Water use of grasslands, agroforestry systems and indigenous forests

The biotic and abiotic components of ecosystems affect each other through complex interactions and processes. These dynamic interactions give ecosystems their distinct identities and provide ecosystem services critical to human survival (e.g. water, energy and nutrients). However, human activities (e.g. commercial forestry, agriculture) have placed increasing demands on specific ecosystem services. The effect of these activities on ecosystem processes has been the focus of numerous Water Research Commission (WRC) studies. Some of these have determined man’s impact on plant-water use, biomass production (energy) and water use efficiency (biomass produced per unit of water transpired, termed productive green-water use). For example, measurements of evapotranspiration (ETa) from different vegetation types showed that annual water use is strongly related to the proportion of the year in which a dense canopy of transpiring leaves is maintained. Thus, evergreen vegetation such as riparian fynbos and plantations of introduced tree species exhibit a relatively high annual ETa, when compared to seasonal grasslands and deciduous trees that only maintain their transpiring canopy during summer. Quantification of the annual volumes of water used by these different vegetation types, under differing climatic and site conditions, has been possible through these studies. At a stand scale, measurements of the different components of evapotranspiration have allowed the partitioning of beneficial (transpiration) and non-beneficial (evaporation) fluxes. At a catchment scale measurements have quantified the proportional allocation of water to the different components of the water balance. Three case studies are presented to illustrate this. In a stand of Jatropha curcas, measurements of daily total evaporation rates during December to February (summer) on clear hot days ranged between 3 mm·d-1 to 4 mm·d-1. However, due to the deciduous nature of the species, water use was negligible (< 1 mm·d-1) during winter (May to August). At a catchment scale, studies in a montane grassland ecosystem of the KwaZulu-Natal Drakensberg showed that the partitioning of the main hydrological fluxes into streamflow and evaporation was dependent on the wetness of the hydrological year. In average to wet years (>1 200 mm precipitation) the hydrological flux was equally split between evaporation (650 mm) and runoff (550 mm), while in drier years evaporation became the dominating component of the water balance (752 mm vs. 356 mm, respectively). The data provided an important baseline for comparison with other impacted ecosystems (especially commercial forestry). Finally, results of a variety of studies on the growth and water use of indigenous trees growing in natural forest and plantation systems suggest that, compared to introduced tree species, indigenous species use substantially less water, show lower water use efficiency, and grow more slowly. Advantages to such indigenous systems potentially include lower management costs, higher product values, a wider range of non-wood products and a lower hydrological impact. Their usefulness may be greatest on sensitive sites (e.g. riparian zones, water-stressed catchments, land cleared of alien plants, land with a high erosion risk, degraded forest) where land use systems with a reduced environmental impact are required.Keywords: evaporation, transpiration, grassland, indigenous trees, Jatropha curca

Environmental enrichment reduces signs of boredom in caged mink

Animals housed in impoverished cages are often labelled 'bored'. They have also been called 'apathetic' or 'depressed', particularly when profoundly inactive. However, these terms are rarely operationally defined and validated. As a negative state caused by under-stimulation, boredom should increase interest in stimuli of all kinds. Apathy (lack of interest), by contrast, should manifest as decreased interest in all stimuli, while anhedonia (loss of pleasure, a depressive symptom) should specifically decrease interest in normally rewarding stimuli. We tested the hypotheses that mink, a model carnivore, experience more boredom, depression-like apathy, or anhedonia in non-enriched (NE) cages than in complex, enriched (E) cages. We exposed 29 subjects (13 E, 16 NE) to ten stimuli categorized a priori as aversive (e.g. air puffs), rewarding (e.g. evoking chasing) or ambiguous/neutral (e.g. candles). Interest in stimuli was assessed via latencies to contact, contact durations, and durations oriented to stimuli. NE mink contacted all stimuli faster (P = 0.003) than E mink, and spent longer oriented to/in contact with them, albeit only significantly so for ambiguous ones (treatment*type P<0.013). With stimulus category removed from statistical models, interest in all stimuli was consistently higher among NE mink (P<0.0001 for all measures). NE mink also consumed more food rewards (P = 0.037). Finally, we investigated whether lying down while awake and stereotypic behaviour (both increased by NE housing) predicted these responses. Lying awake positively co-varied with certain measures of increased exploration. In contrast, stereotypic 'scrabbling' or locomotion (e.g. pacing) did not. Overall, NE mink showed no evidence of apathy or depression, but instead a heightened investigation of diverse stimuli consistent with boredom. This state was potentially indicated by spending much time lying still but awake (although this result requires replication). Boredom can thus be operationalized and assessed empirically in non-human animals. It can also be reduced by environmental enrichment

A new approach to modelling streamflow reductions resulting from commercial afforestation in South Africa: scientific paper

The Department of Water Affairs and Forestry has, for some time, needed a comprehensive tool to incorporate the impacts of commercial afforestation on water resources into water use isation and allocation processes. Simulation modelling on a national scale, using the ACRU model, was identified as one possible solution. However, in order to establish confidence in the national simulation results, it was necessary to first verify model output against reliable observed data from process studies and long-term catchment afforestation experiments. In the verification phase, long term reductions in streamflow resulting from afforestation were satisfactorily simulated for five research catchments. Some problems were experienced with catchments in the Western Cape, with verifications on shorter duration experiments and the simulation of specific evaporative processes. Modelling of low flows was less successful than for total flows. In the second phase (the generation of the national database), simulations were first performed for the dominant Acocks (1988) veld type (i.e. 0% afforestation) within 843 Quaternary Catchments exhibiting afforestation potential (to determine baseline streamflow), followed by simulations of streamflow after 100% afforestation with eucalyptus, pine and wattle respectively. The difference between the unafforested and afforested simulations equated to streamflow reduction caused by afforestation. This culminated in the generation of maps and tables expressing reductions in streamflow per Quaternary Catchment, which represents a working solution for immediate application but may be improved upon with further work. Southern African Forestry Journal No.196, 2003: 27-3