Biotic Translocation of Phosphorus: The Role of Deer in Protected Areas

Werner Flueck

doi:10.3390/su1020104

Abstract

Biogeochemical cycles are cornerstones of biological evolution. Mature terrestrial ecosystems efficiently trap nutrients and certain ones are largely recycled internally. Preserving natural fluxes of nutrients is an important mission of protected areas, but artificially leaky systems remain common. Native red deer (Cervus elaphus) in the Swiss National Park (SNP) are known to reduce phosphorus (P) in preferred feeding sites by removing more P than is returned with feces. At larger scales it becomes apparent that losses are occurring due to seasonal deer movements out of the SNP where most deer end up perishing. Thus, the SNP contributes to producing deer which translocate P to sink areas outside the SNP due to several artificial factors. An adult female dying outside of SNP exports about 1.8 kg of P, whereas a male dying outside of SNP at 8 years of age exports 7.2 kg of P due also to annual shedding of antlers. Averaged over the vegetated part of the SNP, the about 2,000 deer export 0.32 kg/ha/yr of P. Other ungulate species using the SNP and dying principally outside of its borders would result in additional exports of P. Leakiness in this case is induced by: a) absence of the predator community and thus a lack of summer mortalities and absence of several relevant non-lethal predator effects, b) hunting-accelerated population turnover rate, and c) deaths outside of SNP principally from hunting. The estimated export rate for P compares to rates measured in extensive production systems which receive 10-50 kg/ha/yr of P as fertilizer to compensate the losses from biomass exports. Assumptions were made regarding red deer body weight or population turnover rate, yet substituting my estimates with actual values from the SNP would only affect somewhat the magnitude of the effect, but not its direction. The rate of P loss is a proxy for losses of other elements, the most critical ones being those not essential to autotrophs, but essential to heterotrophs. High deer turnover rates combined with accelerated biomass export warrants detailed mass balances of macro and micro nutrients, and studies of biogeochemical cycles in protected areas are essential if preserving natural processes is a mandate.

Highlights

The dynamic of biogeochemical cycles is a cornerstone of biological evolution [1]
It was concluded that the net rate of P loss was likely too small to explain the observed changes in vegetation composition and that the grazing patterns of red deer directly induced these successions, but they considered the possibility that long-term, small net soil-P losses indirectly drive plant succession from short-grass to tall-grass vegetation, because nutrient depletion could reduce grazing pressure in shortgrass vegetation and enable the characteristic tall-grass species to establish
While true for the small study area with artificially high soil P reserves, it does not hold for the Swiss National Park (SNP) area because the scale of processes reaches beyond the boundary of this protected area

Summary

Introduction

As pristine ecosystems tend to be nearly closed with regard to several nutrients, many protected areas such as national parks have the explicit obligation to preserve as much as possible the ecological stoichiometry, that is natural patterns of energy and material flows. This is based on the tenet that the recent biodiversity is a result of patterns of energy and material flows established during the development of the ecosystem together with the prevailing patterns of natural disturbances. Other ecological megatrends like removal and export of biomass in relation to biogeochemical cycles, have received less attention

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