Effects of Nitrogen Deposition on Greenhouse-Gas Fluxes for Forests and Grasslands of North America

Nitrogen deposition across North America has been influencing fluxes in greenhouse gas pollutants such as carbon dioxide, nitrous oxide, and ozone.  In the face of climate change, it is crucial for us to understand the spatial patterns and effects of nitrogen deposition on greenhouse gasses. Templer et al.(2012) discussed spatial patterns of nitrogen deposition and tropospheric ozone and then summarized the known effects of nitrogen deposition on greenhouse gases in North American terrestrial ecosystems.  The authors investigated the causes and implications of emissions such as nitrogen and ozone, and then created an exposure index that analyzed regions affected by both emissions.  The index showed that forests in Eastern U.S. and California’s Sierra Nevada mountains had the highest levels of nitrogen deposition and ozone exposure.—Anthony Li
Templer, P. H., Pinder, R. W., Goodale, C. L. 2012. Effects of nitrogen deposition on greenhouse-gas fluxes for forests and grasslands of North America.  Frontiers in Ecology and the Environment  10.10 547–553

In this paper, the authors investigate the spatial patterns of nitrogen deposition and tropospheric ozone and its implications on other greenhouse-gas pollutants.  Due to the industrial sector, emissions of nitrogen oxides and ammonia have been on the rise.   Both of these pollutants contribute to the formation of aerosols in the atmosphere, which are responsible for decreasing the amount of light available.  Nitrogen oxides also drive the formation of tropospheric ozone and the removal of atmospheric methane.  Nitrogen deposition also largely impacts carbon released from plants and soils, because it enhances carbon dioxide uptake in plants and reduces carbon dioxide release from soils by decomposition. Tropospheric ozone is a byproduct of the photo-oxidation process of nitrous oxides, and often occurs in areas with nitrogen deposition.  Ozone is itself a greenhouse gas and can decrease carbon dioxide uptake in plants by damaging their root production and stomates.  Tropospheric ozone currently accounts for 22% of global warming, and is predicted to reduce rates of primary productivity by up to 16%.  Methane is another greenhouse gas pollutant that was also investigated in this study.  Methane concentrations are affected by nitrogen oxides multiple ways.  In soils, nitrogen enrichment slows the consumption of atmospheric methane by bacteria whereas in wetlands, nitrogen enrichment can enhance methane production.  However, the effect that increased nitrous oxides have on removing methane from the atmosphere is more prominent than the previous two effects.  Data for these pollutants were obtained from previous studies and were then compared with each other regionally using an exposure index that the authors developed.
Collected data show that nitrogen deposition on Eastern U.S. averages 8.5 kg nitrogen per hectare year while on the West coast it averages less than 4 kg nitrogen per hectare year.  The Eastern U.S. has hotspots of nitrogen deposition near urban areas and sites of intensive livestock operations, but the differences between rural and urban areas are not as pronounced as those in the West.  Along the East Coast, an analysis revealed that the nitrogen deposition stimulated forest growth in the hardwood forests.  The forests on the West Coast are noticeably drier and limited in nitrogen, so increased fire frequency and subsequent carbon release may result from the nitrogen deposition.  Southern Canada also experienced elevated rates of atmospheric nitrogen deposition, more so in areas downwind of the agricultural and industrial regions of southern Ontario.  Nitrogen deposition on the East Coast also increased rates of nitric oxide and nitrous oxide production, with the former being produced significantly faster.  Authors note how this is for the better, as nitrous oxide is roughly 300 times more potent in warming potential than carbon dioxide is per molecule.  Nitrogen deposition causes nitrous oxide emissions to increase by 30 to 90 gigagrams while causing atmospheric methane to increase by 40 to 110 gigagrams. Nitrous oxide and methane emissions contribute to warming and can partially offset the cooling that results from increased uptake of carbon dioxide.  The index that the authors used showed forests in Eastern U.S. and California’s Sierra Nevada mountains amongst the regions with highest levels of nitrogen deposition and ozone exposure.  The index also showed that the highest exposure for grasslands occurred in California, Texas, and Kansas.
While the results of this study show how detrimental nitrogen deposition can be, the authors also note that regulation of nitrous oxide emissions has resulted in significant reductions over the past decade.  With more standards being implemented, nitrogen oxides are predicted to decrease by up to 47% by 2030 and 67% by 2050, relative to 2006 nitrogen oxide levels.   Lower levels of nitrogen oxides will likely lead to lower carbon dioxide uptake by plants and lowered nitrous oxide emitted from soils.  As opposed to nitrous oxide however, ammonia levels are unlikely to decline.  Even though standards are projected to decrease nitrogen deposition, increasing levels of atmospheric carbon dioxide are likely to increase the demand for nitrogen in vegetation.  This shows how implemented standards may mean nothing if we do not seek to lower carbon dioxide emissions.  In summary, rates of nitrous oxide, ammonia emissions, and atmospheric nitrogen deposition are elevated over much of North America.  Heightened nitrogen deposition results in greater carbon dioxide uptake by vegetation and increased nitrous oxide emissions from soils.  The net effect of nitrogen deposition in the U.S. is equivalent to an annual uptake of 170 Tg of carbon dioxide equivalent gases.  Despite the heightened nitrous oxide, ammonia, and nitrogen deposition, standards are expected to decrease nitrogen deposition in the coming years.  The impacts of this will be two-sided, as lowered rates of nitrogen deposition result in slower forest growth and carbon storage, but also result in lower emissions of nitrous oxide.

Mitigation Potential of Agricultural Emissions using a Variety of Options in the Tropics

The release of greenhouse gases, primarily methane<!–[if supportFields]> XE “methane (CH4)” <![endif]–><!–[if supportFields]><![endif]–> is an important issue that needs to be considered in the agricultural sector. However, other gases are released from the agricultural sector as well, including carbon dioxide and nitrous oxide<!–[if supportFields]> XE “nitrous oxide (N2O)” <![endif]–><!–[if supportFields]><![endif]–>. Furthermore, in the context of climate change, changes made in agricultural practices as well as changes made in livestock-related practices, can play a role in reducing greenhouse gas emissions. Thornton and Hererrero (2010) used a method that involved the estimation of four different types of adoption on the production of carbon dioxide and methane. Each adoption could be applied at two levels: complete adoption and optimistic, but plausible adoption rates. Furthermore, they used two different types of methods: carbon sequestration<!–[if supportFields]> XE “carbon sequestration” <![endif]–><!–[if supportFields]><![endif]–> of degraded rangelands and the usage of agroforestry practices. Both these methods were applied in tropical regions, namely in tropical Central and South America and sub-Saharan Africa<!–[if supportFields]> XE “Africa” <![endif]–><!–[if supportFields]><![endif]–>. The authors found that despite the mitigation potential rates having not much impact on the global total from agricultural greenhouse gas emissions, the resulting carbon payments from offsets in gas emissions could be a source of income for farmers who are not very well off.— Nitya Chhiber
Herrero, M. and Thornton, P.K. 2010. Potential for reduced methane<!–[if supportFields]> XE “methane (CH4)” <![endif]–><!–[if supportFields]><![endif]–> and carbon dioxide emissions from livestock and pasture management in the tropics. Proceedings of the National Academy of Sciences 16, 19667 – 19672, doi: 10.1073/pnas.0912890107

Thornton and Herrero used the RUMINANT model to provide estimates of production of methane<!–[if supportFields]> XE “methane (CH4)” <![endif]–><!–[if supportFields]><![endif]–>, milk, and meat. This model is structured around inputs and outputs. The inputs are the fermentable nutrients and the outputs are the products of fermentation, which include methane. The study involved analyzing four different mitigation options under two different types of adoption rates: complete adoption and optimistic but plausible adoption. The four mitigation options mainly had an impact on the production of carbon dioxide and methane gases.
The highest mitigation potential for greenhouse gas emissions was the one associated with the method of restoration of the degraded rangelands in sub-Saharan Africa<!–[if supportFields]> XE “Africa” <![endif]–><!–[if supportFields]><![endif]–> and Central and South America at observed or plausible adoption rates. The next two methods, which are beneficial in terms of their mitigation potential, are the agroforestry option and improvements in the use of improved pastures and crop residue digestibility. It is interesting to note that despite having one of the highest mitigation potentials of all options, the agroforestry option, which involves the sequestration<!–[if supportFields]> XE “sequestration” <![endif]–><!–[if supportFields]><![endif]–> of carbon due to the replacement of concentrates by leaves of Leucaena leucocephal<!–[if supportFields]> XE “Leucaena leucocephal” <![endif]–><!–[if supportFields]><![endif]–> in their diet, there are cultural manifestations. In countries in the developing world, the number of livestock is a form of symbolic capital but this method is related to the reduction in livestock numbers.

Brazialian GHG Production

On November 4th, 2009 Brazilian officials announced that the country was enacting voluntary Greenhouse Gas (GHG) emissions reduction goals of 36.1-38.9% less than projected 2020 levels. Although the government claimed it would not accept any mandatory international emissions levels, it did inventory anthropogenic GHG emissions according to the United Nations Framework Convention on Climate Change (UNFCCC) which designates five categories of Energy, Industrial Process, Agriculture, Land Use Change and Forestry, and Waste. The authors of this paper (Cerri et al. 2010) analysed governmental and non-governmental reports on the GHG emissions from each of these sectors within Brazil in order to find where the most significant emissions were and thus where the most potential for reductions exists. Their research found that four main sources were responsible for 90% of the countries GHG output: Forest and Grassland Conversion (i.e. deforestation), Fossil Fuel Combustion, Enteric Fermentation (methane released from cattle dung and flatulance) and Agriculture Soils (soil carbon lost in tillage, erosion and land degradation). These areas were examined by the authors and the potential GHG savings of each were calculated.–Asa Kamer
            
Cerri, Carlos., Bernoux, Martial., Maia, Stoecio., Cerri, Carlos., 2010. Greenhouse Gas Mitigation Options in Brazil for Land-use Change, Livestock and Agriculture. Scientia Agricola 67.

Cerri et al. addressed the GHG emissions of Brazil by focusing on the mitigation potential in each of the most emitting sectors to either sink more carbon or emit less. Business as usual scenarios were projected and mitigation strategies were extrapolated to measure the potential savings of various mitigation strategies by 2020. Their accounting strategy used two formulas to measure mitigation options. The first followed the 1996 Guidelines for National Greenhouse Gas Inventories given by the International Panel on Climate Change. The second was a tool to evaluate carbon balance impacts of forestry and agriculture management on GHG emissions developed by the Food and Agriculture Organization of the United Nations. Both metrics were used to evaluate the GHG implications of the changing dynamics of forestry, agriculture and energy in Brazil.
    The most significant contributer to climate change in Brazil is deforestation. The Amazon rainforest is a vast natural carbon sink. Rainforest ecosystems sequester more carbon naturally than almost any other kind. In calculating Brazil’s contribution to climate change the preservation of this forest represents the largest mitigation potential. In 2007 the Brazilian government adopted a policy which sets the goal of decreasing the rate of deforestation by 30% every set of three years. The current rate is 12,185 square kilometers per year and but considering this government goal the rate by 2020 could be less than half of the current pace. From a GHG management perspective the forests are a crucial carbon sequestration oppurtunity. Although many Brazilian forests are under heavy threat the replanting of forests is also a consideration for GHG management.  
    In Brazil the enteric fermentation from cattle is the third largest contributor to carbon dioxide emissions and the largest to methane gas emmissions. Brazil accounts for a quarter of the developing world’s milk production and one fifth of it’s meat production so mitigation of cattle based emissions will have relatively large impacts. There are a variety of means to reduce this source of GHG: breeding to select for breeds which emit less methane, improving productivity of meat and milk productivity so less cattle are required for the same amount of product, manure management which focuses on correctly using waste as an organic fertilizer so as to sink carbon back into the soil rather than have it be released gaseously, and the use of digestors which capture the methane from cattle and convert it into a usable fuel.
    Tillage of Brazilian fields releases significant GHG. Rather than remain in the soil, carbon is released when the topsoil is turned over yearly to add fertilizer, shape beds and remove weeds. The alternative to this practice is to convert land into a no till system which allows the soil to hold more water and increase it’s stability against erosion. Tilling integrates air into deeper layers of soil stimulating microbial activity, this results in the increases decomposition of organic material which releases greater amounts of carbon from the soil. In this way previously tilled fields which have been depleted of carbon over years represent a vast potential carbon sink. There are currently 28 HA of no till land in production in Brazil and the government climate mitigation efforts aim for 40 HA of no till land by 2020.
    In addition to these main sources of agricultural and forestry GHG mitigation, the paper also covered several other methods which, while not as significant individually, could also add up to large GHG reduction if all enacted effectively. These include reducing methane released from decomposing matter in flooded rice fields through better water management and increasing the sustainable production and use of bio-ethanol and biodiesel.
    The authors estimated that increasing carbon sinks represent 19-39% of mitigation potential and reducing emissions represents 61-81%. Since the authors accounted for the increased use of bio fuel crops as a GHG savings for both the agriculture and energy sectors, their estimates for the mitigation potential of Brazil were even higher than that of the government.

Ambient Ozone Levels

Ambient ozone, a secondary pollutant formed by reactions between nitrogen oxides and volatile organic compounds in the presence of sunlight, has consistently been linked to adverse health effects. Future ozone levels are particularly sensitive to climate change as its formation depends strongly on weather conditions. Chang et al. (2010) examined the risk of future ozone levels on non-accidental mortality via statistical modeling. The authors used data from climate model outputs, historical meteorology, and ozone observations, and a health surveillance database to model present-day relationships between observed ozone concentrations and meteorology, future ozone concentrations, daily community-level mortality counts, and relative risks associated with short-term exposure to ambient ozone. The study estimated that there will be an increase of 0.43 ppb in average ozone concentration during the 2040s compared to 2000, corresponding with a 0.01% increase in mortality rate and 45.2 premature deaths in the study communities. Carolyn Campbell
Chang, H.H., Zhou, J., Fuentes, M., 2010. Impact of climate change on ambient ozone level and mortality in southeastern United States. International Journal of Environmental research and Public Health 7, 2866–2880.

Ground-level ozone is mainly found in urban settings due to emissions from industrial facilities, power generation, and vehicle exhaust. It is linked to adverse health effects including morbidity and mortality for cardiovascular and respiratory diseases. There is concern that climate change will lead to increased levels of ozone, as weather factors such as temperature, wind speed, cloud cover, solar radiation, and atmospheric mixing affect ozone’s formation. In the Eastern United States, episodes of high ozone are usually associated with slow moving high-pressure systems characterized by warm temperature, light wind, and cloudless skies.
The study by Chang et al. seeks to quantify the impact of future ozone levels on non-accidental mortality in 19 communities throughout Alabama, Florida, Georgia, Kentucky, Mississippi, North Carolina, South Carolina, and Tennessee. First, the authors modeled present-day relationships between observed ambient maximum daily 8-hour average ozone concentrations and three meteorology variables during 2000. Next the authors estimated the association between acute exposure to ambient ozone and mortality. Future ozone concentrations were predicted using future daily forecasts of temperature, solar radiation, and cloud-cover. Finally, the authors calculated the number of attributable deaths using the total number of deaths in 2000, the difference in average ozone between 2000 and 2040, ad the overall relative risk of mortality per ppb increase in ozone concentration.
It was found that ozone concentration is positively associated with temperature and solar radiation, but negatively associated with total cloud cover. Additionally, the association between weather variables and ozone levels can vary across states. The estimated adverse association between daily mortality per 10 ppb unit increase in maximum 8-hour ozone level on day with lag 0, 1, and 2 was 0.11, 0.23, and 0.11 respectively, with an overall relative risk of 0.26. Average 2041–2050 ozone levels were predicted to increase by 0.43 ppb compared to 2000, corresponding to a 0.01% increase in mortality rate associated with future ozone levels due to climate change alone.
The study suggests that ambient ozone levels and corresponding deaths will increase in the future due to climate change. However, the health impact analysis does not account for future regulatory policies that control local and regional emissions of ozone precursors including expected changes in population structure, behaviors, and size and the effects of other pollutants and meteorology on ozone levels. While climate change will likely have an effect on ozone levels, other factors may also influence the number of attributable deaths.  

An Analysis of radiative forcing by anthropogenic economic sectors

When forming policies to mitigate climate change, it is imperative that the actions incorporate current levels of CO2 , ozone (O3), and aerosol particles. Of those three, O3 emissions are especially worrisome as the pollutant is mainly responsible for the warming that occurs in the atmosphere. Additionally, aerosols can also contribute to climate change by affecting the properties of clouds. These modifications include increased number of cloud droplets and smaller droplet sizes, when in turn can result in decreased precipitation and evaporation of clouds. While these chemical species are essential to understanding climate forcing, Unger, et al. (2010), argue that the emissions are not the cause, but the symptoms of climate change. The main focus when creating mitigation policy should therefore focus on the primary origin of climate change: anthropogenic factors. To better diminish changes from anthropogenic radiative forcing, Unger et al. suggest quantifying climate impact by economic sector. — Aly Stark 
Unger, N., Bond, T., Wang, J., Koch, D., Menon, S., Shindell, D., Bauer, S., 2010. Attribution of climate forcing to economic sectors. PNAS, 107: 3382 – 3387

 Unger et al. argue that the IPCC’s traditional method of examining radiative forcing is ineffective. This method examines individual pollutants and their changes over various times periods, but does not consider possible interactions between chemicals or the potential for effects caused by multiple pollutants. Therefore, to ensure smart climate policy, a complete evaluation that is sector-based is required. This study presented a comprehensive look at the total climate forcing, with emissions broken down into 13 components of the economic sector. Also included was an analysis short-lived species pollutants and aerosol radiative forcing.  Unger et al. found that aerosols from three different sectors (industry, power, and biomass burning) are contributing to larger quantities of cloud droplets, which in turn increases total cloud cover and cloud optical depth. These effects amplify reflectivity.  However, aerosol effects from other sectors were found to be insignificant. Additionally, positive radiative forcing was found in the power and industry sectors, suggesting that these sectors are major sources of SO2 emissions and contribute greatly to anthropogenic sulfate accumulation. Lastly, the climate impacts of emissions from 2000 to future time designations 2020 and 2100 are considered with regards to the current emission sectors. The biomass burning and industry sectors were found to have the greatest amount of negative radiative forcing, driven by considerable cooling effects. On the other end of the spectrum, the aviation sector was found to have the smallest amount of radiative forcing, likely due to less fuel use compared to other anthropogenic activities. Looking ahead at 2100, Unger et al. found that the radiative effects change and positive forcing is significantly perpetuated by the power industry.
To effectively combat climate change, emissions should be categorized by anthropogenic sectors. Although uncertainties in radiative forcing can occur from causes such as physical, chemical, and optical processes, this model is still stronger than past IPCC methods of examining climate forcing and the spatial effects of pollutant emissions. As a result of this radiative forcing assessment, Unger et al. found that both short-lived and long-lived species must be considered, as well as time period analysis of climate effects of cooling aerosols. Further, to best mitigate anthropogenic climate change, actions should be taken in on-road transportation, household biofuel, and animal husbandry sectors.

Savings of 19% Net GHG Flux to Atmosphere Possible With Fertilization of Crops in Early Spring

Phillips et al. (2009) conducted an experiment to determine whether the timing of fertilizer application to maize crop in Central North Dakota affects the greenhouse gas (GHG) fluxes during the growing season. Plots were fertilized either in early spring (April 1) or in late spring (May 13). It was hypothesized that the plots fertilized in early spring would produce lower net GHG emissions, due to the lower air and soil temperatures, which inhibit the microbial production and consumption of GHG. The three GHG measured include, methane, carbon dioxide, and nitrous oxide. Fertilization of the plots in early spring had a net GHG flux of 19% less than the plots which were fertilized in late spring. Over 98% of the GHG emissions came from carbon dioxide, as opposed to methane or nitrous oxide. — <!–[if supportFields]> CONTACT _Con-3EF86BDE1 \c \s \l <![endif]–>Maria Harwood<!–[if supportFields]><![endif]–>
Phillips, R., Tanaka, D., Archer, D., Hanson, J., 2009. Fertilizer Application Timing Influences Greenhouse Gas Fluxes Over a Growing Season. Journal of Environmental Quality 38, 1569–1579.

 Phillips et al. measured methane, carbon dioxide, and nitrous oxide gases, in conjunction with soil pH, electrical conductivity, texture, bulk density, total C and N, water holding capacity of the soil, air temperature near soil surface, and soil temperature 10cm below the surface. The plot measurements were taken between 1000 to 1200 hr, during the time period that is most representative of the daily fluxes, 1 to 4 times per week. These factors were measured to determine what was producing the changes in GHG emissions. The experiment was conducted over 5 months on the northern Great Plains in 5 plots, each 0.30 ha, that wer fertilized with urea in early spring, and 5 plots fertilized in late spring.
Both methane and carbon dioxide emissions showed effects from the early versus the late fertilization of the maize crop. The fluxes were greater within the soil for the plots that were fertilized in late spring. The time-integrated net GHG flux for soils that were fertilized in late spring was greater than the soils fertilized in early spring. Nitrous oxide did not show any difference in flux between the two treatments. Carbon dioxide was responsible for over 98% of the total GHG flux emissions. A net GHG flux lost to the atmosphere of 19% could be avoided in central North Dakota if fertilizer is applied to fields in early spring, before temperatures rise above 10°C. When the soil and air temperatures rise above 10°C, the microbial activity in the soil gets stimulated with the addition of urea fertilizer, producing greater GHG emissions.

The importance of gas-aerosol interactions in policy making

In current emission comparisons, the most cost effective method is one which employs multicomponent climate change mitigation strategies. These strategies involve analyzing both the direct and indirect effects of various linked emissions. However, the information of indirect effects between most gaseous pollutants and aerosols is absent. Shindell et al. (2009) took two approaches to calculate the impact of emissions on aerosols and the influence of these on radiative forcing. They found that the global warming potential (GWP) is substantially larger when the direct effects of aerosol interactions are considered and increases further when aerosol-cloud interactions are taken into account. Therefore, as atmospheric chemistry links methane, ozone, and aerosols, the policies regarding multigas mitigation should take gas-aerosol interactions into consideration.  Alyson Stark
Shindell, D., Faluvegi, G., Koch, D., Schmidt, G., Unger, N., Bauer, S., 2009. Improved Attribution of Climate Forcing to Emissions. Science 326: 716-718.

Shindell et al. relied heavily on averaged radiative forcing (RF) to compare various emissions and to estimate GWP. To find the response of atmospheric composition to both the collective and individual effects of emissions, the researchers calculated abundance based RF, which measured the effects of all emissions changing concurrently, and emissions based forcing, which instead attributed the response to a specific pollutant. Using these two techniques, Shindell et al. estimated several 100-year GWPs. These computations demonstrated that, with the absence of aerosol responses, the results were similar to previous studies. However, once the radiative effects are regarded, the GWP becomes larger in both methane and carbon monoxide (CO). Compared to the initial situation with no aerosol, the possible methane emission range increases, from approximately 25 to a range of 25-40 over a 100 year horizon. Similarly, the CO emissions initially begin at a 1-3 range and increases to a 3-8 range.  However,  the accuracy of these values is essential, and it there still remains much uncertainty in the predictions. For example, increases in these values also increases carbon dioxide, which perpetuates higher GWPs, and leads to more uncertain policymaking. 

Effects of deforestation on the regional climate of the Maya lowlands in Guatemala

The Petén basin of northern Guatemala, often referred to as the Maya lowlands, is experiencing massive deforestation. From 2000 to 2008, 2.64% percent of this region has been deforested. Such large-scale deforestation has been shown to affect regional surface temperatures and moisture (Manoharan et al., 2009). While forested areas do not differ much from deforested areas in the wet season, in the dry season deforested areas experience much higher surface temperature and lower moisture contents when compared to forested areas. Such regional climatic changes could make the restoration of deforested areas increasingly difficult. Martin Selasco
Manoharan, V., Welch, R., Lawton, R., 2009. Impact of deforestation on regional surface temperatures and moisture in the Maya lowlands of Guatemala. Geophysical Research Letters 36, L21701

V. Manoharan, R. Welch, and R. Lawton measured surface temperature, soil moisture, and vegetation in twelve regions of the Petén basin, each with an area of 30 squared kilometers. Out of the twelve regions studied, six are considered forested, three are considered partially forested, and three are considered deforested. The measurements were taken from 2000 to 2008 on clear days. They found the surface temperatures were similar during the wet season regardless of habitat or year. During the dry season, forested areas were found to be 3–4º C warmer than in the wet season, a measurement that remains relatively constant from 2000 to 2008. However, deforested areas were an average of 8º C warmer than forested regions during the dry season in 2000, and 4º C warmer than forested regions in the dry season in 2008. Soil moisture was found to be high in forested areas in the wet season regardless of year. However, deforested areas and partially deforested areas had noticeably lower soil moisture in the wet season during this period. As would be expected, forested areas were found to have less soil moisture overall during the dry season. Comparatively, deforested and partially deforested areas had much lower soil moisture in the dry season (an average of 36% saturation for deforested and partially deforested areas in 2008 compared to an average of 70% saturation for forested areas in 2008). In addition to these findings, a 9.3% decrease in forest cover was found in partially deforested areas from 2000 to 2008.
Overall, the findings suggests that forested regions have a relatively stable environment, but that deforestation leads to increased seasonal variations in soil moisture and surface temperature, with particularly noticeable effects during the dry season. Such climatic changes could negatively affect forest regeneration in affected areas.

Carbon storage in old-growth and second growth western larch forests of the Inland Northwest, USA

The deforestation of old-growth western larch forests in Montana has been shown to significantly reduce the total amount of carbon storage in the regional ecosystem (Bisbing et al. 2010). In a study that compared the amount of carbon stored in old-growth and second growth larch forests, old growth forests were found to have about three times more carbon than second growth forests. Martin Selasco
Bisbing, S., Alaback, P., and DeLuca, T., 2010. Carbon storage in old-growth and second growth fire-dependent western larch (larix occidentalis Nutt.) forests of the Inland Northwest, USA. Forest Ecology and Management 259, 1041-10

S.M. Bisbing, P.B. Alaback, and T.H. DeLuca sampled 15 pairs of adjacent old-growth and second growth larch stands in Flathead National Forest, Montana. The second growth forests that they sampled had been clear-cut between 1961 and 1979. They measured the amount of carbon found in mineral soil, forest floor, coarse woody debris, overstory, understory, and coarse roots, and then used the data to calculate the ecosystem total.

For old growth larch forests, the average total carbon captured was 305 million grams of carbon per hectare, but for second growth forests, this total was only 98 million grams of carbon per hectare. While the average amount of carbon stored in the understory was greater in second growth forests than in old-growth forests, this value only makes up less that 0.1% of the total carbon captured by the ecosystem. The differences in the amount of carbon found in mineral soil were statistically insignificant. However, the forest floor, the overstory, coarse roots, and coarse woody debris were all found to store significantly more carbon in old growth larch forests. The results also demonstrated the amount of carbon in the different parts of old growth and second growth larch forests. In old growth forests, they found the majority of the carbon in the overstory, but in second growth forests the biggest source of carbon was mineral soil. Overall, the significant loss of stored carbon from clear-cut logging suggests a need to preserve the old-growth larch forests, and that there be increased retention of large structural elements to help reduce carbon loss.

Estimating rainforest biomass stocks and carbon loss from deforestation and degradation in Papua New Guinea 1972–2002: Best estimates, uncertainties, and research needs

Papua New Guinea, a small country located in the South Pacific, contains large areas of tropical forest that play an important role in the global carbon cycle. A recent study estimated that in 2001 deforestation and forest degradation in Papua New Guinea was responsible for somewhere between 2 and 7% of global tropical carbon emissions (Bryan et al. 2010). More importantly however, this study suggests that there is a great deal of uncertainty in estimating carbon fluxes due to a lack of field measurements in this area. Furthermore, it suggests that in order to reduce carbon emissions caused by tropical deforestation, accurate and reliable biomass measurements are needed Papua New Guinea’s rainforests. Martin Selasco
Bryan, J., Shearman, P., Ash, J., Kirkpatrick, J., 2010. Estimating rainforest biomass stocks and carbon loss from deforestation and degradation in Papua New Guinea 1972–2002: Best estimates, uncertainties, and research needs. Journal of Environmental Management 91, 995–1001.
J. Bryan, P. Shearman, J. Ash, and J.B. Kirkpatrick used 22 unlogged biomass measurements to estimate the carbon stock of unlogged forests, and relied on tree censuses set up by the International Tropical Timber Association to calculate the biomass densities of logged forests. They then used high-resolution maps to calculate the amount of deforestation that occurred between 1972 and 2002. Using this data, they estimated that 1178 million tons of carbon was lost due to deforestation and degradation between 1972 and 2002.
While the researchers were able to generate a range of estimates on the carbon flux of Papua New Guinea, they expressed a large degree of uncertainty in these estimates. They attributed much this uncertainty to the measurements of unlogged biomass. Part of the problem was that these unlogged biomass measurements were not collected in range of environments, but rather tended to focus on commercial species because of their harvesting potential. They suggest that stands of Nothofagus may be over-represented in their study. Furthermore, they point out a lack of a standard approach for measuring biomass. In response to this, the researchers propose a national field survey that uses a standardized methodology to collect biomass data in unlogged forests. Acquiring such measurements would be extremely helpful in effectively reducing Papua New Guinea’s carbon emissions due to tropical deforestation.Papua New Guinea, a small country located in the South Pacific, contains large areas of tropical forest that play an important role in the global carbon cycle. A recent study estimated that in 2001 deforestation and forest degradation in Papua New Guinea was responsible for somewhere between 2 and 7% of global tropical carbon emissions (Bryan et al. 2010). More importantly however, this study suggests that there is a great deal of uncertainty in estimating carbon fluxes due to a lack of field measurements in this area. Furthermore, it suggests that in order to reduce carbon emissions caused by tropical deforestation, accurate and reliable biomass measurements are needed Papua New Guinea’s rainforests.
Bryan, J., Shearman, P., Ash, J., Kirkpatrick, J., 2010. Estimating rainforest biomass stocks and carbon loss from deforestation and degradation in Papua New Guinea 1972–2002: Best estimates, uncertainties, and research needs. Journal of Environmental Management 91, 995–1001.

J. Bryan, P. Shearman, J. Ash, and J.B. Kirkpatrick used 22 unlogged biomass measurements to estimate the carbon stock of unlogged forests, and relied on tree censuses set up by the International Tropical Timber Association to calculate the biomass densities of logged forests. They then used high-resolution maps to calculate the amount of deforestation that occurred between 1972 and 2002. Using this data, they estimated that 1178 million tons of carbon was lost due to deforestation and degradation between 1972 and 2002.
While the researchers were able to generate a range of estimates on the carbon flux of Papua New Guinea, they expressed a large degree of uncertainty in these estimates. They attributed much this uncertainty to the measurements of unlogged biomass. Part of the problem was that these unlogged biomass measurements were not collected in range of environments, but rather tended to focus on commercial species because of their harvesting potential. They suggest that stands of Nothofagus may be over-represented in their study. Furthermore, they point out a lack of a standard approach for measuring biomass. In response to this, the researchers propose a national field survey that uses a standardized methodology to collect biomass data in unlogged forests. Acquiring such measurements would be extremely helpful in effectively reducing Papua New Guinea’s carbon emissions due to tropical deforestation.