Photosynthesis and respiration of black spruce at three organizational scales: shoot, branch and canopy.

To gain insight into the function of photosynthesis and respiration as processes operating within a global ecosystem, we measured gas exchange of mature black spruce (Picea mariana (Mill.) B.S.P.) trees at three organizational scales: individual shoots, whole branches and a forest canopy. A biochemical model was fitted to these data, and physiological parameters were extracted. Pronounced seasonal variation in the estimated model parameters was found at all three organizational scales, highlighting the need to make physiological measurements throughout the year. For example, it took over 100 days for physiological activity to increase from zero during the springtime thaw to its yearly maximum. Good agreement was found between parameter values estimated for the different organizational scales, suggesting that, in the case of aerodynamically rough, largely mono-specific forest canopies, physiological parameters can be estimated from eddy covariance flux measurements. The small differences between photosynthetic parameters estimated at the different scales suggest that the overall spatial organization of photosynthetic capacity is nearly optimized for carbon uptake at each scale.

A simple method for predicting the consequences of land management in urban habitats.

Land management in urban areas is characterized by the diversity of its goals and its physical expression in the landscape, as well as by the frequency and often rapidity of change. Deliberate or accidental landscape alterations lead to changes in habitat, some of which may be viewed as environmentally beneficial, others as detrimental. Evaluating what is there and how changes may fit into the landscape context is therefore essential if informed land-management decisions are to be made. The method presented here uses a simple ecological evaluation technique, employing a restricted number of evaluation criteria, to gather a spatially complete data set. A geographical information system (GIS) is then used to combine the resulting scores into a habitat value index (HVI). Using examples from Wolverhampton in the United Kingdom, existing real-world data are then applied to land-management scearios to predict probable landscape ecological consequences of habitat alteration. The method provides an ecologically relevant, spatially complete evaluation of a large, diverse area in a short period of time. This means that contextual effects of land-management decisions can be quickly visualized and remedial or mitigating measures incorporated at an early stage without the requirement for complex modeling and prior to the detailed ecological survey. The strengths of the method lie in providing a detailed information baseline that evaluates all habitats, not just the traditional "quality" habitats, in a manner that is accessible to all potential users-from interested individuals to professional planners.

Coupling of carbon and water interactions in forest stands.

Some measured values of the ratio transpiration rate/assimilation rate (E/A) for a Sitka spruce stand in Scotland and an oak-hickory stand are presented and compared with E/A for some agricultural crops. Typical midday values of E/A (on a molar basis) range from 100 to 900. Analysis suggests that this variation can be explained by differences in climate, canopy conductance and degree of coupling of the vegetation to the atmosphere. During the day, E/A varied considerably in the tree stands at the same time as there were changes in radiation, vapor saturation deficit and temperature. A lumped parameter, 'big leaf' model of canopy transpiration and assimilation was used to provide insight into how this complex of variables might influence E/A. The model predicted little response to radiation, but increase in E/A with increasing vapor saturation deficit and temperature, in agreement with the trends in the data. It was concluded that there is a great need for measurements of E/A of stands in relation to nutrient and water stress.