Effects of Livestock Grazing on Honey Production in a Mediterranean Rangeland Ecosystem

Abstract

Livestock husbandry has played an integral role for human societies in the Mediterranean Basin. While ruminant grazing traditionally comprised part of diverse agrosilvopastoral systems, in recent decades it has experienced substantial intensification in Mediterranean countries due to European Union subsidies and production for international markets. Apiculture has also played an important role in rural Mediterranean livelihoods for millennia, and is important globally both for apicultural products and crop pollination. Honeybees have faced worldwide losses in recent decades, along with a decline of floral resources, although the drivers of these changes are not well understood. The aim of this study is to (1) evaluate the impact of livestock grazing on Mediterranean vegetation structure and floral resources; (2) determine the relationship, between grazing intensity and the productivity of managed honeybee hives, and; (3) determine the economic effect, if any, that overgrazing has on apicultural activities in the region. Methods. I measured vegetation condition and floral resources across a broad range of livestock grazing intensities in a Mediterranean phryganic ecosystem on the islands of Naxos and Paros in the Aegean Sea (Greece). 14 study plots were surveyed, and the vegetation metrics of canopy gap, basal gap, vegetation height, plant species richness, spring flower coverage, thyme flower coverage, and thyme bush coverage were measured. As a proxy for grazing intensity, I used stocking rates, as well as biomass removed by grazers, quantified as the amount of ruminant dung collected along standardized transects. I monitored beehive productivity by weighing beehives every 10 to 14 days over the course of the summer flowering season. I established transects in the vicinity of the beehives, and repeated the same vegetation measurements used in the 14 study plots to determine vegetation condition around each beehive site. Mixed models were utilized in order to determine the relationship between beehive productivity and surrounding vegetation characteristics. In addition, I conducted surveys with a majority of beekeepers on each island to determine potential economic effects of grazing intensity on apiculture. Results. I found grazing to significantly impact vegetation cover and floral resources. Canopy gap and basal gap sizes were positively correlated with grazing intensity, while plant species richness was negatively associated with grazing intensity. Standing vegetation biomass decreased with increased grazing intensity, whether quantified as stocking rate or amount of plant matter consumed. Spring flower coverage also decreased with amount of plant matter consumed by livestock. However, cover of Conehead thyme (Coridothymus capitatus), the most important apicultural plant in the region, and a chemically defended taxon, actually benefitted from light to intermediate grazing conditions and followed a hump-shaped curve peaking at intermediate stocking rates. As a result, progressive increases in stocking rate had mixed effects on floral resources, leading to an overall reduction in general flower cover and diversity, while simultaneously leading to denser populations of thyme. Mixed models revealed that beehive productivity during the main honey-producing period was positively associated with increased thyme flower area, stocking rate, thyme bush area, canopy gap, and basal gap (in decreasing order of importance). Interviews with beekeepers also revealed that grazing intensity was positively correlated with the need for higher amounts of supplemental bee food outside the short summer thyme season, elevated antiparasitic drug expenditures, as well as increased total costs (including feed, drug, labor and hive replacement expenditures). These expenses erased higher iii income from elevated thyme honey production in grazed areas. Notably, the surveys showed no correlation between grazing intensity and net profits. As a matter of fact, comparison of the economic apiculture models on the neighboring islands of Naxos (mostly heavily grazed) and Paros (mostly ungrazed) revealed that beekeeping operations on Paros, by virtue of their lower costs, generated higher overall returns, despite producing less honey. Conclusions. This study highlights the central importance of C. capitatus, a prolific nectarproducing species, for honey production in the Aegean. Despite the fact that C. capitatus benefits from low to intermediate levels of grazing, due to competitive release, livestock husbandry has largely negative effects on apiculture in the Aegean. By extending the scope of this study beyond the traditionally considered first order metrics (honey production) to include additional factors (previously externalized beehive maintenance costs), I show any increases in thyme honey production in grazed regions are negated by concomitant increased costs for bee food, drugs, labor and elevated beehive replacement rates. Thus my data suggest that light levels of grazing are best suited to maximize economic returns from apiculture in the Aegean Sea region.