Effects Of Selection And Prescribed Fire Disturbances On Longleaf Pine Seedling Regeneration

Longleaf pine （Pinus palustris） is known as the best timber tree in southern UnitesStates. Prior to European settlement, this ecosystem was widely distributed throughout thewhole Atlantic and Gulf Coastal Plain. Since then the ecosystem has suffered a progressiveexploitation, decline and resulted in unbalanced ecosystem, with current levels estimated atless than5%. Therefore, depending on the economic and ecological benefits, restoration anddevelopment of longleaf pine ecosystem have become the main tasks of sustainable forestmanagement in Unites States.Uneven-aged selection would create open environment which are benefit to seedlingregeneration. The prescribed fire provide some benefits that are reducing the competitionfrom understory vegetation, releasing nutrients immobilized to the infertile soil, andsubsequently more rapid uptake by seedling, burning harmful insects and pathogens andreducing litter cover in developing longleaf pine regeneration, and finnaly stimulatinglongleaf pine ecosystem restoration and sustainable developmentThe study focused on seedling regeneration in three original main longleaf pine growtharea（sSDE，ERI，BRF）. The effects and influences of the selection （single-tree and group-tree）and fire （burn season and frequency） disturbances on seedling regeneration were explored andanalyzed, and hope these results will provide a sound scientific basis for longleaf pine naturalregeneration and sustainable development, and promote U.S. important porject-from genes toecosystems, translating longleaf pine ecosystem management and restoration, and also can beprefered as important references for different ecological forest system restoration. The mainfindings are as follows:⑴The regeneration density and frequency under different selection system in threestudy areas were recorded and analyzed, and the selection management improved theregeneration density and frequency. The regeneration density in stands was sequenced as: noselection<single-tree selection<group-tree selection. The regeneration frequency was higherthan80%in single-tree selection and group-tree selection system, less than50%in noselection stands. The regeneration frequency had the significant linear relation with the basal area.⑵The seedling height growth was higher in group-tree selection stands than its in noselection stands, and the small seedling was0.71cm a^-1and the large seedling was10.01cma^-1, respectively. The small seedling survival rate was higher than40%, and6.95%higherthan its in the no selection stands; the large seedling survival rate higher than70%, and25.91%higher than its in the no selection stands. The large seedling survival rate increasedwith the selection density and stand density decrease, and the small seedling survival ratedecreased with the selection density increase.⑶Comparing the seedling groundline diameter（GLD） under different selection system,the average GLD was1.89mm for two years in group-tree selection stands, and1.86mm insingle-tree selection stands, which was0.38mm higher than in the no selection stands.⑷The regression analysis was used to predict the root depth of longleaf pine seedlings.The results presented the maximum root depth （58.18cm） should appear in the group-treeselection stands, and was consistent with the observed value. The diameter at10cm depth ofthe taproot from different class seedlings under different selection system was notsignificantly different between the predicted and observed values, only the diameter at10cmdepth of the small seedlings taproot under group-tree selection had significant differencebetween the predicted and the observed values.⑸Regression analyses gave some relations between understory light environment andsoil moisture and seedling growth. A negative trend was between seedling growth and canopyclosure, but a positive trend with light fraction, and all these relations were significant ingroup-tree selection stands. A positive relationship existed between mean percent soilmoisture and seedling growth for all seedlings but the relationships were weak, and thehighest r2was0.14.⑹The new seedling recruitments and grass-stage seedlings were most abundant bywinter prescribed fire burn, and than the autumn and summer burn. No difference was foundbetween the autumn and summer burn for seedling denstiy. The comparison of the GLD fromtwo stage seedlings presented the GLD of new seedling recruitments and grass-stageseedlings were got the highest value after winter prescribed fire, and the lowest value aftersummer prescribed fire.⑺Most categories of vascular and non-vascular plants did not significantly respond tothe fire treatments in longleaf pine ecosystem. Grasses in the unburned no burn plots persistat very low levels of less than2%total cover, while grasses in all of the fire-treated plotsexceed a total cover of20%, with the biennial fire treatment approaching40%foliar cover.Biennial burning increased the overall foliar cover of grasses by2500%over that present in the unburned no burn areas.⑻The understories of all fire-treated plots contained significantly higher numbers ofvascular plant species than did the unburned no burns. Species richness for the biennial firetreatment was highest, with39species present, followed by the annual fire treatment, whichsupported34species, and the triennial fire treatment, which resulted in31species. Only17plant species were typically found in the understories of the unburned no burn plots.⑼Fire treatment resulted in a significant decline in litter cover on the forest floor. Noburn plots had the highest litter cover, averaging19%. Litter cover of15%on trienniallyburned plots was not significantly less than no burns. However, litter cover of9%onbiennially burned plots and11%on annually burned plots was significantly less than ontriennially burned and no burn plots.⑽Standing biomass of herbaceous understory plants was significantly higher on all firetreated plots than on the no burn areas. The largest standing biomass of602kg·hm^-2wasmeasured on the biennial fire treatment, and total284kg·hm^-2for the triennial fire treatment,217kg·hm^-2on the annual fire treatment, and the smallest15kg·hm^-2occurred on the no burnstands.Uneven-aged selection would assure “continuous forest cover in stands. Prescribed firewould improve the stand strucutre and understory composition in longleaf pine ecosystem.The combination of these two managements will promote regeneration survival and growth,and speed up the sustainable development of longleaf pine ecosystem.