DOI: 10.5061/dryad.cjsxksncn
title: Tillage agriculture and afforestation threaten tropical savanna plant communities across a broad rainfall gradient in India

description: The consequences of land-use change for savanna biodiversity remain
 undocumented in most regions of tropical Asia. One such region is western
 Maharashtra, India, where old-growth savannas occupy a broad rainfall
 gradient and are increasingly rare due to agricultural conversion and
 afforestation. To understand the consequences of land-use change, we
 sampled herbaceous plant communities of old-growth savannas and three
 alternative land-use types: tree plantations, tillage agriculture, and
 agricultural fallows (n=15 sites per type). Study sites spanned 457 to
 1954 mm of mean annual precipitation—corresponding to the typical rainfall
 range of mesic savannas globally. Across the rainfall gradient, we found
 consistent declines in old-growth savanna plant communities due to
 land-use change. Local-scale native species richness dropped from a mean
 of 12 species/m2 in old-growth savannas to 8, 6, and 3 species/m2 in tree
 plantations, fallows, and tillage agriculture, respectively. Cover of
 native plants declined from a mean of 49% in old-growth savannas to 27% in
 both tree plantations and fallows, and 4% in tillage agriculture.
 Reductions in native cover coincided with increased cover of invasive
 species in tree plantations (18%), fallows (18%), and tillage agriculture
 (3%). In analyses of community composition, tillage agriculture was most
 dissimilar to old-growth savannas, while tree plantations and fallows
 showed intermediate dissimilarity. These compositional changes were driven
 partly by the loss of characteristic savanna species: 65 species recorded
 in old-growth savannas were absent in other land uses. Indicator analysis
 revealed 21 old-growth species, comprised mostly of native savanna
 specialists. Indicators of tree plantations (9 species) and fallows (13
 species) were both invasive and native species, while the 2 indicators of
 tillage agriculture were invasive. As reflective of declines in savanna
 communities, mean native perennial graminoid cover of 27% in old-growth
 savannas dropped to 9%, 7%, and 0.1% in tree plantations, fallows, and
 tillage agriculture, respectively. Synthesis: Agricultural conversion and
 afforestation of old-growth savannas in India destroys and degrades
 herbaceous plant communities that do not spontaneously recover on fallowed
 land. Efforts to conserve India’s native biodiversity should encompass the
 country’s widespread savanna biome and seek to limit conversion of
 irreplaceable old-growth savannas.
description: During September and October 2021, the peak growing season for
 herbaceous plants, we sampled a total of 60 sites, n = 15 in each of the
 four land use types (Fig. 1). Prior to the field sampling, we randomly
 selected sites with the goal of stratifying across the rainfall gradient.
 For the stratification, we created a regional map based on the long-term
 MAP from a thirty-year period (1970 to 2000; 1 km<sup>2</sup>
 resolution; Fick & Hijmans, 2017). While our goal was to sample
 sites stratified by MAP, we ultimately sampled fewer sites than expected
 in the 1500 to 2000 mm interval. This was because the wettest portion of
 the MAP gradient occupied a small area and contained only a few sites that
 met our selection criteria.   At each of the 60 sites,
 we establish three 200-m<sup>2</sup> sampling plots (20 m × 10
 m) oriented in a random compass direction. In western Maharashtra,
 old-growth savannas and tree plantations typically occur as large patches:
 our old-growth sites ranged from 6 to 6160 ha with a median of 40 ha; tree
 plantations ranged from 8 to 403 ha with a median of 66 ha. Given their
 large area, we were able to randomly locate plots within old-growth and
 plantation sites without concern they would overlap or extend beyond the
 site. By contrast, the size of tillage agriculture and fallow sites was
 small (0.1 to 0.4 hectares). To capture variation in the tillage
 agriculture and fallow land-use types, we sampled three separate fields,
 each with one plot that we oriented to fit within the field. For all four
 land use types, we ensured that the three plots at each site were located
 within a circular area of diameter &lt; 3 km. At some sites,
 availability of suitable tillage agriculture and fallowed fields, as well
 as challenges to acquire permission from landowners, resulted in our
 sampling of fields that were adjacent to one another. In these cases, we
 ensured that there were at least 20 m between plots. We
 measured herbaceous plant communities in seven 1-m<sup>2</sup>
 sub-plots, positioned along the center line of the
 200-m<sup>2</sup> plot, and calculated the mean of the seven
 sub-plots for subsequent data analyses. We visually estimated percent
 cover by species (excluding crops in tillage agriculture) and used this
 data to determine local-scale species richness (i.e., species per 1
 m<sup>2</sup>) and community composition. To measure and
 identify woody species within each 200-m<sup>2</sup> plot, we
 used a variety of sampling techniques suitable for individuals of
 different size classes (Foster et al., 1998). For trees with a diameter at
 breast height (DBH, 1.3 m) ≥10 cm (i.e., large trees), we measured DBH of
 all individuals in the 200-m<sup>2</sup> plot. For trees of
 DBH ≥ 1 cm and &lt; 10 cm (i.e., small trees), we sampled a 2 × 20-m
 subplot (40 m<sup>2</sup>) positioned along the center line of
 the plot. To estimate percent cover of shrubs (multi-stemmed woody
 plants), we used a 20-m line-intercept (Canfield, 1941). Lastly, we
 quantified woody regeneration by counting the number of seedlings, small
 tree saplings, and woody resprouts &lt; 1.3 m tall or &lt; 1 cm
 DBH in the seven 1 m<sup>2</sup> plots. For identification,
 nomenclature, and classification of plant functional groups and
 native/invasive status, we referred to several floras for the region
 (Supplementary methods). To characterize soils, we
 collected two 10-cm diameter samples of the top 10-cm of mineral soil
 (excluding leaf litter and duff) from the ends of the 20-m center line of
 the plot, which we pooled for each site. The samples were analyzed by the
 Soil Science Laboratory of the College of Agriculture, Pune, India for pH,
 electrical conductivity, organic carbon, available nitrogen, phosphorus,
 potassium, cation exchange capacity, and soil texture.
description: # Tillage agriculture and afforestation threaten tropical savanna plant
 communities across a broad rainfall gradient in India
 [https://doi.org/10.5061/dryad.cjsxksncn](https://doi.org/10.5061/dryad.cjsxksncn) The dataset contains one sheet, and variables for each column are described below. Please refer to Methods section in the paper for more details. ## Description of the data and file structure | Column name | Variable description | Unit | | ----------- | -------------------- | ---- | | site\_code | code of the site used | | | site\_name | site name | | | landuse | one of the four land use types surveyed | | | MAP | Mean Annual Precipitation from Worldclim for that site | mm | | MAT | Mean Annual Temperature from Worldclim for that site | Celcius | | Total\_Cover | Total (Native+Invasive) herbaceous plant cover per meter square | % | | Total\_Richness | Total (Native+Invasive) number of species of herbaceous plants per meter square | | | Native\_Richness | Number of native herbaceous plant species per meter square | | | Native\_Cover | Cover of native herbaceous plant species per meter square | % | | Invasive\_Cover | Cover of invasive herbaceous plant species per meter square | % | | Native\_PG\_Cover | Cover of native perennial graminoids per meter square | % | | Total\_AG\_Cover | Cover of annual graminoids per meter square | % | | Total\_PF\_Cover | Cover of perennial forbs per meter square | % | | Total\_AF\_Cover | Cover of annual forbs per meter square | % | | BA\_small\_trees | Basal area of small trees (DBH ≥ 1 cm and &lt; 10 cm) per 40 square meter | sq. m | | BA\_large\_trees | Basal area of large trees (DBH ≥10 cm) per 200 square meter | sq. m | | shrub\_intercept | percent cover of shrubs intercepted per 20 meters | % | | woody\_seedling\_density | average number of seedlings, small tree saplings, and woody resprouts &lt; 1.3 m tall or &lt; 1 cm DBH per square meter | sq. m | | bioclim\_PC1 | First Principal Component of the PCA performed on the bioclimatic variables | | | soil\_PC1 | First Principal Component of the PCA performed on the soil variables | | ## Sharing/Access information The authors would appreciate being contacted by data reusers. Email: nerleka1@msu.edu