Response of non-vascular epiphytes to simulated climate change in a montane moist evergreen broad-leaved forest in southwest China
Highlights
► We assess the potential effects of predicted climate change on four epiphytes. ► We simulate climate change by using altitudinal gradients as a proxy. ► Non-vascular epiphytes are susceptible to simulated climate change. ► Drought has directly deleterious effects on epiphytic bryophytes. ► Nephromopsis pallescens can be used as bio-indicator to monitor climate change.
Introduction
Evergreen broad-leaved forests contribute to global biodiversity, and are important to the sustainable development of subtropical regions of China (Wang et al., 2005, Wu, 1980). Montane moist evergreen broad-leaved forests (MMEBFs) are a subgroup of evergreen broad-leaved forests, and occurs mainly in tropical and subtropical mountains at high altitude in Yunnan Province, south-western China (Wu, 1987). Due to the high rainfall, high relative humidity (RH), the presence of large trees, and absence of widespread human disturbance, the MMEBF located in the Ailao Mountains is especially rich in epiphytes, with 460 epiphytic species and an estimated biomass of 10.7 t ha−1 (Li et al., 2011, Ma, 2009, Xu and Liu, 2005).
The world is warming, with increases in global average air temperature and widespread melting of snow and ice (IPCC, 2007). Further warming may occur if emissions of greenhouse gases continue at or above current rates (IPCC, 2007). Global climate models predict a declining trend of relative humidity (RH) over most tropical land surfaces (Foster, 2001). Even a slight rise in the concentration of CO2 will increase the elevation at which clouds form in tropical montane forests (Still et al., 1999). In parallel with these global trends, over the past 40 years, the annual temperature has increased at a rate of 0.3 °C decade−1 in Yunnan Province (southwestern China) (Fan et al., 2011), while the air RH has shown a decreasing trend in tropical regions of Yunnan (He et al., 2007). Further, the annual temperature is predicted to increase by 2.2 °C and the annual precipitation to decrease by 130 mm by the 2050s, compared with the current condition in the MMEBF (Hijmans et al., 2005, Ramirez and Jarvis, 2008).
Climate change has triggered plant responses in many parts of the world, including shifts in species distribution and changes in physiology (Thuiller et al., 2005), and is gaining increasing attention worldwide (Jump and Penuelas, 2005, Ryan, 1991, Thuiller et al., 2005). Studies on impacts of climate change on epiphytes are scarce, even though they have been predicted as being sensitive to atmospheric changes because they are anchored in the forest canopy and lack access to water and nutrients on the forest floor or from the host vascular system (Benzing, 1998, Hietz, 1998, Gradstein, 2008, Nadkarni and Solano, 2002).
Because non-vascular epiphytes are poikilohydric and lack roots and an outer waxy cuticle, they are probably more sensitive to changes in ambient climatic conditions than are vascular epiphytes. Model simulations by Ellis et al. (2007a) suggested that an epiphytic lichen (Lecanora populicola (DC) Duby) in the United Kingdom may expand in its potential range to future climate change. In the British Isles, lichen species in southern regions will increase in extent, while those in the north will decrease in response to future climate change (Ellis et al., 2007b). Some non-vascular epiphytes have already been affected by climate change in central Europe, where certain Atlantic and Mediterranean species have extended their ranges into north and north-eastern Europe in the last decades because of global warming (Frahm and Klaus, 2001). Translocation experiments in Bolivia indicated that global warming may influence the structure of epiphytic communities (Jácome et al., 2011).
Among the few studies that assessed the potential impact of climate change on non-vascular epiphytes, most evidence has been derived from modeling work (e.g. Ellis et al., 2007a, Ellis et al., 2007b, Ellis et al., 2009). Empirical studies are needed to confirm model projections. Previous empirical studies have focused on either range shifts or community dynamics, with few addressing the specific influences related to climate change on the growth and health of non-vascular epiphytes. In this study, we transplanted three common cryptogamic epiphyte species (two bryophytes, one lichen) from high elevation to medium and low elevation sites and monitored their growth and health at regular intervals in a subtropical MMEBF in the Ailao Mountains. Another bryophyte species was monitored in situ at the three translocation sites. During the study period, southwest China experienced the worst regional drought event in the past 100 years from the end of 2009 to early 2010 (Qiu, 2010, Stone, 2010, Wang, 2010).
The three objectives of this study are to: (1) assess the potential impact of predicted climate change on the growth and health of four common non-vascular epiphytes in the MMEBF; (2) verify whether target species are affected by drought; and (3) assess the potential of the target species as indicators of climate change.
Section snippets
Study sites
We conducted this study in the Xujiaba region of south-western China (24°32′N, 101°01′E) in a protected section of a 5100 ha pristine MMEBF in Ailao Mountains National Nature Reserve (23°35′–24°44′N, 100°54′–101°01′E), at 2000–2600 m altitude (Li, 1983). The study site is affected by both the south sub-current of the west current from India and Pakistan and the southwestern monsoon, so it experiences a striking alternation of dry and wet conditions (Qiu and Xie, 1998). January and July are
Microclimate
Repeated measure GLM showed significant effects of site over 1 year on temperature, RH, and leaf wetness (Table 1). Mean air temperature at the high site was 8.8 °C, which was significantly lower than temperature at the medium (9.7 °C) and low (10.6 °C) site. The air RH showed a reverse trend compared with air temperature, with mean values of 94.7%, 90.7%, and 88.7%, at the high, medium, and low sites, respectively. Mean leaf wetness at the high site (34.3) was significantly higher than the other
Response of non-vascular epiphytes to simulated climate change
Results of the microclimate measurement confirmed that air temperature decreased, but water availability increased with altitude rising. The mean temperature increase by 1.8 °C and RH decrease by 6% in the low site compared with that in the high site during the study period. As was mentioned above, the MMEBF studied here is predicted to become warmer and drier (Hijmans et al., 2005, Ramirez and Jarvis, 2008), the experimental exposure of epiphytes from high site to lower sites can be considered
Acknowledgments
This study was supported by the National Natural Science Foundation of China (Nos. U1133605, 30870437), the QCAS Biotechnology Fund (No. GJHZ1130), and Knowledge Innovation Program of Chinese Academy of Science (No. KSCX2-YW-Z-1019). We thank the Management Authority of Ailao Mountains National Nature Reserve and the Ecological Station of Ailao Mountains for granting permission and providing meteorological data. We thank Mr. Jin-Hua Qi and Yuan-Lin Yao for assistance in the field surveying and
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