Trees on farms to support natural capital: An evidence-based review for grazed dairy systems.

Intensification of the dairy industry globally, combined with a changing climate, has placed increased pressure on natural capital assets (and the flow of ecosystem services) on farms. Agroforestry is widely promoted as an intervention to address these issues. While some benefits of integrating trees on farms, such as carbon sequestration and biodiversity, are reasonably well known, less is known about other potential benefits, such as on-farm production. Understanding and quantifying these benefits would inform farm planning and decision-making. We used a systematic review approach to analyse the evidence base for biophysical ecosystem services from woody systems (including shelterbelts, riparian plantings, plantations, pasture trees, silvopasture and remnant native vegetation) provided to grazed dairy enterprises. We identified 83 publications containing 123 records that fit our review criteria of reporting on biophysical ecosystem services from woody systems on dairy farms relative to a grazed pasture comparison. For each relationship between a woody system and ecosystem service, we assessed the level of support, strength and predominant direction of evidence, and summarised the causal relationships (woody system ≫ mechanism ≫ outcome). Shelterbelts and riparian plantings were the most commonly reported woody systems. Linkages between woody systems and ecosystem services were largely positive, with the types of services provided and their importance differing among systems. Mean evaluation scores for the strength of the evidence were moderate to strong. However, the number of records for each relationship was often low. Consequently, only eight of the 30 causal pathways identified had high confidence; a further 14 had medium confidence indicating that these have good potential to deliver benefits but warrant further work. Although the evidence here was largely qualitative, our results provide strong support for the internal benefits that natural capital assets, such as on-farm woody systems, can provide to the productivity and resilience of grazed dairy enterprises.

Mid-infrared spectroscopy for rapid assessment of soil properties after land use change from pastures to Eucalyptus globulus plantations.

There is an increasing demand for rapid and cost effective techniques to accurately measure the effects of land use change on soil properties. This study evaluated the ability of mid-infrared spectroscopy (MIRS) coupled with partial least squares regression (PLSR) to rapidly predict soil properties affected by land use change from agriculture (mainly pasture) to Eucalyptus globulus plantations in south-western Australia. We measured total organic carbon (TOC), total nitrogen (Total N), TOC/Total N (C/N ratio), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and total phosphorus (Total P). The PLSR calibration models were developed using mid-infrared (MIR) spectra (4000 to 450 cm(-1)) and square root transformed measured soil data (n = 180) from 23 paired pasture and E. globulus plantation sites representing the soils and climate of E. globulus plantation estates in south-western Australia. The calibration models for TOC, Total N, C/N ratio and Total P showed excellent correlations between measured and predicted data with coefficient of determination (R(2)) exceeding 0.91 and minimum root-mean-square error (RMSE) of calibration [TOC (R(2) = 0.95, RMSE = 0.36), Total N (R(2) = 0.96, RMSE = 0.10), C/N ratio (R(2) = 0.92, RMSE = 0.14) and Total P (R(2) = 0.91, RMSE = 0.06)]. The calibration models had reasonable predictions for MBC (R(2) = 0.66, RMSE = 0.07) and MBN (R(2) = 0.63, RMSE = 0.06). The calibrated models were validated using soils from 8 independent paired pasture and E. globulus sites (n = 64). The validated predictions were excellent for TOC (R(2) = 0.92, RMSE = 0.40) and Total N (R(2) = 0.91, RMSE = 0.12), but less so for C/N ratio (R(2) = 0.80, RMSE = 0.35), MBC (R(2) = 0.70, RMSE = 0.08) and Total P (R(2) = 0.75, RMSE = 0.12). The results demonstrate the potential of MIRS-PLSR to rapidly, accurately and simultaneously determine several properties in land use change affected soils.

Testing the generality of above-ground biomass allometry across plant functional types at the continent scale.

Accurate ground-based estimation of the carbon stored in terrestrial ecosystems is critical to quantifying the global carbon budget. Allometric models provide cost-effective methods for biomass prediction. But do such models vary with ecoregion or plant functional type? We compiled 15 054 measurements of individual tree or shrub biomass from across Australia to examine the generality of allometric models for above-ground biomass prediction. This provided a robust case study because Australia includes ecoregions ranging from arid shrublands to tropical rainforests, and has a rich history of biomass research, particularly in planted forests. Regardless of ecoregion, for five broad categories of plant functional type (shrubs; multistemmed trees; trees of the genus Eucalyptus and closely related genera; other trees of high wood density; and other trees of low wood density), relationships between biomass and stem diameter were generic. Simple power-law models explained 84-95% of the variation in biomass, with little improvement in model performance when other plant variables (height, bole wood density), or site characteristics (climate, age, management) were included. Predictions of stand-based biomass from allometric models of varying levels of generalization (species-specific, plant functional type) were validated using whole-plot harvest data from 17 contrasting stands (range: 9-356 Mg ha(-1) ). Losses in efficiency of prediction were <1% if generalized models were used in place of species-specific models. Furthermore, application of generalized multispecies models did not introduce significant bias in biomass prediction in 92% of the 53 species tested. Further, overall efficiency of stand-level biomass prediction was 99%, with a mean absolute prediction error of only 13%. Hence, for cost-effective prediction of biomass across a wide range of stands, we recommend use of generic allometric models based on plant functional types. Development of new species-specific models is only warranted when gains in accuracy of stand-based predictions are relatively high (e.g. high-value monocultures).

Ecophysiological responses of a young blue gum (Eucalyptus globulus) plantation to weed control.

Early weed control may improve the growth of forest plantations by influencing soil water and nutrient availability. To understand eucalypt growth responses to weed control, we examined the temporal responses of leaf gas-exchange, leaf nitrogen concentration (N) and water status of 7-month-old Eucalyptus globulus L. trees in a paired-plot field trial. In addition, we monitored the growth, leaf N and water status of the competing vegetation in the weed treatment. By the end of the 11-month experiment, complete weed control (WF treatment) of largely woody competitors increased the basal diameter of E. globulus by 14%. As indicated by pre-dawn water potentials of > - 0.05 MPa, interspecies competition for water resources was minimal at this site. In contrast, competition for N appeared to be the major factor limiting growth. Estimations of total plot leaf N (g m(-2) ground) showed that competing vegetation accounted for up to 70% of the total leaf N at the start of the trial. This value fell to 15% by the end of the trial. Despite increased leaf N(area) in WF trees 5 months after imposition of weed control, the photosynthetic capacity (A(1500)) of E. globulus was unaffected by treatment suggesting that the growth gains from weed control were largely unrelated to changes in leaf-level photosynthesis. Increased nutrient availability brought about by weed control enabled trees to increase investment into leaf-area production. Estimates of whole-tree carbon budget based on direct measurements of dark respiration and A(1500) allowed us to clearly demonstrate the importance of leaf area driving greater productivity following early weed control in a nutrient-limited site.

Observed and modelled leaf area index in Eucalyptus globulus plantations: tests of optimality and equilibrium hypotheses.

This paper reports on variation in leaf area index (L) in five Eucalyptus globulus Labill. plantations in response to application of nitrogen, thinning at age 2 years and variation in climate wetness index (the ratio of rainfall to potential evaporation). Observed L is compared with: (i) L predicted to optimize net primary productivity for a given average annual temperature, annual water use and potential evaporation (L(opt)) and (ii) L calculated as a linear function of climate wetness index (L(eq)). L peaked in fertilized plots at between 4 and 5 years of age or immediately after canopy closure. The value of L from canopy closure to age 8 years was not strongly related to annual rainfall or climate wetness index. At two sites with total soil nitrogen <1.2 mg g(-)(1), L in fertilized plots was about two units greater than in unfertilized plots. This difference persisted until measurements ended in 2004 when the trees were 8 years old. The L of plots thinned to 300 and 600 stems ha(-)(1) at age 2 years recovered quickly and was not significantly different from L in unthinned plots when the trees were 8 years old. L(opt) was a good predictor of the leaf area index of 8-year-old plots of E. globulus when nitrogen and phosphorus were non-limiting (model efficiency (EF) was 0.5). For the same plots, L(eq) underestimated observed L by an average of two units, and the model efficiency was low (-3.25). Data from two nitrogen-limited sites demonstrated that for fertilized plots L(opt) (EF = 0.6) was a much better predictor of L than L(eq) (EF = -3.36). At the same sites, L(eq) (EF = 0.42) was a better model for predicting L of unfertilized plots than L(opt) (-3.59). These results provide evidence that comparing observed L with L(opt) can identify stands limited by factors other than growing climate.

A comparison of growth, photosynthetic capacity and water stress in Eucalyptus globulus coppice regrowth and seedlings during early development.

Eucalyptus globulus Labill., a globally significant plantation species, is grown commercially in a multiple rotation framework. Second and subsequent crops of E. globulus may be established either by allowing the cut stumps to resprout (commonly referred to as coppice) or by replanting a new crop of seedlings. Currently, long-term growth data comparing coppice and seedling productivity in second or later rotations in southern Australia is limited. The capacity to predict productivity using these tools is dependent on an understanding of the physiology of seedlings and coppice in response to light, water and nutrient supply. In this study, we compared the intrinsic (independent of the immediate environment) and native (dependent on the immediate environment) physiology of E. globulus coppice and second-generation seedlings during their early development in the field. Coppice not only grew more rapidly, but also used more water and drew on stored soil water to a depth of at least 4.5 m during the first 2 years of growth, whereas the seedlings only accessed the top 0.9 m of the soil profile. During the same period, there was no significant difference between coppice and seedlings in either their stomatal response to leaf-to-air vapour pressure difference (D) or intrinsic water-use efficiency; CO(2)- and light-saturated rates of photosynthesis were greater in seedlings than that in coppice as were the quantum yield of photosynthesis and total leaf chlorophyll content. Thus, at a leaf scale, seedlings are potentially more productive per unit leaf area than coppice during early development, but this is not realised under ambient conditions. The underlying cause of this inherent difference is discussed in the context of the allocation of resources to above- and below-ground organs during early development.