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Ngugi M.R.,Biodiversity and Ecosystem science | Botkin D.B.,University of California at Santa Barbara
Ecological Modelling | Year: 2011

One of the key problems confronting ecological forecasting is the validation of computer models. Here we report successful validation of a forest dynamics model Ecosystem Dynamics Simulator (EDS), adapted from the JABOWA-II forest succession model. This model and many variants derived from it have successfully simulated growth dynamics of uneven-aged mixed forests under changing environment with a moderate amount of input data. But rarely are adequate time-series data available for quantitative model validation. This study tested the performance of EDS in projecting the tree density, tree diameter at breast height (dbh), tree height, basal area and aboveground biomass of uneven-aged, mixed species sclerophyll forests in St. Mary state forests of eastern Australia. The test data were collected between 1951 and 2005. Every tree was uniquely numbered, tagged and measured in consecutive re-measurements. Projected growth attributes were compared with those observed in an independent validation dataset. The model produced satisfactory projections of tree density (91.7%), dbh (92.3%), total tree height (82.8%), basal area (89.3%) and aboveground biomass (87.6%) compared to the observed attributes. These results suggest that the EDS model can provide reasonable capability in projecting growth dynamics of uneven-aged, mixed species sclerophyll forests. © 2011 Elsevier B.V. Source

Borsboom A.C.,Biodiversity and Ecosystem science | Couper P.J.,Biodiversity Inc. | Amey A.,Biodiversity Inc. | Hoskin C.J.,Biodiversity Inc.
Australian Journal of Zoology | Year: 2010

Many threatened species occur as small, isolated populations. Understanding the extent and genetic distinctiveness of these populations is essential for management. Nangura spinosa is a critically endangered skink known from two small populations in dry rainforest in south-east Queensland. We conducted targeted surveys between 2001 and 2010 at the two known N. spinosa sites (Nangur National Park, Oakview National Park area) and in 22 nearby forest blocks with potentially suitable habitat. N. spinosa was found only at the two previously known sites, which are ∼36km apart. The skink appears to be declining at Nangur NP, to an estimated extent of occurrence of 7.4ha and potentially no more than 35 adults. In contrast, we increase the extent of occurrence at Oakview to 360ha, where the population is at least in the hundreds. Sequencing of two mtDNA genes revealed considerable genetic divergence between the two populations (3.8% for ND4; 1.2% for 16S), suggesting an extended period of separation. Population fragmentation is therefore not the result of recent land clearing, but of long-term isolation by unsuitable habitat. Each population should be considered a distinct management unit. More data are required on population size and trends, recruitment and threats, particularly for the Nangur population. © CSIRO 2010. Source

Ngugi M.R.,Biodiversity and Ecosystem science | Botkin D.B.,University of California at Santa Barbara | Doley D.,University of Queensland | Cant M.,Ecological Assessment | Kelley J.,Biodiversity and Ecosystem science
Ecological Modelling | Year: 2013

Availability of quantitative information on growth increment, biomass accumulation and growth dynamics of fragmented and degraded forest ecosystems is a common challenge in restoration work. Ecological models of forest dynamics have the potential to provide a structure through which data, observations and assumptions can be combined and explored. The utility of such models, however, is often limited by lack of validation. In this paper we used growth data for 143,200 tree measurements, in 121 plots spanning up to 70 years of forest monitoring from uneven-aged mixed species callitris forests of Australia to test the Ecosystem Dynamics Simulator (EDS). These are among the least known and most degraded forest communities in Australia and are known habitat for threatened and rare fauna species including brush-tailed rock wallaby (Petrogale penicillata), glossy black-cockatoo (Calyptorhynchus lathami), grey falcon (Falco hypoleucos), golden-tailed gecko (Strophurus taenicauda) and others. We determined growth parameters for 26 woody species and applied these to the EDS to validate projected stand structure and growth. The model projections explained 93.9% (diameter at breast height (dbh)), 88.9% (basal area), 90.5% (stem density) and 88.6% (aboveground biomass) of the observed variation. To our knowledge, this is one of the most accurate validations of forest dynamics simulation achieved to date. Diameter growth rates for most species were <0.3cmyr-1 and reproduced well by the EDS, for all the species in the callitris forest communities. These growth rates indicate that exceptionally long periods will be required to restore the degraded or cleared forests to a mature state. Results can guide restoration and sustainable management of callitris forest ecosystems by providing projected measurable forest attributes to meet multiple goals, including harvesting of forest resources, carbon storage and conservation of biodiversity. © 2013 Elsevier B.V. Source

Ngugi M.R.,Biodiversity and Ecosystem science | Johnson R.W.,Biodiversity and Ecosystem science | McDonald W.J.F.,Biodiversity and Ecosystem science
Ecological Modelling | Year: 2011

Restoration of abandoned and degraded ecosystems through enhanced management of mature remnant patches and naturally regenerating (regrowth) forests is currently being used in the recovery of ecosystems for biodiversity protection and carbon sequestration. Knowledge of long-term dynamics of these ecosystems is often very limited. Vegetation models that examine long-term forest growth and succession of uneven aged, mixed-species forest ecosystems are integral to the planning and assessment of the recovery process of biodiversity values and biomass accumulation. This paper examined the use of the Ecosystem Dynamics Simulator (EDS) in projecting growth dynamics of mature remnant brigalow forest communities and recovery process of regrowth brigalow thickets. We used data from 188 long-term monitored plots of remnant and regrowth forests measured between 1963 and 2010. In this study the model was parameterised for 34 tree and shrub species and tested with independent long-term measurements. The model closely approximated actual development trajectories of mature forests and regrowth thickets but some inaccuracies in estimating regeneration through asexual reproduction and mortality were noted as reflected in stem density projections of remnant plots that had a mean of absolute relative bias of 46.2 (±12.4)%. Changes in species composition in remnant forests were projected with a 10% error. Basal area values observed in all remnant plots ranged from 6 to 29m2ha-1 and EDS projections between 1966 and 2005 (39 years) were 68.2 (±10.9)% of the observed basal area. Projected live aboveground biomass of remnant plots had a mean of 93.5 (±5.9)tha-1 compared to a mean of 91.3 (±8.0)tha-1 observed in the plots. In regrowth thicket, the model produced satisfactory projections of tree density (91%), basal area (89%), height (87%) and aboveground biomass (84%) compared to the observed attributes. Basal area and biomass accumulation in 45-year-old regrowth plots was approximately similar to that in remnant forests but recovery of woody understorey was very slow. The model projected that it would take 95 years for the regrowth to thin down to similar densities observed in original or remnant brigalow forests. These results indicated that EDS can produce relatively accurate projections of growth dynamics of brigalow regrowth forests necessary for informing restoration planning and projecting biomass accumulation. © 2010 Elsevier B.V. Source

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