Ecological restoration, the process of assisting ecosystem recovery following damage by humans, is a critically important practice across the globe. However, the variability in outcomes of restoration action is notoriously large, making it challenging to reliably achieve restoration goals. In this dissertation, I focus on the responses of plant populations that have been reintroduced as part of restoration in two settings: (1) a landscape affected by a large, human-caused fire and (2) experimentally fragmented landscapes. Habitat fragmentation/degradation resulting from altered disturbance regimes (including fire) are leading causes of biodiversity decline and result in local extirpations. In response to these losses, reintroduction efforts are common in ecological restoration. Through four studies, I evaluate reintroduced plant population responses through the processes of plant establishment, seed dispersal, and population growth.I conducted two studies in a recently-burned subtropical upland forest system, in which fire was historically infrequent, in Hawaiʻi: a study on plant-soil feedbacks of two locally-dominant tree species and a study on early establishment of one species post-fire after reintroduction. The interactions between plants and microbes, as mediated by the soil ("plant-soil feedbacks" or PSFs), can influence where and how plants establish from seed. Despite the importance of PSFs and their potential to be altered by fire, little is known about how fire affects PSFs. I investigated PSFs for two nitrogen-fixing leguminous trees inside and outside of a recently burned area. I found that there were largely positive PSF relationships, where both species perform better in soil of conspecifics, relative to heterospecifics. Additionally, I found that fire can reduce the strength of pairwise PSFs between these species, which may result in altered patterns of local coexistence. In the other study, I examined how local environmental conditions modify seedling establishment of a dominant tree species, reintroduced by seed post-fire. I found that elevation was of overarching importance for plant establishment, with context-dependent effects of tree canopy and grass cover, depending on elevation. Together, these two studies show post-fire restoration in this system should account for the soil microbial community and environmental context when selecting areas for plant reintroduction.To examine plant reintroduction in fragmented landscapes, I conducted two studies in a habitat fragmentation experiment in South Carolina: (1) a study on abiotic seed dispersal and (2) a study on recruitment patterns of developing populations. For both studies, I examined developing populations at four distances from patch edges in connected and isolated patches and high and low edge-to-area ratio patches. I found that local-scale seed dispersal distances are greater in patch centers and that dispersal is more directional towards patch edges, but that patch connectivity and edge-to-area ratio did not affect these patterns. In the recruitment study, I examined populations 7 years after reintroduction and looked at both how the number of recruited individuals varied and how a suite of mechanisms may drive differences. I found that, for some species, edges mediate recruitment patterns, but that patch connectivity and edge-to-area ratio do not. In terms of mechanisms for these patterns, I found that edges may operate through factors like canopy cover, which is higher at patch edges than centers. These two studies show that fragmentation does modify plant populations and processes following reintroduction.Together, my findings illustrate how aspects of habitat fragmentation and disturbance affect plant reintroduction efforts. My work contributes to the growing field of interpreting variation in restoration outcomes and may help to guide successful restoration going forward.
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