Spatially-explicit Modeling of Siberian Boreal Forests

Circumpolar boreal forests contain one half of the terrestrial carbon stores, and have been shown to be susceptible to climate change. As climate regimes shift, the total biomass and species composition may change in ways that may promote further warming on the regional level through atmosphere-vegetation feedbacks. The purpose of this project is to develop a spatially explicit model for simulation of structure and dynamics of boreal forest through space and over time. The current model builds on previous forest gap models, and incorporates additional functionality, both, in the programing and the modeling realms. With the new model, we will be able to study the long-term and large-scale responses of the boreal forest to climate change, through the simulation a grids of plots, each approximately 0.1 hectare in size. The spatially-explicit aspect of the model will enable studying the propagation of insect outbreaks and wildfires across the landscape, as both of these types of disturbances are expected to increase in frequency, intensity, and duration with climatic shifts. The model output – changes in the sizes of trees on the plots, the total and species-specific biomass and basal area, as well as species composition, will be imaged and georeferenced in GIS software. Introduction Siberian Boreal Forest Boreal forests are located between 50N and 70N latitude on the continents of Eurasia and North America, with some regional variability along the southern and northern boundaries. Approximately one third of the global carbon storage is in the above-ground and below-ground biomass within the boreal forests. The largest continuous expanse of forest is found in Russia and constitutes over approximately two thirds of the total boreal forest biome. Boreal forests are floristically simple, which renders their biomass and species diversity more susceptible to climate change. Due to the warming predicted and observed in Eurasian boreal forests, this ecosystem potentially plays a significant role in the planetary carbon cycle, as the changes in forest dynamics may further propagate regional and global warming of ambient air temperatures through a complex system of vegetation-atmosphere feedbacks. Predicting future changes in the Russian boreal forest is intrinsically a modeling issue, as the spatial expanse of the forest and the temporal scale of patterns and processes do not lend themselves to direct measurement or observation. Herein, the approach of spatiallyexplicit model-based synthesis of forest dynamics will be utilized to study the structure and processes of this vast boreal landscape on multiple levels and over time, including an exploration of forest response to climate change. Beyond the large stores of carbon, there are complex internal interactions within the boreal ecosystem. Regional changes in vegetation can lead to changes in regional albedo, which may affect regional climate through atmospherevegetation feedbacks. Of great concern is the replacement of deciduous Larch species (Larix spp.) with evergreen conifer species (Abies spp., Picea spp., Pinus spp.) accompanying an increase in ambient winter temperatures. Larch is a deciduous conifer and, as such, loses foliage in the fall. Consequently, the regional albedo of larchdominated forests in the winter is closer to that of snow, and reflects a significant portion of the incoming solar radiation. In contrast, evergreen trees maintain the same albedo throughout the year. Figure 1 shows a comparison of annual average albedo of conifer (pine) versus deciduous larch stands in a snow-free environment (redrawn from [14]); the albedo of larch is greater than any other conifer. Needle-leaf forests absorb more insolation, while board leaves reflect more and, hence, have a higher albedo. Albedo also depends on foliage nitrogen content. There is evidence that the large-scale replacement of larch and a shift to evergreen dominance by dark conifers, decreases the average regional albedo and drives a positive feedback loop between the ambient temperature and vegetation cover, which may result in further warming and climate changes through alteration of the radiation budget on the regional level, generating a positive radiative