Effect of recurrent fires on soil nutrient dynamics in a tropical dry deciduous forest of Western Ghats,India

The role of forest fires in the soil dynamics and global carbon cycle has not been comprehensively studied in tropical forests as the effects of fire on tropical forest soils can be extremely variable. This study was aimed to understand how repeated fires affect physical and chemical properties of soil in a tropical dry deciduous forest and alter soil fertility and health. The study was carried out in the dry deciduous forest of Mudumalai Tiger Reserve. Soil samples were collected from unburned (B0) to six-time burned (B6) plots. Samples were collected from each plot from three different depths viz. 0–10 (Top), 10–20 (Middle), and 20–30 cm (Bottom) and analyzed for soil physical and chemical properties. Soil pH, EC, WHC decreased with increasing fire frequencies while bulk density increased. Organic Carbon, Total N, and available P decreased with increasing fire frequencies whereas extractable K initially increased but decreased with the very high frequency of fires. NO₃^?N slightly decreased with high fire frequencies but NH₄^?N decreased significantly with increasing fire frequency. These results provide a new insight regarding the influence of repeated fires on soil that will be valuable to understand the effect of fire on the recovery of soils and nutrient dynamics.     

Carbon density and accumulation in woody species of tropical dry forest in India

We studied the carbon density and accumulation in trees at five sites in a tropical dry forest (TDF) to address the questions: how is the TDF structured in terms of tree and carbon density in different DBH (diameter at breast height) classes? What are the levels of carbon density and accumulation in the woody species of TDF? Is the vegetation carbon density evenly distributed across the forest? Does carbon stored in the soil reflect the pattern of aboveground vegetation carbon density? Which species in the forest have a high potential for carbon accumulation? The WSG among species ranged from 0.39 to 0.78 g cm⁻³. Our study indicated that most of the carbon resides in the old-growth (high DBH) trees; 88-97% carbon occurred in individuals ?19.1 cm DBH, and therefore extra care is required to protect such trees in the dry forest. Acacia catechu, Buchanania lanzan, Hardwickia binata, Shorea robusta and Terminalia tomentosa accounted for more than 10 t ha⁻¹ carbon density, warranting extra efforts for their protection. Species also differed in their capacity to accumulate carbon indicating variable suitability for afforestation. Annually, the forest accumulated 5.3 t-C ha⁻¹ yr⁻¹ on the most productive, wettest Hathinala site to 0.05 t-C ha⁻¹ yr⁻¹ on the least productive, driest Kotwa site. This study indicated a marked patchy distribution of carbon density (151 t-C ha⁻¹ on the Hathinala site to 15.6 t-C ha⁻¹ on the Kotwa site); the maximum value was more than nine times the minimum value. These findings suggest that there is a substantial scope to increase the carbon density and accumulation in this forest through management strategies focused on the protection, from deforestation and fire, of the high carbon density sites and the old-growth trees, and increasing the stocking density of the forest by planting species with high potential for carbon accumulation.     

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.     

Anthropogenic disturbances and status of forest and wildlife in the dry deciduous forests of Chhattisgarh state in India

The advent of modern forces and the changes in socioeconomic patterns of forest dwellers have increased the pressures on the forests. In order to mitigate such pressures and also to protect the forests and wildlife the model of protected areas networks has shifted and enhanced such pressures in the unprotected natural forests due to several reasons. Being a low profile category of protected status and continuous human settlements, the present study highlights the case of dry deciduous forests of Sarguja district of Chhattisgarh state of India. The major objectives of this study were to quantify the status of forests and wildlife and also to determine the extent of anthropogenic disturbances faced by the dry deciduous forests of central India. Transect and silent drive count methods were used for sampling wildlife and quadrat method was used for sampling vegetation. Besides, the local uses of various forest produces were also studied in view of understanding the people dependency on forests. The forest vegetation, in the study area, was pre-dominated by Shorea robusta, which had Madhuca indica, Diospyrus melanoxylon and Buchnania lanzan as the major companion species. The forest had either the high girth class mature tree species or the saplings. The low vegetation cover and density were due to the high anthropogenic pressures mainly in the form of heavy livestock grazing and collection of ethnobotanically important species. The study though reveals that the area is not rich in wildlife and the forest is fragmented, the area still supports some important species, which include many rare and endangered plants and animals. The findings of this study have been discussed in view of the management and conservation of the forest and wildlife in the dry deciduous forests.     

Soil carbon stock assessment in the tropical dry deciduous forest of the Sathanur reserve forest of Eastern Ghats,India

Climate change and carbon mitigation through forest ecosystems are some of the important topics in global perspective. Tropical dry forests are one of the most widely distributed ecosystems in tropics, which remain neglected in research. The soil organic carbon (SOC) stock was quantified on a large scale (30 1-ha plots) in the dry deciduous forest of the Sathanur reserve forest of Eastern Ghats. The SOC stock ranged from 16.92 to 44.65 Mg/ha with a mean value of 28.26 ± 1.35 Mg/ha. SOC exhibited a negative trend with an increase in soil depth. A significant positive correlation was obtained between SOC stocks and vegetation characteristics viz. tree density, shrub basal area, and herb species richness, while a significant negative correlation was observed with bulk density. The variation in SOC stock among the plots obtained in the present study could be due to differences in tree abundance, herb species richness, shrub basal area, soil pH, soil bulk density, soil texture etc. The present study generates a large-scale baseline data of dry deciduous forest SOC stock, which would facilitate SOC stock assessment at the national level as well as to understand its contribution on a global scale.     

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.     

Temporal patterns of storage and flux of N and P in young Teak plantations of tropical moist deciduous forest,India

Teak(Tectona grandis Linn.f.) ranks among the top five tropical hardwood species and is being promoted for use in plantations in its non-native range due to its high economic value.However,there is a general lack of data on ecosystem functioning of teak plantations.We aimed at understanding storage and flux of nutrients related to young plantations of teak.Cycling of nitrogen(N) and phosphorus(P) in a chronosequence of plantations(1,5,11,18,24 and 30 years) was studied in the Moist Deciduous Forest Region of North India with the objective of investigating the nutrient cycling pattern at younger age since the current trend of harvesting age of the species in several tropical countries is being drastically reduced for quick return from this high value crop.Standing state,nutrient uptake,nutrient return and nutrient retranslocation in these plantations were estimated by tree harvesting and chemical analysis methods.The range of total standing nutrient across all these plantations was 20.3 to 586.6 kg·ha-1 for N and 5.3 to 208.8 kg·ha-1 for P.Net uptake of N ranged from 19.4 to 88.9 kg·ha-1·a-1 and P from 3.8 to 18.1 kg·ha-1·a-1.Retranslocation of N and P among all the stands ranged from 8.7 to 48.0 kg·ha-1·a-1 and 0.01 to 3.5 kg·ha-1·a-1,respectively.Range of total nutrient return was 25.8 to 91.3 kg·ha-1·a-1 for N and 2.7 to 10.1 kg·ha-1·a-1 for P.N and P use efficiency was between 107.4 and 192.5 g dry organic matter(OM) g-1 N,and 551.9 and 841.1 g OM g-1 P,respectively.The turnover time ranged from 2.04-13.17 years for N and between 2.40-22.66 years for P.Quantity of N and P in the soil nutrient pool ranged from 2566.8 to 4426.8 kg·ha-1 and 372 to 520 kg·ha-1,Storage and flux of components in different plant parts of different aged plantations were assessed and depicted in compartment models.Percentage storage in soil,litter and vegetation ranged from 82% to 99%,0.6% to 2.4% and 0.5% to 15% for N,respectively,and from 63% to 98%,0.5% to 2% and 1% to 35% for P,respectively.This information could be useful in managing external nutrient manipulation to crops of different ages for optimum biomass production or carbon sequestration.     

Relationship between annual rainfall and tree mortality in a tropical dry forest: Results of a 19-year study at Mudumalai,southern India

Variability in rainfall is known to be a major influence on the dynamics of tropical forests, especially rates and patterns of tree mortality. In tropical dry forests a number of contributing factors to tree mortality, including dry season fire and herbivory by large herbivorous mammals, could be related to rainfall patterns, while loss of water potential in trees during the dry season or a wet season drought could also result in enhanced rates of death. While tree mortality as influenced by severe drought has been examined in tropical wet forests there is insufficient understanding of this process in tropical dry forests. We examined these causal factors in relation to inter-annual differences in rainfall in causing tree mortality within a 50-ha Forest Dynamics Plot located in the tropical dry deciduous forests of Mudumalai, southern India, that has been monitored annually since 1988. Over a 19-year period (1988–2007) mean annual mortality rate of all stems >1 cm dbh was 6.9 ± 4.6% (range = 1.5–17.5%); mortality rates broadly declined from the smaller to the larger size classes with the rates in stems >30 cm dbh being among the lowest recorded in tropical forest globally. Fire was the main agent of mortality in stems 1–5 cm dbh, elephant-herbivory in stems 5–10 cm dbh, and other natural causes in stems >10 cm dbh. Elephant-related mortality did not show any relationship to rainfall. On the other hand, fire-related mortality was significantly negatively correlated to quantity of rainfall during the preceding year. Mortality due to other causes in the larger stem sizes was significantly negatively correlated to rainfall with a 2–3-year lag, suggesting that water deficit from mild or prolonged drought enhanced the risk of death but only with a time lag that was greater than similar lags in tree mortality observed in other forest types. In this respect, tropical dry forests growing in regions of high rainfall variability may have evolved greater resistance to rainfall deficit as compared to tropical moist or temperate forests but are still vulnerable to drought-related mortality.     

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.     

尼加拉瓜Chacocente野生动物保护区三种干旱落叶阔叶树种的天然更新动态(英文)

在尼加拉瓜Chacocente野生动物保护区对极又平荚木,毛风铃木和Lonchocarpus minimiflorus(Donn.Sm.)树种的天然更新进行了调查,并分析了更新异质性与地形坡度和入射光的关系。从2001到2003连续3年记录了高度10m以下和直径10cm以下的苗木和幼树。结果表明,3个树种的天然更新的个体数量的密度明显不同,并随时间存在差异。与极叉平荚木相比,L.minimiflorus和毛风铃木天然更新密度较大,只有毛风铃木种群密度方面的净变化是正相关。在树冠部分曝光的条件下,在缓坡和陡坡上更新较好,形成了分布聚集分布,尤其是L.minimiflorus和毛风铃木。仅靠天然更新不足以维持这些树种理想的立木数量,应当采取直接的恢复措施以促进天然更新过程。参47表3图3。