In this post Kei Uchida and Atushi Ushimaru discuss their recent paper “Land abandonment and intensification diminish spatial and temporal β-diversity of grassland plants and herbivorous insects within paddy terraces

For our recent article published in the Journal of Applied Ecology we studied the traditional paddy terraces of the agricultural lands in Hyogo Prefecture, Japan (Photo 1, Uchida & Ushimaru 2015) and compared them with abandoned and intensified paddy terraces. Farmers manage traditional agricultural lands using traditional management practices (i.e. through an intermediate disturbance regime), which maintains many endangered species (Photo 2) and biological heterogeneity.

Photo 1. Semi-natural grasslands on the levees of paddy field margins and irrigation ponds. The edges between paddy fields and secondary forests are maintained by periodic mowing. Paddy terraces are shown with dry rice straw (Photo by Kei Uchida).
Photo 1. Semi-natural grasslands on the levees of paddy field margins and irrigation ponds. The edges between paddy fields and secondary forests are maintained by periodic mowing. Paddy terraces are shown with dry rice straw (Photo by Kei Uchida).

In Japan, semi-natural grasslands on the levees of paddy field margins, which are maintained by periodic mowing, harbour high biodiversity, although only small fractions of such terraces currently remain due to changes in land use. Changes in management practice (i.e. mowing frequency) and loss of surrounding forests due to land-use changes drive the decline of within-terrace species pools and turnover of species diversity.

Land abandonment and intensification of agricultural lands have reduced species pools and heterogeneity of species diversity in agricultural landscapes worldwide. Loss of environmental heterogeneity resulting from land-use changes can lead to the homogenization of biodiversity at multiple spatiotemporal scales (Benton, Vickery & Wilson 2003). Several studies have examined reductions in species heterogeneity after land-use changes at very large spatial scales, whereas those occurring at small spatial scales (field-scale <1 ha) have hardly been explored, even though small-scale processes can affect biodiversity patterns at larger scales. Therefore we decided to study small-scale heterogeneity that may be diminished due to land-use changes.

Photo 2. Traditional management practice maintains high heterogeneity of species diversity and species pools at within-paddy terraces. (left) Hemerocallis citrina var. vespertina, (centre) Platycodon grandiflorus, (right) Polytremis pellucida pellucida on Cirsium japonicum (Photos by Kei Uchida).
Photo 2. Traditional management practice maintains high heterogeneity of species diversity and species pools at within-paddy terraces. (left) Hemerocallis citrina var. vespertina, (centre) Platycodon grandiflorus, (right) Polytremis pellucida pellucida on Cirsium japonicum (Photos by Kei Uchida).

The results of our study indicated significant declines in species pools on the abandoned and intensive terraces compared to traditional terraces, although heterogeneity does remain in these terraces. Contrary to our predictions, most spatiotemporal turnover of species diversity in traditional terraces was not higher than in terraces where land use had changed.

We noted that most plant and herbivore species occurred in <1 plot per traditional terrace (infrequently observed species, Photo 2). In our previous studies, we found that land abandonment and intensification caused large declines of infrequently observed plant and herbivore species in the same study area. Our new results suggested that land-use changes cause large declines in infrequently observed species, which in turn diminish species pools.

This study shows that traditional management practice maintains high biodiversity, although land-use changes drive reduction of biodiversity. Extensive traditional management likely enhances the spatiotemporal heterogeneity of organisms at a within-field scale, but these practices have largely been abandoned due to land-use changes in rural areas. We suggest that traditional mowing practices are essential to conserve species pools. To restore biodiversity in terms of species pools, we recommend reduction in mowing frequency in intensified terraces and reintroduction of mowing practices in abandoned fields.

References

Uchida & Ushimaru (2015) Land abandonment and intensification diminish spatial and temporal β-diversity of grassland plants and herbivorous insects within paddy terraces, Journal of Applied Ecology, DOI: 10.1111/1365-2664.12443.

Benton, Vickery & Wilson (2003) Farmland biodiversity: is habitat heterogeneity the key? Trends in Ecology and Evolution, 18, 182-188.

Advertisements