Clive Welham

Carbon sequestration in a boreal forest ecosystem: results from the ecosystem simulation model, FORECAST

Abstract The effect of alternative harvesting practices on long-term ecosystem productivity and carbon sequestration was investigated with the ecosystem simulation model, FORECAST. Three tree species, white spruce ( Picea glauca ), trembling aspen ( Populus tremuloides ), and lodgepole pine ( Pinus contorta var. latifolia ), were each used in combination with different rotation lengths. An additional run was conducted to investigate the effect of nitrogen addition to aspen. Results were also compared with a natural disturbance scenario in which a mixedwood stand composed of all three species was subjected to a catastrophic wildfire, on a 150-year fire cycle. All simulations included an understory grass competitor, Calamagrostis canadensis , and the total simulation length for each scenario was 300 years. Carbon stored in soil represented a large, relatively stable pool and showed only minor long-term responses to harvesting activities. Tree biomass and litter pools, in contrast, fluctuated widely in concert with the harvest cycle. Calamagrostis was relatively unimportant as a carbon pool. Total ecosystem carbon increased with rotation length regardless of species, and this was attributable largely to changes in the live biomass pool. A 150-year pine, and a 200-year spruce rotation, were the only scenarios in which average total carbon storage exceeded that in the natural disturbance scenario. For equivalent rotation lengths, total carbon storage was the greatest in aspen, followed by pine and spruce, respectively. Application of nitrogen fertilizer to aspen increased average total carbon storage by 9%. This increase was attributable primarily to the storage in wood products and live biomass pools. The proportion of total carbon stored in the soil pool decreased as harvest frequency declined (i.e., at longer rotation lengths), while the proportion stored in litter pools was roughly equivalent among all scenarios. However, there was a consistent decline in soil carbon across the 300-year simulation period for managed stands. The natural disturbance scenario, in contrast, showed an increase in soil carbon over the same period. Species-specific biomass accumulation rates (an index of ecosystem productivity) were maximal in the shortest rotations for aspen, but in mid-length rotations for pine and spruce. Short rotation scenarios showed a marked drop in site productivity over subsequent rotations. The application of nitrogen fertilizer reduced the relative drop in site productivity for aspen. Our results suggest a trade-off between ecosystem storage capacity and timber production. By selecting the appropriate tree species and rotation length, however, it is possible to either balance these competing demands, or favour one value versus the other.

Yield decline in Chinese-fir plantations: a simulation investigation with implications for model complexity

A variety of competing hypotheses have been described to explain yield decline in Chinese-fir (Cunninghamia lanceolata (Lamb.) Hook.) plantations. The difficulty in implementing field experiments suggests ecosystem modeling as a viable option for examining alternative hypotheses. We present a conceptual model of Chinese-fir yield decline and explore its merits using the ecosystem-based FORECAST model. Model results suggest that yield decline is caused primarily by a decline in soil fertility, largely as a consequence of slash burning in conjunction with short rotations. However, as tree leaf area declines, there is a transition (over subsequent rotations) from seed rain based competition to bud bank based competition, increasing the competitive impact of minor vegetation on tree growth. Short rotations increase understory survival between rotations and may cause a gradual shift from tree dominance to shrub/herb dominance over subsequent rotations. These effects are most evident on nutrient-poor sites, but...

Testing the performance of a forest ecosystem model (FORECAST) against 29 years of field data in a Pseudotsuga menziesii plantation

The ability of the forest ecosystem management model FORECAST to project a 29-year record of stand response to factorial thinning and fertilization treatments in a Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) plantation at Shawnigan Lake (Vancouver Island, British Columbia, Canada) was assessed. Model performance was evaluated firstly using for calibration a regional data set and secondly with site-specific data from control plots. Model output was compared against field measurements of height, diameter, stem density, component biomass (aboveground), and litterfall rates and estimates of nutrient uptake, foliar N efficiency, and understory vegetation biomass. When calibrated with regional data, results from graphical comparisons, three measures of goodness-of-fit, and equivalence testing demonstrated that FORECAST can produce predictions of good to moderate accuracy depending on the variable of interest. Model performance was generally better when compared with field measurements (e.g., top height, ...

Morphological plasticity of white clover (Trifolium repens L.) in response to spatial and temporal resource heterogeneity

Heterogeneity in resource distribution has been an important selective force shaping morphological plasticity in plants. When resources are patchily distributed, changes in morphology are assumed to affect placement of the resource-acquiring structures (roots and leaves) such that they enhance the plants capacity for resource uptake. Morphological development of four white clover (Trifolium repens) genets was studied in two glasshouse experiments. In the spatial experiment, two substrates (potting soil and sand) were used to create the following discrete patch combinations, sand-sand, soil-sand, sand-soil, and soil-soil. Stolons grew across each combination and consecutive ramets from a given stolon permitted rooting in each substrate pair. In the temporal experiment, the two ramets were first rooted in sand only. After a predetermined period, the sand was replaced and the same substrate combinations created as in the spatial experiment. In each experiment, total developmental time within a given substrate combination was held constant. All measurements were conducted on the second (i.e., younger) of the ramet pairs. In the spatial experiment, ramets rooted in soil had significantly greater branching frequencies than ramets rooted in the sand substrate, regardless of genotype or the preceding substrate type. Ramets occupying the sand-sand combination had the lowest branching frequencies but branch production for the ramet rooted in sand was higher if the preceding ramet was rooted in soil. The substrate occupied by a preceding ramet had no influence upon branching propensity if a ramet was rooted in soil. There were no significant differences in branching frequencies between the sand and soil substrates in the temporal experiment. The relationship between branching and substrate thus depended upon whether a ramet was exposed to a given substrate type during its early development. In both experiments, branched ramets in the soil-soil combinations had significantly greater shoot mass than corresponding ramets in the sand-sand combinations. Internode length was significantly shorter in the soil versus sand combinations of the spatial experiment but was unaffected by substrate in the temporal experiment. Leaf area and stolon width showed significant genotype×treatment interactions in both experiments but no consistent trends were evident; petiole length was unaffected by substrate.

Application of a Hybrid Forest Growth Model to Evaluate Climate Change Impacts on Productivity, Nutrient Cycling and Mortality in a Montane Forest Ecosystem.

Climate change introduces considerable uncertainty in forest management planning and outcomes, potentially undermining efforts at achieving sustainable practices. Here, we describe the development and application of the FORECAST Climate model. Constructed using a hybrid simulation approach, the model includes an explicit representation of the effect of temperature and moisture availability on tree growth and survival, litter decomposition, and nutrient cycling. The model also includes a representation of the impact of increasing atmospheric CO2 on water use efficiency, but no direct CO2 fertilization effect. FORECAST Climate was evaluated for its ability to reproduce the effects of historical climate on Douglas-fir and lodgepole pine growth in a montane forest in southern British Columbia, Canada, as measured using tree ring analysis. The model was subsequently used to project the long-term impacts of alternative future climate change scenarios on forest productivity in young and established stands. There was a close association between predicted sapwood production and measured tree ring chronologies, providing confidence that model is able to predict the relative impact of annual climate variability on tree productivity. Simulations of future climate change suggest a modest increase in productivity in young stands of both species related to an increase in growing season length. In contrast, results showed a negative impact on stemwood biomass production (particularly in the case of lodgepole pine) for established stands due to increased moisture stress mortality.

Linking Climate Change and Forest Ecophysiology to Project Future Trends in Tree Growth: A Review of Forest Models

Climate change is already altering tree species ranges, with tree lines shifting upwards and polewards around the world (Dullinger et al., 2004; Soja et al., 2007; Harsch et al., 2009). A recent analysis of the potential effects of climate change on tree distribution in British Columbia (western Canada) suggested that important timber species including white spruce and lodgepole pine may lose suitable habitat and suffer adversely from a combination of warming trends and reduced growing season precipitation (Hamann & Wang, 2006). In contrast, species such as Douglas fir and ponderosa pine may actually expand their range and potentially show improved growth rates in parts of their existing range. A recent study in the mountains of interior British Columbia showed how at high elevation, trees historically responded positively to increased temperatures, while at low elevations trees showed a negative response to growing season maximum temperature and a positive correlation with growing season precipitation (Lo et al., 2010a, 2010b). Given these species-specific responses it is not surprising that recent research has failed to identify direct links between warmer temperatures and observed changes in species ranges (Dullinger et al., 2004; Wilmking et al., 2004). The important ecological and socio-economic consequences of such changes have prompted multiple modelling efforts to predict the future location of habitat suitable for tree species and to assess the potential implications for tree growth of changes in climate. Defining such areas and estimating the losses or gains due to climate change in timber production have important consequences on forest management and conservation. The most popular approaches to project future areas of suitable habitat for commercial tree species have involved analysis of historical records of tree lines in boreal and alpine environments (Dullinger et al., 2004), using climate envelope models (Hamann & Wang, 2006). Similarly, dendroclimatology (studying historical tree growth rates by analyzing tree ring width) has been used to link climate and tree growth rates (Wilmking et al., 2004; Lo et al., 2010a, 2010b). These approaches are based mostly on climatic information, although their combination with other information such as soil or topography has been used to

Maintaining Ecosystem Function by Restoring Forest Biodiversity – Reviewing Decision-Support Tools that link Biology, Hydrology and Geochemistry

Land use change in forest ecosystems is a worldwide problem. In many cases, however, the change is only temporary, and after a period of economic activity, the original forest must be reclaimed back to its original (or as close as possible) estate. A typical case is in open-pit mining. In many juridictions there is a legal requirement for the company to engage in restorative activities designed to bring back biodiversity and function to those areas espoiled by mining.

A cost–benefit model for plant–plant interactions: a density-series tool to detect facilitation

Generally, only the net outcome of plant–plant interactions is measured in population and community ecology research, with few attempts to determine the relative importance of negative (competition) and positive (facilitation) interactions between subordinate species. Changes in the intensity of interactions along gradients, between life-stages, or with changing densities, and the use of selective removals enhance our capacity to infer positive and negative interactions. However, the most powerful examples at least in detecting facilitation typically involve measuring changes with or without a nurse-plant or benefactor species and often involve only a very limited numbers of species. In plant competition studies, however, greater number of species are commonly tested and density-dependent series are not an uncommon tool to test for net negative interactions. Here, we develop a cost–benefit model that can be used to comprehensively calculate the average expected net gain per individual at every point in a density series provided several response variables are recorded at each density. The utility of this model is demonstrated using both hypothetical data and several empirical data sets, and it is used to infer either both positive and negative net effects. Expected net gain can also serve as an accurate estimate of mean fitness per individual at a given density provided appropriate performance measures were recorded within the primary study. Within a single density series, both facilitation and competition can occur and were detectable using this method. This approach emphasizes the current view that both negative and positive interactions play a role in shaping plant communities. Furthermore, it is evident that facilitation can be detected using the manipulative density series typically associated with competition studies and not just using the typical target nurse-plant methodology. Finally, this method is a significant advance over the current practice of tallying up single responses within a study to estimate outcomes by providing a single, synthetic measure of the net gain or cost of interactions.

The Role of Ecosystem-level Models in the Design of Agroforestry Systems for Future Environmental Conditions and Social Needs

Forestry is the art (skill), practice, science, and business of managing forest ecosystems to sustain an ecologically possible and socially desirable balance of forest resources and other ecosystem services and values. Agroforestry could be defined similarly, but in reference to agro-ecosystems and tree-crop-animal resources. When practiced by indigenous cultures, agroforestry has been based on their experience-based wisdom about what works and what does not (Hsiung 1996). However, if a different set of agroforestry values (e.g. a new crop or tree species) and/or a new agroforestry system for which there is little or no experience are to be sustained, this experience-based approach must be supplemented with an understanding of the ecological processes that underlie both the traditional systems and the new set of values. Because social unrest, wars, diseases, natural disasters, and the continuing urbanization of the world’s population result in the loss of traditional rural knowledge, the design of future agroforestry systems will have to be based as much or more on an understanding of the processes responsible for production and sustainability of multiple values and environmental services as it has on traditions and experience in the past. When properly implemented, the approach of experience + process-level understanding can capture the benefits of traditional systems but also have the flexibility to respond to the changing needs and desires of individuals and societies, and to changing social and environmental conditions.