Ecosystem services and biodiversity in urban environments

Here I consider the effect of land-use change by urbanisation on organic carbon (C) storage within three study areas in north-east England. I found that the contiguous urban extent of Darlington, Durham and Newcastle had increased by 67%, 229% and 65% respectively between 1945 and the present, and that the total C stored within the land occupied had decreased by around one-third. Decreases in C storage have occurred due to the replacement of agricultural land with urban land-uses of lower C storage value; notably, there have been large gains in low- to moderate-density residential areas and commercial land-uses. The greatest loss of C has been from the soil C pool, as the surface area occupied by soil, and soil depth, are greatly reduced in built urban land-uses compared to agriculture. Next, I investigated the spatial congruence between C storage and biodiversity in an urbanised area, using birds as a biodiversity indicator taxon. I found that land-uses with greatest C storage value per unit area also had the highest bird species richness and diversity, whilst land-uses with lowest C storage value had among the lowest bird species richness and diversity. However, the relationship was not straightforward; most notably, species richness and diversity were high in low- to moderate-density housing, despite these land-uses having low C storage value. Beta-diversity increased among land-uses, further highlighting the biodiversity value of some moderate to low C storage land-uses within the urban matrix. When not categorised by land-use, the overall spatial relationship between C storage and species richness and diversity was positive, and tree and woody vegetation C pools had the strongest positive relationship with bird species richness and diversity. I discuss the results with respect to UK urban planning options aimed at meeting both C emissions and biodiversity conservation targets, whilst also considering the continued well-being of increasing urban human populations.