Abstract:Planted and invading non-native plant species can alter fire regimes through changes in fuel loads and in the structure and continuity of fuels, potentially modifying the flammability of native plant communities. Such changes are not easily predicted and deserve system-specific studies. In several regions of the southern hemisphere, exotic pines have been extensively planted in native treeless areas for forestry purposes and have subsequently invaded the native environments. However, studies evaluating alterations in flammability caused by pines in Patagonia are scarce. In the forest-steppe ecotone of northwestern Patagonia, we evaluated fine fuels structure and simulated fire behavior in the native shrubby steppe, pine plantations, pine invasions, and mechanically removed invasions to establish the relative ecological vulnerability of these forestry and invasion scenarios to fire. We found that pine plantations and their subsequent invasion in the Patagonian shrubby steppe produced sharp changes in fine fuel amount and its vertical and horizontal continuity. These changes in fuel properties have the potential to affect fire behavior, increasing fire intensity by almost 30 times. Pruning of basal branches in plantations may substantially reduce fire hazard by lowering the probability of fire crowning, and mechanical removal of invasion seems effective in restoring original fuel structure in the native community. The current expansion of pine plantations and subsequent invasions acting synergistically with climate warming and increased human ignitions warrant a highly vulnerable landscape in the near future for northwestern Patagonia if no management actions are undertaken.
Post planting assistance techniques during early ontogeny may be a determining factor for tree survival in stressful habitats. In the eastern region of NW Patagonia, stands of the fast-growing exotic conifers Pinus ponderosa (Ponderosa pine) and Pseudotsuga menziesii (Douglas fir) are being established in places which are currently, or were in the past, occupied by native Austrocedrus chilensis (mountain cypress) forests. We hypothesize that mitigation techniques could (1) reduce photoinhibition and consequently increase the net photosynthesis rate of plants under high radiation conditions due to increases in the dissipation of radiation with Kaolin, (2) improve water availability in soils using hydrogel, and (3) reduce the effects of chills and frosts events in the species that are most susceptible to environmental stress, A. chilensis and P. menziesii, achieving similar values to those measured in the most resistant species, P. ponderosa using film-forming polymers such as Poly-1-p-Menthene. The short-term responses of seedlings to solar radiation, soil water availability and air temperature were evaluated through gas exchange capacities. Our results indicate that the effects of the different techniques depend on the susceptibility of the species to environmental stress. Kaolin treatment increased stomatal conductance, photosynthesis and transpiration rates in all species. For the hydrogel assay, higher pot volumetric water content was observed in treated plants than in control plants. Pinus ponderosa showed a lower response to the application of hydrogel, while a positive response was observed in A. chilensis and no effect in P. menziesii. The frost mitigation technique evaluated proved unsuitable for the three study species, but appears to work as an anti-desiccant for P. menziesii. In order to optimize the process of planting and establishment for a particular species, the package of techniques needs to be evaluated regarding the requirements and susceptibility to environmental stress of that species.
Previous studies of afforestation in Patagonia indicate that 30-50 % tree cover produces positive effects on the pasture. This coverage level is achieved by applying pruning and strong thinning to reduce the volume of timber production per area unit. From an economic standpoint, in order to not reduce the income level of the system, it is necessary to find tree species that could replace ponderosa pine (Pinus ponderosa) and maximize income per volume unit of wood. We evaluated the feasibility of implementation of five broadleaved tree species (native and exotic) with higher intrinsic wood quality than ponderosa pine. We tested the influence of tree cover generated by a framework of silvopastoral plantation on the increase in survival, regrowth and absolute increase in height, and compared ecophysiological variables (net photosynthetic activity, stomatal conductance, intrinsic water use efficiency) of different species to the status of a traditional plantation without tree cover. Additionally values of air temperature and relative humidity were registered under both cover conditions. Preliminary results support the conclusion that three of these five species could be considered as alternatives to ponderosa pine species for establishing silvopastoral systems with higher timber value. Our Based on the results, the use of tree cover generated under the current plantations of P. ponderosa could increase the success of the establishment of these species.
Interspecific hybrids of E. grandis × E. camaldulensis were generated to widen the plantation area. The aim of this study was to assess root capability and development for six different clones of eucalyptus grown in substrates made with three different composts derived from poultry manure. A factorial design was used to assess the effect of different composts on six growth variables. The analysis detected a greater effect from the genotype than the substrate. E. grandis × E. camaldulensis hybrid vegetative propagation was successful in alternative substrates formulated from composted poultry manure. GC8 was the genotype that showed the greatest differences for four the different variables among the substrates, being both the most sensitive and the one with the highest values for all parameters measured. The hybrids' vegetative propagation was determined in alternative substrates formulated from poultry manure compost. The physicochemical characteristics of substrates composed of pine bark and sawdust provided adequate conditions for the growth of eucalyptus. GC8 was the genotype most sensitive to the use of different substrates, showing significant differences in the ratio of roots/callus, radicular dry weight, and cutting dry weight. These clones might be a good option for evaluating compost-based substrates for forestry applications.
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