Are human-induced changes good or bad to dynamic landscape connectivity?

Land managers must find a compromise between rapidly changing landscapes and biodiversity conservation through ecological networks. Estimating ecological networks is a key approach to enhance or maintain functional connectivity by identifying the nodes and links of a graph, which represent habitats and their corresponding functional corridors, respectively. To understand the current state of biodiversity, it is necessary to consider dynamic landscape connectivity while relying on relevant land cover maps. Although a current land cover map is relatively easy to produce using existing data, this is challenging for past landscapes. Here we investigated the impact of changes in landscape connectivity in an urban landscape at a fine scale on the habitat availability of two bird species: the tree pipit Anthus trivialis and the short-toed treecreeper Certhia brachydactyla. These species, exhibiting different niche ecologies, have shown contrasting population trends at a medium-term scale. The occurrences of C. brachydactyla were better correlated with resistance values that maximise the use of corridors, whereas the occurrences of A. trivialis better fitted with intermediate resistance values. The statistical approach indirectly highlighted relevant information about the ecology the capacity of both species to use urban habitats. Landscape connectivity increased for both species over the 24-year study period and may have implications for local abundances, which could explain, at the national scale, the increase in populations of C. brachydactyla, but not the decrease in populations of A. trivialis. Thus, more attention must be paid on rural habitats and their associated species that are more impacted by human activities, but efforts could also be achieved in urban areas especially for highly corridor-dependent species. Studying dynamic landscape connectivity at a fine scale is essential for estimating past and future land cover changes and their associated impacts on ecological networks, to better reconcile human and biodiversity concerns in land management.

Mapping past land cover on Poitiers in 1993 at very high resolution using GEOBIA approach and open data.

The land cover data presented here is a reconstruction of the past landscape (1993) at Very High Resolution (VHR) for the city of Poitiers, France. This reconstruction is based on multiple sources of images and data. We combined the strengths of both mono-temporal and multi-temporal classifications. Orthophotos were created at a spatial resolution of 0.5 m using aerial raw images from the French National Geographic Institute (IGN), taken during two aerial missions in July and August 1993. These orthophotos were merged at a spatial resolution of 5 m to conduct a first object-based classification using Landsat-5 TM images. The goal was to identify croplands, grasslands, coniferous and deciduous forests, urban areas, water bodies, and shadows. This learning-based classification employed a dataset consisting of 1371 polygons and demonstrated strong classification performances, achieving an overall accuracy of 86.31% and a kappa index of 0.832. On the other hand, mono-temporal classifications at a 0.5 m spatial resolution were carried out on each orthophoto to extract trees and herbaceous vegetation, especially in urban contexts. As mono-temporal classifications contained less information, we used a larger number of polygons for the learning step: 3849 and 5173 polygons for the northern and southern classifications, respectively. The segmentation step performed better in urban areas compared to rural areas. Consequently, the performance of classifications was evaluated separately for both contexts. Urban areas exhibited excellent performances, achieving kappa indices of 0.897 and 0.881 for the northern and southern classifications, respectively, whereas only tree vegetation was accurately detected in rural areas. To compensate for the lack of information such as buildings, railways, or roads, we modified the BD TopoⓇ dataset from IGN. This land cover map provides highly detailed information, facilitating the understanding of urban sprawl and changes in urban and rural vegetation surrounding the city of Poitiers. Due to these reasons, this freely accessible map can be utilized by researchers, land managers, and private companies for addressing urban and ecological challenges.