The effects of small-scale environmental heterogeneity on seed germination in experimental treefall gaps in New Zealand

Abstract

Seed germination of woody species was studied in treefall gaps in NewZealand to assess how environmental heterogeneity affects regeneration fromseed. Gaps were created in a relictual Pinus radiataplantation destined for restoration to native forest. Seeds of the nativespecies Alectryon excelsus, Macropiperexcelsum, and Fuchsia excorticata, and theinvasive alien species Cytisus scoparius andBerberis darwinii were sown in sites differing inexposure,with and without 3 cm of pine litter. Litter promoted germinationof Alectryon and Macropiper,independent of site. Without litter, percent germination ofMacropiper was negatively correlated with percent open skyoverhead. Germination of Fuchsia was significantly higherin treefall gaps than in the forest understory, with litter having littleeffect. Cytisus germinated most successfully in sitesexposed to direct solar radiation, with or without litter. Percent germinationof Berberis was high in all sites, and was consistentlypromoted by litter. Glasshouse trials for each species showed the same effectsof litter cover as found in the field. These results suggest thatmicroenvironmental heterogeneity can be an important influence on the speciescomposition of regenerating vegetation within and around treefall gaps.