Recovery Of Aboveground Biomass Research Articles

Above-ground Biomass Recovery in Managed Tropical Forest in the Jari Valley, Eastern Amazon

Tropical forests play an important role in maintaining the regional rainfall regime and global climate, besides representing a significant stock of carbon. This study aimed at evaluate above-ground biomass (AGB) recovery, after reduced-impact logging (RIL) in a managed forest on the Jari River valley. The data were collected in 15 plots (100 m × 100 m) in the management area of the Jari Florestal Company. To estimate AGB we used a local equation adjusted for forests in the eastern Amazon. AGB before logging ranged from 157.9 Mg ha-1 to 619.9 Mg ha-1, with an average of 362.5 Mg ha-1. AGB after logging ranged from 151.2 Mg ha-1 to 632.8 Mg ha-1, with an average of 322.4 Mg ha-1. The time of monitoring of the plots and logging intensity were the main factors that influenced the recovery of the AGB. In 12 years after the RIL, the forest was able to recover its initial stocks of AGB, in places of low exploitation intensity.

Overwhelming effects of autumn-time drought during seedling establishment impair recovery potential in sown and semi-natural pastures in Portugal

Climate change-induced alterations to precipitation may affect the regeneration dynamics of plant species, with the occurrence of drought influencing germination and seedling establishment. In Mediterranean grasslands, typically dominated by C3 annual species, germination occurs rapidly once sufficient rain falls in autumn. However, a single large precipitation event may be followed by a dry spell, with possible consequences for vegetation composition and productivity. We investigated the effects of autumn-time drought on germination and seedling establishment, and the subsequent recovery potential, in semi-natural and sown pastures. Although the majority of grasslands in Portugal are semi-natural, sowing legume-rich seed mixtures is an increasingly common agricultural practice in Portugal. Our results show an overwhelming effect of autumn-time drought on seedling establishment, with the semi-natural pasture being more compromised than the sown pasture. However, after the recovery period, the semi-natural pasture exhibited tendentially higher aboveground biomass recovery than the sown pasture. The differential species sensitivity to autumn-time drought and subsequent implications for recovery potential may be important for the agricultural practice of sown pastures, justifying additional research for drought-tolerant cultivar improvement to maintain productivity with climate change.

Recovery of above-ground tree biomass after moderate selective logging in a central Amazonian forest

Abstract: We examined the recovery and dynamics of living tree above-ground biomass (AGB) after selective logging in an Amazonian terra firme forest managed by a private company. The forest consisted of 24 blocks (including one set aside for conservation) selectively logged in different years on a managed schedule. Trees ≥10 cm in diameter at breast height (dbh) were surveyed in 2006 in 192 0.25-ha plots, in 2010 in 119 plots, and in 2012-2013 in 54 plots. A logistic growth model factoring in logging dynamics and mean AGB of a block in these years was established. Referencing the mean AGB of the unlogged forest, the model indicated that the logged forest would take on average 14 years to regain its preharvest AGB after selective logging at 1.9 trees ha-1 (dbh > 50 cm). In 2010 and 2012-2013, the AGB increased significantly for small and large trees (10-20 cm and >60 cm dbh, respectively) in the logged forest. In contrast, it decreased significantly for medium-sized trees (30-50 cm dbh) in the unlogged forest. Comparisons with the previous studies mainly conducted in the other regions of Amazon suggested that the estimated AGB recovery period with moderate logging intensity was almost appropriate and likely acceptable to forest managers.

Soil properties and neighbouring forest cover affect above-ground biomass and functional composition during tropical forest restoration

Questions: We studied the importance of soil properties and neighbouring forest cover in affecting plant community biomass and assembly during the tropical forest restoration process. We also investigated how compositional responses depended on traits expected to influence individual success. Location: Forest restoration sites across anthropogenic grasslands in mixed use agricultural watersheds, eastern Sao Paulo state, Brazil. Methods: We identified and measured all woody individuals (DBH >= 5 cm) in four 200-m(2) plots per site. Then we translated these measurements into above-ground biomass (AGB), and related AGB variability to neighbouring forest cover, soil texture and chemical fertility using mixed effect models. We assessed the effect of these predictors on different species groups, arranged according to variation in wood density, tree height or habitat selectivity, through multivariate abundance models. Results: GB ranged between 0 and 104.7 t/ha (median of 10.4 t/ha), with high variation within, as well as between, watersheds. Sand percentage, forest cover and the interaction between soil nutrient concentrations and sand percentage were good predictors of measured AGB. The most parsimonious model projected a seven growing seasons AGB recovery of 70.90 t/ha, when a site is on fertile soils with 10% sand and surrounded by forest cover of 50%. In contrast, only 5.24 t/ha is predicted on acidic-poor soils with 67% sand and 0% forest cover. Increasing forest cover favoured smaller trees and habitat generalists while increasing sand percentage inhibited taller species and forest specialists. Sand percentage constrained softwoods in fertile soils. Conclusion: Our results confirm that the likelihood of restoration to pre-disturbance conditions is constrained in contexts of higher degradation, such as when agricultural use adversely affects soil properties and/or motivates extreme deforestation. Lower AGB found on sandy soils suggests that forest recovery is sensitive to local drought intensification. Given regional projections for extended dry seasons, restoration approaches could consider targeting alternative reference states, rather than historical/undisturbed ones, under highly altered environments, while aiming to improve soil and microclimate conditions to allow moist tropical forest recovery where feasible.

Biomass resilience of Neotropical secondary forests.

Land-use change occurs nowhere more rapidly than in the tropics, where the imbalance between deforestation and forest regrowth has large consequences for the global carbon cycle. However, considerable uncertainty remains about the rate of biomass recovery in secondary forests, and how these rates are influenced by climate, landscape, and prior land use. Here we analyse aboveground biomass recovery during secondary succession in 45 forest sites and about 1,500 forest plots covering the major environmental gradients in the Neotropics. The studied secondary forests are highly productive and resilient. Aboveground biomass recovery after 20 years was on average 122 megagrams per hectare (Mg ha(-1)), corresponding to a net carbon uptake of 3.05 Mg C ha(-1) yr(-1), 11 times the uptake rate of old-growth forests. Aboveground biomass stocks took a median time of 66 years to recover to 90% of old-growth values. Aboveground biomass recovery after 20 years varied 11.3-fold (from 20 to 225 Mg ha(-1)) across sites, and this recovery increased with water availability (higher local rainfall and lower climatic water deficit). We present a biomass recovery map of Latin America, which illustrates geographical and climatic variation in carbon sequestration potential during forest regrowth. The map will support policies to minimize forest loss in areas where biomass resilience is naturally low (such as seasonally dry forest regions) and promote forest regeneration and restoration in humid tropical lowland areas with high biomass resilience.

Long-term changes in above ground biomass after disturbance in a neotropical dry forest, Hellshire Hills, Jamaica

We used data from experimental plots (control, partially cut and clear-cut) established in 1998, in a tropical dry forest (TDF) in Jamaica, to assess changes in above ground biomass (AGB) 10 years after disturbance. The treatments reduced AGB significantly in 1999 (partially cut: 37.6 %, clear-cut: 94.4 %) and after 10 years, AGB did not recover overall, nor did it recover in the clear-cut plots. Partially cut plots, however, recovered the lost AGB in 10 years via growth of uncut trees, which contributed significantly to biomass recovery, with only minor contributions from recruited trees and coppice shoots. For clear-cut plots, coppice shoots contributed significantly to the recovered AGB when compared with recruited biomass. Together, they recovered 26 % of AGB lost, despite recovering 78 % of the density and height of the control plots. The probability of survivorship decreased for trees with higher pre-treatment AGB values, but was higher for trees with multiple stems in 1998, regardless of treatment. The magnitude of biomass reduction varied among the species assessed and this had a differential effect on their ability to recover AGB. We estimate that it will take approximately 45.4 years for the clear-cut plots to recover pre-treatment AGB; this is significantly longer than AGB recovery time for some successional rainforests on abandoned pastures/farmland. Consequently, this TDF may not be as resilient as tropical rainforests.

不同起始状态对草原群落恢复演替的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 不同起始状态对草原群落恢复演替的影响 DOI: 10.5846/stxb201202220241 作者: 作者单位: 内蒙古大学生命科学学院,内蒙古大学生命科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家科技支撑计划项目(2011BAC02B03);国家自然科学基金项目(31160476, 31060076);内蒙古自治区自然科学基金重点项目(2010Zd16) The effects of different original state on grassland community restoration succession Author: Affiliation: College Of Life Sciences Of Inner Mongolia University,College Of Life Sciences Of Inner Mongolia University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:内蒙古典型草原,由于过度放牧利用,绝大部分草原处于退化状态。为了使退化草原得到较好的恢复,以锡林郭勒盟白音锡勒牧场典型草原为研究对象,比较分析了在不同起始状态下的草原群落,经过6a的自然恢复,其各自的群落组成,地上生物量及共有种的植株高度、节间长、叶长、叶宽,土壤紧实度和容重。结果表明:1)不同放牧率的植物群落,经过6a的禁牧恢复,群落类型发生了变化且群落趋于一致。2)当放牧率SR≤5.33羊/hm2(SR4)时,演替起始状态对草原群落地上生物量的恢复没有影响;当放牧率SR＞5.33羊/hm2时,演替起始状态对草原群落地上生物量的恢复产生影响,其结果是导致当前生物量降低,不利于草原的恢复。3)不同放牧率植物群落的植物个体特征趋于一致, "个体小型化"现象消失。同时,也说明群落恢复演替的起点不同,正常化的时间没有太大的变化。4)不同放牧率植物群落的土壤紧实度和容重经过6a的禁牧恢复,没有得到完全恢复,但均达到一致的水平。 Abstract:The Xilinggol steppe is one of the four biggest grasslands in China, and is representative of the semi-arid grasslands in Asia. To discover whether the initial state (6 years previously) of various degraded grassland communities has had an effect on recovery of these communities and in what way this effect is evidenced, research was undertaken on vegetation that has undergone 6 years of recovery through non-grazing, after varying degrees of degradation under different grazing rates. The experimental study site is in the middle reaches of the Xilin River, 500 meters west of the Inner Mongolia Grassland Ecosystem Research Station of the Chinese Academy of Sciences, from 43°26'-44°08'N and 116°04'-117°05'E. The following is the general situation of the surveyed land. The grazing experiment at the study site began in summer 1989. The sample plot is degraded grassland, in which Artemisia frigida and small grasses dominate, and the experimental grazing animal was sheep. There are 6 conditions, including five different stocking rates (1.33, 2.67, 4.00, 5.33 and 6.67 sheep/hm2) and a non-grazing control. Having been grazed at various rates for 16 years through 2005, the structure and function of the ecological system (plant community, soil physical and chemical properties) have experienced significant changes. Grassland ecological systems are in different degrees of degradation. To examine the recovery process of such grassland ecological systems after suspension of grazing, the grazing experiment was stopped in 2005. By 2011, the grassland ecosystems had recovered to their natural state. Investigation and sampling were conducted in August 2011. In recent years, under the influence of high use and adverse natural factors, the majority of the Inner Mongolian steppe has been in a state of degradation. In order to facilitate recovery of the degraded grasslands, the present research was conducted on a typical steppe at Baiyinxile Ranch in Xilinggol. The author analyzed a series of indicators of the state of various grassland communities (each after 6 years of natural recovery), which include plant community composition, aboveground biomass, plant height, internode length, main species leaf length, leaf width, soil compactness, and soil bulk density. The findings suggest that: 1) After 6 years of non-grazed recovery, communities of different stocking rates have changed their community type, and the communities tend to be consistent. 2) Initial successional stages have no significant effect on aboveground biomass recovery when the stocking rate is less than 5.33 sheep/hm2; however, if the stocking rate is more than 5.33 sheep/hm2, the initial successional stages lead to a decrease in current biomass. In other words, a higher stocking rate is unfavorable to the recovery of grassland. 3) Individual plant characteristics of communities at different grazing rates tend to be consistent, and the individual miniaturization phenomenon disappear. At the same time, this shows that even though the starting point of community recovery and succession is variable, the normalization time is nearly constant. 4) After 6 years of recovery, the soil compactness and bulk density of communities with different grazing rates did not fully recover, but tended to be consistent. 参考文献 相似文献 引证文献

Integral assessment of the regrow capacity of alpine plants

A method for the comparative assessment of the regrow capacity (the ability of plants to the after-mowing recovery of above-ground biomass) of herbs in natural plant communities has been proposed. The method is based on the combined use of biomass parameters and the data on the number of shoots for the cases of the single and double removal of the biomass. The regrow capacity of 42 alpine species from four different plant communities has been assessed. The average weighted regrow capacity score decreases in the following series: Geranium-Hedysarum meadows > alpine lichen heaths ≥ alpine snow-bed communities ≥ Festuca varia meadows.

Increasing native, but not exotic, biodiversity increases aboveground productivity in ungrazed and intensely grazed grasslands

Species-rich native grasslands are frequently converted to species-poor exotic grasslands or pastures; however, the consequences of these changes for ecosystem functioning remain unclear. Cattle grazing (ungrazed or intensely grazed once), plant species origin (native or exotic), and species richness (4-species mixture or monoculture) treatments were fully crossed and randomly assigned to plots of grassland plants. We tested whether (1) native and exotic plots exhibited different responses to grazing for six ecosystem functions (i.e., aboveground productivity, light interception, fine root biomass, tracer nitrogen uptake, biomass consumption, and aboveground biomass recovery), and (2) biodiversity-ecosystem functioning relationships depended on grazing or species origin. We found that native and exotic species exhibited different responses to grazing for three of the ecosystem functions we considered. Intense grazing decreased fine root biomass by 53% in exotic plots, but had no effect on fine root biomass in native plots. The proportion of standing biomass consumed by cattle was 16% less in exotic than in native grazed plots. Aboveground biomass recovery was 30% less in native than in exotic plots. Intense grazing decreased aboveground productivity by 25%, light interception by 14%, and tracer nitrogen uptake by 54%, and these effects were similar in native and exotic plots. Increasing species richness from one to four species increased aboveground productivity by 42%, and light interception by 44%, in both ungrazed and intensely grazed native plots. In contrast, increasing species richness did not influence biomass production or resource uptake in ungrazed or intensely grazed exotic plots. These results suggest that converting native grasslands to exotic grasslands or pastures changes ecosystem structure and processes, and the relationship between biodiversity and ecosystem functioning.

Changes in Structure, Composition, and Nutrients During 15 Yr of Hurricane‐Induced Succession in a Subtropical Wet Forest in Puerto Rico

ABSTRACTThe trajectory of hurricane‐induced succession was evaluated in a network of forest plots measured immediately before and 3 mo, 5, 10, and 15 yr after the direct impact of a Category 4 hurricane. Comparisons of forest structure, composition, and aboveground nutrients pools were made through time, and between species, life‐history groups and geomorphic settings. The hurricane reduced aboveground biomass by 50 percent, causing an immediate decrease in stem density and diversity indices among all geomorphic settings. After 15 yr, basal area and aboveground biomass returned to pre‐hurricane levels, while species richness, diversity indices, and stem densities exceeded pre‐hurricane levels. Differences in species composition among geomorphic settings had not returned after 15 yr but differences in stem densities and structure were beginning to emerge. Significant differences were observed in the nutrient concentration of the three species that comprised the most aboveground biomass, and between species categorized as secondary high‐light species and primary, low‐light species. Species whose abundance was negatively correlated with the mature forest dominant also had distinct nutrient concentrations. When total aboveground nutrient pools were compared over time, differences in leaf nutrients among species were hidden by similarities in wood nutrient concentrations and the biomass dominance of a few species. The observed successional trajectory indicates that changes in species composition contributed to fast recovery of aboveground biomass and nutrient pools, while the influence of geomorphic setting on species composition occurs at time scales >15 yr of succession.

Festuca campestris alters root morphology and growth in response to simulated grazing and nitrogen form

Summary 1. Large herbivores are known to spatially concentrate and alter the form of nitrogen (N) in grassland systems, which can modify aboveground plant chemical composition and productivity, and result in shifts in grazing pressure in these areas. Root responses to grazing under high N inputs may facilitate these changes, but their responses are less well understood. 2. We examined biomass, root morphology and demography, and nitrogen pool responses of Festuca campestris Rydb. seedlings grown in pots in an environmental chamber and subject to heavy fertilization with isotopically‐labelled N in a NO3‐N or NH4‐N fertilizer treatment, and to no clipping or clipping to 4 cm twice during the experiment. 3. Festuca campestris exhibited re‐growth patterns after defoliation that reflected preferential allocation to aboveground shoots, with percent recovery of shoot biomass twice that of roots. Clipping did not increase the risk of root mortality. Instead, reduced root biomass in clipped plants resulted from slowed elongation and decreased production of new roots. Although roots with smaller diameters and at lower density had a greater risk of root mortality, clipping did not alter the mean root diameter or level of root branching. 4. Under high N fertilization, NH4‐N increased the amount of aboveground biomass, ameliorated the effects of clipping on root production and further reduced the risk of root mortality in clipped plants. N‐form had no effect on root morphology. 5. While total plant N uptake and the percent utilization of fertilizer were lower in clipped plants, total plant nitrogen accumulated per root biomass (g g−1) at harvest was higher in clipped plants. 6. Our findings indicate that where defoliation is coupled with high nitrogen return, Festuca campestris recuperates by increasing nitrogen uptake, shifting production to favour recovery of aboveground biomass, and mitigating carbon losses by decreasing investment in new, actively growing roots. Because application of a more mobile form of nitrogen (NO3‐N) did not alter root morphology, root physiological responses may be most important for re‐growth when nitrogen is not limiting. Root reductions associated with grazing may have a greater impact in locations where grazer‐mediated nitrogen return is spatially decoupled from defoliation.

Untangling a Decline in Tropical Forest Resilience: Constraints on the Sustainability of Shifting Cultivation Across the Globe

ABSTRACTShifting cultivators depend on forest biomass inputs to nourish their crops. For them, forest resilience has an immediate impact: it affects crop productivity. A decline in the rate of recovery following shifting cultivation would ultimately affect local, regional and global carbon budgets, with feedbacks to climate. Yet the long‐term impacts of shifting cultivation have been quantified in only six locations. In this study, we reanalyze data from these locations to determine whether the rate of biomass recovery is the same from cycle to cycle. Further, using case studies in Southern Yucatan, Mexico and West Kalimantan, Indonesia, we investigate the ecological and socioeconomic factors that affect forest resilience and thus determine whether or not shifting cultivation is sustainable. The reanalysis links aboveground biomass recovery following shifting cultivation to site productivity, forest age, fallow length, history of cultivation, and soil texture. Across locations, biomass accumulation rate declines by 9.3 percent with each cycle of shifting cultivation. Per cycle change in biomass accumulation rate is significantly more negative in younger forests and forests that experience a shorter fallow period. However, more detailed analyses for two case studies suggest that a purely ecological framework is of limited effectiveness in explaining variability in the effect of repeated shifting cultivation. Rather, socioeconomic factors such as migration, subsidies, roads, and settlement history can alter the outcome of shifting cultivation by limiting the accumulation and use of local knowledge.

Above-ground biomass dynamics after reduced-impact logging in the Eastern Amazon

Changes in above-ground biomass (AGB) of 17 1ha logged plots of terra firme rain forest in the eastern Amazon (Brazil, Paragominas) were monitored for four years (2004–2008) after reduced-impact logging. Over the same time period, we also monitored two 0.5ha plots in adjacent unlogged forest. While AGB in the control plots changed little over the observation period (increased on average 1.4Mgha−1), logging resulted in immediate reductions in ABG that averaged 94.5Mgha−1 (±42.0), which represented 23% of the 410Mgha−1 (±64.9) present just prior to harvesting. Felled trees (dbh>55cm) accounted for 73% (±15) of these immediate losses but only 18.9Mgha−1 (±8.1) of biomass was removed in the extracted logs. During the first year after logging, the annual AGB balance (annual AGB gain by recruitment and growth−annual AGB loss by mortality) remained negative (−31.1Mgha−1year−1; ±16.7), mainly due to continued high mortality rates of damaged trees. During the following three years (2005–2008), average net AGB accumulation in the logged plots was 2.6Mgha−1year−1 (±4.6). Post-logging biomass recovery was mostly through growth (4.3±1.5Mgha−1year−1 for 2004–2005 and 6.8±0.9Mgha−1year−1 for 2005–2008), particularly of large trees. In contrast, tree recruitment contributed little to the observed increases in AGB (1.1±0.6Mgha−1year−1 for 2004–2005 and 3.1±1.3Mgha−1year−1 for 2005–2008). Plots with the lowest residual basal area after logging generally continued to lose more large trees (dbh ≥70cm), and consequently showed the greatest AGB losses and the slowest overall AGB gains. If 100% AGB recovery is desired and the 30-year minimum cutting cycle defined by Brazilian law is adhered to, current logging intensities (6treesha−1) need to be reduced by 40–50%. Such a reduction in logging intensity will reduce financial incomes to loggers, but might be compensated for by the payment of environmental services through the proposed REDD (reduced emissions from deforestation and forest degradation) mechanism of the United Nations Framework Convention on Climate Change.

Tree diversity, composition, forest structure and aboveground biomass dynamics after single and repeated fire in a Bornean rain forest

Forest fires remain a devastating phenomenon in the tropics that not only affect forest structure and biodiversity, but also contribute significantly to atmospheric CO2. Fire used to be extremely rare in tropical forests, leaving ample time for forests to regenerate to pre-fire conditions. In recent decades, however, tropical forest fires occur more frequently and at larger spatial scales than they used to. We studied forest structure, tree species diversity, tree species composition, and aboveground biomass during the first 7 years since fire in unburned, once burned and twice burned forest of eastern Borneo to determine the rate of recovery of these forests. We paid special attention to changes in the tree species composition during burned forest regeneration because we expect the long-term recovery of aboveground biomass and ecosystem functions in burned forests to largely depend on the successful regeneration of the pre-fire, heavy-wood, species composition. We found that forest structure (canopy openness, leaf area index, herb cover, and stem density) is strongly affected by fire but shows quick recovery. However, species composition shows no or limited recovery and aboveground biomass, which is greatly reduced by fire, continues to be low or decline up to 7 years after fire. Consequently, large amounts of the C released to the atmosphere by fire will not be recaptured by the burned forest ecosystem in the near future. We also observed that repeated fire, with an inter-fire interval of 15 years, does not necessarily lead to a huge deterioration in the regeneration potential of tropical forest. We conclude that burned forests are valuable and should be conserved and that long-term monitoring programs in secondary forests are necessary to determine their recovery rates, especially in relation to aboveground biomass accumulation.

Evaluation of aboveground and belowground biomass recovery in physically disturbed seagrass beds

Several studies addressed aboveground biomass recovery in tropical and subtropical seagrass systems following physical disturbance. However, there are few studies documenting belowground biomass recovery despite the important functional and ecological role of roots and rhizomes for seagrass ecosystems. In this study, we compared the recovery of biomass (g dry weight m(-2)) as well as the biomass recovery rates in ten severely disturbed multi-species seagrass meadows, after the sediments were excavated and the seagrasses removed. Three sites were located in the tropics (Puerto Rico) and seven in the subtropics (Florida Keys), and all were originally dominated by Thalassia testudinum. Total aboveground biomass reached reference values at four out of ten sites studied, two in the Florida Keys and two in Puerto Rico. Total belowground biomass was lower at the disturbed locations compared to the references at all sites, apart from two sites in the Florida Keys where the compensatory effect of opportunistic species (Syringodium filiforme and Halodule wrightii) was observed. The results revealed large variation among sites in aboveground and belowground biomass for all species, with higher aboveground recovery than belowground for T. testudinum. Recovery rates for T. testudinum were highly variable across sites, but a general trend of faster aboveground than belowground recovery was observed. Equal rates between aboveground and belowground biomass were found for opportunistic species at several sites in the Florida Keys. These results indicate the importance of belowground biomass when assessing seagrass recovery and suggest that the appropriate metric to assess seagrass recovery should address belowground biomass as well as aboveground biomass in order to evaluate the full recovery of ecological services and functions performed by seagrasses. We point out regional differences in species composition and species shifts following severe disturbance events and discuss ecological implications of gap dynamics in multi-species seagrass meadows.

Long-term monitoring of post-fire aboveground biomass recovery in a lowland dipterocarp forest in East Kalimantan, Indonesia

Between 1988 and 2000, changes in the above-ground biomass (AGB) of trees in an East Kalimantan lowland forest, damaged by fires in 1982–83 and 1998, were estimated using allometric functions and an annual inventory of stem diameter. The original vegetation of the study site was lowland dipterocarp forest which has since been affected by selective logging and wild fires. The 1982–83 fire killed large trees of primary species and the opened sites became dominated by a few pioneer species. Between 1988 and 1997, a few pioneer tree species, namely Macaranga spp., dominated a heavily disturbed stand (HDS). Primary tree species that survived the 1982–83 fire dominated a lightly disturbed stand (LDS). A moderately disturbed stand (MDS) contained vegetation intermediate between the HDS and the LDS. In 1997, there were 553, 499 and 356 trees ha-1 in the HDS, MDS and LDS, respectively. Macaranga trees accounted for 70, 40 and 11 of the total number of trees in the HDS, MDS, and LDS, respectively. In 1997, the AGB of trees in the HDS, MDS, and LDS was 117, 280, and 315 Mg ha-1, respectively. The proportion of biomass accounted for by Macaranga trees for the HDS, MDS, and LDS was 34, 8 and 1, respectively. The pioneer trees did not compensate for the loss of aboveground biomass resulting from the death of large primary trees. The fire in 1998 again decreased AGB of the stands. In 2000, the AGB of trees in the HDS, MDS, and LDS was 27, 106, and 219 Mg ha-1, respectively. The sites opened up by the 1998 fire were covered with the pioneer seedlings and seemingly dominated by the pioneer trees with a larger number of stems per ha, but lower biomass as compared to the original forest (> 400 Mg ha-1).

Modeling soil quality thresholds to ecosystem recovery at Fort Benning, GA, USA

The objective of this research was to use a simple model of soil carbon (C) and nitrogen (N) dynamics to predict nutrient thresholds to ecosystem recovery on degraded soils at Fort Benning, Georgia, in the southeastern USA. Artillery, wheeled, and tracked vehicle training at military installations can produce soil disturbance and potentially create barren, degraded soils. Ecosystem reclamation is an important component of natural resource management at military installations. Four factors were important to the development of thresholds to recovery of aboveground biomass on degraded soils: (1) initial amounts of aboveground biomass, (2) initial soil C stocks (i.e., soil quality), (3) relative recovery rates of biomass, and (4) soil sand content. Forests and old fields on soils with varying sand content had different predicted thresholds for ecosystem recovery. Soil C stocks at barren sites on Fort Benning were generally below predicted thresholds to 100% recovery of desired future ecosystem conditions defined on the basis of aboveground biomass. Predicted thresholds to ecosystem recovery were less on soils with more than 70% sand content. The lower thresholds for old field and forest recovery on more sandy soils were apparently due to higher relative rates of net soil N mineralization. Calculations with the model indicated that a combination of desired future conditions, initial levels of soil quality (defined by soil C stocks), and the rate of biomass accumulation determine the predicted success of ecosystem recovery on disturbed soils.

Tropical forest recovery: legacies of human impact and natural disturbances

Land-use history interacts with natural forces to influence the severity of disturbance events and the rate and nature of recovery processes in tropical forests. Although we are far from an integrated view of forest recovery processes, some generalizations can be made. Recovery of forest structure and composition is relatively rapid following disturbances that primarily impact forest canopies, such as hurricanes. Recovery is considerably slower following disturbances that heavily impact soils as well as aboveground vegetation, such as bulldozing, heavy or long-term grazing, and severe fires, often with long-lasting effects on species composition. The landscape matrix plays a critical role in local recovery processes. Proximity of disturbed areas to remnant forest patches promotes more rapid recovery, which depends heavily on seed dispersal. Recovery of aboveground biomass is constrained by soil fertility and texture across regions as well as across soil types within a region. Restoration of soil fertility may be a prerequisite for forest recovery on sites with severely degraded soils. Despite evidence of rapid forest recovery following large-scale deforestation, many degraded areas of today's tropics will require human assistance to recover forest structure, species composition, and species interactions typical of mature tropical forests.

Vegetative response of Arctostaphylos uva-ursi to experimental cutting and burning

Arctostaphylos uva-ursi uses vegetative resprouting to recover rapidly after disturbances. This study aims to widen knowledge of its regeneration response, so it was subjected to experimental cutting and burning. Fifteen pairs of small circular plots (50 cm diameter) were situated at random in an area where this species is abundant and forms homogeneous carpets with close to 100% cover. One plot of each pair was burned and the other one was cut. Initial biomass was estimated as dry weight from the cut plots. A 50 cm diameter circular sampling quadrat, divided into two concentric circles, was used in order to determine cover recovery and the way in which this occurred (predominantly by colonization from outside or uniformly over the whole surface). Initial recovery was very fast after both disturbances, exceeding 30% cover from the fourth month. Recovery of aboveground biomass was also similar on comparing both types of disturbance, but statistically significant differences with respect to initial values were detected.

Succession in the Elfin Woodland of the Luquillo Mountains of Puerto Rico

Twenty tree species were observed growing on a plane wreck site in elfin woodland 18.5 yr after the crash. About three-quarters of 1172 arborescent stems were elfin forest primary species. Total aboveground biomass averaged 776 g/m2 and was classified thus: 30 percent arborescent dicots; 13 percent palms; 31 percent ferns; and 26 percent grasses and herbs. Total aboveground biomass recovery after 18.5 yr appeared linear, and, at the observed rate, it would require nearly two centuries for the site to return to its original biomass.