| Phenology -- the seasonal timing of life-history events -- is a critical dimension of natural history. In plants, reproductive phenology is particularly important, affecting gene flow, population persistence and species boundaries. Phenology is also one of the earliest and most noticeable traits by which organisms respond to climate change. However, these responses are complex, and only beginning to be understood, especially in the montane and alpine environments that are among the ecosystems most vulnerable to climate change. Drawing from diverse data sets and employing multiple methodologies, I examined how climate affects phenology in Rhododendron spp. of Mt. Yulong, Yunnan, China.;Mt. Yulong is a center of diversity for Rhododendron, home to a suite of species that are diverse, dominant, and ecologically and culturally salient. They are also extraordinarily well represented by a unique set of historical plant collections. In Chapter 1, I reassemble these historical collections to build a proxy record of Rhododendron phenology, and use this record to show that although increased annual temperatures are associated with earlier flowering, increased fall temperatures are associated with delayed flowering. These contrasting effects have resulted in opposing changes in flowering time, even during rapid recent anthropogenic warming.;In Chapter 2, I comprehensively monitor flowering phenology in the most common Rhododendron species on Mt. Yulong over gradients of season and elevation. I measure individual response to inter-annual temperature change, contextualize the results within the herbarium record established in Chapter 1, and characterize the effects of phenology on reproductive success. Mt. Yulong Rhododendron spp. show an elaborate sequenced progression of flowering over season and elevation. Phenological response to temperature varies among species, elevation, and season. Both phenology and response to temperature directly impact reproductive success, making this progression vulnerable to future climate change.;In Chapter 3, I build a community phylogeny and test phylogenetic signal to examine how phylogeny affects this phenological progression. Uniquely among phenological traits, last flowering day shows a phylogenetic signal, and is associated with flower size and fruit size. I suggest that this pattern may be driven by the limited time for fruit development before the onset of cold temperatures in autumn and highlight the unique and asymmetric pressures on phenology at seasonal extremes.;In chapter 4, I explore the dynamics of ecological knowledge of Rhododendron phenology around Mt. Yulong in two ethnic groups: the indigenous Naxi and immigrant Nuosu Yi. Local knowledge is rich and local understandings of changes and drivers parallels results from Chapter 1 and 2. While these knowledge systems are dynamic and able to adapt to change, they are also threatened by urbanization and changing lifeways.;In combination, these studies reveal the complexity of phenological response to climate change. Our multiple methodologies allow a deeper exploration than simple 'earlier spring' models of phenological response, while similar patterns seen among the diverse data sources increases our confidence in each. Mt. Yulong Rhododendron spp. flower in a progression over season and elevation, constrained to some degree by phylogeny. Both phenology and response to temperature directly impact reproductive success. Their responses to temperature vary among species and across elevations, and the effects of warming in different seasons drive contrasting responses. |
