1Rhododendron ponticum is a serious invasive alien plant in the British Isles and is of 2 significant conservation and economic concern. Here, we integrate information on both the 3 life-history and spatial dynamics of this species within an individual-based, spatially-explicit 4 model and investigate the effectiveness of different control strategies. Importantly, we 5 simulate seed movement and dispersal using a mechanistic seed dispersal model. We 6 investigate the effectiveness of initiating control at the edge versus the core of the infestation, 7 with and without returning each year to remove seedlings. We compare these results to an 8 age-dependent strategy whereby the oldest plants are removed each year. Age-dependent 9 control, in which the oldest plants were removed first, was the most effective strategy 10 investigated, both in terms of the probability of successful eradication and the number of 11 years taken to control. We demonstrate that this is because the older (and taller) plants 12 towards the core produce more seeds that, on average, travel further. Indeed, our results 13 suggest that the expansion of the invading front is actually driven as much by seeds that 14 disperse long distances from these larger plants as by the seed rain from recently matured 15 plants located much closer to the front. Finally, we investigate the potential use of "quarantine 16 lines" -corridors of unsuitable habitat that are sufficiently wide to contain an infestation, 17 preventing spread to vulnerable areas. This study has provided generic insights into best 18 practice for management based on the current understanding of the biology and ecology of 19 this pernicious, invasive plant. 20 21
Alternative silvicultural systems to clearfelling are being adopted in Great Britain as a means of increasing the species and structural diversity of conifer plantation forests. One area where knowledge is lacking is the critical level of below-canopy light for survival and growth of young seedlings. This was investigated by planting seedlings of European larch Larix decidua (Mill.), Scots pine Pinus sylvestris L., Sitka spruce Picea sitchensis (Bong.(Carr.)), Douglas fir Pseudotsuga menziesii (Mirb.(Franco.)), and western hemlock Tsuga heterophylla (Raf. (Sarg.)) in a Sitka spruce plantation thinned to 3 different spacings. The incident light intensity beneath the canopy ranged from about 2 to over 60 per cent of full light. Planting in an adjoining open area provided an indication of growth under full light. Growth and survival of these seedlings were followed for 4 growing seasons. The highest seedling survival was found under the widest spacing and declined with closer spacing and lower light intensity. Only Douglas fir and western hemlock seedlings survived at the closest spacing, and in low percentages. The tallest seedlings of each species were found in the open grown conditions but survival was variable due to increased weed competition. Species-specific growth responses showed little difference under high light conditions but performance at low light was generally consistent with shade tolerance rankings in the literature except that Sitka spruce shade tolerance was slightly lower than expected. Minimum light requirements for these species increased from 10 to 30 per cent of full light with decreasing shade tolerance. Other studies of incident light in Sitka spruce plantations indicated that target basal areas in the range 25-30 m 2 ha -1 are required if these light conditions are to be met, which suggests an irregular shelterwood system with frequent interventions should be favoured.
Despite promising research in the 1980s showing the potential of Scots pine (Pinus sylvestris L.) for the reconstruction of past summer temperatures in the Scottish Highlands, little dendroclimatic work has been attempted in this region since. This reflects, in part, the limited number of sparsely distributed remnant natural/semi-natural pine woodlands in the Scottish Highlands and the lack of old growth forest therein. On average, most of the pine trees dated in this region are around 225 years in age. Here, we present the first results of an ongoing interdisciplinary initiative to develop a long Scottish chronology through the acquisition of modern, historical and subfossil pine material from the native pinewoods, historic structures and lakes of the Scottish Highlands. Radiocarbon dating of 25 subfossil pine timbers recovered from lake sediments identified the presence of preserved material covering the last 8000 years with initial clusters focused on the last two millennia and early-mid Holocene. Although developing a well-replicated 8000 year pine chronology will take many years, this preliminary study indicates that a millennial length pine chronology from the northwest Cairngorm region is a feasible and realistic objective in the near future. The importance of such a record in this climatically important sector of northwest Europe cannot be underestimated.
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