Trees provide multiple ecosystem services (ES) and are generally considered an important natural-based approach for climate change adaptation and mitigation. In urban areas, proper pruning practices can help enhance ES provided by trees, but in areas with issues of typhoons or storms, routinely intensive pruning may reduce ES. Therefore, it is critical to determine proper pruning intensity in balancing the ES provision and life/property protection. With the aim of promoting sustainable urban forestry management, we applied the i-Tree Eco to quantify ES and ES values of air pollution removal and runoff avoidance provided by a total of 87,014 Taipei street trees and developed an analytical method to estimate the potential loss caused by different pruning intensities. Based on the i-Tree Eco estimates, the Taipei street trees on average provide ES values of air pollution removal and runoff avoidance at $2.31 and $1.87 USD/tree/y, respectively. By changing the ratio of crown missing as a surrogate for different pruning intensities, we found that with a less than 25% pruning intensity, the decline ratio of ES values was relatively constant, and the potential loss was estimated at $0.47 USD/tree/y at the 25% pruning intensity. As such, in general maintenance situations, we recommend a less than 25% pruning intensity. However, during typhoon or monsoon seasons, a less than 45% pruning intensity is suggested to balance the ES provision and public safety with an estimated loss at $0.96 USD/tree/y. We also suggest creating visualization maps incorporating the potential ES and the local in situ environmental and tree conditions at a community level to support decision making for a more comprehensive management plan. Based on the framework and method developed in this study, the science-based information can be used to assist maintenance practices and highlight the potential ES values to be enhanced by choosing proper pruning intensity for a more sustainable future.
Chamaecyparis obtusa var. formosana is an ecologically and economically important species in Taiwan, with a high affinity for fog immersion. Our study aims to identify possible stress factors that induced seedling mortality and investigate how different ecological factors influence early-stage safe site requirements of the seedlings. We focused on the effect of large-scale climatic variables, small-scale microhabitat conditions, and biotic interactions on seedling survival and establishment by applying seasonal seedling survival monitoring and establishment survey on both regional and local scale. We identified two alternative ways of seedling death, by environmental-induced mortality and by herbivory. Opposite effects of the same environmental factors on different causes of mortality showed that seedlings might need to balance the risks posed by both causes to optimize their growing conditions. On a regional scale, we observed limited effect of regional climatic variables (namely fog frequency) on seedlings' establishment and survival but noted a similar seasonal survival pattern among regions. We hypothesize that short-duration droughts during the transition from Plum rain to typhoon season is one of the key mechanisms of environmental-induced mortality. On a local scale, we found that decayed coarse wood debris (CWD) facilitates seedling establishment by providing a "safe site", likely due to increased colonization of small-stature bryophytes and decreased litterfall accumulation. The effect of bryophytes on seedling establishment varies depending on their thickness, with thicker ones having stronger negative effects. Aside from the bryophytes, the accumulation of litter significantly hindered seedling establishment. We argue that to safeguard the regeneration of Chamaecyparis obtusa var. formosana population, preserving CWD in the forest floor as a safe site for the seedlings after tree-replacing disturbance in natural forests is essential, particularly under ongoing climate change where more frequent and prolonged drought events are predicted.
Urban trees provide multiple ecosystem services (ES) to city residents and are used as environmentally friendly solutions to ameliorate problems in cities worldwide. Effective urban forestry management is essential for enhancing ES, but challenging to develop in densely populated cities where tradeoffs between high ES provision and issues of periodic disaster-caused risks or maintenance costs must be balanced. With the aim of providing practical guidelines to promote green cities, this study developed an AI-based analytical approach to systematically evaluate tree conditions and detect management problems. By using a self-organizing map technique with a big dataset of Taipei street trees, we integrated the ES values estimated by i-Tree Eco to tree attributes of DBH, height, leaf area, and leaf area index (LAI) to comprehensively assess their complex relationship and interlinkage. We found that DBH and leaf area are good indicators for the provision of ES, allowing us to quantify the potential loss and tradeoffs by cross-checking with tree height and the correspondent ES values. In contrast, LAI is less effective in estimating ES than DBH and leaf area, but is useful as a supplementary one. We developed a detailed lookup table by compiling the tree datasets to assist the practitioners with a rapid assessment of tree conditions and associated loss of ES values. This analytical approach provides accessible, science-based information to appraise the right species, criteria, and place for landscape design. It gives explicit references and guidelines to help detect problems and guide directions for improving the ES and the sustainability of urban forests.
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