How does the 120-year cycle mast seeding of dwarf bamboo affect the rodent population?

Background:In 2017,large-scale flowering,seeding,and dying events of dwarf bamboo(Sasa borealis)occurred in a wide range in central Japan for the first time in 120 years.This phenomenon of S.borealis,like the mast seeding of trees,could be expected to provide a large amount of food for seed-eating rodents and gradually affect their ecology and population dynamics.We captured rodents in survey plots in a secondary broad-leaved forest with the phenomenon from 2018 to 2019 to investigate the species,the number of individuals,growing stage,sex,and body mass.In addition,we also compared the capture data for 2 years(2018–2019)with that for the mast seeding year(2017)and 6 years before it(2011–2016).Results:The mast seeding of S.borealis greatly increased the population size of rodents,especially Apodemus speciosus and A.argenteus.Conversely,Eothenomys smithii did not show such an increase.Most of the captured rodent individuals were already adults at the time of new capture,and the proportion of male juveniles was extremely low.These results suggest that the mast seeding of S.borealis created unusually rich food availability for the population concentration of rodents due to their immigration.However,body mass was not significantly different before and after the mast seeding.In addition,the increased populations of the two Apodemus species did not decline 2 years after the S.borealis masting,contrary to the previously reported decrease of rodent populations after tree masting.Conclusions:Our results indicate that the mast seeding of S.borealis affected the population dynamics of Apodemus species over a long time and their individual composition of different growth stages.However,it did not affect their body mass.

Constraints on treeline advance in a warming climate:a test of the reproduction limitation hypothesis

Aims Several mechanistic hypotheses have been developed to explain the existence of alpine treelines worldwide.The reproduction limita-tion hypothesis(RLH)postulates that reproductive processes such as seed production and dispersal are restricted in treeline envi-ronments,thereby limiting the establishment of new individuals in advance of extant treelines.Despite its popularity,no study has tested this hypothesis in a comprehensive fashion.In this experi-ment,we attempted to answer whether there are enough viable seeds being dispersed beyond treeline for sexually mediated tree-line advance,and what the implications of climate change might be on these processes.Methods We established 30 plots across two aspects(north vs.south)and three elevational habitats(forest,treeline and tundra)in a white spruce(Picea glauca)boreal forest-alpine tundra ecotone in south-west Yukon,Canada.In each plot,tree characteristics,seed produc-tion and predispersal damage were measured.Additionally,eight dispersal trays were positioned in each plot to measure seed rain,and germination trials with and without predation exclosures were constructed in a subset of plots to quantify dispersal and germina-tion success.Important Findings Results were highly variable both temporally and spatially.In 2014,a mast year,69%of adult trees produced cones compared to 0.4%in the following year.Higher density of trees in forest plots compared to treeline and tundra resulted in greater seed production at lower elevations.Across all plots,88%of seeds were damaged before dispersal or were not viable.Treeline plots had significantly greater predispersal damage.Seed rain was greater in south-facing plots than north-facing plots.Less than 2%of seeds produced on the landscape were dispersed into Tundra plots,located 50 m above treeline.There was a net movement of seeds from the north-facing slope to the south at our study site,likely due to prevailing winds during the dispersal period.Germination counts were more than double on north-facing slopes and one-third higher inside exclo-sures.Cumulatively,the results provide some evidence for the RLH.Collectively,the high amount of predispersal damage and non-viable seeds,variability associated with dispersal and significant seed predation can functionally influence treeline dynamics.These findings suggest that global treeline distribution models,which rely largely on temperature,may not be entirely accurate for predicting treeline advance-at least at finer temporal scales.Many stochas-tic factors need to align temporally for successful advance,which is likely to result in a lag of many decades between the period of temperature amelioration and an increased number of trees beyond extant treelines.