عنوان مقاله [English]
Biodiversity is a network of all living organisms, including plants, animals, fungi and other living organisms. In fact, biodiversity refers to the diversity of life and the interactions between living organisms. Agricultural biodiversity as a subset of biodiversity refers to the part of biodiversity used by farmers to produce food. It is well documented that conservation of agricultural biodiversity is crucial for maintaining multifunctional characteristics of agroecosystem as a basis for sustainable crop production. Quantification and monitoring the spatio-temporal variations of crop biodiversity are essential elements for the purpose of biodiversity conservation. Such studies, however, with focusing on spatial variability and temporal changes of crop diversity is largely overlooked. On the other hand, recent studies have shown that merely use of traditional measures such as Shannon and Simpson diversity indices may cause misinterpretation of the results. Therefore, using new measures such as species intactness indices would help to find out the amount of intactness in individual or a number of species over a long period of time. Therefore, the main objective of this study was evaluation of changes over time in crop species diversity at regional scale. Furthermore, two new groups of biodiversity indices for quantification of temporal variation of biodiversity are compared with the common diversity indices.
Materials and Methods
In this study, crop diversity intactness and traditional diversity indices were investigated for North, Central (Razavi) and South Khorasan provinces (located at Northeast of Iran). Long‑term data (1983-2008) regarding cultivated area of different crop species within selected cities across three studied provinces were collected from official databases. Time course of crop species diversity was quantified using 3 groups of indices.
- Traditional indices i.e. species richness and Shannon species diversity index (H'), where H' was calculated on the basis of relative cultivated area of species.
- Species intactness indices based on occurrence, calculated by the difference between crop species diversity at the reference time (reference diversity) and observed species diversity at any given time.
- Species intactness indices based on abundance, estimated from the difference between cultivated area (frequency) of crop species at reference time and any given time during the study period.
Finally, time trend of each group of indices was evaluated using regression analysis.
Results and Discussion
Results showed that in three studied provinces both species richness which demonstrates the number of cultivated crop species and Shannon divesity index were increased during the period of 1983-2008. However, Shannon index for Torbate Heydariye, Farooj, Jajarm was decreased over the study period. Although traditional indices showed an improvement of crop diversity over time, they are not able to distinguish the structural changes in the crop species composition. For example if new exotic crop species were introduced, Shannon index would show higher diversity because of higher richness. Intactness indeices of crop species indicated a decreasing trend compare with reference years (i.e. 1983 to 1988), showing changes in crop species composition over the studied period which is in contrast with the results of traditional indices. It is supposed that this discrepancy is due to the crucial change of crop diversity pattern and substitution of some local crops by exotic species and vast expansion of intensive cropping systems across three studied provinces. In fact, in the studied regions, introduction of new exotic crops is led to neglection of some indigenes species.
The results of this study indicated that using diversity intactness indices are superior over traditional diversity measures when the objective of the study is evaluation of structural changes in crop species diversity over time . Overall, intactness of crop diversity in three studied provinces was decreased which is seemingly the results of introduction of new crop species and intensification of production systems.