Can't see the forest for the fields

7/31/2019 Can't see the forest for the fields

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YO,

If you're looking for previous versions of stuff, before people have edited it, you can trytools----> revision history

-Kyle

Introduction

Hey guys,really sorry for posting this late. I've got a little less than two pages of very rough text. I

still need to put in a transition paragraph.-KyleSO, i copy pasted everything on word and formatted it and its a lil over 11 pages

already 1.5 spaced....he sent us our grade for the presentation and told ussomething about the CO2 so i think i should put a pharagraph on it for theosybean, altough i cant find any paper that talks about it.....anyway what im tryingto say is that if kyle writes more and i write more we might be over the 12 pages

and we are going to have to cut down. -julia

The phrase slash and burn(and this is a phrase?) conveys graphic images of industriallogging outfits cutting down huge swathes of virgin forest followed by apocalyptic clouds ofblack smoke carrying away nutrients as the slash is burnt off. The denuded fields are thenoften used for intensive grazing or modern industrial agriculture, where bare soil is subject

to erosion and local climatology changes dramatically. Throughout large swathes of theAmazon, this is indeed the case; from 1978 to 1988 the deforestation rate in the Brazilianamazon was of15,000 km2 year-1, and 230,000 km2 were deforested in 1988. The news iseven starker for flora and fauna - the rate of habitat fragmentation and degradation is38,000 km2 year-1 in the same time period, leaving 588,000 km2 adversely affected (Skoleand Tucker 1993). Severe rates of forest loss continued in some areas of the Brazilian(amazon?), at a rate from 1% to 4% during the 1990s (Achard, Eva et al. 2002). The barefields are then used either used(?) for cattle grazing, or as modern monocrop agriculture.The modern farming methods used are susceptible to high rates of soil erosion, and requirehigh inputs of petrochemical derived fertilizers and pesticides. The switch to modernindustrial agriculture, as well the associated biodiversity loss is well not only well

documented,(this does not make any sense to me) but also well publicized by various

environmental organizations. Less well known is that the changes in vegetation cover havea large impact on the radiative, energy and water balance of the affected regions. Thispaper how(this paper shows how?)the transition from forests to fields has a significantimpact on climate at the local, regional, and even global scales.First though (this could be changed), it is important to note that is in fact possible to raisecrops from cleared and burnt forests in a sustainable way. As in many geographical issues,it is a question ofscale: traditional slash and burn (henceforth referred to as swiddenagriculture) only uses small patches of land for short periods of time. Traditional swiddenagriculture is typified by small hamlet communities (such as the Hanuno culture described


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in the 50s) which select small areas within walking distance and clear them with knives or

axes. At this stage root plants are cultivated, which survive the subsequent burning (Conklin1957). The ashes release nutrients stored in the biomass back to the soil, which will supportintensive agriculture for several years before yields decrease. Fields are then left to liefallow (typically seven to ten years). Since swidden agriculture has been practiced formillennia by innumerable cultures throughout the world, it should come as no surprise that

there are many different kinds of shifting (swidden) agriculture. The Amazon basin is noexception, as it includes various rain forest peoples (can you say this?) with many differentsystems, manipulating two key variables: the production/fallow ratio and the amount ofcrop diversity (which ranges from monocrops to high-diversity intercrops) (Beckerman1983).However, increased population growth and socioeconomic demand for cash crops leadfarmers to attempt cultivation of marketable crops in smaller areas of inherited land. Also,pressure to maximize production per unit of labour and the perception that swiddenagriculture as primitive and inefficient (?) drives the conversion from traditionalswidden agriculture to modern farming. Farmers often start the process of gradual transitionwhen they notice their yields decreasing after working their fields more often (Padoch 1998).Before moving on to(should we change this?) examine the climatological changes of the

forest to field transition, we(can we say we?) should touch on two more questions toestablish a baseline for the unconverted forest areas since the assumption that land-usechange from swidden agriculture to large field pasturelands or agriculture is the directionof progressive development is controversial.(what???) First, the assumption that thesecondary growth forest, which occurs after the small swidden patches are allowed toregrow, are vastly inferior to primary forest in terms of ecological function andbiodiversity is not holding up to close scrutiny. (?) More recent scientific enquiry, suchas Schmidt-Vogts study of Northern Thailands highly intercropped swidden plots, indicatethat secondary growth can closely parallel primary growth in terms of species diversity andecological function. Of particular interest to the climatologist is that the complex structure ofthe rainforest was reproduced both quickly and accurately, meaning that the climatology ofsecondary growth swidden forest has little to distinguish itself from primary growth forest

(Schmidt-Vogt 1998).The second question deals with an age old debate- whether conservative local ways of livingare outdated with advent of new technology and knowledge. During the Green Revolutionof the mid to late 20th century, it was commonly assumed that modern monocroppingrepresented a pinnacle of efficiency and productivity vis--vis primitive farming methods.Today, Agronomists are ambivalent about the benefits of allowing/promoting developmentof forests, since overwhelming evidence clearly point to the fact that intercropped swiddensystems preserve nutrients, and are actually more productive when measured by yield/unitof land. Also, monocropping is possible (common for some in the Amazon)(huh?),which allows some of the economies of scale, such as planting and monitoring, which drivedown labour costs in modern farming to be applied to swidden systems (Beckerman 1983).I dont really get this last sentence and i think that maybe we should have another extraending sentence for the intro. - julia

Achard, F., H. D. Eva, et al. (2002). "Determination of deforestation rates of theworld's humid tropical forests." Science 297(5583): 999-1002.Beckerman, S. (1983). "Does the Swidden Ape the Jungle?" Human Ecology 11(1):1-12.Conklin, H. C. (1957). "Hanunoo agriculture: a report on an integral system ofshifting cultivation in the Philippines." Unasylva - An International Review of Forestryand Forest Products - Food and Agriculture Organization of the United Nations 11(4).


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Padoch, C., Harwell, E., Susanto, A. (1998). "Swidden, sawah, and in-between:agricultural transformation in Borneo." Human Ecology 26(1): 3-20.Schmidt-Vogt, D. (1998). "Defining degradation: the impacts of swidden on forestsin northern Thailand." Mountain Research and Development 18(2): 135-149.Skole, D. and C. Tucker (1993). "Tropical deforestation and habitat fragmentation inthe Amazon: satellite data from 1978 to 1988." Science 260(5116): 1905.

Forests

The Amazon Rainforest is located at 15 to the North and 25 to the Southof the equator. The climate is hot and humid, with the rainy season rangingfrom December to June and the dry season from June to December. High

evaporation rates drive extensive cloud cover as well as an average of about2 m of rainfall per year. The high cloud cover is the main controller ofincoming solar radiation, with solar angle playing a secondary role. Cloudcover in the Amazon basin results in far from ideal conditions for theradiation balance. The temperature in the area shows little seasonalvariation with a maximum range of betweem 24 32 C and minimumrange of 20 25 C. The dry seasons is typically one to three degreeswarmer than the wet season. The climate of the Amazon is affected by largescale synoptic effects such as El Nino which affects the climate by increasingthe amount of precipitation. (da Rocha, Goulden et al. 2004)The average canopy height of the rainforest is around 35 m (Salati andNobre 1991). The deep canopy traps much of the incident solar radiation,and thus reflectivity is very low; observed values for albedo are 0.12 0.13(citation?) on average, though this varies depending on the season and timeof day. The albedo of vegetation can be calculated by considering thescattering coefficients for leaves and soil, the leaf area index, the leaf angledistribution and the angle of incident radiation (Gash and Shuttleworth

1991). Since tropical rainforests are dense, incoming solar energy willundergo multiple absorptions, transmissions and reflections by leaves beforereaching the ground. As a result, the soil heat flux values will only be about2% of net radiation with an average flux value of 4 W/m2 entering the soil

during the day and leaving the soil during nighttime. There is little seasonalvariation in soil temperature because the energy stored during the day in thebiomass, air and soil is lost at night by radiative cooling to space (da Rocha,Goulden et al. 2004).During the wet season, there is a reduction in the amount of incoming short-wave radiation as well as net radiation because of the presence of clouds.Evaporation and sensible heat fluxes are higher during the dry season. TheLatent heat flux varies more during the wet season.


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Over the course of a day, the sensible heat flux reaches a maximum beforenoon and decreases to negative values at night. The latent heat flux reachesa maximum shortly after noon. There is a time lag because evaporation isdriven by the sensible heat flux before noon; values of latent heat fluxapproach zero at night. The Bowen ratio, calculated by dividing the sensible

heat flux by the latent heat flux, peaks in the morning and decreases duringthe day because of the increasing water vapour deficit. The aerodynamicconductance of the rainforest is very high; the rapid mixing observed abovethe rainforest is attributed to the roughness of the surface. The highestvalues for aerodynamic conductance are observed before noon when thewind speed is most significant. Lowest values for aerodynamic conductanceare observed at night when convective mixing is depressed. The canopyconductance peaks before noon and declines in the afternoon due to theclosure of stomata. Canopy conductance is greater during the wet season(da Rocha, Goulden et al. 2004).Evapotranspiration is an important component of the rainforest as it isstrongly linked to the energy balance. The diurnal variation ofevapotranspiration roughly follows the diurnal balance of net radiation,though it is greatly affected by changes in water availability (da Rocha,Goulden et al. 2004). Evapotranspiration variations depend on rainfall,photosynthetically active radiation (PAR), net radiation, mean and minimumair temperature, vapour pressure deficit (VPD), wind speed, and soiltemperature (Karam and Bras 2008). Soil moisture availability does nothave a great effect on evapotranspiration in the rainforest because of thelow values observed for soil heat flux. At night, the photo-response ofstomata causes them to close, and there is consequently little transpiration.

Most precipitation over the rainforest is recycled evaporation from therainforest itself. Therefore, evaporation plays a significant role in thepatterns of precipitation. Most precipitation observed over the rainforestoccurs shortly after noon (1 to 4 p.m.) (da Rocha, Goulden et al. 2004).CO2 fluxes depend greatly on the forest biomass. During the day, the forestacts as a sink for CO2 as it vegetation is actively photosynthesizing. Atnight, the forest acts as a source of CO2 as vegetation is actively respiring;windy condition at this time could enhance net loss of carbon to theatmosphere. The CO2 flux affects temperature, precipitation, vegetation andsoil respiration rates. CO2 fluxes between the soil and the atmosphere can

be measure by the use of an infrared gas analyzer (IRGA), together with avented dynamic chamber system. However to measure the exchange of CO2between the forest and the atmosphere at different levels, a flux tower canbe used. Data can be analyzed using the eddy covariance method (Salimon,Davidson et al. 2004).

da Rocha, H. R., M. L. Goulden, et al. (2004). "Seasonality of water and heat fluxesover a tropical forest in eastern Amazonia." Ecological Applications 14(4): S22-S32.


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Gash, J. H. C. and W. J. Shuttleworth (1991). "TROPICAL DEFORESTATION - ALBEDOAND THE SURFACE-ENERGY BALANCE." Climatic Change 19(1-2): 123-133.Karam, H. N. and R. L. Bras (2008). "Climatological Basin-Scale AmazonianEvapotranspiration Estimated through a Water Budget Analysis." Journal ofHydrometeorology 9(5): 1048-1060.Salati, E. and C. A. Nobre (1991). "POSSIBLE CLIMATIC IMPACTS OF TROPICAL

DEFORESTATION." Climatic Change 19(1-2): 177-196.Salimon, C. I., E. A. Davidson, et al. (2004). "CO2 flux from soil in pastures andforests in southwestern Amazonia." Global Change Biology 10(5): 833-843.

Pastures

Radiation Balance of Pastures compared to Forests

The net radiation, or radiation budget, at the surface can be described as Rn = (SinSout) + (LinLout)

where the short wave and long wave radiation components are: incident (S in) and reflected (Sout)

solar radiation; and incident (Lin) and emitted (Lout) terrestrial radiation. The components of theradiation balance, particularly the outward terrestrial radiation, vary based on differences in

vegetation covers, also between wet and dry season periods.

One study in particular, Randow et al, compared the average daily values of radiation

components, measured in Wm-2

, over a forest and pasture site in the Amazon Basin. Theincoming short wave radiation and incoming long wave radiation were fairly similar between the

two sites. In contrast, the outgoing reflected shortwave radiation increased from 26.1 Wm-2

for

the forest to 40.6 Wm-2

for the pasture (Randow et al 2004). Likewise, the outgoing long wave

radiation for the pasture was higher, with a value of 451.5 Wm-2

, in comparison to 448.0 Wm-2

for the forest (Randow et al 2004). Since the outgoing long wave radiation is mainly dependent

on surface temperature, the flux density values reveal the effect of higher diurnal temperature

variation observed in the pasture. Due to the increase in outgoing long wave and reflected shortwave radiation over the pasture, the net radiation balance was of a lower value, 124.2 Wm -2, in

comparison to 143.2 Wm-2 of net radiation over the forest (Randow et al 2004).

Correspondingly, the albedo increased from 0.13 to 0.20 for the forest site and pasture site

respectively (Randow et al 2004). Therefore, in summary, the reflected shortwave radiation

increases by about 55% when changing from forest to pasture. Combined with an increase of4.7% in long wave radiation loss, this causes an average reduction of 13.3% in net radiation in

the pastures, compared with the forest.

It is important to keep in mind that these are the annual daily values, but seasonal variation in

incident solar radiation may be caused by greater cloud cover during the wet season (Rocha et al1996). Correspondingly, the greater cloud cover during the wet season would reduce the average

incident solar radiation. On the other hand, the incident long wave radiation, largely affect by

atmospheric humidity, is lower in the dry season than in the wet season, for both sites.

Energy Balance of Pastures compared to ForestsThe amount of available energy, radiation balance, influences the sensible and latent heat fluxes

over forests and pastures. Due to the fact that pastures have the removal of energy storage in an


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elevated canopy air space and biomass, the energy flux densities will vary between the two sites,

as well as between wet and dry seasons.

The experiment conducted by Randow et al, also measured sensible and latent heat flux densitiesfor the forest and pasture sites, including measurements for the wet and dry season. As expected,

large difference between the two sites and seasons are noticed. In the wet season, net sensible

heat flux density, 45.5 Wm-2

, for the pasture is higher than the sensible heat flux density for theforest, 31.6 Wm-2. In contrast, the latent heat flux density is lower for the pasture, 83.0 Wm -2, in

comparison to the value of 104.5 Wm-2 for the forest (Randow et al 2004). The same trend being

true for the dry season, pastures have a higher sensible heat flux density but a lower latent heat

flux density in comparison to a forest. Moreover, in the wet season, the evaporation fraction,(evaporation / net radiation) at the pasture is 17% lower than at the forest, where this difference

in evaporation increases from 17% to 24% during the dry season.

The increase in sensible heat over the pasture is due to the specific heat capacity and increased

temperature of the soil (Joes et al 2008). Where as the decrease in latent heat over the pasture,

compared to the forest, can be explained by the loss of available water for evapotranspiration. The Bowen ratio, the ratio of the sensible and latent heat fluxes, is a critical influence on the

hydrological cycle, through its role in boundary layer development, weather and climate. The

Bowen ratio varies little over the year in the forest, however dramatic seasonality is observed forthe pasture site. The Bowen ratio for the pasture, changes from 0.3-0.6 in the wet season to 0.6-

0.8 in the dry season due to water stress (Randow et al 2004). Generally, the monthly mean

Bowen ratios, measured from the eddy correlation method, shows that pasture has larger Bowenratio, and greater seasonality, in comparison to the forests.

CO2 and water

Seasonal changes in CO2 fluxes in the forest are small, in comparison to the large reductions in

evaporation and photosynthesis observed for a pasture (Randow et al 2003).Both sites present the typical patterns of vegetated area, with negative fluxes during the day due

to the fact that photosynthetic activity is higher than respiration; and positive fluxes during thenight, due to respiration activity only.

Daytime CO2 fluxes are approximately 20-28% lower in the pasture compared to the forest,

indicting a decrease in productivity (Randow et al 2004). As the reduction in the nocturnal

respiration, 44%-57% lower in comparison to the forest, is larger than the reduction in thedaytime uptake, the combined effect is a 19-67% higher daily uptake of CO2 in the pasture

compared to the forest (Randow et al 2004). This higher photosynthetic uptake of CO2 can be

explained by the constantly renewed vegetation growth and photosynthesis, as the cattle removes

the biomass.

CitationsRandow, C. von, and et al. "Comparative measurements and seasonal variations in energy and carbon exchange over

forest and pasture in South West Amazonia." Theoretical and Applied Climatology 78(2004): 5-26.


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Jose, Jose San, and et al. "Land-use changes alter radiative energy and water vapor fluxes of a tall-grass

Andropogon field and a savanna-woodland continuum in the Orinoco lowlands." Tree Physiology 28(2008): 425-

435.

Rocha, Humberto R., and et al. "A vegetation-atmosphere interaction study for Amazonia deforestatoin using

fieldvdata and a 'single column' model." Quarterly Journal of the Royal Meterorological Society 122(1996): 567-

594.

Cropping

hey guys, everything in red are things that i think don't sound good or are

repetitive so if u have an idea on how to make them better go ahead...just don'tdelete what was there before but instead put what you think will be better inparenthesis right beside it. you can also use parenthesis to give comments on

everything else. Ill upload the rest tomorrow morning. thank you!- julia

There is a generic difference between mono-cropping lands and pasture or forested landswhich is that crops are grown every year (even twice a year), while forests take a longertime to develop, and their characteristics will not change significantly during the course ofthe year. Due to this, the fluxes between the soybean crop and the atmosphere will varygreatly during the year and will depend on the stage of development of the crop. However,an annual average for each component of the radiation balance, energy balance or anyother variable can be used to asses the differences between the three land uses.It has been determined by Sampaio et al. that soybean crops have a higher annual albedothan forest. As mentioned previously, the albedo of the forest ranges on average between

0.12 and 0.13. This strongly contrasts strongly with the albedo of soy crops which can rangefrom 0.17 to a value as high as 0.25 throughout the year in Brazil (Sampaio et al., 2007). Itwas also determined that the annual average of the leaf area index of the soybean crop isgoing to be lower than that of the forest, (The average leaf are index of soy crops is alsosignificantly lower than that of forests) even if the highest leaf area index is recorded at thesoybean crop when the plants are fully developed. The amount of outgoing longwaveradiation is going to be higher over the soybean crop than over the forest. Moreover, thenet radiation decreases when forests are converted into soybean crops. This will haveseveral implications in the local and regional climate of the Amazon.The distinct variables of the energy balance for a soybean crop differ greatly throughout theyear. The latent heat flux of soybean is highest when the soybean plants are fullydeveloped. At this same stage, the sensible heat flux is negative for most of the day. After

the soybean has been harvested, the latent heat flux decreases and the sensible heat fluxincreases dramatically. However, due to the fact that the crop absorbs less radiation(increased albedo) the latent heat flux of soybean is lower than that of forest in an annualscale. This leads to a decrease in evapotranspiration when forest is converted into soybeancrops (Costa et al., 2007). Lower evapotranspiration is also due to the fact that soybean hasa lower aerodynamic roughness (Costa et al., 2007). On the other hand, sensible heatfluxes are higher over soybean than over forested lands and this is going to contribute to asmaller decrease in evapotranspiration (Sampaio et al., 2007). Due to the differences insensible and latent heat fluxes between soybean crops and forest, the Bowen ratio is going


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to be higher over the crop than the forest. (get bowen ratio number for soybean and forestfrom part 1)Due to this decrease of water output into the atmosphere, there is going to be a decreasein precipitation, this decrease being higher during the dry season (Sampaio et al., 2007). Adecrease in precipitation is related to a decrease in cloud cover. In general, there is going tobe a greater effect on the climate if the forest is converted to soybean than if it is converted

to pasture. Even if conversion of land from forest to pasture already results in a decrease inevapotranspiration, cloud cover and thus precipitation, all of these changes are going to beattenuated when forest is converted into soybean crops.

Costa, M. H., S. N. M. Yanagi, et al. (2007). "Climate change in Amazonia caused bysoybean cropland expansion, as compared to caused by pastureland expansion."Geophysical Research Letters 34(7): 4.

Sampaio, G., C. Nobre, et al. (2007). "Regional climate change over easternAmazonia caused by pasture and soybean cropland expansion." GeophysicalResearch Letters 34(17): 7.

Conclusion

Tropical forests in the Amazon basin are being destroyed at an alarming rate(Salati and Nobre 1991). Though the traditional methods of swidden practiced inthe area for generations have not resulted in significant changes to theregional climate, current methods of deforestation are unsustainable andhave drastic effects on the climate of the region. The most commonconversions of tropical forests are conversion to pastureland following slashand burn methods and subsequently conversion to soybean monocropping(Sampaio, Nobre et al. 2007). Looking at the microclimate of a forest, pastureand soybean crop helps to explain these regional changes, and will helppredict the global changes (that the) deforestation of the Amazon will have.The main changes to the microclimate resulting from deforestation are due

to changes in albedo and canopy height. Deforestation almost always resultsin an increased level of albedo. Deforestation typically results in an increaseof albedo of about 8% (Gash and Shuttleworth 1991). (we can put these twosentences together) The Amazon Rainforest has a low albedo with littlevariation throughout the year, whereas pastures have a consistent buthigher value for albedo. Values for albedo in a soybean cropland varydepending on the time of year; for example, dramatically different values


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are observed for mature crops in comparison to after crops are harvested.Albedo directly following harvesting is generally quite low. However, albedorises quickly after the soil has dried and becomes lighter; high values foralbedo are also observed when soybean crops are mature (Costa, Yanagi et al.2007). Decreased albedo will result in less available net radiation and will

lead to lower sensible and latent heat fluxes (Salati and Nobre 1991).The decreased roughness that accompanies deforestation has a great affecton the aerodynamic conductance of the region. The high roughness of aforest contributes to high aerodynamic conductance and consequently fastevaporation of intercepted water (da Rocha, Goulden et al. 2004). Roughness isreduced dramatically in pastures. Roughness is also reduced in soy crops,particularly following harvesting (Costa, Yanagi et al. 2007). Loweredaerodynamic conductance in combination with the higher stomatalconductance observed in pastures and soybean crops results in uncoupling.As a result, lower evaporation of intercepted water will be observed indeforested areas. Another effect of decreased aerodynamic conductance isthe depression of convection, resulting in the build-up of large temperaturegradients at the surface of both pastures and soy crops. This temperaturegradient will increase the emitted longwave radiation, and further reduce theenergy available for evapotranspiration (Salati and Nobre 1991). This depressedconvection will also decrease the depth of the boundary layer. (Gash andShuttleworth 1991)

Other noteworthy changes include shallower roots in pasture vegetation andsoy crops. Particularly in pastureland, which is not irrigated, the vegetationwill be more susceptible to drying and will evaporate less water (Gash andShuttleworth 1991). Because of the decreased latent heat flux and the shorter

canopy, less water will be stored in the canopy and greater temperaturefluctuations will result the local fauna that are adapted to lower foresttemperatures and low diurnal fluctuation will likely be greatly affected. Aswell, lower LAI values in pastures and soybean crops means that less CO2will be assimilated. (Salati and Nobre 1991).While traditional swidden methods result in the retention of nutrients in thearea, conversion to soybean monocropping vastly reduces the nutrients inthe soil, and therefore converting back to old growth forest in the future willbe much less feasible. **kyle source**Using the above changes to the local climate GCMs are attempting to predictthe changes to the regional and global climates. GCMs that model Amazondeforestation typically predict changes to the water cycle (Salati and Nobre1991). Much of the rainfall in the Amazon basin is recycled evaporated waterfrom the rainforest, (da Rocha, Goulden et al. 2004) thus the widespreadreduction in evaporation throughout the rainforest will reduce precipitationover the area as well. The widespread changes in albedo are predicted byGCMs to reduce cloud cover and precipitation in the region. Predicted valuesof reduced rainfall are around 100mm of rainfall per year (Gash and


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Shuttleworth 1991). These dryer conditions can make the rainforest moresusceptible to forest fires (Salati and Nobre 1991). Soy crops have higheraverage value of albedo when averaged throughout the year, therefore ithas been predicted that the reduction in precipitation will be more adversebecause of soy crops as compared to pasturelands (Costa, Yanagi et al. 2007).

It is important to consider what the effects regional climate change will haveon biodiversity. The Amazon rainforest is a large source of the worlds

biodiversity (Fearnside 2008). Changes to rainfall regimes can significantlyaffect the flora and fauna of the region, and make the region moresusceptible to forest fires and invasive species, such as vegetation fromnearby savannahs. This can lead to a positive feedback in which furtherdestruction of the rainforest will occur due to establishing savannahvegetation, further changing the regional climate of the area (Salati and Nobre1991).The effects of increasing levels of carbon dioxide in the atmosphere havelong been associated with an increase in global surface temperatures.Massive amounts of carbon dioxide are released into the atmosphere whenrainforest is burnt down. Because the pastureland and soybean have lowerassimilative capacities of carbon dioxide, these land changes will alsocontribute to higher levels of carbon dioxide in the atmosphere. Globalwarming and climate change are therefore possible results of widespreaddeforestation in the Amazon.On a smaller scale, evaporation from the Amazon basin is a large source ofwater to dryer climates, particularly to the south. A reduction in levels ofevaporation in the Amazon basin will therefore likely contribute to lowerlevels of rainfall in regions outside of the Amazon as well.

One other postulated effect of deforestation in the Amazon is an effect onthe Hadley-Walker circulation. The release of latent heat by evaporatedwater from the Amazon basin is a source of heat that drives the Hadley-Walker circulation to redistribute heat to higher latitudes. A reduction inevaporation therefore from the Amazon can weaken the Hadley-Walkercirculation (Salati and Nobre 1991).The Amazon is an important source of ecosystem services that we dependon. However, large scale deforestation in the manner that is being practicedwill lead to effects that will disturb climate and biodiversity worldwide(Fearnside 2008). In order to better understand these global effects, it is useful

to look at the changes to the microclimates of these transitions. Only oncethese small changes are well understood can we model with great accuracythe diverse effects deforestation will have on the world; perhaps this willhelp in finding ways to reduce human impact on the worlds climate in the

future.Costa, M. H., S. N. M. Yanagi, et al. (2007). "Climate change in Amazonia caused bysoybean cropland expansion, as compared to caused by pastureland expansion."Geophysical Research Letters 34(7): 4.


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agriculture to large field pasturelands or agriculture is the direction of progressive development

is controversial.

Firstly, the assumption that the secondary growth forest, which occurs after the small swiddenpatches are allowed to regrow, are vastly inferior to primary forest in terms of ecological

function and biodiversity does not hold true. More recent scientific enquiry, such as Schmidt-

Vogts study of Northern Thailands highly intercropped swidden plots, indicate that secondarygrowth can closely parallel primary growth in terms of species diversity and ecological function.

Of particular interest to the climatologist is that the complex structure of the rainforest was

reproduced both quickly and accurately, meaning that the climatology of secondary growth

swidden forest has little to distinguish itself from primary growth forest (Schmidt-Vogt 1998).

The second question deals with an age old debate- whether conservative local ways of living are

outdated with advent of new technology and knowledge. During the Green Revolution of themid to late 20th century, it was commonly assumed that modern monocropping represented a

pinnacle of efficiency and productivity vis--vis primitive farming methods. Today,

Agronomists are ambivalent about the benefits of allowing/promoting development of forests,since overwhelming evidence clearly point to the fact that intercropped swidden systems

preserve nutrients, and are actually more productive when measured by yield/unit of land.

However, increased population growth and socioeconomic demand for cash crops lead farmers

to attempt cultivation of marketable crops in smaller areas of inherited land. Also, pressure tomaximize production per unit of labour and the perception that swidden agriculture is primitive

and inefficient, drives the conversion from traditional swidden agriculture to modern mono-crop

farming (Padoch 1998).Many studies have significantly improved the understanding of the response of the forest

ecosystem to environmental conditions. However, many of these flux studies focus on primary

forest, and little attention is paid to the impacts of changes in surface vegetation cover. To assess

the effects of these changes requires comparative measures over different vegetation cover,including. The paper will attempt to show how the transition form forests to fields has a

significant impact on climate at the local, regional and even global scales.

Amazon Basin Forests: Background and flux densities

Location and ClimateThe Amazon Rainforest is located at 15 to the North and 25 to the South of the equator. Theclimate is hot and humid, with the rainy season ranging from December to June and the dry

season from June to December. High evaporation rates drive extensive cloud cover as well as an

average of about 2 m of rainfall per year. This high cloud cover is the main controller ofincoming solar radiation, with solar angle playing a secondary role. The cloud cover in the

Amazon basin results in far from ideal conditions for the radiation balance. In addition, thetemperature in the area shows little seasonal variation with a maximum range of between 24 32

C and minimum range of 2025 C. Moreover, the dry season is typically one to three degrees

warmer than the wet season. This described climate of the Amazon is affected by large scalesynoptic effects such as El Nino which influence the climate by increasing the amount of

precipitation. (da Rocha, Goulden et al. 2004)


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Radiation and Energy BalanceThe average canopy height of the rainforest is around 35 m (Salati and Nobre 1991). The deep

canopy traps much of the incident solar radiation, and thus reflectivity is very low; observedvalues for albedo are 0.120.13 on average, though this varies depending on the season and

time of day (Salati and Nobre 1991). The albedo of vegetation can be calculated by considering

the scattering coefficients for leaves and soil, the leaf area index, the leaf angle distribution and

the angle of incident radiation (Gash and Shuttleworth 1991). Since tropical rainforests aredense, incoming solar energy will undergo multiple absorptions, transmissions and reflections by

leaves before reaching the ground. As a result, the soil heat flux values will only be about 2% of

net radiation with an average flux value of 4 W/m2

entering the soil during the day and leavingthe soil during nighttime. There is little seasonal variation in soil temperature because the energy

stored during the day in the biomass, air and soil is lost at night by radiative cooling to space (da

Rocha, Goulden et al. 2004).

During the wet season, there is a reduction in the amount of incoming short-wave radiation as

well as net radiation due to the presence of clouds. Moreover, evaporation and sensible heatfluxes are higher during the dry season and the latent heat flux varies more during the wet

season.

The variability in radiation is the driving force behind the forests energy balance, influencing

the latent and sensible heat flux densities. (connecting sentence...)

Over the course of a day, the sensible heat flux reaches a maximum before noon and decreases tonegative values at night. In contrast, the latent heat flux reaches a maximum shortly after noon.

There is a time lag because evaporation is driven by the sensible heat flux before noon; values of

latent heat flux approach zero at night. The Bowen ratio, calculated by dividing the sensible heat

flux by the latent heat flux, peaks in the morning and decreases during the day because of the

increasing water vapour deficit.

The aerodynamic conductance of the rainforest is very high; the rapid mixing observed above the

rainforest is attributed to the roughness of the surface. The highest values for aerodynamic

conductance are observed before noon when the wind speed is most significant. Lowest valuesfor aerodynamic conductance are observed at night when convective mixing is depressed. The

canopy conductance peaks before noon and declines in the afternoon due to the closure of

stomata and canopy conductance is greater during the wet season (da Rocha, Goulden et al.2004).

Evapotranspiration is an important component of the rainforest as it is strongly linked to the

energy balance. The diurnal variation of evapotranspiration roughly follows the diurnal balanceof net radiation, though it is greatly affected by changes in water availability (da Rocha, Goulden

et al. 2004). Evapotranspiration variations depend on rainfall, photosynthetically active radiation(PAR), net radiation, mean and minimum air temperature, vapour pressure deficit (VPD), wind

speed, and soil temperature (Karam and Bras 2008). Soil moisture availability does not have a

great effect on evapotranspiration in the rainforest because of the low values observed for soilheat flux. At night, the photo-response of stomata causes them to close, and there is consequently

little transpiration. Most precipitation over the rainforest is recycled evaporation from the


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rainforest itself. Therefore, evaporation plays a significant role in the patterns of precipitation,

where most precipitation observed over the rainforest occurs shortly after noon, 1 to 4 p.m. (daRocha, Goulden et al. 2004).

CO2 exchange with the atmosphereLikewise, in connection to the energy balance of the rainforest, CO

2fluxes depend greatly on the

forest biomass. During the day, the forest acts as a sink for CO2 as the vegetation is activelyphotosynthesizing. At night, the forest acts as a source of CO2 as the vegetation is actively

respiring; and windy condition at this time can enhance net loss of carbon to the atmosphere. The

CO2 flux affects temperature, precipitation, vegetation and soil respiration rates, where the fluxes

between the soil and the atmosphere can be measure by the use of an infrared gas analyzer(IRGA), together with a vented dynamic chamber system. However, to measure the exchange of

CO2 between the forest and the atmosphere at different levels, a flux tower can be used and data

can be analyzed using the eddy covariance method (Salimon, Davidson et al. 2004). (transition sentence)Looking at the microclimate of a pasture and soybean crop, in comparison to a rainforest, helps

to explain regional changes, and will help predict the global changes that deforestation of the

Amazon will have.

Pastures

Radiation balance of pastures compared to forestsThe net radiation, or radiation budget, at the surface can be described as

Rn = (SinSout) + (LinLout)where the short wave and long wave radiation components are: incident (S in) and reflected (Sout)

solar radiation; and incident (Lin) and emitted (Lout) terrestrial radiation. The components of the

radiation balance, particularly the outward terrestrial radiation, vary based on differences in

vegetation covers, also between wet and dry season periods.

One study in particular, Randow et al, compared the average daily values of radiation

components, measured in Wm-2

, over a forest and pasture site in the Amazon Basin. The

incoming short wave radiation and incoming long wave radiation were fairly similar between thetwo sites. In contrast, the outgoing reflected shortwave radiation increased from 26.1 Wm-2 for

the forest to 40.6 Wm-2

for the pasture (Randow et al 2004). Likewise, the outgoing long wave

radiation for the pasture was higher, with a value of 451.5 Wm-2

, in comparison to 448.0 Wm-2

for the forest (Randow et al 2004). Since the outgoing long wave radiation is mainly dependent

on surface temperature, the flux density values reveal the effect of higher diurnal temperature

variation observed in the pasture. Due to the increase in outgoing long wave and reflected short

wave radiation over the pasture, the net radiation balance was of a lower value, 124.2 Wm-2

, incomparison to 143.2 Wm-2 of net radiation over the forest (Randow et al 2004).

Correspondingly, the albedo increased from 0.13 to 0.20 for the forest site and pasture site

respectively (Randow et al 2004). Therefore, in summary, the reflected shortwave radiation

increases by about 55% when changing from forest to pasture. Combined with an increase of4.7% in long wave radiation loss, this causes an average reduction of 13.3% in net radiation in

the pastures, compared with the forest.


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It is important to keep in mind that these are the annual daily values, but seasonal variation in

incident solar radiation may be caused by greater cloud cover during the wet season (Rocha et al

1996). In the same way, the greater cloud cover during the wet season would reduce the averageincident solar radiation. On the other hand, the incident long wave radiation, largely affect by

atmospheric humidity, is lower in the dry season than in the wet season, for both sites.

Energy balance of pastures compared to forestsThe amount of available energy, radiation balance, influences the sensible and latent heat fluxes

over forests and pastures. Due to the fact that pastures have the removal of energy storage in anelevated canopy air space and biomass, the energy flux densities will vary between the two sites,

as well as between wet and dry seasons.

The experiment conducted by Randow et al, also measured sensible and latent heat flux densities

for the forest and pasture sites, including measurements for the wet and dry season. As expected,

large difference between the two sites and seasons were noticed. In the wet season, net sensible

heat flux density, 45.5 Wm-2, for the pasture is higher than the sensible heat flux density for theforest, 31.6 Wm

-2. In contrast, the latent heat flux density is lower for the pasture, 83.0 Wm

-2, in

comparison to the value of 104.5 Wm-2

for the forest (Randow et al 2004). The same trend beingtrue for the dry season, pastures have a higher sensible heat flux density but a lower latent heat

flux density in comparison to a forest. Moreover, in the wet season, the evaporation fraction,

(evaporation / net radiation) at the pasture is 17% lower than at the forest, where this difference

in evaporation increases from 17% to 24% during the dry season.

The increase in sensible heat over the pasture is due to the specific heat capacity and increasedtemperature of the soil (Joes et al 2008). Where as the decrease in latent heat over the pasture,

compared to the forest, can be explained by the loss of available water for evapotranspiration.

The Bowen ratio, the ratio of the sensible and latent heat fluxes, is a critical influence on the

hydrological cycle, through its role in boundary layer development, weather and climate. The

Bowen ratio varies little over the year in the forest, however dramatic seasonality is observed forthe pasture site. The Bowen ratio for the pasture, changes from 0.3-0.6 in the wet season to 0.6-

0.8 in the dry season due to water stress (Randow et al 2004). Generally, the monthly mean

Bowen ratios, measured from the eddy correlation method, shows that pasture has larger Bowenratio, and greater seasonality, in comparison to the forests.

Differences in CO2 and water exchange for pastures compared to forests (there is nothing

about water here so maybe just put CO2?)

Seasonal changes in CO2 fluxes in the forest are small, in comparison to the large reductions inevaporation and photosynthesis observed for a pasture (Randow et al 2003).Both sites present the typical patterns of vegetated area, with negative fluxes during the day due

to the fact that photosynthetic activity is higher than respiration; and positive fluxes during the

night, due to respiration activity only.

Daytime CO2 fluxes are approximately 20-28% lower in the pasture compared to the forest,indicting a decrease in productivity (Randow et al 2004). As the reduction in the nocturnal


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respiration, 44%-57% lower in comparison to the forest, is larger than the reduction in the

daytime uptake, the combined effect is a 19-67% higher daily uptake of CO2 in the pasturecompared to the forest (Randow et al 2004). This higher photosynthetic uptake of CO2 can be

explained by the constantly renewed vegetation growth and photosynthesis, as the cattle removes

the biomass.

Soybean mono-crop fields

There is a generic difference between mono-cropping lands, pasture and forested lands, bymeans of vegetative growth. For crop land, the crops are grown every year, even twice a year,

while forests take a longer time to develop, and their characteristics will not change significantly

during the course of the year. Due to this, the fluxes between the soybean crop and the

atmosphere will vary greatly during the year and will depend on the stage of development of thecrop. However, an annual average for each component of the radiation balance, energy balance

or any other variable can be used to asses the differences between the three land uses.

Radiation balance of soybean fields in comparison to forestsIt has been determined by Sampaio et al. that soybean crops have a higher annual albedo than

forest. As mentioned previously, the albedo of the forest ranges on average between 0.12 and0.13. This strongly contrasts with the albedo of soy crops which can range from 0.17 to a value

as high as 0.25 throughout the year in Brazil (Sampaio et al 2007). It was also determined that

the annual average of the leaf area index of the soybean crop is significantly lower than that ofthe forest, even when the plants are fully developed. Therefore, the amount of outgoing long

wave radiation is higher over the soybean crop than over the forest. Moreover, the net radiation

decreases when forests are converted into soybean crops, which will have several implications in

the local and regional climate of the Amazon.

Energy balance of soybean fields in comparison to forestsThe distinct variables of the energy balance for a soybean crop differ greatly throughout the year,

for example the latent heat flux density of soybean fields is highest when the soybean plants are

fully developed. At this same stage, the sensible heat flux is negative for most of the day. Oncethe soybean has been harvested, the latent heat flux decreases and the sensible heat flux increases

dramatically. Nevertheless, due to the fact that the crop absorbs less radiation, the latent heat flux

of soybean is lower than that of forest in an annual scale.

Correspondingly, this leads to a decrease in evapotranspiration when forest is converted intosoybean crops (Costa et al., 2007). This decrease in evapotranspiration can also be due to the fact

that soybean has a lower aerodynamic roughness (Costa et al., 2007). On the other hand, sensible

heat fluxes are higher over soybean fields than over forested lands, contributing to a smallerdecrease in evapotranspiration (Sampaio et al., 2007). Due to the differences in sensible and

latent heat fluxes between soybean crops and forest, the Bowen ratio is going to be higher overthe soybean fields than the forest. (get bowen ratio number for soybean and forest from part 1)

With a decrease in water released into the atmosphere, a decrease in precipitation occurs, where

this decrease in precipitation is higher during the dry season (Sampaio et al., 2007). Similarly,this decrease in precipitation is associated to a decrease in cloud cover.


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In general, there is going to be a greater effect on the climate if the forest is converted to soybean

than if it is converted to pasture. Even if conversion of land from forest to pasture already resultsin a decrease in evapotranspiration, cloud cover and thus precipitation, all of these changes are

going to be attenuated when forest is converted into soybean crops. (not clear, might not be

necessary)

Conclusion

Local changesTropical forests in the Amazon basin are being destroyed at an alarming rate (Salati and Nobre1991). Though the traditional methods of swidden practiced in the area for generations have not

resulted in significant changes to the regional climate, current methods of deforestation are

unsustainable and have drastic effects on the climate of the region. The most common

conversions of tropical forests are conversion to pastureland following slash and burn methodsand subsequently conversion to soybean monocropping (Sampaio, Nobre et al. 2007). Looking at

the microclimate of a forest, pasture and soybean crop helps to explain these regional changes,

and will help predict the global changes that deforestation of the Amazon will have.

The main changes to the microclimate resulting from deforestation are due to changes in albedoand canopy height. Deforestation almost always results in an increased level of albedo, typically

an increase in albedo of approximately 8% (Gash and Shuttleworth 1991). The Amazon

Rainforest has a low albedo with little variation throughout the year, whereas pastures have a

consistent but higher value for albedo. Values for albedo in a soybean cropland vary dependingon the time of year; for example, dramatically different values are observed for mature crops in

comparison to after crops are harvested. Albedo directly following harvesting is generally quite

low. However, albedo rises quickly after the soil has dried and becomes lighter; high values for

albedo are also observed when soybean crops are mature (Costa, Yanagi et al. 2007). Decreased

albedo will result in less available net radiation and will lead to lower sensible and latent heatfluxes (Salati and Nobre 1991).

The decreased roughness that accompanies deforestation has a great affect on the aerodynamic

conductance of the region. The high roughness of a forest contributes to high aerodynamicconductance and consequently fast evaporation of intercepted water (da Rocha, Goulden et al.

2004). Roughness is reduced dramatically in pastures and soy crop fields, particularly following

harvesting of crops (Costa, Yanagi et al. 2007). The lowered aerodynamic conductance incombination with the higher stomatal conductance observed in pastures and soybean crops

results in uncoupling. Consequently, lower evaporation of intercepted water will be observed in

deforested areas. Another effect of decreased aerodynamic conductance is the depression of

convection, resulting in the build-up of large temperature gradients at the surface of bothpastures and soy crops. This temperature gradient will increase the emitted long wave radiation,

and further reduce the energy available for evapotranspiration (Salati and Nobre 1991).

Additionally, this depressed convection will also decrease the depth of the boundary layer (Gashand Shuttleworth 1991).

Other noteworthy changes include shallower roots in pasture vegetation and soy crops.

Particularly in pastureland, which is not irrigated, the vegetation will be more susceptible to


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drying and will evaporate less water (Gash and Shuttleworth 1991). Due to the decreased latent

heat flux and the shorter canopy, less water will be stored in the canopy and greater temperaturefluctuations will result the local fauna that are adapted to lower forest temperatures and low

diurnal fluctuation. As well, lower LAI values in pastures and soybean crops means that less CO 2will be assimilated (Salati and Nobre 1991). While traditional swidden methods result in the

retention of nutrients in the area, conversion to soybean monocropping vastly reduces thenutrients in the soil, and therefore converting back to old growth forest in the future will be much

less feasible.

Regional changesUsing the above changes to the local climate, Global Climate Models (GCMs) are attempting tocalculate the changes on the regional and global climates, predicting that Amazon deforestation

will adversely influence the water cycle (Salati and Nobre 1991). Much of the rainfall in the

Amazon basin is recycled evaporated water from the rainforest, (da Rocha, Goulden et al. 2004)

thus the widespread reduction in evaporation throughout the rainforest will reduce precipitationover the area as well. Likewise, the widespread changes in albedo that are predicted by GCMs

will reduce cloud cover and precipitation in the region. Predicted values of reduced rainfall are

around 100mm of rainfall per year (Gash and Shuttleworth 1991), where these dryer conditionscan make the rainforest more susceptible to forest fires (Salati and Nobre 1991). Soybean crops

have a higher value of albedo, when averaged throughout the year, therefore it has been

predicted that the reduction in precipitation will be more adverse with the conversion of forest tosoybean crops, compared to pasturelands (Costa, Yanagi et al. 2007).

It is important to consider what effect regional climate change will have on biodiversity, where

the Amazon rainforest is a large source of the worlds biodiversity (Fearnside 2008). Changes torainfall regimes can significantly affect the flora and fauna of the region, making the area more

susceptible to forest fires and invasive species, such as vegetation from nearby savannahs. Thiscan lead to a positive feedback in which further destruction of the rainforest will occur due to

establishing savannah vegetation, further changing the regional climate of the area (Salati andNobre 1991).

Global changesThe effects of increasing levels of carbon dioxide in the atmosphere have long been associated

with an increase in global surface temperatures. Massive amounts of carbon dioxide are released

into the atmosphere when rainforest is burnt down. Because the pastureland and soybean havelower assimilative capacities of carbon dioxide, these land changes will also contribute to higher

levels of carbon dioxide in the atmosphere. Global warming and climate change are therefore

possible results of widespread deforestation in the Amazon.

On a smaller scale, evaporation from the Amazon basin is a large source of water to dryerclimates, particularly to the south. A reduction in levels of evaporation in the Amazon basin willtherefore likely also contribute to lower levels of rainfall in regions outside of the Amazon. One

other postulated effect of deforestation in the Amazon is the influence on the Hadley-Walker

circulation. The release of latent heat by evaporated water from the Amazon basin is a source of

energy that drives the Hadley-Walker circulation to redistribute heat to higher latitudes. Areduction in evaporation in the Amazon therefore can weaken the Hadley-Walker circulation

(Salati and Nobre 1991).


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The Amazon Basin is an important source of ecosystem services that we depend on. However,

large scale deforestation in the manner that is being practiced will lead to effects that will disturb

climate and biodiversity worldwide (Fearnside 2008). In order to better understand these globaleffects, it is useful to look at the changes to the microclimates of these transitions. Only once

these small changes are well understood can we model with great accuracy the diverse effects

deforestation will have on the world; perhaps this will help in finding ways to reduce human

impact on the worlds climate in the future.

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forests." Science 297(5583): 999-1002.

Beckerman, S. (1983). "Does the Swidden Ape the Jungle?" Human Ecology 11(1): 1-12.

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Philippines." Unasylva - An International Review of Forestry and Forest Products - Food and Agriculture

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Costa, M. H., S. N. M. Yanagi, et al. (2007). "Climate change in Amazonia caused by soybean cropland

expansion, as compared to caused by pastureland expansion." Geophysical Research Letters 34(7): 4.

da Rocha, H. R., M. L. Goulden, et al. (2004). "Seasonality of water and heat fluxes over a tropical forest in

eastern Amazonia." Ecological Applications 14(4): S22-S32.

da Rocha, Humberto R., and et al. "A vegetation-atmosphere interaction study for Amazonia deforestatoin

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Fearnside, P. M. (2008). "Amazon forest maintenance as a source of environmental services." Anais Da

Academia Brasileira De Ciencias 80(1): 101-114.

Gash, J. H. C. and W. J. Shuttleworth (1991). "Tropical DeforestationAlbedo and the Surface Energy

Balance" Climatic Change 19(1-2): 123-133.

Jose, Jose San, and et al. "Land-use changes alter radiative energy and water vapor fluxes of a tall-grass

Andropogon field and a savanna-woodland continuum in the Orinoco lowlands." Tree Physiology 28(2008):

425-435.

Karam, H. N. and R. L. Bras (2008). "Climatological Basin-Scale Amazonian Evapotranspiration Estimated

through a Water Budget Analysis." Journal of Hydrometeorology 9(5): 1048-1060.

Padoch, C., Harwell, E., Susanto, A. (1998). "Swidden, sawah, and in-between: agricultural transformation in

Borneo." Human Ecology 26(1): 3-20.

Randow, C. von, and et al. "Comparative measurements and seasonal variations in energy and carbon

exchange over forest and pasture in South West Amazonia." Theoretical and Applied Climatology 78(2004):

5-26.

Schmidt-Vogt, D. (1998). "Defining degradation: the impacts of swidden on forests in northern Thailand."

Mountain Research and Development 18(2): 135-149.


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Skole, D. and C. Tucker (1993). "Tropical deforestation and habitat fragmentation in the Amazon: satellite

data from 1978 to 1988." Science 260(5116): 1905.

Salati, E. and C. A. Nobre (1991). "Possible Climatic Impacts of Tropical Deforestation" Climatic Change

19(1-2): 177-196.Salimon, C. I., E. A. Davidson, et al. (2004). "CO2 flux from soil in pastures and forests in southwestern

Amazonia." Global Change Biology 10(5): 833-843.

Sampaio, G., C. Nobre, et al. (2007). "Regional climate change over eastern Amazonia caused by pasture and

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Can't see the forest for the fields