Years Of Encroachment Research Articles

Mangroves dramatically increase carbon storage after 3 years of encroachment

In North America, the dynamic ecotonal boundary between mangrove and salt marsh is currently fluctuating in response to freeze-free winters, which can cause rapid alterations in a number of wetland processes and attributes. Permanent plots were established in pure salt marsh habitat along the Atlantic coast of Florida in 2015, and by 2018, mangrove saplings had encroached into plots. In this study, above- and belowground biomass measurements and soil C in the top 10-cm soil profile were quantified in 2018 and compared to 2015 data to better understand the effects of mangrove encroachment on C storage in salt marsh habitat. Plant and soil fractions were tested for δ13C stable isotopic signatures to elucidate soil C sources. In 3 years, mangrove biomass increased dramatically and soil C doubled in pure salt marsh plots, consequently increasing total C in the system. Soil organic matter increased, while there was no change in soil C:N. δ13C values suggest that soil C was derived mainly from salt marsh soil organic matter, especially that of belowground, rather than aboveground biomass. These results provide real-time, quantitative data on the encroachment of mangroves into salt marshes over a relatively short period of time.

Estimating Ecosystem Nitrogen Addition by a Leguminous Tree: A Mass Balance Approach Using a Woody Encroachment Chronosequence

Difficulty in quantifying rates of biological N fixation (BNF), especially over long time scales, remains a major impediment to defining N budgets in many ecosystems. To estimate N additions from BNF, we applied a tree-scale N mass balance approach to a well-characterized chronosequence of woody legume (Prosopis glandulosa) encroachment into subtropical grasslands. We defined spatially discrete single Prosopis clusters (aged 28–99 years), and for each calculated BNF as the residual of: soil N (0–30 cm), above- and below-ground biomass N, wet and dry atmospheric N deposition, N trace gas and N2 loss, leaching loss, and baseline grassland soil N at time of establishment. Contemporary BNF for upland savanna woodland was estimated at 10.9 ± 1.8 kg N ha−1 y−1, equal to a total of 249 ± 60 kg N ha−1 over about 130 years of encroachment at the site. Though these BNF values are lower than previous estimates for P. glandulosa, this likely reflects lower plant density as well as low water availability at this site. Uncertainty in soil and biomass parameters affected BNF estimates by 6–11%, with additional sensitivity of up to 18% to uncertainty in other scaling parameters. Differential N deposition (higher rates of dry N deposition to Prosopis canopies versus open grasslands) did not explain N accrual beneath trees; iterations that represented this scenario reduced estimated BNF estimates by a maximum of 1.5 kg N ha−1 y−1. We conclude that in this relatively well-constrained system, small-scale mass balance provides a reasonable method of estimating BNF and could provide an opportunity to cross-calibrate alternative estimation approaches.

The impact of black wattle encroachment of indigenous grasslands on soil carbon, Eastern Cape, South Africa

Black wattle (Acacia mearnsii, De Wild.) is a fast growing tree species introduced into South Africa in the nineteenth century for commercial purposes. While being an important source of timber and firewood for local communities, black wattle is an aggressive invasive species and has pervasive adverse environmental impacts in South Africa. Little is known about the effects of black wattle encroachment on soil carbon, therefore the aim of this study was to investigate the impact of black wattle encroachment of natural grassland on soil carbon stocks and dynamics. Focussing on two sites in the Eastern Cape, South Africa, the study analysed carbon stocks in soil and litter on a chronosequence of black wattle stands of varying ages (up to >50 years) and compared these with adjacent native grassland. The study found that woody encroachment of grassland at one site had an insignificant effect on soil and litter carbon stocks. The second site showed a clear decline in combined soil and litter carbon stocks following wattle encroachment. The lowest stock was in the oldest wattle stand, meaning that carbon stocks are still declining after 50 years of encroachment. The results from the two sites demonstrate the importance of considering changes in soil carbon when evaluating ecosystem effects of invasive species.

The North American Small Fruit Industry 1903-2003. II. Contributions of Public and Private Research in the Past 25 Years and a View to the Future

Molecular biology offers great promise for improvement of small fruit crops, both by genetic modification (Jimenez-Bermudez et al., 2002; Martin, 2002; McNicol and Graham, 1999; Mezzitti et al., 2002a, 2002b; Morgan et al., 2002; Serres et al., 1997) and by use of markers. Polashock and Vorsa (2002b) used markers for separation and estimation of genetic similarity among American cranberry (Vaccinium macrocarpon Ait.) clones where years of encroachment by wild vines and seedlings has left the identity of propagation stock in question. Marker assisted selection (MAS) has been successfully applied to many crops (Staub et al., 1996), and may be a valuable tool for small fruit crops, especially for disease resistance breeding (Graham and Smith, 2002; Lerceteau-Kohler et al., 2002; Nourse et al., 2002). MAS is not a tool that will benefit all breeding programs (Luby and Shaw, 2001), but it has already found use. For example, the Driscoll Strawberry Associates, Inc. (DSA) strawberry-breeding program now routinely screens about one-fourth of its 80,000-plus annual seedling population for one or more selectable marker. We realize significant savings in time and expense by using this process for select populations. Unfortunately, the acceptance of genetically modified (GM) foods in North America and Europe has been poor, especially for fresh produce. Consumers are wary of GM food, unless it is clearly safe and clearly of benefit to the consumer. Until recently, most of the work has focused on traits that would improve production, not those that clearly enhance the safety or nutritional value of the harvested crop (Aharoni and OʼConnell, 2002; Jimenez-Bermudez et al., 2002; Martin, 2002; Morgan, 2002; Owens et al., 2002; Zeldin et al., 2002). We still must wait to see the benefit of this area of research. Programs that can use a combination of traditional breeding, marker assisted selection when appropriate, and transformation will probably be in the strongest position in the future (Polashock and Vorsa, 2002a).