Vegetation and soil carbon‐13 isoscapes for South America: integrating remote sensing and ecosystem isotope measurements

Abstract

C of plant leaf and soil endmembers. Our approach relies upon the near-universal restriction of C 4 photosynthesis to the herbaceous growth form and the differing performance of C 3 and C 4 grasses in various climates, along with land-cover and crop-type distributions. Specifically, we predict the percentage cover of C 3 and C 4 vegetation in each 5-minute grid cell (;10 km) based on input gridded layers of vegetation growth form fractional cover, crop-area/crop-type distributions, and a high spatial resolution climate data. We develop a consistent set of rules to harmonize the different data layers. The d 13 C of vegetation in South America is then estimated based on the C 3 /C 4 composition in each land grid cell, assuming constant mean values for closed C 3 tropical forest (À32.3%), open C 3 forest ecosystems (À29.0%), C 3 herbaceous cover (À26.7%) and C 4 herbaceous cover (À12.5%). In addition to using the mean isotope values, we also incorporate the measured standard deviation for each category. Soil d 13C is estimated for the C 4 -favored climate regions of South America using two, largely independent approaches: one that is derived from our vegetation d 13 C prediction and one that is based on a previously published relationship between fractional woody cover and the d 13 C of soil organic carbon. Finally, we present preliminary maps of relative uncertainty in the estimates of vegetation growth form, generated by integrating global measures of accuracy with local measures of neighborhood variability. These maps demonstrate that the highest uncertainty is found in savanna ecosystems, which contain the most heterogeneous vegetation cover and structure along with a high percentage of C 4 grass cover.

A multi‐isotope (δ2H, δ13C, δ15N) approach to establishing migratory connectivity of Barn Swallow (Hirundo rustica)

“…Feather samples grown in the wintering grounds (n ¼ 488) were clustered into four groups (G1: n ¼ 37; G2: n ¼ 109; G3: n ¼ 181; and G4: n ¼ 161) based on differences in Bowen et al (2005) along with prior information about the distribution of C3 and C4 plants in South America (Powell et al 2012).…”

“…A theoretical spatial distribution of d 13 C based on vegetation types in South America was obtained from Powell et al (2012). From this, a dichotomous surface of C3-and C4-dominated vegetation zones was created.…”

“…However, this field is in its infancy and few attempts have been made to combine multiple isotopes to better infer connections at large spatial scales (Hobson et al 2012a, Hobson et al 2012b (West et al 2010). Recently, plant-d 13 C isoscapes based on predictions of the distribution and relative abundance of C3 and C4 vegetation have also been established for Africa (Still and Powell 2010) and South America (Powell et al 2012). These developments have led to attempts to simultaneously combine isoscapes based on several elements (Hobson et al 2012a, Hobson et al 2012b, Hobson et al 2012d).…”

Switching Hemispheres: A New Migration Strategy for the Disjunct Argentinean Breeding Population of Barn Swallow (Hirundo rustica)

“…Naturally molted tail feathers from 100 individuals from Argentina were used to assign Barn Swallows to their molting origins by using normal probability density functions [15]–[17] to assess the likelihood that the observed data ( δ 2 H f , δ 13 C) could have resulted from growth at given locations within the δ 2 H isoscape of [18] and δ 13 C isoscape of [19] following methodology described in [15]. To this end, the amount-weighted mean precipitation δ 2 H isoscape corresponding to the growing season of South America [18] was first converted into an equivalent feather δ 2 H ( δ 2 H f ) isoscape using the empirical equation reported for non ground-foraging Neotropical migrants [20]: …”

“…A theoretical spatial δ 13 C-distribution of vegetation in South America was obtained from [19], [21]. From this, we created a dichotomous surface of C3- and C4-dominated vegetation zones.…”