Abstract
Natural regeneration is less expensive than tree planting, but determining what species will arrive and establish to serve as templates for tropical forest restoration remains poorly investigated in eastern Africa. This study summarises seedling recruitment under 29 isolated legacy trees (14 trees comprised of three exotic species and 15 trees comprised of seven native species) in tea plantations in the East Usambara Mountains, Tanzania. Among the findings were that pioneer recruits were very abundant whereas non-pioneers were disproportionately fewer. Importantly, 98% of all recruits were animal-dispersed. The size of legacy trees, driven mostly by the exotic Grevillea robusta, and to some extent, the native Milicia excelsa, explained abundance of recruits. The distribution of bird-dispersed recruits suggested that some bird species use all types of legacy trees equally in this fragmented landscape. In contrast, the distribution of bat-dispersed recruits provided strong evidence that seedling composition differed under native versus exotic legacy trees likely due to fruit bats showing more preference for native legacy trees. Native, as compared to exotic legacy trees, had almost two times more non-pioneer recruits, with Ficus and Milicia excelsa driving this trend. Implications of our findings regarding restoration in the tropics are numerous for the movement of native animal-dispersed tree species in fragmented and disturbed tropical forests surrounded by farmland. Isolated native trees that bear fleshy fruits can attract more frugivores, resulting not only in high recruitment under them, but depending on the dispersal mode of the legacy trees, also different suites of recruited species. When selecting tree species for plantings, to maximize visitation by different dispersal agents and to enhance seedling recruit diversity, bat-dispersed Milicia excelsa and Ficus species are recommended.
Highlights
IntroductionTropical forests have been modified by human disturbance for centuries, but in the Anthropocene era, habitat loss and fragmentation have escalated to the point that once extensive forests are dissected landscapes
This study summarises seedling recruitment under 29 isolated legacy trees (14 trees comprised of three exotic species and 15 trees comprised of seven native species) in tea plantations in the East Usambara Mountains, Tanzania
Tropical forests have been modified by human disturbance for centuries, but in the Anthropocene era, habitat loss and fragmentation have escalated to the point that once extensive forests are dissected landscapes
Summary
Tropical forests have been modified by human disturbance for centuries, but in the Anthropocene era, habitat loss and fragmentation have escalated to the point that once extensive forests are dissected landscapes. In the Eastern Afromontane biodiversity hotspot of eastern Africa, habitat fragmentation and loss are considered among the two greatest threats to biodiversity [1]. The East Usambara Mountains, Tanzania, are one of the most species and endemic rich sites in this biodiversity hotspot, but extensive tracts of forest were deforested and converted to tea plantations during the British colonial administration when tea was introduced from India as a cash crop [2]. The post-colonial period has added further threats to the forest in the East Usambaras, including subsistence agriculture which has encroached into the protected and unprotected forest [2]. In eastern Africa, experimental forest restoration is scant to non-existent, and knowledge is limited on the restoration process and potential tree species to plant
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