• Energy Research

Forest growth in relation to weather and soils is studied using a physiological simulation model. Growth potential depends on physiological characteristics of the plant species in combination with ambient weather conditions (mainly temperature and incoming radiation). For a given site, growth may be lower because of incomplete canopy closure, shortage of water and nutrients, and the occurrence of growth-disturbing factors such as pests, diseases, and damage to the plants, e.g. by windthrow or frost. Attention is focused on the main growth-limiting factors, i.e. canopy closure, and the availability of water, nitrogen and phosphorus, so that differences in growth between different sites can be explained as a function of the properties of plant and soil, and of the ambient weather at a particular site. The model is applied to even-aged Douglas fir stands in the Netherlands because of the availability of field data for testing and evaluating it.The life cycle of trees and forests encompasses many years, and in order to be able to study overall stand dynamics, the model aims at simulating growth over periods of several decades. This allows the results of the model to be evaluated against data from permanent field plots, that are also being used in conventional, descriptive research on growth and yield. Furthermore, simulating forest growth over such long periods makes the results from the model comparable with the results of practical forest management. Variations in growth during the year are caused by changes in incoming radiation, temperature and water availability in the soil. To simulate this, time intervals of one day are used for the main part of the simulation model.The particular value of simulation models in forestry lies in the possibility they offer of combining different aspects of growth in an overall approach, and of studying stand dynamics over a long period of time without having to rely entirely on expensive and time-consuming field trials. Moreover, in a situation where the environment for forest growth may change e.g. as the result of industrial pollution, or as a consequence of gradual climatic changes, modelling is one of the important means by which to assess these changes and potential damage.The subject of the study, an even-aged coniferous forest stand, is described in terms of the biomass components foliage, branches, stems and roots. These four components are the main state variables in the model. To enable comparisons to be made between the results from the model and the data from permanent field plots, only stem biomass and stem volume are considered, together with the number of trees. This reflects a top-down approach to growth, which is calculated as total stand growth per unit of soil surface area, before it is distributed over individual trees. In addition to state variables that denote biomass amounts, stand structure is also characterized by stand height, average dimensions of the tree crowns, and total depth of the rooted soil profile. All other state and intermediate variables of the trees (such as the Leaf Area Index of the stand), are derived from simulated biomass components and stand structure. In the model, ambient weather is characterized using meteorological data from a local weather station: total daily global radiation, daily minimum and maximum temperatures, daily vapour pressure of the air, average wind speed at 10 m above short vegetation, and precipitation. The latter is characterized by daily rainfall and the average number of rainfall events per day. Only the rooted soil profile is used to describe the soil compartment. Soil moisture retention properties are the main variables for the hydrological submodel. The simulation of nutrient dynamics is based on the total amount of nutrients retained in the rooted soil profile and incorporated in the stand biomass. Nutrient inputs to the system are described by forcing functions, and used as input to the model.Chapter 3 shows how primary production is calculated for the whole stand. Canopy assimilation is calculated from the distribution of photosynthetically active radiation over the foliage, together with the photosynthesis/light response curve at ambient temperature for the surface of an individual leaf. The assimilation submodel uses a three- point Gaussian integration, as described recently by Goudriaan (1986), and Spitters (1986). The distribution of photosynthetically active radiation over the foliage accounts for gaps in the canopy, and allows for clustering of the foliage, as in the case of grouping of needles around branches in old stands. Typical aspects of canopy assimilation in Douglas fir stands, are the evergreen habitus of the stand, and the generally low maximum photosynthesis rates, (around 15 kg CH 2 O ha -1h -1). These low rates of photosynthesis are coupled with high stomatal resistances for the diffusion of both carbon dioxide and water vapour.After canopy assimilation has been estimated, net growth is calculated by accounting for maintenance respiration, and by allocating the assimilates available for growth to the biomass components. Growth respiration is taken into account when converting assimilate products to structural dry matter. To calculate maintenance respiration, sapwood is distinguished from heartwood. It is found that the hypothesis (Boysen Jensen, 1928; Kira and Shidei, 1967) that tree growth declines with age of the trees because maintenance requirements increase with accumulation of stem biomass does not hold when maintenance requirements are related to sapwood only. Sapwood (like foliage, branches and roots) has a limited life-span, and the maximum value it attains during stand development depends on site productivity. This maximum value is reached within 15 years of the time of maximum annual increment. Growth respiration is calculated by taking the chemical composition of the biomass formed into account. The allocation of assimilates to the biomass components is based on a distribution key derived from published data. The distribution of growth over the biomass components changes during stand development, and also depends on the productivity of the site. Stem dry weight increment is converted to volume increment by dividing the estimated dry weight increment by the basic density of the stem wood formed, i.e. the oven-dry weight per unit of fresh volume. Individual tree increment is calculated by dividing total stem volume increment by the number of trees in the stand, and only an average value for diameter at breast height is calculated from tree volume and height, using an empirical regression equation.Chapter 4 describes the hydrological part of the model. The three main aspects considered in the model are: a) interception of precipitation by the canopy and the resulting net infiltration to the soil compartment; b) the soil moisture balance; c) and uptake and transpiration of soil moisture by the trees. Coniferous forests in western Europe are often located on sandy soils with a limited soil moisture holding capacity and restricted capillary rise. This means that in periods of drought, availability of soil moisture becomes limiting for growth. In the model, therefore, it suffices to simulate water availability with an elementary summary model that keeps track of soil moisture. Soil moisture content and the rate of infiltration are simulated by assuming that the soil horizons are filled to field capacity by a sharp wetting front proceeding from the top of the soil profile downwards. Root uptake is assumed to proceed until soil moisture is depleted to the wilting point. Field capacity and wilting point are derived from soil suction curves, and depend on physical soil characteristics.Tall forest stands have considerable aerodynamic roughness, and this means that the aerodynamic resistance to the transport of water vapour from the surface of the foliage to the overlying atmosphere is small (around 10 s m -1). Besides, the large stomatal resistance of Douglas fir needles results in a minimum canopy resistance for the transpiration flux of 100 to 200 s m -1; therefore, precipitation intercepted by the vegetation will evaporate at rates several times the transpiration rate under the same atmospheric conditions. Therefore, interception represents a real loss that has to be accounted for. To estimate interception, the amount of intercepted precipitation is subtracted from daily precipitation.Daily transpiration is estimated with the Penman-Monteith combination equation, with total canopy resistance as one of the input variables. This resistance depends on: a) the vapour pressure deficit of the air (here assumed to pose a lower limit on stomatal resistance), b) the water status of the foliage, expressed in terms of needle water potential, and c) the stomatal opening resulting from photosynthesis. All three effects on stomatal resistance are calculated independently, and the largest resistance is used in the model to estimate total canopy resistance. The influence of vapour pressure and plant water status (through needle water potential), Is assumed to be the same for all foliage in the canopy. The stomatal resistance estimated from net photosynthesis rates varies with varying photosynthesis rates inside the canopy. As in the calculation of canopy assimilation, a Gaussian integration procedure is used to estimate the weighted average foliage resistance. The resulting transpiration rates are found to be unexpectedly low during the growing season. Total annual transpiration, however, is in accordance with published data, and the simulated change in soil moisture during 1983 compares well with measurements from the field plots. It is concluded that on dry soils like those frequently occupied by coniferous stands in the Netherlands, water shortage may have considerable influence on growth, even though transpiration rates are low. In its present state the model can be used to calculate the reduction In growth caused by water shortage, for different sites, and for stands of different structure.In chapter 5 the simulation of nutrient dynamics and the influence of nitrogen and phosphorus on growth are described. As it has been shown many times that nitrogen and phosphorus may limit growth of coniferous stands on sandy soils, only these two elements are incorporated in the model. No attempt is made to model the dynamics of nitrogen and phosphorus in detail; instead, an elementary model with time steps of one year is used in combination with the simulations of daily canopy assimilation and hydrology. Soil supply of nitrogen and phosphorus is estimated from total soil content, by taking into account an unstable and a stable pool of nutrients in the soil, each with different turnover rates. The demand for nitrogen and phosphorus by the growing vegetation depends on the concentrations of these elements in the tissue, and on the amounts redistributed before dead biomass is shed, in combination with an estimated rate of biomass increment. By adjusting the concentration in the tissue for the next period of growth, demand and supply are balanced, and the influence of nutrient availability on growth during the following year is estimated using an empirical relationship between foliage nutrient concentration and growth. This approach assumes the existence of maximum and minimum concentrations of both nutrients in the tissue. Above the maximum concentration there is no further uptake; below the minimum, growth ceases.The final results from the model, together with the measurement series from permanent field plots are given in chapter 6. The field plots used to calibrate the model are discussed first; after this the model is tested against an independent set of data. Overall model behaviour seems to follow field measurements reasonably, both in the field plots used for calibration and in the independent (control) plot. Maximum increment rates as measured in the field are well reflected in the simulations, as is the decline in stem increment in older trees. Most of the discrepancies between predicted and real values are found to occur at higher ages of the stand. It is concluded that this is probably because the model overestimates light interception, because it takes no account of effects of uneven distributions of the trees in the field. This becomes more important when stands are thinned at high ages, when the crowns have only a limited ability to occupy the available growing space.Together with the evaluation of model behaviour, the value of the use of modelling in forestry in general, and of the use of a physiologically-based model like the one used here, is discussed. These models are needed for analysing growth and yield, and for contributing to the understanding of forest primary production. Moreover, they can be used to bridge the gap between widely different aspects of forest growth such as forest hydrology and forest nutrition. By integrating the main aspects of forest growth, these models also allow the main factors that determine total stand growth to be ascertained. As a result, possibilities for yield improvement, and the areas where research is mostly needed, can be identified. In the present case study, it appears that canopy growth often declines in the course of years because of decreased light interception. Current forestry practice in the Netherlands often includes an intensive thinning programme aimed at creating space for the individual crop trees. But this decreases stand growth. In general, this is not the intention, and therefore the efficacy thinning operations at higher stand ages that open up the stand to a degree that can no longer be utilized by the remaining trees, has to be reassessed.Not only does availability of soil moisture limit growth; nitrogen and phosphorus availability may also play an important role in determining the production level of a stand. The elementary model used indicates the extent to which both nitrogen and phosphorus may influence stand growth, and the results are evaluated against the results of fertilizer experiments carried out in Douglas fir on a range of sites during the 1950s and the 1960s (Blok et al., 1975). The increase In atmospheric input of nitrogen, resulting from, among others, intensive livestock farming and manure-spreading on agricultural lands, has greatly increased nitrogen supply. As a result, widespread phosphorus deficiency has become apparent. In the Netherlands, all but the best sites currently available suffer from severe phosphorus deficiency. This situation, where widespread nitrogen deficiency has changed into a deficiency of phosphorus, demands attention from researchers and forest managers. Increasing phosphorus availability through additional. fertilization can be expected to boost primary production and thus increase yield.One of the possible applications of the model is to calculate the growth potential of a wide range of available soil types and growing conditions, thereby allowing potential forest growth to be assessed. It can also be used to evaluate management interventions. If employed in a target-oriented mode the model could be used to evaluate the efficacy of applying fertilizer. Some of the growth- or stand-disturbing factors will have to be incorporated in the model before it can be used to calculate economic yield or optimal felling regimes.The simulation programme is available upon request.

Short rotation bioenergy crops for energy production are considered an effective means to mitigate the greenhouse effect, mainly due to their ability to substitute fossil fuels. Alternatively, carbon can be sequestered and stored in the living biomass. This paper compares the two land use categories (forest land and non-forest land) for two management practices (short rotation vs. long rotation) to study mitigation potential of afforestation and fossil fuel substitution as compared to carbon storage. Significant carbon benefit can be obtained in the long run from using lands for growing short rotation energy crops and substituting fossil fuels by the biomass thus produced, as opposed to sequestering carbon in the biomass of the trees. When growth rates are high and harvest is used in a sustainable manner (i.e., replanting after every harvest), the opportunities for net carbon reductions appear to be fossil fuel substitution, rather than storage in ecosystem biomass. Our results suggest that at year 100 a total of 216 Mg C ha-1 is sequestered for afforestation/reforestation using long rotation sal (Shorea robusta Gaertn.f) species, as opposed to offset of 412 Mg C ha-1 for carbon storage and fossil fuel substitution for short rotation poplar (Populus Deltoides Marsh) plantations. The bioenergy option results in a continuous stream of about 3 Mg C ha-1 yr-1 of carbon benefits per year on forest land and 4 Mg C ha-1 yr-1 on non-forest land. Earlier studies have shown that in India waste land availability for establishing energy plantations is in the range of 9.6 to 36.5 Mha. Thus, using the 758 Tg biomass per year generated from 9.6 Mha waste land gives a mitigation potential in the range of 227 to 303 Tg C per year for carbon storage and fossil fuel substitution from poplar plantation for substituting coal based power generation. Depending upon the land availability for plantation, the potential for energy generation is in the range of 11,370 PJ, possibly amounting to a bioenergy supply of 43% of the total projected energy consumption in 2015. Further studies are needed to estimate the mitigation potential of other species with different productivities for overall estimation of the economic feasibility and social acceptability in a tropical country like India

Bespreking van de invloed die omgevingsfaktoren hebben op de fysiologische processen in planten, die de basis vormen van de primaire produktie en de overeenkomsten daarvan ten aanzien van bosgroei aan de hand van een simulatiemodel. Met dit simulatiemodel kan de potentie van bosgroei op een bepaalde standplaats worden berekend, de beperkingen worden vastgesteld, gevolgen van storingen worden berekend en de gevolgen van veranderingen van afzonderlijke faktoren worden nagegaan

More frequently occurring droughts, related to climate change, lead to reduced growth and loss of vitality in trees. The recent drought of 2018 was extreme, long-lasting and resulted in high evaporative demands due to the concurrent high temperatures. The aim of this study was to compare the drought resilience of nine temperate tree species in the Netherlands, and to determine their responses to the severe drought of 2018 in comparison with five earlier drought events since 1970. To assess drought effects on tree species, we analysed tree-ring series of 678 trees in 45 plots throughout the Netherlands. Resilience indices were calculated based on growth reactions and growth recovery after drought. Furthermore, the impact of drought events on species productivity was quantified. We observed species-specific differences in growth responses to drought timing. All species in nearly all sites responded with growth reductions to drought, except sessile oak (Quercus petraea (Matt.) Liebl.). The most productive species in our study were found to be drought sensitive, with productivity losses of up to 30 % during drought in some sites. Productivity losses were highest on the driest soils. Resilience to the 2018 drought did not differ significantly from other drought years for six out of the nine studied species. However, 77.5 % of the individual trees of all studied species did not fully recover in growth within the following two years. Low post-drought growth remains poorly understood and should be taken into account in future studies to safeguard the health and productivity of the forest under climate change. We consider sessile oak a promising species for future forests in the Netherlands. Based on our results, we provide an outlook on future resilience and growth potential of the species studied under projected climate change for the Netherlands.

En los bosques tropicales, la luz y la disponibilidad de agua son los factores más importantes para el crecimiento y la supervivencia de las plántulas, pero una frecuencia cada vez mayor de sequía puede afectar la regeneración de los árboles. Una pregunta central es si la sequía y la sombra tienen efectos interactivos sobre el crecimiento y la supervivencia de las plántulas. Aquí, presentamos los resultados de un experimento de invernadero, en el que las plántulas de 10 especies de árboles ghaneses se expusieron a combinaciones de fuerte sequía estacional (riego continuo versus retención de agua durante nueve semanas) y sombra (5% de irradiancia versus 20% de irradiancia). Evaluamos los efectos de la sequía y la sombra sobre la supervivencia y el crecimiento de las plántulas y la plasticidad de 11 rasgos subyacentes relacionados con la asignación de biomasa, la morfología y la fisiología. La supervivencia de las plántulas en condiciones secas fue mayor en la sombra que en la luz alta, lo que respalda la "hipótesis de facilitación" de que la sombra mejora el rendimiento de la planta a través de mejores condiciones microclimáticas, y rechaza la hipótesis de compensación de que la sequía debería tener un impacto más fuerte en la sombra debido a la reducción de la inversión radicular. Las plantas sombreadas tenían una fracción de biomasa baja en las raíces, en línea con la hipótesis de compensación, pero compensaron esto con una longitud de raíz específica más alta (es decir, longitud de raíz por unidad de masa de raíz), lo que resultó en una longitud de raíz similar por masa de planta y, por lo tanto, una capacidad de absorción de agua similar a las plantas de alta luminosidad. La mayoría (60%) de los rasgos estudiados respondieron de forma independiente a la sequía y la sombra, lo que indica que dentro de las especies las tolerancias a la sombra y la sequía no están en equilibrio, sino en gran medida desacopladas. Cuando se analizaron las respuestas de las especies individuales, entonces, para la mayoría de los rasgos, solo de una a tres especies mostraron efectos interactivos significativos entre la sequía y la sombra. La respuesta desacoplada de la mayoría de las especies a la sequía y la sombra debería proporcionar una amplia oportunidad para la diferenciación de nichos y la coexistencia de especies en una variedad de condiciones de agua y luz. En general, nuestros resultados de invernadero sugieren que, en ausencia de competencia de raíces, las plántulas de árboles de bosques tropicales sombreados pueden sobrevivir a una sequía prolongada. Dans les forêts tropicales, la lumière et la disponibilité en eau sont les facteurs les plus importants pour la croissance et la survie des semis, mais une fréquence croissante de sécheresse peut affecter la régénération des arbres. Une question centrale est de savoir si la sécheresse et l'ombre ont des effets interactifs sur la croissance et la survie des semis. Ici, nous présentons les résultats d'une expérience en serre, dans laquelle des semis de 10 espèces d'arbres ghanéens ont été exposés à des combinaisons de forte sécheresse saisonnière (arrosage continu contre rétention d'eau pendant neuf semaines) et d'ombre (irradiance de 5% contre irradiance de 20%). Nous avons évalué les effets de la sécheresse et de l'ombre sur la survie, la croissance et la plasticité des semis de 11 traits sous-jacents liés à l'allocation de la biomasse, à la morphologie et à la physiologie. La survie des semis dans des conditions sèches était plus élevée à l'ombre qu'en haute lumière, soutenant ainsi l '« hypothèse de facilitation » selon laquelle l'ombre améliore les performances des plantes grâce à des conditions microclimatiques améliorées, et rejetant l'hypothèse de compromis selon laquelle la sécheresse devrait avoir un impact plus fort à l'ombre en raison de la réduction de l'investissement racinaire. Les plantes ombragées avaient une faible fraction de biomasse dans les racines, conformément à l'hypothèse du compromis, mais elles compensaient cela par une longueur racinaire spécifique plus élevée (c.-à-d., longueur racinaire par unité de masse racinaire), ce qui entraînait une longueur racinaire par masse végétale similaire et, par conséquent, une capacité d'absorption d'eau similaire à celle des plantes très légères. La majorité (60 %) des traits étudiés ont réagi indépendamment à la sécheresse et à l'ombre, ce qui indique que dans les espèces, les tolérances à l'ombre et à la sécheresse ne sont pas compensées, mais en grande partie découplées. Lorsque les réponses des espèces individuelles ont été analysées, pour la plupart des traits, seules une à trois espèces ont montré des effets interactifs significatifs entre la sécheresse et l'ombre. La réponse découplée de la plupart des espèces à la sécheresse et à l'ombre devrait offrir de nombreuses possibilités de différenciation des niches et de coexistence des espèces dans diverses conditions d'eau et de lumière. Dans l'ensemble, nos résultats en serre suggèrent qu'en l'absence de compétition racinaire, les semis d'arbres forestiers tropicaux ombragés pourraient survivre à une sécheresse prolongée. In tropical forests light and water availability are the most important factors for seedling growth and survival but an increasing frequency of drought may affect tree regeneration. One central question is whether drought and shade have interactive effects on seedling growth and survival. Here, we present results of a greenhouse experiment, in which seedlings of 10 Ghanaian tree species were exposed to combinations of strong seasonal drought (continuous watering versus withholding water for nine weeks) and shade (5% irradiance versus 20% irradiance). We evaluated the effects of drought and shade on seedling survival and growth and plasticity of 11 underlying traits related to biomass allocation, morphology and physiology. Seedling survival under dry conditions was higher in shade than in high light, thus providing support for the "facilitation hypothesis" that shade enhances plant performance through improved microclimatic conditions, and rejecting the trade-off hypothesis that drought should have stronger impact in shade because of reduced root investment. Shaded plants had low biomass fraction in roots, in line with the trade-off hypothesis, but they compensated for this with a higher specific root length (i.e., root length per unit root mass), resulting in a similar root length per plant mass and, hence, similar water uptake capacity as high-light plants. The majority (60%) of traits studied responded independently to drought and shade, indicating that within species shade- and drought tolerances are not in trade-off, but largely uncoupled. When individual species responses were analysed, then for most of the traits only one to three species showed significant interactive effects between drought and shade. The uncoupled response of most species to drought and shade should provide ample opportunity for niche differentiation and species coexistence under a range of water and light conditions. Overall our greenhouse results suggest that, in the absence of root competition shaded tropical forest tree seedlings may be able to survive prolonged drought. في الغابات الاستوائية، يعد الضوء وتوافر المياه من أهم العوامل لنمو الشتلات والبقاء على قيد الحياة، ولكن قد يؤثر تواتر الجفاف المتزايد على تجديد الأشجار. أحد الأسئلة المركزية هو ما إذا كان للجفاف والظل تأثيرات تفاعلية على نمو الشتلات والبقاء على قيد الحياة. هنا، نقدم نتائج تجربة الدفيئة، حيث تعرضت شتلات 10 أنواع من الأشجار الغانية لمزيج من الجفاف الموسمي القوي (الري المستمر مقابل حجب المياه لمدة تسعة أسابيع) والظل (5 ٪ إشعاع مقابل 20 ٪ إشعاع). قمنا بتقييم آثار الجفاف والظل على بقاء الشتلات ونموها ومرونتها لـ 11 سمة أساسية تتعلق بتخصيص الكتلة الحيوية والمورفولوجيا وعلم وظائف الأعضاء. كان بقاء الشتلات في ظل الظروف الجافة أعلى في الظل منه في الضوء العالي، مما يوفر الدعم لـ "فرضية التيسير" التي تعزز الظل أداء النبات من خلال تحسين الظروف المناخية الجزئية، ورفض فرضية المفاضلة القائلة بأن الجفاف يجب أن يكون له تأثير أقوى في الظل بسبب انخفاض الاستثمار الجذري. كان للنباتات المظللة جزء منخفض من الكتلة الحيوية في الجذور، بما يتماشى مع فرضية المفاضلة، لكنها عوضت عن ذلك بطول جذر محدد أعلى (أي طول الجذر لكل وحدة كتلة جذر)، مما أدى إلى طول جذر مماثل لكل كتلة نباتية، وبالتالي، قدرة امتصاص مياه مماثلة للنباتات عالية الإضاءة. استجابت غالبية السمات (60 ٪) التي تمت دراستها بشكل مستقل للجفاف والظل، مما يشير إلى أن تحمل الظل والجفاف داخل الأنواع ليس في المفاضلة، ولكنه غير مقترن إلى حد كبير. عندما تم تحليل استجابات الأنواع الفردية، أظهر نوع واحد فقط إلى ثلاثة أنواع تأثيرات تفاعلية كبيرة بين الجفاف والظل بالنسبة لمعظم السمات. يجب أن توفر الاستجابة غير المقترنة لمعظم الأنواع للجفاف والظل فرصة كبيرة للتمايز المتخصص والتعايش بين الأنواع في ظل مجموعة من ظروف المياه والضوء. بشكل عام، تشير نتائج الاحتباس الحراري لدينا إلى أنه في غياب المنافسة الجذرية، قد تكون شتلات أشجار الغابات الاستوائية المظللة قادرة على البقاء على قيد الحياة بعد الجفاف المطول.

This paper reports on the net carbon flux caused by deforestation and afforestation in India over the period from 1982 to 2002, separately for two time periods, 1982¿1992 (PI) and 1992¿2002 (PII), using the IPCC 2006 guidelines for greenhouse gas inventories. The approach accounts for forest and soil C pool changes for (a) forest areas remaining as forests, (b) afforested areas and (c) deforested areas. The data set used were remote sensing based forest cover for three time periods (1982, 1992, 2002), biomass increments, biomass expansion factors and wood density. In addition a number of required coefficients and parameters from published literature were adopted. In the 1982¿2002 period, the forest cover changed from 64.20 Mha in 1982 to 63.96 and 67.83 Mha in 1992 and 2002 respectively. During the PI and PII periods, plantations were also established of 0.2 and 0.5 Mha yr¿1, while the annual deforestation rate was about 0.22 and 0.07 Mha in these periods, respectively. The average net flux of carbon attributable to land use change decreased from a source level of 5.65 Tg C yr¿1 (or 0.09 Mg C ha¿1 yr¿1) during PI (1982¿1992) to a sink level of 1.09 Tg C yr¿1 (or 0.02 Mg C ha¿1 yr¿1) during PII (1992¿2002). Over recent years, Indian forests have acted as a small carbon sink. The results indicate that the conversion of land to forest (regeneration/afforestation) led to a net uptake of 0.86 and 1.85 Tg C yr¿1 in PI and PII, respectively. By contrast, the net C emissions from the forest land conversion to another land use (deforestation) resulted in annual emissions of 9.9 and 3.2 Tg C during PI and PII, respectively. The cumulative net carbon flux from Indian forests due to land use change between 1982 and 2002 was estimated as 45.9 Tg C. The largest fluxes result from the conversion of forest land to cropland and waste lands, and since there are uncertainties in input variables (due to very large spatial heterogeneity) that affect net C flux from land use change, there is an urgent need for more reliable district-based data to facilitate accurate and refined estimates in future. This study was intended to improve consistency and completeness in the estimation and reporting of greenhouse gas emissions and removals

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