Teng Chiu Lin

Influence of typhoon disturbances on the understory light regime and stand dynamics of a subtropical rain forest in northeastern Taiwan

In 1996 and 1997 we examined the effects of typhoon disturbance on the understory light environment and sapling dynamics of the Fu-shan Experimental Forest, a subtropical rain forest in northeastern Taiwan. Mean understory light levels were approximately 30% of those in the open immediately following the two 1996 typhoons which affected the forest, yet in 1997, following two more typhoons, mean understory light levels were 10%–20% of those in the open. The decline of understory light levels to those present prior to the typhoons was more rapid in 1996 than in 1997, even though the two typhoons in 1996 were more intense than those in 1997. This difference might be the result of the timing of the typhoons. In 1996 the typhoons occurred earlier in the growing season, before August 1 rather than the middle and end of August in 1997. The regular defoliation caused by the frequent typhoons that impact Fu-shan (average of 1.4 per year) and the low stature of the forest (mean canopy height of 10.6 m), results in much higher light levels beneath the canopy (9%–30% of levels in the open) than those found in most tropical and temperate forests. As a result, understory light levels are not limiting the distribution of canopy tree saplings within the forest and there is no evidence that canopy gaps play an important role in canopy tree regeneration within the Fu-shan Experiment Forest. This is in contrast with the pattern reported for some tropical forests. With frequent typhoons impacting northeastern Taiwan, the forests of this region are perpetually recovering from wind disturbances.

Assessing growing season beginning and end dates and their relation to climate in Taiwan using satellite data

Due to the close relationship between climate and plant phenology, changes in plant phenological patterns have been used as a surrogate of climate change. We analysed Moderate Resolution Imaging Spectroradiometer (MODIS) images to investigate the onset, offset and length of growing season, as well as spatial and inter-annual patterns of Normalized Difference Vegetation Index (NDVI) across six types of vegetation/land use in Taiwan. Regression models indicate that temperature was moderately to strongly related to NDVI for each of the six vegetation/land-use types (coefficients of determination (R 2)  =  0.45–0.86). There was a 1–2 month lag time between changes in temperature and NDVI in the forests that are distributed in mid- to high-elevation areas, but not in low-elevation unirrigated fields, paddy fields and urban areas. The relationship between precipitation and changes in NDVI was only significant for unirrigated fields and urban areas (R 2  =  0.37–0.43). Growing season ended considerably earlier at low elevations than at high elevations, possibly because of the earlier start and more severe dry period in low-elevation areas, such that the length of the growing season was longer in the forests than in the unirrigated fields, paddy fields and urban areas.

Relating vegetation dynamics to temperature and precipitation at monthly and annual timescales in Taiwan using MODIS vegetation indices

To predict the responses of the timing, duration, and density of photosynthetically active plant cover to a changing climate, it is necessary to first quantitatively describe the relationships between temporal and spatial patterns of vegetation cover and both spatial and inter-annual variation in temperature and precipitation. We examined these relationships at multiple scales in Taiwan using monthly maximum composite values of MODIS-NDVI and MODIS-EVI between 2000 and 2012. The two vegetation indices were highly correlated to each other on a monthly basis for non-forest land-cover types, but correlated poorly in forests, probably due to the saturation of NDVI. However, the two indices were equally sensitive in detecting the onset and offset of growing season for all vegetation types. We found that EVI was positively related to both precipitation and temperature on a monthly timescale, although the relationships were not significant at the annual timescale. The much greater variation in monthly than in annual precipitation and temperature probably explains this difference. At low elevations, precipitation had a positive effect and temperature had a negative effect on EVI; however, at high elevations, which are mostly forested, both were positively related to EVI (although precipitation effects were not significant). We interpret this as evidence of water limitation of photosynthetic cover in the warmer, low-elevation parts of the island, whereas in the higher-elevation areas precipitation was usually adequate to satisfy evapotranspirative demand. This study illustrates the importance of examining the effects of precipitation and temperature on plant growth at a range of spatial and temporal scales. Specifically, finer spatial and temporal scales of analysis may better reveal climatic controls over vegetation growth than broader scales of analysis.

The Occurrence of Crassulacean Acid Metabolism in Epiphytic Ferns, with an Emphasis on the Vittariaceae

The potential for nighttime CO2 uptake and/or increases in tissue acidity characteristic of crassulacean acid metabolism (CAM) was investigated, to varying degrees, in 12 species of Vittariaceae as well as in seven species in four other families of tropical epiphytic ferns. Evidence of CAM (actually CAM cycling, i.e., diel changes in tissue acidity without nighttime atmospheric CO2 uptake), though highly variable, was found in two species of Vittariaceae. The ecophysiological significance of this finding is puzzling, because the occurrence of these plants in deeply shaded, extremely moist habitats is rare, if not unique, among plants expressing any degree of CAM. The results of this study confirm that CAM among the ferns is not limited to the Polypodiaceae, and they emphasize the polyphyletic nature of the evolution of CAM among higher plants.

Ecophysiology and Plant Size in a Tropical Epiphytic Fern, Asplenium nidus, in Taiwan

Recent studies indicate that, especially in epiphytes, plant size has a strong influence on the ecophysiology of individual leaves of a plant. Extensive data sets that address this phenomenon, however, are limited to a few taxa of flowering plants. It was the purpose of this study to examine numerous physiological parameters in individuals of varying sizes of Asplenium nidus, a widespread epiphytic tropical fern, in a rain forest in northeastern Taiwan. Although stomatal dimensions and frond thickness did not vary with plant size, frond stomatal densities were higher in larger plants. Frond elemental concentration did not vary with plant size for nitrogen, magnesium, phosphorus, and sodium, while the concentrations of carbon, calcium, and potassium changed with plant size, though in different ways. The osmotic concentration of liquid expressed from the fronds did not change with plant size, nor did chlorophyll concentrations and chlorophyll a/b ratio. Fronds excised from smaller plants contained more water yet lost water at lower rates in laboratory drying experiments. Although rates of net CO2 exchange of the fronds measured in situ in the field appeared to increase with plant size, this increase and other size‐related differences in gas exchange parameters were not significant. Although some aspects of the ecophysiology of this epiphytic fern varied with changes in plant size, most physiological parameters did not. Thus, the results of this study lend only little support to past findings that plant size is an important consideration in ecophysiological studies of plants.

Precipitation Chemistry at the Lienhuachi Experimental Forest in Central Taiwan

This paper examines weekly wet-only precipitation chemistry in the Lienhuachi Experimental Forest between October 2004 and September 2005. The volume-weighted mean annual pH was 4.84, lower than the Taiwan Environmental Protection Adminstrations criterion for acid rain (pH＜5.0). It was also lower than the value measured 13 years ago at the same site (5.51), despite decreases in the emissions of acidic pollutants over the same period of time. Coincident decreases in the emission of particulate pollutants with high concentrations of acid-neutralizing base cations, as well as differences in the collection methods (wet-only versus bulk precipitation) are possible explanations for the observed differences in precipitation pH. Seasonally, pH was lower in spring and winter than in summer and fall. This pattern is in agreement with many other studies throughout Taiwan and is often attributed to the high contribution of pollutants transported from China in the winter and spring. The rates of S and inorganic N deposition, of 11.5 and 13.8 kg ha-1 yr-1, respectively, were higher than those in the northeastern US where high acid deposition is a major concern in forest nutrient cycling and health. The impacts of such high acidic deposition on forest ecosystems need to be thoroughly examined. The rate of S deposition observed in the Lienhuachi Experimental Forest is similar to those of several other forest ecosystems in central Taiwan, whereas the rate of N deposition at the Lienhuachi Experimental Forest is considerably higher. It appears that areas of high N deposition are more localized than those of S deposition. The application of commercial fertilizers around the Lienhuachi Experimental Forest may explain the observed higher N deposition at our study site compared to other forest ecosystems in central Taiwan.

Canopy CO2 concentrations and Crassulacean acid metabolism in Hoya carnosa in a subtropical rain forest in Taiwan: consideration of CO2 availability and the evolution of CAM in epiphytes

The potential importance of CO2 derived from host tree respiration at night as a substrate for night time CO2 uptake during CAM was investigated in the subtropical and tropical epiphytic vine Hoya carnosa in a subtropical rainforest in north-eastern Taiwan. Individuals were examined within the canopies of host trees in open, exposed situations, as well as in dense forests. Although night time CO2 concentrations were higher near the epiphytic vines at night, relative to those measured during the day, presumably the result of CO2 added to the canopy air by the host tree, no evidence for substantial use of this CO2 was found. In particular, stable carbon isotope ratios of H. carnosa were not substantially lower than those of many other CAM plants, as would be expected if host-respired CO2 were an important source of CO2 for these CAM epiphytes. Furthermore, laboratory measurements of diel CO2 exchange revealed a substantial contribution of daytime CO2 uptake in these vines, which should also result in lower carbon isotope values than those characteristic of a CAM plant lacking daytime CO2 uptake. Overall, we found that host-respired CO2 does not contribute substantially to the carbon budget of this epiphytic CAM plant. This finding does not support the hypothesis that CAM may have evolved in tropical epiphytes in response to diel changes in the CO2 concentrations within the host tree canopy.

Demography of the upward-shifting temperate woody species of the Rhododendron pseudochrysanthum complex and ecologically relevant adaptive divergence in its trailing edge populations

Trailing edge populations of upward migrating species induced by postglacial climatic warming can be evolutionarily significant in the face of global warming. We tested for population size changes between lower- and higher-elevation populations located in the same mountainous regions of the upward-shifting temperate woody species of the Rhododendron pseudochrysanthum complex in Taiwan. We also tested whether natural selection evoked adaptive divergence in trailing edge populations of this species complex. We genotyped 26 expressed sequence tag-simple sequence repeat (EST-SSR) loci of 185 individuals from nine populations of the R. pseudochrysanthum complex including Rhododendron rubropunctatum, Rhododendron hyperythrum, Rhododendron morii, and R. pseudochrysanthum. R. rubropunctatum populations in the R. pseudochrysanthum complex possessed the lowest estimates of genetic diversity and effective population size. Higher-elevation R. pseudochrysanthum populations had lower effective population sizes than lower-elevation R. morii populations in Hohuanshan and Tahsueshan, as revealed by estimates using both MIGRATE-N and approximate Bayesian computation (ABC). R. rubropunctatum populations diverged significantly from populations of other members of the R. pseudochrysanthum complex. An outlier potentially under positive selection specific to R. rubropunctatum populations was identified and strongly associated with ecologically relevant environmental variables. Postglacial climatic warming has a significant influence on population isolation in the R. pseudochrysanthum complex. The results indicate adaptive evolution in the trailing edge populations, i.e., R. rubropunctatum populations of the upward shifting R. pseudochrysanthum complex.

Fog and precipitation chemistry at a mid-land forest in central Taiwan.

We analyzed fog and bulk precipitation chemistry at a cloud forest in central Taiwan where mountain agriculture activities are highest. There were 320 foggy days (visibility <1000 m) recorded between April 2005 and March 2006. Fog was most frequent between April 2005 and July 2005 and in March 2006 (153/153 d) and least frequent in January 2006 (21/31 d). The total fog duration was 2415 h, representing 28% of the sampling period. Compared with bulk precipitation, fog was disproportionally enriched in NO(3)(-) and SO(4)(2-) relative to K(+), Ca(2+), Mg(2+), and NH(4)(+), resulting in higher a content of nitric acid and sulfuric acid than weak acids or neutral salts and, therefore, higher acidity (median pH, 4.9) in fog than in bulk precipitation (median and mean pH, 5.5). The very high input of NH(4)(+) (47 kg N ha(-1) yr(-1)) through bulk precipitation suggests that the use of fertilizer (ammonium sulfate and animal manure) associated with mountain agriculture has a major impact on atmospheric deposition at the surrounding forest ecosystems. The input of inorganic N reached 125 kg N ha(-1) yr(-1) and likely exceeded the biological demand of the forest ecosystem. Sulfate is the most abundant anion in fog at Chi-tou and in precipitation at various forests throughout Taiwan, suggesting that the emission and transport of large quantities of SO(2,) the precursor of SO(4)(2-), is an island-wide environmental issue.

Impacts of increasing typhoons on the structure and function of a subtropical forest: Reflections of a changing climate

Due to their destructive and sporadic nature, it is often difficult to evaluate and predict the effects of typhoon on forest ecosystem patterns and processes. We used a 21-yr record of litterfall rates to explore the influence of typhoon frequency and intensity, along with other meteorological variables, on ecosystem dynamics in a subtropical rainforest. Over the past half century there has been an increasing frequency of strong typhoons (category 3; >49.6 m s−1; increase of 1.5 typhoons/decade) impacting the Fushan Experimental Forest, Taiwan. At Fushan strong typhoons drive total litterfall mass with an average of 1100 kg ha−1 litterfall typhoon−1. While mean typhoon season litterfall has been observed to vary by an order of magnitude, mean litterfall rates associated with annual leaf senescence vary by <20%. In response to increasing typhoon frequency, total annual litter mass increased gradually over the 21-year record following three major typhoons in 1994. Monthly maximum wind speed was predictive of monthly litterfall, yet the influence of precipitation and temperature was only evident in non-typhoon affected months. The response of this subtropical forest to strong typhoons suggests that increasing typhoon frequency has already shifted ecosystem structure and function (declining carbon sequestration and forest stature).