Juergen Bauhus

Dynamics of carbon and nitrogen mineralization in relation to stand type, stand age and soil texture in the boreal mixedwood.

In the boreal mixed forest, stand composition generally changes from deciduous to mixed to coniferous stands during postdisturbance succession. Our objective was to determine the influence of forest composition on the quality of soil nitrogen and carbon as determined by C and N mineralization during the course of a long-term in vitro incubation (282 days). Three stand types (Populus tremuloides, Betula papyrifera, and conifers (mixture of Abies balsamea and Picea glauca)), of two ages (50 and 124 years since fire) growing on two soil types (clay and till) were considered. Expressed on an organic C basis, our results showed a greater N mineralization for deciduous than coniferous stands, both in the mineral soil and the forest floor, a higher N mineralization in the mineral soil of older stands as compared with young ones, and in till than in clay soils. Mineralization of C was higher in the forest floor of clay soils as compared to till soils while the opposite was found in the mineral soil. It was also higher in both soil layers of older sites. The observed diAerences in N and C mineralization among stand types, stand ages and deposits appeared to be due to diAerences in the most labile fraction of soil organic matter because these diAerences were observed within 100 days of incubation. The ratio of C mineralized‐N mineralized was greater in coniferous than deciduous soils in both soil layers, indicating a lesser quality of organic matter under coniferous stands. Despite significant diAerences among the above-listed factors for N and C mineralization on an organic C basis, the pool size of mineralized (or mineralizable) N and C was generally not significantly diAerent between the diAerent forest and soil types because of an inverse relationship between quality and quantity of soil organic matter. Correlation and multiple regression analysis indicated that clay content (negatively), C‐N ratio (negatively), available P as well as exchangeable Mn were related to the mineralization of N. 7 2000 Elsevier Science Ltd. All rights reserved.

Decomposition rates of coarse woody debris—A review with particular emphasis on Australian tree species

We reviewed the decay patterns and lifetimes (time to reach 95% mass loss) of coarse woody debris (CWD) on the forest floor. The objectives were to identify the factors influencing the decomposition process of CWD and to provide estimates of lifetimes for CWD from Australian tree species. This information is required for greenhouse accounting of forestry activities and land use change as well as the sustainable management of CWD in forest ecosystems. The analysis of a global data set on decay rates of CWD showed that, in particular, the mean annual temperature was a main driver of decomposition, accounting for 34% of the variation in decay rates. The Q 10 , the factor by which biological processes accelerate when temperature increases by 10°C, was 2.53. Additional determinants of CWD decay rates were the initial density of wood and the diameter of logs. Median and average lifetimes derived from 184 decay rates were 49 and 92 years, respectively, which is considerably higher than the 10-year default for all litter proposed by the Intergovernmental Panel on Climate Change. The pattern of decay in most cases followed a negative exponential curve. To overcome the paucity of information on decomposition of CWD in Australian forests and woodlands, decay rates for a large number of species were derived from wood durability and decay resistance studies. For native Australian species, lifetimes ranged from 7 years in Eucalyptus regnans to 375 years in E. camaldulensis. The lifetimes for timber durability Classes 1-4 were 54, 39, 26 and 11 years, respectively, below 30° latitude and without the influence of termites. However, the experimental conditions under which durability and decay resistance are commonly determined are substantially different from the situation under which CWD decomposes in the field. These estimates must therefore be regarded as minimum lifetimes for CWD of most species. To determine decay rates of CWD with greater certainty, long-term field experiments in a wide range of ecosystems are required. BT0 at sdebr e J

Composition, structure, light attenuation and nutrient content of the understorey vegetation in a Eucalyptus sieberi regrowth stand 6 years after thinning and fertilisation

In this study, we investigated the effects of commercial thinning and fertiliser application 6 years after treatment on the structure, composition, and nutrient concentrations of understorey vegetation in a Eucalyptus sieberi regrowth forest in East Gippsland. The stand was thinned at age 26 years, reducing the basal area by ca. 50% and lowering the stocking from ca. 1350 to ca. 250 stems ha-1. Whereas the species diversity and richness of the understorey were not significantly affected by the treatments, thinning promoted the abundance of herbaceous species, and fertilisation increased the proportion of ground ferns such as Pteridium esculentum. Fertilisation with 100 kg N ha-1 and 100 kg P ha-1 decreased the foliage N concentration in Tetrarrhena juncea and Gonocarpus teucrioides, and increased the foliage P concentrations in four of the five most frequent species. This suggested that the understorey was more limited by P than by N. The photosynthetically active radiation above the understorey was 41% of that in the open in thinned stands and 32-34% in unthinned stands, showing that 6 years after thinning the canopy density had not yet returned to pre-treatment levels. However, light attenuation within the understorey did not differ among treatments, confirming that the understorey cover had not increased in response to increased light and nutrient availability. The small changes in the understorey may be attributed to the fact that light and nutrients are not the major factors limiting its development, and that most species are well adapted to disturbance.

Does the addition of litter from N-fixing Acacia mearnsii accelerate leaf decomposition of Eucalyptus globulus?

Nutrient cycling in mixed-species plant communities may be enhanced in comparison to what might be expected from the component species. In this study, we investigated (1) whether the admixing of nitrogen-rich litter from Acacia mearnsii can accelerate the decomposition of Eucalyptus globulus leaf litter and (2) whether eucalypt litter originating from mixed stands with acacias decomposes faster than litter from pure eucalypt stands. To address the first question, pure and mixed litter was incubated in the laboratory for 110 days at 25 ◦ C in the following proportions: 100%E, 75%E : 25%A, 50%E : 50%A, 25%E : 75%A and 100%A, where %E and %A refers to the proportion of eucalypt and acacia in the microcosms, respectively. Since mass loss and N loss of litter in the 50 : 50 mixture was higher than for pure eucalypt but not higher than for acacia, it appears that acacia litter accelerated decomposition of eucalypt litter but not vice versa. Decomposition rates increased with N concentration in the combined litters up to 1.1% N, above that point it remained constant. To address the second question, eucalypt litter from pure and mixed stands was incubated in microcosms. The loss of mass, N and P after 110 days was not different for eucalypt litter originating from mixed (75E : 25A, 50E : 50A, 25E : 75A) and pure (100E) plantations. Together, these studies suggest that admixture of A. mearnsii to E. globulus has the potential to accelerate decomposition and N cycling, and that the species interactions are most pronounced in the 50 : 50 mixture. Mixing of the two species in plantations has so far had no influence on the decomposability of eucalypt litter.

Silvicultural practices in Australian native State forests—An introduction

Summary Silviculture is the manipulation of forest stand structure and dynamics to achieve specific forest management objectives. In this paper the proceeding contributions from four State forest services about their silvicultural practices in native forests are introduced and reflected upon in the light of likely future directions in Australian forest management. Increasing ecological knowledge and changing social and economic demands on forests necessitate the continuous development and improvement of silvicultural practices. The role of silviculture in delivering sustainable forest management is discussed and some future challenges in native forest silviculture in a post-Regional Forest Agreement environment are presented. Reconciling management of native forests for biodiversity and for production of timber and non-timber products will be a major task, which may only be achieved through silvicultural planning at the landscape level. Further development and refinement of sustainability indicators will ...

Strong positive biodiversity-productivity relationships in a subtropical forest experiment

Forest ecosystems contribute substantially to global terrestrial primary productivity and climate regulation, but, in contrast to grasslands, experimental evidence for a positive biodiversity-productivity relationship in highly diverse forests is still lacking1. Here, we provide such evidence from a large forest biodiversity experiment with a novel design2 in subtropical China. Productivity (stand-level tree basal area, aboveground volume and carbon and their annual increment) increased linearly with the logarithm of tree species richness. Additive partitioning3 showed that increasing positive complementarity effects combined with weakening negative selection effects caused a strengthening of the relationship over time. In 2-species mixed stands, complementary effects increased with functional distance and selection effects with vertical crown dissimilarity between species. Understorey shrubs reduced stand-level tree productivity, but this effect of competition was attenuated by shrub species richness, indicating that a diverse understorey may facilitate overall ecosystem functioning. Identical biodiversity-productivity relationships were found in plots of different size, suggesting that extrapolation to larger scales is possible. Our results highlight the potential of multi-species afforestation strategies to simultaneously contribute to mitigation of climate change and biodiversity restoration.