Shifts in plant community composition across a conservation reserve program chronosequence and associated soil chemical properties of Amarillo loamy sand in the Texas high plains
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The Conservation Reserve Program (CRP) was initiated in the United States of America (USA) by 1985 to reduce soil loss due to wind erosion on highly susceptible former agricultural land. By 2012 the program led to the establishment of 11.9 million hectares of perennial grassland vegetation in the USA. Currently 1.35 million hectares are enrolled in Texas with most of it situated in the Southern High Plains (SHP) region. The recovery process of secondary succession has been demonstrated to be variable in time and space, and a clear understanding how plant communities are affected needs further evaluation. Here 18 fields under contracts with the CRP, formerly under long term monocultural crop production, were arranged according time within the restoration process to create a chronoseqence that allow for comparisons regarding development of plant community composition and soil chemical properties over time. Plant community composition was assessed by sampling plant cover, grouping in functional groups and calculating the Shannon diversity index. The results of this study underlie the importance of native perennial bunchgrasses such as Bouteloua curtipendula (side-oats grama) and Bouteloua gracilis (blue grama) in being major components of the seeding mixtures of restored CRP fields at the Southern High Plain (SHP) region. Fields seeded predominantly with these species show higher basal and foliar cover after 14 years of recovery than fields seeded with species better adapted to regions with higher moisture availability. Especially B. curtipendula is demonstrated to be the major contributor to soil cover. Further basal cover was found to be lower at fields that were seeded monospecific to Eragrostris curvula (weeping lovegrass) as well as species diversity tend to be negatively affected by non-native species such as E. curvula and B. ichaemum. Soil chemical characteristics such as soil organic matter content correlated with basal cover. As basal cover did not increase over the chronosequence soil organic matter content did not increase over time. Plant available micronutrients as copper and manganese decreased over time, suggesting the need of management implications to potentially further enhance CRP sites ecosystem quality. Early conservation efforts met the first goal of the CRP, but ecosystem benefits may be enhanced when seeding mixtures are predominantly composed of native short grass species. Further, time effects across the chronosequence used in this study are very likely confounded by individual plant traits.