Secondary Forest Sites Research Articles

Protective role of reactive aluminum phases to stabilize soil organic matter against long-term cultivation in the humid tropics under volcanic influence

ABSTRACT Cultivation can cause rapid depletion of soil organic matter (SOM), particularly in the humid tropics. Understanding the factors controlling SOM storage is a key step toward effective soil management for sustainable crop production. While clay + silt content is known to be an important factor for soil organic carbon (SOC) storage, recent studies have shown greater importance of oxalate-extracted Al (Alo; roughly corresponds to short-range-order aluminosilicate minerals and organo-Al complexes) and Fe (Feo). However, the extent to which these mineralogical factors control the response of SOM pool to land-use changes remains unclear, especially in the tropics. This study aimed to clarify the factors regulating SOM content in croplands compared to secondary forests or home gardens in Negros Occidental, Philippines. Along two line transects having a wide range of Alo contents, soil samples were collected at a depth of 0 − 10 cm from sugarcane sites (n = 33; long-term continuous cultivation of >70 years) that were paired with either secondary forests (n = 10) or home gardens (n = 20). Sugarcane sites had significantly lower SOC and total nitrogen (N) contents than secondary forest and home garden sites, whereas there was no clear difference between the latter two land uses. Both SOC and total N contents showed significant positive correlations with Alo content and, to a much less extent, with Feo content, but not with clay + silt content. The slope of the regression line between SOC and Alo was indifferent between sugarcane and the other two land uses, while the intercept was significantly lower in the sugarcane sites. These results suggest the protective role of Alo phases in both agricultural and forest soils and the presence of unprotected SOM (e.g. plant litter) in the latter sites. Furthermore, δ13C analysis suggested that the proportion of forest (C3 plant) derived carbon remaining in the sugarcane soils ranged between 10% and 50% and increased with Alo content. Together, our study showed indirect evidence of Alo-induced stabilization of SOM against long-term cultivation under the humid tropical environment.

Development of Polymorphic Index Model for Assessing Subtropical Secondary Natural Oak Forest Site Quality Under Complex Site and Climate Variables

Site and climate conditions are the key determinants controlling dominant height growth and forest productivity, both independently and interactively. Secondary natural oak forests are a typical forest type in China, especially in Hunan Province, but little is known about the site index of this forest under the complex site and climate variables in the subtropics. Based on survey data of dominant trees and site variables from 101 plots in Hunan oak natural secondary forests and climate data obtained using spatial interpolation, we used the random forest method, correlation analysis, and the analysis of variance to determine the main site and climate factors affecting oak forest dominant height and proposed a modeling method of an oak natural secondary forest site index based on the random effect of site–climate interaction type. Of the site variables, elevation affected stand dominant height the most, followed by slope direction and position. Winter precipitation and summer mean maximum temperature had the greatest impact on stand dominant height. To develop the modeling method, we created 10 popular base models but found low performance (R2 ranged from 0.1731 to 0.2030). The optimal base model was Mitscherlich form M3 (R2 = 0.1940) based on parameter significance tests. Since site and climate factors affect the site index curve, the dominant site and climate factors were combined into site types and climate types, respectively, and a nonlinear mixed-effects approach was used to simulate different site types, climate types, site–climate interaction types, and their combinations as random effects. Site–climate interaction type as a random factor enhanced model (M3.4) performance and prediction accuracy (R2 from 0.1940 to 0.8220) compared to the optimum base model. After clustering the 62 site–climate interaction types into three, five, and eight groups using hierarchical clustering, a mixed-effects model with the random effects of eight groups improved model performance (R2 = 0.8265) and applicability. The modeling method developed in this study could be used to assess a regional secondary natural oak forest site index under complex site and climate variables to evaluate the forest productivity.

Species-richness, abundance, and body size of stream-breeding anurans across land-use types in Sabah, Malaysia (Borneo)

Approximately 70% of Earth’s surface is impacted by human land-use. While numerous studies have demonstrated that species richness is higher in primary (undisturbed) forest than in secondary forest or agriculture sites, some studies fail to detect differences in species richness across land-use type. Recent work suggests that individual-level changes such as body size or body condition can occur more rapidly than population- or community-level processes, such as abundance and species richness, respectively. Thus, body size and condition may be more sensitive measures of environmental changes. We examined body size, body condition, abundance, and species richness of anurans in primary forest, secondary forest, and agriculture in Sabah, Malaysian Borneo, to determine whether individual-, population-, and community-level measures show similar sensitivities to land-use type. We found that observed anuran species richness and estimated population size are lower in agriculture than in primary or secondary forest, as were body size (SVL), mass, and body condition of female Meristogenys orphnocnemis. Further, anuran body condition (all species pooled) was higher in primary forest than agriculture or secondary forest, and size (SVL), mass, and body condition of male M. orphnocnemis were higher in primary forest than in agriculture or secondary forest areas. Collectively, our data demonstrate that primary forests are the best habitat for anurans in Sabah, and that individual-level processes such as size, mass, and body condition, show larger differences across land-use type than population- (abundance) or community-level processes (species richness). These data highlight the importance of primary forest for preserving anuran biodiversity in Borneo.

Effects of tree density and herbaceous plants on tree seedling survival across the growing and non-growing season in a temperate forest

Tree seedling survival is critical for estimating forest recruitment, but it remain elusive about how neighboring tree’s density and herbaceous plants affect it. To assess the relative importance of tree density and herbaceous plants on tree seedling survival during the growing season and non-growing season, we established a two-year experiment with seedling census and removal of herbaceous plants in both secondary and old-growth temperate forest sites in the temperate forests of northeastern China. A total of 3,443 seedlings in 17 tree species were surveyed in this study. We found that both tree density and herbaceous plants significantly affected tree seedling survival, but the specific effects depended on shade tolerance, seedling growth stage and growing season. Conspecific adult neighbors had significant negative effects on the survival of shade-tolerant seedlings during the growing season, while conspecific seedling densities positively correlated with shade-intolerant seedlings. Herb removal significantly improved the survival of newly germinated and shade-intolerant seedlings during the growing season. Furthermore, we found that the survivals of both newly germinated and established seedlings differed seasonally in response to adult, seedling neighbors and herb removal. Herb removal enhances seedling survival during the non-growing season by offsetting the negative effects of conspecific adult neighbors during the growing season. Our findings provide new evidence for seedlings’ shade tolerance, growth stage and seasonal dependence of density dependence in temperate forests, and highlight the significance of herbaceous plants for seedling survival, an important factor that has been neglected in many previous studies.

Impact of landscape patterns on herb-layer diversity and seed size of Schima superba in urban remnant vegetation: A case study in Guangzhou, Southern China

In order to explore which ecological strategies the remnant vegetation is taken to adapt to urbanization, we investigated three kinds of typical remnant vegetation (grassland, plantation, and secondary forest) in 16 sample sites along the urban–rural gradient in the city of Guangzhou. In this study, we examined plant species composition, and plant diversity, and analyzed the seed of the dominant tree species Schima superba (S. superba) in the secondary forest sites. Those indicators are strongly related with ecological strategies. Eighteen landscape pattern characteristics were determined to reveal the extent of landscape fragmentation. Geographic Information System (GIS), linear regression, and Canonical Correspondence Analysis (CCA) were conducted to analyze the influence of landscape pattern characteristics on plant communities. Results showed that (1) Fragmentation of landscape patterns caused by urbanization has a negative impact on the diversity of herb-layer plants, the dominant species of grassland in the city center are mainly weeds, such as Bidens pilosa and Neyraudia reynaudiana. (2) In order to adapt to the pressure of landscape fragmentation, seeds of S. superba have developed into a larger size, with a competitive advantage over smaller ones. (3) Two different ecological strategies of plant communities adapting to urbanization: The pioneer weeds in grasslands, with high reproductive and dispersal ability, have adopted a r-selection strategy and the dominant tree species with higher survival rates, larger individuals, and longer life spans, have adopted a K-selection strategy to resist disturbance, as well as with a larger seed size to increase viability and settlement ability.

Leaf-litter frog abundance increases during succession of regenerating pastures

Abstract The extensive clearing and modification of forests by anthropogenic activities is a major driver of biodiversity loss. Declines of common species are especially concerning because of the potentially large cascading effects they might have on ecosystems. Regrowth of secondary forests may help reverse population declines by restoring habitats to similar conditions prior to land conversion but the value of these secondary forests to fauna is not well understood. We compared the abundance of a direct-developing terrestrial frog, Craugastor stejnegerianus, in riparian and upland habitats of pasture, secondary forest, and mature forest sites. Mean abundance per transect was lower in upland pasture compared to mature forest. Secondary forest had similar abundance to mature forest regardless of age. We show that conversion of forest habitat to pasture represents a conservation threat to this species. However, riparian buffers help mitigate the negative effect of conversion of forest to pasture, and regrowth of secondary forest is an effective management strategy for restoring the abundance of this common leaf-litter species.

Impacts of deforestation and forest regeneration on soil bacterial communities associated with phosphorus transformation processes in the Brazilian Amazon region

Land-use change has negative impacts on the biodiversity of plants and animals. However, we lack studies and/or information about the impacts of land-use change on the biodiversity of soil microorganisms, especially those involved in the phosphorus (P) transformation processes. This represents a great concern since some microbial groups are extremely important to different P transformation processes and regulate P availability in tropical and subtropical regions. In our study, we used shotgun DNA-metagenomic sequencing and P fractionation analysis to assess the effects of forest-to-pasture conversion on the dynamics of soil bacterial groups involved in the P transformation processes and their potential functions. Additionally, we assessed if the dynamics of these specific soil bacterial groups were recovered after pasture abandonment and with secondary forest establishment. Our results demonstrated that the land-use change altered the total amount of P and its fractions in the soils. The bacterial community structure was affected by changes in soil chemical properties, mainly by changes in the aluminum, total P, and labile P contents. The bacterial groups involved in the P transformation processes and their potential functions were also affected by changes in land use. The pasture soil harbored a distinct bacterial community when compared to the primary and secondary forest sites. In general, forest-to-pasture conversion increased bacterial groups involved in the P mineralization, including Firmicutes, Cyanobacteria, and Gemmatimonadetes. Conversely, we observed an increase of Proteobacteria members (e.g., Bradyrhizobiaceae and Beijerinckiaceae) and genes related to P solubilization and mineralization after pasture abandonment and with the secondary forest re-establishment. Our multi-analytical approach suggests that forest-to-pasture conversion has negative impacts on the biodiversity of bacterial groups involved in the P transformation processes and their potential functions, while the secondary forest re-establishment can stimulate resilience. Taken together, our results indicated that the bacterial groups involved in the P transformation and their potential functions can be gradually recovered and reach intermediate and/or even similar levels to those observed in undisturbed forest sites. This brings new insights and helps to improve our knowledge about the impacts of anthropogenic actions on the soil microbiome in the Amazon region.

Ant communities in disturbed subtropical landscapes: is climate more important than stochastic processes?

Functional trait-based approaches have provided advances in the understanding of community assembly rules. Broad generalisations remain, however, limited due to the idiosyncratic nature of taxa and ecosystems, especially in tropical regions. We use fine scale resolution (30m grid) environmental variables and community surveys from nearly 100 secondary tropical forest sites to study niche-based or neutral assembly mechanisms in ground dwelling ants. This provides a unique opportunity for understanding fine scale drivers of taxonomic, functional and phylogenetic diversity in a region characterized by large topographic and climatic differences on a relatively small geographic scale. Precipitation emerged as the most consistent environmental correlate, in shaping taxonomic, phylogenetic and functional aspects of the communities. Functional diversity was weakly associated with topography and temperature related variables. The fourth corner model revealed that femur, scape and mandible length were key traits in response to precipitation, and that communities showed a functional homogenization towards shorter appendages at wetter sites. Our results suggest that neutral and deterministic assembly processes act in concert to shape the taxonomic, phylogenetic and functional aspects of leaf litter ant assemblages. The use of multiple complementary metrics and approaches along environmental gradients are powerful to reveal the subtilities of assembly processes and provide insight into the ways future communities might change.

Riparian buffers provide refugia during secondary forest succession

AbstractAimSecondary forests regenerating from human disturbance are increasingly becoming a predominant forest type in many regions, and they play a significant role in forest community dynamics. Understanding the factors that underlie the variation in species responses during secondary succession is important for understanding community assembly and biodiversity monitoring and management. Because species vary in ecology and behaviour, responses to ecosystem change should vary among species. Here, we show that habitat type (riparian, upland), phylogeny, and species traits mediate anuran and lizard probability of occurrence and species richness in pasture and secondary forest.LocationSarapiquí and Osa Peninsula, Costa Rica.MethodsWe used phylogenetic occupancy models to estimate assemblage‐level and species‐specific responses to forest succession in 30 chronosequence sites that include pasture, secondary forest regenerating from pasture, and mature forest sites.ResultsFor the majority of species, we found increasing probability of occurrence in upland habitats as forest regenerated from pasture to secondary forest and similar probability of occurrence in riparian habitats across pasture, secondary forest, and mature forest sites. Species' responses to forest stage were phylogenetically correlated, and the trend was especially strong for anuran response to pasture sites. Anurans with lentic larval habitat had a positive occupancy response to pasture upland habitat, and anurans with lotic larval habitat had a variable response to different forest stages compared to mature forest.Main ConclusionsOur study, which focuses on sites that are minimally isolated from mature forest reference sites, indicated that anuran and lizard occupancy rapidly recovered to a level similar to mature forest in a relatively short time span (approximately 20 years). Riparian habitats are key ecosystem features in our system and provide refugia for organisms in early successional stages. Maintenance of vegetation along streams shows that we can mitigate forest conversion by maintaining riparian buffers.

Quantitative estimation of reclamation status of a dry secondary forest using “measure of climax”: A novel approach

Determination of reclamation status of secondary forests is particularly urgent in human impacted landscapes for conservation of biodiversity and other ecosystem services. However, there is a lack of a quantitative method to estimate the recovery status of secondary forest globally. In the present work, the authors have attempted to estimate the recovery status of a dry secondary forest of Similipal Biosphere Reserve (SBR), India quantitatively with a nearby primary forest. We have formulated an equation (measure of climax stage) to estimate the secondary forest for its possible climax stage (early climax stage/mid climax stage/stable climax stage/non climax stage) based on species richness. For this study, the value of “measure of climax stage” between 0 and 0.2 is considered as stable climax stage, 0.2–0.6 as mid climax stage and 0.6–1 as early climax stage. On the other hand, the value >1 was considered as a non-climax stage of the forest. Accordingly, the studied secondary forest was estimated as to be in mid climax stage (measure of climax stage = 0.4230) even after c. 25 years of successional stage. We have also estimated the recovery stage of a secondary dry forest in SBR by fitting it with a suitable equation and found that the time frame for the stable climax stage is more than 50 years. ANOVA analysis indicates that there is no significant difference observed in the case of soil nutrient contents (except Electrical Conductivity) between primary and secondary forest sites. This developed equation may be implicated in the evaluation of reclamation status of secondary and degraded forest lands globally. Further, in-depth study is encouraged for the development of a modern climax concept to understand the ecological restoration process in a better way.

Climate consequences of temperate forest conversion to open pasture or silvopasture

Land use change, particularly the conversion of forest to agriculture, is an important driver of climate change but is rarely considered a major factor in northern temperate regions. This study explored the climate impacts of temperate forest clearing for agriculture in the northeastern United States, hypothesizing that compared to managed cool-season pasture, forest conversion to silvopasture would moderate changes in surface temperature, soil greenhouse fluxes, and soil carbon and nutrient losses. To test this hypothesis, we conducted two land use change experiments, one in New York and the other in New Hampshire, USA. In both locations, forests have regenerated following a period of forest clearing, intensive agricultural management, and farm abandonment, such that secondary forests currently comprise ~60–80% of the land base. In both experiments, we measured microclimatic variables of air and soil temperature and soil moisture, soil greenhouse gas emissions of CO2 and N2O, and soil carbon and nitrogen content. Using a mixed-effects modeling framework, we found that near-surface air and soil temperatures were highest in converted pasture plots, lowest in reference secondary forest areas, and intermediate in the converted silvopasture treatment. Soil respiration followed a similar pattern, with elevated soil CO2 fluxes in open pastures as compared to converted silvopasture and reference secondary forest sites. Although we detected few changes in soil C among treatments, we observed higher soil N stocks and soil N2O fluxes in converted pastures but not in the converted silvopasture treatment. Our results suggest that silvopasture may offer a biogeochemical “middle ground” between intact secondary forests and managed open fields, retaining the climate benefits of forests while enabling expansion of the agricultural land base. Understanding the climate impacts of forest conversion to open pasture or silvopasture is critical to better anticipate the climate consequences of potentially re-emerging agricultural land uses, both across the northeastern US and other temperate forest regions globally.

Land Use Effect on Quality of Plateau Soils: A Case Study of Ososo in Northern Edo State, Nigeria

The study examined land use effect on quality of plateau soils, using Ososo in Northern Edo State, Nigeria as a case study. The objectives were to examine the status of soils under the different land uses and evaluate variation in the physicochemical properties of soils among the investigated sites. A total of thirty-six soil samples were collected from secondary forest, cocoa plantation and quarry site at 0 - 15 and 15 - 30 cm depths. Soil quality indicators were analyzed in the laboratory, while data were examined by descriptive and inferential statistics. Due to the effect of mining activities, quarry site had lower mean values of soil organic matter, total organic carbon, total nitrogen, available phosphorous, effective cation exchange capacity, potassium, copper and manganese while iron, zinc and calcium were lower in secondary forest. However, Na and ECEC were higher in cocoa plantation. The study further revealed that though the examined land uses had varied effects on the soil properties; quarry site impacted the soil quality parameters more negatively compared to the secondary forest and cocoa plantation land use types. Significant variation (p < 0.05) in sand, clay and available phosphorous was detected in the topsoil of the different land uses. The research concluded that the status of the soil nutrients was low. To improve the quality of the plateau soils, liming and the use of animal droppings, town refuse ash and plant remains is recommended.

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

Establishment success of Brazil nut trees in smallholder Amazon forest restoration depends on site conditions and management

1. Forest landscape restoration (FLR) has gained momentum globally and guidance is needed to identify those species, sites and planting methods that increase restoration success. Incorporating native Non-Timber Forest Product (NTFP) species in FLR approaches provides an opportunity to simultaneously deliver ecological and economic benefits. The Brazil nut tree is one of the most valuable Amazonian NTFP species and could fulfil a cornerstone role in Amazon FLR. However, the factors defining establishment success within Brazil nut restoration activities remain unknown.2. Here, we evaluate the effect of management practices, restoration site (pastures, agroforestry, secondary forest and canopy gaps in old growth forest) and environmental conditions on the establishment success (tree growth, survival and fruit production) of Brazil nut restoration projects implemented by smallholders in the Peruvian Amazon. We performed a field study at 25 restoration sites of 1–38 years in age, where we conducted measurements on 481 trees and interviewed 21 smallholders. We used mixed effect models to identify drivers of performance.3. Twenty years after planting, diameter growth in secondary forests was 38%, 34%, and 24% higher than in canopy gaps, pastures, and agroforestry sites, respectively. Survival rate was similar for trees planted in pastures and secondary forests, but 15–20% higher there than trees planted in agroforestry sites, and 7–12% higher than in canopy gaps. Fruit production was 262% higher for reproductive trees in secondary forest sites compared to pastures, but production probability did not differ between restoration sites. These results show that secondary forests are the most suitable sites for planting Brazil nut trees.4. In addition to restoration site effects, we also found significant effects of management practices. Survival rate increased with application of fire for clearing and weeding and economic investments and decreased with potentially inefficient herbivore protection. Fruit production was lower for trees planted further away from smallholders’ homes. These results show that smallholders’ management has a substantial effect on establishment success.5. Our findings suggest a significant importance of post-planting maintenance of trees to increase success of FLR projects. Further, our study shows that evaluation of past restoration activities can guide future forest restoration in tropical landscapes.

Seed-rain-successional feedbacks in wet tropical forests.

Tropical forest regeneration after abandonment of former agricultural land depends critically on the input of tree seeds, yet seed dispersal is increasingly disrupted in contemporary human-modified landscapes. Here, we introduce the concept of seed-rain-successional feedbacks as a deterministic process in which seed rain is shaped by successional dynamics internal to a forest site and that acts to reinforce priority effects. We used a combination of time series and chronosequence approaches to investigate how the quantity and taxonomic and functional composition of seed rain change during succession and to evaluate the strength of seed-rain-successional feedbacks, relative to other deterministic and stochastic mechanisms, in secondary wet forests of Costa Rica. We found that both successional niches and seed-rain-successional feedbacks shaped successional trajectories in the seed rain. Determinism due to successional niche assembly was supported by the increasing convergence of community structure to that of a mature forest, in terms of both functional and taxonomic composition. With successional age, the proportions of large-seeded, shade-tolerant species in the seed rain increased, whereas the proportion of animal-dispersed species did not change significantly. Seed-rain-successional feedbacks increased in strength with successional age, as the proportion of immigrant seeds (species not locally represented in the site) decreased with successional age, and the composition of the seed rain became more similar to that of the adult trees at the forest site. The deterministic assembly generated by seed-rain-successional feedback likely contributed to the increasing divergence of secondary forest sites from each other during succession. To the extent that human modification of tropical forest landscapes reduces connectivity via factors such as forest cover loss, our results suggest that seed-rain-successional feedbacks are likely to increasingly shape regeneration trajectories in and amplify floristic heterogeneity among tropical secondary forests.

New records of buffy-tufted-ear marmoset Callithrix aurita (É. Geoffroy, 1812), in a protected area of Teresópolis, Brazilian Atlantic Forest

Callithrix aurita, an Atlantic Forest endemic primate, is a threatened species due to habitat loss, deforestation, interspecific competition and hybridization. In 2018, it entered the list of the world's 25-most threatened primate species, therefore, new occurrence sites must help in its conservation. Transects in the Montanhas de Teresópolis Municipal Natural Park and occasional sampling on the surrounding roads, using playback, have been carried out between March 2020 and January 2021. Eleven new records were made of the occurrence of the species in and around the PNMMT, in secondary forest sites with altitudes between 711 and 1000m. These records reinforce the importance of the Park for the conservation of this primate. The presence of this species can help the planning and management of this protected area, indicating areas for preservation.

Abundance, distribution and substrate association of Hong Kong stag beetles (Coleoptera: Lucanidae) in secondary forests

Abstract Ecological studies conducted on lucanids in Asia are limited, resulting in considerable knowledge gaps in the fundamental ecology of these charismatic species (e.g. larval substrate associations), despite their potential importance in wood decomposition. We conducted 25 transect surveys in secondary forest sites in Hong Kong and sampled wood parameters and site‐level wood availability data to test whether these habitat features significantly affected abundance or occurrence of lucanids. Out of 412 wood fragments sampled, we found two species: Prosopocoilus oweni was broadly distributed across sites (but still uncommon at the level of wood fragments occurring in 6.07%) while Nigidius sinicus was comparatively rarer (occurring in 0.73% of examined wood fragments). The dominant species P. oweni was more likely to appear in wood fragments in later decay stages and can be classified as a secondary forest generalist with respect to wood resource utilisation. The surveys failed to detect four additional lucanid species known in Hong Kong (Neolucanus sinicus, E. gracilis, P. biplagiatus, and Aegus chelifer) potentially because of their rarity or usage of other habitats or microhabitats. Protection of existing secondary forests in Hong Kong is recommended to secure supply of suitable habitat and resources. Results obtained by standardised surveys can furthermore serve as a baseline for future assessment of lucanid population change. This study provides ecological insights into lucanids within secondary forest ecosystems of subtropical and tropical Asia.

Assessment of forest degradation condition in Natmataung National Park Watershed, Myanmar

Abstract. Oo Y, Suanpaga W, Muenpong P. 2021. Assessment of forest degradation condition in Natmataung National Park Watershed, Myanmar. Biodiversitas 22: 1354-1362. Natmataung National Park (NTNP) is an important biodiversity hotspot in Myanmar, yet it is threatened by various anthropogenic activities, leading to deforestation and forest degradation. As such, the park needs to be restored to bring back its main function of conserving biodiversity. Ecological restoration in NTNP needs assessment of forest restoration potential through forest degradation condition. This research aimed: (1) to assess forest stand parameters of tree density, basal area, Above Ground Biomass (AGB), and Above Ground Carbon (AGC) at plot level and study area level through sampling with fixed area in the NTNP watershed, (2) to compare the accessed forest stand parameters of old-growth forest (OF) and secondary forest (SF) (per plot individual level and per stem individual level) and tree species richness and diversity of OF and SF (per plot individual level only) in order to know the forest degradation condition. A total of 69 square plots were sampled to achieve such aims. This study found two main results: (1) the estimation of stand parameters in both OF and SF at the plot level and study area level had acceptable statistical proration: (2) stand parameters at stem level had significant differences in which OF had overall higher values of parameters than in SF. Based on the results of this study, we recommend that the OF sites should be conserved through sustainable forest management, while the SF sites should be restored to mimic condition in OF through the implementation of assisted natural regeneration (ANR) with highest dominant native tree species, and the abandoned fallow lands should be restored using pioneer native tree species.

冀北山地天然次生林土壤生态化学计量特征及影响因素

为了探究天然次生林植被及立地因子对土壤养分含量的影响，量化植被与立地因子对土壤养分的影响比例，为合理抚育冀北山区次生林，提高次生林生产力提供依据，以冀北山地分布的天然次生林为研究对象，选取代表性的地段并设置面积为20 m×20 m的样地，以均匀布点与多点混合为原则，按照0-20、20-40、40-60 cm土层取样。测定土壤pH值、土壤有机碳（Soil organic carbon，SOC）、全氮（Total nitrogen，TN）、全磷（Total phosphorus，TP）、全钾（Total potassium，TK）、速效磷（Available phosphorus，AP）、速效钾（Available potassium，AK）含量，并计算土壤碳、氮、磷计量比。结果表明：不同深度土层土壤TN与SOC之间保持显著相关（P<0.001），SOC、C∶N与AK之间呈显著正相关（P<0.01）；研究区域冀北山地次生林3层不同深度土壤C∶N平均值（27.74、29.96、29.44）与C∶P平均值（158.86、128.63、119.20）明显高于全国土壤C∶N（11.90）与C∶P（60.00）平均值，N∶P平均值（6.45、4.59、4.70）与全国平均水平（3.56）基本相当，对各深度层土壤N∶P值与土壤TN、TP值进行相关性分析发现，TN值与N∶P的相关性更加显著，说明影响N∶P值的主要因素为氮素量的限制。环境因子对3层不同深度土壤的养分指标分别做出48.64%、53.45%及49.23%的解释比例（P<0.001），因子交互后的解释能力相较因子自身的解释能力更强，地形因子与其他因子相交互后，解释比率分别为其单独解释比例的6.45、8.06、3.21倍。从立地条件角度讲，地形因子能够对土壤养分空间分布产生一定的影响，抚育过程中对地形因子的作用应当予以重视。;In order to explore the effects of natural secondary forest vegetation and site factors on soil nutrient concentration, quantify the ratio of vegetation and site factors on soil nutrition, provide a basis for rationally tending secondary forests in the mountainous area of northern Hebei and improving secondary forest productivity, the natural secondary forests distributed in the mountains of northern Hebei Province were selected as the research object and a representative plot was selected and a sample plot with an area of 20m×20m was selected. The principle of uniform distribution and multi-site mixing was adopted when 0-20 cm, 20-40 cm and 40-60 cm soil layer sampling. Soil pH value (Soil pH value), soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), total potassium (TK), and available phosphorus (AP), available potassium (AK) content were measured in experiment. Based on the results of experiment, soil carbon, nitrogen, and phosphorus stoichiometric ratio were calculated. The results showed that the soil TN and SOC of different depths maintained an extremely significant correlation(P<0.001)among different soil layers, there was also a significant positive correlation between SOC, C∶N and AK(P<0.01).The average values of C∶N ratio of three layers of soils at different depths in the secondary forest in northern Hebei mountainous area (27.74,29.96 and 29.44) and C∶P ratio (158.86, 128.63 and 119.20) were significantly higher than the average level of national soil C∶N (11.90) and C∶P (60.00).Besides, N∶P averages (6.45, 4.59 and 4.70) was basically equivalent to the national average (3.56). The correlation analysis of the soil N∶P value and the soil TN and TP values of each depth layer showed that the correlation between the TN value and the N∶P value was more significant, indicating that the factor why N∶P value was affected was the limitation of nitrogen. Environmental factors accounted for 48.64%, 53.45%, and 49.23% of soil nutrient index of the three layers of soil at different depths (P<0.001). The explanatory power after the factor interaction was stronger than that of the factor itself. After interacting with other factors, the explanatory ratios of terrain factors were 6.45, 8.06, and 3.21 times of the separate ones. From the perspective of site conditions, topographical factors did have a certain impact on the spatial distribution of soil nutrition, and the role of topographical factors in the process of tending should be paid attention to.

Epigeal fauna and soil attributes in a cover-cropped organic vegetable system

ABSTRACT: This study assessed the effect of cover crop biomass on the epigeal fauna of an organic eggplant (Solanum melongena L.) cropping system. A randomized block design was used, with four cover crop treatments: brachiaria, crotalaria, millet, and cocktail (brachiaria, crotalaria and millet). The epigeal faunal indices were determined at each plot. The epigeal fauna of a secondary forest site was also assessed for comparison. Epigeal individuals were collected using pitfall traps at two sampling periods (110 and 180 days after mowing cover crops). Soil samples were collected for determination of physical and chemic properties. 2032 individuals were captured in the first sampling and 3806 individuals in the second. The highest values of wealth in the first collection were observed in the millet and cocktail areas. Cluster analysis showed similarity of epigeal faunal groups between millet and brachiaria plots at the first sampling and between cocktail and crotalaria sites at the second sampling. Co-inertia analysis showed a significant covariance between epigeal fauna at the second sampling and soil properties. The cover crops management had a beneficial influence on the activity, wealth and ecological indexes, in both sampling periods. The positive association observed between epigeal faunal groups and soil physical and chemical properties demonstrates the efficiency of cover crops in improving soil quality in organic cropping systems.