Tropical Secondary Forests Research Articles

Carbon removals from nature restoration are no substitute for steep emission reductions

Carbon removals from nature restoration are no substitute for steep emission reductions

Fast-growing native tree species to the secondary forest of East Kalimantan, Indonesia: Physicochemical properties of woody materials for bioelectricity feedstocks

Abstract. Yuliansyah. Haqiqi MT, Setiawan KA, Setiawan A, Saputra PD, Romadlon HSI, Mukhdlor A, Ramadhan R, Amirta R. 2022. Fast-growing native tree species to the secondary forest of East Kalimantan, Indonesia: Physicochemical properties of woody materials for bioelectricity feedstocks. Biodiversitas 23: 3379-3386. The conversion of woody biomass into electricity through a thermochemical process has recently attracted significant attention worldwide to promote green energy production. It provides a low-cost and straightforward operation promising for developing rural areas, especially with limited transportation access. In East Kalimantan Province, almost all remote areas are surrounded by forests with high tree species diversity, which is the potential to be utilized for sustainable feedstocks in electric power plants. This study pointed out the energy potential produced from woody biomass of selected fast-growing tree species native to East Kalimantan secondary tropical forest: Elaeocarpus ferrugineus (Jacq.) Steud., Ficus aurata (Miq.) Miq., Fordia splendidissima (Blume ex Miq.) Buijsen, Lindera lucida (Blume) Boerl., Mallotus paniculatus (Lam.) Mull. Arg. and Schima wallichii (DC). Their wood physicochemical properties were firstly investigated. Furthermore, each species' wood quality for solid energy purposes was presented as the fuel value index (FVI). The results revealed that the change from greenwood into wood chip effectively removed the moisture content, thus improving efficiency to achieve higher energy potency. Our findings showed that the highest energy potency was obtained from the wood chip of F. splendidissima (3.61 MWh/ton), followed by S. wallichii (2.98 MWh/ton). A similar pattern was also found in FVI determination showing that the wood chip of S. Splendidissima had the greatest value (8970). Therefore, we observed that the high quality of S. splendidissima compared to other selected fast-growing species indicates its high suitability for further large-scale crop plantation to supply wood chips for biomass-based electricity generation.

Impacts of invasive tree species Bellucia pentamera on plant diversity, microclimate and soil of secondary tropical forest in West Sumatra, Indonesia

Abstract. Solfiyeni, Syamsuardi, Chairul, Mukhtar E. 2022. Impacts of invasive tree species Bellucia pentamera on plant diversity, microclimate and soil of secondary tropical forest in West Sumatra, Indonesia. Biodiversitas 23: 3135-3146. The invasion of alien species in a region can alter species diversity. Bellucia pentamera Naudin is considered an alien invasive plant that has spread from Mexico to tropical America, and it is now invading some areas in Indonesia, including the tropical forest of Sumatra. Yet, the effects of its invasion on vegetation and the abiotic environment are not yet well understood. The objective of this study was to investigate the impacts of B. pentamera on species diversity and structure of vegetation, and microclimate and soil conditions of secondary tropical forests in West Sumatra. Vegetation analysis was conducted in secondary forest Bukit Tengah Pulau, South Solok, with three levels of dominance of B. pentamera namely: site 1 and 2 (60% and 16% dominance of B. pentamera respectively) and site 3 (no individual of B. pentamera). Sampling was conducted using a nested plot to collect data for tree, sapling and understorey vegetation for each site. The results showed the total number of tree species at sites 1, 2, and 3 were 23 species, 46 species, and 74 species respectively. For sapling, 20 species were found at site 1, 31 species at site 2, and 58 species at site 3. For understorey plants, 13, 16 and 36 species were detected at site 1, 2 and 3 respectively. The number of species at tree and sapling levels differed significantly among sites. The basal area also differed significantly among sites but not for sapling level. Site 1 was dominated by B. pentamera with Important Value Index (IVI) 130.8%), followed by Croton argyratus (27.63%), and Ficus variegata (26.47%). At site 2, B. pentamera dominated with IVI of 33.68%, followed by Lepisanthes sp. (20.01%) and Sizygium sp. (14.44%). Site 3 was dominated by Palaquium warsurifolium with IVI of 21.15% followed by Croton argyratus (20.02%) and Macaranga hypoleuca (13.21%). Diversity index (H') for tree-level was moderate at site 1 (H' = 1.78) and high at sites 2 and 3 (H' = 3.48 and 4.05). Similarly, the index for sapling was moderate at site 1 (H'= 2.12) and high at sites 2 and 3 (H'= 3.22 and 3.84). For understorey, the diversity index was low at site 1 (H'= 0.82) and moderate at sites 2 and 3 (H'= 1.8 and 2.86). Sites invaded by B. pentamera had a lower soil water content and higher temperature and light intensity, although they had higher nitrogen and phosphorus contents. Our findings suggest that the invasion of B. pentamera had negative impacts on plant biodiversity and microclimate, yet the impact was not clear cut on the soil.

Delayed wet season increases soil net N mineralization in a seasonally dry tropical forest

Seasonal precipitation regime plays a vital role in regulating nutrient dynamics in seasonally dry tropical forests. Present evidence suggests that not only wet season precipitation is increasing in the tropics of South China, but also that the wet season is occurring later. However, it is unclear how nutrient dynamics will respond to the projected precipitation regime changes. We assessed the impacts of altered seasonal precipitation on soil net N mineralization in a secondary tropical forest. Since 2013, by reducing throughfall and/or irrigating experimental plots, we delayed the wet season by two months from April–September to June–November (DW treatment) or increased annual precipitation by 25% in July and August (WW treatment). We measured soil net N mineralization rates and assessed soil microbial communities in January, April, August and November in 2015 and 2017. We found that a wetter wet season did not significantly affect soil microbes or net N mineralization rates, even in the mid-wet season (August) when soil water content in the WW treatment increased significantly. By contrast, a delayed wet season enhanced soil microbial biomass and altered microbial community structure, resulting in a two-fold increase in net N mineralization rates relative to controls in the early dry season (November). Structural equation modeling showed that the changes in net N mineralization during the early dry season were associated with altered soil microbial communities, dissolved organic N, and litterfall, which were all affected by enhanced soil water content. Our findings suggest that a delayed wet season could have a greater impact on N dynamics than increased precipitation during the wet season. Changes in the seasonal timing of rainfall might therefore influence the functioning of seasonally dry tropical forests.

Relationship Between Growth Trajectories and Functional Traits for Woody Trees in a Secondary Tropical Forest

Absolute growth rates change with tree size and age, shifting throughout species ontogeny. The study on interspecific variation in plant traits has generated important insights into the life-history strategies and their consequences for ecosystem functioning. However, it remains unknown to what extent – and even if – species’ functional traits are related to the variation in their growth trajectories. We set out to model growth trajectories of 45 woody species from the Brazilian Atlantic Forest in a secondary subtropical forest under regeneration, aiming to understand if species can be grouped by their growth patterns throughout ontogeny and if these groups could be classified in distinct ecological strategies based on key plant traits. We used a maximum likelihood estimation approach to predict growth trajectories using three ecologically relevant parameters [maximum growth rate (Gmax), diameter at maximum growth rate (Dopt), and the ontogenetic variability in growth rate (K)] followed by multivariate analyses to detect associations among phylogenetic relationships, plant traits, and growth parameters and classify species into growth pattern groups. Across species, growth trajectory parameters varied widely. The cluster analysis identified three distinct groups based on growth trajectories parameters, which were not functionally or ecologically well defined. Our findings supports the idea that traits describing plant size and tree shape, such as maximum height, canopy volume and height to diameter ratio, were generally the best predictors of species growth parameters throughout ontogeny, even though traits representing resource-use and reproductive strategies also played a significant role. Growth-trait framework can be understood as a continuum of multi-trait combinations where, at one end of the gradient, we find trees with higher growth rate and larger diameters supporting a voluminous canopy combined with lower investment in leaf tissue and smaller diaspore; at the other end, taller trees supporting a smaller canopy with higher investment in leaf tissue and longer diaspore. Ultimately, we have shown that tree architecture, leaf and reproductive traits significantly influence growth trajectory along tree ontogeny, which may be the reason why objectively grouping species based on growth-trajectories parameters is ineffective, at least in highly diverse secondary subtropical forests undergoing regeneration.

A ten-year record reveals the importance of tree species’ habitat specialization in driving successional trajectories on Hainan Island, China

Tropical secondary forests play an increasing role in biodiversity conservation and climate change mitigation, but the underlying mechanisms driving the successional trajectory to old-growth forests are still not fully characterized. Species with different dispersal abilities or habitat preferences affect the compositional similarity of secondary forests to old-growth forests. We studied the dynamics of forest succession in twelve 1-ha plots of tropical secondary forests on Hainan Island, China, using ten years of census data (2010–2020). We compared the variations in demographic rates and community composition among three successional stages, with four plots each in young secondary forest (YS), old secondary forest (OS), and old-growth forest (OG). The effects of five species groups (generalists, rare species, and specialists in each of the three successional stages) on successional trajectory were explored using sensitivity analysis. Species richness in the OS only reached 65% of OG after 60 years of succession. The diameter growth, mortality, and recruitment rates were the highest in the YS and the lowest at the OG. Growth decreased and recruitment increased during the second census period (2015–2020) during which there were two extended droughts, but there was no significant change in mortality rate. The successional trajectories of YS and OS showed a slow but directional trend towards the OG, with a weak stochastic component. The five species groups made different contributions to the successional trajectory. Generalists contributed to the convergence of secondary forests to old-growth forests, while old-growth specialists contributed to divergence. Secondary species usually contributed to divergence with old-growth forest, and young-secondary specialists had a stronger effect than old-secondary specialists. The divergence effect of rare species on similarity occurred only when presence data were used. When based on abundance data, rare species had little effect on community similarity. Overall, our results indicated that the successional trajectories of our tropical secondary forests moved towards OG but the recovery rate was slow. Both deterministic and stochastic processes contribute to secondary succession, but deterministic processes dominated. Furthermore, it is necessary to emphasize the different contributions of species with different habitat specialization to the successional trajectory, in order to better predict successional outcomes and prioritize conservation targets.

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.

Developmental morphoanatomy of the fruit of Isertia hypoleuca Benth. (Rubiaceae)

Isertia Schreb. is a Rubiaceae associated with secondary tropical forests, represented by fifteen species distributed in Central and South America. The fruit of Isertia hypoleuca Benth. displays morphological peculiarities which, along with imprecise use of fruit terminology and typology, hamper its classification. We studied I. hypoleuca Benth. pericarp and seed morphologically and anatomically with the objectives of establishing the ontogenetic stages of fruit development and correcty interpret fruit typology. Four stages were recorded; main features are differences in exocarp color, biomass increment, and endocarp and exotesta sclerification process. Based on ontogeny, we classifiy the fruit of I. hypoleuca as a drupe.

Bird species inventory in secondary tropical montane cloud forest at Cloudbridge Nature Reserve, Talamanca Mountains, Costa Rica

The tropical montane cloud forests (TMCF) of the Talamanca Mountains of Costa Rica are a unique and understudied habitat that is home to a high number of endemic bird species. Cloudbridge Nature Reserve is a TMCF reforestation reserve lying on the Pacific slope of Cerro Chirripó in the cantón of Pérez Zeledón. Here, we synthesize data collected at Cloudbridge between March 2016 and May 2020 from multi-year point count, walking, call-playback, and camera trap surveys along with photographs collected from February 2007 to April 2021 to present a bird species inventory of the reserve. In total, 204 bird species from 40 families, including 40 endemic species, were identified, and monthly presence summarized for each species. We discuss the implications of our findings for understanding TMCF avian communities, as well as the importance of year-round surveys using a variety of techniques to better capture overall avian diversity.

热带次生林不同林层植物叶片非结构性碳水化合物的季节变化及其对氮磷添加的响应

非结构性碳水化合物（Non-structural Carbohydrates，NSCs）是植物生长代谢过程中重要的能量来源。通过在华南热带次生林进行氮磷添加试验，探究不同林层植物叶片NSCs的季节变化及其对氮磷添加的响应，取样时间为2019年1月、4月、7月和10月。结果表明：1）植物叶片NSCs存在显著的种间差异，磷（P）添加对叶片淀粉和NSCs含量具有显著影响，且物种与磷添加的交互作用显著影响叶片淀粉含量。2）黑嘴蒲桃和紫玉盘叶片NSCs含量对氮（N）添加的响应较为敏感，而白车和竹节叶片NSCs含量对P添加的响应较为敏感，氮磷同时添加（+NP）对植物叶片NSCs的增效作用最好。3）植物叶片NSCs存在显著的季节性变化，且季节与林层间的交互作用对叶片可溶性糖和NSCs含量具有显著影响。4）不同林层植物对氮磷添加的响应不同，氮磷添加使林下层植物叶片可溶性糖含量增高，林冠层降低，在干季，N添加会使林下层植物叶片淀粉含量增高，林冠层降低。P添加的影响恰好与之相反。在湿季，氮磷添加使林下层和林冠层植物叶片的淀粉含量增加。5）林冠层植物叶片NSCs含量高于林下层，且林下层植物叶片NSCs含量和可溶性糖与淀粉的比值均表现为干季高于湿季。因此，叶片NSCs之间的变化差异反映了不同植物的碳利用策略，NSCs含量对氮磷添加的响应变化可以反映出热带森林植物在生长发育过程中碳供给和消耗的动态变化情况，为探索热带次生林植物碳利用策略及共存机制提供科学依据。;Non-structural carbohydrates (NSCs) are important energy sources in the process of plant growth and metabolism. In this paper, we conducted field-based experiment with nitrogen (N) and phosphorus (P) addition, to explore the seasonal changes of leaf NSCs in different forest layers and its response to N and P additions in a secondary tropical forest in south China. Leaf samples were conducted in January, April, July, and October 2019. The results showed that:1) There were significantly interspecific differences on the leaf NSCs. Phosphorus addition had a significant impact on starch and NSCs contents, and the interactions between species and P addition significantly affected the starch content. 2) Leaf NSCs of Syzygium bullockii and Uvaria microcarpa were sensitive to N addition, while those of Syzygium levinei and Carallia brachiate were sensitive to P addition, and N and P co-addition (+NP) had the best synergistic effect on leaf NSCs. 3) There were significantly seasonal changes on leaf NSCs, and the interaction between seasons and forest layers significantly affected soluble sugar and NSCs content. 4) The responses of plants in different forest layers to N and P addition were different. N and P additions increased the leaf soluble sugar content in the understory and decreased those in the overstory plants. In dry season, N addition increased the leaf starch contents in the understory and decreased in the overstory species. However, P addition had the opposite effect. In wet season, N and P additions increased the starch content of plant leaves in understory and overstory. 5) Leaf NSCs content in overstory was higher than that in understory. The leaf NSCs content and soluble sugar/starch ratio of understory plants were higher in the dry season than those in wet season. Therefore, the variation of NSCs in different plant leaves reflects the carbon (C) utilization strategies, and the change of NSCs content in response to N and P addition can reflect the dynamic changes of C supply and consumption during the growth and development of tropical forest plants, which provides scientific basis for exploring C utilization strategies and coexistence mechanisms of plants in secondary tropical forest.

Unprecedented large-area turnover estimates for the subtropical Brazilian Atlantic Forest based on systematically-gathered data

Secondary forests play an important role as landscape elements, providing carbon uptake, biodiversity recovery, and income for rural communities. We aimed to present change estimates for three forest types in the subtropical Atlantic Forest, namely evergreen rainforest (ERF), Araucaria forest (AF), and semi-deciduous forest (SF). We used data gathered on 303 systematically-distributed permanent plots distributed across ∼23% of the subtropical Brazilian Atlantic Forest, which nowadays is mostly composed of secondary stands. We found positive mean net changes in tree density ha−1 yr−1, basal area ha−1 yr−1, and aboveground biomass (AGB) ha−1 yr−1 for all forest types. The ERF had a statistically significantly greater mean net change in AGB ha−1 yr−1 than those of the other forest types. Relative to initial and final stocks though, mean annual rates of gain and loss (% ha−1 yr−1) for the abovementioned forest attributes were statistically equivalent among the forest types. Estimated mean net changes in AGB for the studied forest types ranged from 4.9 to 8.1 Mg ha−1 for a 5-year period. The mean net changes we found are smaller than those reported for secondary tropical forests, possibly due to climate constraints and increased sampling variability. The AGB stocks of the inventoried forests accounted, on average, to one-third of the stocks of local mature forests. Therefore, the carbon sink potential of these forests is not exhausted yet. In general, species richness, structural diversity, and community-weighted mean wood density had significant effects on annual rates of AGB gain and loss in the ERF and AF, presumably mediated by forest development stage. Greater gain rates were found on plots with smaller structural diversity and wood density in both forest types. Likewise, greater loss rates were found on plots with smaller structural diversity and wood density in the ERF, suggesting that light-demanding species are being substituted by more selective species. Conversely, greater loss rates were not found on plots with smaller structural diversity and wood density in the AF, possibly because light-demanding species are still finding favorable environments for their persistence. Our findings can contribute to reducing uncertainties in large-area estimates of AGB stocks, growth, and carbon uptake rates. The implementation of large-scale inventories should be encouraged to improve carbon cycle models under different climate change scenarios.

Multidimensional tropical forest recovery

Resilient secondary tropical forests?Although deforestation is rampant across the tropics, forest has a strong capacity to regrow on abandoned lands. These “secondary” forests may increasingly play important roles in biodiversity conservation, climate change mitigation, and landscape restoration. Poorteret al. analyzed the patterns of recovery in forest attributes (related to soil, plant functioning, structure, and diversity) in 77 secondary forest sites in the Americas and West Africa. They found that different attributes recovered at different rates, with soil recovering in less than a decade and species diversity and biomass recovering in little more than a century. The authors discuss how these findings can be applied in efforts to promote forest restoration. —AMS

Carbon storage estimation in a secondary tropical forest at CIEE Sustainability Center, Monteverde, Costa Rica

Secondary growth tropical rainforests have the potential to sequester large amounts of atmospheric carbon dioxide and as such are an important carbon sink. To evaluate a local forest, a Carbon Neutrality Program was initiated at the Council on International Educational Exchange, San Luis Campus, Monteverde, Costa Rica. The study was conducted on 50 hectares of forest classified as Premontane Wet Forest. The forest, part of the Arenal-Monteverde Protected Zone, is estimated to be aproximately 50 years old and is in the upper regions of the San Luis valley at 1100 m elevation. Assessment of the carbon stock in trees was carried out in two permanent, 1 hectare plots, 100 m by 100 m, Camino Real and Zapote. The plots were divided into 25 subplots, 20 m by 20 m totaling 400 m2 per subplot. Ten subplots in each area were studied which represented 1.6% the total surface area of the forest. All of the trees were measured within the subplots that had a diameter at breast height ≥ 10 cm and the height of 10% of the trees measured. The estimated total CO2 sequestered by the campus forest was 18,210 ton (in 2019).

Functional recovery of secondary tropical forests

One-third of all Neotropical forests are secondary forests that regrow naturally after agricultural use through secondary succession. We need to understand better how and why succession varies across environmental gradients and broad geographic scales. Here, we analyze functional recovery using community data on seven plant characteristics (traits) of 1,016 forest plots from 30 chronosequence sites across the Neotropics. By analyzing communities in terms of their traits, we enhance understanding of the mechanisms of succession, assess ecosystem recovery, and use these insights to propose successful forest restoration strategies. Wet and dry forests diverged markedly for several traits that increase growth rate in wet forests but come at the expense of reduced drought tolerance, delay, or avoidance, which is important in seasonally dry forests. Dry and wet forests showed different successional pathways for several traits. In dry forests, species turnover is driven by drought tolerance traits that are important early in succession and in wet forests by shade tolerance traits that are important later in succession. In both forests, deciduous and compound-leaved trees decreased with forest age, probably because microclimatic conditions became less hot and dry. Our results suggest that climatic water availability drives functional recovery by influencing the start and trajectory of succession, resulting in a convergence of community trait values with forest age when vegetation cover builds up. Within plots, the range in functional trait values increased with age. Based on the observed successional trait changes, we indicate the consequences for carbon and nutrient cycling and propose an ecologically sound strategy to improve forest restoration success.

Soil Fungal Community Composition Correlates with Site-Specific Abiotic Factors, Tree Community Structure, and Forest Age in Regenerating Tropical Rainforests.

Simple SummaryRegenerating forests represent over half of all tropical forests. While regeneration processes of trees and animal groups have been studied, there is surprisingly little information about how the diversity and community composition of fungi and other microorganisms change and what ecological roles play in tropical forest regeneration. In this study, we compared the diversity and community composition of trees and soil fungi among primary forests and regenerating forests of different ages in two sampling areas in southern Costa Rica. Our study shows that while forest age has a significant influence, environmental factors, such as mesoclimate and soil chemistry, have stronger effects on both fungal and tree communities. Moreover, we observed that the more dissimilar tree communities are between any two sites, the more dissimilar the composition of fungal communities. The results presented here contribute to a better understanding of the successional processes of tropical forests in different regions and inform land use and forest management strategies, including, but not limited to, conservation, restoration, and sustainable use.Successional dynamics of plants and animals during tropical forest regeneration have been thoroughly studied, while fungal compositional dynamics during tropical forest succession remain unknown, despite the crucial roles of fungi in ecological processes. We combined tree data and soil fungal DNA metabarcoding data to compare richness and community composition along secondary forest succession in Costa Rica and assessed the potential roles of abiotic factors influencing them. We found a strong coupling of tree and soil fungal community structure in wet tropical primary and regenerating secondary forests. Forest age, edaphic variables, and regional differences in climatic conditions all had significant effects on tree and fungal richness and community composition in all functional groups. Furthermore, we observed larger site-to-site compositional differences and greater influence of edaphic and climatic factors in secondary than in primary forests. The results suggest greater environmental heterogeneity and greater stochasticity in community assembly in the early stages of secondary forest succession and a certain convergence on a set of taxa with a competitive advantage in the more persisting environmental conditions in old-growth forests. Our work provides unprecedented insights into the successional dynamics of fungal communities during secondary tropical forest succession.

Large wild herbivores slow down the rapid decline of plant diversity in a tropical forest biodiversity hotspot

Abstract The UN declaration of the Decade of Ecosystem Restoration 2021–2030 emphasizes the need for effective measures to restore ecosystems and safeguard biodiversity. Large herbivores regulate many ecosystem processes and functions; yet, their potential as a nature‐based solution to buffer against long‐term temporal declines in biodiversity associated with global change and restore diversity in secondary forests remains unknown. By means of an exclusion experiment, we tested experimentally the buffering effects of large wild herbivores to avert against long‐term biodiversity collapse in old‐growth and secondary tropical forests in the Atlantic Forest of Brazil where sapling abundance and species richness declined c. 20% over the course of 10 years. The experiment comprised 50 large herbivore exclosure‐open control plot pairs (25 at the old‐growth forest and 25 at the secondary forest), where 2 m2 were monitored in every plot during a 10‐year period. Large herbivores were able to decelerate diversity declines and compositional change in the species‐rich old‐growth forest, but only decelerated compositional change in the secondary forest. In contrast, declines in species richness and abundance were unaffected by large herbivores on either forest. The buffering effects of large herbivores were strongly nonlinear and contingent on the initial level of diversity at the patch scale: highly diverse communities suffered the strongest collapse in the absence of large herbivores. Thus, larger buffering effects of large herbivores on the old‐growth forest are the logical consequence of large herbivores buffering the many high diversity plant communities found in this forest. Conversely, as the secondary forest held fewer high diversity patches, buffering effects on the secondary forest were weak. Synthesis and applications. Our study indicates that large herbivores have moderate yet critical effects on slowing down community change and diversity loss of highly diverse plant communities, thus suggesting that the conservation of (and potentially trophic rewilding with) large herbivores is a fundamental nature‐based solution for averting the global collapse of the strongholds of biodiversity. Its buffering effects on biodiversity loss operate at very small spatial scales, are likely contingent on successional stage and are most effective in old‐growth or high diversity secondary forests.

Analyzing canopy height variations in secondary tropical forests of Malaysia using NASA GEDI

Tropical forests play a significant role in regulating the average global atmospheric temperature encompassing 25 % of the carbon present in the terrestrial biosphere. However, the rapid change in climate, arising from unsustainable human practices, can significantly affect their carbon uptake capability in the future. For understanding these deviations, it is important to identify and quantify the large-scale canopy height variations arising from previous anthropogenic disturbances. With the advent of NASA GEDI spaceborne LiDAR (light detection and ranging), it is now possible to acquire three-dimensional vertical structural data of forests globally. In this study, we evaluate the applicability of GEDI for analyzing relative canopy height variations of secondary tropical forests of different age groups located across multiple geographical regions of peninsular Malaysia. The results for RH98 GEDI metric trends for the lowland and hill forests category across 4 different disturbance groups show a positive correlation between mean relative height and secondary forest ages. The consistency of these findings with previous studies in the region indicate the usefulness of GEDI to provide valuable insights into the patterns and drivers of forest height variation. Thus, this study contributes toward the operationalization of spaceborne LiDAR technology for monitoring forest disturbances and measuring biomass recovery rates and should help support large-scale sustainable forest management initiatives with respect to the tropical forests of Malaysia.

Physical structure and biological composition of canopies in tropical secondary and old-growth forests.

The area of tropical secondary forests is increasing rapidly, but data on the physical and biological structure of the canopies of these forests are limited. To obtain such data and to measure the ontogeny of canopy structure during tropical rainforest succession, we studied patch-scale (5 m2) canopy structure in three areas of 18–36 year-old secondary forest in Costa Rica, and compared the results to data from old-growth forest at the same site. All stands were sampled with a stratified random design with complete harvest from ground level to the top of the canopy from a modular portable tower. All canopies were organized into distinct high- and low-leaf-density layers (strata), and multiple strata developed quickly with increasing patch height. The relation of total Leaf Area Index (LAI, leaf area per area of ground) to patch canopy height, the existence of distinct high and low leaf- density layers (strata and free air spaces), the depth and LAI of the canopy strata and free air spaces, and the relation of the number of strata to patch canopy height were remarkably constant across the entire successional gradient. Trees were the most important contributor to LAI at all stages, while contribution of palm LAI increased through succession. We hypothesize that canopy physical structure at the patch scale is driven by light competition and discuss how this hypothesis could be tested. That canopy physical structure was relatively independent of the identity of the species present suggests that canopy physical structure may be conserved even as canopy floristics shift due to changing climate.

Dispersal limitation, soil, and fire affect functional properties of tropical secondary forests on abandoned cattle ranching landscapes

Forest age is a major predictor of secondary forest functional properties and through the chronosequence approach continues to be a principal focus in local, landscape, and regional-scale studies of secondary succession. Recent work has shown that patterns of temporal change in functional properties differ markedly between wet and seasonally dry lowland forests, suggesting that decreasing light and increasing water availability, respectively, are the main drivers of successional change. Meanwhile, however, the potentially marked effects of anthropogenic factors (especially fire), soils, climate, and dispersal limitation on the variation of forest characteristics over landscapes remain poorly understood. We studied the functional properties of seasonally dry secondary forests 5–35 years after pasture abandonment on the Nicoya Peninsula, Costa Rica. We measured 11 functional traits for 63 dominant tree and palm species in 52 plots of 0.12 ha. We used linear regression and variation partitioning to determine the relative importance of soil, climate, site use, fire history, spatial factors, and forest age in the determination of community weighted mean (CWM) trait values. CWM leaf trait and stem trait spectra of the 52 plots were orthogonal in a PCA ordination. Our seasonal forest hypothesis, that forest functional properties become more acquisitive with age as suggested by other authors, was not supported, perhaps because our chronosequence was relatively short. Our fire tolerance hypothesis was that bark thickness, wood specific gravity and resprouting capacity would increase with time of exposure to fires. This hypothesis was not supported for bark thickness. Rather, our results suggest that wood specific gravity and resprouting capacity are better predictors of fire tolerance. Also, our results suggest that >10 years of exposure to fire generates changes in forest fire tolerance strategies from high CWM bark thickness to high wood specific gravity. Finally, we tested our dispersal limitation hypothesis, that spatial variables, expressed as principal coordinates of neighbor matrices (PCNM) eigenfunctions, predict variation in forest functional properties, using variation partitioning analysis with matrices of climate, soil, anthropogenic and spatial variables. The results (overall model R2 = 0.46) indicated that spatial variables, followed by soil (acidity, depth, and extractable Mn), are the best overall predictors of forest functional traits values, supporting this hypothesis. Overall, fire, dispersal limitation and soil characteristics explain the functional properties of these secondary forests, with no effect of age in the 5–35 years range. This indicates a critical need for sampling designs and analytical approaches that take into account all these factors to advance understanding of tropical seasonal forest recovery at the landscape scale.

Shade-Grown Coffee in Colombia Benefits Soil Hydraulic Conductivity

Secondary tropical forests and coffee agroforestry systems contain fewer trees than native forests but can positively impact soil hydrological functions, such as water infiltration compared to the pasture land that they replace. However, for both land uses it remains in how far the soil hydraulic characteristics are comparable to that of native forest. Therefore, we investigated the saturated hydraulic conductivity (Ks) and some hydrophysical soil attributes in four land-use types: (i) a shade-grown coffee; (ii) a natural regenerated forest 15 years ago; (iii) a pasture; and (iv) a reference forest, in the municipality of La Jagua de Ibirico, César department, Colombia. We determined historical land use and conducted soil sampling, using the Beerkan method to determine the Ks values. We also measured canopy cover, vegetation height, diameter at breast height and total number of trees in the forest covers. Our results indicate that Ks values were similar for the coffee and the reference forest, reflecting the positive effect of trees on soil hydrological functioning in agroforestry systems. Our results suggest that 15 years of forest regeneration after land abandonment in Sub-Andean Forest, can improve the soil hydraulic attributes. Additionally, soil water repellency was observed for the reference forest soil.