Mapping & ModelingResearch

Ecological Modeling: Red Spruce

The Journal, Ecological Modeling recently published two articles about red spruce.

Title: Climate change effects on red spruce decline mitigated by reduction in air pollution within its shrinking habitat range by Koo, K. A.; Patten, B. C.; Teskey, R. O.; Creed, I. F.; — pp. 81-90
Ref#: 78097632IE

Title: Projection of red spruce (Picea rubens Sargent) habitat suitability and distribution in the Southern Appalachian Mountains, USA by Koo, K. A.; Madden, M.; Patten, B. C.; — pp. 91-101
Ref#: 78097633IE

Both articles are available for purchase here

The effects of climate change within forest systems are of great concern, especially subalpine and alpine tree species, which are adapted to lower optimal temperatures and have low genetic diversity. Understanding ecosystem complexity may give insight on the future effects of climate change on red spruce growth in the Great Smoky Mountains of the Southeastern U.S. Ecosystem complexity is manifested in indirect effects resulting from the modification of direct interactions between ecosystem factors. Since indirect effects are difficult to capture in either broad-scaled descriptive or fine-scaled experimental studies and operate both within scales (local, regional, or global) and across scales (local to regional to global), systems modeling, which can incorporate both multifactorial direct and indirect interactions within an ecosystem, is used to study indirect effects. Much of the research thus far has focused on within-scale interactions with little focus on interactions across scales. Therefore, there is little understanding of issues at regional and global scales, which, in turn, decreases the ability to predict the impact of global and regional environmental changes on the local scale. The authors used a model known as the Annual Radial Increment Model (ARIM). ARIM uses photosynthetic inputs, respiratory outputs, and hierarchically organized environmental controls represented as direct and indirect interactions among biotic and abiotic factors to explain within- and across-scale interactions at global, regional, and local scales.

A previous study utilizing ARIM found acidic rain and clouds caused interactions between air pollutants, precipitation, cloud immersions, and topographic factors were dominant factors in red spruce decline at higher elevations, while drought stress induced by interactions among high temperature, less precipitation, topographic factors, and coexisting species was responsible for the majority of decline in red spruce at lower elevations. Air pollution had relatively minor effects on low elevation growth. The purpose of this study is to examine the effects of future scenarios of climate change and air pollution on red spruce growth, while accounting for complex within- and across-scale interactions. The authors hypothesize that climate change will result in a decline in red spruce growth in the Great Smoky Mountains National Park (GSMNP) with differing effects on high vs. low elevations. Potential synergistic or antagonistic effects between climate change and atmospheric pollution are currently unknown. This study explores the influences of those two interacting factors on the red spruce ecosystem.

The study area was the virgin red spruce-Fraser fir ecosystem in the GSMNP located in the southern Appalachians. Climatic conditions there result in a red spruce ecosystem with a short growing season (100-150 days) and exposure to frequent cloud immersion and high velocity winds. The forest is further impacted by acidic atmosphere pollution, extreme weather, and balsam woody adelgid infestation.

ARIM estimates annual red spruce growth as a relative performance to a long-term mean and assumes that relative annual growth behaves as an open system in response to annual variation in photosynthesis and respiration in association with environmental factors. Results revealed negative effects on modeled red spruce growth at both high and low elevations with the effects at high elevation lower (1.1% decline) than low elevation (8.6%). Air pollution also impacted both elevations negatively. With a 10% increase in air pollution, high and low elevation red spruce growth decreased at 8.7% and 2.0% respectively. A 10% decrease in air pollution resulted in a 10.3% and 2.0% increase in growth at high and low elevations respectively. Analysis of covariance analyses showed a significant effect between air pollution and climate change at high elevations.

Red spruce has a higher expected vulnerability to climate change than other conifers due to its low genetic diversity and adaptation to low optimal temperatures. Winter warming may result in early bud burst in the spring, leaving buds vulnerable to frost damage. Increased summer temperatures may also result in photo-inhibition. However, increased winter temperatures could also result in a longer growing season.

Understanding the multiple interactions that can operate within- and across-scales is an important step in predicting future global effects on local tree growth; however, one must also understand the constraints of systems modeling. One limit is the requirement of long term data (at least 20 years) in order to operate this modeling approach. Another constraint is that this approach assumes that a long-term average represents an equilibrium condition between an organism and its environment. Forests will acclimate and adapt in response to changing climate conditions, therefore potentially changing the equilibrium condition. There is also a lack of information on the acclimation range of red spruce, which limits the ability to predict the magnitude of global climate change effects on

the red spruce ecosystem. Projection of red spruce (Picea rubens Sargent) habitat sustainability and distribution in the Southern Appalachian Mountains, USA Red spruce has experienced widespread growth decline and high mortality during the last half century. Approximately 75% of all southern spruce-fir forest is found within the Great Smoky Mountains National Park (GSMNP). Accurate prediction of red spruce spatial distribution in relation to temporally changing environmental factors is necessary for management. Species distribution models (SDMs) are used to predict plant and animal distributions by modeling rare and endangered species; future distributions of organisms as a function of climatic and land-use change; distributions of invasive species; and variations in species assemblage and community structure under environmental change.

The predictions of SDMs have been scrutinized due to insufficient attention to the multiplicity of ecological and physiological causes involved. Ecosystem complexity, the ecological and physiological processes governing species distribution, entails more indirect than direct effects. Indirect effects are more difficult to assess and have not been as well studied. There has also been less focus on across-scale effects when compared to within-scale effects. The goal of this study is to introduce a new approach to SDMs to predict red spruce habitat suitability and range, incorporating direct and indirect, and within- and across-scale interactions.

The study area is the approximately 2070 square km that compose the GSMNP in the southern Appalachians. The ARIM.SIM temporal simulation model of tree growth predicts annual radial growth as mean standardized ring widths of tree populations at high (>1700m) versus low (<1700m) elevations in relation to multiple environmental factors. The main model of ARIM.SIM consists of eight variables affecting photosynthesis and respiration:

  1. Radiation
  2. Water
  3. Nutrients
  4. Carbon dioxide
  5. Herbivory
  6. Weather disturbance
  7. Air pollution
  8. Soil-mediated disturbance.

Values for the eight variables were indirectly estimated from submodels involving multiple direct and indirect interactions.

The resulting habitat suitability index indicated red spruce absence below 1400m of elevation and low habitat suitability at high elevation habitats (1800-2028m) and on the edge of low elevation (about 1400m). Medium suitability habitats are located on south-facing and gentle slopes far from streams at low elevations (1400-1600m). High suitability habitats are located at steep and east-facing slopes near streams at low elevations (1400-1600m) and at the intermediate elevation range (1600-1800m). Red spruce distribution at high, medium, and low elevations was based on three ecological mechanisms. Air pollution was the dominant influence at high-elevation, involving acidic rain and cloud induced leaf injury and nutrient leaching, which results in growth decline and mortality of seedlings and saplings. Water availability and radiation were the dominant influences at low elevations. Higher temperatures and less precipitation reduced photosynthesis through photo-inhibition and increased evapotranspiration. Lower elevations were potentially subject to less of an effect from air pollution due to less exposure to acid rain and clouds. Optimum temperature, sufficient precipitation, and less acid rain and clouds resulted in the highest habitat suitability at the intermediate elevations.

Both articles are available for purchase here