Biomass In Secondary Forests Research Articles

Resilience of Aboveground Biomass of Secondary Forests Following the Abandonment of Gold Mining Activity in the Southeastern Peruvian Amazon

Amazon rainforests are critical for providing a wide range of ecosystem services. In the Southeastern Peruvian Amazon; however, goldmining activities are causing severe soil degradation and forest loss. We analyzed aboveground biomass (AGB), forest structure, and species diversity recovery during secondary succession in 179 forest plots. Our study provides the first field-based quantification of AGB recovery following the abandonment by two types of goldmining (heavy machinery and suction pumping) in Madre de Dios (Peru). We found that successional secondary forests in areas subjected to suction pumping were more resilient than those in areas subjected to heavy machinery. After 20 years, mean AGB in suction pumping mining areas had reached 56% of reference forest AGB, while in areas of heavy machinery mining it was only 18%. Mining type, stand age, and distance from the forest edge had a significant effect on AGB. The influence of the distance from the forest edge on AGB varies according to mining type because the effects of species diversity on AGB are mediated by the distance from the forest edge. Our results clearly showed the dynamics of AGB recovery across a secondary succession after goldmining, and the contrasting responses of AGB between the two mining types. Our study disentangles the importance of key factors in forest recovery after mining and improves understanding of the resilience of biomass accumulation in these highly degraded ecosystems.

Vicarious calibration of GEDI biomass with Landsat age data for understanding secondary forest carbon dynamics

The recovery of biomass in secondary forests plays a vital role in global carbon sequestration processes and carbon emission mitigation. However, accurately quantifying the accumulation rate of aboveground biomass density in these forests is challenging owing to limited longitudinal field data. An alternative monitoring strategy is characterizing the mean biomass at a single point in time across stands with a range of known ages. This chronosequence approach can also be used with remotely sensed data by combining biomass measured with platforms such as NASA’s Global Ecosystem Dynamics Investigation (GEDI) mission with forest age strata provided by historic Landsat imagery. However, focusing on the low-biomass conditions common in newly regenerating forests will accentuate commonly observed over-prediction of low biomass values. We propose a vicarious calibration approach that develops a correction for GEDI’s biomass models in young forests, which may be mapped using Landsat time series, using an assumption that the aboveground biomass of newly cleared forests is zero. We tested this approach, which requires no additional local field data, in the U.S. Pacific Northwest, where extensive inventory data from the USDA Forest Service are available. Our results show that the calibration did not significantly improve the fit of predicted biomass as a function of age across 12 ecoregions (one-side t-test; p = 0.20), but it did significantly reduce bias for the youngest age groups with respect to reference data. Calibrated GEDI-based biomass estimates for < 20 year old forests were more accurate than 2006 IPCC defaults in most ecoregions (with respect to authoritative inventory estimates) and may represent a basis for refining carbon storage expectations for secondary forests globally.

Modeling Biomass for Natural Subtropical Secondary Forest Using Multi-Source Data and Different Regression Models in Huangfu Mountain, China

Forest biomass estimation is an important parameter for calculating forest carbon storage, which is of great significance for formulating carbon-neutral strategies and forest resource management measures. We aimed at solving the problems of low estimation accuracy of forest biomass with complex canopy structure and high canopy density, and large differences in the estimation results of the same estimation model under complex forest conditions. The Huangfu Mountain Forest Farm in Chuzhou City was used as the research area. As predictors, we used Gaofen-1(GF-1) and Gaofen(GF-6) satellite high-resolution imaging satellite data, combined with digital elevation model (DEM) and forest resource data. Multiple stepwise regression, BP neural network and random forest estimation models were used to construct a natural subtropical secondary forest biomass estimation model with complex canopy structure and high canopy closure. We extracted image information as modeling factors, established multiple stepwise regression models of different tree types with a single data source and a comprehensive data source and determined the optimal modeling factors. On this basis, the BP neural network and random forest biomass estimation model were established for Pinus massoniana, Pinus elliottii, Quercus acutissima and mixed forests, with the coefficient of determination n (R2) and root mean square error (RMSE) as the judgment indices. The results show that the random forest model had the best biomass estimation effect among different forest types. The R2 of Quercus acutissima was the highest, reaching 0.926, but the RMSE was 11.658 t/hm2. The R2 values of Pinus massoniana and mixed forest were 0.912 and 0.904, respectively. The RMSE reached 10.521 t/hm2 and 6.765 t/hm2, respectively; the worst result was the estimation result of Pinus elliottii, with an R2 of 0.879 and an RMSE of 14.721 t/hm2. The estimation result of the BP neural network was second only to that of the random forest model in the four forest types. From high precision to low precision, the order was Quercus acutissima, Pinus massoniana, mixed forest and Pinus elliottii, with R2s of 0.897, 0.877, 0.825 and 0.753 and RMSEs of 17.899 t/hm2, 10.168 t/hm2, 18.641 t/hm2 and 20.419 t/hm2, respectively. In this experiment, the worst biomass estimation performance was seen for multiple stepwise regression, which ranked the species in the order of Quercus acutissima, Pinus massoniana, mixed forest and Pinus elliottii, with R2s of 0.658, 0.622, 0.528 and 0.379 and RMSEs of 29.807 t/hm2, 16.291 t/hm2, 28.011 t/hm2 and 23.101 t/hm2, respectively. In conclusion, GF-1 and GF-6 combined with data and a random forest algorithm can obtain the most accurate results in estimating the forest biomass of complex tree species. The random forest estimation model had a good performance in biomass estimation of primary secondary forest. High-resolution satellite data have great application potential in the field of forest parameter inversion.

ALLOMETRIC MODELS FOR ESTIMATING TREE BIOMASS OF DRYLAND SECONDARY FOREST IN EAST HALMAHERA

Pendugaan biomassa hutan sekunder diperlukan untuk mendukung pengurangan emisi karbon dioksida melalui peningkatan cadangan karbon hutan. Umumnya, biomassa hutan diduga secara tidak langsung menggunakan model-model alometrik biomassa pohon yang disusun berdasarkan pengambilan sampel destruktif dari sejumlah pohon contoh. Ketersediaan model-model alometrik biomassa untuk hutan sekunder di Indonesia masih terbatas, khususnya untuk ekosistem hutan sekunder di bagian timur Indonesia. Penelitian ini bertujuan untuk menyusun model-model alometrik biomassa pohon jenis campuran di hutan sekunder Halmahera Timur, Maluku Utara, serta untuk membandingkan akurasi model-model alometrik lokal tersebut dengan model-model alometrik lain yang umum digunakan dalam pendugaan biomassa hutan sekunder. Pengukuran biomassa pohon dilakukan secara destruktif terhadap 18 pohon jenis campuran (dengan kisaran diameter 5,4 – 36,9 cm) di hutan sekunder. Sampel-sampel dari tiap bagian pohon (batang, cabang, ranting, dan daun) dianalisis di laboratorium untuk menentukan biomassa tiap pohon contoh. Model-model alometrik disusun menggunakan analisis regresi non-linier, yang kemudian dibandingkan dengan model-model alometrik lain. Penelitian ini menunjukkan bahwa biomassa pohon jenis campuran di lokasi penelitian dapat diduga secara akurat menggunakan model M7 yang menggunakan peubah diameter, tinggi dan kerapatan kayu. Model alometrik lokal tersebut lebih akurat dibandingkan dengan model-model alometrik lain yang umum digunakan untuk pendugaan biomassa hutan tropis. Alternatifnya, model M3 yang menggunakan peubah diameter dan tinggi juga dapat digunakan ketika data kerapatan kayu tidak tersedia. Model-model alometrik lokal dari penelitian ini dapat memperkaya ketersediaan model-model alometrik biomassa untuk ekosistem hutan sekunder di bagian timur Indonesia.

Allometric Models for Estimating Tree Biomass of Dryland Secondary Forest in East Halmahera

Biomass estimation of secondary forests is required to support the emission reduction of carbon dioxide through an enhancement of forest carbon stocks. Commonly, forest biomass is indirectly estimated using tree biomass allometric models that are developed based on a destructive sampling of sample trees. The availability of biomass allometric models for secondary forests in Indonesia is still limited, particularly for secondary forest ecosystems in eastern Indonesia. This study aimed to develop allometric biomass models for mixed-species trees in a secondary forest of East Halmahera, North Maluku, and to compare their accuracies with some other allometric biomass models that commonly used for estimating biomass of secondary forests. The tree biomass measurement was conducted by using a destructive sampling of 18 mixed-species trees (with diameter range of 5,4 – 36,9 cm) in a secondary forest. The samples of each tree component (stem, branch, twig, and leaf) were analyzed in a laboratory to determine the biomass of each sample tree. Allometric models were developed by using a non-linear regression analysis, which were then compared with other allometric models. This study revealed that the biomass of mixed-species trees in the study area could be estimated accurately using the M7 model that used diameter, height, and wood density variables. Such local allometric model was more accurate than other allometric models commonly used for estimating tropical forest biomass. Alternatively, the M3 model that used diameter and height variables could also be used when wood density data was not available. The local allometric models from this study can enrich the availability of biomass allometric models for secondary forest ecosystems in eastern Indonesia.

Which allometric models are the most appropriate for estimating aboveground biomass in secondary forests of Madagascar with Ravenala madagascariensis?

Abstract In Madagascar, allometric models have been developed only for the primary forests. There have been no specific models for the secondary forests. However, with a view to extending the geographic scope of the REDD+ 1 mechanism, it deems important to consider the secondary forests of which the potential of carbon sequestration remains unknown. In eastern part of Madagascar, the secondary forests are mostly colonized by Ravenala madagascariensis, an endemic monocotyledonous plant. The main goal of this study was to develop local allometric models for secondary forests with Ravenala madagascariensis. Models for Ravenala madagascariensis were developed separately from those of other woody species. The second goal was to test the validity of the existing allometric equations for the woody species into the study sites, namely three pantropical models developed by Brown, Chave et al. and the best fitted local model developed by Vieilledent et al. for the dense humid forest in Madagascar. Using the destructive method, 120 stems of Ravenala madagascariensis and 115 trees were harvested, weighed and measured. As results, the best fitted local model for the woody species was A G B = E X P ( − 1.515 + 1.912 ln ( D ) + 0.471 ln ( H ) + 0.732 ln ( ρ ) ), where AGB is the aboveground biomass in kg, H the total height in m, D the diameter at the breast height in cm and ρ the wood specific gravity. For Ravenala madagascariensis, the model which only considered total height was the most appropriate: A G B = E X P ( − 4.996 + 5.654 ln ( H ) − 0.772 ( ln ( H ) ) 2 ). Comparing with the existing equations, errors of estimates were higher for the pantropical models and a slight overestimation was observed while applying that of Vieilledent et al. It is thus recommended to choose the local site specific models for estimating the aboveground biomass for the secondary forests with Ravenala madagascariensis in the eastern part of Madagascar.

Estimation of secondary forest parameters by integrating image and point cloud-based metrics acquired from unmanned aerial vehicle

To better assess spatial variabilities in subtropical secondary forest biomass, the goal of the present study was to employ small-footprint, discrete-return light detection and ranging and unmanned aerial vehicles, integrated with structure from motion (UAV-SFM) data, to accurately estimate the stand characteristic parameters of subtropical forests. The Lorey’s height, density, basal area, volume, and aboveground biomass (AGB) of 30 plots (O10 m) were modeled using an array of SFM point cloud metrics and image color metrics (forestry vegetation coverage and color index set). Further, the individual models developed using stepwise multiregression analysis and a branch-and-bound algorithm were employed to examine the best models. Overall, the results indicated that the coefficient of determination ( R 2) for Lorey’s height ( R 2 = 0.58 to 0.95), volume ( R 2 = 0.29 to 0.71), and AGB ( R 2 = 0.27 to 0.64) were significantly enhanced compared with the density ( R 2 = 0.18 to 0.48), and basal area ( R 2 = 0.24 to 0.52). Utilizing independent stand-level data from ground inventory, our results revealed that, overall, the model fit was significant for most stand characteristic parameters, with relationships close to a 1:1 line, thereby indicating no significant bias [relative root mean square error ( rRMSE ) = 5.32 % to 27.04%]. Our image metrics had a statistically significant association with Lorey’s height (rRMSE decreased by 0.08%), volume (rRMSE decreased by 0.58%), and AGB (rRMSE decreased by 3.11%), which provided additional explanatory power in the regression analysis. This research demonstrated the potential of UAV-SFM as a technology to accurately assess subtropical forest carbon while providing an improved elucidation of the positive effects of image color metrics.

Disentangling how management affects biomass stock and productivity of tropical secondary forests fallows

A better understanding of biomass production in secondary forests after cultivation is essential for assessing the resilience of slash and burn systems and their capacity to deliver ecosystem services. Biomass production is influenced by management legacies, landscape configuration and soil, but these drivers are rarely studied simultaneously, nor is the role of changes in vegetation properties in linking them to biomass production. We assessed how management legacies affect biomass in secondary forests created by slash and burn in the central Congo Basin, and tested whether changes in productivity could be attributed to changes in stem density, functional diversity, functional identity or soil. Using data from 6452 trees in 96 fallow plots nested in 3 study sites, we looked for the main determinants of aboveground biomass (AGB) of woody vegetation in fallow systems. Next, using a subset of 58 plots in fallow fields aged 5 to 10 years, we used confirmatory path analysis to explore the relations between management history, soil, vegetation properties and biomass productivity. The sampled fallow fields had, on average, 58.4 (±46.2) Mg ha−1 AGB. AGB was positively related to both fallow age and to the proportion of remnant trees in AGB and negatively related to the number of previous cultivation cycles. Biomass productivity varied with the number of previous slash-and-burn cycles, with notable declines in the fourth cycle. The effect of management history was mainly through a reduction in the dominance of fast growing tree species and in the number of regenerating stems, which were also indirectly affected by an increase in C. odorata cover. Soil fertility status and the biomass of remnant trees also modified biomass productivity. Our findings suggest that under the current management intensity the capacity of the slash and burn system to provide important ecosystem functions, such as carbon sequestration, is declining.

Nutrient limitation in tropical secondary forests following different management practices.

Secondary forests now make up more than one-half of all tropical forests, and constraints on their biomass accumulation will influence the strength of the terrestrial carbon (C) sink in the coming decades. However the variance in secondary tropical forest biomass for a given stand age and climate is high and our understanding of why is limited. We constructed a model of terrestrial C, nitrogen (N), and phosphorus (P) cycling to examine the influence of disturbance and management practices on nutrient limitation and biomass recovery in secondary tropical forests. The model predicted that N limited the rate of forest recovery in the first few decades following harvest, but that this limitation switched to P approximately 30-40yr after abandonment, consistent with field data on N and P cycling from secondary tropical forest chronosequences. Simulated biomass recovery agreed well with field data of biomass accumulation following harvest (R2 =0.80). Model results showed that if all biomass remained on site following a severe disturbance such as blowdown, regrowth approached pre-disturbance biomass in 80-90yr, and recovery was faster following smaller disturbances such as selective logging. Field data from regrowth on abandoned pastures were consistent with simulated losses of nutrients in soil organic matter, particularly P. Following any forest disturbance that involved the removal of nutrients (i.e., except blowdown), forest regrowth produced reduced biomass relative to the initial state as a result of nutrient loss through harvest, leaching and/or sequestration by secondary minerals. Differences in nutrient availability accounted for 49-94% of the variance in secondary forest biomass C at a given stand age. Management lessons from this study are the importance of strategies that help retain nutrients on site, recognizing the role of coarse woody debris in immobilization and subsequent release of nutrients, and the potential for nutrient additions to enhance biomass growth and recovery in secondary tropical forests.

Nationally Representative Plot Network Reveals Contrasting Drivers of Net Biomass Change in Secondary and Old-Growth Forests

Uncertainty about the mechanisms driving biomass change at broad spatial scales limits our ability to predict the response of forest biomass storage to global change. Here we use a spatially representative network of 874 forest plots in New Zealand to examine whether commonly hypothesised drivers of forest biomass and biomass change (diversity, disturbance, nutrients and climate) differ between old-growth and secondary forests at a national scale. We calculate biomass stocks and net biomass change for live above-ground biomass, below-ground biomass, deadwood and litter pools. We combine these data with plot-level information on forest type, tree diversity, plant functional traits, climate and disturbance history, and use structural equation models to identify the major drivers of biomass change. Over the period 2002–2014, secondary forest biomass increased by 2.78 (1.68–3.89) Mg ha−1 y−1, whereas no significant change was detected in old-growth forests (+0.28; −0.72 to 1.29 Mg ha−1 y−1). The drivers of biomass and biomass change differed between secondary and old-growth forests. Plot-level biomass change of old-growth forest was driven by recent disturbance (large tree mortality within the last decade), whereas biomass change of secondary forest was determined by current biomass and past anthropogenic disturbance. Climate indirectly affected biomass change through its relationship with past anthropogenic disturbance. Our results highlight the importance of disturbance and disturbance history in determining broad-scale patterns of forest biomass change and suggest that explicitly modelling processes driving biomass change within secondary and old-growth forests is essential for predicting future changes in global forest biomass.

Decomposition of ground biomass of secondary forest and yield of annual crops in no tillage

ABSTRACT The objective of this work was to evaluate the dynamics of decomposition process of chopped secondary forest system, previously enriched with legumes Inga velutina Willd. and Stryphnodendron pulcherrimum (Willd.) Hochr. and the contribution of this process to the nutrient input to the cultivation of corn and bean under no-tillage. The experimental design was a randomized block, split plot with four replications. The plots were two species (I. velutina and S. pulcherrimum) and the subplots were seven times of evaluation (0, 7, 28, 63, 189, 252, 294 days after experiment installation). There was no difference (p ≥ 0.05) between the secondary forest systems enriched and no interaction with times for biomass waste, decomposition constant and half-life time. The waste of S. pulcherrimum trees had higher (p &lt; 0.05) C/N ratio than that I. velutina. However, this one was higher (p &lt; 0.05) in lignin content. Nevertheless, the dynamics of residue decomposition was similar. The corn yield was higher (p &lt; 0.05) in cultivation under I.velutina waste. Meanwhile, the beans planted after corn, shows similar (p &gt; 0.05) yield in both areas, regardless of the waste origin.

Establishment of allometric models and estimation of biomass recovery of swidden cultivation fallows in mixed deciduous forests of the Bago Mountains, Myanmar

We established allometric models for fallow forests following swidden cultivation, to estimate biomass accurately in the fallows around a village in the Bago Mountains, Myanmar. By harvesting 160 individual trees from 53 species and 132 sample culms from four bamboo species, allometric equations were determined between tree/culm size variables, such as diameter at breast height (D130) and tree/culm height (H), and plant biomass components such as trunk/culm, branch, and leaf biomass in the fallows. The correlation coefficient for the allometric model for total above-ground tree biomass as a function of D1302H was high (0.956), although the value for leaf biomass was relatively low (0.626). In addition, best-fit allometric relationships for four bamboo species were established. All allometric models involving total above-ground biomass for all bamboo species had significantly high R2 values: 0.817 for G. nigrociliata, 0.877 for B. polymorpha, 0.910 for B. tulda, and 0.963 for D. strictus. A comparison between the present models and previously reported equations for above-ground biomass for tropical forests revealed that our allometric models followed the general trend for biomass estimation, with substantial differences among forest types. In addition, our results suggest that when allometric models are developed using destructive sampling methods, either all mixed species combined or select dominant species can be used, although the optimal approach would include models with all species combined to estimate biomass accumulation for mixed-species forests. Using the best-fit allometric models for trees and bamboo, we estimated tree and bamboo biomass at the community level, supplemented by understory and vine biomass. Biomass accumulation in the study area generally increased with fallow age, with a large contribution of bamboo in the fallows. To estimate biomass of secondary forests accurately, especially fallow forests, relevant allometric relationships and the intensity of swidden cultivation must be considered.

TROPICAL FOREST BIOMASS AND ITS RELATIONSHIP WITH P - BAND SAR DATA

The objective of this research is to show the potential of P-band polarimetric SAR images to define the space of&#x0D; attributes of primary and regenerating forest and also to estimate aerial biomass of such formations. The approach used&#x0D; was the analysis of the relation between backscatter and biomass data estimated by four specific allometric equations.&#x0D; The Bivariate Intensities HH-HV image was segmented and the mean s° of each segment was converted into biomass&#x0D; by the best fit function (the heat capacity model) and following that the biomass was mapped. As a conclusion, the best&#x0D; allometric equations for primary and secondary forest biomass estimation were defined, considering the different&#x0D; polarizations of P-band SAR data. The methodology used in this treatment of P-band data might improve the regional&#x0D; monitoring of Amazonian land cover change, a process whose speed was accelerated as a result of human action in the&#x0D; Amazon during the last two decades.

Rapid Recovery of Biomass, Species Richness, and Species Composition in a Forest Chronosequence in Northeastern Costa Rica

ABSTRACTSecondary forests are a vital part of the tropical landscape, and their worldwide extent and importance continues to increase. Here, we present the largest chronosequence data set on forest succession in the wet tropics that includes both secondary and old‐growth sites. We performed 0.1 ha vegetation inventories in 30 sites in northeastern Costa Rica, including seven old‐growth forests and 23 secondary forests on former pastures, ranging from 10 to 42 yr. The secondary forest sites were formerly pasture for intervals of &lt;1–25 yr. Aboveground biomass in secondary forests recovered rapidly, with sites already exhibiting values comparable to old growth after 21–30 yr, and biomass accumulation was not impacted by the length of time that a site was in pasture. Species richness reached old‐growth levels in as little as 30 yr, although sites that were in pasture for &gt; 10 yr had significantly lower species richness. Forest cover near the sites at the time of forest establishment did not significantly impact biomass or species richness, and the species composition of older secondary forest sites (&gt;30 yr) converged with that of old growth. These results emphasize the resilience of tropical ecosystems in this region and the high conservation value of secondary forests.

Secondary forest succession after the cessation of swidden cultivation in the montane forest area in Northern Thailand

As controls over swidden cultivation have tightened since the 1980s, the number of abandoned fallow fields has increased in mountainous areas of Northern Thailand. The objective of this study was to investigate the recovery of species composition, diversity (Shannon's H′), and aboveground biomass in secondary forests that were abandoned after swidden cultivation for more than 20 years. A census of trees in secondary forest abandoned after upland rice cultivation or poppy cultivation and in uncultivated forest stands was conducted in a Karen village in Doi Inthanon National Park. Castanopsis acuminatissima and other Fagaceae species were the dominant species in uncultivated forest stands, while Schima wallichii was the most dominant species in secondary forest stands. The dominance of S. wallichii, Machilus bombycia, and Eurya acuminate var. wallichiana was higher in stands that had experienced poppy cultivation, resulting in the lower species diversity. Aboveground biomass in stands abandoned after upland cultivation with no history of poppy cultivation was higher than in stands that had a history of poppy cultivation. This is probably because tree stumps, which act as reservoirs for rapid recovery, were left after abandonment of upland rice cultivation. Cluster analysis revealed three different stand groups, based on presence/absence data of each species. Stands used only for upland rice cultivation were found in the stand group characterized by Fagaceae species, while stands abandoned after poppy cultivation and stands abandoned after upland rice cultivation that were located in the area where poppy had been cultivated in the past tended to be included in the stand group characterized by E. acuminate var. wallichiana. The species presence/absence composition results in stands with a history of poppy cultivation show that these areas take more time to reach climax species composition.

Burning of secondary forest in Amazonia: Biomass, burning efficiency and charcoal formation during land preparation for agriculture in Apiaú, Roraima, Brazil

In a burn of 5-year-old secondary forest cleared for agriculture in Roraima, Brazil, carbon partitioning was measured for above-ground portions of both secondary forest (regrowth) and the remains of original forest, felled and burned six years previously. Above-ground dry weight biomass averaged 43.0 ± 6.5 Mg (megagrams = metric tons) per hectare (Mg ha −1) for secondary forest and 105.8 ± 23.7 Mg ha −1 for original forest remains. Pre- and post-burn above-ground biomass loadings were estimated by cutting and weighing six 60-m 2 plots and by line-intersect sampling (LIS) done along the axis of each post-burn plot (three transects), plus two supplementary LIS transects. High variability of initial biomass made LIS more reliable for assessing change in material >10 cm in diameter; quantities for diameter classes <10 cm relied on direct weighing. Above-ground carbon pools were reduced by 67.8% in secondary forest and 32.0% in original forest remains. Burning released 28.8 Mg C ha −1 (original forest remains plus secondary forest biomass), or 41.6% of the pre-burn total carbon stock in biomass. The remainder of the carbon either remained as residual biomass (39.2 Mg C ha −1 or 56.5% of pre-burn C) or as charcoal and ashes (1.4 Mg C ha −1 or 2.0%). Carbon stock in charcoal increased from 0.50 Mg C ha −1 to 1.07 Mg C ha −1, a net gain of 0.57 Mg C ha −1, or 0.8% of the pre-burn above-ground carbon stock. The net gain of charcoal carbon was composed of 0.21 Mg C ha −1 from secondary forest biomass and 0.36 Mg C ha −1 from original forest remains; 1.1% of the above-ground secondary forest carbon was converted to charcoal, while the corresponding percentage for original forest remains was 0.7%. Ashes contained an additional 0.29 Mg C ha −1, of which 0.11 Mg C ha −1 can be attributed to secondary forest biomass and 0.18 Mg C ha −1 to original forest remains. If the carbon in ashes is assumed to be finely powdered charcoal, this stock adds 0.21% to the charcoal formation percentage for secondary forest and 0.36% to that for original forest remains. The overall charcoal-formation percentage was 1.6%, or 2.0% if ashes are included. Charcoal-formation percentages in this study are lower than those sometimes assumed in global carbon models; nevertheless, charcoal can represent an important sink of atmospheric carbon over long time scales.

NUTRIENT LOSS AND REDISTRIBUTION AFTER FOREST CLEARING ON A HIGHLY WEATHERED SOIL IN AMAZONIA

Over the past three decades, tropical forest clearing and burning have greatly altered the Amazonian landscape by increasing the cover of pastures and secondary forests. The alteration of biogeochemical processes on these lands is of particular interest on highly weathered Oxisols that cover large areas in the region because of concerns regarding possible nutrient limitation in agricultural land uses and during forest regrowth. The objectives of this study were to quantify (1) the reaccumulation of nutrients in biomass of secondary land uses, (2) changes in soil nutrient contents, (3) internal nutrient cycles, and (4) input–output budgets for the landscape mosaic.Nutrient stocks and fluxes were quantified from 1996 to 1998 in mature forest, 19‐yr‐old secondary forest, degraded pastureland, and managed pastureland in the Brazilian state of Pará. Mature forests contain 130 Mg C/ha in aboveground biomass while secondary forest, degraded pasture, and managed pasture contain 34, 4, and 3 Mg C/ha, respectively. Reaccumulation of N, P, K, Ca, and Mg in aboveground biomass of secondary forest was 20%, 21%, 42%, 50%, and 27% of that present in mature forest, while degraded pasture contained 2%, 4%, 15%, 11%, and 6%. Managed pasture had similar accumulations as degraded pasture except for Ca (3%).Changes in soil stocks of C, N, and P were not detected among land uses, except in fertilized managed pastures, where total soil P (0–10 cm) was elevated. Conversely, Mehlich‐III‐extractable P of all secondary lands were very low (&lt;1 μg/g) and were 1 kg/ha less than contents (0–10 cm) in mature forest. NaOH‐extractable P was present in 100‐fold higher concentrations and may gradually contribute to meeting plant demands over decadal time scales. Soil cation contents (0–20 cm) were elevated in secondary lands with increases of ∼85, 500, and 75 kg/ha for K, Ca, and Mg, respectively. These increases could account for a substantial portion of cation contents originally in the aboveground biomass of mature forest.The recycling of nutrients through ∼9.0 Mg·ha−1·yr−1 of litterfall in secondary forest of 132, 2.8, 32, 106, and 23 kg·ha−1·yr−1 for N, P, K, Ca, and Mg, respectively, is similar to mature forest. Nutrient returns in both pasturelands were smaller for all elements except K, which was similar to the forested sites. In these pasture ecosystems, grass turnover has replaced litterfall return as the predominate mechanism of nutrient recycling.Soil solution fluxes of total N were higher in mature forest (12 kg·ha−1·yr−1 at 25 cm depth) compared to secondary lands (&lt;4 kg·ha−1·yr−1), indicating that cycling of available forms of N has diminished. Conversely, fluxes of cationic elements appear elevated in secondary lands and are charge balanced in solution by HCO3− derived from biological activity in the soil surface. Despite detectable increases in soil cation fluxes, rainwater inputs and stream water outputs of these elements across the watershed were not significantly different.The aggregate picture for this landscape is one in which the secondary forest, although still of smaller stature and lower in species diversity compared to mature forest, is recuperating important nutrient cycling functions. Conversely, pasturelands, which dominate the landscape, are not only of smaller stature, but are also accumulating and cycling a smaller total mass of nutrients. This ecosystem conversion has released C and N from biomass mostly to the atmosphere and has redistributed K, Ca, and Mg from biomass mostly to the soil. Presently, base cation enriched soils are slowly re‐equilibrating to an acidic condition through decadal‐scale processes of plant uptake and biogenically driven soil leaching. Our mass balance approach has revealed low soil available N and P, diminished rates of cycling of these elements in secondary lands, and low precipitation inputs of P, which may constrain long‐term recuperation of ecosystem carbon.

Allometric equations for pioneer tree species and estimation of the aboveground biomass of a tropical secondary forest in East Kalimantan

To estimate the aboveground biomass of tropical secondary forests dominated by pioneer species, allometric equations to relate diameter at breast height with the dry mass of the aboveground organs of several pioneer species were developed. The aboveground biomass of secondary forests was estimated using four methods based on the allometric equations. Biomass estimated with an allometric equation for all species combined was equivalent to that estimated with species-specific allometric equations. However, the estimated biomass based on a general-purpose allometric equation was substantially higher than that using other allometric equations. The allometric equation for all species combined is suitable for estimating the biomass of a secondary forest from the view points of accuracy and labor.

Monitoring secondary tropical forests using space-borne data: Implications for Central America

Tropical secondary forests, which play an important role in carbon sequestration, may be monitored using space-borne sensors. Secondary forest biomass or age estimation from space-borne data may be used to quantify the carbon sink these forests represent. At current capabilities, roughly three successional stages up to 15 years of age may be identified from Landsat TM data. Using synthetic aperture radar, reliable biomass estimates may be made up to approximately 60 tons/ha. The potential for overcoming these limitations is reviewed, including the synergy of radar and optical imagery and the unprecedented spatial and spectral resolutions of new sensors. Most of the available literature to date is from the Amazon; in this paper, applicability to Central America is considered, which has a much more heterogeneous landscape and the dynamics of secondary growth have a special significance in the framework of conservation biology and carbon sequestration. We conclude that critical issues in this region will be topographical correction and stratification according to ecological and site quality variables.

Secondary forest structure and biomass following short and extended land-use in central and southern Amazonia

A study was conducted on the effect of extended land-use on secondary forest biomass accumulation in the Amazon. Structural measurements were made in a series of secondary forest stands, from 4–30 y old, in Brazil and Bolivia. Half of the stands were forest regrowth following clearance and only 1 y of cultivation; the other half were regrowth following 4 y or more of continuous pasture in Brazil and three or more rotations of medium-fallow agriculture in Bolivia. Above-ground live biomass was estimated using published allometric equations. Total biomass ranged from 17 to 207 Mg ha−1. Biomass of pioneer trees was poorly related to stand age, while that of later-successional trees increased linearly with age. Total biomass accumulation in Bolivia averaged 5.4 Mg ha−1 y−1 over the entire age sequence. Biomass accumulation for regrowth following short-term use was not greater than that for regrowth following medium-fallow agriculture. In Brazil, biomass accumulation averaged 9.1 Mg ha−1 y−1 over the first 12 y of regrowth and 5.9 Mg ha−1 y−1 over the entire age sequence. Biomass accumulation was significantly slower, around 5.0 Mg ha−1 y−1, for regrowth following continuous pasture than for regrowth following 1 y of cultivation.