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United States Department of Agriculture (USDA) 2008

WOODY PLANT PROLIFERATION IN RANGELANDS : RATES, PATTERNS AND CONSEQUENCES

Woody Plant Rangelands

United States Department of Agriculture (USDA) Research, Education & Economics Information System (REEIS)

Titre : WOODY PLANT PROLIFERATION IN RANGELANDS : RATES, PATTERNS AND CONSEQUENCES

Identification : ARZT-1360210-H12-181

Pays : Etats Unis

Durée : Jan 1, 2008 à Sep 30, 2013

Domaine : Soil, Plant, Water, Nutrient Relationships ; Management of Range Resources ; Basic Plant Biology ; Rangelands and grasslands, general ; Soil and land, general

Partenaire : UNIVERSITY OF ARIZONA 888 N EUCLID AVE TUCSON,AZ

Objectifs
Understanding and predicting the functional consequences of ecosystem state changes (e.g., from grassland to shrubland) requires basic information on plant growth dynamics and population biology that can be directly linked to biogeochemistry and primary production. Research on the recently completed Hatch project using large-scale time-series aerial photography clearly identified several key gaps in our knowledge base that will be directly addressed using complimentary combination of ground-based monitoring and field experimentation approaches. Objective 1 : Quantify the nature and extent of density-dependent interactions among Prosopis velutina shrubs on contrasting soil types ; and determine how these are affected by stand canopy cover, basal area and livestock grazing. The following hypotheses will be tested : (H1) Conspecific P. velutina shrubs compete with each other and in so doing, regulate stand structure and maximum cover via density-dependent (DD) interactions. More specifically, DD interactions (H1a) will vary in intensity in a manner proportional to the distance and size of the nearest conspecific neighbor ; and accordingly (H1b) will be inversely proportional to stand basal area or canopy area. Rationale : basal area (BA) and canopy area (CA) integrate the net outcome of various positive and negative conspecific interactions. As BA or CA increase at the neighborhood or stand level, competition for resources (light, water, nutrients) should become stronger. (H1c) DD interactions will be stronger on fine-textured soils than on coarse-texture soils (other factors held equal). Rationale : Fine-textured soils will retain resources nearer the surface where P. velutina lateral roots and grass roots co-occur. Use of these resources by grasses will limit their availability to P. velutina plants and thus accentuate DD interactions. And finally, (H1d) DD interactions will be inversely related to grazing pressure on grasses. Rationale : Grazing typically reduces grass root biomass and resource uptake thus freeing up resources for shrubs and hence relaxing DD interactions. This relaxation may be more important on fine-textured soils than on coarse-textured soils (H1d). Objective 2 : (i) Quantify the errors that occur when applying canopy area-biomass relationships derived from individual shrub plants to multiple-plant patches ; and (ii) derive patch-level canopy area-biomass algorithms that can be robustly appropriately applied to aerial photography and satellite imagery. The following hypotheses will be tested : (H2a) Knowledge of error structure will enable development of robust correction factors that can be used to reliably apply individual plant based allometric relationships to multi-plant patches ; (H2b) measurements quantifying patch shape and shape complexity can be used in conjunction with knowledge of error structure (H2a) to improve canopy area-biomass algorithms. Objective 3. Quantify growth rates of P. velutina plants in relation to initial plant size, nearest neighbor distance, soil type, and climate

Présentation : USDA

Page publiée le 22 septembre 2015, mise à jour le 6 novembre 2017