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Deforestation Effects on Biological and Other Important Soil Properties in an Upland Watershed of Bangladesh

S.M. Sirajul Haque
Institute of Forestry and Environmental Sciences, University of Chittagong, Chittagong 4331, Bangladesh.

Sanatan Das Gupta
Department of Renewable Resources, University of Alberta, Edmonton, Canada.

Sohag Miah
Research Fellow, Institute of Forestry and Environmental Sciences, University of Chittagong, Chittagong-4331, Bangladesh.

Abstract/ Executive Summary:

Deforestation occurs at an alarming rate in upland watersheds of Bangladesh and has many detrimental effects on the environment. This study reports the effects of deforestation on soil biological properties along with some important physicochemical parameters of a southern upland watershed in Bangladesh. Soils were sampled at 4 paired sites, each pair representing a deforested site and a forested site, and having similar topographical characteristics. Significantly fewer (p≤0.001) fungi and bacteria, and lower microbial respiration, active microbial biomass, metabolic and microbial quotients were found in soils of the deforested sites. Soil physical properties such as moisture content, water holding capacity, and chemical properties such as organic matter, total N, available P and EC were also lower in deforested soils. Bulk density and pH were significantly higher in deforested soils. Available Ca and Mg were inconsistent between the two land uses at all the paired sites. Reduced abundance and biomass of soil mesofauna were recorded in deforested soils. However, soil anecic species were more abundant in deforested soils than epigeic and endogeic species, which were more abundant in forested soils than on deforested sites.

Keywords: Deforestation effects, Biological properties, Soil animals, Upland watershed, Bangladesh

Location:

Start Date:

End Date:

Program Area: Conservation and Biodiversity

Commodity: Soil Physical Properties

Objectives:

The objective of the present study was to assess the effects of deforestation on soil biological properties along with other important physicochemical parameters in the Chittagong region under the population pressure of >8 million at present compared to 1.3 million in 1901 (Wikipedia 2010).

Methodology:

Site description We sampled soils at 4 paired sites, two from Dulhazara and one from Tankawati in Chittagong district and one from Ghagra in Rangamati district. All paired sites were on upland watersheds of Chittagong and Chittagong Hill tracts. Descriptions of each site are given below: Deforested land at Dulhazara with adjacent bamboo-dominated forest The first deforested land was situated to the north-east of Safari Park, Dulhazara, Cox’s Bazar at 21^o 40′08″ N and 092^o 04′53″E on gently sloping (2%) well drained land. The area lacked trees but was covered to about 1.5 m height in partially burnt vegetation mainly consisting of herbs and shrubs in patches. Grass coverage was 30% and litter cover was 1 cm thick at a biomass density of 400 kg ha-1. During our soil sampling graziers were burning vegetation with the aim of growing new shoots that would be more palatable to their livestock. About 30 years earlier this deforested site had ecological conditions similar to those of today’s Safari Park, a protected area adjacent to the study area and supporting natural Dipterocarpus turbinatus (garjan) forest. The adjacent tree covered area was Dulahazara natural garjan forest located at 21°40′10″ N and 092°05′02″ E and now managed as a Safari park under full protection from any biotic interference. This forest land was on gentle slopes (2%) with bamboo coverage of about 70%. Calamus viminalis (cane) and other shrubs occupied 12% and trees occupied the rest. Tree canopy coverage at this site was 30% with undergrowth coverage of 90% without any grasses. Diameters of D. turbinatus trees ranged from 12 to 75 cm and heights ranged from 15m to 29 m. Because tree sizes varied greatly, the number of trees per unit area ranged from 150 to 225 per hectare. Uniform litter depth was 3.67 cm at a biomass density of 5323 kg⋅ha-1. Deforested land at Dulhazara with adjacent D. turbinatus dominated forest The second deforested site was on low hills at 10 m above mean sea level and adjacent to Dulahazara Safari Park, Cox’s Bazar and 20 m west of the first deforested site (above). This defor-ested site was on slopes of 0 to 4% had no trees, and vegetation consisting of herbs and shrubs grew to heights of 1−2.5 m giving coverage of 30% to 40%. Litter was completely burnt and ashes were present on the surface. Soil sampling and analysis From the four paired sites 5 replicated soil samples were collected from a depth of 0−5 cm, mixed thoroughly to give a composite sample and brought to the laboratory in labeled polythene bags that had been sterilized with 95% ethyl alcohol. In the laboratory, samples were divided into two sub-soil samples: one used for the determination of physical and chemical properties and the other kept in refrigerator at 4ºC temperature for determining biological properties. Determination of physico-chemical properties Moisture content was determined drying the soil in an oven at 105°C for 8 hours. Bulk density of soils was determined by the core method. Moist soil pH was determined using a TOA pH meter in triplicate at 1:2 soil-water ratios. Electric conductivity was measured using a digital conductivity meter (TOA, Japan). Soil organic carbon and organic matter were determined using the loss on ignition method according to Ball (1964) and total nitrogen by the micro-Kjeldahl method (Jackson 1973). Available phosphorus was extracted with Bray and Kurtz No.2 extractant and measured by SnCl2 reduced molybdophosphoric blue color method using a spectrophotometer (Jackson 1973). Available calcium and magnesium were quantified following Petersen (2002). Determination of basal respiration Basal respiration in soil was estimated according to Dubey & Maheswari (2002). One hundred grams of moist soil was taken into a sterile 500 mL conical flask. Three test tubes, each containing freshly prepared 10 mL of 1N-NaOH, were placed inside this conical flask. Each conical flask was then closed with a rubber stopper and sealed with wax. A set of blank experiments was run as the control. The conical flasks were then incubated at 30°C for 7 days, after which the 1N-NaOH solution was removed from the test tube and titrated against 0.1N-HCl in a conical flask adding 2 or 3 drops of phenolphthalein indicator. The end point of the reaction turned from pink to colorless.

Source of Information: Journal of Forestry Research (2014) 25(4): 877?885

Article Link (Online Journal): DOI 10.1007/s11676-014-0534-2

Funding Source:

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Achievement/Findings:

This study has shown that deforestation adversely affected important physico-chemical and biological properties such as fungal and bacterial populations, microbial respiration, active microbial biomass and metabolic quotients in soil. These biological properties are related through biochemical processes such as decomposition, nitrification, ammonification, nitrogen fixation, and denitrification in maintaining ecological balance and overall environment in a region. At present deforestation is intense in this important hilly watershed of Bangladesh mainly due to settlement of the rapidly growing human population and clearing of forests to fulfill daily needs along with many other reasons. Few scattered trees remained over most of the watershed although in the distant past all hills were covered with luxurious naturally growing forest. Absence of forests particularly on hilly topography causes many environmental consequences. Given the nature of current global environmental stresses, presence of permanent vegetation, i.e., forests in such hilly watersheds are critically important today. Theoretically this is possible to achieve by encouraging and maintaining natural levels of plant biodiversity on hills following monsoon rainfall in addition to proper management of indigenous tree plantations. Such measures would help to conserve and enhance environments for growing myriads of organisms in soils and hence for overall healthy environment in this hilly watershed. To achieve these benefits, however, requires policy decisions and enforcement of the policy in the country.

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