| 摘要: | Tradescantia fluminensis (wandering Jew, family Commelinaceae) is a serious invasive environmental weed in many regions in world wide including Taiwan. The weed commonly forms dense, monospecific mats that prevent native forest regeneration. It also reduces indigenous biodiversity, alters litter decomposition and changes soil nutrient availability. While there is a general awareness of the global march of invasive weeds there are relatively few studies ecological impacts and distributions of this species on the system they invade in Taiwan.
This thesis is concerned with the combined effects of climate and spatial distribution of the sub-tropical invasive plant, T. fluminensis. The contribution of this thesis is to undertake an integrated assessment of the distribution change for this species in Yangmingshan National Park, Taiwan. On the basis that temperature variables affect species distribution at larger scales, while land use, habitat, disturbance and dispersal mechanisms affect distribution at regional scales, two separate analyses was undertaken which based on laboratory analysis and field surveys. At broad-leaved forest remnants in Yangmingshan, we showed that T. fluminensis biomass increased logistically with available light, to a maximum at PAR of 1.098 -1.567 W/m2 or 2-4% of direct sunlight and with Red / Far Red ratio ranging from 0.204-0.655.The maximum T. fluminensis coverage was greater at the wetter site with 78.21± 14.64% soil moisture level. Above ground temperature also plays a major role for the distribution of T. fluminensis in Yangmingshan. The laboratory experimental data revealed the optimum temperature for better growth of T. fluminensis was 25 °C constant day and night temperature regime in growth chamber. The other temperature regimes in growth chambers such as 30/25°C, 25/20°C, 20/15°C day and night respectively act as suboptimize and the temperature regimes 35/30°C and 10/5 °C day and night respectively recorded slowest growth rate of fresh weight, root and side branches length increment of tested plant.
Many authors describe climate change, land use change and invasive species are transforming global biodiversity at multiple scales. Projections are for threats to biodiversity from these global changes to continue into the future, with varied and discernible distribution changes for many species. Concomitantly, these global changes will interact with each other to further exacerbate the problem, as exemplified in this study. In Yangminshan, climate change is expected to increasing the potential invasibility of T. fluminesis as past 60 years analysis of regional temperature shows slight increment up-to-date. It will create favorable environment for better growth of T. fluminensis especially in broad leaf forests and shift their range more towards higher elevation and will pose a greater risk to native habitats than at present.
Conventional control is difficult and very costly. Therefore an initiation of integrated target control and tree planting to improve the canopy cover with biological control programme are suggested as a means to arrest the decline of T. fluminesis affected forest remnants. |
