Selective cutting of woody species in a Mexican tropical dry forest: Incompatibility between use and conservation

A major challenge of forest management is to maintain the biodiversity and integrity of the forests while at the same time satisfying human needs through productive activities. While selective extraction of natural resources has less severe consequences on biodiversity and ecosystem function than complete removal of vegetation, such consequences need to be evaluated in detail. “Varas” or stems cut from small trees of tropical dry forests (TDF) in the Pacific Coast of Mexico have been used as plant support stakes in horticultural fields (mainly tomato crops) since the middle of the last century. In this study, we evaluated the effects of selective cutting of plant support stakes on the diversity of woody vegetation of a TDF in northwestern Mexico. Stakes were cut by local harvesters before our assessment of cutting effects. In each of three cutting treatments (T₀ = uncut, T₁ = one cut event, and T₂ = two cut events), we established three sampling plots each consisting of ten 50 m × 2 m parallel transects. All woody plants (stems ≥1.0 cm diameter at 1.3 m height, DBH) were identified and measured on each transect. Species richness (S) decreased as the number of cuts increased (T₀ = 65 species, T₁ = 50 species, and T₂ = 38 species). The Simpson (C) and the Shannon (H′) diversity indices, as well as the rarefaction curves and non-parametric estimates of diversity (Chao1 and ACE) confirmed this tendency of change. Comparison of dominance–diversity curves showed that the woody plant community loses equitability with every additional stake cutting event. The total number of stake providing species did not vary notably across treatments (T₀ = 8 species, T₁ = 9 species, and T₂ = 7 species), but four species reduced their dominance considerably in T₂, while Croton septemnervius, the most used species, increased its abundance and relative basal area with each additional stake harvest, reaching a representation of more than 59% of total number of stems in T₂. The reduction in species diversity, changes in patterns of dominance, and the proliferation of species associated to disturbed sites suggest that current practices of selective cutting require adjustments to make this forest management application more consistent with local conservation of woody plant species diversity and community structure.     

Effect of human disturbance on the structure and regeneration of forests in the Nevado de Toluca National Park, Mexico

Sample plots were established in the principal forest types in the the Nevado de Toluca National Park, Mexico including those dominated by Pinus hartwegii, Abies religiosa, Quercus laurina and Alnus jorullensis. The vertical structure was defined by three strata in the coniferous forests and two strata in the broadleaved forests. Timber harvesting in Abies religiosa and Quercus laurina forests and fires generated by humans in Pinus hartwegii forests impeded the recruitment of saplings. Mature trees were also heavily impacted by logging in Pinus hartwegii forests. On the contrary, Alnus jorullensis forests were increasing due to the disturbance of Pinus and Quercus forests, as well abandoned crop lands within the park. A combination of logging, uncontrolled fire, and grazing appears to be compromising the recruitment of important tree species in this national park. These factors, together with human settlements, have also increased the proportion of early successional species. Changes in forest structure from human disturbance indicate a need to control these activities if conservation goals are not to be compromised.     

Composition,structure and diversity of phyllostomid bat assemblages in different successional stages of a tropical dry forest

Studies on successional dynamics in tropical systems have mostly focused on plant communities and mainly have been conducted in tropical humid areas. Here, we document changes in the structure of bat assemblages among secondary successional stages of a neotropical dry forest. We specifically focused on the speciose phyllostomid bat family, comprising most of the foraging guilds found among neotropical bats, including nectarivores and frugivores that play important roles in processes of plant reproduction and forest regeneration. To investigate bat species richness, diversity and abundance during successionnal processes, we mist-netted bat assemblages in 12 sites belonging to 4 different successional stages, namely pastures (0 yrs), early (3–5 yrs), intermediate (8–12 yrs) and late successional stage (>50 yrs). A capture effort of 142 nights using five mist-nets per night yielded 606 phyllostomid bats belonging to 16 species. Late stage was the most speciose sustaining all species found in the study (16 species against 9 for early and intermediate stages and 4 in pastures), and was the only environment where rare species occurred. Species found within any one successional stage were a combination of species found at the previous stage plus additional ones. This additive pattern appeared to be driven by the natural abundance of species, as the abundant species were found across more succesisonal stages than rarer species. Bats were significantly less speciose and less abundant in pastures, regardless of the foraging guild. Bat diversity and abundance did not differ significantly among early, intermediate and late stages. However, nectarivores were more abundant in early compared to late stage, probably as a consequence of differences in patterns of food availability. We conclude that areas of forest, recognized as late stage in our study, are the most important reservoirs of species richness. Secondary vegetation also contains diverse bat assemblages, while pastures only harbour a few abundant and vagile species occasionally crossing this habitat. We suggest that land-use regulations in this region focus on maintaining connectivity of a mosaic of areas of secondary and mature vegetation to insure the conservation of bat diversity as well as their important ecological interactions.     

Edge effects on soil seed banks and understory vegetation in subtropical and tropical forests in Yunnan,SW China

Human-induced forest edges are common in many forest landscapes throughout the world. Forest management requires an understanding of their ecological consequences. This study addressed the responses of three ecological groups (non-forest species, secondary forest species and primary forest species) in edge soil seed banks and edge understory vegetation, and explored the relationship between the invasion of non-forest species in edge understory vegetation and the accumulation of their seeds in edge soil seed banks. The soil seed banks and understory vegetation were sampled along transects established at the edges of a continuous subtropical evergreen broad-leaved forest tract (Lithocarpus xylocarpus forest) bordering anthropogenic grasslands and three tropical seasonal rain forest fragments (Shorea wantianshuea forest) bordering fallows. Species composition in both soil seed banks and understory vegetation showed great difference among edge sites. In soil seed banks, the dominance (relative abundance and relative richness) of each ecological group did not change significantly along the edge to interior gradient. In understory vegetation, the invasion of non-forest species concentrated on the first several meters along the edge to interior gradient. The dominance of secondary forest species decreased with distance from the edge, while the dominance of primary forest species increased with distance from the edge. In forest edge zones, the invasion of a majority of non-forest species in understory vegetation lags behind the accumulation of their seeds in soil seed banks. Forest edges do not act as a good barrier for the penetration of non-forest species seeds. The lack of non-forest species in understory vegetation must then be due to conditions that are not appropriate for their establishment. Therefore, to prevent germination and survival of non-forest species further into the forest, management should focus on maintaining interior forest conditions.     

Contemporary climate infuence on variability patterns of Anadenanthera colubrina var. cebil,a key species in seasonally dry tropical forestsOA

The distribution of many plant species has been shaped by climate changes, and their current phenotypic and genetic variability refect microclimatically suitable habitats. This study relates contemporary climate to variability patterns of phenotypic traits and molecular markers in the Argentinean distribution of Anadenanthera colubrina var.cebil, as well as to identify the most relevant phenotypic trait or molecular marker associated with those patterns.Individuals from four populations in both ...     

Contribution of participatory forest management towards conservation and rehabilitation of dry Afromontane forests and its implications for carbon management in the tropical Southeastern Highlands of Ethiopia

Participatory forest management (PFM) has been applied as an approach to create a framework for collaborative forest management between local communities and government forestry agencies. This study was designed to assess the contribution of PFM approach in improving forest status in the Southeastern Highlands of Ethiopia. Landsat satellite imageries of four years were used to evaluate the trends and rate of deforestation before and after PFM interventions. Socio-economic data were collected from sample household surveys, key participants, focus group discussions, and field observations. The results showed that there was high rate of deforestation before PFM intervention as forestland has decreased by 19% (2531 ha) between 1990 and 2000. However, after the PFM intervention (2000–2016), the forest cover has increased by 247 ha (2.2%). During this period, net 1016 ha of shrub-lands were converted into forestland owing to significant forest regeneration. In addition, most sampled households (94% and 96% from lower and upper altitudes, respectively) perceived that PFM had significantly contributed to improve forest regeneration in their locality. This study revealed that PFM can serve as a stepping stone for carbon financing mechanisms to reduce greenhouses emission and enhance carbon sinks via forest resources.     

Comparison of soil physical properties in evergreen and deciduous forests in central Cambodia

We investigated soil physical properties in three forest types in tropical lowland monsoon forests in central Cambodia under the same climatic conditions, i.e., Kanhaplic Haplustults in dry evergreen forest (KH-E), Arenic Haplustults in dry deciduous forest (AH-D), and Arenic Ultic Alorthods in mixed evergreen–deciduous forest (AA-M), to clarify the relationship between forest types and soil physical properties. The clay content was correlated with water content at ψ = −9.8 and −1500 kPa (WC10 and WC1500), available water capacity (AWC), and the van Genuchten (vG) parameter N (P < 0.01). vG parameter N was in the order AH-D > AA-M > KH-E whereas vG parameter α had a high value in KH-E soil at 0–100 cm in depth. The cumulative AWC (AWCcl, mm) at a soil depth of 0–200 cm was higher in the AH-D than in the KH-E, and was not considered a major factor affecting the distribution of different forest types under the same climatic conditions. The unsaturated hydraulic conductivity (K) at 0–100 cm in depth, estimated by use of models, was higher in AH-D than in KH-E mostly at matric potential ψ > −10 kPa. The low K in KH-E at ψ > −10 kPa was considered favorable for evergreen trees to retain the soil water for the transpiration in the dry season, and the matric potential in KH-E showed more gentle decreases in the early dry seasons than AH-D. Thus the differences in K among generally sandy soil types could possibly affect the establishment of different forest types in the study area with the same climate.     

Effects of land use change on biodiversity and ecosystem services in tropical montane cloud forests of Mexico

Tropical montane cloud forests deliver important goods and services to society, such as timber, the supply and purification of fresh water, and carbon sequestration. In spite of their relevance, current deforestation rates are very high, at the expense of affecting the provision of ecosystem services. We explore the impact of land use change in terms of provision of ecosystem services by following two approaches, one very detailed (focused on hydrological services – water quality) and another one with a broader perspective (at a large scale and considering the ecosystem service value (ESV) of several ecosystems and their ecosystem services at the same time). In the highlands of the State of Veracruz, previously forested lands were converted into coffee plantations and cattle ranches. To evaluate the role of species composition and community structure on water quality, we studied nine small watersheds (<15 ha) covered by pristine cloud forest, coffee plantations and cultivated grassland (three each). Species richness of the three land use types was similar, although species composition was as different as 90%. Overall species diversity as well as that of woody species, and growth form diversities decreased in the transformed land uses. Water quality of streams flowing through these watersheds declined: nutrients (nitrate), conductivity, cations, chloride and suspended solids were lowest in the forest streams and highest in streams from coffee watersheds, whereas grasslands were intermediate. We also calculated ecosystem service values (using the transfer value method) and estimated economic market–non-market gains and losses owing to land transformation. Loss of natural ecosystems may imply a significant economic loss to society in terms of ecosystem services, although market gains may still lead land owners to land conversion because revenues are higher. Adequate Payment for Ecosystem Services may be a good option to prevent deforestation, but the compensation should be at least equal to the opportunity cost of the promoted land use. Our estimates are indicative of the urgent need to go beyond water quantity as the most relevant ecosystem service considered in PES schemes.     

Comparison between old-growth stands and secondary stands regenerating after clear-felling in warm-temperate forests of Yakushima, southern Japan

In order to infer successional changes in structure, species composition and diversity of warm-temperate forest, we compared secondary stands regenerating after clear-felling (41–64-years old) with old-growth stands at altitudes between 300 and 800 m on Yakushima Island, southern Japan. Stem density and maximum stem diameter differed between secondary and old-growth stands, but basal area and aboveground biomass did not. At lower altitudes, the dominant species in old-growth stands with a strong sprouting capacity (Castanopsis cuspidata) also dominated secondary stands, and species composition of secondary and old-growth stands was similar. At higher altitudes, by contrast, the dominant species in old-growth stands (Distylium racemosum) had little sprouting capacity and was poorly represented in diverse secondary stands, which were dominated by Castanopsis or other less abundant species. Secondary stands had greater species diversity (Shannon–Wiener index) than old-growth stands, particularly at higher altitudes. This was due to greater species richness resulting from higher stem density per area, but not to greater evenness. We grouped the component species that share ecologically similar traits into four guilds (fagaceous, primary evergreen, secondary evergreen and deciduous species). Secondary stands were characterized by greater numbers of deciduous and secondary evergreen species. We concluded that different sprouting capacities of dominant species and different regeneration traits among guilds are responsible for the change in species composition and diversity during succession.     

Sustainability of tropical dry forests: Two case studies in southeastern and central Brazil

In this study, we review the current available information on the social–ecological context of Brazilian tropical dry forests (TDFs), a vegetation type that covers approximately 3% of the country territory. For this purpose, we conducted a comparative analysis of two case studies, one study in the north of Minas Gerais state and the other in Paranã River Basin, situated in southeastern and central Brazil, respectively. We compiled published bibliographical and census-based data for the two regions, concerning the historical human occupation and land use and the environmental and development policies affecting TDF management and sustainable use. Brazilian TDFs usually occur in semi-arid climates, and have been intensely converted mainly to extensive pasturelands in large farms, thus leading to high income concentration in those areas. Our case studies involve less-developed regions that support populations with very low human development indices, which is the norm for Brazilian TDFs. Many of these are traditional populations, such as indigenous and slave descendents, with peculiar cultural practices only recently considered in government policies proposed for the forest management. Though the two regions have similar land use histories, current social–ecological scenarios are very different. In the north of Minas Gerais, TDF conversion policies were debated intensely for the last 15 years, recently resulting in a state law specifically generated to regulate TDF use. Also, this region has 20 conservation units (CUs), some of them delimited inside the territories of the several traditional populations that inhabit TDF areas. This process caused enduring conflicts that can affect both CUs’ effectiveness and the sustenance of these populations. In the Paranã River Basin, there is no specific policy towards TDFs, whose use is regulated by the 43-year-old Brazilian Federal Forest Code. There are only four CUs in this region, and most traditional populations were expelled from their original territories and consequently lost their cultural identity. Government sustainability strategies are limited to the establishment of CUs, a response that may disregard social demands and cultural practices, depending on the local context. Given the uniqueness and threat level to TDFs, specific and more diversified policies towards land use should be established for these ecosystems in order to stimulate low-impact activities that maintain ecosystem services and improve the livelihoods of TDF inhabitants.     

Ecology and regeneration of tropical dry forests in the Americas: Implications for management

Dry forests represent the most endangered ecosystem in tropical regions and continue to be one of the most sought after environments for human colonization, development and production. In spite of this, dry forests are one of the least well studied tropical habitats. This special issue is dedicated to reviewing much of the information that exists about tropical dry forest in the Americas. The introduction summarizes the articles presented herein, highlighting management strategies that are suggested throughout the special issue that may be useful for conserving tropical dry forest environments.     

Diversity and structure of regenerating tropical dry forests in Costa Rica: Geographic patterns and environmental drivers

Much of the dry tropical forest biome has been converted to agricultural land uses over the past several centuries. However, in conservation areas such as those in the Guanacaste and Tempisque regions of Costa Rica, tropical dry forests are regenerating due to management practices including fire suppression. To better understand the patterns of secondary succession occurring in Costa Rican tropical dry forest, we established 60 20 × 50 m plots in mature and regenerating forests in the Sector Santa Rosa (formerly known as Parque Nacional Santa Rosa) and Palo Verde National Park. Plots were stratified into three plant communities: tropical dry oak forest (Quercus oleoides) (SROAK), Santa Rosa tropical dry forest (SRTDF), and Palo Verde tropical dry forest (PVTDF). In these plots we measured and identified and all individuals >10 cm DBH, measured but did not identify stems <10 cm but taller than 1.3 m, counted woody seedlings (<1.3 m height) and analyzed soil chemical and physical properties.     

Influence of climatic conditions,topography and soil attributes on the spatial distribution of site productivity index of the species rich forests of Jalisco,Mexico

This paper presents an approach based on field data to model the spatial distribution of the site productivity index （SPI） of the diverse forest types in Jalisco, Mexico and the response in SPI to site and cli-matic conditions. A linear regression model was constructed to test the hypothesis that site and climate variables can be used to predict the SPI of the major forest types in Jalisco. SPI varied significantly with topog-raphy （elevation, aspect and slope）, soil attributes （pH, sand and silt）, climate （temperature and precipitation zones） and forest type. The most important variable in the model was forest type, which accounted for 35% of the variability in SPI. Temperature and precipitation accounted for 8 to 9% of the variability in SPI while the soil attributes accounted for less than 4% of the variability observed in SPI. No significant differences were detected between the observed and predicted SPI for the individual forest types. The linear regression model was used to develop maps of the spatial variability in predicted SPI for the individual forest types in the state. The spatial site productivity models developed in this study provides a basis for understanding the complex relationship that exists between forest productivity and site and climatic conditions in the state. Findings of this study will assist resource managers in making cost-effective decisions about the management of individual forest types in the state of Jalisco, Mexico.     

Changes in soil properties and vegetation characteristics along a forest-savanna gradient in southern Venezuela

Vegetation cover in the Gran Sabana highlands (southern Venezuela) appears as a complex mosaic of tall to low forests, bush vegetation and savannas. In this study we described the changes in structure and floristic composition along a forest-savanna gradient consisted of tall forest (TF), medium forest (MF), low forest (LF) and open savanna (S), and analyse the possible reasons for the observed changes. The results showed no obvious differences in the soils properties along the vegetation gradient. All sites presented shallow soils (<50 cm depth) with high percentage of sand and with dominance of quartz, kaolinite and oxides of iron and aluminum. The soil chemical characteristics were unfavorable and similar along the vegetation gradient. The major soil difference was related with the presence of an organic layer on the soil surface of TF and MF and their absence on the soils of LF and S. Abundant residues of large trees were found on the forest floor of TF, MF and LF. These residues presented no signs of burning in TF, while in MF and particularly in LF were charred. This observation joined to the presence of charcoal within the mineral soil of S and the absence of the organic surface layer in LF and S indicated that fire has affected with different intensity or frequency the studied vegetation gradient. Large differences in the structure and floristic composition were found between TF, MF, LF and S. These differences could not be explained by changes in the mineralogical and chemical characteristics of the soil but only by fire which triggers the conversion. We concluded that the studied vegetation gradient represents stages in a temporal change from forest to savanna caused by fire, and this change has implied an impoverishment of tree species, a drastic reduction of biomass in terms of basal area, a drastic change of the floristic composition and the loss of the organic surface layer, which play an important role to maintain the fertility of these soils.     

Composition,structure, and management potential of secondary dry tropical vegetation in two abandoned henequen plantations of Yucatan,Mexico

Data on the composition and stand dynamics of abandoned henequen (Agave fourcroydes) fields of different ages are presented and their management potential discussed. The study was carried out in the Hacienda of Kancabchen, Yucatan, Mexico in 12- and 26-year-old secondary forests. Species richness and diversity were greater as the stand grew older. Even though 73% of species have the capacity to regenerate from coppiced shoots, only between 30 and 50% of the individuals actually regenerate from coppiced shoots in both communities, respectively. According to the Sørensen similarity index both stands are similar in composition (73%), while the Motyka index indicates that they differ in biomass distribution (17%). This could be due to soil conditions and the management of these areas, or a combination of both. The 26-year-old abandoned henequen stand still has pioneer species dominating and has very few late successional species present. Slow-growing tree species on the 26-year-old stand were expected, but their absence could be due to the lack of seed sources, a limited dispersal capability, or to an arrested succession due to human perturbation and management. Eight species dominated the stands, accounting for more than 60% of the total importance values. Most species present in both stands are widely used locally and are commercialized inside the rural communities. Potential management strategies could involve forest thinning to remove competition and favor those species used by the communities, those with potential to increase soil fertility, and those that could have semi-commercial purposes. Management could also include enrichment with other species such as Cedrela odorata and Apoplanesia paniculata that are widely used and were previously present as part of the native vegetation of the area.     

Succession and management of tropical dry forests in the Americas: Review and new perspectives

Understanding tropical forest succession is critical for the development of tropical forest conservation strategies worldwide, given that tropical secondary forests can be considered the forests of the future. Tropical dry forests (TDF) are among the most threatened tropical ecosystems, there are more secondary forests and forest restoration efforts that require a better understanding of successional processes. The main goal of this synthesis for this special issue on the ecology and management of tropical dry forests in the Americas is to present a summarized review of the current knowledge of the ecology and management implications associated to TDF succession. We explore specific issues associated to tropical dry forest succession with emphasis on the use of chronosequences, plant diversity and composition, plant phenology and remote sensing, pollination, and animal–plant interactions; all under the integrating umbrella of ecosystem succession. We also emphasize the need to conduct socio-ecological research to understand changes in land-use history and its effects on succession and forest regeneration of TDF. We close this paper with some thoughts and ideas associated with the strong need for an integrating dimension not considered until today: the role of cyberinfrastructure and eco-informatics as a tool to support sound conservation, management and understanding of TDF in the Americas.     

Diversity of secondary woody species in relation to species richness and cover of dominant trees in thermophilous deciduous forests

One of the prominent compositional features of thermophilous deciduous forests of southern Europe is their richness in secondary woody species (AWS). To date, no studies have focused on the diversity and contribution to the ecosystem functions and socio-economic benefits provided by these species. Here, we first characterized species richness and diversity for three main functional groups of AWS, sporadic trees, shrubs and vines, in 53 representative stands of central Italy. Secondly, we explored variations in AWS diversity and composition along a four-level gradient of species richness of dominant trees under comparable site conditions. The 40 AWS taxa recorded showed a remarkable taxonomic singularity at both the genus and the family rank. Dominant tree species richness had no significant effect on AWS species richness and composition, while Shannon diversity of AWS, especially shrubs, was associated with cover of the dominant trees. Each AWS possessed, on average, ca. five ability traits over a total of 13 considered that contributed to important ecosystem functions or expected socio-economic benefits such as wood and food production, conservation of genetic resources (wild crop relatives) and ornamentals. This highlights the key role of AWS, and in particular of sporadic trees, for enhancing multifunctionality of thermophilous deciduous forests.     

Interacting effects of canopy gap, understory vegetation and leaf litter on tree seedling recruitment and composition in tropical secondary forests

We experimentally investigated interacting effects of canopy gaps, understory vegetation and leaf litter on recruitment and mortality of tree seedlings at the community level in a 20-year-old lowland forest in Costa Rica, and tested several predictions based on results of previous studies. We predicted that experimental canopy gaps would greatly enhance tree seedling recruitment, and that leaf litter removal would further enhance recruitment of small-seeded, shade-intolerant seedlings in gaps. We created a large (320–540 m²) gap in the center of 5 out of 10 40 m × 40 m experimental plots, and applied the following treatments bimonthly over a 14-month-period in a factorial, split–split plot design: clipping of understory vegetation (cut, uncut), and leaf litter manipulations (removal, addition, control). As expected, experimental gaps dramatically increased tree seedling recruitment, but gap effects varied among litter treatments. Litter addition reduced recruitment in gaps, but enhanced recruitment under intact canopy. Species composition of recruits also differed markedly between gap treatments: several small-seeded pioneer and long-lived pioneer species recruited almost exclusively in gaps. In contrast, a few medium-to-large-seeded shade-tolerant species recruited predominantly under intact canopy. Leaf litter represents a major barrier for seedling emergence and establishment of small-seeded, shade-intolerant species, but enhances emergence and establishment of large-seeded, shade-tolerant species, possibly through increased humidity and reduced detection by predators. Periodic clipping of the understory vegetation marginally reduced tree seedling mortality, but only in experimental gaps, where understory vegetation cover was greatly enhanced compared to intact canopy conditions. Successful regeneration of commercially valuable long-lived pioneer trees that dominate the forest canopy may require clear-cutting, as well as weeding and site preparation (litter removal) treatments in felling clearings. Management systems that mimic natural canopy gaps (reduced-impact selective logging) could favor the regeneration of shade-tolerant tree species, potentially accelerating convergence to old-growth forest composition. In contrast, systems that produce large canopy openings (clear-cutting) may re-initiate succession, potentially leading to less diverse but perhaps more easily managed “natural plantations” of long-lived pioneer tree species.     

Contributions of root and stump sprouts to natural regeneration of a logged tropical dry forest in Bolivia

A major impediment to the sustainable management of tropical dry forests in Bolivia is the scarcity of natural regeneration of commercial timber tree species. Where regeneration is present, true seedlings of many species are outnumbered by vegetative sprouts from roots, broken stems, and the stumps of felled trees. This study evaluates the importance of resprouts promoted by logging operations for the regeneration of commercially important canopy tree species. The objectives of the study were: (1) to characterize stump and root sprouting behaviors of canopy tree species harvested for timber; (2) to quantify the effect of logging on relative abundances and growth rates of stump sprouts, root sprouts, and true seedlings; (3) to relate the species-specific probabilities of stump sprouting to stump diameter and stump height; and (4) to explore how sprouting varies with the ecological requirements of canopy tree species. The study was carried out 1–5 years after logging of a privately owned land in a Bolivian tropical dry forest. Twenty-seven of the 31 species monitored resprouted at least occasionally, among which Centrolobium microchaete (Leguminosae-Fabaceae) and Zeyheria tuberculosa (Bignoniaceae) were the most frequent stump sprouters, and Acosmium cardenasii (Leguminosae-Fabaceae) and C. microchaete were the most frequent root sprouters. In all species the number of sprouts declined with increasing stump diameter and stump height. The probability of stump resprouting differed among species but did not vary consistently with stump diameter, except in Z. tuberculosa in which it declined. Approximately 45% of juveniles <2 m tall of canopy tree species originated from root or stem sprouts. Light-demanding species tended to regenerate more from seeds and root sprouts than from stumps. Seedling densities were higher in microsites opened by logging, while root and stem sprouts were equally common across microsites. Given their abundance and the fact that root and stem sprouts at least initially grew faster than true seedlings, we conclude that vegetative regeneration in this tropical dry forest is an important mode of post-logging regeneration especially for species that regenerate poorly from seed. Resprout management should be considered as a potentially effective strategy for the procurement of regeneration following logging, especially for species that do not readily recruit from seed.     

Seasonal and spatial variation of nitrogen dynamics in the litter and surface soil layers on a tropical dry evergreen forest slope

Seasonal and spatial variability of litterfall and NO₃⁻ and NH₄⁺ leaching from the litter layer and 5-cm soil depth were investigated along a slope in a tropical dry evergreen forest in northeastern Thailand. Using ion exchange resin and buried bag methods, the vertical flux and transformation of inorganic nitrogen (N) were observed during four periods (dry, early wet, middle wet, and late wet seasons) at 15 subplots in a 180-m × 40-m rectangular plot on the slope. Annual N input via litterfall and inorganic N leached from the litter layer and from 5-cm depth soil were 12.5, 6.9, and 3.7 g N m⁻² year⁻¹, respectively, whereas net mineralization and the inorganic N pool in 0–5-cm soil were 7.1 g N m⁻² year⁻¹ and 1.4 g N m⁻², respectively. During the early wet season (90 days), we observed 82% and 74% of annual NO₃⁻ leaching from the litter layer and 5-cm soil depth, respectively. Higher N input via leaf litterfall in the dry season and via precipitation in the early wet season may have led to higher NO₃⁻ leaching rate from litter and surface soil layers during the early wet season. Large spatial variability in both NO₃⁻ vertical flux and litterfall was also observed within stands. Small-scale spatial patterns of total N input via litterfall were significantly correlated with NO₃⁻ leaching rate from the surface soil layer. In tropical dry evergreen forests, litterfall variability may be crucial to the remarkable seasonal changes and spatial variation in annual NO₃⁻ vertical flux in surface soil layers.