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

Mapping reference evapotranspiration from meteorological satellite data and applications

Reference evapotranspiration (ETo) is an agrometeorological variable widely used in hydrology and agriculture. The FAO-56 Penman-Monteith combination method (PM method) is a standard for computing ETo for water management. However, this scheme is limited to areas where climatic data with good quality are available. Maps of 10-day averaged ETo at 5 km Ă 5 km grid spacing for the Taiwan region were produced by multiplying pan evaporation (Epan), derived from ground solar radiation (GSR) retrieved from satellite images using the Heliosat-3 method, by a fixed pan coefficient (Kp). Validation results indicated that the overall mean absolute percentage error (MAPE) and normalized root-mean-square deviation (NRMSD) were 6.2 and 7.7%, respectively, when compared with ETo computed by the PM method using spatially interpolated 10-day averaged daily maximum and minimum temperature datasets and GSR derived from satellite inputs. Land coefficient (KL) values based on the derived ETo estimates and long term latent heat flux measurements, were determined for the following landscapes: Paddy rice (Oryza sativa), subtropical cypress forest (Chamaecyparis obtusa var. formosana and Chamaecyparis formosensis), warm-to-temperate mixed rainforest (Cryptocarya chinensis, Engelhardtia roxburghiana, Tutcheria shinkoensis, and Helicia formosana), and grass marsh (Brachiaria mutica and Phragmites australis). The determined land coefficients are indispensable to scale ETo in estimating regional evapotranspiration

Typhoon Disturbance and Forest Dynamics: Lessons from a Northwest Pacific Subtropical Forest

Abstract Strong tropical storms are known to affect forest structure, composition, and nutrient cycles in both tropical and temperate regions, although our understanding of these effects disproportionally comes from regions experiencing much lower cyclone frequency than many forests in the Northwest Pacific. We summarized the effects of typhoons on forest dynamics at Fushan Experimental Forest (FEF) in northeastern Taiwan, which averages 0.49 major typhoons annually, and compared their resistance and resilience to those of forests in other regions. Typhoons cause remarkably few tree falls at FEF; multiple typhoons in 1994 felled only 1.4% of canopy trees, demonstrating high structural resistance. The most important effect of typhoons in this ecosystem is defoliation, which maintains high understory light levels and enhances heterogeneity, sustaining diversity without large canopy gaps. The vulnerability of taller trees to being blown down has resulted in the short-stature FEF (mean canopy height is 10.2 m). As the FEF is P-limited and a large fraction of total annual P export occurs during typhoons, these storms may have the effect of reducing productivity over time. DIN and K+ export only remain elevated for days at FEF, in contrast to the several years observed in Puerto Rico. High resilience is also evident in the rapid recovery of leaf area following typhoons. Heavy defoliation and slow decomposition are among the processes responsible for the high resistance and resilience of FEF to typhoon disturbance. These key structural features may emerge in other forest ecosystems if the frequency of major storms increases with climate change