Effects Of Non-cultivated Land On Landscape Heterogeneity Of Cultivated Land System

Landscape heterogeneity is the basis for maintaining biodiversity and ecosystem services in cultivated land system,while non-cultivated land is the "ecological skeleton" in cultivated land system,which provides strong support for most ecological processes.However,with the rapid development of modern agriculture,a large number of non-cultivated land disappeared from the cultivated land system,and the cultivated land system presented a highly homogeneous situation,simple landscape structure and single type,leading to a series of consequences such as the decline of biodiversity and ecosystem stability.Previous studies have shown that landscape heterogeneity can be improved by reserving shelterbelt,grassland and hedge to construct a certain proportion of non-cultivated land,but the proportion of non-cultivated land is not a simple linear relationship with the landscape heterogeneity of cultivated land system,and the proportion of non-cultivated land is a necessary but not sufficient condition of landscape heterogeneity.As in the protection of cultivated land under the premise of effective promotion of landscape heterogeneity,this paper,the following four typical county as the research area,liaohe plain in determining the optimal dimensions,on the basis of the entropy Rao quadratic index(Q)characterization of landscape heterogeneity,through the single variable regression analysis to determine the non-cultivated land proportion and the corresponding relation of landscape heterogeneity,Clear to build strong landscape heterogeneity threshold,the proportion of minimum non-cultivated land USES the redundancy analysis(RDA)proven forest land,water,grass,trench of five types of non-cultivated land and rural roads to the influence degree of the landscape heterogeneity,by nonparametric test to determine the differences of landscape heterogeneity cultivated land system structure characteristics whether there was a significant difference,The Bioenv function in the vegan package of R language was used to determine the optimal combination of non-cultivated land types and structural characteristics to improve landscape heterogeneity.Finally,variance decomposition(VPA)was used to determine the impact of non-cultivated land combination and structure on landscape heterogeneity.The results show that:(1)The average value of landscape heterogeneity reached the highest in 20%-30% of non-cultivated land,which was about 1.4.With the increase of the proportion of non-cultivated land,the average value of landscape heterogeneity increased first and then decreased,and the average value of landscape heterogeneity was the strongest in the range of20%-30%.When the landscape heterogeneity of cultivated land system is strong,the lower limit of the proportion of non-cultivated land is obviously higher than that of other cultivated land systems,so the strong landscape heterogeneity needs a certain proportion of non-cultivated land as support.(2)the liaohe plain county cultivated land system in the actual situation of existing non-cultivated land proportion as a benchmark,under the existing conditions,5% to build strong landscape heterogeneity threshold,the proportion of minimum non-cultivated land non-cultivated land ratio from 16% to 20% range improve landscape heterogeneity,on the production and the ecological space efficiency highest,non-cultivated land proportion was18.6%,Landscape heterogeneity has the greatest room for improvement.There were differences in landscape heterogeneity under any proportion of non-cultivated land.When the proportion of non-cultivated land exceeds 5%,it can achieve a low proportion to create a strong landscape heterogeneity.When the proportion of non-cultivated land exceeds 16%,the difference of landscape heterogeneity tends to be stable,and reaches 18.6%,the difference of landscape heterogeneity is the largest.When the proportion of non-cultivated land exceeds20%,the difference of landscape heterogeneity gradually decreases.Therefore,the landscape heterogeneity of 16% to 20% non-cultivated land has the greatest room for improvement.(3)Woodland was the non-cultivated land type that contributed most to improving landscape heterogeneity,and woodland + water area + ditch was the best combination of non-cultivated land for improving landscape heterogeneity.All the five types of non-cultivated land had significant positive effects on landscape heterogeneity(P<0.01),but different non-cultivated land types and combinations have different degrees of explanation for the difference of landscape heterogeneity.Woodland has the highest explanation rate of landscape heterogeneity,which is about 29%.(4)The connectivity between non-cultivated land and the complexity of boundary shape are directly proportional to landscape heterogeneity.There were significant differences in landscape shape index(LSI),mean nearest neighbor distance index(ENN-MN),landscape separation index(DIVISION)and landscape SPLIT index(P<0.05),COHESION index +COHESION index(AI)was the most important combination of non-cultivated patch level indexes affecting landscape heterogeneity.(5)The interaction between the composition and structure of non-cultivated land is the most important factor for the difference of landscape heterogeneity.The results of Mantel test showed that the composition and structure of non-cultivated land had significant effects on landscape heterogeneity(P<0.01).The independent explanation rate of non-cultivated land composition and structure to landscape heterogeneity was weak,which was 8.5% and 11.8%,respectively.The interaction rate of non-cultivated land composition and structure to landscape heterogeneity was 53.1%.Therefore,the interaction between them is the most powerful factor influencing landscape heterogeneity.The liaohe plain county non-cultivated land proportion as a benchmark that exist in the current farmland system,improve the landscape heterogeneity in the future,should be at least5% of the non-cultivated land layout in the farmland system,and 16% to 20% in the presence of non-cultivated land proportion of cultivated land system build strong connectivity of woodland + ditch + water non-cultivated land combination,improve the efficiency of landscape heterogeneity is the highest.