The Impacts Of Climate Change And Anthropogenic Disturbances On Forest Composition And Structure Of The Mixed Korean Pine And Broadleaf Forests Of The Xiaoxing'an Mountains

The mixed Korean pine and broadleaf forests of the Xiaoxing'an Mountains are located in the temperate forest zone of Northeast China,and it provided a large amount of timber for country in the past half a century.Excessive and cumulative timber harvesting decreased the quality of the mixed Korean pine and broadleaf forests,and most of these forests have degraded into over-harvesting forests and secondary poplar-birch forests.The dominance of Korean pine dropped dramatically due to human consumption of its seeds and poor natural regeneration.Thus,restoring Korean pine is an urgent issue of management in the temperate forests of Northeast China.In order to restore the mixed Korean pine and broadleaf forests and increase forest stocking,the State Forestry Administration of China implemented the Natural Forest Protection Project in 1998 and the Commercial Harvest Exclusion policy in 2015.Currently,forests in the Xiaoxing'an Mountains have a high potential to sequestrate carbon since they are young and mainly in the middle-aged stage.In the absence of disturbance,the secondary poplar-birch forests will gradually die of theirs longevity in the next 50 to 100 years,which will result in the loss of forest aboveground biomass.Whether the lost biomass will exceed the accumulated biomass of forest growth and decrease the accumulated rate of aboveground biomass.Disturbance favors maintaining the diversity of the forest landscape,but the commericial harvest exclusion policy reduces disturbance.It is unclear that landscape scale.Additionally,it is unclear whether the policy favor restoring the dominance of the zonal species Korean pine.Although multiple General Circulation Models(GCMs)predicted increases in temperature and precipitation in the mixed Korean pine and broadleaf forests region,which may favor Korean pine,these predictions varied seasonally.Furthermore,it is unclear whether drought may occur when both temperature and precipitation increase.The uncertainties of future climates increase the uncertainties of restoring Korean pine.The resistant treatment and the adaptive treatment are generally recognized management strategies for coping with climate change.The resistant treatment focus on reducing stand density to maintain current forest composition and structure.The adaptive treatment focus on increasing diversity of forest composition and structure to ensure forest have large potential to cope with climate change.In the face of climate change,it is unclear how Korean pine responds to the above climate change management treatments.Moreover,a series of treatments,such as adjusting harvesting quotas,classified forest management,and commercial harvest exclusion,reduced timber economic income.Given the economic value of Korean pine seeds,pine cone harvesting has gradually become a prominent source of income in the region.Currently,Korean pine cone harvesting was a limiting factor affecting the regeneration and dominance of Korean pine.Climate change will promote the growth and establishment of Korean pine,but pine cone harvesting will directly reduce the provenanvce of Korean pine,which will adversely affect the dominance and regeneration of Korean pine.Thus,it is unclear how pine cone harvesting will affect the dominance and regeneration of Korean pine in the context of climate change.Specifically,could climate change offset the adverse effects of pine cone harvesting on the dominance and regeneration of Korean pine? Which one of succession,pine cone harvesting and climate change is the dominant factor affecting the dominance and regeneration of Korean pine? Whether pine cone harvesting slow the migration of leading edge of Korean pine to higher latitudes?In this paper,we parameterized the ecosystem process-based model,LINKAGES(3.0)with current and future daily climate data under Representative Concentration Pathway(RCP)8.5 scenarios from four General Circulation Models(GCMs),that is,GFDL-CM3,HadGEM2-ES,MIROC5,and MRI-CGCM3.We evaluated the response of species and productivity to climate change by LINKAGES.We parameterized the forest landscape model LANDIS PRO(7.0)using forest survey data,such as forest stand map,and species biological traits to simulate the effects of succession and disturbance(e.g.,harvest and pine cone harvesting)on forest composition and structure.LANDIS PRO 7.0 took into account of the effects of climate change on species and stand through two parameters: seedling establishment probability(SEP)and maximum growing space occupied(MGSO).We estimated SEP for each species and MGSO on eight land types under each climate scenario by the outputs(species biomass and total biomass)from LINKAGES.We coupled LINKAGES and LANDIS PRO in the above way to simulate the impacts of succession,climate change and anthropogenic disturbances on forest composition and structure.We took the Classified Forest Management treatment used in the Natural Forest Protection Project in the past as a baseline scenario,and we estimated the effects of the current Commercial Harvest Exclusion policy on the mixed Korean pine and broadleaf forests.However,the Commercial Harvest Exclusion policy might reduce forest compositional and structural diversity once it was implemented for a long term.Given the potential negative effects,additional thinning was considered to alleviate the adverse effects.Thus,we designed three management scenarios: the H scenario(the Classified Forest Management treatment),the NCH scenario(the Commercial Harvest Exclusion policy),and the M scenario(mitigation management,i.e.,additional thinning).Then,we simulated the three scenarios by the above framework and evaluated the impacts of the Commercial Harvest Exclusion policy on composition and structure of the mixed Korean pine and broadleaf forests.Meanwhile we verified the simulation results by forest survey data.Reducing stand density or increasing forest compositional and structural diversity were usually considered to cope with future climate change.Generally,reducing stand density could maintain current species composition,and high diversity was hypothesized to promote forest with a greater range of potential responses to future uncertainty.We designed two proactive treatments: the resistant(reducing stand density)and the adaptive(increasing forest compositional and structural diversity)treatments,and a baseline treatment excluding any management.We estimated the impacts of proactive managements on the dominance and regeneration of Korean pine under RCP8.5 scenarios from four GCMs by the above framework.We also designed a full factorial experiment of climate change(current climate or RCP8.5 scenarios)and pine cone harvesting(with or without).Then,we assessed the effects of pine cone harvesting on the dominance and regeneration of Korean pine under RCP 8.5 scenarios from four GCMs by the above framework.The main conclusions are as follows:(1)The total basal area predicted by LANDIS PRO in 2010 had a high correlation with the forest survey data during the same period(r=0.71)and a significant linear relationship(p<0.05),and there was no significant difference between the predicted and the observed total basal area(F=1.90,p>0.05),and thus the total basal area predicted by LANDIS PRO was credible.There also were no significant difference between the predicted and the observed basal area by species(p>0.05),and thus forest composition predicted by LANDIS PRO was also credible.(2)The Commercial Harvest Exclusion(NCH)policy had potential to increase forest aboveground carbon and abundance of old-growth forests.However the NCH policy made forest at the risk of decrease in the accumulated rate of aboveground biomass since individuals in old-growth forests died of its longevity at the long term.The NCH policy decreased diversity of forest composition and age structure,and thus it might be adverse to providing diverse habitats and maintaining biodiversity.In addition,the NCH policy also decreased the dominance of the rare and protected species,such as Korean pine,amur linden,manchurian ash,manchurian walnut,and amur corktree,and thus it was not conducive to restoring the dominance of Korean pine.Additional thinning increased diversity of forest composition and structure,and increased the dominance of the rare and protected species(such as Korean pine)than the NCH policy.Thus additional thinning partly alleviated the negative effects with the NCH policy but failed to regulate the potential risk of decrease in the accumulated rate of aboveground biomass.(3)The uncertainties of Korean pine response to management treatments increased over time under climate change,and the uncertainties were associated with the regeneration of Korean pine.The effects of proactive treatments on Korean pine were site-specific,and the competition between Korean pine and the rare and protected broadleaf tree species might offset the positive effects.Proactive treatments promoted the leading edge of Korean pine to shift poleward,while they had less impact on its trailing edge.We recommended applying the adaptive treatment to promote Korean pine under future climatic conditions since the adaptive treatment most increased the dominance and regeneration of Korean pine.(4)Pine cone harvesting decreased the dominance and regeneration of Korean pine.Climate change had potential to alleviate the negative effects of pine cone harvesting on regeneration but failed to eliminate them.Climate change eliminated the adverse impacts of pine cone harvesting on the dominance of Korean pine at the short and medium term,but failed at the long term.Succession was the most important factor affecting the dominance of Korean pine.Succession was significantly more important than the pine cone harvesting at the short term,however pine cone harvesting played a leading role in regeneration of Korean pine at the medium and long term.Climate change was not a major factor in determining the dominance and regeneration of Korean pine throughout simulation.The effects of pine cone harvesting and climate change on the dominance of Korean pine are lagged.Although climate change promoted the migration of Korean pine to high latitude region,the pine cone harvesting slowed the migration,which was adverse to Korean pine altering its distribution to adapt to future climate change.(5)Given the potential adverse effects of the Commercial Harvest Exclusion policy,the policy should not be implemented for a long term.We recommended harvesting some old-growth forests to avoid the above risk after banning commercial harvest for 40 years.Future forest management should not only ensure that forests maintain high level of carbon storage,but also focus on increasing the potential to sequestrate carbon.Additionally,harvesting old-growth forests was instrumental in maintaining compositional and structural diversity,and further increasing the adaptability of the mixed Korean pine and broadleaf forests to climate change.Korean pine cone harvesting severely hindered its regeneration and reduced its dominance.Anthropogenic disturbances such as cone harvesting should be strictly limited to restore and to maintain the dominance and regeneration of Korean pine under climate change.