The development of a classification system for inland aquatic ecosystems in South Africa

A classification system is described that was developed for inland aquatic ecosystems in South Africa, including wetlands. The six-tiered classification system is based on a top-down, hierarchical  classification of aquatic ecosystems, following the functionally-oriented hydrogeomorphic (HGM)  approach to classification but incorporating structural attributes at the lower levels of the hierarchy. At Level 1, a distinction is made between inland, estuarine and shallow marine systems using the degree of connectivity to the open ocean as the key discriminator. Inland systems are characterised by the  complete absence of marine exchange and/or tidal influence. At Level 2, inland systems are grouped according to the most appropriate spatial framework for the particular application. At Level 3, four  primary Landscape Units are distinguished (Valley floor, Slope, Plain, Bench) on the basis of the  topographic position within which a particular inland aquatic ecosystem is situated, in recognition of the influence that the landscape setting has over hydrological and hydrodynamic processes acting within an aquatic ecosystem. Level 4 identifies HGM Units, defined primarily according to landform, hydrological characteristics and hydrodynamics. The following primary HGM Units (or HGM Types), which represent the main units of analysis for the classification system, are distinguished at Level 4A: (1) River; (2) Floodplain Wetland; (3) Channelled Valley-Bottom Wetland; (4) Unchannelled Valley-Bottom Wetland; (5) Depression; (6) Seep; (7) Wetland Flat. Secondary discriminators are applied at Level 5 to classify the hydrological regime of an HGM Unit, and Descriptors at Level 6 to categorise a range of biophysical attributes. The HGM Unit at Level 4 and the Hydrological Regime at Level 5 together constitute a Functional Unit, which represents the focal point of the classification system. The utility of the  classification system is ultimately dependent on the level to which ecosystem units are classified, which is in turn constrained by the type and extent of information available.Keywords: freshwater ecosystems, hydrogeomorphic (HGM) units, inland water ecosystems,  wetlands, wetland classification syste

Positive effects of liana cutting on seedlings are reduced during El Niño‐induced drought

1.Liana cutting is a management practice currently applied to encourage seedling regeneration and tree growth in some logged tropical forests. However, there is limited empirical evidence of its effects on forest demographic rates in Southeast Asia.2.We used 22 four‐hectare plots in the Sabah Biodiversity Experiment (a reduced impact logging site) enrichment line planted with 16 dipterocarp species to assess the effects of complete liana cutting on tree growth and survival. We compared plots where lianas were only cut along planting lines (standard enrichment line planting) with those with one (2014) or two rounds (2011 and 2014) of complete liana cutting. 3.We found increased seedling growth following the first complete liana cut in 2011 relative to the enrichment line planting, consistent with previous studies. The response after three years to the cutting in 2014 depended on whether lianas had been previously cut or not: in twice‐cut plots, seedling growth was not significantly different from the standard enrichment planting controls, whereas growth in plots with only one complete cut in 2014 was significantly slower. Seedling survival decreased through time for both once‐ and twice‐cut liana treatments but remained stable in controls. 4.Sapling growth after the 2014 liana cutting showed a similar pattern to seedling growth, while tree growth following the 2014 liana cutting was significantly lower than controls regardless of whether lianas were cut twice (2011 and 2014) or once (2014). 5.Differences in response between the two rounds of liana cutting were likely due to changes in precipitation ‐ 2011 was followed by consistent rainfall while 2014 was followed by two severe droughts within two years. 6.Synthesis and applications. Our results generally support the widely‐reported positive effects of liana cutting on tree growth and survival. However, reduced growth and survival after the 2015/16 El Niño suggests that drought may temporarily undermine the benefits of liana cutting in logged tropical forests. Managers of similar areas in SE Asia should consider halting liana cutting during El Niño events. In other tropical areas, seedling survival should be monitored to assess to what extent results from SE Asia are transferable.</p

Positive effects of liana cutting on seedlings are reduced during El Niño‐induced drought

1.Liana cutting is a management practice currently applied to encourage seedling regeneration and tree growth in some logged tropical forests. However, there is limited empirical evidence of its effects on forest demographic rates in Southeast Asia.2.We used 22 four‐hectare plots in the Sabah Biodiversity Experiment (a reduced impact logging site) enrichment line planted with 16 dipterocarp species to assess the effects of complete liana cutting on tree growth and survival. We compared plots where lianas were only cut along planting lines (standard enrichment line planting) with those with one (2014) or two rounds (2011 and 2014) of complete liana cutting. 3.We found increased seedling growth following the first complete liana cut in 2011 relative to the enrichment line planting, consistent with previous studies. The response after three years to the cutting in 2014 depended on whether lianas had been previously cut or not: in twice‐cut plots, seedling growth was not significantly different from the standard enrichment planting controls, whereas growth in plots with only one complete cut in 2014 was significantly slower. Seedling survival decreased through time for both once‐ and twice‐cut liana treatments but remained stable in controls. 4.Sapling growth after the 2014 liana cutting showed a similar pattern to seedling growth, while tree growth following the 2014 liana cutting was significantly lower than controls regardless of whether lianas were cut twice (2011 and 2014) or once (2014). 5.Differences in response between the two rounds of liana cutting were likely due to changes in precipitation ‐ 2011 was followed by consistent rainfall while 2014 was followed by two severe droughts within two years. 6.Synthesis and applications. Our results generally support the widely‐reported positive effects of liana cutting on tree growth and survival. However, reduced growth and survival after the 2015/16 El Niño suggests that drought may temporarily undermine the benefits of liana cutting in logged tropical forests. Managers of similar areas in SE Asia should consider halting liana cutting during El Niño events. In other tropical areas, seedling survival should be monitored to assess to what extent results from SE Asia are transferable.</p

The value of biodiversity for the functioning of tropical forests: insurance effects during the first decade of the Sabah biodiversity experiment

One of the main environmental threats in the tropics is selective logging, which has degraded large areas of forest. In SE Asia, enrichment planting with seedlings of the dominant group of dipterocarp tree species aims to accelerate restoration of forest structure and functioning. The role of tree diversity in forest restoration is still unclear, but the ‘insurance hypothesis’ predicts that in temporally and spatially varying environments planting mixtures may stabilize functioning owing to differences in species traits and ecologies. To test for potential insurance effects, we analyse the patterns of seedling mortality and growth in monoculture and mixture plots over the first decade of the Sabah biodiversity experiment. Our results reveal the species differences required for potential insurance effects including a trade-off in which species with denser wood have lower growth rates but higher survival. This trade-off was consistent over time during the first decade, but growth and mortality varied spatially across our 500 ha experiment with species responding to changing conditions in different ways. Overall, average survival rates were extreme in monocultures than mixtures consistent with a potential insurance effect in which monocultures of poorly surviving species risk recruitment failure, whereas monocultures of species with high survival have rates of selfthinning that are potentially wasteful when seedling stocks are limited. Longer-term monitoring as species interactions strengthen will be needed to more comprehensively test to what degree mixtures of species spread risk and use limited seedling stocks more efficiently to increase diversity and restore ecosystem structure and functioning