Anthony R. Palmer

An automated procedure for estimating the leaf area index (LAI) of woodland ecosystems using digital imagery, MATLAB programming and its application to an examination of the relationship between remotely sensed and field measurements of LAI

Leaf area index (LAI) is one of the most important variables required for modelling growth and water use of forests. Functional-structural plant models use these models to represent physiological processes in 3-D tree representations. Accuracy of these models depends on accurate estimation of LAI at tree and stand scales for validation purposes. A recent method to estimate LAI from digital images (LAID) uses digital image capture and gap fraction analysis (Macfarlane et al. 2007b) of upward-looking digital photographs to capture canopy LAID (cover photography). After implementing this technique in Australian evergreen Eucalyptus woodland, we have improved the method of image analysis and replaced the time consuming manual technique with an automated procedure using a script written in MATLAB 7.4 (LAIM). Furthermore, we used this method to compare MODIS LAI values with LAID values for a range of woodlands in Australia to obtain LAI at the forest scale. Results showed that the MATLAB script developed was able to successfully automate gap analysis to obtain LAIM. Good relationships were achieved when comparing averaged LAID and LAIM (LAIM = 1.009 - 0.0066 LAID; R2 = 0.90) and at the forest scale, MODIS LAI compared well with LAID (MODIS LAI = 0.9591 LAID - 0.2371; R2 = 0.89). This comparison improved when correcting LAID with the clumping index to obtain effective LAI (MODIS LAI = 1.0296 LAIe + 0.3468; R2 = 0.91). Furthermore, the script developed incorporates a function to connect directly a digital camera, or high resolution webcam, from a laptop to obtain cover photographs and LAI analysis in real time. The later is a novel feature which is not available on commercial LAI analysis softwares for cover photography. This script is available for interested researchers.

An analysis of the sensitivity of sap flux to soil and plant variables assessed for an Australian woodland using a soil–plant–atmosphere model

Daily and seasonal patterns of tree water use were measured for the two dominant tree species, Angophora bakeri E.C.Hall (narrow-leaved apple) and Eucalyptus sclerophylla (Blakely) L.A.S. Johnson & Blaxell (scribbly gum), in a temperate, open, evergreen woodland using sap flow sensors, along with information about soil, leaf, tree and micro-climatological variables. The aims of this work were to: (a) validate a soil-plant-atmosphere (SPA) model for the specific site; (b) determine the total depth from which water uptake must occur to achieve the observed rates of tree sap flow; (c) examine whether the water content of the upper soil profile was a significant determinant of daily rates of sap flow; and (d) examine the sensitivity of sap flow to several biotic factors. It was found that: (a) the SPA model was able to accurately replicate the hourly, daily and seasonal patterns of sap flow; (b) water uptake must have occurred from depths of up to 3 m; (c) sap flow was independent of the water content of the top 80 cm of the soil profile; and (d) sap flow was very sensitive to the leaf area of the stand, whole tree hydraulic conductance and the critical water potential of the leaves, but insensitive to stem capacitance and increases in root biomass. These results are important to future studies of the regulation of vegetation water use, landscape-scale behaviour of vegetation, and to water resource managers, because they allow testing of large-scale management options without the need for large-scale manipulations of vegetation cover.

Drought and resprouting plants

Many species have the ability to resprout vegetatively after a substantial loss of biomass induced by environmental stress, including drought. Many of the regions characterised by ecosystems where resprouting is common are projected to experience more frequent and intense drought during the 21st Century. However, in assessments of ecosystem response to drought disturbance there has been scant consideration of the resilience and post-drought recovery of resprouting species. Systematic differences in hydraulic and allocation traits suggest that resprouting species are more resilient to drought-stress than nonresprouting species. Evidence suggests that ecosystems dominated by resprouters recover from disturbance more quickly than ecosystems dominated by nonresprouters. The ability of resprouters to avoid mortality and withstand drought, coupled with their ability to recover rapidly, suggests that the impact of increased drought stress in ecosystems dominated by these species may be small. The strategy of resprouting needs to be modelled explicitly to improve estimates of future climate-change impacts on the carbon cycle, but this will require several important knowledge gaps to be filled before resprouting can be properly implemented.

Is Climate Change a Possible Explanation for Woody Thickening in Arid and Semi-Arid Regions?

Increased woody plant density (woody encroachment or woody thickening) is a globally observed phenomenon. Similarly, increased atmospheric carbon dioxide concentrations and decreased pan evaporation rates are globally observed phenomena. In this paper, we propose that the former (increased woody plant density) is a product of the latter. We propose that decreased stomatal conductance and increased rates of carbon fixation arising from an enriched atmospheric carbon dioxide concentration, in conjunction with reduced rates of pan evaporation, result in increased woody plant density. We suggest that this is analogous to the increased woody plant density that is observed along rainfall gradients that span arid to mesic environments. From this conceptual model, we make three predictions, namely, that (a) long-term trends in tree water-use-efficiency should reveal increased values; (b) run-off data should show an increase where woody thickening is occurring; (c) enriched CO2 experiments should reveal an enhanced plant water status. These three predictions are discussed and shown to be supported by experimental data.

Biodiversity in Southern Africa

2010, Klaus Hess Publishers, Sudetenland-Str. 18, 37085 Göttingen, Germany; and PO Box 90624, Windhoek, Namibia Hardcover, 3 volumes, XLIV + 1375 pp + CD-ROM ISBN 9789991657301 (Namibia and South Africa), 9783933117441 (Germany and rest of the world). Price R600/€75

Degradation of communal rangelands in South Africa: towards an improved understanding to inform policy

In South Africa, the relative extent of range degradation under freehold compared to communal tenure has been strongly debated. We present a perspective on the processes that drive rangeland degradation on land under communal tenure. Our findings are based on literature as well as extensive field work on both old communal lands and ‘released’ areas, where freehold farms have been transferred to communal ownership. We discuss the patterns of degradation that have accompanied communal stewardship and make recommendations on the direction policy should follow to prevent further degradation and mediate rehabilitation of existing degraded land.

Sustainability of the South African livestock sector towards 2050. Part 1: Worth and impact of the sector.

Copyright resides with the authors in terms of the Creative Commons Attribution 2.5 South African Licence. See: http://creativecommons.org/licenses/by/2.5/za Condition of use: The user may copy, distribute, transmit and adapt the work, but must recognise the authors and the South African Journal of Animal Science ________________________________________________________________________________ Abstract Livestock production in South Africa contributes substantially to food security. It is also a topic of public debate because of lack of knowledge and wrong information. This article aims to provide information on the worth and impact of the livestock sector; information and statistics providing a baseline to guiding sustainability towards 2050. Seventy percent of agricultural land in South Africa can be utilized only by livestock and game and species are found in all provinces with high concentrations in the eastern higher rainfall regions. Statistics in 2010 indicate 13.6 million beef cattle, 1.4 million dairy cattle, 24.6 million sheep, 7.0 million goats, 3 million game species (farmed), 1.1 million pigs, 113 million broilers, 31.8 million layers and 1.6 million ostriches. The gross value of livestock products increased by 185% from 1995/2000 to 2006/2010. In relation to field crops and horticulture, livestock products increased their position from 42% to 47% of gross agricultural value. The main reason was a rise in the value and demand for livestock foods, particularly meat. Livestock foods contribute 27% of the consumer food basket on a weight basis. Consumption of livestock foods resembles that of developing countries with meat consumption being 50 90 g/capita/day, milk and dairy products 120 130 g /capita/day and eggs 15 20 g/capita/day. Since this is the average for the country with consumption by the rich and poor often differing tenfold, consumption of livestock foods by the poor is of concern, given the many health attributes of livestock foods. The livestock sector in South Africa is a major role player in the conservation of biodiversity through a variety of welladapted indigenous and non-indigenous breeds and rare game species. It has also shown commitment to rangeland/ecosystem conservation through conservative stocking rates, with several studies and observations reporting improvement in the condition of the natural resource. The sector has always been a major employer, but employment rate has declined steadily since 2000 because of increased minimum wages, fewer commercial farmers and increased property size. Some 245 000 employees with 1.45 million dependants, in addition to dependants on communal land and emerging farms, are employed on 38 500 commercial farms and intensive units with wages amounting to R 6 100 million (South African rand). Livestock farming is the backbone of the socio-economy and provides the sustenance of most nonmetropolitan towns and rural communities. ________________________________________________________________________________

Remote sensing and change detection in rangelands

During the 20 th century, we have witnessed an improvement in the quality of imagery available for rangeland auditing, from the earliest mono-chromatic aerial photographs, followed by the first infra-red images, to the abundance of high resolution, multi-spectral imagery currently available. Of overwhelming concern is the difficulty of translating this information into a useful tool for making decisions about land management and intervention strategies. At one level, the land manager is always playing catch-up, as the technology for viewing and analysing imagery improves and out-strips his capacity. He is close to the land, making daily decisions about production and condition, but the images are snapshots taken two to three months earlier. To most land managers, remote sensing has remained illusive, seldom allowing the manager to use it to its full potential. In contrast, the policy maker, backed by GIS laboratories and remote sensing specialists, is confronted by plausible scenarios of degradation and transformation. After intervening, he is seldom active long enough to witness changes in the remotely derived land condition indices and fails to adapt decisions. Bridging this divide remains a challenge to the remote-sensing community and some possible mechanisms are suggested. The major limiting factor for the wider utilisation of satellite imagery in rangeland assessment remains the cost of the imagery. Unless first world data suppliers show their commitment to sustainable development in real terms, data costs will remain a limiting factor.

Vegetation mapping of the Great Fish River basin, South Africa: Integrating spatial and multi-spectral remote sensing techniques

We present a remote sensing based vegetation mapping technique well suited to a heterogeneous, semi-arid environment. 10 structural vegetation classes were identified and described on the ground. Using Landsat-TM from two different seasons and a combination of three conventional classification techniques (including a multi-temporal classi- fication) we were unsuccessful in delineating all of the desired vegetation classes. We then employed a simple tex- tural classification index, known as the Moving Standard Deviation Index (MSDI), that has been used to map degrada- tion status. MSDI measures spatial variations in the land- scape and is calculated by passing a 3 x 3 standard deviation filter across the Landsat-TM red band. High MSDI values are associated with degraded or disturbed rangelands whilst low MSDI values are associated with undisturbed rangeland. A combination of two conventional multi-spectral techniques and MSDI were used to produce a final vegetation classifica- tion at an accuracy of 84 %. MSDI successfully discrimi- nated between two contrasting vegetation types of identical spectral properties and significantly strengthened the accu- racy of the classification. We recommend the use of a tex- tural index such as MSDI to supplement conventional veg- etation classification techniques in heterogeneous, semi-arid or arid environments.

The use of pre-dawn leaf water potential and MODIS LAI to explore seasonal trends in the phenology of Australian and southern African woodlands and savannas

Trends in global soil moisture are needed to inform models of soil–plant–atmosphere interactions. Predawn leaf water potential (Ψpd), a surrogate for soil moisture and an index of plant water stress, has been routinely collected in Australian forests, woodlands and savannas, but the associated leaf area index (LAI) has seldom been available to enable the preparation of a Ψpd on LAI relationship. Following an analysis of Ψpd and MODIS LAI data from Australian forests, woodlands and savannas, we identified patterns in Ψpd which provide an understanding of the role of soil-moisture status in controlling LAI. In the savanna of northern Australia, the MODIS LAI product had a basal value of 0.96 during the dry season as compared with a mean value of 2.5 for the wet season. The dry season value is equivalent to the LAI of the tree component and corresponds with ground-truthed LAI. Ψpd is lowest (more negative) during the height of the dry season (late October) at −2.5 MPa, and highest (−0.1 MPa) during the wet season (early March). We present two models which predict Ψpd from the MODIS LAI product. These may be useful surrogates for studying trends in soil moisture in highly seasonal climates and may contribute to climate change research.