Intensive Production and Management of Marandu Palisadegrass (Urochloa brizantha ‘Marandu’) Accelerates Leaf Turnover but Does Not Change Herbage Mass

Pasture intensification through higher stocking rates, nitrogen fertilization and intensified grazing management in beef cattle production optimizes pasture use by increasing the forage harvested. We aimed to assess its effects on the morphogenesis and canopy structure of Urochloa brizantha ‘Marandu’ (marandu palisadegrass) pastures. The treatments consisted of marandu palisadegrass pastures managed under continuous stocking and a canopy height of 25 cm, with different levels of intensification: extensive, semi-intensive, and intensive systems N-fertilized with 0 kg, 75 kg, and 150 kg N ha−1 year−1, respectively, as ammonium nitrate (32% of N), with four replicates (paddocks) in a completely randomized design. Phyllochron (9.8 days) and leaf lifespan (34.7 days) were shorter in intensified pastures, whereas herbage mass was similar among treatments. Extensive pastures had a higher proportion of senescent material; thus, more intensive systems showed higher proportions of leaves and stems, although the leaves-to-stem ratio remained similar across production systems. The defoliation interval was lower in intensive (14.4 days) and higher in extensive (18.7 days) treatments. Thus, pasture intensification accelerates leaf appearance, decreases leaf lifespan, shortens the tiller defoliation interval and increased herbage accumulation rate but does not change herbage mass. The extensive system produces excessive forage losses due to dead material.

Monitoring Mega-Crown Leaf Turnover from Space

Spatial and temporal patterns of tropical leaf renewal are poorly understood and poorly parameterized in modern Earth System Models due to lack of data. Remote sensing has great potential for sampling leaf phenology across tropical landscapes but until now has been impeded by lack of ground-truthing, cloudiness, poor spatial resolution, and the cryptic nature of incremental leaf turnover in many tropical plants. To our knowledge, satellite data have never been used to monitor individual crown leaf phenology in the tropics, an innovation that would be a major breakthrough for individual and species-level ecology and improve climate change predictions for the tropics. In this paper, we assessed whether satellite data can detect leaf turnover for individual trees using ground observations of a candidate tropical tree species, Moabi (Baillonella toxisperma), which has a mega-crown visible from space. We identified and delineated Moabi crowns at Lopé NP, Gabon from satellite imagery using ground coordinates and extracted high spatial and temporal resolution, optical, and synthetic-aperture radar (SAR) timeseries data for each tree. We normalized these data relative to the surrounding forest canopy and combined them with concurrent monthly crown observations of new, mature, and senescent leaves recorded from the ground. We analyzed the relationship between satellite and ground observations using generalized linear mixed models (GLMMs). Ground observations of leaf turnover were significantly correlated with optical indices derived from Sentinel-2 optical data (the normalized difference vegetation index and the green leaf index), but not with SAR data derived from Sentinel-1. We demonstrate, perhaps for the first time, how the leaf phenology of individual large-canopied tropical trees can directly influence the spectral signature of satellite pixels through time. Additionally, while the level of uncertainty in our model predictions is still very high, we believe this study shows that we are near the threshold for orbital monitoring of individual crowns within tropical forests, even in challenging locations, such as cloudy Gabon. Further technical advances in remote sensing instruments into the spatial and temporal scales relevant to organismal biological processes will unlock great potential to improve our understanding of the Earth system.

GROWTH RESPONSES OF PALM SEEDLINGS TO DIFFERENT LIGHT INTENSITIES STIMULATING CANOPY GAPS WITH AN ECOPHYSIOLOGICAL APPROACH

LATIFAH, D., CONGDON, R. A. & HOLTUM, J. A. 2016. Growth responses of palm seedlings to different light intensities stimulating canopy gaps with an ecophysiological approach. Reinwardtia 15(2): 81 – 98. — Palms (Arecaceae) mainly grow in rainforests and many occur in disturbed areas like canopy gaps created by natural disturbances such as cyclones in Australia. Knowledge of seedling growth in different light intensities is essential to assist rainforest restoration in disturbed or marginal lands. The aim of this research was to investigate the effects of different light intensities on the seedling growth of Arenga australasica (H. Wendl. & Drude) S. T. Blake ex H. E. Moore, Calamus australis Mart., C. moti F. M. Bailey, Hydriastele wendlandiana (F. Muell.) H. Wendl. & Drude and Licuala ramsayi (F. Muell.) H. Wendl. & Drude. Seedling growth experiments (pot trials) were conducted in a glass house using shade cloth providing four different levels of shading: 59, 29, 17 and 6% sunlight. The growth rate, leaf turnover, leaf area, total chlorophyll, chlorophyll a:b ratio, vigor, above-ground and below-ground biomass and growth indices (LAR, SLA and LWR) of palm seedlings were measured. As a result of these measurements the relative shade tolerance of the five species was determined. The seedlings of Arenga australasica were classified as intermediate-shade intolerant species. Hydriastele wendlandiana seedlings were shade-intolerant. Calamus australis and C. moti seedlings are intermediate-shade intolerant. Licuala ramsayi seedlings were found to be a shade-tolerant.

REGENERATION STRATEGIES OF PALMS (ARECACEAE) IN RESPONSE TO CYCLONIC DISTURBANCES

LATIFAH, D., CONGDON, R. A. & HOLTUM, J. A. 2016. Regeneration strategies of palms (Arecaceae) in response to cyclonic disturbances. Reinwardtia 15 (1): 43 ? 59. — Tropical cyclones may act as important ecological drivers in northern Australia including north Queensland, as several cyclones impact this region each year between November and May. Extensive research has been conducted to investigate how regeneration of rainforest plant communities respond to frequent cyclonic disturbances. However, there have been few such studies on palms although they are important components of many rainforests. This research aimed to investigate the effects of canopy gaps following cyclonic disturbance (case study: Cyclone Larry) on regeneration of Arenga australasica (H. Wendl. & Drude) S. T. Blake ex H. E. Moore, Calamus australis Mart., C. moti F. M. Bailey, Hydriastele wendlandiana (F. Muell.) H. Wendl. & Drude and Licuala ramsayi var. ramsayi (F. Muell.) H. Wendl. & Drude. The field research was carried out at five sites in three areas located in northern Queensland: Tam O’Shanter/Djiru National Park, Clump Mountain National Park and Kurrimine Beach Conservation Park. Observations were made of recruitment, growth rate, leaf turnover and life history. We found that responses of palm regeneration following cyclonic disturbance varied among study sites; however, the recruitment of several species was favoured in gaps created by cyclones. The results also provide information on the various stages in the life cycle of the study palms.

Leaf growth and senescence rates of three pasture grasses and wheat

A glasshouse study was conducted under ideal conditions to determine leaf appearance, elongation, and senescence rates along with life span and leaf length characteristics of four grass species: wheat (Triticum aestivum L.), brown back wallaby grass (Rytidosperma duttonianum (Cashmore) Connor and Edgar), phalaris (Phalaris aquatica L.), and annual ryegrass (Lolium rigidum Gaud.). This study provided a comprehensive characterisation of leaf turnover rates for the entire life cycle of these grasses, some of which are poorly characterised. Importantly, leaf senescence rate has been captured in the same conditions as the other leaf rates of the life cycle. Leaf position proved to be a significant explanatory variable in each of the leaf turnover rates. The relationships between leaf position and the components of leaf turnover were most commonly represented by non-linear models. Further studies may be necessary to validate these statistical models to field situations. However, this information will be useful to calibrate the senescence algorithms of plant growth models in agricultural decision support tools, which may then be applied to simulation studies including the assessment of grass curing for planning activities such as resource allocation, wildfire suppression, and execution of prescribed burning programs by fire management agencies.