The Preliminary Research On Effects Of Grazing To Insect Diversity In Songnen Grasslands

The effects of large herbivore with single and mixed grazing on insect diversitywere investigated by sweeping-net on Leymus chinensis community,the Songnengrasslands.The response and regulations of insect diversity under grazing of largeherbivore were tried to indicate by analyzing the change of insect species richness,abundance,evenness,Shannon-Wiener index and effective diversity after largeherbivore single and mixed grazing.The experimental results may provide data forrestraining outbreak of the pest under grazing management in grassland ecosystem,and provide scientific evidence for maintaining grassland ecosystem healthy.The main results are as follows:(1)Insect diversity was obviously affected by grazing.In 2007,insect diversityvaried differently by large herbivores grazing.Compare to pre-grazing,insect speciesrichness increased after goat and cattle+sheep mixed grazing,and it decreased afterother grazing treatments.Insect evenness increased after large herbivores grazing,except for three large herbivores mixed-grazing.The variety of insect effectivediversity was similar to Shannon-Wiener index of insect,and decreased after sheepand cattle+sheep+goat grazing,while they increased after other large herbivoresgrazing.In 2008,compare to pre-grazing,insect species richness,Shannon-Wienerindex,effective diversity increased after each large herbivores grazing treatment,butevenness increased after goat+sheep grazing,while it decreased after other grazingtreatments.(2)Insect abundance was different in the two years results.In 2007,comparewith pre-grazing,insect abundance decreased after large herbivores grazing,exceptthat it increased after cattle+goat and cattle+goat+sheep grazing.In 2008,compare topre-grazing,insect abundance increased after each large herbivores grazing.(3)Different changes of insect diversity were showed under different largeherbivore species and combination.Insect species richness increased by differentlarge herbivore species and combination grazing,insect Shannon-Wiener indexdecreased by cattle and sheep grazing in 2007,and sheep grazing in 2008,butincreased others grazing treatments in 2007 and 2008.Different large herbivorespecies and combination have different influence on insect evenness,either increasingor decreasing by each grazing treatments.Insect effective diversity decreased each grazing treatments,except for sheep grazing.(4)Insect abundance differently increased by different large herbivore speciesand combination grazing.Furthermore,the effects of different large herbivorespecies and combination on insect abundance were significant in 2007 and 2008(2007:F7,16＝21.58,P<0.0001,2008:F7,16＝25.333,P<0.0001).Overall,insect diversity was changed by large herbivore grazing,and thechangeable degree of insect diversity was different between pre-grazing andpost-grazing of single and mixed large herbivore.At the same time,compare tosingle large herbivore grazing,insect diversity were obviously higher by largeherbivores mixed grazing,especially insect species richness.So mixed grazing bylarge herbivores was considered in practical grazing management,which maycontrol abundance outbreak of an insect,and maintaining stable and grasslandecosystem healthy.