Exploring the Ecological History of a Tropical Agroforestry Landscape Using Fossil Pollen and Charcoal Analysis from Four Sites in Western Ghats, India

Contrary to expectations, some human-modified landscapes are considered to sustain both human activities and biodiversity over the long-term. Agroforestry systems are among these landscapes where crops are planted under native shade trees. In this context, ancient agroforestry systems can provide insight into how farmers managed the landscape over time. Such insight can help to quantify the extent to which tropical forests (especially habitat-specialist trees) are responding to local and landscape-level management. Here, we extracted fossil pollen (indicator of past vegetation changes) and macroscopic charcoal (indicator of biomass burning) from four forest hollows’ sedimentary sequences in an ancient agroforestry system in Western Ghats, India. We used a mixed-modelling approach and a principal components analysis (PCA) to determine past trajectories of forest change and species composition dynamics for the last 900 years. In addition, we reconstructed the long-term forest canopy dynamics and examined the persistence of habitat-specialist trees over time. Our results show that the four sites diverged to a surprising degree in both taxa composition and dynamics. However, despite these differences, forest has persisted over 900 years under agricultural activities within agroforestry systems. This long-term analysis highlights the importance of different land-use legacies as a framework to increase the effectiveness of management across tropical agricultural lands

Alpha diversity of lianas in a tropical evergreen forest in the Anamalais, Western Ghats, India

Species richness, abundance, size-class distribution, climbing mode and spatial patterns of lianas were investigated in a 30-ha permanent plot of tropical evergreen forest at Varagalaiar in the Anamalais, Western Ghats, India. Each hectare was subdivided into 10 m 10 m quadrats, in which all lianas 1 cm d.b.h. were measured, tagged and identified. The total liana density was 11, 200 individuals (373 ha-1) and species richness was 75 species, representing 66 genera and 37 families. The richness estimators employed for species and family accumulation curves after 100 times randomization of sample order, have stabilized the curves at 16th and 15th hectares, respectively. A greater proportion of lianas was twiners (55% of species and 44.4% of density) and root climbers (5% of species and 14% of density), and a few were tendril climbers, reflecting the late successional stage of the forest. In the size-class distribution, 82% of abundance and 97% of species richness fell within 1-3 cm diameter threshold. The dominance of succulent diaspore type signifies the faunal dependence of lianas on vertebrate frugivores for dispersal. The diversity, population density and family composition of lianas of our site is compared with those of other tropical forests. The need for biomonitoring of this synusia in the permanent plot for forest functioning is emphasized

Tree-liana relationships in a tropical evergreen forest at Varagalaiar, Anamalais, Western Ghats, India

In a 30-ha permanent plot of tropical evergreen forest at Varagalaiar, Indian Western Ghats, all trees [greater-than-or-equal] 30 cm girth at breast height (gbh) were examined for the presence of lianas [greater-than-or-equal] 1 cm dbh. The plot contained 13 445 trees in 152 species and 11 200 lianas in 75 species. Twenty-eight per cent of trees supported lianas and the mean number of lianas per tree was 0.38 ± 0.72. Association analysis between lianas and trees of 16 tree families and 20 abundant tree species indicated that tree susceptibility to lianas was better pronounced at species rather than at family level. Overall, at Varagalaiar site, the aggregation of lianas followed neither Poisson nor clumped distribution. Among the four dominant tree families Dipterocarpaceae and Clusiaceae fit to the negative binomial model better than Euphorbiaceae and Meliaceae. These four families differed in their susceptibility level with 34.6% , 36.7% , 24.1% and 27.7% of trees [greater-than-or-equal] 30 cm gbh respectively supporting lianas. At the species level, the proportion of trees with lianas was positively correlated with the mean branch free bole height of trees [greater-than-or-equal] 30-40 and [greater-than-or-equal] 40 cm gbh classes, and the mean number of lianas per tree was also positively correlated with the mean branch bole height of trees [greater-than-or-equal] 30 cm gbh. Of the 16 abundant families, Euphorbiaceae contributed 31% and dominated the lower canopy, but its susceptibility to lianas was lower when compared to most other families

Impacts of selective logging on diversity, species compostion and biomass of residual lowland dipterocarp forest in central Western Ghats, India

International audienceStudies on the residual impact of logging on the diversity and composition of tropical forests are scarce in India. We examined the impact of selective logging on tree species richness, composition and structure prevalent after 27 years. Trees ≥ 30 cm girth at breast height were inventoried in four 1 ha plots in selectively logged patches and two 1 ha plots in an adjacent unlogged patch of lowland dipterocarp forest continuum, Uppangala, central Western Ghats, India. We enumerated 2343 trees (598 trees ha–1) belonging to 116 species (63 species ha–1) and 1345 trees (672 trees ha–1) belonging to 68 species (55 species ha–1) in logged and unlogged plots, respectively. The species richness in logged plots as compared to unlogged plots varied with spatial scale of sampling: at 1 ha scale two logged plots had higher species richness whereas it was high in only one plot at 400 m2 scale. Logged plots had low floristic similarity between them and also with the unlogged plots. Mantel and partial Mantel tests proved that logging was the main driver for the species composition rather than the elevation and spatial distance. Higher abundance of species belonging to canopy, intermediate and light wood categories and lower density of emergent, understory and medium wood types were recorded in the logged plots. As compared to unlogged plots, logged plots had 20–59% less above ground biomass (AGB) due to paucity of larger trees, especially in the emergent and medium wood types but higher AGB in canopy and hardwood categories. Our study shows the residual impact of logging even after 27 years and suggests that the recovery process may depend on the resurgence of emergent and medium wood categories

Patterns of liana diversity in tropical evergreen forests of peninsular India

The quantitative liana inventories made in five peninsular Indian independent forest sites, distributed in the Western Ghats, Eastern Ghats and on the Coromandel coast, were examined particularly with reference to site altitude and forest stature. Liana diversity totaled 148 species in 101 genera of 47 families, in a total sample of 47 ha. The coefficient of variability in species distribution among the five sites was used to identify an oligarchy in liana species by taking 55 abundant species from the species pool. Ordination analysis, based on presence-absence as well as relative density of liana species indicated a geographical differentiation among the five sites in both the ordinations with respect to site altitude. Liana density (stems\u3e1.6cm diameter) decreased with increasing altitude, whereas richness was highest at intermediate elevations. The mean liana density across the forest sites showed a weak negative correlation with forest stature. The lianas encountered in the five study sites fell under six climber types, of which twining was the chief climbing mechanism, both in terms of species diversity and density, and tendril climbers were more abundant in dry evergreen forests than in the wet evergreen forests. In liana diaspore dispersal modes, the majority of evergreen forest species possessed animal dispersal guilds, whereas wind-dispersal was prevalent in semi-evergreen and dry evergreen forests

Tree diversity and carbon storage cobenefits in tropical human‐dominated landscapes

A lack of spatial congruence between carbon storage and biodiversity in intact forests suggests limited cobenefits of carbon‐focused policies for conserving tropical biodiversity. However, whether the same applies in tropical human‐dominated landscapes (HDLs) is unclear. In India's Western Ghats Biodiversity Hotspot, we found that while HDL forests harbor lower tree diversity and aboveground carbon stocks than relatively intact forests, positive diversity–carbon correlations are more prevalent in HDLs. This is because anthropogenic drivers of species loss in HDLs consistently reduce carbon storing biomass volume (lower basal area), and biomass per unit volume (fewer hardwood trees). We further show, using a meta‐analysis spanning multiple regions, that these patterns apply to tropical HDLs more generally. Thus, while complementary strategies are needed for securing the irreplaceable biodiversity and carbon values of intact forests, ubiquitous tropical HDLs might hold greater potential for synergizing biodiversity conservation and climate change mitigation