Litterfall, seed size, and predator-free time window enhance survival of a keystone palm in an Atlantic forest restored site

ABSTRACT Although enrichment planting is recommended to increase biodiversity in restoration, environmental filters can prevent the establishment of sowed/planted species. Euterpe edulis is a keystone palm in the Brazilian Atlantic forest, whose fruits are consumed by many animals. We assessed the viability of direct seeding of this palm in an Atlantic forest restored site in Southeast Brazil, guided by these questions: 1) Does germinability vary among seeds covered and uncovered by litterfall and according to litterfall depth? 2) Can direct seeding be impaired by seed predation? 3) Does seed size affect seed predation and seedling vigor? We found litterfall favored germination by reducing soil evaporation, but litterfall depth did not affect germination. Seed predation was low, as seed location was probably unpredictable to rodents. Smaller seeds were more removed, possibly because the larger ones impose transportation costs on small rodents. By removing the smaller seeds, predators may favor the production of larger and more vigorous seedlings. Direct seeding of E. edulis can be successful if implemented in medium regeneration stages of Atlantic forest sites, where shade and moisture provided by litterfall, and absence of mid- to large-sized seed predators, allow seeds to overcome the constraints on germination and predation.

摘要
尽管在生态恢复中推荐采用富集种植（enrichment planting）以提升生物多样性，但环境过滤作用仍会阻碍播种或定植物种的成功定居。Euterpe edulis是巴西大西洋森林中的关键棕榈种，其果实为多种动物所取食。本研究以巴西东南部一处大西洋森林恢复样地为研究对象，评估该棕榈的直接播种造林可行性，研究围绕以下问题展开：1. 被凋落物覆盖与未覆盖的种子，其萌发率是否存在差异？且萌发率是否随凋落物厚度发生变化？2. 种子捕食是否会对直接播种造林造成阻碍？3. 种子大小是否会影响种子捕食概率与幼苗活力？
研究发现，凋落物可通过降低土壤蒸发促进种子萌发，但凋落物厚度对萌发无显著影响。种子捕食率较低，这可能是因为啮齿动物难以定位种子的位置。小型种子被取食移除的概率更高，这或许是因为大型种子会给小型啮齿动物带来更高的搬运成本。捕食者移除小型种子的行为，可能会间接促进大型且更具活力的幼苗的形成。
若在大西洋森林恢复至中等阶段的样地中开展E. edulis的直接播种造林，即可取得成功：此类样地具备凋落物提供的遮阴与湿润环境，且不存在中大型种子捕食者，能够帮助种子克服萌发与捕食带来的限制。