Abstract:

Objective: Facing the requirements of implementing the major national strategy of Yellow River Basin ecological protection and high-quality development, and of promoting the integrated management of “mountains, rivers, forests, farmlands, lakes and grasslands” systems in China, the traditional approaches of forestry development and vegetation restoration in dryland regions, such as the Loess Plateau, must be changed by adding the considerations of water resources limitation and the impacts on water resources, and by paying attentions to the optimization of multiple forest functions/services. It is required to explore how to overcome the long-standing problems of neglecting water carrying capacity, low afforestation survival rate and poor tree growth, river runoff reduction and endangering to regional water supply safety, and the overall low functions of forests, so that to achieve the overall improvement of the multifunctionality of forests through their scientific management. Method: To meet the scientific and technical requirements of deep understanding of forest-water interrelations and of multifunctional forest management (MFFM), long-term studies since 2000 on the dryland forest ecohydrology and MFFM techniques were carried out in the Jinghe River basin and the regional important source-water area of the rocky Liupan Mountains on the Loess Plateau of northwest China. These studies were designed around the key issues of “structure”, “pattern”, “process”, “coupling”, and “scale”, using the multiple methods of observation comparison and statistical analysis as well as model simulation, at multiple scales from single tree to region. Result: The studies showed that: 1) The essence of high-quality forestry development is MFFM with quantitative and precise decision-making. Therefore, it is required to deeply understand and precisely quantify the impacts of site conditions and stand structure on the multiple functions of forests, to clarify the importance order of forest functions based on their complex interactions and supply-demand relations, and to optimize the competing functions to meet the societal demands of both dominant and other functions simultaneously under the precondition of ensured forest stability, by the rational designing and regulation of forest quantity, quality (structure) and spatial distribution pattern within basins. 2) The forest-water coordinated and multifunctional management approach was proposed, this means that besides considering the restrictions of available land area and seedlings and site quality for afforestation, new considerations should be added to the water resources management and MFFM through embedding them into the traditional single-function oriented decision processes of forest management. These decision processes involve four decision levels, they are the rational forest cover of basins (how much to afforest?), forest spatial distribution (where to afforest?), vegetation type and tree species composition (with which tree species?) and stand structure (how to manage forests?). 3) The related technical achievements were summarized according to the decision levels. For determining the reasonable forest cover of loess basins, the potential forest cover merely based on the annual precipitation limit can be updated to the reasonable forest cover by considering both the precipitation limit and water yield requirement through using the established empirical relations and the simulation results of watershed hydrological models. 4) For making the decisions of reasonable spatial distribution of forests within basins, the water yield differences among site types and their responses to afforestation should be utilized with the help of simulation results of distributed hydrological models or the regional vegetation carrying capacity calculation system developed in this study. For the MFFM decision at stand scale, a five-step decision-making procedure was suggested, namely, site quality classification, determining main functions and their priorities for each site type, investigating the structure characteristics of existing forest stands, diagnosing the structure and functions of existing forest stands, and compiling a structure/function-oriented management plan. For setting up the reference and goal of MFFM, ideal stand structures of multifunctional water-retention forests with different degrees of detail were proposed: the generalized ideal stand structure expressed as “3×0.7+X” (canopy density around 0.7, 0.6–0.8; ground coverage above 0.7; ratio of tree height to DBH below 0.7 m/cm, at least not higher than 0.9; X presents other requirements), the multifunctional density of middle-aged larch (Larix principis-rupprechtii) plantations determined by weighing the density needs of individual functions and stand stability, the varying multifunctional densities of larch plantations along elevations and ages determined based on the variation rules of main forest functions and their priorities. Conclusion: The theoretical advancement and technical feasibility of forest-water coordinated multifunctional management has been proved, as a viable way to realize the high-quality forestry development in dryland regions. Through a thorough understanding and quantitative analysis of the multiple functions with varying environment and forest structure, combined with the application of MFFM techniques proposed in this paper, the rational forest quantity (forest cover), quality (structure), and distribution pattern can be scientifically designed and adjusted, to realize the overall promotion of multiple functions to better meet the diverse societal demands. However, the achievements are still limited, thus more theoretical and technical research of forest-water coordinated and multifunctional management of forests should be carried out according to local situations to help the life community governance of “mountains, rivers, forests, farmlands, lakes and grasslands” systems and the ecological protection and high-quality development of the Yellow River Basin.

Key words: forest functions/services, multifunctional forest management, forest-water interrelations, dryland regions, Loess Plateau, plantation ofLarix principis-rupprechtii