Effects of leaf litter depth on the emergence and seedling growth of deciduous forest tree species in relation to seed size1

KOSTEL-HUGHES, F T P YOUNG, AND J D WEHR. (Louis Calder Center-Biological Field Station and Department of Biological Sciences, Fordham University, PO receptacle 887, Armonk, NY 10504). issues of leaf litter depth upon the emergence and seedling development of deciduous forest tree species in relation to se size. J Torrey Bot Soc 132: 50-61 2005.-Leaf litter has a major impact upon soil microenvironmental conditions and in like manner can be an important influence upon seedling recruitment and hence plant community conformation We conducted a greenhouse experiment to examine the impact of leaf litter from temperate deciduous forests upon the emergence and growth of tree seedlings in relation to se size. Our treatments were bare (no litter), shallow (1-2 cm reaching far down 140 g.m^sup -2^), and of great depth (ca. 5 cm deep, 420 gm^sup -2^) litter. Se sizes ranged from 07-3636 mg For Betula lenta (se mass = 07 mg) emerging see the verb on bare soil was greater than 50% approximately 12% in shallow litter, and no emerging see the verb in deep litter. Percent emerging see the verb for Liquidambar styraciflua (seed mass = 6 mg) was highest in bare soil and shallow litter treatments (64-69%) and was reduc by the agency of more than 80% in the of great depth litter treatment. Ailanthus altissima (se mass = 30 mg) and Quercus velutina (se mass = 1900 mg) exhibited no significant differences in emerging see the verb among litter depth treatments whereas, for Quercus rubra (se mass = 3636 mg) percent emerging see the verb was over 50% greater below deep litter than under shallow litter. Seedling increase also differed in response to the litter treatments. For the sum of two units smallest-seeded species, B. lenta and L styraciflua, seedling robustness (aboveground biomass divided through seedling height) was greatest in the bare treatment. Seedling robustness of Q velutina decreased with increased litter profundity while Q. rubra had its greatest seedling robustness in the shallow litter treatment. For A. altissima, seedling robustness and root:shoot ratio the couple decreased with increased litter deepness Our results suggest that the sum of two units smallest-seeded species are better adapted to colonizing post-disturbance sites where there is likely to be les litter, whereas the sum of two units largest-seeded oak species are better-suited to establishing in forests with a thicker litter layer. This is consistent with the communities in which these species typically are lay the foundation of The enhanced seedling growth of A. altissima in bare-to-shallow litter conditions may be individual of the attributes that accounts for the succes of this highly invasive non-native species in urban forests in the of recent origin York City metropolitan area which have shallower litter than nearby rural forests.

Key words: germination, recruitment, regeneration, urban forests, non-native species.

Leaf litter has lengthy been recognized for its importance in the nutrient dynamics of plant communities (see review in Facelli and Pickett 1991a). More lately researchers have begun to focus upon how litter directly and indirectly influences abiotic conditions and biotic interactions, thus playing a major part in structuring many plant communities (Facelli and Pickett 1991a, Xiong and Nilsson 1997 Xiong and Nilsson 1999) Studies have concentrated upon the effects of leaf litter upon seed germination and seedling establishment because of the potential importance of this life stage for determining coming time community composition (Grubb 1977, Harper 1977) and because of the sensitivity of this life stage to the soil microenvironmental conditions (light, temperature, and moisture) upon which litter can exert major impacts.

Leaf litter can bring diurnal and annual thermal amplitude in forests by means of decreasing the amount of solar radiation reaching the soil and by means of providing insulation for the soil (MacKinney 1929 Molofsky and Augspurger 1992) Soil moisture is typically greater (Beatty and Shole 1988) and fluctuates les (Tao et al. 1987) beneath leaf litter than when bare. Larger patches of litter have been lay the foundation of to have greater soil organic matter and lower soil mass density than smaller litter patches (Dighton et al. 2000) Leaf litter intercepts and changes the quality of light reaching the soil (Vazquez-Yanes et al. 1990 Facelli and Pickett 1991b Schimpf and Danz 1999) Litter also not aways a physical barrier that can interfere with semens reaching the soil, the emerging see the verb of seedlings, and seed visibility to predators (Shaw 1968 Facelli and Pickett 1991a, Myster and Pickett 1993 Vellend et al. 2000)

Leaf litter is heterogeneously distributed within and across forests. The distribution of leaf litter upon the forest floor can differ to be paid to slope and aspect (Frankland et al. 1963) canopy overlay (Molofsky and Augspurger 1992), topography (Dwyer and Meriam 1981 Beatty and Shole 1988) fire (Enright and Lamont 1989) urbanization (Kostel-Hughes et al. 1998) successional stage (Persson et al. 1987 Facelli and Carson 1991) understory (George and Bazzaz 1999 Dighton et al. 2000) and cutting side effects (Facelli and Carson 1991 Matlack 1993 Didham and Lawton 1999 Haskell 2000) Differences in microenvironmental conditions created through litter are thus likely to be similarly heterogeneous. sperms which are also patchily distributed (Bigwood and Inouye 1988) are species-specific in their reply to these conditions. Microenvironmental conditions, se availability, and species answer to microenvironmental conditions, can therefore differ greatly and together determine seedling germination and establishment in the community (Grubb 1977 Harper 1977)