Study On Diversity And Spatial Distribution Pattern Of Woody Plants In Fragmented Woodlots In Huaxi University Town,Guizhou

To examine the spatial distribution pattern of species richness associated with species-area relationships and SLOSS(single large or several small)effect in fragmented Karst habitats.We used the line-transect technique to survey woody plants on 26 fragmented karst woodlots with an area of 0.26–282.5 ha in Huaxi University Town,Guizhou Province from April to August 2019.Using Google Earth Pro as the base map,we positioned line-transects in each woodlot with a length roughly proportional to the size of the woodlot.We investigated and identified woody plant species within 1 m generally but 3 m for large trees on either side of line-transects.Based on this survey,we studied the species-area relationship,small island effect,SLOSS effect(a single large patch or several small patches of equal area have higher species richness),βdiversity and its components,and the results as follows:(1)Composition and distribution of families,genera,and species:A total of 383species of woody plants belonging to 184 genera and 103 families were recorded in an area of about 10km~2 in our 26 fragmented woodland patches.There are 25–110 species of woody plants in each woodland patch,with an average of 60.85±9.02(mean±1.96*SE)species per patch.Among the families,Rosaceae and Leguminous plants are the most,and among the genera,Rubus,Lonicera and Zanthoxylum are the most common.Among the species,the most frequent species are Pyracantha fortuneana and Viburnum chinshanense,with an occurrence rate of 100%;followed by Broussonetia papyrifera,with an occurrence rate 96%;followed by Coriaria nepalensis,Rosa cymose and Zanthoxylum bungeanum with an appearance rate of 92%.In addition,the occurrence frequency of Rubus coreanus,Smilax glaucochina and Rhus chinensis is also more frequent.Among the woody plants recorded in this survey,76.54%of the species are only distributed in 1-4 patches,and among them,about 64%of the species only appear in one patch.(2)Relationship between species richness and geographic parameters:the species richness in each patch has a significant positive correlation with area,and a significant negative correlation with isolation and perimeter area ratio,which are consistent with what predicted by island biogeography theory.The possible reason is that,in general,the larger woodlot area,the greater the diversity of habitats,the greater the number of habitats,the more available resources,the lower extinction rate,and the higher biodiversity;the greater the isolation,the greater distance from the species pool,the lower migration rate,the smaller chance of new species colonization,and the extinction rate of existing species may be higher,so the species richness will be less;the greater the perimeter-to-area ratio,the greater possibility of species being disturbed by external sources,and the more unstable habitat conditions,the greater possible edge effect,which will have a negative effect on species richness.(3)Species-area relationship and small island effect test:The regression model results showed that there was a significant positive correlation between species richness and area of woodlots,in line with the species-area relationship proposed by island biogeography theory:the larger area of woodlots,the greater richness of woody plant species.Further analysis showed that no small island effect for species-area relationship in study area,and the number of species changes greatly with the increase or decrease in area.The possible reason is that no conditions((i.e.,extinction irrespective of area hypothesis,habitat quality hypothesis,nutrient subsidy hypothesis,or incidental disturbance)for the small island effect in this area.(4)Analysis results of SLOSS effect:The cumulative observed richness of woody plant species(383)on 26 fragmented woodlots was significantly higher than the value(116)theoretically predicted by the best liner model,supporting the hypothesis that several small woodlots contained more species than a single woodlot of equal area.The saturation index of the species accumulation curves from small to large area and from large to small area(ratio of the former to the latter)was greater than 1,indicating that several small woodlots may contained more species than a single large woodlot of equal area.(5)Relationship betweenβdiversity and its decomposition components and geographic parameters:The turnover component ofβdiversity among the patches is absolute main component,indicating that the species among patches have high complementarity,which may be related to different habitat qualities among patches.The difference in perimeter area ratio,that is,edge effect,had no significant effect on overallβdiversity,turnover component,and nested component,because the perimeter area ratio here does not represent the habitat crisscross zone of different communities,but a certain degree of reflection of the area of the islands occupied by the non-habitat matrix along the edge of the patch,which may cause the positive and negative edge effects to cancel each other.While the area difference has no significant effect on the overallβdiversity and nesting components,and a significant positive effect on the turnover components,indicating that the relation ofβdiversity of the woody plant community among the patches in this study area and the patch area difference is not significant.The relationship may be the result of spatial turnover component and nested component canceling each other out.It shows that studying for influence of environmental parameters on the pattern ofβdiversity should not only focus on overallβdiversity,but should also focus on the relationship between its decomposition components and environmental parameters,so as to draw more accurate conclusions.In addition,the difference in isolation has a positive and significant effect on overallβdiversity and its nested component,but has no significant effect on turnover component.The possible reason is that with the increase in isolation,the distance from the large patch species pool is getting farther and farther.Some species are sensitive to changes in habitat and area or have minimum area requirements,and the largest patch cannot be supplemented in time,these species were the first to go extinct on small patches,while similar species on large patches continue to exist,making small patches more likely to become a subset of large patches or tend to transform into subsets,forming or promoting the formation of nesting pattern.In addition,different from the mobility of animals,woody plants are site plants.Even small microhabitats may change the growth conditions of plants.In addition,because of the strong effect of habitat heterogeneity in karst areas,species diversity may be enriched.In general,in fragmented habitats,species richness has obvious correlation with patch area,isolation degree,and perimeter area ratio,which are consistent with the effect direction of area and isolation degree predicted by island biogeography theory and prediction results of negative edge effect.The larger area and the lower isolation of the patch,the higher diversity of habitat and more available resources,the higher species richness,and small island effect does not exist in study area,and total number of species in several small patches of woodlot is more than single large patch of equal area.In addition,the turnover component dominates theβdiversity of woody plant species.All patches need to be protected and no priority for protection.Moreover,isolation and area have different effects onβdiversity and its decomposition components,and protection strategies should be formulated based on the contribution of turnover component and nested component to overallβdiversity.Although further research is still needed,the current research results show that scattered small patches may still have important values for biodiversity conservation and should not be ignored in conservation practices.Therefore,protection of large and small patches should be strengthened to prevent further fragmentation.