Pontus Olofsson

A global land-cover validation data set, part I: fundamental design principles

A number of land-cover products, both global and regional, have been produced and more are forthcoming. Assessing their accuracy would be greatly facilitated by a global validation database of reference sites that allows for comparative assessments of uncertainty for multiple land-cover data sets. We propose a stratified random sampling design for collecting reference data. Because the global validation database is intended to be applicable to a variety of land-cover products, the stratification should be implemented independently of any specific map to facilitate general utility of the data. The stratification implemented is based on the Köppen climate/vegetation classification and population density. A map of the Köppen classification was manually edited and intersected by two layers of population density and a land water mask. A total of 21 strata were defined and an initial global sample of 500 reference sites was selected, with each site being a 5 × 5 km block. The decision of how to allocate the sample size to strata was informed by examining the distribution of the sample area of land cover for two global products resulting from different sample size allocations to the 21 strata. The initial global sample of 500 sites selected from the Köppen-based stratification indicates that these strata can be used effectively to distribute sample sites among rarer land-cover classes of the two global maps examined, although the strata were not constructed using these maps. This is the first article of two, with the second paper presenting details of how the sampling design can be readily augmented to increase the sample size in targeted strata for the purpose of increasing the sample sizes for rare classes of a particular map being evaluated.

A global land-cover validation data set, II: augmenting a stratified sampling design to estimate accuracy by region and land-cover class

A global validation database that can be used to assess the accuracy of multiple global and regional land-cover maps would yield significant cost savings and enhance comparisons of accuracy of different maps. Because the global validation database should expand over time as new validation data are contributed, the sampling design must be constructed so that it is simple to increase the sample size from a specific region (e.g. a continent or country) or from targeted land-cover classes to improve standard errors of the accuracy estimates. Stratified random sampling provides the desired adaptability to augment a sample to address regional or class-specific accuracy objectives. The proposed global validation database will be initiated from a baseline global stratified sample and then this baseline sample will be augmented to address accuracy objectives related to a specific map or region. The strata are constructed from a modified Köppen climate classification and population density. The theory and formulas for estimating accuracy from the combined baseline and augmented stratified samples are presented, and an example application is provided in which the regional accuracy of a land-cover map is assessed. The stratification used for the baseline global sample is retained when the augmented sample is subsequently selected. Alternatively, it is possible to ‘restratify’ the design so that the land-cover classes of a particular map are used as strata when selecting an augmented sample. The protocol for restratifying the design is presented, but the complexity of this option makes it less practical than retaining the initial strata when selecting an augmented sample.

Land use change in New England: a reversal of the forest transition

New England has been a prime example of the idea of forest transition. Deforestation commenced in the early seventeenth century and intensified up until the late 1800s. Following abandonment of farmland, forest cover increased until recent years. In this article, we examine recent trends of forest change in New England. What does the continuation of forest transition look like? What are the drivers and characteristics of land change beyond the initial transition? Land use change, not including areas of forest harvest, was mapped across New England (Maine excluded) between 1990 and 2005 using satellite data. A total of 133,000 ha were deforested for use as residential or commercial development. The net forest loss was 129,000 ha (2.8% of the forest present in 1990). If the observed pattern is present elsewhere, we could be witnessing a secondary phase of forest transition that involves a loss of forest driven by urban growth rather than agricultural expansion. The accuracy of the forest change map was assessed and the area estimates of forest change are based on both the map and the accuracy assessment results.

Carbon implications of forest restitution in post-socialist Romania

The collapse of socialism in 1989 triggered a phase of institutional restructuring in Central and Eastern Europe. Several countries chose to privatize forests or to return them to pre-socialist owners. Here, we assess the implications of forest restitution on the terrestrial carbon balance. New forest owners have strong incentives to immediately clearcut their forests, resulting in increased terrestrial emissions. On the other hand, logging generally decreased after 1989 and forests are expanding on unused or abandoned farmland, both of which may offset increased logging on restituted forests. We mapped changes in forest cover for the entire country of Romania using Landsat satellite images from 1990 to 2010. We use our satellite estimates, together with historic data on logging rates and changes in forest cover, to parameterize a carbon book-keeping model for estimating the terrestrial carbon flux (above and below ground) as a consequence of land use change and forest harvest. High logging rates during socialism resulted in substantial terrestrial carbon emissions and Romania was a net carbon source until the 1980s. After the collapse of the Soviet Union forest harvest rates decreased dramatically, but since restitution laws were implemented they have increased by 60% (from 15 122 ± 5397 ha y �1 in 2000 to 23 884 ± 11 510 ha y �1 in 2010), but still remain lower than prior to 1989. Romania currently remains a terrestrial carbon sink, offsetting 7.6% ± 2.5% of anthropogenic carbon emissions. A further increase in logging could result in net emissions from terrestrial ecosystems during the coming decades. However, forest expansion on degraded land and abandoned farmland offers great potential for carbon sequestration.

Time series analysis of satellite data reveals continuous deforestation of New England since the 1980s

Land cover and land change were monitored continuously between 1985 and 2011 at 30 m resolution across New England in the Northeastern United States in support of modeling the terrestrial carbon budget. It was found that the forest area has been decreasing throughout the study period in each state of the region since the 1980s. A total of 386 657 ± 98 137 ha (95% confidence interval) of forest has been converted to other land covers since 1985. Mainly driven by low density residential development, the deforestation accelerated in the mid-1990s until 2007 when it plateaued as a result of declining new residential construction and in turn, the financial crisis of 2007–08. The area of forest harvest, estimated at 226 519 ± 66 682 ha, was mapped separately and excluded from the deforestation estimate, while the area of forest expansion on non-forested lands was found to not be significantly different from zero. New England is often held as a principal example of a forest transition with historical widespread deforestation followed by recovery of forestlands as farming activities diminished, but the results of this study support the notion of a reversal of the forest transition as the region again is experiencing widespread deforestation. All available Landsat imagery acquired after 1985 for the study area were collected and used in the analysis. Areas of land cover and land change were estimated from a random sample of reference observations stratified by a twelve-class land change map encompassing the entire study area and period. The statistical analysis revealed that the net change in forest area and the associated modeled impact on the terrestrial carbon balance would have been considerably different if the results of the map were used without inferring the area of forest change by analysis of a reference sample.

Implications of land use change on the national terrestrial carbon budget of Georgia

BackgroundGlobally, the loss of forests now contributes almost 20% of carbon dioxide emissions to the atmosphere. There is an immediate need to reduce the current rates of forest loss, and the associated release of carbon dioxide, but for many areas of the world these rates are largely unknown. The Soviet Union contained a substantial part of the worlds forests and the fate of those forests and their effect on carbon dynamics remain unknown for many areas of the former Eastern Bloc. For Georgia, the political and economic transitions following independence in 1991 have been dramatic. In this paper we quantify rates of land use changes and their effect on the terrestrial carbon budget for Georgia. A carbon book-keeping model traces changes in carbon stocks using historical and current rates of land use change. Landsat satellite images acquired circa 1990 and 2000 were analyzed to detect changes in forest cover since 1990.ResultsThe remote sensing analysis showed that a modest forest loss occurred, with approximately 0.8% of the forest cover having disappeared after 1990. Nevertheless, growth of Georgian forests still contribute a current national sink of about 0.3 Tg of carbon per year, which corresponds to 31% of the country anthropogenic carbon emissions.ConclusionsWe assume that the observed forest loss is mainly a result of illegal logging, but we have not found any evidence of large-scale clear-cutting. Instead local harvesting of timber for household use is likely to be the underlying driver of the observed logging. The Georgian forests are a currently a carbon sink and will remain as such until about 2040 if the current rate of deforestation persists. Forest protection efforts, combined with economic growth, are essential for reducing the rate of deforestation and protecting the carbon sink provided by Georgian forests.

Assessing the global warming potential of human settlement expansion in a mesic temperate landscape from 2005 to 2050

Expansion of human settlements is an important driver of global environmental change that causes land use and land cover change (LULCC) and alters the biophysical nature of the landscape and climate. We use the state of Massachusetts, United States (U.S.) to present a novel approach to quantifying the effects of projected expansion of human settlements on the biophysical nature of the landscape. We integrate nationally available datasets with the U.S. Environmental Protection Agencys Integrated Climate and Land Use Scenarios model to model albedo and C storage and uptake by forests and vegetation within human settlements. Our results indicate a 4.4 to 14% decline in forest cover and a 35 to 40% increase in developed land between 2005 and 2050, with large spatial variability. LULCC is projected to reduce rates of forest C sequestration, but our results suggest that vegetation within human settlements has the potential to offset a substantial proportion of the decline in the forest C sink and may comprise up to 35% of the terrestrial C sink by 2050. Changes in albedo and terrestrial C fluxes are expected to result in a global warming potential (GWP) of +0.13 Mg CO2-C-equivalence ha(-1)year(-1) under the baseline trajectory, which is equivalent to 17% of the projected increase in fossil fuel emissions. Changes in terrestrial C fluxes are generally the most important driver of the increase in GWP, but albedo change becomes an increasingly important component where housing densities are higher. Expansion of human settlements is the new face of LULCC and our results indicate that when quantifying the biophysical response it is essential to consider C uptake by vegetation within human settlements and the spatial variability in the influence of C fluxes and albedo on changes in GWP.

Forest Changes and Carbon Budgets in the Black Sea Region

The temperate forests in the Black Sea region contain some of the last remaining intact forests between southern Europe and West Asia. The collapse of the Soviet Union brought great political and institutional changes to the region that have already impacted these forests, which have experienced long land use and management histories. In this chapter, we review and synthesize research on forest changes and carbon budgets that are associated with decentralization in the Black Sea countries, focusing specifically on Bulgaria, Georgia, Romania, and Ukraine. Our analysis shows that each of these countries followed a different path in forest management, somewhat mimicking their own history of transition from centrally controlled to market-based economies. In Romania and Bulgaria, a period of economic hardship and weakened institutions resulted in large-scale forest changes, but the net effect of these and other historic forest disturbance events has allowed Bulgaria and Romania to remain a terrestrial carbon sink. Although increases in logging could result in net carbon emissions, great potential exists for carbon sequestration as a result of forest expansion on degraded and abandoned farmland, particularly in Romania. Georgia continues to struggle with establishing and enforcing forest management with a suitable mix of private and public uses to meet the growing demand, particularly for energy. To this end, the future of Georgia’s forests and its carbon implications remain uncertain and will mostly depend on its relationships with Russia and its ability to exploit its status as an energy corridor. Ukraine also continues to struggle with establishing suitable forest administration and ownership with high rates of illegal logging. However, natural forest regrowth on large tracts of abandoned farmland can sequester unprecedented amounts of carbon, and large-scale afforestation programs can greatly aid this process. These findings suggest that all these countries could play an important role in the terrestrial carbon budgets of the Black Sea region. This outcome is partly connected to the land use legacy of the Soviet Union: large areas of relatively young and regrowing forests, a result of high forest harvesting rates during the latter half of the 20th century, have tremendous carbon sequestration potential in each country that is reviewed here. At the same time, the effects of this legacy are quickly replaced with land use and forest management decisions that are made today.