Ecology of vascular epiphytes in urban forests with special reference to the shrub epiphyte Griselinia lucida
Bryan, C. L. (2011). Ecology of vascular epiphytes in urban forests with special reference to the shrub epiphyte Griselinia lucida (Thesis, Master of Science (MSc)). University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/5713
Permanent Research Commons link: https://hdl.handle.net/10289/5713
This research investigated the ecology of vascular epiphytes and vines in the Waikato region of the North Island, and the water relations of the shrub hemiepiphyte Griselinia lucida. The main goal was to develop robust recommendations for the inclusion of epiphytic species in urban forest restoration projects. To achieve this, three broad questions were addressed: 1. How are vascular epiphytes and vines distributed throughout the nonurban and urban areas of the Waikato region, and how does this compare to other North Island areas? 2. Why are some epiphyte and vine species absent from urban Hamilton and what opportunities exist for their inclusion in restoration projects? 3. How does Griselinia lucida respond to desiccation stress and how does this compare to its congener G. littoralis? To investigate questions one and two, an ecological survey of the epiphyte communities on host trees in Waikato (n=649) and Taranaki (n=101) was conducted, alongside canopy microclimate monitoring in five Waikato sites. Results show that epiphyte and vine populations in Hamilton City forests represent only 55.2 % of the total Waikato species pool, and have a very low average of 0.8 epiphyte species per host. In contrast, the urban forests of Taranaki support 87.9 % of the local species pool and have an average of 5.5 species per host tree. The low diversity and abundance in urban Waikato can be primarily attributed to the alteration of canopy microclimates by edge effects. Mean temperature and vapour pressure deficits in Waikato were 1.9 °C and 1.1 kPa (respectively) higher in the canopy of small urban patches than the larger, nonurban forests. These warmer and drier conditions are speculated to be interrupting species accumulation and community formation processes. This phenomenom is not as pronounced in Taranaki which has larger trees and higher rainfall. Epiphyte diversity and abundance was also found to be associated with seed dispersal distances and the size, bark type, and architecture of host trees. To link the microclimate findings with physiological limitations of epiphytes and to address question three, a desiccation tolerance experiment was conducted on the shrub hemiepiphyte Griselinia lucida. Moderate and severe levels of desiccation stress were applied to seedlings of G. lucida and its terrestrial congener, G. littoralis. Both species endured over two months of drought with negligible mortality. In G. lucida, stomatal conductance reduced to zero, and leaf bulk elastic modulus reduced from 8.09 (±0.51) MPa in the control group to 3.66 (±0.61) MPa under severe stress. When compared to G. littoralis, G. lucida exhibited a more acute response to stress and recovered faster with rewatering. However, the overall response of each species was similar and both species can be classified as desiccation postponers. To summarise and combine the findings of this research with existing information on Griselinia lucida, a contribution to the New Zealand Biological Flora Series for this species is presented. Recommendations for the inclusion of epiphytes in restoration projects are presented. Reintroductions should use epiphyte and vine species that are appropriate for the conditions of the target forest, and focus on large host trees in relatively humid microclimates.
University of Waikato
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