Recovery Of Aboveground Biomass Research Articles

Losses of low-germinating, slow-growing species prevent grassland composition recovery from nutrient amendment.

Nutrient enrichment often alters the biomass and species composition of plant communities, but the extent to which these changes are reversible after the cessation of nutrient addition is not well-understood. Our 22-year experiment (15 years for nutrient addition and 7 years for recovery), conducted in an alpine meadow, showed that soil nitrogen concentration and pH recovered rapidly after cessation of nutrient addition. However, this was not accompanied by a full recovery of plant community composition. An incomplete recovery in plant diversity and a directional shift in species composition from grass dominance to forb dominance were observed 7 years after the nutrient addition ended. Strikingy, the historically dominant sedges with low germination rate and slow growth rate and nitrogen-fixing legumes with low germination rate were unable to re-establish after nutrient addition ceased. By contrast, rapid recovery of aboveground biomass was observed after nutrient cessation as the increase in forb biomass only partially compensated for the decline in grass biomass. These results indicate that anthropogenic nutrient input can have long-lasting effects on the structure, but not the soil chemistry and plant biomass, of grassland communities, and that the recovery of soil chemical properties and plant biomass does not necessarily guarantee the restoration of plant community structure. These findings have important implications for the management and recovery of grassland communities, many of which are experiencing alterations in resource input.

Plant vegetative propagation plays a considerable role in the regeneration following slash-and-burn agriculture in Caatinga dry forest

Slash-and-burn agriculture is a common practice in dry forests worldwide. Understanding the relative importance of different regeneration mechanisms following this disturbance provides insights into forest regeneration dynamics and resilience. We assessed differences in structural components, the relative contribution of vegetative and sexual reproduction, and the taxonomic composition of woody assemblages among different habitats in a Brazilian Caatinga dry forest after slash-and-burn agriculture. We assessed vegetation parameters (i.e., basal area, height, species richness, and the frequency of each regeneration mechanism) in recently abandoned fields, regenerating forest stands and old-growth forest stands. Overall, trees originates from root suckers accounted for at least 40% of the individuals, stems, and basal areas across the habitats. The structure of regenerating stands was similar to old-growth stands except for species composition, total number of roots, and number of primary roots. The aboveground basal area varied in total values, but not averages, among habitats, indicating a rapid recovery of aboveground biomass after slash-and-burn agriculture. Conversely, recently abandoned fields had higher belowground basal area and basal area of primary roots, revealing that the trees in these habitats emit more roots even with fewer individuals. There was a high degree of species turnover among the habitats, probably due to both species selection by farmers and environmental effects. Nevertheless, the dominant species presented both regeneration mechanisms across the habitats. Our findings thus show that the Caatinga dry forest regeneration considerably relies on the ability of woody plant species to emit root suckers in addition to sexual reproduction, which should be considered for better management practices as slash-and-burn agriculture is and will continue to be practiced.

Recovery of aboveground biomass, soil carbon stocks and species diversity in tropical montane secondary forests of East Africa

Tropical montane forests are fragile ecosystems that provide a wide range of ecosystem services including hydrological services, biodiversity protection and storing carbon in the above and belowground and soils contributing to climate change mitigation. The world’s tropical montane forests are increasingly exposed to degradation and their recovery after disturbance has not been adequately quantified. Here, using information from 47 plots in three blocks of the Mau Forest Complex of Kenya, we assessed the changes in aboveground biomass (AGB), tree species diversity, soil carbon and nitrogen stocks following forest clearance. AGB recovered at an annual rate of 6.42 Mg ha−1 yr−1 in the first 20 years, the rate then slowed down to 4.46–4.67 Mg ha−1 yr−1 at around 25–30 years. Around 25 years after disturbance, AGB in recovering forests was 70 % (198.32 ± 78.11 Mg ha−1) of the AGB in the old secondary forest (OSF) (282.86 ± 71.64 Mg ha−1) and was statistically indistinguishable. Stem density, species diversity and richness indices did not show significant differences across recovery classes. There was no significant difference in soil carbon and nitrogen stocks across classes with the soil carbon (184.1 ± 41 Mg ha−1) of the young secondary forest (<10 years) being 84.5 % of that of the OSF (217.9 ± 51.8 Mg ha−1). This study reports a rapid rate of AGB and carbon accumulation within 20 years of disturbance, and high levels of species richness in these previously disturbed fragments of tropical montane forests of East Africa.

Drought diminishes aboveground biomass accumulation rate during secondary succession in a tropical forest on Hainan Island, China

With rising temperatures and altered annual precipitation patterns, climatic factors are likely to play an increasingly important role in controlling the biomass accumulation rate of tropical secondary forests. However, the relative importance of biotic and abiotic factors and demographic progresses (growth, mortality, and recruitment) driving biomass dynamics in these ecosystems remain largely unclear, especially in tropical Asia. We explored aboveground biomass (AGB) dynamics in old-growth and secondary tropical forests on Hainan Island, China, across two consecutive five-year intervals (2010–2020). Drought frequency was higher in the second vegetation census interval. We studied the relationships of AGB and its three demographic components with drought frequency, tree diversity, soil nutrient and microorganismal abundance, and successional stage. We found that AGB accumulation rate decreased as AGB increased gradually during secondary succession. The different drought frequency between the two intervals was the dominant factor predicting the net change of AGB. With high-frequency droughts, the loss of AGB intensified and the increment rate of AGB decreased, especially in old-growth forests during second interval (2015–2020). Considering the impact of the three demographic progresses on net change in AGB, the relative influence of mortality was the largest (61.1%), followed by growth (38.3%) and recruitment (0.6%). Successional stage was another major factor affecting AGB and its dynamics, showing a positive relationship with AGB stock and a negative relationship with net AGB change. Species richness and fungal richness had a significant positive association with AGB, while soil available nutrient had a significant negative relationship. Overall, our results show that drought frequency had a strong impact on AGB dynamics, and that the resilience of AGB accumulation to drought decreased in later successional stages. Thus, with the intensification of global climate change, the effects of high-frequency drought events should be taken into account when studying the factors affecting AGB recovery in tropical secondary forests.

Influences of fern and vine coverage on the above-ground biomass recovery in a Bornean logged-over degraded secondary forest

ABSTRACT Tropical secondary forests are widespread in the anthropogenically modified landscapes. Because tropical secondary forests were known to show a steady rate of above-ground biomass (AGB) recovery, they were expected to play a crucial role in carbon sequestration. However, in a preliminary survey of logged-over forests in Borneo, some patches covered with ferns and vines do not seem to recover steadily despite the fact that several decades have passed since the last logging. The presence and abundance of fern/vine thickets may affect the AGB recovery, but few studies have investigated the effects of the thickets. We established a total of seventeen 20-m radius circular plots in logged-over forests, Sabah, Malaysia, with a varying degree of fern/vine coverage, and tested the hypothesis that the greater fern/vine coverage would retard the AGB recovery. The net AGB accumulation rate from 2014 to 2019 was lower in the forests with a higher fern/vine coverage. Our lower bound of the accumulation rate was much lower than the previously reported rates elsewhere. The number of newly recruited and small-diameter trees was lower, and the mortality of remnant trees was higher with increasing fern/vine coverage. The growth rate of the extant pioneer trees, which are expected to significantly contribute to the initial build-up phase of the secondary succession, was inhibited when ferns and vines covered the canopy. Our study suggests that the secondary succession is arrested and the recoverability of forest stands is lower than formerly predicted when they are covered by thick ferns and vines.

Modeling Tree Recovery in Wind-Disturbed Forests with Dense Understory Species under Climate Change

Future climate conditions will alter the frequency and intensity of typhoons. Thus, post-windthrow management, which can enhance tree recovery in wind-disturbed forests with dense understory species, is essential for sustainable forest management to adapt to climate change. This study explores management options that can recover the above-ground biomass (AGB) and tree species composition after windthrow damage even under climate change. A case study area was established in the Oshima–Hiyama National Forest in southern Hokkaido, northern Japan, which were damaged by typhoons in late August 2016. We incorporated the understory species Sasa kurilensis as understory vegetation into the LANDIS-II Net Ecosystem Carbon and Nitrogen Succession extension v6.3 model to simulate the outcome of tree establishment under climate change. AGB recovery up to the year 2100 at 1,753 damaged grid cells was simulated for the Intergovernmental Panel on Climate Change representative concentration pathway (RCP) 2.6 and 8.5 scenarios. Different post-windthrow management cases were designed by varying the treatment of fallen trees and the types of trees planted. The results demonstrated that salvage logging and planting successfully recovered the AGB by 2050 at the landscape scale regardless of the climate change scenario, whereas leaving fallen trees in the damaged site or salvage logging only did not facilitate the recovery of AGB. Leaving fallen trees in damaged grid cells as ecological legacies recovered the AGB only in damaged grid cells with a sufficient number of advanced seedlings of adequate types of species irrespective of the climate change scenario. The decreasing water equivalent of snowpack in the RCP scenarios caused Sasa kurilensis mortality and promoted the recovery of AGB of trees. The dominant species recovered in natural forests, which experienced either salvage logging or leaving trees in the damaged site, varied among climate change scenarios. The warmer climate condition facilitated the recovery of Fagus crenata by 2100. These results can help designing a robust forest recovery even in uncertain future climate.

Deferment associated to contrasting grazing intensities affects root/shoot biomass allocation in natural grasslands

AbstractQuestions(i) How does a strategic deferment influence both shoot and root biomass in South American Campos natural grassland after a long time of contrasting livestock grazing intensities? (ii) How do functional strategies of plants to tolerate or avoid grazing affect patterns of aboveground and belowground biomass?LocationA natural Campos grassland in the Central Depression of Rio Grande do Sul State, Southern Brazil (latitude 30°05′27″ S, longitude 51°40′18″ W, and altitude 46 m).MethodsWe studied the effects of deferments (spring or autumn) at moderate and severe livestock grazing intensities (maintained by adjusting contrasting forage allowances during 25 years) on the cover of dominant species, and aboveground and belowground biomass. The experiment was arranged in a completely randomized design with three replications of grazing exclusions, applied simultaneously at moderate and severe grazing intensities. Measurements of above‐ and belowground biomass and the coverage of the five dominant species were performed before and after grazing exclusion periods.ResultsUnder severe grazing intensity, erect‐growing grasses were replaced by prostrate species, which were able at least to maintain the belowground biomass found at moderate grazing intensity. In response to deferments, severe grazing intensity changed toward a significant increase in aboveground biomass and in the coverage of plants with erect growing habit. However, total belowground biomass remained unaffected by exclusions in both grazing intensities. The relation of root:shoot biomass was lower under moderate grazing intensity, and showed a negative response to deferment treatments at severe grazing intensity.ConclusionLong‐term contrasting grazing intensities applied in South American Campos grasslands determine several changes in above‐ and belowground relationships. Prevalence of prostrate plants under severe grazing is associated with a high partitioning capacity of assimilates toward the subterranean biomass, higher than in the tall species predominant under moderate grazing. The fast recovery of aboveground biomass, the maintenance of the underground biomass and the increase of tall grasses in response to deferments reveals the high resilience capacity of this ecosystem after a long‐term period of overgrazing.

The eco‐evolutionary history of Madagascar presents unique challenges to tropical forest restoration

AbstractHigh biodiversity and endemism combined with persistently high deforestation rates mark Madagascar as one of the hottest biodiversity hot spots. Contemporary rising interest in large‐scale reforestation, both globally and throughout Madagascar itself, presents a promising impetus for forest restoration and biodiversity conservation across the island. However, Madagascar may face unique restoration challenges due to its equally unique eco‐evolutionary trajectory, which must be understood to enable successful ecological restoration. We conducted a systematic review of potential barriers to restoration for terrestrial forest biomes (rain forests, dry forests, and subhumid highland forests) in Madagascar. Our results indicate that aboveground biomass recovery of Malagasy forests appears to be slower than other tropical forests. We suggest four key synergistic factors that inhibit restoration in Madagascar: (a) lack of resilience to shifting nutrient and fire regimes arising from widespread high‐intensity shifting cultivation; (b) predominance of nutrient‐poor, highly weathered ferralitic soils; (c) vulnerability of regenerating native trees to competition with invasive species due to their evolutionary isolation; and (d) low seed dispersal into regenerating forests due to the unique dependence of Malagasy trees on dispersal by forest‐dependent endangered or extinct primates. However, we note that rigorous experimental study of regenerating forests in Madagascar is currently lacking. There are great opportunity and need for such research to disentangle drivers and interactions inhibiting forest restoration. These studies would enable reforestation practitioners to effectively capitalize on current global momentum to implement the large‐scale restoration necessary for the conservation of Madagascar's numerous endemic species.Abstract in Malagasy is available with online material

Climatic and biotic factors influencing regional declines and recovery of tropical forest biomass from the 2015/16 El Niño

The 2015/16 El Niño brought severe drought and record-breaking temperatures in the tropics. Here, using satellite-based L-band microwave vegetation optical depth, we mapped changes of above-ground biomass (AGB) during the drought and in subsequent years up to 2019. Over more than 60% of drought-affected intact forests, AGB reduced during the drought, except in the wettest part of the central Amazon, where it declined 1 y later. By the end of 2019, only 40% of AGB reduced intact forests had fully recovered to the predrought level. Using random-forest models, we found that the magnitude of AGB losses during the drought was mainly associated with regionally distinct patterns of soil water deficits and soil clay content. For the AGB recovery, we found strong influences of AGB losses during the drought and of [Formula: see text]. [Formula: see text] is a parameter related to canopy structure and is defined as the ratio of two relative height (RH) metrics of Geoscience Laser Altimeter System (GLAS) waveform data-RH25 (25% energy return height) and RH100 (100% energy return height; i.e., top canopy height). A high [Formula: see text] may reflect forests with a tall understory, thick and closed canopy, and/or without degradation. Such forests with a high [Formula: see text] ([Formula: see text] ≥ 0.3) appear to have a stronger capacity to recover than low-[Formula: see text] ones. Our results highlight the importance of forest structure when predicting the consequences of future drought stress in the tropics.

Restoration plantations accelerate dead wood accumulation in tropical premontane forests

Dead wood stores 10–20% of global forest carbon stocks, but its recovery and restoration in secondary tropical forests are poorly documented. In this study, we evaluated (1) the recovery pattern of dead wood volumes across a chronosequence of secondary tropical forests that used to be former coffee plantations, and (2) the efficiency of two common restoration strategies to recover dead wood volumes similar to those found in old-growth forests, all in a tropical premontane landscape in southern Costa Rica. Restoration strategies consisted of plantations and natural regeneration. Plantations consist of plots where two endemic (Terminalia amazonia and Vochysia guatemalensis) and two naturalized (Inga edulis and Ertyhrina poeppegiana) species were planted in rows. Natural regeneration consists of plots where no trees were planted, but where agriculture or cattle are excluded though fencing and vegetation is allowed to regenerate naturally. We hypothesized that (1) dead wood volumes increase with forest age following a logistic shape, and that (2) restoration plantations recover dead wood volumes more quickly compared to naturally regenerated forests. We measured dead wood volumes in a total of 35 forest fragments that were former coffee plantations or are currently old-growth forests and 10 restoration plots containing either natural regeneration or restoration plantations that were former fallow or pasture using strip transects. Dead wood volumes significantly increased with forest age following a logistic shape, starting with very low values in early ages (3–5 years), increasing rapidly (6–50 years), and ending with high and relatively stable values after 50 years of age. In addition, plantations (16 to 17 years old) recovered 41% of dead wood volumes found in old-growth forests > 100 years old, whereas naturally regenerated forests of the same age only recovered 1.7% of dead wood volumes found in old-growth forests. Our study shows that restoration plantations not only accelerate the recovery of above ground biomass, but also accelerate the recovery of dead wood in premontane Neotropical ecosystems. This indicates that tree planting positively affects carbon storage, and potentially the preservation of dead wood-associated biodiversity.

Long-term cumulative impacts of windthrow and subsequent management on tree species composition and aboveground biomass: A simulation study considering regeneration on downed logs

Post-windthrow management delays forest biomass recovery by altering the situation of disturbance legacies and can change the species composition. Although the short-term effects of post-windthrow management have been well studied, we do not have enough knowledge about the long-term effects of post-windthrow management on species composition and biomass recovery. Those effects associated with an increase in the windthrow frequency are also unknown. Although forest landscape models can effectively evaluate these effects, conventional models do not represent the regeneration process on downed logs, which is essential for simulating forest succession. We focused on hemiboreal forests in northern Japan and aimed to (1) incorporate the regeneration process on downed logs into LANDIS-II, which is one of the most used forest landscape models; (2) evaluate the long-term effects of post-windthrow management on tree species composition and aboveground biomass recovery; and (3) evaluate the associated long-term effects of interactions between post-windthrow management and increased windthrow frequency. We incorporated the regeneration process on downed logs into LANDIS-II by regulating the probability of the establishment of species that depend on dead wood, such as spruce, according to the availability of well-decayed dead wood. The incorporation of this process resulted in simulations of trends in species composition and aboveground biomass recovery after post-windthrow management that were more accurate than those produced by the original model. In the modified LANDIS-II simulation, reductions in dead wood and advanced seedlings due to salvage logging had little effect on the tree species composition or aboveground biomass recovery; however, the complete destruction of advanced seedlings by scarification induced a delay in aboveground biomass recovery and a shift to birch-dominated forests that continued for 100 years. In addition, the reduction in dead wood due to salvage logging decreased the number of seedlings, especially of dead wood-dependent species, that established after windthrow. When the windthrow frequency doubled, this decrease in seedlings induced a delay in aboveground biomass recovery, and a substantial decrease in dead wood-dependent species biomass occurred after a subsequent windthrow event. However, after the second windthrow event and following scarification, the forest recovered in the same way as after the first windthrow because the destruction of advanced seedlings and understory plants, namely, dwarf bamboo (Sasa spp.), by scarification reset the site conditions. To conserve the species composition and aboveground biomass of hemiboreal forests under climate change, which is expected to increase windthrow frequency, salvage logging and scarification should be avoided.

Nitrogen addition amplifies the nonlinear drought response of grassland productivity to extended growing-season droughts.

Understanding the response of grassland production and carbon exchange to intra-annual variation in precipitation and nitrogen addition is critical for sustainable grassland management and ecosystem restoration. We introduced growing-season drought treatments of different lengths (15, 30, 45 and 60 d drought) by delaying growing-season precipitation in a long-term nitrogen addition experiment in a low diversity meadow steppe in northeast China. Response variables included aboveground biomass (AGB), ecosystem net carbon exchange (NEE), and leaf net carbon assimilation rate (A). In unfertilized plots drought decreased AGB by 13.7% after a 45-d drought and 31.7% after a 60-d drought (47.6% in fertilized plots). Progressive increases in the drought response of NEE were also observed. The effects of N addition on the drought response of productivity increased as drought duration increased, and these responses were a function of changes in AGB and biomass allocation, particularly root to shoot ratio. However, no significant effects of drought occurred in fertilized or unfertilized plots in the growing season a year after the experiment, N addition did limit the recovery of AGB from severe drought during the remainder of the current growing season. Our results imply that chronic N enrichment could exacerbate the effects of growing-season drought on grassland productivity caused by altered precipitation seasonality under climate change, but that these effects do not carry over to the next growing season.

Active restoration leads to rapid recovery of aboveground biomass but limited recovery of fish diversity in planted mangrove forests of the North Brazil Shelf

Coastal degradation has spurred active restoration of mangrove ecosystems, from local initiatives to global commitments to increase mangrove forest area by 20% over the next decade. Mangrove restoration projects typically have multiple objectives, including carbon storage, coastal resilience, and fisheries recovery. How planting seedlings, the most common form of active restoration, can promote recovery of mangrove ecosystem functions remains an urgent research need. We quantified multiple ecosystem outcomes of Guyana's national mangrove restoration program, approximately a decade after seedling planting, and compared restoration outcomes with conditions in intact and degraded mangrove forests. Multivariate analyses indicate that intact and restored sites' environmental conditions were similar to each other but different from degraded sites. Aboveground biomass in restored sites (103 Mg ha−1) was 13 and 99% greater than intact (89.4 Mg ha−1) and degraded (0.12 Mg ha−1) sites, respectively. Active restoration successfully increased seedling abundance of both planted and unplanted species, with similar abundance between intact and restored sites. In contrast, fish communities in restored sites remained similar to degraded sites. Restored sites were dominated by a single algivorous fish species, with lower species diversity and commercially valuable fisheries than intact sites. Our results demonstrate that active restoration is a viable option to restore mangrove forest tree biomass and tree species composition in this region. However, even under a best‐case scenario for mangrove forest restoration, fisheries did not recover during our study's timespan. Long‐term monitoring and controlled experiments will be essential to further understand restoration outcomes for multiple ecosystem services in mangrove forests.

Quad-pol advanced land observing satellite/phased array L-band synthetic aperture radar-2 (ALOS/PALSAR-2) data for modelling secondary forest above-ground biomass in the central Brazilian amazon

ABSTRACT Secondary forests (SFs) are one of the major carbons sinks in the Neotropics due to the rapid carbon assimilation in their above-ground biomass (AGB). However, the accurate contribution of SFs to the carbon cycle is a great challenge because of the uncertainty in AGB estimates. In this context, the main objective of this study is to explore full polarimetric Advanced Land Observing Satellite/Phased Array L-band Synthetic Aperture Radar-2 (ALOS/PALSAR-2) data to model SFs AGB in the Central Amazon. We carried out the forest inventory in 2014, measuring 23 field plots. Supplementary land-use classification history was used to create 120 additional independent sample plots by adjusting growth curves using SFs age and previous land-use intensity from field plots and literature database. Multiple Linear Regression (MLR) analysis was performed to select the best model by corrected weighted Akaike Information Criterion (AICw) and validated by the leave-one-out bootstrapping method. The best-fitted model has six parameters and explained 65% of the above-ground biomass variability. The prediction error was of Root Mean Square Error of the Prediction (RMSEP) = 8.8 ± 3.0 tonnes ha−1 (8.8%). The most explanatory variables for modelling secondary forest AGB were those that result from multiple scattering (Shannon Entropy), volumetric scattering (Bhattacharya decomposition), and double-bounce scattering (ratio VV/HH, vertically transmitted and received polarization/horizontally transmitted and received polarization). Including past-use of SF areas in the model with the Landsat time series classification, as the frequency of clear cuts and the number of years of active land-use before abandonment, the MLR has increased by 10%, achieving 71% of the variability explained by the model. The uncertainty report showed that ground truth AGB estimation (inventory, allometry, and plot expansion factors) might represent 50% of the errors in the modelling estimation. In contrast, Synthetic Aperture Radar (SAR) inversion models (SAR error and regression) have achieved 20%. The results showed that additional information on secondary forest land-use history could improve the performance of AGB recovery models, as well as can be used to expand the sampling units on tropical forests.

Forest restoration methods, seasonality, and penetration resistance does not influence aboveground biomass stock on mining tailings in Mariana, Brazil.

The restoration methods applied on the areas affected by the Fundão tailings dam collapse have a high priority in Mariana region. We evaluated the effect of different restoration methods and site preparation techniques, depth and seasonality on penetration resistance of tailings, and how these predictors affect tree aboveground biomass in areas affected by the Fundão dam collapse in Mariana, Brazil. No significant differences in penetration resistance and aboveground biomass between treatments were observed, but significant differences were observed between seasonal periods. The main univariate model explained the significant effects of depth and seasonality, mainly by a negatively wet effect on penetration resistance. According to the best models (univariate and multivariate) were those that had depth as a predictor. This study showed how penetration resistance can be an indicator to select the best period for restoration process in areas affected by the collapse of the Fundão dam, but no limit to the aboveground biomass recovery on tailing.

Model-Based Estimation of Amazonian Forests Recovery Time after Drought and Fire Events

In recent decades, droughts, deforestation and wildfires have become recurring phenomena that have heavily affected both human activities and natural ecosystems in Amazonia. The time needed for an ecosystem to recover from carbon losses is a crucial metric to evaluate disturbance impacts on forests. However, little is known about the impacts of these disturbances, alone and synergistically, on forest recovery time and the resulting spatiotemporal patterns at the regional scale. In this study, we combined the 3-PG forest growth model, remote sensing and field derived equations, to map the Amazonia-wide (3 km of spatial resolution) impact and recovery time of aboveground biomass (AGB) after drought, fire and a combination of logging and fire. Our results indicate that AGB decreases by 4%, 19% and 46% in forests affected by drought, fire and logging + fire, respectively, with an average AGB recovery time of 27 years for drought, 44 years for burned and 63 years for logged + burned areas and with maximum values reaching 184 years in areas of high fire intensity. Our findings provide two major insights in the spatial and temporal patterns of drought and wildfire in the Amazon: (1) the recovery time of the forests takes longer in the southeastern part of the basin, and, (2) as droughts and wildfires become more frequent—since the intervals between the disturbances are getting shorter than the rate of forest regeneration—the long lasting damage they cause potentially results in a permanent and increasing carbon losses from these fragile ecosystems.

Recovery of aboveground biomass, species richness and composition in tropical secondary forests in SW Costa Rica

Tropical secondary forests comprise about half of the world’s tropical forests and are important as carbon sinks and to conserve biodiversity. Their rate of recovery varies widely; however, particularly older secondary forests are difficult to date so that the recovery rate is uncertain. As a consequence, factors affecting recovery are difficult to analyse. We used aerial surveys going back to 1968 to date 12 secondary forests in the wet tropics of SW Costa Rica and evaluated the recovery of aboveground biomass, tree species richness and tree species composition in relation to nearby old-growth forests and previous land use. To confirm the validity of the space-for-time substitution, the plots were re-censused after four years. We found fast rates of aboveground biomass accumulation, especially in the first years of succession. After 20 years AGB had reached c. 164 Mg/ha equivalent to 52% of the biomass in old-growth forests in the region. Species richness increased at a slower pace and had reached c. 31% of old-growth forests after 20 years. Recovery rates differed substantially among forests, with biomass at least initially recovering faster in forests after clearcuts whereas species numbers increased faster in forests recovering from pastures. Biomass recovery was positively related to the forest cover in the vicinity and negatively to species richness, whereas species richness was related to soil parameters. The change during the four years between the censuses is broadly in line with the initial chronosequence. While the recovery of tropical secondary forests has been studied in many places, our study shows that various environmental parameters affect the speed of recovery, which is important to include in efforts to manage and restore tropical landscapes.

Long-term growth responses of three Flindersia species to different thinning intensities after selective logging of a tropical rainforest

Studies in low-diversity temperate forests clearly establish that thinning leads to increased growth of remaining trees. However, few studies have investigated the long-term impacts of thinning regimes on the growth responses of tropical timber species. In this study, we analysed data collected over a period of 46 years to assess the long-term growth responses and growth patterns of remnant trees of three key commercial species (Flindersia brayleyana F. Muell., Flindersia bourjotiana F. Muell. and Flindersia pimenteliana F. Muell.). We also examined how initial tree size, crown size and crown position within canopy, and neighbourhood competition affected growth rates of the three Flindersia species. Within these species, we assessed growth responses of trees above 10 cm diameter at breast height (DBH) in an Australian tropical rainforest, to different intensities of thinning i.e. logging only as a control and low-, medium- and high-intensity thinning (L, LT, MT and HT, respectively). Medium and high intensity treatments facilitated recruitment of all three Flindersia species into the >10 cm DBH class while medium intensity thinning resulted in the greatest average annual basal area increments (BAIs). The lower individual BAI of Flindersia species in HT was due to fewer large Flindersia trees remaining after thinning, combined with large numbers of recruits and slow growth of small remnant trees. BAI in HT increased initially, with a peak during 1981–1989 and then decreased. BAI was constant and varied little over time within the other treatments. High intensity thinning had prolonged impacts on the growth patterns of Flindersia trees over 46 years. Tree initial DBH, crown size and crown position within canopy explained most variation in individual BAIs of Flindersia trees. Both thinning intensity and measurement periods explained variation in individual BAIs of Flindersia trees. Larger remnant Flindersia trees with broad and dominant crowns tended to grow faster. BAIs of individual trees were negatively correlated with neighbourhood competition. If the goal of tropical native forest management is to improve productivity of target species, the results indicate that thinning should be sufficiently intense to reduce neighbourhood competition while maintaining large diameter commercially desirable trees with large and dominant crowns, which may consequently facilitate the timber volume and above-ground biomass recovery after selective logging.

Above-ground biomass recovery following logging and thinning over 46 years in an Australian tropical forest

Managed tropical forests are a globally important carbon pool, but the effects of logging and thinning intensities on long-term biomass dynamics are poorly known. We investigated the demographic mechanisms of above-ground biomass recovery over 48 years in an Australian tropical forest following four silvicultural treatments: selective logging only as a control and selective logging followed by low-, medium- and high-intensity thinning. Initial biomass recovery rates following thinning were poor predictors of the long-term changes. Initial biomass recovery from 1969 to 1973 was slow and was largely concentrated on an increase in the biomass of residual stems. From 1973 to 1997, above ground biomass (AGB) increased almost linearly, with a similar slope for all sites. From 1997 to 2015, the rate of biomass accumulation slowed, especially for the L treatment. All thinning treatments stimulated more recruitment and regrowth of non-harvested remaining trees compared to the untreated control. Biomass at both the low and medium intensity treatments has almost fully recovered to 98% and 97% of pre-logging biomass levels respectively. The predicted times of complete above-ground biomass recovery for the logging only and high intensity treatments are 55 and 77 years respectively. The slower biomass recovery at the logging only site was largely due to increased mortality in the last measurement period. The slower recovery of the high intensity site was due to a combination of a higher initial reduction in biomass from thinning and the increased mortality in the last measurement period. The high mortality rates in the most recent measurement period are likely due to the impacts of two cyclones that impacted the study site. Our results suggest that it will take at least around 50 years for this site to recover to its pre-harvest biomass, much longer than many of the cutting cycles currently used in tropical forest management.

Forest aboveground biomass stock and resilience in a tropical landscape of Thailand

Abstract. Half of Asian tropical forests were disturbed in the last century resulting in the dominance of secondary forests in Southeast Asia. However, the rate at which biomass accumulates during the recovery process in these forests is poorly understood. We studied a forest landscape located in Khao Yai National Park (Thailand) that experienced strong disturbances in the last century due to clearance by swidden farmers. Combining recent field and airborne laser scanning (ALS) data, we first built a high-resolution aboveground biomass (AGB) map of over 60 km2 of forest landscape. We then used the random forest algorithm and Landsat time series (LTS) data to classify landscape patches as non-forested versus forested on an almost annual basis from 1972 to 2017. The resulting chronosequence was then used in combination with the AGB map to estimate forest carbon recovery rates in secondary forest patches during the first 42 years of succession. The ALS-AGB model predicted AGB with an error of 14 % at 0.5 ha resolution (RMSE=45 Mg ha−1) using the mean top-of-canopy height as a single predictor. The mean AGB over the landscape was 291 Mg ha−1, showing a high level of carbon storage despite past disturbance history. We found that AGB recovery varies non-linearly in the first 42 years of the succession, with an increasing rate of accumulation through time. We predicted a mean AGB recovery rate of 6.9 Mgha-1yr-1, with a mean AGB gain of 143 and 273 Mg ha−1 after 20 and 40 years, respectively. This rate estimate is about 50 % larger than the rate prescribed for young secondary Asian tropical rainforests in the 2019 refinement of the 2006 IPCC guidelines for national greenhouse gas inventories. Our study hence suggests that the new IPCC rates, which were based on limited data from Asian tropical rainforests, strongly underestimate the carbon potential of forest regrowth in tropical Asia. Our recovery estimates are also within the range of those reported for the well-studied Latin American secondary forests under similar climatic conditions. This study illustrates the potential of ALS data not only for scaling up field AGB measurements but also for predicting AGB recovery dynamics when combined with long-term satellite data. It also illustrates that tropical forest landscapes that were disturbed in the past are of utmost importance for the regional carbon budget and thus for implementing international programs such as REDD+.