Young Secondary Forest Research Articles

Diversity and Distribution of Monocot Understory Herbs during Tropical Forest Succession in Northeastern Costa Rica

Broad-leaved monocot herbs form one of the most common and diverse growth forms of Neotropical plants. Their significance and frequency of occurrence is particularly notable in the understories of tropical rainforests, where they form a dominant element. We assessed and quantified changes in the cover and diversity of understory herb communities in a chronosequence of 1 ha permanent plots established as part of a multidisciplinary study on tropical forest regeneration in the Atlantic lowlands of northeastern Costa Rica. Sampled were two young stands cleared 12 years ago, two secondary forests with 21 and 39 of years of recovery since clearance, and two stands in old-growth primary forest. Changes in species composition during succession were assessed using Chao’s Jaccard similarity index. Observed species richness ranged from 15 to 26 species in individual plots, with the greatest number of species in the 21-year intermediate-age and fewest in the young 12-year plots. Herb species sampled represented 6 families, 15 genera, and 39 species, with the Araceae contributing the largest number of species. Ten species were sampled in all six stands, while fourteen species were found exclusively in one plot. Herb density (ramets m−2) showed a hump-shade trend, with peak density in the intermediate stands and a lower level in mature and young secondary forests. Mean herb cover in 25 m2 quadrats ranged from 2.0% (young stand) to 22.7% (intermediate-age stand) and differed significantly both among stand types and among sites. Both observed and estimated species richness increased along the chronosequence as a whole, with the highest number of species in primary forest, although only slightly higher than in intermediate-age stands. Over half of the species exhibited some degree of clonal growth, with the extent of clonal spread varying among species and forest stands. Although we did not find a clear pattern between clonality and forest age, we observed a greater number of clonal patches in secondary over primary forest stands.

Seasonal movements of small-island birds along habitat and elevation gradients highlights the conservation value of small-scale agroforests

Knowledge on species distributions and seasonal movement patterns within landscapes is important for understanding their ecology and roles in agroecosystems, and is critical for enabling their effective conservation and monitoring, particularly in small-island states where conservation resources are limited. We undertook bird surveys to examine species distributions across a range of agricultural land-use intensities and elevations on the Caribbean island of Grenada by collecting data over 6 repeated monthly surveys (3 wet season, 3 dry season) at sites located in a variety of habitats spread over 6–300 m elevation. We observed a gradual upslope increase in bird species diversity and abundance from the mid-wet season to the late-dry season, as well as a movement from reduced-canopy habitats to closed-canopy habitats in the dry season. The mid-elevation hillsides of Grenada consist of a diverse mosaic of closed canopy secondary forest patches, interspersed among more open agroforests and small-scale cropping and grazed areas. These agroecosystems appear to provide important habitats to birds throughout the year, especially open canopy agroforests in the wet season. We also found that open mixed agroforests contained a greater diversity of fruit, flower, and seed resources than closed canopy habitats such as secondary forest, cacao agroforests, young secondary forests, or dry forest scrub; and that plant food diversity was highest in the wet season. However, bird abundance significantly increased in closed canopy forest habitats during the dry season, suggesting that intact canopy forests provide important dry season habitat for many Grenadian birds, which may be particularly important for species in drier lowland areas experiencing more intensive agricultural land use and urban and resort development. Overall, this research demonstrates the importance of maintaining the functional connectivity of treed habitats at local and landscape scales for species conservation, as well as the contribution of diverse, small-scale agriculture to maintaining small-island bird communities.

Trophic position determines the persistence of neotropical understory birds after forest disturbance.

Habitat loss and degradation are key drivers of the current biodiversity crisis. Most research focuses on the question of which traits allow species to persist in degraded habitats. We asked whether a species' trophic position or niche width influences the resilience of species in degraded habitats and to what extent habitat degradation affects trophic interactions between species. We used nitrogen isotope ratios (15N:14N, expressed as δ15N value) to quantify and compare trophic positions and niche widths of understory birds inhabiting old-growth and young secondary forests in the Pacific lowlands of Costa Rica. We found that a species' trophic position rather than its trophic niche width determined its persistence in secondary forests. Species feeding at lower trophic levels in old-growth forests were less likely to persist in secondary forests than those occupying a higher trophic position in old-growth forests. This pattern is likely induced by the occurrence of relatively large-bodied habitat specialists with a flexible and high-trophic level diet in secondary forests. These habitat specialists likely caused generalist bird species to lower their trophic position relative to conspecifics in old-growth forests. Regarding trophic niche widths, species in secondary forests tend to have larger niche widths than old-growth forest species. However, as old-growth forest specialists and generalists did not differ in their niche widths, no systematic effect of trophic niche width on species persistence after forest disturbance was found. This is the first study that shows a systematic effect of trophic position on the persistence of a wide range of bird species in a disturbed forest ecosystem. It therefore provides important insights into species' responses to habitat degradation and the conservation value of secondary forests. To improve habitat quality for old-growth forest birds and facilitate avian seed dispersal, the creation of large contiguous forest patches should be prioritised when implementing reforestation measures.

Compositional changes at neighborhood and stand scales during recovery of a tropical lowland rainforest after shifting cultivation on Hainan Island, China

Understanding compositional changes during secondary forest recovery is crucial for effective restoration efforts. While previous research has predominantly focused on shifts in species composition at the stand scale, this study delves into the recovery dynamics in three compositional aspects of location (neighbor distances), size (tree diameters), and species (tree species) at both stand and neighborhood scale. The investigation spans nine chronosequence plots within a tropical lowland rainforest ecosystem after shifting cultivation, including three each for young-secondary forests (18–30 years), old-secondary forests (60 years), and old-growth forests (without obvious human interference). The quantification of location, size, and species composition involved categorized neighbor distances (Near, Moderate, Far-distance), tree diameters (Small, Medium, Large-tree), and tree species (Pioneer, Intermediate, Climax-species) into three groups, respectively. Compositional changes at the stand scale (plot) were directly based on these groups, while at the neighborhood scale, assessment involved combination types of these groups within a neighborhood (comprising three adjacent trees). At the stand scale, neighbor distances shifted from Near to Moderate and Far, tree diameters transitioned from Small to Medium and Large, and tree species of Pioneer gave way to Climax. Meanwhile, at the neighborhood scale, there was a notable decline in the aggregations of Near-distance (N), Small-tree (S), and Pioneer-species (P), while the mixtures of Far and Moderate-distance (F-M), Large and Small-tree (L-S), and Climax and Intermediate-species (C–I) experienced a marked increase. The compositional change exhibited a recovery pattern, with the fastest recovery in neighbor distances, followed by tree diameters and tree species. Moreover, compositional recovery in tree diameters and tree species at the neighborhood scale generally lagged behind that at the stand scale. The study suggests that rapid restoration of secondary forest can be achieved by different targeted cutting according to the recovery stages, aimed at reduce the Pioneer-species, Small-tree and Near-distance in neighborhood. Our findings underscore that analyzing the compositional changes in three aspects at two scales not only provides a profound understanding of secondary forest recovery dynamics, but also offers valuable insights for guiding practices in the restoration of degraded forest ecosystems.

Elevated litterfall phosphorus reduces litter and soil organic matter pools in exotic-dominated novel forests in Singapore

Abstract The estimation of leaf litter turnover is often limited to early-stage decomposition using unrepresentative models and litter types. In tropical secondary forests, particularly exotic-dominated novel forests, the characterisation of litter turnover remains poor. This study estimated the annual turnover of in-situ leaf litter across four forest successional types in Singapore using a Weibull residence time model. Litter turnover and nutrient dynamics diverged between young secondary and old-growth forests. In particular, within novel forests, annual phosphorus return via leaf litterfall was three times that of primary forests, while the mass loss of in-situ leaf litter was highest among all forest successional types, estimated at 92.8% annually with a mean residence time of 176 days, resulting in a litter pool size a third that of primary forests. Our findings suggest that tree species composition and species-specific effects shaped the observed variations in litter turnover and nutrient dynamics across forest successional types and forest stands, whereas tree species richness, canopy structure, soil nutrient levels, and microclimate were found to be non-predictors. Taken together, our study provides an insight into litter turnover in human-modified tropical landscapes increasingly characterised by novel forests, potentially leading to a reduction in surface litter and soil organic carbon pools.

Isopod mouthpart traits respond to a tropical forest recovery gradient.

Functional trait ecology has the potential to provide generalizable and mechanistic predictions of ecosystem function from data of species distributions and traits. The traits that are selected should both respond to environmental factors and influence ecosystem functioning. Invertebrate mouthpart traits fulfill these criteria, but are seldom collected, lack standardized measurement protocols, and have infrequently been investigated in response to environmental factors. We surveyed isopod species that consume plant detritus, and tree communities in 58 plots across primary and secondary forests in Singapore. We measured body dimensions (body size traits), pereopod and antennae lengths (locomotory traits), dimensions of mandible structures (morphological mouthpart traits), and mechanical advantages generated by mandible shape (mechanical mouthpart traits) for six isopod species found in these plots and investigated if these traits respond to changes in tree community composition, tree diversity, and forest structure. Morphological mouthpart traits responded to a tree compositional gradient reflecting forest recovery degree. Mouthpart features associated with greater consumption of litter (broader but less serrated/rugose lacinia mobilis [an important cutting and chewing structure on the mandible]) were most prevalent in abandoned plantation and young secondary forests containing disturbance-associated tree species. Feeding strategies associated with fungi grazing (narrower and more serrated/rugose lacinia mobilis) were most prevalent in late secondary forests containing later successional tree species. Since morphological mouthpart traits likely also predict consumption and excretion rates of isopods, these traits advance our understanding of environment-trait-ecosystem functioning relationships across contrasting tropical forest plots that vary in composition, disturbance history, and post-disturbance recovery.

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.

Impacts of land use history on leaf litter input, chemical composition, decomposition and related nutrient cycling in young and old secondary tropical lowland rainforests (Sumatra, Indonesia)

BackgroundNutrient cycle in tropical forests is mainly driven by litter fall amounts and by litter decay due to litter physical and chemical properties. Apart from differences in site conditions, different successional stages of tropical rainforests may influence nutrient inputs to the soil via differences in litter fall and decay.MethodsWe studied leaf litter fall, decomposition and related nutrient input to the soil in two secondary tropical rainforest types differing in land-use intensity and history in the lowlands of Sumatra (Indonesia).ResultsMean annual litter fall was by 29.5% higher in the old than in the young secondary forests. In contrast, annual litter decomposition differed only marginally (54.9% vs. 52.1%) in young vs. old secondary forests. Litter chemical composition (C, N, P, K contents) did not differ between the forest types. Litter decomposition was also not different between the forest types (4.6% vs. 4.3% loss of initial weight per month). Consequently, annual nutrient input to the soil was primarily affected by differences in leaf litter production, thus, old secondary forests exceeded that of young secondary forests by 30% and 24% for C and N, but was not different regaring P and K among the two forest types.ConclusionsThe results indicate that litter nutrient inputs to the soil in the two types of secondary tropical lowland forests are most strongly influenced by aboveground litter production rather than litter chemical quality or litter decay. We conclude that the restoration status of secondary tropical lowland forests is crucial for the nutrient status of these forest ecosystems.

Caracterización de poblaciones de especies endémicas en bosque tropical seco semideciduo. Parque Nacional Machalilla, Manabí, Ecuador

ABSTRACT Seasonally dry tropical forests are ecosystems of high endemism and floristic diversity, but they have been relatively not well-studied ecosystems and are very much threatened by anthropic pressures. This study aimed to evaluate the dendrometric and horizontal structure characteristics of the population of 12 endemic plant species in the semideciduous forest of the Equatorial Pacific Coastal Cordillera of the Machalilla National Park, Manabí, Ecuador. This is one of the most extensive protected areas on the Ecuadorian coast, located in the Tumbes-Chocó-Magdalena biogeographic region. It is considered one of the 25 hotspots worldwide. We selected 12 species that hypothetically co-exist in this semideciduous forest (Bursera graveolens, Eriotheca ruizii, Handroanthus chrysanthus, Ziziphus thyrsiflora, Geoffroea spinosa, Myroxylon balsamum, Priogymnanthus apertus, Melicoccus bijugatus, Nectandra reticulata, Simira ecuadorensis, Coccoloba ruiziana, Klarobelia lucida). We studied five 2500 m2 transects, where dendrometric variables (tree height, diameter at breast height-DBH, basal area, altimetric and diameter classes) were evaluated. We evaluated the horizontal structure variables of populations like absolute/relative abundance, dominance and frequency, and the importance value index (IVI and IVN). In 12,500 m2, the results identified 331 individuals. M. balsamum was the highest species (9.41 m), while E. ruizii had the highest DBH (21.03 cm) and the biggest basal area (0.05 m2). The species with the highest absolute/relative abundance and frequency were S. ecuadorensis and H. chrysanthus, and the latter had the highest absolute dominance (1.23 m2•ha−1). S. ecuadorensis presented the highest importance value index based on 100 and 300, followed by H. chrysanthus and Z. thyrsiflora. P. apertus, M. balsamum, E. ruizii and C. ruiziana obtained intermediate values. The least ecological weight was for N. reticulata, K. lucida, M. bijugatus and G. spinosa. No B. graveolens individuals were observed in the studied transects in this forest because this species was found at altitudes < 240 m a.s.l. The results of the altimetric and diameter classes indicated that the studied sector corresponds to a relatively young secondary forest affected by natural and anthropic factors.

Shifting cultivation and logging change soil organic carbon functional groups in tropical lowland rainforests on Hainan Island in China

Recent evidence has demonstrated that tropical forest secondary succession has significant influences on soil organic C (SOC) storage. However, the changes in the SOC functional groups with forest restoration are still uncertain. In this study, the stock and functional groups of SOC in tropical forest recovery after two types of disturbance were measured, and the key influencing factors were analyzed. The SOC stocks were significantly higher in the young-secondary forests after shifting cultivation and in the clear cut forests than in the old-growth forests. However, the shifting cultivation and logging practices significantly increased the ratio of carbohydrate C to N-alkyl/methoxyl C (CC/MC), indicating that the decomposition degree of SOC in the old-growth forests was higher. The proportion of aromatic C in soil was higher in the young-secondary forests after shifting cultivation than in the old-growth forests. The proportion of aromatic C in litter and fine roots, the α-diversity of soil fungal and bacterial communities, and soil phosphorus were positively correlated with soil aromatic C between the shifting cultivation secondary and old-growth forests. The proportion of O-alkyl C in soil was higher in the logged forests than in the old-growth forests. The proportion of O-alkyl C in litter was positively correlated with O-alkyl C in soil between the logged and old-growth forests. Our results suggest that the labile O-alkyl C functional group recovers more rapidly after logging practices, and restoration after shifting cultivation increases the labile carbohydrate C functional group and aromaticity in tropical lowland rainforests. However, SOC has greater chemical stability in terms of the decomposition degree in tropical old-growth forests.

Tree-ring data reveal trees are suffering from severe drought stress in the humid subtropical forest

The young secondary forests in subtropical regions of China play an important role in the global carbon cycle and China’s ecological and economic security. These values are closely related to tree radial growth (RW), primarily affected by climate changes, especially climate warming. Here, we measured the RW of six common tree species in subtropical China (Cunninghamia lanceolata, Pinus massoniana, Metasequoia glyptostroboides, Liquidambar formosana, Choerospondias axillaris, and Lithocarpus glaber) and quantified how each responded to climate warming. Temperature and moisture were the main climate factors limiting the growth of tree species in the study area. The growth of tree species other than L. formosana and P. massoniana was negatively correlated with temperature and positively correlated with relative humidity. Precipitation in the growing season was negatively correlated with the growth of L. formosana and M. glyptostroboides and positively affected the growth of the other tree species. The radial growth trends of trees growing in similar terrain and climate conditions were similar, but their degree of variation was different. Compared to broad-leaved tree species (L. formosana, C. axillaris, and L. glaber), coniferous tree species (C. lanceolata, P. massoniana, and M. glyptostroboides) were more climate-sensitive, particularly C. lanceolata. Climate warming can potentially extend the growing period and promote the radial growth of the study tree species, but more often leads to drought stress that inhibits radial growth. The long-term drought during 2004–2015 significantly reduced the radial growth of most species, especially conifers which are more vulnerable to drought than broad-leaved trees. Our results highlight that most tree species in the humid subtropical forest in South China are suffering from severe drought stress, which significantly affects forest carbon sequestration. It is probably a good warning for current plantation policy and species selection to better achieving the “Carbon Peaking & Carbon Neutrality” goals of the Chinese government.

Assessing the recovery in species, size and location diversities of a lowland tropical rainforest after shifting cultivation by multiple indices at stand and neighborhood scales

Tropical forests are rapidly being converted for agricultural use, but abandoned agricultural lands can recover naturally through secondary succession. However, comprehensive knowledges of how species composition, size structure and spatial patterning (represented by species, size and location diversities) change during recovery at multiple scales are still lacking. Our aim was to explore these change patterns to understand the underlying mechanisms of forest recovery and propose corresponding solutions for restoring regrowing secondary forests. Here, twelve 1ha forest dynamics plots (4 plots each in young-secondary forests (YS), old-secondary forests (OS) and old-growth forests (OG) from a chronosequence of tropical lowland rainforest after shifting cultivation) were used to assessed the recovery in species, size and location diversity of trees at stand (plot) and neighborhood (focal tree and its neighbors) scale by using 8 indices. The relative recoveries of YS and OS were quantified by dividing each of the indices in YS and OS to those in OG. Results showed that species and size diversity increased while location diversity decreased with the recovery process. The relative recovery of location diversity was higher than those of species and size diversity in both YS and OS, while species diversity was only higher than size diversity in YS. The relative recovery of species diversity at neighborhood scale was higher than that at stand scale in OS, while there were no differences between scales in size and location diversity. Additionally, using only the Shannon index and Gini coefficient at two scales can provide consistent insights into the recovery patterns of diversity as indicated by the 8 indices. Our study demonstrated that recovery rates of secondary forests relative to old-growth counterparts could be comprehensively quantified using multiple diversity indices in three types at two scales. This quantitative assessment on the relative recovery of disturbed forests could be helpful in applying appropriate management activities and selecting rational approaches to speed up restoration process of degraded forest ecosystems.

Spatial Distribution of Secondary Forests by Age Group and Biomass Accumulation in the Brazilian Amazon

Secondary forests provide essential ecosystem services, especially in helping to mitigate climate change with the storage of carbon in the aboveground biomass of tree species. In this context, the present research aimed to analyze the spatial distribution of secondary forests and estimate the aboveground biomass accumulation of land cover of different ages in the state of Pará. The spatial patterns of the secondary forests in Pará state were evaluated with hot spot analysis algorithms using data from the TerraClass project for the 2004–2014 time period. The results showed that the spatial distribution of the secondary forests did not occur randomly in space, but suggested local geopolitical influences. The younger secondary forests had the most deforested areas during the study period. Approximately 5% of Pará had its secondary forests deforested in 2014. In general, the balance of the secondary forests was positive. The aboveground biomass accumulation differed according to the secondary forest ages during the study period as evaluated in two pilot areas. It was observed that the secondary forests &gt; 10 years old in pilot area A had an average of 23% of old-growth forest aboveground biomass in the same area, while in pilot area B, the secondary forests &gt; 10 years old had an average of 32.7% of old-growth forest aboveground biomass.

A simulation model of functional habitat connectivity demonstrates the importance of species establishment in older forests

Fragmented natural habitats, such as old-growth forests, have been often considered island-like systems. However, whereas the isolation of real islands is mostly a function of their spatial arrangement, the biodiversity of old-growth forest patches is also affected by how well the surrounding suboptimal habitats, such as younger forests, can support the functional connectivity between the old-forest fragments. The latter topic remains largely unclear due to the lack of mechanistic knowledge about the processes behind species’ affinity for old forest. Although in animal ecology, functional connectivity has often been investigated with mechanistic agent-based models, these have rarely been applied for passively dispersing organism groups. We used a pattern-oriented modeling approach by combining a spatially explicit agent-based model and an empirical biodiversity dataset of Estonian old-growth nemoral forest sites, to study how forests of different ages between the old-forest fragments are exploited by different passively or slowly dispersing functional groups. We found that the establishment of ground layer vegetation, epiphytes, ectomycorrhizal and pathogenic fungi is significantly restricted in the younger forests, whereas no clear difference between forest-age classes emerged for survival. Our results thus suggest that establishment, not survival, is the main process behind the species’ affinity for old forest, concurring with studies that have demonstrated the importance of suitable microhabitat availability in older forests. We conclude that young secondary forests do not support the connectivity – and consequently, biodiversity – of many old-forest specific groups.

Occupancy and abundance of a West African mangabey species (Cercocebus atysAudebert, 1797) in forest patch habitat

AbstractSooty mangabeys are Old World primates from the Upper Guinea Rainforests of West Africa. They suffer from habitat degradation due to deforestation and hunting for the bush‐meat trade. Tiwai Island and adjacent small islands are a small protected area surrounded by the Moa River that is known for its high diversity of primate species. We evaluated the occupancy and abundance of sooty mangabeys on Tiwai Island and the surrounding islands using camera traps during 2008–2011. Over two seasons, we obtained a naïve occupancy rate of 0.77 for Tiwai Island but only 0.19 for surrounding smaller islands. We used Abundance‐Induced Heterogeneity Model and Royle Repeated Count Model to estimate the abundance of 326 ± 92 (SE) and 530 ± 102 (SE) individuals of sooty mangabeys respectively. Based on these occurrences, sooty mangabeys usually appeared in riparian, mature and young secondary forests. Activity patterns of sooty mangabeys based on circadian patterns of detections confirmed that they were diurnal with several activity peaks during the daylight hours. The results of this study suggest that a viable population of sooty mangabeys still inhabits Tiwai Island and its vicinity, but that their core population is primarily limited to the Tiwai Island reserve. Thus, there is a need to protect the island and its adjacent habitats to ensure the conservation of sooty mangabeys in particular and other primate species in general.

Forest conversion adversely affects native Macrobrachium shrimp assemblages in tropical Malaysian streams

Abstract Commodity‐driven forest conversion represents one of the most severe threats to freshwater biodiversity in Southeast Asia, notably causing population declines and the extinction of freshwater fish species. Although a variety of freshwater taxa are likely to be adversely affected by forest conversion, little is known about the impact on ecologically and economically important invertebrates such as decapod crustaceans. This study evaluated the impact of forest conversion and land‐use change on freshwater Macrobrachium shrimp species, using species richness, abundance, and environmental data collected from 20 streams across southern Peninsular Malaysia. Streams were located in three types of landscape: forest; oil palm plantation; and mixed land use, comprising young secondary forest, small‐scale plantations, patches of open and sparsely vegetated areas, and agricultural fields and clearings. Generalized linear models showed that even incomplete change from forest habitats to mixed land use and oil palm plantation resulted in significantly lower Macrobrachium native species richness and higher non‐native species abundance. Native species richness was positively correlated with canopy cover, leaf litter, substrate size, and dissolved oxygen, and was negatively correlated with water temperature and conductivity. Native species richness was also negatively correlated with non‐native species abundance, with non‐native species abundance increasing along the human disturbance gradient. These results highlight the need for riparian habitat protection to conserve native Macrobrachium and limit the spread of non‐native species. A management priority should be to maintain or restore optimum instream habitat conditions for shrimps, which would also benefit fish and other benthic macroinvertebrates. Suitable riparian management requires substantial support and funding from multiple stakeholders, but it can be aligned with other catchment‐based strategies to optimize the use of limited resources available for freshwater biodiversity conservation.

Vapour pressure deficit and solar radiation are the major drivers of transpiration in montane tropical secondary forests in eastern Madagascar

Young secondary tropical forests occupy a larger area than mature forests nowadays but our understanding of their ecohydrological functioning, particularly with respect to tree water uptake, remains poor. Deep soil water uptake may make mature forests resilient to periods of water stress, but little is known in this regard for young forests with possibly less extensive root networks. We, therefore, studied sap flow dynamics for one year in two 50 m x 50 m forest plots: a young secondary forest (YSF, 5–7 years) and a semi-mature forest (SMF; 20 years) in montane eastern Madagascar. Temporal variations in the depth of water uptake were inferred from the stable isotope compositions of soil- and xylem water. Transpiration rates were low for both forest sites (265 and 462 mm y−1 for the YSF and SMF, respectively). Vapour pressure deficit and global radiation explained most of the variation in transpiration rates at both sites. There was little evidence of transpiration limitation by soil water, despite an extended dry season. Trees in the YSF extracted water mostly from the intermediate soil depth (30–70 cm) during the dry season. In the SMF, the depth of uptake increased as the dry season progressed for some species (Abrahamia, Brachylaena and Cryptocaria), but not for others (Ocotea and Eugenia). Although the transpiration rates are low for both forests, they are comparable to results reported for other tropical montane sites after normalising for net energy input and leaf area. Estimated evapotranspiration totals (including interception loss, understorey and litter evaporation) were 679 mm and 1063 mm y−1 for the YSF and SMF, respectively (42% and 61% of precipitation, respectively). These results suggest that the stage of forest regrowth affects water uptake, and thus the water balance during forest succession.

Size‐dependent intraspecific variation in wood traits has little impact on aboveground carbon estimates in a tropical forest landscape

Abstract There is increasing evidence that intraspecific trait variation plays a role in governing rates of ecosystem functioning. While wood traits such as wood specific gravity (WSG) and wood carbon concentration (WCC) are key drivers of forest aboveground carbon (AGC) stocks, the sources of intraspecific variation in these wood traits and the consequences of this variation on AGC are poorly known, especially in the tropics. Here, we investigated intraspecific variation in wood specific gravity (WSG) and wood carbon concentration (WCC) from 556 individual trees belonging to 15 species that well characterize different successional stages of seasonal evergreen forests in Southeast Asia. Specifically, we tested the contribution of individual or species characteristics (tree size, growth rate and regeneration guilds) and local environmental conditions (topographic wetness index and successional stages) to intraspecific variation in WSG and WCC, and assessed the consequences of intraspecific variation in these wood traits on AGC estimates in 14 permanent forest plots established along a successional gradient in Khao Yai National park, Thailand. We found that tree size was the main driver of intraspecific variation in WSG and WCC as tree sizes increased from 10–100 cm in diameter, WSG increased by 7.3%, while WCC increased by 2.4% in heartwood, 1.6% and 2.7% in sapwood without and with volatile carbon included. There was no effect of the topographic wetness and other local environment condition in wood traits led to a slight overestimation of AGC in young secondary forests (+0.09% to +1.29%) and a small underestimation in older forests (−0.86% to −2.87%), but overall AGC estimates (13 of 14 forest plots) remained within error margins (the 95% interval). Our study provides evidence that tree size variation translates into intraspecific variability in wood traits, whereas local environmental conditions related to topography successional stages had no effect on wood trait variability. While size‐dependent variation in WSG and WCC have largely been undocumented and thus ignored in forest carbon assessment approaches, we highlight that it has a limited impact on AGC estimates, indicating that it does not invalidate current forest carbon stock estimation approaches. Read the free Plain Language Summary for this article on the Journal blog.

Conservative N cycling despite high atmospheric deposition in early successional African tropical lowland forests

BackgroundAcross the tropics, the share of secondary versus primary forests is strongly increasing. The high rate of biomass accumulation during this secondary succession relies on the availability of essential nutrients, such as nitrogen (N). Nitrogen primarily limits many young secondary forests in the tropics. However, recent studies have shown that forests of the Congo basin are subject to high inputs of atmospheric N deposition, potentially alleviating this N limitation in early succession.MethodsTo address this hypothesis, we assessed the N status along a successional gradient of secondary forests in the Congo basin. In a set-up of 18 plots implemented along six successional stages, we quantified year-round N deposition, N leaching, N2O emission and the N flux of litterfall and fine root assimilation. Additionally, we determined the N content and C:N stoichiometry for canopy leaves, fine roots, and litter, as well as δ15N of canopy leaves.ResultsWe confirmed that these forests receive high amounts of atmospheric N deposition, with an increasing deposition as forest succession proceeds. Additionally, we noted lower C:N ratios, and higher N leaching losses, N2O emission, and foliar δ15N in older secondary forest (60 years). In contrast, higher foliar, litter and root C:N ratios, and lower foliar δ15N, N leaching, and N2O emission in young (< 20 years) secondary forest were observed.ConclusionsAltogether, we show that despite high N deposition, this early forest succession still shows conservative N cycling characteristics, which are likely indicating N limitation early on in secondary forest succession. As secondary succession advances, the N cycle gradually becomes more open.

Changes in taxonomic and functional diversity of dung beetles along a forest disturbance gradient in tropical karst ecosystems on islands of Vietnam

AbstractTropical karst ecosystems are an exceptionally unique and important landscape element of South East (SE) Asia. Unfortunately, these ecosystems have been increasingly disturbed due to forest conversions to anthropogenic land uses, illegal logging, and limestone quarrying. Karst regions have a high degree of endemic species, so their loss is likely to have negative consequences for species conservation as well as ecological processes. We investigated dung‐beetle communities from primary forests (PF), old secondary forests (&gt;15 years since abandonment, OSF), young secondary forests (&lt;10 years since abandonment, YSF), and Acacia plantations (&lt;10 years old, AP) of karst ecosystems on Cat Ba Island (northern Vietnam). Our main aim was to provide a thorough and quantitative assessment of the taxonomic and functional diversity of dung beetles in the examined forests, and subsequently to determine the value of specific types of disturbed forests for biodiversity conservation. In total, 1458 dung beetles of 34 taxa were recorded. Community composition varied significantly among the forest types and was broadly separated into two groups: old‐growth forests (i.e., PF and OSF) and young‐growth forests (i.e., YSF and AP). While YSF and AP hosted severely impoverished dung‐beetle communities, OSF with a high forest canopy cover and high ground vegetation cover harbored species‐rich dung‐beetle communities similar to those found in PF. However, functional diversity significantly differed between PF and OSF. The data also revealed that community responses were due to changing patterns of trait compositions rather than species richness.