Landscape connectivity is the degree to which the landscape facilitates or impedes the movement of organisms or ecological processes among patches. The maintenance of landscape connectivity is one of the key issues in ecological conservation and construction. The Conversion From Farmland to Forest is a long-term ecological project in China. However, along with the rapid urbanization and industrialization in China, the relationships between landscape connectivity and forest restoration has not been fully explored. The emergent questions concern the connectivity of restored forest landscapes, whether or not this connectivity benefits the local flora and fauna, and how to evaluate the importance of agricultural patches that are to be converted prior to the onset of forest restoration.
Based on the theory of landscape connectivity, the forest connectivity in Gongyi City, Henan Province is investigated using indicators such as the number of components (NC), the integral index of connectivity (IIC) and the importance value of IIC (dIIC). With the help of GIS, we examined how landscape connectivity of the forest in the hilly and low mountain areas varied according to distance threshold values ranging from 50 meters to 10000 meters, and identified the most appropriate distance threshold values for analyzing forest landscape connectivity. On this basis, we then looked into the importance values of the agricultural patches that were to be converted, determined the contribution of each pre-conversion agricultural patch to the connectivity of the future forest landscape, and elucidated the selection criteria and restoration priorities of important patches in the early stages of forest restoration according to local topographical features.
The results show that the low mountain forest has higher IIC values than the forest in the hilly areas under all distance thresholds. The most appropriate distance threshold for hilly areas is 750 meters, and 500 meters or less for low mountains. The dIIC values indicate that few patches are in the "very high" and "high" categories of contribution to forest landscape connectivity: three arid land patches in the hilly areas (respectively 35.14, 20.16 km² and 15.39 km² in descending order of importance value, accounting for 17.06%, 9.79% and 7.47% of the total hilly arid land area) and five arid land patches in the low mountains (respectively 3.65, 2.47, 1.35, 1.96 km² and 1.15 km² in descending order of importance value, accounting for 10.05%, 6.80%, 3.71%, 5.38% and 3.167% of the total low mountain arid land area). We also determined the preferable sequence of converting farmland to forest according to the topographical features, especially the slope characteristics, of the arid land patches in the "very high" and "high" categories.
The case study shows that the analysis of landscape connectivity should be used as a criterion for selecting important patches in forest restoration planning. The analytical method introduced in this paper is relatively easy to implement, and thus has application potentials in ecological restoration management.