Forests 2015, 6, 360-379; doi:10.3390/f6020360 OPEN ACCESS forests ISSN 1999-4907 www.mdpi.com/journal/forests Article A Process-Based Approach to Estimate Chinese Fir (Cunninghamia lanceolata) Distribution and Productivity in Southern China under Climate Change Yuhao Lu 1,*, Nicholas C. Coops 1,†, Tongli Wang 2,† and Guangyu Wang 3,† 1 Department of Forest Resources Management, University of British Columbia, 2424 Main Mall, Vancouver V6T 1Z4, BC, Canada; E-Mail: [email protected] 2 Department of Forest and Conservation Sciences, University of British Columbia, 2424 Main Mall, Vancouver V6T 1Z4, BC, Canada; E-Mail: [email protected] 3 Faculty of Forestry, University of British Columbia, 2424 Main Mall, Vancouver V6T 1Z4, BC, Canada; E-Mail: [email protected] † These authors contributed equally to this work. * Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel.: +1-604-822-6452; Fax: +1-604-822-9106. Academic Editors: Michael Battaglia and Eric J. Jokela Received: 14 October 2014 / Accepted: 22 January 2015 / Published: 2 February 2015 Abstract: Understanding the distribution and productivity of Chinese fir (Cunninghamia lanceolata) under climate change is critical given the ecological and economic importance of the species. Recently, process-based growth models have grown in their popularity given their simplicity and data availability, and they are increasingly being used to map the distribution and productivity of tree species. In this paper, we study the extent of variation of the current range shift and the productivity of the species under a changing climate. We used the Physiological Principles in Predicting Growth (3-PG) model, which calculates the extent to which climatic variables affect photosynthesis and growth of a species. These variables were then used in a decision-tree model to develop rules to provide a basis for predicting the distribution of the species under current climatic conditions. Once the distribution model was developed the productivity of the species was then assessed. Using climate projections we then simulated the growth and distribution into the future. Results indicate a northward shift from the current range. The growth model also indicates minor increases in productivity in some of the existing distribution areas, principally in central Forests 2015, 6 361 China with limited productivity predicted in newly emerged stands. We conclude that this dual modeling approach has potential to quantify impacts of climate change on selected species and examining differences in climate projections on range and productivity estimation. Keywords: Chinese fir; climate change; modeling; GIS; distribution; productivity; NPP; 3-PG Model 1. Introduction Across China, plantations of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) and Masson Pine (Pinus massoniana) have been utilized for more than one thousand years [1–3]. As one of the most important subtropical coniferous species, Chinese fir plays a major role in the environment, timber supply, and human society. According to Lei [4], forest inventory data indicates that Chinese fir occupies 30% of all plantations in China, covering approximately 9 million ha, principally in southern China with its timber accounting for one quarter of China’s national commercial timber production [5]. Since 1949 the area of Chinese fir plantations has nearly tripled with an increased focus on afforestation and reforestation [6–10]. Chinese fir is a valued timber species due to its high quality wood (i.e., straight and decay resistant) as well as having significant cultural and historic values in China. Chinese fir is often used in building construction and furniture manufacturing [2] as well as in the provision of other ecosystem services including local water supply and organic matter storage [11]. Fast growing plantations also provide an opportunity for increasing terrestrial carbon stocks and therefore are suggested as an approach to efficiently mitigate the impacts of global climate change [12]. Chinese fir is characterized by its fast growth rate when grown in a monoculture plantation, producing volumes of up to 450 m3/ha after 25 years [1,2]. Therefore, a comprehensive knowledge of Chinese fir in terms of its contribution in carbon sequestration will allow a better development of plantation, afforestation, and forest management strategies in general throughout China. Given the ecological, social, and carbon values of Chinese fir, improving our understanding and knowledge of Chinese fir growth and how a changing climate may alter the distribution is needed. This is important particularly due to its popularity as a fast growing plantation species and concerns that the volume yields and carbon storage may progressively deteriorate over multiple rotations [13–15]. Understanding the distribution and productivity of the species both now and into the future is critical, when linked to local management strategies, such as silvicultural practices, as it provides an estimate of the commercial value of the species, timber supply, and assessment of the other ecosystem goods and services the species provides. Climatic factors such as temperature and precipitation strongly affect the physiology of a tree species [16,17], and as a result, changes in climate are likely to alter both the distribution and growth of the species in the future. China, like most regions globally, is undergoing climatic changes in terms of temperature, precipitation, and accordingly their seasonal and regional variations [18–20]. In response to climate change, four possible responses of both organisms and ecosystems are expected—first, changes in phenology and physiology of living organisms; second, changes in the Forests 2015, 6 362 distribution of species; third, changes in the community compositions and interactions among components; fourth, the arrangement and dynamics of ecosystems [21]. Once climate changes beyond the tolerances of a species, the survival and productivity of the species will be compromised. Under this changing climate regime, it is unclear whether the historic colonized distributions of certain species will remain and stay as productive as they currently are. Modeling growth and species distributions is therefore necessary for assessing forest stands and will specifically benefit foresters in terms of scheduling harvest rotation, predicting profits, and more importantly mitigating a changing climate. Conventional statistical growth and yield approaches are often used to predict future stand growth but are based on past climate/growth relations and are therefore limited in their capacity to estimate stand growth under more variable future climate conditions. In addition, changes in future climate are likely to alter the structure of Chinese fir’s geographic distribution. Yet, to model species distribution often requires sophisticated algorithms and detailed parametrization. In this paper we assessed the impact of changing climate on Chinese fir by applying a simple process-based model in two phases. First, we input species’ parameters and climate projections into a simple physiological model driven with monthly climate data to derive the environmental constraints on the species range. Second, we employed the constraints generated in the first phase to predict the productivity and distribution of the species. Both current and future climate projections were modeled in this study for further analysis and comparisons. With this research we build on the work of Liu et al. (2014) [22] who recently used a PnET modeling approach to access both productivity (i.e., NPP) and distribution changes in Chinese fir across southern China under different climate change projections. We advance knowledge in two key ways: First by applying a hybrid physiological model, with which we can, in detail, assess the main climatic restrictions to growth of the species across its entire range, which is important for assessing the future impacts of climate change. Second, utilizing a hybrid model, which allows the prediction of variables of key interest to forest managers, such as stand volume and basal area—the growth potential of future forest plantations can be spatially and temporally assessed. 2. Experimental Section 2.1. Study Area Our research is focused on southern, sub-tropic region of China (Figure 1) where the current distribution of Chinese fir extends from the pacific coast of Fujian, Zhejiang in the east, to the south coast of Guangdong and Guangxi, to the west of Yunnan, Sichuan, to the north of Shanxi and Henan Provinces. The elevation ranges from 800 m above sea level in the Southeast to 2500 m in the southwest. The annual mean temperature ranges from 15 °C–20 °C and the mean temperature in January of 1 °C–2 °C. However it is sensitive to lack of humidity and requires annual precipitation around 800–2000 mm. The best suitable microclimate normally ranges between monthly 16 °C–19 °C and the annual precipitation around 1300–1800 mm [2]. Chinese fir requires deep fertile well-drained-acidic soil with a pH value around 4.5–6.5, but can also grow on slightly alkaline soil [2]. Forests 2015, 6 363 Figure 1. Study area—Provinces with present natural distribution of Chinese fir. 2.2. Climate Data ClimateAP [23] was used to generate climate data across the region. ClimateAP is a climate data downscaling tool developed for the Asia Pacific region, which extracts and downscales PRISM [24] and WorldClim [25] 1961–1990 monthly normal data (2.5 × 2.5 arc minute,