Analysing subtle threats to conservation: A nineteen year assessment of fragmentation and isolation of Spanish protected areas

Natural habitat fragmentation in and isolation of protected areas (PAs) are two ancillary but common threats that may have serious consequences to biodiversity conservation in the long term. They were assessed in four PA networks of diverse legal and managerial regimes across a highly biodiverse country, Spain, between 1987 and 2006, a period of intense development in the country: Nature Reserves (NRs), Nature Parks (NPs), Sites of Community Importance (SCIs) and Special Protection Areas (SPAs). ‘Contagion edge proportion’ was used to assess inner PA fragmentation by artificial land uses-land covers (LULCs), whereas two PA isolation indicators were compared: (a) increased proportion of artificial LULCs in the 500 m-buffers surrounding each protected polygon (PP); and (b) shortest distance to the nearest PA in 2006. In those 19 years, fragmentation increased in all PA networks except in Nature Reserves (NRs), which likely reflects high conservation effectiveness of stringent legislation. Isolation by artificial LULCs also increased in that period for all PA categories. NPs were the PA category with the highest values of fragmentation and isolation by 2006. Nevertheless, fragmentation and isolation values were still low on average by 2006 for all PA categories, although fine-scale fragmentation and isolation could not be assessed. Both PA isolation indicators yielded different results and were thus complementary. ‘Distance to major cities’ was the most strongly correlated variable with both pressures, which suggests that greater attention should be paid to such pressures to peri-urban PAs by territorial planners