Predicting reproductive success of insect- versus bird-pollinated scattered trees in agricultural landscapes

Agricultural landscapes in southern Australia were once dominated by temperate eucalypt woodlands of which only fragmented patches and scattered trees in paddocks remain. This study focuses on the decline of scattered trees in the Mount Lofty Ranges and South East agricultural regions of South Australia. A combination of digitized aerial photography and satellite imagery was used to extend a previous assessment of decline undertaken in the early 1980s and increase the period over which decline was assessed to 58–72 years. A total of 17 049 scattered trees were counted from the earliest time period assessed over 11 sites of which 6 185 trees were lost by 2008 — a 36 % decline. Recruitment of 2 179 trees during this period was evident. Imagery indicates that clearing for agricultural intensification is the primary cause of the decline. A range of management options and policy settings are required to reverse the decline notwithstanding the challenges of implementation at a landscape scale across privately owned land.

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The patterns of grazed pasture associated with scattered trees across an Australian temperate landscape: an investigation of pasture quantity and quality

The Rangeland Journal ◽

10.1071/rj10068 ◽

2011 ◽

Vol 33 (2) ◽

pp. 121 ◽

Cited By ~ 12

Author(s):

Phoebe Barnes ◽

Brian R. Wilson ◽

Mark G. Trotter ◽

David W. Lamb ◽

Nick Reid ◽

...

Keyword(s):

Vegetation Index ◽

Near Infrared ◽

Parent Material ◽

Agricultural Landscapes ◽

Tree Canopy ◽

Canopy Reflectance ◽

Near Infrared Reflectance ◽

Pasture Production ◽

Normalised Difference Vegetation Index ◽

Scattered Trees

Scattered paddock trees occur across agricultural landscapes in Australia. However, in the temperate regions of Australia their numbers are rapidly declining and they may be lost across much of the landscape in 200 years. Here we examined the spatial distribution of green (GDB), senescent (SDB) and total (TDB) dry pasture biomass, and nutrient status of the GDB fraction around scattered Eucalyptus trees on three parent materials (basalt, granite and meta-sediment) in native and sown pastures across a range of grazed temperate landscapes in northern New South Wales. We used a combination of destructive harvests and a handheld active optical canopy reflectance sensor (AOS) with an integrated GPS to examine pasture biomass around scattered trees. The harvested pasture biomass data indicated that under grazed conditions the presence of scattered trees did not introduce significant radial trends in TDB or GDB out to a distance of 3.5 canopy radii regardless of tree species or parent material. The red and near-infrared reflectance-based Normalised Difference Vegetation Index (NDVI), as measured by the AOS, did indicate a consistent azimuthal trend with larger GDB on the southern side of the tree and lower GDB on the northern side in the native pasture. However, this observation must be qualified as the regression coefficient for the relationship between NDVI and GDB was significant but weak (best r2 = 0.42), and SDB reduced its predictive capacity. We also found a higher percentage of GDB under the canopy than in the open paddock. We suggest that the combination of these results may indicate higher grazing pressure under trees than in the open paddock. Pasture nutrient concentration (P, K and S) was higher in both native and sown pastures beneath the tree canopy compared with the open paddock. This study indicates that, in this temperate environment, scattered trees do not adversely affect pasture production, and that they can improve some pasture nutrients.

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Ecological connectivity in fragmented agricultural landscapes and the importance of scattered trees and small patches

Ecological Processes ◽

10.1186/s13717-021-00284-7 ◽

2021 ◽

Vol 10 (1) ◽

Author(s):

Darrel Chin Fung Tiang ◽

Andrew Morris ◽

Mathew Bell ◽

Christopher N. Gibbins ◽

Badrul Azhar ◽

...

Keyword(s):

Regional Scale ◽

Structural Connectivity ◽

Movement Patterns ◽

Agricultural Landscapes ◽

Theoretic Approach ◽

Fine Scale ◽

Scattered Trees ◽

Gap Crossing ◽

Cost Paths ◽

Least Cost Paths

Abstract Background Fragmentation and habitat loss can restrict species movement and reduce connectivity, negatively impacting biodiversity. Characterising the overall connectivity of an area can inform better management of human modified landscapes. Contemporary connectivity modelling methods seldom incorporate fine-scale movement patterns associated with movement between fine-scaled structural connectivity elements such as scattered trees, roadside corridors and small patches of habitat. This study aims to characterise connectivity within the Karuah-Myall catchments, a typical woodland ecosystem that is fragmented by agriculture, using least-cost path analysis and a graph-theoretic approach; it focuses on how fine-scaled vegetation such as scattered trees support connectivity. We mapped scattered (and paddock) trees within this agricultural landscape where the main human modified land use was pasture. We modelled connectivity for a general representative woodland species using an interpatch dispersal distance and gap crossing threshold, and resistance from different land cover types. The gap crossing distance threshold was used to model movement between fine-scaled vegetation features. We compared the least-cost paths modelled with and without scattered trees. Results Our results show that by excluding scattered trees, least-cost paths across the cleared pasture landscape did not reflect the types of movement patterns typically observed from field studies, such as those associated with a foray-search strategy used by small and medium mammals and birds. The modelling also shows that the Karuah-Myall catchments are well connected and provide value to biodiversity beyond the catchment borders, by connecting coastal vegetation to the Great Eastern Ranges national wildlife corridor initiative. Conclusion Connectivity models that exclude fine-scale landscape features such as scattered trees and small, linear patches risk misrepresenting connectivity patterns. Models of regional-scale connectivity can be influenced by the presence or absence of even the smallest features, such as scattered trees.

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