OPTIMAL FOREST MANAGEMENT OF STANDS UNDER CLIMATE UNCERTAINTIES.
At present, the global climate change shows a general increase in atmospheric temperature and precipitation. The past 50 years (1956-2005) mean global temperature increased at a rate of 0.10 to 0.16 ?C per decade, which is nearly twice the average over the past 100 years. This temperature rise is largely caused by an increase in greenhouse gases in the atmosphere of which CO2 is the most important. Global atmospheric CO2 concentration increased from a pre-industrial value of about 280 ppm to 379 ppm in 2005, where the annual increase during the period 1995-2005 was on average 1.9 ppm per year (IPCC, 2007). The report also states further that climate change will amplify existing risks and create new risks for natural and human systems.
Many more scientific reports and Journals at various levels are increasingly empirically postulating and modelling the widespread impact of climate change on both global physical and natural systems.
The impact of climate change on global forest ecosystem functioning and dynamics cannot also be ruled out, globally, climate change scenarios has been recorded and observed to have considerably lead to the change of forest productivity and growth range shifts, and health status.
The best example that comes to mind was in the context of temperate forest, despite the obvious fact that the temperate forests cover about 10.4 million km2, (an estimated 40-50% of their original extent) contributing to approximately 25% of the world’s forest cover today and contains an estimated 99-159 Pg. of carbon, which is about 11% of the global carbon stock has been relatively stable in terms of composition and diversity and on the increase in past years but recently has been showing some considerable stress in a reversal of tree growth, increasing tree mortality and changes in fire regimes, insect outbreaks, and pathogen attacks all due to the impact of climate change as reported by major recent publications illustrated in the IPCC report of 2017 . In north-eastern France for example the widespread and the recent declines in growth rates of European beech (Fagus sylvatica L.) have been attributed to decreasing water availability. Charru et al (2010).
Denis Loustau et al (2005) has also modelled the impact of climate change effects on the potential production of French plains forests at the sub-regional level under different management scenarios and predicted and analysed the climate impact on potential forest production over the period 1960–2100. In all, the models used predicted a slight increase in potential forest yield until 2030–2050, followed by a plateau or a decline around 2070–2100, with overall, with a greater increase in yield in North-eastern France.
Marcus Lindner et a (2014) further states that climate change in the European context may impact forests in ways that are partly opposing and therefore can require adaptation activities that are difficult to design and to plan precisely and why? planning adaptation strategies seems to be a complex and challenging task, as gradual changes and the more catastrophic impacts of extreme events require different activities. (Marcus Lindner et a 2014).
The economic cost of climate change on European forest at large has been modelized, analysed and presented in few reports, Hanewinkel et al (2013) has modelled the economic gains or loss applicable to climate change on European forest/land and based on their report, it was expected the value of European forest land will decrease owing to the decline of economically valuable species in the absence of effective countermeasures. The report also found out that by 2100-depending on the interest rate and climate scenario applied-this loss will varies between 14% and 50% (mean: 28% for an interest rate of 2%) of the present value of forest land in Europe, excluding Russia, and may total several hundred billion Euros. The model shows that-depending on different realizations of three climate scenarios being modelled in the report, by 2100, between 21 and 60% (mean: 34%) of European forest lands will be suitable only for a Mediterranean oak forest type with low economic returns for forest owners and the timber industry and reduced carbon sequestration.
Coming to France and based on the economic importance of the two species in this discuss, the earlier explanation that climate change is certain to affect the growth rate and the productivity of these species especially for Beech (Fagus sylvatica L.) which stands to be more vulnerable (Charru et al (2010),and further predicted to face a higher drought sensitivity and problems in coming years (Daniela Diaconu et al (2015) and thus, it would not be wrong to perceive (but not proved) that the economic value of the species would not also be affected as such.
The past vis-a vis the present and future silvicultural practices for most European economic and important trees (here emphases on Beech and Douglas firs) could also be predicted to face a drastic adjustment in designs, intensity a frequency in the light of the growing trends and treats of the climate change forcing(severity) to create a proper adaptive strategies and practices to preserve the ecological and the economical integrity of the tree species. For example, Koen Kramer et al (2009) and Daniela Diaconu et al (2015) in different scenarios has modelized the effect of different thinning intensities and timings on Beech and diverse but interesting results were observed and reported in those reports that points to the fact that climate change will affect the future silvicultural practices of the specie.
More so, until now, the beech silviculture and management in France has been coordinated by natural regeneration and widely has an average rotation age which is generally 140 to 150 years, meanwhile based on the growing implication of climate change impacts, most researches were suggesting a shorter rotation of up to 100 to 120 years through earlier and more vigorous thinning, leading to wider crowns, wider growth rings, lower wood density, and less internal wood constraints (Teissier du Cros et al, 1981).
Douglas fir, which is originally a native of North American coastal range locations but now widely spread across the continental Europe including France has been recorded to be best suited to well-drained soils of good depth and of moderate fertility and thus well adapted to the soil profile of France especially the central France regions.
As far as forest areas are concerned the data refers to the end of 1992. France has 304,000ha of Douglas fir plantations (about 2.1 % of the forest area), 209,000ha (69%) are concentrated in five Regions which have more than 30,000 hectares each, and 95,000ha in the other 15 Regions (Jean de Champs,1984).
Compared to the beech species, the normal rotation lengths for Douglas fir are between 50 and 65 years, depending on the site productivity and early and high pruning regimes has been widely used and practiced and carried out selectively at an early stage.
The broad and forgoing objective of the study is to investigate the optimal forest and economic management that should be best adopted under the uncertain climate change scenarios as it affects the forest stands , the thesis tends to make use of models(empirical model) to simulate growth for Beech and Douglas firs under different silvicultural schedules and intensities(e.g. the intensity of thinning, the removal strategy, the nature of the thinning etc.),under diverse climate change scenarios(catastrophic or moderate) to eventually create the best adaptive silvicultural strategy and decisions that would be most viable based on the future climatic status and tendencies while also considering in detail the economic implication of such output decisions and the simulated scenarios.
A study of this nature is very pertinent especially in the context of France (vosge forest) and the growing important of the tree species in question that has been predicted to face certain degree of side effects (Charru et al (2010) and (Anne-Sophie Sergent et al 2014), both ecologically and economically in relation to the growing threat of climate change and future forest management decisions in France.
The use of empirical, tree centred and distance- independent tree growth models (in this case the fagacces) is situatable and justifiable while considering the proven fact that the model is practically developed and adopted for broad leaved species especially for the pure beech and oak plantations and also due to the lack of yield models for the management of these tree species (Gilles Le Moguédec,2011), also due to the top–down organisation of the model , it combines the properties of a stand growth model (robustness and reliability) and some of tree-cantered models (individual stem profiles )and hence well appropriate for a study like this.
The research work as stated earlier will further critically make use of discounting economic principle via optimum rotation age calculations and the land value evaluation metrics to further investigate the economic assessment (gain or loss) of the all the modelled outputs under the different climate change scenarios and simulations to generate assumptions and formulations via economic models for the future management of the tree species in question.