Study On The Influence Of Food-hoarding Rodents On Early-stage Regeneration Of Forest Gaps

In the forest ecosystem,many small mammals mitigate seasons of food shortage or take short-term resources by scatter-hoarding seeds in their caches as long-term food supplies,which play an important role in promoting the formation of soil seed bank and natural regeneration of the forest,and facilitate the seedling establishment.Animal's food-hoarding behaviour is influenced by multiple environmental factors,for example forest-gap,one of the most frequent disturbance outcome occurring in various types of forests.Forest gaps have been demonstrated maintain species dynamics and enhance biological diversity of forest ecosystems by creating environmental heterogeneity and modifying abundances and distribution of abiotic and biotic resources.At present,although the factors,such as the light,humiture,soil nutrient,affects seedling regeneration in forest gaps have been extensively studied,the more important roles that significantly contribute to seed dispersal and seedling establishment through scatter-hoarding tree seeds are largely ignored.There remains uncertain whether the scatter-hoarding animals,under the interference of the forest gaps,influence seed bank dynamics and seedling establishment.In this thesis,according to the study of the animals scatter-hoarding behaviour in the forest gap microhabitat,relying on small radio transmitters,infrared camera,and GUDs technologies,we analysed:(1)the influence of forest gap predation risks on the behaviour of scatter-hoarding animals by field surveying;(2)the influence of animals on the seed bank dynamics in forest-gap by investigating volumes of storage and germination of natural and artificial soil seed banks in both gaps with different size and under canopies;(3)the influence of animal predation and forest gaps on seedling growth by observing seedling growth in different habitats around the forest gaps;and(4)the chemical-defence characteristics of the forest-gap seedlings in reaction to insect predators by exploring the herbivory of the leaves of Q.mongolia seedlings.The main conclusions are as follows:1.The process of seed rain and the abundance of food had influences on the patch use of rodents in gaps with different size and under canopies.Based on live-trapping and infrared camera capturing,we identified A.peninsulae,S.vulgaris,C.rufocanus and T.sibiricus as the main seed predators and dispersers.The forest gap affected animal's predation,with higher predation risk of small rodents in gaps than under canopies,and the predation risk increased with an increase of gap size.There was higher predation risk during the prophase of seed rain than that of metaphase and anaphase of seed rain,and the predation risk in the middle gaps decreased with the seed rain process.The food abundance made no difference to predation risk in both large gaps and under canopies,however,the predation risks in middle and small gaps increased with an increase of the food abundance.2.Seed characteristics and interspecific interference had effect on rodents food-hoarding behaviour in gaps and under canopies.(1)The big walnuts buried in the gaps outnumber the small ones,and the seed survival time in the gap overrun that under canopies,but had no linear relationship with the seed weight.(2)Small rodents tended to dispersal seeds of Q.aliena more quickly than the seeds of J.mandshurica and Q.mongolica,and 65.3% of released seeds of J.mandshurica were scatter-hoarded in the gaps.The corresponding data for Q.mongolica and Q.aliena were 29.9% and 21.4%,respectively,and among the scatter-hoards of J.mandshurica made by small rodents,18.5% of them were established in the gaps,while only 5.3% and 3.7% of scatter-hoards of Q.mongolica and Q.aliena were found in the gaps.(3)Under the interspecific interference,small rodents prefered to dispersal and eat the seeds of P.koraiensis,while tended to scatter-hoard more seeds of J.mandshurica(about 70%),than that of P.koraiensis(about 10%).Interspecific interference promotes the seed dispersal of the two species,while decreases the scatter-hoarded seeds of P.koraiensis.Among the scatter-hoards of J.mandshurica made by small rodents,2.7% and 3.5% of them were established in the gaps and in the gaps edges,while only 0.93% of scatter-hoards of P.koraiensis were found in the gap-edges,but no P.koraiensis seeds in the gaps.Habitats of gap-edges and under canopies were without prejudice to the dispersal speed of the two species and their seeds fates after dispersal by small rodents.Interspecific interference was in favour of dispersing seeds of J.mandshurica but went against P.koraiensis,which exerted asymmetrical influences on the two species.3.Scatter-hoarding behaviour of small rodents affected soil seed banks both in the gaps and under canopies.(1)The density of Q.mongolica seeds surviving on the overground were remarkably more than that of J.mandshurica,and the seed density increased with the sizes of the gaps,with the highest seed density in the overground at the gap-edges,and higher in the center of gaps than under canopies.The density of the seeds buried below the ground are in line with each other between the two species,which was influenced by the size of gaps,with the greatest seeds density buried under the canopies,and higher density in middle gaps than that in the large and small gaps.(2)The wire netting could protect soil seed banks from small rodents' predation,and the density of seed bank in gaps was significantly higher than that of under canopies.The density of Q.mongolica seeds surviving in the seed bank was more than that of J.mandshurica and P.koraiensis.The locations of seed bank and treatments(with-or without-wire netting)had an integrative effect on its survival amount,i.e.the wire netting exerted little protection of the seed bank in the soil under canopies.Setting up a wire netting in the gaps made no noticeable difference to the proportion of P.koraiensis in the soil seed banks.(3)The germination rate of seeds in gaps was obviously higher than that under canopies,a rise in the gaps protected by the wire netting,but without change under canopies.There were significant differences in germination rates among the three species,with the germination rate of Q.mongolica(25.4%)higher than that of J.mandshurica(16.7%)and P.koraiensis(7.5%).(4)The large seeds of Q.mongolica were more vulnerable to rodents predation,thus more small seeds survived and germinated both in the gaps and under canopies.4.The gap size and within-gap position had influence on the growth of seedlings.(1)The seedling of Q.mongolica in the gaps,from 2015 to 2016,grew rapidly,fastest in the middle gaps.The seedlings in large and middle gaps showed the secondary flush growth and stronger photosynthesis,thereby grew faster.The net photosynthetic rate was a little bit lower in large gaps than that in middle gaps,which were the highest.(2)Although an effect of within-gap positions on seedling growth was detected,it was highly dependent on gap size.Seedlings adjacent to gap edges were smaller than that close to the gap and in the north better than in the south,but this phenomenon was not found in either large or small gaps.Gap size was the main factor affecting growth of Q.mongolica seedlings.Gaps with middle size tended to show more profound effects on seedling performance than gaps with large and small size.5.The forest gaps microhabitat influenced seedling predation of Q.mongolica.(1)Seedlings of Q.mongolica were less likely to be pruned during the sampling period in the gaps relative to the associated canopy forests,and the less possibility of the cotyledons removed and the shoot clipping by small rodents,but the more possibility of cotyledon removed than shoot clipping.(2)The relative abundances of 1-year seedlings were not significantly different in gaps with different size.The rate of the cotyledon removed and shoot clipping decreased with increase of the size of forest-gap.Similar patterns were found in the proportions of seedlings with both cotyledons and shoots clipped by small rodents among different gaps.The proportions of seedlings with cotyledons removed by small rodents at the final survey were not different between gaps with contrasting sizes and the associated closed canopy forests.(4)Seedlings with both shoots and cotyledons clipped accounted for more than 66% of the seedlings damaged by small rodents;Seedlings only with cotyledons removed by small rodents showed high level of survival(100 %),while seedlings with both shoots and cotyledons clipped were less likely to survive(7.9 %),which regenerated only in the large gaps(3.9%).6.The forest-gap microhabitat had influence on herbivory frequency of Q.mongolica seedlings,material distribution and chemical-defence of the seedlings of Q.mongolica.(1)The proportion of leaves herbivory in the forest gaps was higher than that under canopies,with a 70% proportion of leaf cutting,a 15% of epidermis defoliation,less than 2% of leaf mine.The size of the forest gaps had influence on the rate of insects preying on seedling,with the most serious herbivory founded in the middle gaps,little influence on the rate of leaf mine,among which the herbivory frequency of leaf mine in the small gaps was the highest(1.89±0.87%),and less than 1% both in the large gaps and under canopies.(2)The leaf water content of J.mandshurica(74.8%)was remarkably higher than that of Q.mongolica(63.3%),so as well higher under canopies than that in the forest gaps.The leaf total phenolics content in the forest was higher than that under canopies,the leaf total phenolics content of Q.mongolica seedlings being the same as that of J.mandshurica.There was a negative correlation between herbivory frequency and contents of water and soluble sugar,but a positive correlation with the leaf total phenolics content,and the starch content had little influence on the herbivory frequency of Q.mongolica seedlings.