Old Secondary Forest Research Articles

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.

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.

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.

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.

Importance of Quercus spp. for diversity and biomass of vascular epiphytes in a managed pine-oak forest in Southern Mexico

Forestry management modifies the diversity, structure, and functioning of intervened forests. Timber extraction reduces tree density and basal area, leading to changes in the communities of vascular epiphytes. The objective of this study was to evaluate the diversity and biomass of vascular epiphytes in Quercus trees remaining in two pine-oak forest stands that have been subjected to two stages of the Silvicultural Development Method (release cutting, and thinning) in comparison with an unharvested old-secondary forest in southern Mexico. For each treatment, richness of epiphytes present on 60 oak trees was recorded and their dry biomass estimated. We calculated the true diversity (Hill numbers) and beta diversity using the Jaccard coefficient of similarity, and generated rank abundance curves per taxonomic epiphyte group (bromeliads, orchids, ferns and others). For each treatment, the relationships between overall diversity and epiphyte biomass to the host trees basal area were analyzed using log linear models. We recorded a total of 67 species of epiphytes species belonging to 10 families hosted by five species of oaks. The greatest species richness (0D) was recorded in the old-secondary forest. Fewer common (1D) and dominant (2D) species were recorded in the release cutting than in the other treatments. Epiphyte diversity and biomass were both slightly related to host tree basal area. Composition of epiphytes was similar (60%) among treatments, although orchids, bromeliads, and other families were more diverse in the old-secondary forest. Most bromeliad species were shared across all treatments, although orchids presented the most exclusive species in the unharvested forest. The bromeliad Tillandsia seleriana provided the greatest contribution to biomass in all treatments, followed by the orchid Camaridium densum. Generalized linear models indicated that epiphyte diversity was significantly related to treatment, and epiphyte biomass to basal area of host trees. Although forest management affects diversity, composition, and abundance of vascular epiphytes, most of their diversity and biomass can be maintained despite timber harvesting. This requires sparing some mature oaks during logging, as they contribute to conservation, establishment, and development of epiphytic communities, and maintaining untreated areas as a source of propagules for these communities.

Thermal tolerance and the importance of microhabitats for Andean frogs in the context of land use and climate change.

Global warming is having impacts across the Tree of Life. Understanding species' physiological sensitivity to temperature change and how they relate to local temperature variation in their habitats is crucial to determining vulnerability to global warming. We ask how species' vulnerability varies across habitats and elevations, and how climatically buffered microhabitats can contribute to reduce their vulnerability. We measured thermal sensitivity (critical thermal maximum-CTmax ) of 14 species of Pristimantis frogs inhabiting young and old secondary, and primary forests in the Colombian Andes. Exposure to temperature stress was measured by recording temperature in the understorey and across five microhabitats. We determined frogs' current vulnerability across habitats, elevations and microhabitats accounting for phylogeny and then ask how vulnerability varies under four warming scenarios: +1.5, +2, +3 and +5°C. We found that CTmax was constant across species regardless of habitat and elevation. However, species in young secondary forests are expected to become more vulnerable because of increased exposure to higher temperatures. Microhabitat variation could enable species to persist within their thermal temperature range as long as regional temperatures do not surpass +2°C. The effectiveness of microhabitat buffering decreases with a 2-3°C increase, and is almost null under a 5°C temperature increase. Microhabitats will provide thermal protection to Andean frog communities from climate change by enabling tracking of suitable climates through short distance movement. Conservation strategies, such as managing landscapes by preserving primary forests and allowing regrowth and reconnection of secondary forest would offer thermally buffered microhabitats and aid in the survival of this group.

STRUKTUR DAN KOMPOSISI HUTAN DI KAWASAN LINDUNG RANTAU BERTUAH, KABUPATEN SIAK, PROVINSI RIAU

A study on structure and composition of old secondary forest (OSF), young secondary forest (YSF), and old scrub forest (OScF) in Rantau Bertuah Protected Area, Siak Regency, Riau Province, was conducted in September 2018. The purpose of this study was to analyze species composition and structure of forests.The research plot measuring 100 x 100 m (one ha) each was made at OSF, YSF, and OScF. The OSF plot held 33 families, 55 species, and 642 trees with a diameter of ? 10 cm; in YSF 31 families, 56 species, and 450 trees; and in OScF 28 families, 52 species, and 235 trees. At the tree level the OSF was dominated by Calophyllum macrocarpum, Shorea sp., and Gironniera nervosa; the YSF by Palaquium amboinense, Shorea macroptera, and Gironniera nervosa; and the OScF by Macaranga hypoleuca, Gironniera nervosa and Lithocarpus gracilis. Based on the main dominant species and full distribution in the plot, the forest is called the Gironniera nervosa-Lithocarpus gracilis association.

Characterization and Conservation Status of Evergreen Rainforest Understory: Case of Campo Ma'an National Park (Cameroon)

The Campo Ma'an National Park is located in the evergreen rainforest area rich in biological diversity. This biological diversity remains poorly known, especially those of the understory. The objective of the present study is to characterize undersotory tree and to determine their IUCN conservation status. To know the floristic diversity of understory (5 cm ≤ dbh <10 cm) of this forest, a tree inventory using the plots method of 25 m x 25 m, in which 36 plots were placed out on 6 transects of 4 km each. The IUCN Red List was used to determine the status of inventoried species. The result showed a total richness of 256 species belonging to 148 genera and 50 families for the entire site has been identified. The Shannon diversity index is 4.90 and 4.02 for Old secondary forest (OSF) and Secondary forest (SFO), respectively. The floristic background belongs to the field of Guinean-Congolese endemism, with 6 endemic species in Cameroon. The conservation status analysis shows that 22 species are listed as endangered in the red list of the International Union for the Conservation of Nature. This study provides a base for reflection on the integration of understory trees species in inventories and in the development of conservation strategies.

Airborne LiDAR Detects Selectively Logged Tropical Forest Even in an Advanced Stage of Recovery

Identifying historical forest disturbances is difficult, especially in selectively logged areas. LiDAR is able to measure fine-scale variations in forest structure over multiple kilometers. We use LiDAR data from ca. 16 km2 of forest in Sierra Leone, West Africa, to discriminate areas of old-growth from areas recovering from selective logging for 23 years. We examined canopy height variation and gap size distributions. We found that though recovering blocks of forest differed little in height from old-growth forest (up to 3 m), they had a greater area of canopy gaps (average 10.2% gap fraction in logged areas, compared to 5.6% in unlogged area); and greater numbers of gaps penetrating to the forest floor (162 gaps at 2 m height in logged blocks, and 101 in an unlogged block). Comparison of LiDAR measurements with field data demonstrated that LiDAR delivered accurate results. We found that gap size distributions deviated from power-laws reported previously, with substantially fewer large gaps than predicted by power-law functions. Our analyses demonstrate that LiDAR is a useful tool for distinguishing structural differences between old-growth and old-secondary forests. That makes LiDAR a powerful tool for REDD+ (Reduction of Emissions from Deforestation and Forest Degradation) programs implementation and conservation planning.

Produção de serapilheira e aporte de nutrientes em areas de Floresta Atlântica em Santa Maria de Jetibá, ES.

Este estudo foi realizado na Fazenda Espíndula, Santa Maria do Jetibá, ES, com o objetivo de avaliar a deposição de serapilheira e o aporte de nutrientes em áreas com diferentes estádios sucessionais. Foram selecionadas duas áreas com formações vegetais distintas: Floresta Secundária (FS) com cerca de 25 ha, correspondente a uma antiga área de cultivo de mandioca a cerca de 50 anos em processo de sucessão ecológica e onde hoje se encontra uma mata secundária e Floresta Secundária Antiga (FSA) que corresponde a uma área de floresta que foi submetida apenas extração seletiva de madeira para utilização da própria fazenda. Em cada uma das formações vegetais, foram delimitadas áreas de aproximadamente 0,1 ha e, nestas, foram distribuídos aleatoriamente dez coletores cônicos. As coletas foram realizadas mensalmente durante o período de novembro de 2003 a outubro de 2005. O material após secagem foi estratificado, avaliando-se o total aportado, a contribuição das diferentes frações e a entrada de nutrientes. Não foram verificadas diferenças significativas entre o total aportado entre as áreas, sendo os maiores valores de produção, 5,70 Mg ha-1 (FS)e 5,73 Mg ha-1(FSA) observados no verão, possivelmente por causa da ação mecânica de ventos e da chuva. A fração de maior contribuição foi a foliar, correspondendo a 74,62% para a área de Floresta Secundária e 69,46% para a área de Floresta Secundária Antiga.