Qing-Lai Dang

TRIPLEX: a generic hybrid model for predicting forest growth and carbon and nitrogen dynamics

To predict the potential effects of future global environmental changes (e.g. climate, land-use, fire disturbance, and forest harvesting) on the sustainability of forest ecosystems, forest resource managers will need forest simulation models. Basic approaches to modelling forest growth and dynamics include the use of empirical, mechanistic, and hybrid forest simulation models. In this paper, a hybrid, monthly time-step model of forest growth and carbon dynamics (TRIPLEX) is described and tested. The TRIPLEX model integrates the forest production model of 3-PG (For. Ecol. Manage. 95 (1997) 209), the forest growth and yield model of TREENYD3 (Ecol. Model. 90 (1996) 187), and the soil–carbon–nitrogen model of CENTURY4.0 (Global Biogeochem. Cycles 7 (1993) 785). The model is intended to be comprehensive without becoming complex, and minimizes the number of input parameters required, while capturing key processes and important interactions between the carbon and nitrogen cycles of forest ecosystems. It is designed as a hybrid of both empirical and mechanistic components that can be used for (1) making forest management decisions (e.g. growth and yield prediction), (2) quantifying forest carbon budgets, and (3) assessing the effects of climate change in both the short and long term. We tested TRIPLEX against age-dependent growth measurements from 12 permanent sample plots (PSP) in jack pine (Pinus banskiana Lamb.) stands in northern Ontario (Canada). Comparisons of simulated stand growth variables (e.g. tree diameter, height, and stem density) with those observed in PSPs indicated a good agreement over 30 years. Predictions of tree total volume and aboveground biomass were within the expected range for these plots. While the model is promising, future modifications are discussed.

Profiles of photosynthetically active radiation, nitrogen and photosynthetic capacity in the boreal forest: Implications for scaling from leaf to canopy

Profiles of photosynthetically active radiation (PAR), leaf nitrogen per unit leaf area (Narea), and photosynthetic capacity (Amax) were measured in an aspen, two jack pine, and two black spruce stands in the BOREAS northern study area. Narea decreased with decreasing %PAR in each stand, in all conifer stands combined (r=0.52) and in all stands combined (r=0.46). Understory alder had higher Narea for similar %PAR than did aspen early in the growing season. Amax decreased with decreasing Narea, except for the negative correlation between Narea and Amax during shoot flush for jack pine. For the middle and late growing season data, Narea and Amax had r values of 0.51 for all stands combined and 0.60 for all conifer stands combined. For similar Narea the aspen stand had higher Amax than did the conifer stands. Photosynthetic capacity expressed as a percentage of Amax at the top of the canopy (%Amax0) decreased with %PAR similarly in all stands, but %Amax0 decreased at a much slower rate than did %PAR. To demonstrate the implications of the vertical distribution of Amax, three different assumptions were used to scale leaf Amax to the canopy (Acan-max): (1) constant Amax with canopy depth, (2)Amax scaled proportionally to %PAR, and (3) a linear relationship between Amax and cumulative leaf area index derived from our data. The first and third methods resulted in similar Acan-max; the second was much lower. All methods resulted in linear correlations between normalized difference vegetation indices measured from a helicopter and Acan-max (r=0.97, 0.93, and 0.97, respectively), but the slope was strongly influenced by the scaling method.

Effects of Soil Temperature on Biomass Production and Allocation in Seedlings of Four Boreal Tree Species

One-year old seedlings of trembling aspen (Populus tremuloides Michx.), black spruce (Picea mariana (Mill.) B.S.P.), white spruce (Picea glauca (Moench) Voss), and jack pine (Pinus banksiana Lamb.) were subject to seven soil temperatures (5, 10, 15, 20, 25, 30 and 35 8C) for 4 months. All aspen seedlings, about 40% of jack pine, 20% of white spruce and black spruce survived the 35 8C treatment. The seedlings were harvested at the end of the fourth month to determine biomass and biomass allocation. It was found that soil temperature, species and interactions between soil temperature and species significantly affected root biomass, foliage biomass, stem biomass and total mass of the seedling. The relationship between biomass and soil temperature was modeled using third-order polynomials. The model showed that the optimum soil temperature for total biomass was 22.4, 19.4, 16.0 and 13.7 8C, respectively, for jack pine, aspen, black spruce and white spruce. The optimum soil temperature was higher for leaf than for root in jack pine, aspen and black spruce, but the trend was the opposite for white spruce. Among the species, aspen was the most sensitive to soil temperature: the maximum total biomass for aspen was about 7 times of the minimum value while the corresponding values were only 2.2, 2.4 and 2.3 times, respectively, for black spruce, jack pine and white spruce. Soil temperature did not significantly affect the shoot/root (S/R) ratio, root mass ratio (RMR), leaf mass ratio (LMR), or stem mass ratio (SMR) ðP > 0:05Þ with the exception of black spruce which had much higher S/R ratios at low (5 8C) and high (30 8C) soil temperatures. There were significant differences between species in all the above ratios ðP < 0:05Þ. Aspen and white spruce had the smallest S/R ratio but highest RMR while black spruce had the highest S/R but lowest RMR. Jack pine had the highest LMR but lowest SMR while aspen had the smallest LMR but highest SMR. Both LMR and SMR were significantly higher for black spruce than for white spruce. # 2002 Elsevier Science B.V. All rights reserved.

Historic carbon budgets of Ontario’s forest ecosystems

Carbon (C) budgets of Ontario’s forest ecosystems for the period 1920–1990 were calculated using the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS2). Results show that total forest biomass C in Ontario increased from 1.83 Pg (10 15 g) to 2.56 Pg between 1920 and 1970, then decreased to 1.70 Pg by 1990. Carbon in soil and forest floor dead organic matter (DOM) increased from 8.30 to 11.00 Pg between 1920 and 1985 but decreased to 10.95 Pg by 1990. Ontario’s forest ecosystems acted as a C sink sequestering 41–74 Tg (10 12 g) C per year from 1920 to 1975, but became a C source releasing 7–32 Tg C per year (5-year average) after 1975. Disturbances (fire, insects and harvesting) enhanced both direct and indirect C emissions, and also affected average forest age and C sequestration. Net primary production (NPP), net ecosystem production (NEP), and net biome production (NBP) were affected by both disturbances and average forest age. Forests in the boreal (BO, 62.66 M ha), cool temperate (CT, 7.77 M ha) and moderate temperate (MT, 0.20 M ha) regions had different C dynamics. However, boreal forests dominated Ontario’s forest C budget because of the large area and associated C stock. Detailed C budgets for 1990 were also analyzed. The average forest ages in 1990 were 36.2 years for BO, 43.4 years for CT, and 92.1 years for MT regions, respectively. The total C stock of Ontario’s forest ecosystems (excluding peatlands) was estimated to be 12.65 Pg, including 1.70 Pg in living biomass and 10.95 Pg in DOM and soil. Average C density was 179 Mg ha � 1 (10 6 g) (24 Mg ha � 1 for biomass and 155 Mg ha � 1 for DOM and soil). The total net C balance (excluding harvest removal) was � 31.8 Tg. NPP, NEP and NBP were 267.6, � 28.2 and � 40.6 Tg per year, respectively. The young age (36.2) of Ontario’s boreal forests indicates a great potential for C sequestration and storage. Roughly 1 Pg C could be sequestered with a 10-year increase in forest age. A less severe disturbance regime and/or higher NPP would convert Ontario’s forest ecosystems back to a C sink. # 2002 Elsevier Science B.V. All rights reserved.

A component object model strategy for reusing ecosystem models

Most ecosystem simulation models are large monolithic simulation programs that are machine dependent and difficult to reuse by other modelers. One way to effectively reuse existing ecosystem models is to break the models into smaller functional parts. These parts are then reconstructed into standardized model components which can be pieced together to form a new model with the desired characteristics. TRIPLEX is a flexible and customizable prototype model for forest ecosystem simulation that was constructed using three existing models: 3-PG, TREEDYN3, and CENTURY 4.0. Well-established parts of these models were rebuilt as Component Object Model (COM) objects with BORLAND C ++ Builder. These components can be integrated through TRIPLEX’s intuitive user interface to form a customized new model. Model developers from different modeling environments (such as VISUAL BASIC, VISUAL C ++ ,a ndDELPHI) can easily reuse these COM objects. TRIPLEX features a public information unit that supports various components working together. In

Responses of tree seedlings to the removal of Chromolaena odorata Linn. in a degraded forest in Ghana

Chromolaena odorata is a dominant plant species in degraded forest areas in Ghana. This species forms a very dense canopy. Although tree seedlings have been observed growing under the canopy of this species, they have scarcely been seen growing through the canopy of Chromolaena odorata. To study the response of tree seedlings to the removal of Chromolaena odorata, 108 plots were established 20 m apart in a degraded dry semi-deciduous forest in Ghana. Chromolaena odorata was removed from 50% of the plots to release tree seedlings and left the other half intact. Seedling height, the number of leaves per seedling, and seedling mortality were assessed in both released and unreleased plots immediately after the release treatment (June 1998) and again three months later (September 1998). It was found that the seedling height increment and the increase in number of leaves per seedling were three times greater in released plots than the unreleased plots three months after the release treatment. Twenty eight tree species were found in the plots and 89% of the species had higher height growth after the release treatment. Similarly, 93% of the tree species had more new leaves in released plots than in the unreleased plots. Sixty four percent of the species suffered various levels of mortality in the unreleased plots, but all the seedlings of all the species survived in the released plots. The results suggest that there is a great potential to restore the degraded area back to forest using natural seedlings by removing Chromolaena odorata, the competing vegetation.

Assessing the generality and accuracy of the TRIPLEX model using in situ data of boreal forests in central Canada

Abstract TRIPLEX1.0 is a hybrid model that integrates three well-established process models including 3-PG, TREEDYN3.0 and CENTURY4.0. We have conducted calibrations using eight sites to determine and generalize parameters of the TRIPLEX. We also performed model validation using 66 independent data sets to examine the model accuracy and the generality of its application. Simulations were conducted for plots with large sample size from the boreal ecosystem atmosphere study (BOREAS) program, including the northern study area (NSA) near Thompson, Manitoba (55.7° N, 97.8° W) and the southern study area (SSA) near Prince Albert, Saskatchewan (53.7° N, 105.1° W). The calibrations and simulations emphasized on generating average parameters and initial statuses for applying a complex model in a broad region where site detailed information such as photosynthetic capacity, soil carbon, nutrient, soil water, and tree growth is not always available. A suggestion was presented regarding adjusting the sensitive parameter by estimating tree growth rate corresponding to different site conditions. The study actually presented a reasonable and balanced parameter generalization procedure that did not lead to a significant reduction of model accuracy, but did increase the model practicability. The comparison of observations and simulations produced a good agreement for tree density, mean tree height, DBH, soil carbon, above-ground and total biomass, net primary productivity (above-ground) and soil nitrogen in both short- and long-term simulation. Results presented here imply that the set of parameters generalized and suggested in this study can be used as basic referenced values, in which TRIPLEX can be applied to simulate the general site conditions of boreal forest ecosystems.

Developing carbon-based ecological indicators to monitor sustainability of Ontario's forests

With 2% of the world’s forests and 17% of Canada’s forested land, Ontario plays a major role in maintaining Canada’s forests and managing them sustainably. Ontario is developing a set of criteria and indicators of sustainable forest management (SFM) to aid in conservation and sustainable management of its temperate and boreal (BO) forests. The criteria and indicators are intended to provide a framework for describing and assessing processes of SFM at a regional scale; and to improve the information available to the public and decision-makers. This paper describes three ecological indicators, evaluated using a carbon (C) budget model, a forest inventory database, and disturbance records to assess long-term sustainability of Ontario’s forest ecosystems based on the environmental conditions of the past 70 years. Results suggest that total net primary productivity (NPP) of Ontario’s forest ecosystems increased from 1925 to 1975 and then decreased between 1975 and 1990; Ontario’s forest ecosystems acted as a C sink between 1920 and 1980, and a C source from 1981 to 1990, mainly due to decreased average forest age and NPP caused by increased ecosystem disturbance (e.g. fire, insect and disease infestations, harvesting) since 1975. Current estimates from this analysis suggest that there is significant potential for Ontario’s forests to function as C sinks by reducing ecosystem disturbances and increasing growth and storage of C in the young forests throughout the province.

A Soil Temperature Control System for Ecological Research in Greenhouses

We designed and tested a soil temperature control system for plant ecophysiological experiments in greenhouses and growth chambers. The system consists of a plywood box, polyethylene liner, insulation, seedling containers, a water pump, and a flow-through heater or chiller. One hundred and twelve seedling containers (11cm diameter, 13.5 cm high) are mounted in the plywood box. There is a hole at the bottom center of each container to allow the free drainage of irrigation water and fertilizer solution. The space between containers is filled with water that is circulated through the chiller/heater. The water is also circulated within the plywood box by a water pump to increase the uniformity of temperature. The system was tested for three soil temperatures (5, 20, and 30°C) over a period of four months. The containers were filled with a peat-moss vermiculite mixture and planted with tree seedlings. The test showed that the soil temperature was almost equal to the water temperature for all three soil temperatures (regression slop = 0.99, intercept = 0.12,r2 = 1.00). The average soil temperatures were within (0.41°C of the set values. The soil temperature of the 112 containers within the same box followed a normal distribution with a small standard deviation (0.34°C for the 30°C treatment). There was a temperature gradient from the top to the bottom of the container (< 1°C). The direction of the temperature gradient was determined by the direction of temperature difference between the soil and the ambient air. When the soil temperature was lower than air temperature, the soil temperature decreased from the top to the bottom of the container, and vise versa. The soil temperature was higher during the day than at night (difference < 1.5°C).

Low moisture availability inhibits the enhancing effect of increased soil temperature on net photosynthesis of white birch (Betula papyrifera) seedlings grown under ambient and elevated carbon dioxide concentrations

White birch (Betula papyrifera Marsh.) seedlings were grown under two carbon dioxide concentrations (ambient: 360 micromol mol(-1) and elevated: 720 micromol mol(-1)), three soil temperatures (5, 15 and 25 degrees C initially, increased to 7, 17 and 27 degrees C, respectively, 1 month later) and three moisture regimes (low: 30-40%; intermediate: 45-55% and high: 60-70% field water capacity) in greenhouses. In situ gas exchange and chlorophyll fluorescence were measured after 2 months of treatments. Net photosynthetic rate (A(n)) of seedlings grown under the intermediate and high moisture regimes increased from low to intermediate T(soil) and then decreased to high T(soil). There were no significant differences between the low and high T(soil), with the exception that A(n) was significantly higher under high than low T(soil) at the high moisture regime. No significant T(soil) effect on A(n) was observed at the low moisture regime. The intermediate T(soil) increased stomatal conductance (g(s)) only at intermediate and high but not at low moisture regime, whereas there were no significant differences between the low and high T(soil) treatments. Furthermore, the difference in g(s) between the intermediate and high T(soil) at high moisture regime was not statistically significant. The low moisture regime significantly reduced the internal to ambient CO2 concentration ratio at all T(soil). There were no significant individual or interactive effects of treatment on maximum carboxylation rate of Rubisco, light-saturated electron transport rate, triose phosphate utilization or potential photochemical efficiency of photosystem II. The results of this study suggest that soil moisture condition should be taken into account when predicting the responses of white birch to soil warming.