Stratification of density in dry deciduous forest using satellite remote sensing digital data—An approach based on spectral indices

Forest density expressing the stocking status constitutes the major stand physiognomic parameter of Indian forest. Density and age are often taken as surrogate to structural and compositional changes that occur with the forest succession. Satellite remote sensing spectral response is reported to provide information on structure and composition of forest stands. The various vegetation indices are also correlated with forest canopy closure. The paper presents a three way crown density model utilizing the vegetation indices viz., advanced vegetation index, bare soil index and canopy shadow index for classification of forest crown density. The crop and water classes which could not be delineated by the model were finally masked from normalized difference vegetation index and TM band 7 respectively. The rule based approach has been implemented for land use and forest density classification. The broad land cover classification accuracy has been found to be 91.5%. In the higher forest density classes the classification accuracy ranged between 93 and 95%, whereas in the lower density classes it was found to be between 82 and 85%.     

Seasonality and vertical structure of light-attracted insect communities in a dipterocarp forest in Sarawak

Nocturnal flying insects were collected monthly for 13 months using ultra violet light-traps set at various vertical levels in a weakly-seasonal, tropical lowland dipterocarp forest in Sarawak, Malaysia. Abundance, faunal composition, size distribution and guild structure of these samples were analyzed with respect to temperal and vertical distributions. The nocturnal flying insect community in the canopy level was highly dominated by fig wasps (84%) in individual number, and by scarabaeid beetles (28%) in weight. A principal component analysis on monthly catches detected non-random, seasonal trends of insect abundance. The first two principal trends were an alternation of wetter (September to January) and less wet seasons (February to August) and an alternation between the least wet (January to March) and the other seasons. Many insect groups were less abundant in the least wet season than the other seasons, whilst inverse patterns were found in Scarabaeidae and Tenebrionidae. Significantly positive and negative correlations between monthly catch and rainfall were detected only in ovule-feeders and in phloem-feeders, respectively. Delayed, significant negative correlations between monthly catch and 1–3 month preceding rainfall were more frequently detected in phytophages, phloem-feeders, seed-feeders, wood-borers and scavengers. The peak in abundance along vertical levels were found at the canopy level (35 m) for phloem-, ovule-, seed-, root-, fungal-feeders and nectar collectors, at an upper subcanopy level (25 m) for scavengers and aquatic predators, and at a middle subcanopy level (17 m) for ants. Catches at the emergent level (45 m) did not exceed those at the canopy level.     

Short-term photosynthesis measurements predict leaf carbon balance in tropical rain-forest canopy plants

Diel (24 h) courses of net CO₂ exchange of leaves were determined in eight species of tropical rainforest plants on Barro Colorado Island, Panama, during 1990 and 1991. The species included three canopy trees, one liana, two epiphytes and one hemiepiphyte. One of the species studied was growing in a rain-forest gap. Daily carbon gain varied considerably across species, leaf age, and season. The analysis of data for all plants from 64 complete day/night cycles revealed a linear relationship between the diurnal carbon gain and the maximum rate of net CO₂ uptake, A_max. Nocturnal net carbon loss was about 10% of diurnal carbon gain and was positively related to A_max. We conclude that short-term measurements of light-saturated photosynthesis, performed at periodic intervals throughout the season, allow the annual leaf carbon balance in these rain-forest plants to be predicted.     

Understorey vegetation moderates climate in open forests: The role of the skirt-forming grass tree Xanthorrhoea semiplana F.Muell

Microsites are created by abiotic and biotic features of the landscape and may provide essential habitats for the persistence of biota. Forest canopies and understorey plants may moderate wind and solar radiation to create microclimatic conditions that differ considerably from regional climates. Skirt-forming plants, where senescent leaves create hut-like cavities around the stem, create microsites that are sheltered from ambient conditions and extreme weather events, constituting potential refuges for wildlife. We investigate day and night temperatures and humidity for four locations (grass tree cavities, soil, 20 cm above-ground, 1 m above-ground) in a South Australian forest with relatively open canopy of stringybark eucalypts (Eucalyptus baxteri, E. obliqua) and an understorey of skirt-forming grass trees (Xanthorrhoea semiplana) at 5, 10, 20, and 40 m from the forest edge. We also measured the percentage of canopy and understorey covers. Generally, temperature and humidity differed significantly between more sheltered (grass tree cavities, soil) and open-air microsites, with the former being cooler during the day and warmer and more humid during the night. Furthermore, our results suggest that canopy cover tends to decrease, and understorey cover tends to increase, the temperature of microsites. Distance to the edge was not significantly related to temperature for any microsite, suggesting that the edge effect did not extend beyond 10 m from the edge. Overall, grass trees influenced microclimatic conditions by forming a dense understorey and providing cavities that are relatively insulated. The capacity of grass tree cavities to buffer external conditions increased linearly with ambient temperatures, by 0.46°C per degree increase in maximum and 0.25°C per degree decrease in minimum temperatures, potentially offsetting climate warming and enabling persistence of fauna within their thermal limits. These climate moderation properties will make grass trees increasingly important refuges as extreme weather events become more common under anthropogenic climate change.     

Upper thermal limits predict herpetofaunal responses to forest edge and cover

Amphibians and reptiles are sensitive to changes in the thermal environment, which varies considerably in human-modified landscapes. Although it is known that thermal traits of species influence their distribution in modified landscapes, how herpetofauna respond specifically to shifts in ambient temperature along forest edges remains unclear. This may be because most studies focus on local-scale metrics of edge exposure, which only account for a single edge or habitat patch. We predicted that accounting for the combined effect of multiple habitat edges in a landscape would best explain herpetofaunal response to thermally mediated edge effects. We (1) surveyed herpetofauna at two lowland, fragmented forest sites in central Colombia, (2) measured the critical thermal maximum (CT_max) of the species sampled, (3) measured their edge exposure at both local and landscape scales, and (4) created a thermal profile of the landscape itself. We found that species with low CT_max occurred both further from forest edges and in areas of denser vegetation, but were unaffected by the landscape-scale configuration of habitat edges. Variation in the thermal landscape was driven primarily by changes in vegetation density. Our results suggest that amphibians and reptiles with low CT_max are limited by both canopy gaps and proximity to edge, making them especially vulnerable to human modification of tropical forest. Abstract in Spanish is available with online material.     

Canopy photosynthetic production in a Japanese larch forest. II. Estimation of the canopy photosynthetic production

Seasonal changes and yearly gross canopy photosynthetic production were estimated for an 18 year old Japanese larch (Larix leptolepis) forest between 1982 and 1984. A canopy photosynthesis model was applied for the estimation, which took into account the effect of light interception by the non-photosynthetic organs. Seasonal changes in photosynthetic ability, amount of canopy leaf area and light environment within the canopy were also taken into account. Amount of leaf area was estimated by the leaf area growth of a single leaf. The change of light environment within the canopy during the growing season was estimated with a light penetration model and the leaf increment within the canopy. Canopy respiration and surplus production were calculated as seasonal and yearly values for the three years studied. Mean yearly estimates of canopy photosynthesis, canopy respiration and surplus production were 37, 13 and 23 tCO₂ ha⁻¹ year⁻¹, respectively. Vertical trend, seasonal changes and yearly values of the estimates were analyzed in relation to environmental and stand factors.     

用Reinecke盐液曝光计检测树冠内的光合有效辐射

1 引言 传统的植物光合生理生态研究中,多用照度计来测定光照指标,它以人眼对光亮度的响应特性为基础,与植物叶片对光照的响应曲线差异很大;而太阳光谱中只有400—700nm的波段才是光合有效辐射     

Canopy development of a determinate and an indeterminate cultivar of Vicia faba L. under contrasting plant distributions and densities

Field experiments were conducted in 1987 and 1988 to quantify differences in canopy formation between an indeterminate and a determinate genotype of Vicia faba L., grown at two plant densities and three spatial distributions. The number of stems per unit area produced by determinate plants was related to the growth rate before flowering. Leaf production per stem per unit of thermal time was similar in both plant types, but twice as many leaves per stem were produced by the indeterminate cultivar. The indeterminate cultivar produced fewer and smaller leaves in the warmer and drier weather of 1988 than in 1987. The determinate genotype produced similar sizes and numbers of leaves in both years, but fewer tillers developed in 1988 than in 1987. Accordingly, leaf mass per unit ground area was greater in 1987 than in 1988 in both genotypes. Except during early flowering, relationships between leaf mass and leaf area were constant, with higher specific leaf areas in the determinate than the indeterminate genotype. Shoot dry matter partitioning into leaves was identical in both years for indeterminate plants, but differed in determinate ones.
It is concluded that canopy development is regulated through individual leaf weight and leaf number per stem in non-tillering indeterminate, and by stem numbers per unit area in tillering determinate plants.