Covering around 30% of the world’s land area, forests have a crucial role in supporting life on Earth. They support an abundance of ecosystem services, such as providing food and habitat for a variety of species, regulating climate and supporting nutrient cycling, carbon storage and watershed services. Forests also contain scenic landscapes of intrinsic and cultural value.
Human dependence on forests extends their use as a source of food, fuel, medicines and construction materials. Forests are a key driver of industry and economic growth in many parts of the world.
Of perhaps greatest importance is the role of forests in balancing the Earth’s carbon budget. Forests have a key role in sequestering carbon and act as a valuable sink to offset other sources of CO2 in the atmosphere including from deforestation, fire and fossil fuel emissions.
Protecting our forests forms a valuable part of the strategy to mitigate climate change.
Figure 1:Global tree cover based on MODIS data (M. Hansen, UMD)
Credit: Pan et al. 2013
Deforestation and Forest Degradation
The extent of forest loss caused by human disturbance has been substantial and progressive. Over 40% of forest area has been cleared, with most occurring during and following the Industrial Revolution. Over the past decade, the greatest losses were felt in the tropical region, with boreal forest loss placed second.
Plantations and regrowth have resulted in a decrease in the net loss of forests in some countries. However, we are still losing around 13 million hectares of forest each year. South America and Africa continue to experience the greatest net loss of forest.
The undervaluing of forests has increased their susceptibility to development pressures and conversion. Degradation of forests occurs where there is a persistent loss in carbon density over time. The drivers are many and varied and involve human pressure (unsustainable logging, shifting cultivation, grazing, urbanization) and natural factors (fire, disease, pests).
Current rates of deforestation and forest degradation are responsible for around 17% of anthropogenic greenhouse gas emissions (www.unep.org/vitalforest/). This is second only to burning of fossil fuels. The impact of forest loss will be felt at all scales, from global climate change to declining economic value of forest resources and biodiversity and threatened local livelihoods.
Figure 2: Forest net change 1990–2005 (FAO, 2006: Global Forest Resources Assessment 2005)
The International Response
A number of global initiatives are underway that aim to improve the sustainability of forest management practices. Collectively, they aim to promote the development of national forest monitoring systems that utilise satellite Earth observations and improve confidence in greenhouse gas emissions estimates.
The adoption of the UNFCCC in 1992 was a significant step towards tackling the issue of global warming. Member countries participate in strategy development at COP on an annual basis. Key agreements to date include:
– The Kyoto Protocol (COP3, 1997)
– Reducing Emissions from Deforestation and Forest Degradation (REDD; COP13, 2007)
– Reducing Emissions from Deforestation and Forest Degradation (REDD+; COP16, 2010)
The Kyoto Protocol required a commitment from developed countries to reduce their greenhouse gas emissions below a specified level within five-year timeframes (first commitment period: 2008–2012). While accounting for forest carbon management practices, including afforestation, deforestation and reforestation, was part of the process, the conservation of forest carbon stocks was not.
REDD was adopted as a means of including developing countries and the protection of forest carbon stocks in negotiations. Financial incentives are offered to developing countries that implement carbon emissions reduction schemes and a low carbon economy.
REDD+ goes beyond REDD and includes the role of conservation, sustainable management of forests and enhancement of forest carbon stocks. REDD+ countries must commit to periodic measurement, reporting and verification (MRV) in the forest and other land-use sectors in accordance with the IPCC Guidelines. Central to the process is the establishment of a robust and transparent MRV system that uses a combination of satellite EO and forest inventory for producing a validated carbon emissions account.
Assisting in the implementation of REDD+ are the United Nations REDD Programme (UN-REDD), the World Bank’s Forest Carbon Partnership Facility and the Global Environment Facility. These agencies are engaged in capacity building, developing finance mechanisms and assisting countries in their REDD+ preparedness.
COP21 in December 2015 has the aim of achieving universal agreement on climate change mitigation. Countries will submit their proposed approach to long-term reductions in greenhouse gas emissions and adaptation to change. A binding agreement is foreseen to be entered into force from 2020 onward, providing recognition, at last, of the scale and impact of climate change and the desire to tackle it head on.
Forest Information Requirements
Primarily as a consequence of the role of forests in regional to global carbon budgets, there is a requirement for annual spatially explicit national mapping of forest cover and carbon stocks. Spatially explicit information is needed to track activities and drivers and support estimation of greenhouse gas emissions and removals.
The IPCC Good Practice Guidance in greenhouse gas inventory development mandates the following: transparency, completeness, consistency, comparability and accuracy. National forest monitoring systems should provide data and information that is transparent, consistent over time, and suitable for MRV of REDD+ activities and nationally appropriate mitigation actions. Consistency with historical data is necessary for establishing forest reference (and emission) levels. Methods that minimise bias and allow comparison between countries should be used.
The need for forest information extends beyond national forest monitoring and greenhouse gas inventory. The Group on Earth Observations’ (GEO) nine societal benefit areas need some type of information about forests. Information about the status of forest resources is used in forestry operations, natural resource management, conservation and reserve planning, and biodiversity assessment.
The Role of EO Satellites
To meet the requirement for annual spatially explicit national mapping, the availability of gap-free moderate resolution (10–30m) satellite data is essential. Complementary optical and radar satellite sensors are currently operational and both support the development of forest information monitoring systems.
EO satellites and data processing systems have advanced to the point where it is feasible for countries to produce wall-to-wall assessments of forest and land cover change at national scale. Modelling techniques have also evolved to allow extrapolation of forest inventory measurements and their integration with EO data.
These data will enable countries to produce consistent and comparable annual reports on changes in forest carbon, emissions and removals that can support any binding agreement on emissions reductions targets at COP21.
Figure 3: Landsat-based forest cover change mapping in Colombia
Credit: IDEAM, Colombia
Satellite EO is considered a valuable source of activity (change) data for mapping land-use. Optical imagery is widely used and offers the most operational capability today. The long temporal archives of the Landsat series are useful for baseline generation and tracking change in land cover/land-use. The existing Landsat Long-Term Acquisition Plans (LTAP) allow frequent observation (ten attempts globally per year) over forested areas.
The spectral properties in the optical domain are well suited for forest monitoring, although cloud cover can be limiting. Higher resolution data (RapidEye, WorldView, Pléiades) are suited to detection of fine-scale change. Frequent observations are a requirement for capturing discrete events or rapid change in dynamic environments. The European Sentinel-2A mission, launched in June 2015, provides improved global optical coverage and is expected to be useful for tracking disturbance and subtle changes in forest cover, arising through, for example, forest degradation.
Figure 4: The PRODES Landsat deforestation monitoring programme in the Brazilian Amazon
Credit: INPE, Brazil
Radar sensors penetrate cloud and operate independently of the weather, so are particularly useful in tropical regions. The different radar wavelengths are sensitive to different forest structures and above-ground biomass. Longer wavelength L-band radar is suited to monitoring changes in forest extent and estimating biomass in low biomass forests. Dense time-series of C-band observations (Sentinel-1) allow tracking of changes in forest cover. High- resolution products (canopy gaps and height) are possible using data from X-band sensors (TerraSAR-X/TanDEM-X).
Figure 5: Wall-to-wall land cover map over Borneo island derived from ALOS PALSAR data
Credit: D. Hoekman, Wageningen UR, NL
Data from previous generation (JERS-1, ALOS) and current (ALOS-2) L-band radars can be integrated to observe historic and more recent change in forest cover. The ALOS-2 global data acquisition strategy allows two global observation attempts per year and four over tropical regions.
Data from multiple EO sensors are often integrated, as this helps overcome sensor specific limitations such as saturation, operating modes and temporal gaps. Data fusion is often necessary for mapping forest types, degradation and biomass and can improve the detection of change.
Future satellite radars, such as BIOMASS, and space-borne LiDARs (ICESat-2, MOLI and GEDI) may well revolutionise the capacity to monitor changes in forest carbon. By combining long time-series and high resolution data, this will enable better tracking of change as a result of forest dynamics, allowing for better assessments of carbon balances and sequestration potential, as well as habitat quality and biodiversity.
Figure 6: Estimated above ground biomass in eastern Australia, derived from Landsat, ALOS PALSAR and ICESat data
Credit: R. Lucas, UNSW; Credit: JAXA K&C, JRSRP UQ/DSITI, U Aberystwyth
The Global Forest Observations Initiative
The Global Forest Observations Initiative (GFOI; www.gfoi.org) was set up in 2011 to support the goal of reducing greenhouse gas emissions from the forestry and land-use sectors. National forest information systems are recognised to be essential for effective participation in and reporting to international climate change agreements. GFOI supports governments that are establishing national forest monitoring systems by:
– Fostering the sustained availability of satellite data in support of national efforts to better manage forest resources
–Providing assistance (capacity building) on utilising satellite and ground-based observations
– Developing Methods and Guidance Documentation (MGD) on the use of data for national forest monitoring systems, consistent with IPCC guidelines
– Promoting on-going research and development (R&D) and supporting continuous improvements in forest monitoring and reporting systems
GFOI builds on previous experiences of the GEO Forest Carbon Tracking (FCT) task. It aims to extend national forest monitoring efforts to a global level and promote best practice methods consistent with UNFCCC greenhouse gas reporting requirements. GFOI works in parallel with other global initiatives at the Food and Agriculture Organization (FAO), World Bank, IPCC and Global Observation of Forest and Land Cover Dynamics (GOFC-GOLD).
From the outset, GFOI has encouraged countries to develop national forest monitoring systems that use wall- to-wall time-series of satellite observations to better track changes in forest cover. Such a system allows countries to demonstrate long-term national emissions reductions arising from policy and conservation outcomes.
GFOI has identified seven thematic forest map products, derived using satellite EO data, that will enable countries to routinely and precisely measure forest area and carbon stock changes:
– Forest/Non-forest change
– Forest stratification
– All Land-use categories
– Land-use change between forests and other land-uses – Change within forest land
– Near-Real Time forest change indicators
The products represent intermediate inputs for greenhouse gas emissions estimation that provide improved confidence intervals for country emissions estimates. Their production and use is dependent on monitoring needs and will be greater the more activities are to be monitored within the REDD+ spectrum.
Implementing a Global Data Acquisition Strategy
Building on associated CEOS satellite data coordination efforts for GEO FCT, CEOS has assumed responsibility for coordinating satellite acquisitions in support of GFOI activities. Approved in 2011, the CEOS Space Data Strategy for GFOI encompasses three key elements:
– A baseline, coordinated global data acquisition strategy involving a number of core data streams that will be supplied free-of-charge for GFOI purposes;
– A coordinated strategy for national data acquisitions in response to national needs assessments;
– Data supply in support of GFOI R&D activities.
Collaboration between CEOS and GFOI has led to a comprehensive strategy that coordinates acquisitions from both optical and radar satellites, and so maximises the interoperable and synergistic use of the available satellite systems.
GFOI will continue to assist countries in building their national forest monitoring systems in support of sound decision-making and sustainable forestry, and so help ensure the preservation and wise use of forests for future generations.