Controls of plant diversity attributes over above ground biomass in Sal forests of Eastern India

(Dmg, Dmn), diversity (H, ENS), basal area or evenness (E). Estimation of forest Cp enables us to assess the amount of carbon loss during deforestation or the amount of carbon stored during forest regeneration. The present study will directly help in studying the response of climate change on ecosystem productivity, energy and nutrient ow, and for assessing the patterns of carbon sequestration in Indian forests under global climate change.

community. Therefore, tracking species evenness can provide some kind of early warning regarding the disturbances going on in the community (Anonymous, 2015). The variation in both evenness and diversity is being regulated by richness (Hill, 1973), and evenness signi cantly determines the change in species diversity than richness (Mligo, 2018) as it holds a major contribution in the diversity (Triin et al., 2009). Thus, species evenness provides adequate information on change in plant diversity with comparatively higher gradients than richness (Mligo, 2018).
Tropical deciduous forests of India are species rich with irregular distribution of tree densities and basal covers as well as multistoried canopy structures with different microclimate makes it complex to understand the patterns of AGB over space and time within and among the different forests (Behera et al., 2012). Additionally, species diversity, richness, evenness, or dominance represent critical attributes of plant diversity that may have associations with AGB. A very limited study has examined the AGB-plant diversity attributes relationships in forests, perhaps because of the di culty of using AGB as a substitute for productivity in long-lived trees (Vance-Chalcraft et al., 2010). However, describing the relationship between species richness and AGB in forests is useful beyond the context of forest productivity. Therefore, the present study aimed to assess spatial pattern of tree diversity, and AGB by using species speci c volumetric equations in Sal forests of Ranchi, Jharkhand, Eastern India as well as estimation of carbon stock (Cp) based on the AGB results. An effort has also been made to examine the relationships between multiple attributes of plant diversity and AGB.

Study area
The study was conducted in Ranchi district, Jharkhand, Eastern India (Figure 1).. Ranchi is situated between 23.13°N to 23.21°N latitude and 85.51°E to 85.54°E longitude, where the altitude varies from 400 to 700 m above mean sea level (msl). Forests of Ranchi are considered as tropical moist deciduous forests mostly dominated by S. robusta (Dipterocarpaceae), locally known as Sal forests (Champion and Seth, 1968). The study area falls under a humid subtropical climate (as per Koppen Climate Classi cation) and experiences 23.7°C of mean annual temperature and 397 mm precipitation at an average elevation of 650 m leading to pleasant climatic conditions.

Vegetation sampling and analyses
We carried out a comprehensive, and comparative evaluation of tree species diversity, stand basal area, density, and AGB through strati ed random sampling to survey 92 plots each of 0.5 ha Sal forests of Ranchi during September 2016 to October 2018. Location of transects was decided based on grid generation technique following Kumar and Saikia (2020). Girth at breast height (1.37 m above ground) and height of all individual trees (≥10 cm GBH) was measured using measuring tape and range nder in each transect, respectively. GPS locations of each transect at both starting and ending points were also collected to prepare the spatial maps of different plant diversity attributes. Community parameters such as density, basal area were determined according to Misra (1968), and diversity attributes (vegetation indices) including Margalef's index of species richness (Dmg) (Margalef, 1958), Menhinick's index of species richness (Dmn) (Whittaker, 1977), Shannon-Wiener diversity index (H') (Magurran, 1988), Simpson's index (CD) (Simpson, 1949), Pielou's evenness index (E) (Pielou, 1966), and effective number of species (ENS) (Jost, 2006) were calculated using standard formula.
The nondestructive method of biomass estimation was used to determine the AGB of all documented trees, where the basal area, tree height, species-speci c gravity and volume equations were used as inputs. The GBH data collected from the eld were converted into DBH by using formula GBH/π. The volumetric equations and wood speci c gravity provided by the forest survey of India (FSI, 1996) has been used for further analysis of AGB. The general equation used for the volume estimation is-Biomass = Volume ×Wood density Volume = (πd)2 h In the present research, species-speci c volumetric equations were used as mentioned in Table 1. Various plant diversity attributes were linked with transect location and spatially correlated in GIS to deduce the control of AGB over plant diversity attributes. Statistical analyses were performed with SPSS (Version 20) and maps were prepared by using ArcGIS version 10.3.

Spatial pattern of plant diversity attributes
A total of 103 tree species belonging to 81 genera and 33 families are recorded in 46 ha study plots, which is lower than the earlier records from moist Sal forests of northern West Bengal (134 trees) (Kushwaha and Nandy, 2012), and tropical deciduous forest in Mudumalai Wildlife Sanctuary (124 trees in 6.1 ha sampled plots) (Reddy and Ugle, 2008), but quite higher than Western Terai Sal forests of Nepal (28 trees) (Timilsina et al., 2007). Fabaceae (20 spp.) is the most species rich family followed by Moraceae (08 spp.), Euphorbiaceae (07 spp.) and 14 families are monotypic. On the other hand, Ficus (06 spp) is the most species rich genera followed by Terminalia (05 spp.) and 68 genera are monotypic. Tree diversity ranged from 01 to 27 species (mean 12 ± 0.60 SE) in all 92 studied Sal forests of Ranchi. Tree diversity in terms of Shannon-Weiner diversity index (H') was ranged from 0.45 to 2.76 (mean 1.65 ± 0.48 SE), which is falls within the range (0.62-3.96) reported by earlier workers for various tropical deciduous forests of India (Tripathi and Singh, 2009; Naidu and Kumar, 2016; Sahoo et al.,, 2020). Maximum studied forests (42 %) had moderate tree diversity (H': 1.51 to 2.00) followed by less diversity (H': 1.00 to 1.50) forests (28 %), high diversity (H': 2.01 to 2.50) forests (17 %), very less diversity (H': <1.00) forests (9), and very high diversity (H'>2.50) forests (3 %). The possible reason of lower H' in the studied Sal forests may possibly be due to anthropogenic disturbances resulting in habitat destruction, which leads to the survival of less number of tree species and their individuals. The highest tree diversity in terms of Shannon H' (2.76) was recorded in Sal forest located at Koijam, Burmu (JH029) and the highest E (0.87) was recorded in Siram, Burmu (JH030). The values of H', CD, E, Dmg, Dmn, and ENS do not follow a de nite pattern in all studied Sal forests of Ranchi (Table 2).. Evenness index also known as species equitability ranged from 0.25 to 0.87 (mean 0.68 ± 0.11 SE), while ENS ranged from 2 to 16 (mean 6 ± 0.30). ENS denotes the amount of diversity directly compared with the within-community, and among community components, provides more interpretable, and comparable assessments of biodiversity as compared to species richness, H', and CD (Jost, 2007). It is the true diversity of community used to assess species diversity on the basis of H', and responds to either known alteration in assemblage or environmental variables (Cao and Hawkins, 2019). On the other hand, CD ranged from 0.10 to 0.72 (mean 0.34 ± 0.01), which was within the reported range of CD (0.19 to 0.99) for forest vegetation (Whittaker, 1965). Lower CD (0.10) in few studied Sal forests (JH029, and JH030) indicate that dominance is shared by more than one species, and values of CD were lower in contrast with high species diversity (H') (2.76 and 2.74) as species diversity behaves inversely to the index of dominance (CD) (Odum, 1971). Dmg ranged from 0.17 to 11.68 (mean 2.06 ± 0.15) and Dmn ranged from 0.11 to 2.03 (mean 0.78 ± 0.04) in various studied Sal forests of Ranchi. The species richness in terms of Dmg and Dmn were 10.23 and 0.68 respectively for all studied Sal forests of Ranchi.
On the basis of H' and E, Sal forests were classi ed into highly diverse (HD) with H'> 2.00, moderately diverse (MD) (H' = 1.6-2.0), low diversity (LD) (H'<1.6) forests and highly even (HE) with E > 0.75, moderately even (ME), E = 0.6-0.75, and poorly even (LE) E<0.06 forests. Further, unique combination of H' and E (HD-LE, HD-ME, HD-HE, MD-LE, MD-ME, MD-HE, LD-LE, LD-ME, LD-HE) was used to classify all the studied Sal forests of Ranchi (Table 3).. Grouping of H'-E at different nine combinations illustrates that only 03 (3.26%) studied forests (JH003, JH070, and JH077) showed extreme tree diversity with high H' and low E (ETDFs). Similarly, very high tree diversity forests with high H' and moderate E (VHTDFs) was recorded in 11 (11.96 %) studied forests and high tree diversity forests with high H' and high E (HTDFs) was recorded in 04 (4.35 %) studied forests, while only one studied forests (JH002) classi ed as tree diversity forests with moderate H' and low E (TDFs) (Figure 2)..

Relationship between plant diversity attributes and AGB
The relationships between tree basal cover, density, plant diversity attributes (Dmg, Dmn, H', CD, ENS, and E), and AGB was documented in Sal forests of Ranchi. Correlation of basal area with AGB was positive, and statistically signi cant (r = 0.71, p<0.05) indicating that basal area is a major indicator of AGB. Strong relationships between AGB and basal area have also been reported by several workers in various types of forests (Cannell, 1984;Rai and Proctor, 1986). Likewise, high AGB indicate high Cp, so correlation between AGB and Cp was positive and highly signi cant (r = 1.00, p<0.01). AGB showed insigni cant, negative correlation with tree density (r = -0.17) indicating that forests with higher tree density have reduced AGB. Generally, in dense forests, the availability of soil nutrients and water, due to high intraspeci c competition cannot properly availed by plants for their growth and development may be the reason of lower AGB in higher tree density forests. Inverse relationship of total tree density with AGB was also observed in Terai Shorea forest and Shorea-Terminalia forest of south-western part of Nepal ( Table 7, Figure 4a-f),, possibly due to continual disturbance does not allow biomass to concentrate in only the strongest competitors. AGB increased with increase in tree diversity, as high species richness helps in increased nutrient use e ciency (Ruijven and Berendse, 2005). On the other hand, species richness is highly correlated with other plant diversity attributes and a high correlation exists between H' and species richness across tropical forests (Gentry, 1988). The present study also recorded highly signi cant positive correlation of H' with Dmg (r =.49, p<0.01), and Dmn (r =.84, p<0.01). The tropical deciduous forests in India experience frequent, large-scale human disturbances from mining, power generation, grazing, tree felling, and extraction of forest resources (Kumar and Saikia, 2020). Disturbance regimes differ greatly among tropical forests as they experience more frequent or smaller scale disturbances and may account for differences in species richness-AGB relationships in tropical forests (Phillips et al., 1994). In conformity with the present study, positive relationships have been Therefore, positive relationships may be the most obvious expectation for the species richness-AGB relationship in forests. High and positive correlation of AGB with H' and ENS signi es the diversity of tree species in studied forests did have major effects on growth and development by intraspeci c competition among the species. However, AGB was negatively correlated with CD (r = -.57, p<0.01)may be because of CD inversely related to H'. The negative CD-AGB relationships suggest that a few species become more dominant at high biomass, instead of the biomass being distributed evenly among all species (Vance-Chalcraft et al., 2010).

Conclusions
The present study showed that tree density, basal area, AGB and Cp used to be varied in different studied forests as well as tree species. The higher basal cover (144.63 m 2 ha -1 ), and tree density (515 ind. ha -1 ) in all studied forests supports higher AGB (410.69Mg ha -1 ), and Cp (193.06Mg C ha -1 ) in the region. S. robusta being the most dominant tree species, adapts better in sub-tropical climate conditions and has the highest AGB (7074.94 Mg ha -1 ) and Cp (3325.23 Mg C ha -1 ). However, attention should be given for the conservation of other native tree species like Bauhinia variegata (0.015 Mg ha -1 , and 0.007 Mg C ha -1 ), Sterculia urens (0.021 Mg ha -1 , and 0.10 Mg C ha -1 ), Azadirachta indica (0.256 Mg ha -1 , and 0.120 Mg C ha -1 ), and Bauhinia purpurea (0.280 Mg ha -1 and 0.132 Mg C ha -1 ) with low AGB and Cp as these species have also lower density as well as basal cover in the studied Sal forests of Ranchi. Positive, and statistically signi cant correlation (r = 0.81, p<0.05) of basal area with AGB indicates that basal area is a major contributor of AGB. Furthermore, it was found that the carbon storage potential in the forests is in uenced by tree basal area, density, and diversity attributes (Dmg, Dmn, CD, H', ENS, and E). Estimation of forest Cp enables us to assess the amount of carbon loss during deforestation or the amount of carbon stored during forest regeneration. The present study will directly help in studying the response of climate change on ecosystem productivity, energy and nutrient ow, and for assessing the patterns of carbon sequestration in Indian forests under global climate change. Further research is needed to depict the long-term effects of tree harvesting to maintain their productivity and soil fertility status in relation to the sustainability of Sal dominated forests of Ranchi, Jharkhand, Eastern India.

Declarations
Ethics approval and consent to participate  Authors' contributions RK participated in the eld data collection, analyses, and interpretation, and drafted the manuscript; AK helped in analyses as well as preparation of maps and also in nalizing the MS; PS conceived the study, helped in species identi cation and also nalized the manuscript. All authors read and approved the nal manuscript. association in tropical moist deciduous forest from northern India. Biodiversity and Conservation, 21, 1159-1176.