Carbon storage in terrestrial ecosystems: do browsing and grazing herbivores matter?

Abstract

Large mammalian herbivores manifest a strong top-down control on ecosystems that can transform entire landscapes, but their impacts have not been reviewed in the context of terrestrial carbon storage. Here, we evaluate the effects of plant biomass consumption by large mammalian herbivores (>10 kg adult biomass), and the responses of ecosystems to these herbivores, on carbon stocks in temperate and tropical regions, and the Arctic. We calculate the difference in carbon stocks resulting from herbivore exclusion using the results of 108 studies from 52 vegetation types. Our estimates suggest that herbivores can reduce terrestrial above- and below-ground carbon stocks across vegetation types but reductions in carbon stocks may approach zero given sufficient periods of time for systems to respond to herbivory (i.e. decades). We estimate that if all large herbivores were removed from the vegetation types sampled in our review, increases in terrestrial carbon stocks would be up to three orders of magnitude less than many of the natural and human-influenced sources of carbon emissions. However, we lack estimates for the effects of herbivores on below-ground biomass and soil carbon levels in many regions, including those with high herbivore densities, and upwards revisions of our estimates may be necessary. Our results provide a starting point for a discussion on the magnitude of the effects of herbivory on the global carbon cycle, particularly given that large herbivores are common in many ecosystems. We suggest that herbivore removal might represent an important strategy towards increasing terrestrial carbon stocks at local and regional scales within specific vegetation types, since humans influence populations of most large mammals.

Effects of grazing exclusion on carbon sequestration and plant diversity in grasslands of China—A meta-analysis

“…It is well observed that long-term excessive grazing constrains plant growth, disrupts soil structure, and thus renders ecosystem degradation in China's grasslands. Degradation disturbs soil nutrient cycling and induces a mass of carbon loss (Wiesmeier et al, 2009;Tanentzap and Coomes, 2012). Our analysis prove that grazing exclusion can reverse grassland degradation and possess carbon sequestration potential.…”

“…This practice is also proved to increase terrestrial carbon stocks at regional scales (Tanentzap and Coomes, 2012). Therefore, it is expected a great potential to improve forage production and carbon sequestration for the national program of RGLG in China because of large area, long-term implementation and low baseline at the beginning.…”

“…Generally, the effectiveness of grazing exclusion denpends on its duration (Milchunas and Lauenroth, 1993;Su et al, 2005;Wu et al, 2008;McSherry and Ritchie, 2013), environmental conditions (Conant and Paustian, 2002;Derner and Schuman, 2007;Piñeiro et al, 2010; J.S. Wu et al, 2012 and vegetation types (Proulx and Mazumder, 1998;Tanentzap and Coomes, 2012;McSherry and Ritchie, 2013) in specific sites.…”

Optimizing diet and pasture management to improve sustainability of U.S. beef production

“…Pasture C-sequestration was not included because the pasture model did not assess carbon flows. Additionally, reviews on this subject acknowledge that estimates are highly variable and further investigation of climate, plant, animal, soil and microbial factors is required to properly understand potential for C-sequestration (Derner and Schuman, 2007;Tanentzap and Coomes, 2012) as current research is often conflicting (McSherry and Ritchie, 2013) and C-sequestration is site specific. The equations governing the environmental outputs within the model are listed in Table 4.…”

Achieving landscape‐scale deer management for biodiversity conservation: The need to consider sources and sinks

“…In modified landscapes that provide high quality food and lack large predators, deer populations are projected to increase further (Ward 2005, Suominen andDanell 2006). Deer have severe impacts on woodland biodiversity, altering structure (Martin et al 2010, Holt et al 2011, Newson et al 2012, reducing woodland bird abundance (Holt et al 2011, Martin et al 2011, modifying small mammal (Buesching et al 2011) and invertebrate (Allombert et al 2005) assemblages, and affecting ecosystem functions including carbon storage (Tanentzap and Coomes 2012). Currently high deer numbers threaten to jeopardize proposals to mitigate carbon emissions through increased woodfuel production (Fuller and Rothery 2010) and are a vector for Lyme disease (Hartfield et al 2011), with implications for human health.…”