical forests are now a net carbon source
See Chazdon 2008 Science & Baccini et al 2017 figures in notes
*Increasing issues with droughts in the Amazon
*Green are gains and red are losses
*There is balance in some areas – but likely less biodiverse secondary
Globally forest cover has been increasing due to:
Due to:
-Plantations
-Natural regeneration
-Restoration
> 60% of forest globally is degraded, secondary or heavily logged
Chazdon (2008) Science 320: 1458-1460
The case for re and afforestation
*As more converted land becomes degraded and abandoned, opportunities exist to reforest or to newly create forest
*Marginal agricultural land may no longer be profitable to farm – planting trees for carbon sequestration particularly in the uplands may be an option
*Re- and afforestation in the tropical regions could shift them back to being carbon sinks
Chazdon (2008) Science 320: 1458-1460
Forest regeneration
Can secondary forest match primary, old growth forest in terms of:
-Biodiversity?
-Ecosystem function? Cultural, air/water improvement, timber provision, hunting range
-Carbon sink status?
^ There may be a trade off depending on what we aim for and this is important to consider to avoid non-intended outcomes
The regeneration staircase
various options according to time and cost
Reforestation can be natural (succession) or via restoration (tree planting)
ideally:
1. Rehabilitation
2.Reforestation with native trees
3.Natural regeneration
Level Of degradation sets the restoration strategy
^ ‘right tree right location’ native tree regeneration is best approach
Farm abandonment in France for example is currently leading to natural reforestation – should this be managed to assist regeneration for a better future outcome?
see figure from
Chazdon (2008) Science 320: 1458-1460
Reforestation – what trees should we be planting?
*Fast growing pioneer species will give cover quickly, creating a humid, shaded microclimate, allowing germination seedling establishment of shade-tolerant species
^ create nursery conditions for other species
*may act as foci for animal dispersal of later successional species
*Maesopsis eminii has spread widely throughout the East Usambara mountains after widespread planting (widely dispersed by hornbills that consume their fruits)
Viisteensaari et al. (2000) Environmental Conservation 27: 76-81
Locking up carbon and conserving biodiversity
Reforestation Projects receive carbon-based payments for ecosystem
Service:
*Carbon enhancement on abandoned farmland from regenerating secondary forest
*Cost-effective on marginal lands where the opportunity costs are low
The CCBA: Partnership of leading NGOs; develops standards and tools that stimulate, identify and promote high quality multiple-benefit land management projects
The VCS: Validates and verifies forest restoration projects, to ensure they really are sinks for carbon, thus reducing emissions. The resulting carbon credits can be traded on the global carbon market (Emitters buy credits from reducers to ‘offset’ their emissions).
^ the ‘carbon credit trade’
Forest restoration example Kibale NP
A VCS accredited CCB project
^ Trial and error process of finding best-performing trees to plant- tended to be pioneer spp.
> 1,200,000 t of CO2 equivalent of Carbon have been captured since 1995!
Can secondary forest match primary forest C stocks?
Yes - With time, naturally regenerating forest can have carbon stocks approaching primary forest levels
It takes at least 30 years – most gov. Are not ready to commit to this but in Africa and Columbia some uptake is now occurring
See Gilroy et al. (2014) Nature Climate Change 4: 503-507
But what about below ground carbon?
See:
Wang et al. (2017) Functional Ecology
doi: 10.1111/1365-2435.12925
56 yrs after restoration of Chinese
forest, 2° forest still had much lower
soil C stocks than natural forest
Sometimes lower soil C storage in secondary forest
Especially the case for deeper soil layers: secondary forest in total only has enough C to equal ‘old’ C in natural forest
can secondary forest hold a similar level of diversity to primary forest?
Diversity in W Colombian Andean forests:
Bird community composition of older
secondary forests converges on primary forest
So too does beetle community composition:
Parallels convergence of C stocks
Gilroy et al. (2014) Nature Climate Change 4: 503-507
How well are different groups represented in secondary forests?
While some groups are well-represented in secondary forests and this included unique species (moths, large mammals, bees and flies) others are not (trees, lianas, birds)
See Barlow et al 2007 PNAS
How resilient are tropical forests? Tropical forest recovery
A common assumption of tropical forests is that they are *not * resilient to disturbance
Resilience = the ability of a system to absorb disturbance and return to previous state
Regrowth responses after land abandonment was mapped by Poorter et al (2021) across 77 sites
A – How do different attributes respond
B – How long until attributes reach a certain % level seen in old-growth
C- Which attributes are closely linked?
in this study recovery trajectories following abandonment were highly variable
Two different correlations between attributes and influence on the network:
-Strong correlations between soil, and diversity and structure
-Species composition has strong influence (many connections)
-Max diameter influential through heterogeneity and aboveground biomass
see: Poorter et al. (2021) Science 374, 1370–1376
^ observed high level of interactions
Summary
*Forests can regenerate, and level of degradation determines whether this can be natural or needs human intervention
*Carbon sinks and diversity co-benefits potential greater in marginal lands where agriculture not profitable
*More degradation = more input needed, and more time to OGF-equivalent recovery
*Some attributes are quick to recover (soil)
*Others are slower (deeper soil carbon; compositional similarity to OGF; aboveground biomass)
*Some components will never be regained (extinct spp!); how resilient will secondary forests be to future disturbance under climate change?
