Diameter Growth Performance Varies with Species Functional-Group and Habitat Characteristics in Subtropical Rainforests

We examined tree diameter growth in 20 plots subjected to various disturbance intensities (natural, low, moderate and intensive logging) in a bid to understand the general tree growth responses in relation to habitat characteristics in subtropical rainforests of north-eastern New South Wales, Australia. Species-specific regeneration strategy, maximum size and level of shade tolerance were used to classify species into 5 groups; emergent and shade tolerant main canopy (group 1), shade tolerant mid canopy (2), shade tolerant understoreys (3), moderate shade tolerant (4), and shade intolerant (5) tree species. Data series for trees >10 cm diameter at 1.3 m above the ground level (dbh) providing observations spanning over 36 years were used in multilevel regression analyses. The results showed that spatial and temporal effects in tree growth at the stand-level are a combination of the differences between species functional group compositions and environmental gradients. High growth responses were observed in the shade intolerant species while increasing level of shade tolerance and decreasing maximum size decreased trees growth rates. Tree growth increased with altitude on a large scale across regions, and with disturbance intensity on a small scale at the plot (stand) level. Increase in northness (south through flat to north facing sites) increased growth in species group 1 for trees < 67 cm dbh, but beyond this dbh threshold the opposite was true. These showed that saplings of species group 1 may require increased illumination to reach the forest canopy, but once in the canopy, low soil water availability may be limiting to tree growth in the north facing sites. Decrease in northness was associated with increased growth in species group 2 indicating that reduced illumination and improved soil moisture in the south facing sites were conducive for maximum growth in this species group. Maximum growth potential in species group 4 and 5 increased with decrease in eastness, suggesting that the increased afternoon solar radiation and temperature were conducive for high growth rates in these species. Although topographic gradient may determine the spatial and temporal variations in tree growth where growth appeared to increase from the crest down the slope into the creek, its effects on soil fertility and water availability, and interactions between these and other factors may make it difficult to discern clear growth patterns

Distributed empirical algorithms to estimate catchment scale sediment connectivity and yield in a subtropical region

The intensity of soil loss and sediment delivery, representing hydrologic and geomorphic processes within a catchment, accelerates with rapid changes in land cover and rainfall events. An underlying component of sustainable management of water resources is an understanding of spatial and temporal variability and the adverse influences of regional parameters involved in generating sediment following widespread changes in land cover. A calibrated algorithm of soil loss coupled with a sediment delivery ratio (SDR) was applied in raster data layers to improve the capability of a combined model to estimate annual variability in sediment yields related to changes in vegetation cover identified by analyses of SPOT imagery. Four catchments in Kangaroo River State forest were assessed for annual changes in sediment yields. Two catchments were selectively logged in 2007, while the two other sites remained undisturbed. Results of SDR estimates indicated that only a small proportion of total eroded sediment from hillslopes is transported to catchment outlets. Larger SDR values were estimated in regions close to catchment outlets, and the SDR reduced sharply on hillslopes further than 200-300 m from these areas. Estimated sediment yield increased by up to 30% two years after land cover change (logging) in 2009 when more storm events were recorded, despite the moderate density of vegetation cover in 2009 having almost recovered to its initial pre-logging (2005) condition. Rainfall had the most significant influence on streamflow and sediment delivery in all catchments, with steeply sloping areas contributing large amounts of sediment during moderate and high rainfall years in 2007 and 2009. It is concluded that the current scenario of single-tree selection logging utilized in the study area is an acceptable and environmentally sound land management strategy for preservation of soil and water resources

Is maximizing protection the same as minimizing loss? Efficiency and retention as alternative measures of the effectiveness of proposed reserves

We used two measures to compare the effectiveness of 52 conservation criteria in achieving conservation targets for forest types. The first measure was efficiency. Although widely used, efficiency assumes no loss or reduction of biodiversity features before conservation is implemented. This is invalid in many situations. Often, it is more realistic to assume gradual implementation accompanied by incremental, predictable reduction and loss of biodiversity features. We simulated future landscapes resulting from the annual interplay of loss and conservation of forest types. We then based our second measure, retention, on how well criteria scheduled conservation action to prevent targets being compromised. The simulations partly support predictions about the best criteria for scheduling implementation with continuing biodiversity loss. Retention was weakly related or unrelated to efficiency across 52 criteria. Although retention values were sensitive to changes in targets and rates of conservation and forest loss, one criterion consistently produced highest retention values

Catchment scale geostatistical simulation and uncertainty of soil erodibility using sequential Gaussian simulation

Soil erodibility (K) affects sediment delivery to streams and needs to be appropriately quantified and interpolated as a fundamental geographic variable for implementing suitable catchment management and conservation practices. The spatial distribution of K for erosion modelling at non-sampling grid locations has traditionally been estimated using interpolation algorithms such as kriging which do not adequately represent the uncertainty of estimates. These methods cause smoothing effects through overestimating the low values and underestimating the large values. In this study observed values were used to implement a sequential Gaussian simulation (SGS) procedure to evaluate the certainty of modelled data. Soil erodibility values were computed using 41 soil samples taken from the top 10 cm soil layer regularly distributed across four catchments, 367-770 ha in area, within Kangaroo River State forest, New South Wales (NSW). One hundred realisations were applied in the simulation process to provide spatial uncertainty and error estimates of soil erodibility. The results indicated that values simulated by the SGS algorithm produced similar K values for the neighbouring cells. At the pixel level, the SGS approach generated a reliable estimation of soil erodibility in most areas. Spatial variation of the K factor in this study was strongly related to soil landscape differences across the catchments; within catchments slope gradient did not have a substantial impact on the numerical values of the K factor using pixel-by-pixel comparisons of raster grid maps