1.      Introduction

The Central Himalaya accounts for 8.68% of the total Indian Himalayan region (59,436 km²) and harbors rich biodiversity due to geographical and geological peculiarities subtending a wide range of vegetation types [1]. The Himalaya is recognized for its ecosystem services to the Asian region as well as to the world at large for maintaining slope stability, regulating hydrological integrity, sustaining high levels of biodiversity and human wellbeing. The Himalayan biodiversity is severely threatened by natural (catastrophic wind, landslides) and anthropogenic means (overgrazing, overlopping,habitat fragmentation due to overpopulation). The various disturbances present in the area are eroding this rich biological diversity day by day and has led to the expansion of xerophytic conditions[2].One of the most prevalent causes of global deforestation and destruction of wildlife is fire.Forest fire is one of the major disasters in the forests of Uttarakhand that adversely affect many indigenous and endangered species every year.Forest fires spread at different speeds depending on vegetation, weather conditions, and physical features.

Quercusis possibly the greatest natural ecosystem-forming genus of the world, it serves as a ‘keystone’ species in the region because of its significant contribution in soil and water conservation and to sustain rural ecosystems[3].The major forest forming species of the moist temperate forest of the Indian Himalayan region are Oaks (Quercusspp.)[3,4]and Cypress (Cupressus torulosa)[5].  The genus Quercus (oaks) belong to the family Fagaceae. Oaks are one of the most important groups of flowering plants and dominate large regions of the Northern Hemisphere[4]. Quercus includes about 35 species distributed between 1000-3500 m elevations in Indian Himalayan region. Among the 35 species of Oaks, 5 species are evergreen and grow naturally in the Uttarakhand state.

Associated with these oak woodlands isCupressus torulosaD. Don, commonly known as Himalayan cypress which is an evergreen tree in the family Cupressaceae.This species is distributed throughout the Himalayan region at elevation between 1800to 2800m [6]. It is indigenous to Western Himalaya and distributed throughout the outer and middle ranges of Himalaya from Chamba (HP) to the Nepal[7,8]. These forests are of immense significance from the environmental conservation and sustainable development view point as they provide a diverse range of resources and contribute significantly in carbon sequestration and water purification[9].

The herbaceous layer, also referred to as understory or ground layer vegetation is generally defined as all plants (woody or herbaceous) <1m in height, though taller woody vegetation may be included[10,11]. Plants in the understorey layer, maintain the structure and functioning of forests[2,4,12-14].It is considered that oak and mixed oak forests support the herbaceous diversity [3,4]. Across oak forest landscapes, the herbaceous layer harbors great majority of plant diversity, including most rare plant species. In diverse landscapes and significant topographic heterogeneity, herb layer composition and diversity vary along with aspect related gradients of microclimate, soil moisture and fertility[15]. However, increasing anthropogenic pressures such as population explosion, overgrazing, land degradation for agricultural purposes within Himalayan zone from some decades has caused extensive deforestation, massive soil erosion in the hills, floods in the plains and consequently the silting of rivers [16].

Herb layer vegetation is also affected by natural and anthropogenic disturbances to the tree canopy, individual tree falls, catastrophic wind events and timber harvesting, which result in large increase in resource availability[11,17,18].

Fire is a common feature in Indian Himalayan forests every year, causing incalculable damage to the forest wealth and ecosystem. Any fire on a forestland which was not being used as a tool in forest protection and management and is not in accordance with an authorized plan may be referred to as a wildfire[18,19].Primary causes of wildfires may be natural including lightening or volcanic eruption or human induced including smoking, unattended campfires, burning debris and fireworks.Surface fires usually cause minor damage to overstory trees but affect herb layer vegetation directly by killing aboveground stems and indirectly by altering the forest floor and the availability of light, water and nutrients [20,21].Spatial and temporal variation in severity within a fire can have long-lasting impacts on the structure and species composition of post-fire communities and the potential for future disturbances[22]. Several studies showed variable effects of fire on herb layer- vegetation in oak forests [23-26].

In India, normal fire season extends from February to mid-June, early summer months are most prone to human induced fire. Frequently, many fires are caused during the burning of crop remains in the agricultural fields that are located near forest or due to a live cigarette or bidi butt thrown on the ground, even due to cooking and campfire activities of local people or tourists. Sometimes the local people deliberately set fire in Chir Pine (Pinus roxburghii) forests to promote growth of understory herbaceous vegetation which can be used as fodder during the monsoon season. In the summer of 2015, there was a severe fire in Uttarakhand Himalaya including the study area so an attempt has been made to highlight the effects of fire as an agent of transformation which affects biotic and abiotic component of natural ecosystem and thus altering productive, protective functions and services of forest ecosystems. The present paper is an attempt to analyze the effect of wildfire on herbaceous vegetation in cypress mixed oak forests of Nainital, Kumaun Himalaya, India.

2.      Materials and Methods

2.1.  Study Site

The study area islocated near the town of Nainital (29°23′N - 79°27′E, HYPERLINK "http://toolserver.org/~geohack/geohack.php?pagename=Nainital¶ms=29.38_N_79.45_E_"29.38°N- 79.45°E) at an altitude of 1,950 meters above sea level in Kumaun Himalaya. The study site waspresent at and around Aryabhatta Research Institute of Observational Sciences (ARIES) (1900m) in Nainital district and three sites (viz., hill base [1750 m] hill slope [1800m] and hill top [1850 m]were selected(Photo plate 1). During 2015,in summers there was a heavy fire in Uttarakhand Himalaya including the study area.

2.2.  Climate

The climate of Nainital is classified as Koppen climate type, which is characterized by long-cold often snowy winter and short summer. It is temperate and monsoon type (Singh and Singh, 1992) and the year have four distinct seasons viz., monsoon (July to September), post-monsoon (October to November), winter (December to January) and summer (April to mid-June). Climatic data for the year 2016was obtained from the State Observatory at Nainital. The mean annual rainfall was recorded 280.72mm and mean monthly rainfall ranged between 0mm (November) to 1076.34mm (July). The minimum temperature ranged from 6^oC (January) to 25^oC (June) and the mean maximum day temperature varied from 22^oC (December) to 39^oC (May)(Source: ARIES, Nainital) (Figure 1).

2.3.  Sampling

Plant species were collected carefullyfrom the selected three sites (hill top, hill slope, hill base)and the collected specimens were properly spread in between the newspaper sheets for drying. The dried specimens were then mounted on the herbarium sheets of 29.2 x 41.9 cm. The collected plant material was identified by consulting the representative flora [27-30]and with the help of Prof. P.C. Pande, Taxonomist, Department of Botany, DSB Campus, Nainital. The herbarium was prepared by standard methods.

The vegetational analysis of herb species was conducted by doing stratified random sampling based position along a slope gradient by placing 10 quadrats of 1m x 1m size randomly at different locations on each of the three sites (viz., hill base, hill slope and hill top). The size and number of samples were determinedfollowing Saxena and Singh[31]. Grasses were sampled through tiller analysis and each tiller of grass was considered as an individual plant and creeping plants were counted on the basis of presence of functional roots.The vegetational data were quantitatively analyzed for abundance, density and frequency [32]. The Provenance value (PV) of herbs was determined as the sum of the relative frequency and relative density[33]. The ratio of abundance to frequency indicates distribution pattern which may beregular (A/F≤0.025) orrandom (A/F = 0.025 to 0.05) or contagious (A/F ≥0.05)[34]. The diversity index (Hˈ) was computed by using Shannon-Wiener Index [35].The concentration of dominance (CD) was computed by using Simpson’s Index[36], species richness was calculated by following Whittaker [37] and equitability was computed by following Pielou[38] and Index of similarity was calculated following Mueller-Dombois and Ellenburg[39].The statistical analysis was performed using SPSS (version 16.0).

3.      Results

3.1.  Floristic Composition

36 herb species, belonging to 36 genera and 18 families were identified (Table 7)and number of herb species ranged from 15 (hill base) to 18 (hill top).The herbs were roughly distributed in a proportion of about 1/3^rd in each site. From the identified species, pteridophytes were represented by one or two species and the rest of the species were angiosperms. Maximum herb species were contributed by family Asteraceae (7 species) followed by Poaceae (5 species) and Lamiaceae (4 species). Arthraxonlanceolatusdominatedat hill base and hill slope, while Selaginellaspp.dominated at hill top.These results are supported by the fact that higher altitude promotes heterogeneity. Higher number of herb species present at hill top may be due to open canopy of C. torulosa due to which more species got chance to establish themselves.

3.2.  Herb Density and Provenance Value

Maximum herb density was observed at hill top (33.7ind.m^-2) followed by hill slope (21.8 indm^-2) and hill base(19.60 indm^-2). At hill top, the maximum individual herb density was 11.4 ind m^-2for Selaginellabryopterisand minimum 0.1 ind.m^-2 for Cassiaspp. Provenance value (PV) indicated the dominance of S. bryopteris(PV=43.83), predominance of Craniotomeversicolor(PV=20.51) and co-dominance of Parietariaofficinalis(PV=18.73).At hill slope, the maximum individual herb density was 8 ind.m^-2for S. bryopterisand minimum0.2 ind.m^-2forDiclipterabupleuroidesandClematisbuchaniana athill base. Provenance value (PV) indicated the dominance of Arthraxonlanceolatus(PV = 56.43) predominance of S. bryopteris(PV = 47.51) and co-dominance ofAinsliaeaaptera(PV = 14.48). At hill base, maximum individual herb density was 9.30 ind.m^-2 for A. lanceolatusand 0.10 ind.m^-2for Salvia officinalis, Cardamineamara, Bidens alba, Fragaria vesca, Cynodondactylon and Erigeronbelloides(Table 1). In the present study, two types of distributional patterns, viz. random and contagious were observed. Random distribution was rare whereas, contagious distribution was common.

On the basis of percent similarity, Hill base and Hill slope were 20.68% similar, the Hill slope and Hill top showed 18.75% similarity and the Hill Top and Hill base were 48.48% similar in herb layer which showed maximum similarity(Table 2).Across the three sites, maximum diversity was observed in hill slope for S. bryopteris(0.53) and minimum in hill top for Cassia occidentalis(0.02).Maximum concentration of dominance was observed for A.lanceolatus(0.22) in hill base. Equitability was observed maximum for S. bryopterisand A.lanceolatus (0.20) in hill slope. (Table 3)

3.3.  Herb Biomass

Maximum herb biomass(212.57 gm^-2) was observed at hill base, whereas minimum biomass was reported at hill slope (116.22 gm^-2) andthe total biomass at hill top (141.97 gm^-2) ranged in between hill base and hill slope.At hill base, maximum biomass was contributed by D. bupleuroides(25.83%) and minimum biomass was contributed by B. alba(0.10%). At hill slope,A. lanceolatus contributed highest biomass (24.88%) and lowest contribution was reported by P. annua (0.30%). At hill top,C. zizaniodes contributed highest biomass (20.57%) and C. offcinale(0.77%) contributed lowest biomass(Table 4).

3.4.  Dominance Diversity Curves

At hill base, one herb species was clearly dominant, one was predominant and rest of the species showed similar dominance.At hill slope, one herb species was clearly dominant, one was predominant and rest of the species showed similar dominance.At hill top, group of herb species showed similar dominance while one species was clearly dominant (Figure 2).