2.4.4.1 Amazon rainforest

Forests are complex social-ecological systems that provide a diverse range of ecosystem services, including carbon storage, hydrological regulation and the provision of biodiversity-related goods and services (Zemp et al., 2017). The Amazon rainforest, the world’s most biodiverse terrestrial ecosystem, plays a critical role in global climate regulation (Mitchard, 2018). However, human activities and climatic extremes are increasingly threatening the forest’s integrity and the services it provides, leading to tipping cascades. There are already signs of a loss of resilience in large expanses of the Amazon (Boulton et al., 2022; Rocha, 2022 Zemp et al., 2017), with trees taking longer to recover from natural and human-induced disturbances. For a summary of the underlying feedbacks and potential impacts on climate dynamics, see Chapter 1.3.2.1.

In addition to climate-related disturbances, human-induced deforestation and land-use changes driven by agricultural and socio-political development in the Amazon region have led to increased forest dieback (Aragão et al., 2018; Nepstad et al., 2008). In contrast to deforestation, forest degradation is characterised by damages to the structure, composition and function of the forest, with no change in land use (Bourgoin et al., 2021). Extraction of timber and increased use of land for agriculture are the causes that drive this (Lapola et al. 2023). In the Amazon, forest degradation exceeds deforestation and, unlike drivers of deforestation, which have been studied at length, is a complex social-ecological dynamic in which the potential for cascading impacts is less well known (Bourgoin et al., 2021). 

Changes in temperature and precipitation, caused by anthropogenic climate change and large-scale climate phenomena such as El Niño–Southern Oscillation (ENSO) influence plant functioning and forest stability. ENSO-driven fluctuations have been associated with droughts affecting large Amazonian forest areas (Nobre et al., 2016). A tipping cascade can emerge if ENSO shifts to a higher-frequency occurrence, increasing the risk of severe droughts and longer dry seasons, resulting in water loss and increased forest fires. The reduced moisture recycling also leads to increased vapour pressure deficit, which further increases the frequency and intensity of forest water stress (Xu et al., 2022; Staal et al., 2020) and is a key driver in critical plant physiology thresholds (Kath et al., 2022). Forests under water stress are also more susceptible to fires, and this is especially prevalent in forest/pasture margins (Cumming et al., 2012). The recent increased severity of droughts could represent the first manifestations of this ecological tipping point (see Figure 2.4.6). These, along with the severe floods over South West Amazonia as well as the increasing dry season, suggest that the system is oscillating (Lovejoy and Nobre, 2018).

While evidence for the effects of gradual environmental change on forests exists, evidence for tipping points at which feedbacks have caused forest ecosystems to enter alternative stable states remains sparse (Reyer et al., 2015), see Figure 2.4.6. Modelling studies have identified estimates of two potential future tipping points for the Amazon’s transformation: 1) a 3-4°C increase in global temperature (Armstrong McKay et al., 2022; Lovejoy and Nobre, 2018 Nobre et al., 2016; Lenton et al., 2008) or 2) deforestation levels which exceed 40 per cent (Nobre et al., 2016; Lenton et al., 2008; Sampaio et al., 2007).

While the possibility of a system-wide tipping point remains debated, local feedbacks can lead to alternative stable states (Staver et al., 2011) (see also Causal Loop Diagram (CLD), Figure. 2.4.6). Climate change may exceed the adaptation capacity of the forest and subsequently trigger these local-scale tipping elements that cascade through the Amazon rainforest system. As forest dieback occurs, the amount of drier forest edge gradually increases, as well as the risk of fire (Cumming et al., 2012; see also Chapter 1.3.2.1). 

Rainforest fauna are also critical for the dispersal of seeds for many rainforest flora species, and particularly for the larger, fleshy fruits of dominant competitors. Reductions in organism connectivity can thus create a second tipping point that further reduces the capacity of forest to regenerate (CLD, Figure. 2.4.6). Through reduced ecosystem functioning, the forest degradation and dieback has fundamental impacts to regional land-atmosphere processes, which further amplify the risk of droughts, fires and biodiversity loss (Lenton et al., 2019; Aragão et al., 2018; Lenton & Ciscar, 2013), or decreasing rain and thus tipping risk in adjacent ecosystems.

The importance of Amazon moisture for forests and other land use sectors south of the Amazon is multifaceted. The most important is the contribution of dry season Amazon evapotranspiration to rainfall in south-eastern South America. Forests are able to sustain a consistent evapotranspiration rate throughout the year, whereas evapotranspiration in pastures is dramatically lower in the dry season (Lovejoy and Nobre, 2018). There is a heavy reliance on this moisture for agriculture as well as human wellbeing (Lovejoy and Nobre, 2018). Therefore, various large-scale drivers of environmental change are creating cascading impacts and strong feedback effects. These may be summarised as climate and human-induced drivers that influence forest functioning, which then affects moisture cycling, albedo and ecosystem services. In turn, these factors impact socio-economic dimensions such as agriculture as well as climate. 

The governance of the Amazon rainforest represents a complex and multi-faceted challenge due to the conflicting interests and demands placed upon its ecosystem services. As a provider of global public goods, the rainforest is crucial for biodiversity conservation and carbon sequestration, playing a pivotal role in mitigating climate change (Mitchard, 2018; Zemp et al., 2017). However, the immediate benefits derived from activities like logging, mining and deforestation for commercial purposes pose a significant threat to its sustainability. Consequently, the governance of the Amazon is characterised by the intricate interplay between preserving ecosystem services and depleting activities, which are often short-term concentrated benefits (Paes, 2022). As a terrestrial ecosystem, forests fall under the jurisdiction of states, granting them ultimate authority in deciding which ecosystem services are to be realised. The Amazon rainforest, specifically, falls within the jurisdiction of eight South American states, accentuating the intersection of interests between local and global beneficiaries (Paes, 2022; Reydon et al., 2020). Furthermore, the fragmented jurisdiction intensifies the challenges faced in governance, necessitating policy coordination and joint governance among the overlapping countries to ensure the sustainable realisation of globally dispersed services.