Even though any analysis of land-use/land-cover change is subject to technical problems (Coppin & Bauer 1996
; Petit & Lambin 2001
), our results can be considered fairly robust. In fact, while the two CORINE land cover maps were created from two basically different datasets (the CORINE Land Cover 1990 was realized using Landsat 5 images and other ancillary maps; the CORINE Land Cover 2000 was realized using Landsat
7 ETM+ images and a different set of ancillary maps), both were realized using the same methodology and the same land-use/land-cover classes (for more information visit the official CORINE land cover website at the EIONET, European Topic Centre on Land Use and Spatial Information: http://terrestrial.eionet.europa.eu/CLC2000
). Even though EIONET recommends the use of a specific CORINE database to analyse any type of land use change (http://terrestrial.eionet.europa.eu/CLC2000/changes
), Falcucci et al. (2007)
have clearly demonstrated that the original CORINE land cover layers can be used with no problem. Moreover, European Environmental Agency (EEA 2006)
found that CORINE Land Cover 2000, considering the third level of its hierarchical legend, classifies correctly 87% of 8115 field samples. We have no validation for CORINE Land Cover 1990, but we can assume that the error rate was not much different. Moreover, we used only the first level classes of the CORINE legend, thus further minimizing the possible errors.
The PA coverage was extensively checked by Maiorano et al. (2006)
and most of the errors were corrected. We could not exclude that all co-registration errors (between the two land-use/land-cover maps and between the land-cover maps and the PA map) had been removed, thus we performed our analyses using three different cell sizes.
Performing a large number of statistical tests can potentially create a problem with the significance of the results obtained (Rice 1989
; Roback & Askins 2004
). Thus, we tested the statistical significance of our results using the q
-value approach (Storey 2002
; Storey & Tibshirani 2003
; Storey et al. 2004
), which allows for a robust and powerful alternative to the classical p
-value in case many simultaneous tests are being performed.
An important caveat on our results is given by their purely quantitative aspects. The data available on land-use/land-cover do not permit any insight into changes in biomass. However, Tellini-Florenzano (2004)
measured, for a national park in the Apennines, a significant ageing for different types of woods (Fagus sylvatica, Quercus cerris
and other broadleaves, Abies alba
and other conifers). This trend, combined with the retention of dead and dying trees, indicates that the ecological functionality of these forests and woods is potentially fully retained (Falcucci et al. 2007
). Obviously, we cannot extrapolate these results to the entire Italian peninsula, since the national park considered by Tellini-Florenzano (2004)
covers just 36
ha, but there is, at least, an indication of the ecological trends in the land-use/land-cover change that we measured.
Our main finding is that PAs (both considered singularly and as a system) have been effective at protecting the ecosystems within their borders, even in areas with significant and widespread land use pressures (see our results for flat areas and coastal plains). In fact, comparing PAs with neighbouring areas, we clearly demonstrated that PAs are effective at slowing down land-use/land-cover change. Bruner et al. (2001)
obtained similar results but used a dataset built on questionnaires, and their study was harshly criticized (Vanclay 2001
), mainly because their dataset was considered anecdotal rather than substantive. Our results, on the contrary, are based on objective datasets (both CORINE land cover maps can be freely downloaded from the European Environmental Agency website, and the PA coverage can be obtained from the Italian Ministry of the Environment—Directorate for Nature Conservation) that were extensively validated in the field.
Considering land-use/land-cover change without distinguishing the direction of change, there is a clear and statistically significant negative correlation between mean change and PA size. More particularly, we were not able to find any relationship among PAs considered altogether and change towards natural land-use/land-cover classes, but we found that PAs change towards artificial land-use/land-cover classes significantly less than neighbouring control areas.
We have also been able to confirm our initial hypothesis. In particular, considering our results at the national level, we can infer that by increasing the size of PAs, it is possible to favour the change towards more natural habitats and to slow down the change towards artificial habitats ().
This is particularly evident from the results that we obtained for the Alps, the Apennines and the flat areas and coastal plains. In fact, even with the obvious interpretation problems (splitting our sample of PAs, we obtained three sub-samples with a low number of large PAs, especially for the Alps and the Apennines; this implies that the results obtained for the single macro-regions should be considered with caution), we obtained a confirmation of our general results both for areas dominated by land-cover changes towards natural habitats and for areas with a very strong human influence. Falcucci et al. (2007)
showed that the Italian alpine range changed from 1990 to 2000 towards a more natural condition, and we have demonstrated that PAs along the alpine range changed towards natural land-use/land-cover classes more than the rest of the macro-region (with larger PAs changing the most), while the change towards artificial land-use/land-cover classes was lower (with larger PAs changing the least).
From 1990 to 2000, the Apennines also showed a marked change towards natural land-use/land-cover classes (Falcucci et al. 2007
). We were not able to demonstrate a correlation between PA size and the change towards artificial land-use/land-cover classes. This is probably linked to the fact that most of the mid-mountain areas along the Apennines (i.e. most of the areas along the borders of PAs) have been abandoned and naturally reforested (Falcucci et al. 2007
), favouring a land-use/land-cover change towards natural classes. However, we demonstrated that PAs almost always change towards natural land-use/land-cover classes more than their buffers and larger PAs change the most.
Flat areas and coastal plains are the areas where the contrast among PAs and their buffers is greatest. In these areas, most of the changes in the 1990–2000 time frames moved towards artificial land-cover classes (Falcucci et al. 2007
) and, even though all PAs were efficient in slowing down changes towards artificial land-use/land-cover classes, we found a particularly clear relationship between PA size and their efficacy.
The size of PAs has already been related to loss of species, with smaller (isolated) PAs having significantly more problems of species loss than larger ones (Terborgh 1974
; Diamond 1975
). The SLOSS debate focused on many different aspects, mainly relating PA size to species survival or to the number of species (Ovaskainen 2002
). Along the same line, but using completely different analyses, McKinney (2005)
found that larger parks in the USA have relatively less human access for disturbance, with significant advantages over smaller parks. Moreover, Shafer (1995)
reviewed possible sources of damage or threats for small PAs.
However, the problem has never been analysed considering the efficacy of PAs in slowing and/or halting habitat degradation and in favouring habitat restoration. Our results provide, from this point of view, very clear indications towards the importance of large PAs, not only in pristine environments, but also in areas where the main habitat characteristics are and have been shaped by traditional human activities for thousands of years.
A simple explanation of our results may rely on the ecological mechanisms that link PAs to the surrounding lands. Hansen & DeFries (2007)
suggest that small PAs are often part of larger ecosystems and thus their biodiversity and their ecological processes are heavily influenced by what is going on outside their boundaries. Here, we are suggesting that socio-economic phenomena (and other human-related characteristics of PAs) follow the same pattern: larger PAs have their own identity and their own dynamics, while smaller PAs are usually part of larger socio-economic systems and follow the fate of those systems.
More generally, our results suggest that small PAs are not going to be viable in the long term if they are considered as islands surrounded by a ‘human-dominated ocean’ for reasons beyond those of the extinction/recolonization dynamics of animal and plant species. In fact, it is highly probable that ‘negative’ land-use/land-cover changes will continue in the foreseeable future, even exacerbated by climate change (Chapin et al. 2000
). This trend implies that, in a human-dominated landscape, small PAs will sooner or later (probably later than the surrounding areas) lose all the characteristics for which they have been established. However, small PAs are, in most of the western European countries, the only option available for in situ
conservation, and actually they are important for the conservation of small habitat features and of species with limited habitat requirements (Schwartz 1999
), especially when considered as part of a coherent network (Fischer & Lindenmayer 2002
We are not suggesting that we should dismiss small PAs. Conservation areas are still the most important tool available for conservation (Chape et al. 2005
; Lovejoy 2006
), but we need to operate an important shift in our strategies. We cannot rely blindly on a tool that, at least in the industrialized world, is doomed to failure, but we need to change our management strategies and devote much more attention to the non-protected matrix in which PAs must survive.