Structure and regeneration dynamics of dominant tree species along altitudinal gradient in a dry valley slopes of the Bhutan Himalaya

The aim of our study was to characterize the structure and regeneration dynamics of dominant tree species along altitudinal gradient in dry valley slopes of the Bhutan Himalaya. In the typical dry valley slopes of west-central Bhutan, we analyzed forest stratification, tree crown projection, and population structure from lower dry valley bottom (1520 m a.s.l.) to upper humid ridge top (3370 m a.s.l.) across five major forest types: i.e. (1) dry pine forest with Pinus roxburghii as a dominant species; (2) mixed broad-leaved forest with Quercus lanata (evergreen), Quercus griffithii, (deciduous), and Rhododendron arboreum (evergreen) as major canopy species; (3) evergreen broad-leaved forest dominated by Quercus semecarpifolia, Quercus glauca and Quercus oxyodon; (4) cool conifer forest dominated by Abies densa and Tsuga dumosa; (5) cold conifer forest with A. densa and Juniperus recurva as dominants. In general, regeneration pattern of major dominant species shifted from inverse-J (lower altitudes), to sporadic (mid-altitudes), and to uni-modal type (upper altitudes) corresponding to three regeneration trends: (1) invasive at the lower, warm, dry forest under relatively strong human disturbances; (2) stable/balanced at the mid-altitude, in a relatively stable, mature moist evergreen broad-leaved forest with gap regeneration; and (3) poor/low regeneration at the upper, cool, humid conifer forest with a continuously cattle-grazed understory. Overall, regeneration patterns were balanced in all forest types, however care should be taken to prevent excessive exploitation of dry pine forest of lower valley bottom, and to control cattle grazing at higher altitudes. Our findings can be incorporated into management plans for sustainable management and conservation of mountain forests.     

Patterns of rabies occurrence in Bhutan between 1996 and 2009

This study was conducted to evaluate incidence and seasonal trends of rabies in dogs and other domestic animals in Bhutan from 1996 to 2009. Time series analysis approach was used to determine the seasonal trend and temporal association between species-specific rabies cases in animals. A total of 814 rabies cases were reported during the 14-year period, of which cattle and domestic dogs accounted for 55% (447/814) and 39% (317/814) of the cases, respectively. The remaining 6% of the cases (50/814) were reported in horses (2%), cats (2%), pigs (1%) and goats (1%). Rabies cases were reported throughout the year with more reports during spring and summer months. The annual patterns of cases were stable from 1996 to 2005, but the incidence increased during 2006 and 2008. Fifty-nine of the 205 sub-districts reported rabies in animals from 1996 to 2009 with increased incidences in the four districts in southern Bhutan, an area located close to the border towns of India. A significant (P < 0.05) positive cross-correlation was observed between the number of cases in dogs and other domestic animals at time lags (months) 1-3 with the highest correlation (r = 0.94, P < 0.05) observed at time lag 0 (same month) indicating that the peak in rabies incidences occur in the same month when both dogs and other domestic animal cases are reported. Regression analysis predicted rabies in other domestic animal when there are reports of rabies in dogs during the previous months. This study provides useful information about the epidemiology of rabies that can be used to plan a rabies control programme in Bhutan.     

Seroprevalence and associated risk factors of important pig viral diseases in Bhutan

A cross-sectional serological study was conducted in Bhutan between October 2011 and February 2012 to determine the prevalence of antibodies to classical swine fever virus (CSFV), porcine reproductive and respiratory syndrome virus (PRRSV), porcine circovirus type 2 (PCV2), swine influenza virus (SIV) subtype H1N1 and Aujeszky's disease virus (ADV). Furthermore, risk factors for the seropositive status were investigated.     

Regeneration of mixed conifer forests under group tree selection harvest management in western Bhutan Himalayas

Group selection tree harvest has been proposed as an ecologically sustainable silvicultural technique in mixed conifer forests of the western Bhutan Himalayas. To evaluate this silvicultural technique, we studied the ecological consequences of a group selection tree harvest in mixed conifer forests by assessing 127 circular plots (71 in logged and 56 in unlogged stands) in two forest management units (FMUs). Tree species composition and diversity were similar between logged and unlogged stands. Seedling density and height growth vary by species and were influenced by logging and microsites, with generally taller seedlings found in the logged versus unlogged stands. Early successional shade-intolerant species colonized logged stands. Seedlings growing on bare soil scarified by harvesting had medium vigour while seedlings growing on bryophyte mats showed good vigour in both logged and unlogged stands. Moist sites with a northerly aspect supported profuse conifer seedling regeneration, compared to sites with a dry southerly aspect. Damage to conifer seedlings from herbivore browsing was minimal. Conifer seedling density and height growth was negatively affected by competition from herbaceous vegetation, most notably Salvia officinalis. Group selection tree harvest in southern dry exposures in spruce-dominated stands is silviculturally unsuitable because it alters tree succession.     

Genetic variation in barley landraces from Bhutan

Summary In Bhutan, barley is usually grown in mountainous regions over 2,000 m elevation. The barleys investigated were six-rowed naked, and classified into three groups by spike and awn characters; lax spike and long awn, dense spike and long awn, and dense spike and elevated hood. They also varied in spike color; yellow, purple and black. For isozymes, there was no variation at Aat2 and Aat3 loci for aspartate aminotransferase in the Bhutanese barley.However, allelic variations at Est1, Est2 and Est4 loci for esterase were detected, and three genotypes consisting of their allelic combinations were found. Most of the collections were heterogeneous for these features. Combinations between spike-awn types and esterase genotypes were not at random, indicating that genetic diversities resulted from mechanical mixtures of different types. These types were distributed with geographical regularity in Bhutan. In comparing the spike-awn type and esterase genotype in barley collections from other regions of the Himalayas, the Bhutanese barleys were s-imilar to the Tibetan ones, but were much different from the Nepalese barleys. This suggests that the Bhutanese barleys had been introduced from Tibet.     

Milk protein polymorphisms in cattle (Bos indicus), mithun (Bos frontalis) and yak (Bos grunniens) breeds and their hybrids indigenous to Bhutan

In the current study, milk protein variation was examined in cattle (Bos indicus), mithun (Bos frontalis), yak (Bos grunniens) and their hybrid populations in Bhutan to estimate genetic variability, conduct genetic characterization and assess the possibility of gene flow between mithun and cattle. Isoelectric focusing of 372 milk samples from 11 populations detected four molecular types of β‐lactoglobulin (A, B, E and M), five molecular types of α_S1‐casein (A, B, C, E and X) and three molecular types of k‐casein (A, B and X). Mithun and yak shared alleles but were found to exhibit different allele frequencies for the proteins studied. The degree of genetic variability within populations was measured by average heterozygosity and ranged from 24–40% in cattle, 26% for yak and 33% for mithun. We also resolved the traditional mithun and cattle hybridization system via principal component analysis. Our results suggested secondary introgression of mithun genes to the village Thrabum population, and a close genetic relationship between Bhutanese indigenous cattle and Indian cattle.     

Isolation and characterization of influenza A virus (subtype H5N1) that caused the first highly pathogenic avian influenza outbreak in chicken in Bhutan

We characterized Influenza A/H5N1 virus that caused the first outbreak of highly pathogenic avian influenza (HPAI) in chickens in Bhutan in 2010. The virus was highly virulent to chicken, killing them within two days of the experimental inoculation with an intravenous pathogenicity index (IVPI) of 2.88. For genetic and phylogenetic analyses, complete genome sequencing of 4 viral isolates was carried out. The isolates revealed multiple basic amino acids at their hemagglutinin (HA) cleavage site, similar to other "Qinghai-like" H5N1 isolates. The receptor-binding site of HA molecule contained avian-like amino acids ((222)Q and (224)G). The isolates also contained amino acid residue K at position 627 of the PB2 protein, and other markers in NS 1 and PB1 proteins, highlighting the risk to mammals. However, the isolates were sensitive to influenza drugs presently available in the market. The sequence analysis indicated that the Bhutan viruses shared 99.1-100% nucleotide homology in all the eight genes among themselves and 2010 chicken isolate from Bangladesh (A/chicken/Bangladesh/1151-11/2010) indicating common progenitor virus. The phylogenetic analysis indicated that the Bhutan isolates belonged to sub-clade 2.2.3 (EMA 3) and shared common progenitor virus with the 2010 Bangladesh virus. Based on the evidence of phylogeny and molecular markers, it could be concluded that the outbreaks in Bhutan and Bangladesh in 2010 were due to independent introductions of the virus probably through migratory birds.     

The use of camera traps for estimating tiger and leopard populations in the high altitude mountains of Bhutan

We used camera traps in combination with capture-recapture data analysis to provide the first reliable density estimates for tigers and leopards from the high altitude and rugged terrain in Bhutan’s Jigme Singye Wangchuck National Park. Fifty days of camera trapping in each of five study zones collapsed into two trapping blocks, resulted in a sampling effort of 4050 trap days. Camera trapping yielded 17 tiger photos (14 left flanked and 3 right flanked) and 48 leopard photos (25 left flanked and 23 right flanked). Using photos of these left flank, the closed heterogeneous Jackknife Model M_h was the best fit for the capture history data. A capture probability () of 0.04 was obtained for both tigers and leopards, thus generating population size (N) of 8 tigers (SE = 2.12) and 16 leopards (SE = 2.91) with densities of 0.52 tiger 100 km⁻² and 1.04 leopard 100 km⁻². Photographic evidence indicated that tigers and leopards did not overlap in their spatial use of space. Tigers preferred less disturbed areas located further away from settlements, while leopards appeared to be more resilient to disturbances in so far as they were found nearer to human settlements. Camera trapping using a capture-recapture framework was an effective tool for assessing population sizes for tiger and leopard in low density areas such as Bhutan.     

Regeneration and structure of mixed conifer forests under single-tree harvest management in the western Bhutan Himalayas

We examined the regeneration and structure of mixed conifer forests under single-tree harvest management in western Bhutan. Sixteen 900 m² (30 m × 30 m) plots were sampled at four Forest Management Units (FMUs; Chamgang, Gidakom, Paro-Zonglela, and Haa-East) representing the forest type, including half the plots in single-tree harvest stands and half in unlogged stands. In addition, we solicited information on traditional forest management practices from informants using survey questionnaires and collected tree species data from felling records from respective local forest offices. Rural timber demand is concentrated on the removal of straight and well-formed bluepine trees for beams, planks, and scaffolding. Single-tree harvest, however, has not significantly altered stand structures from unlogged stands. Similarly, tree regeneration is not different when comparing single-tree harvest and unlogged stands, except at Chamgang FMU, where seedling densities were generally higher in harvested stands than in unlogged stands. These results indicate that single-tree harvest is not detrimental to regeneration and utilization of mixed conifer forests in western Bhutan.