Received: 3 October 2019 | Revised: 21 February 2020 | Accepted: 10 March 2020 DOI: 10.1111/avsc.12493 RESEARCH ARTICLE Applied Vegetation Science Livestock browsing affects the species composition and structure of cloud forest in the Dhofar Mountains of Oman Lawrence Ball1 | Joseph Tzanopoulos2 1Department of Evolution, Ecology and Organismal Biology, The Ohio State Abstract University, Columbus, OH, USA Questions: It is frequently reported that overstocking of camels, cattle and goats 2 Durrell Institute of Conservation is degrading the Anogeissus cloud forest, which is endemic to a 200-km stretch of and Ecology, School of Anthropology and Conservation, University of Kent, coastal mountains in southern Arabia. However, livestock impacts on the vegeta- Canterbury, UK tion have not been assessed. Furthermore, we have a limited understanding of the Correspondence impacts of large-bodied browsing livestock, such as camels, in woodland and forest Lawrence Ball, Department of Evolution, rangelands. Therefore, in this study, we examine the effects of livestock browsing on Ecology and Organismal Biology, The Ohio State University, Columbus, OH 43210, the species composition, density, and phytomorphology of woody vegetation in the USA. Anogeissus cloud forests in the Dhofar Mountains of Oman. Email: [email protected] Location: Data were collected at 30 sites in the Jabal Qamar mountain range in west- Funding information ern Dhofar, Oman. This material is based upon work supported by the US National Science Foundation Methods: The point-centred quarter method was used to sample the composition, under Grant No. 1617185, the UK Economic density and structure of woody vegetation. Constrained correspondence analysis and Social Research Council under Grant No. 1595870 and the Anglo-Omani Society, UK. was used to quantify the effects of livestock browsing on woody plant species com- position, whilst effects on plant density were analysed using mixed-effects models. Co-ordinating Editor: Norbert Hölzel Standardised major axis regression was used to examine differences in height–diam- eter allometry (stunting) under different stocking rates. Results: Fog density, topographic position and long-term stocking rates were found to be important factors affecting woody species composition. We found lower spe- cies diversity and plant density, and higher frequencies of unpalatable species, under higher stocking rates. Juveniles showed a stronger response to stocking rates than adults, and several common species exhibited stunted morphology under high stock- ing rates. Conclusions: Browsing by large-bodied livestock, such as camels and cattle, can sub- stantially alter the species composition, structure, and phytomorphology of woody vegetation in semi-arid woodlands and forests. Juveniles are particularly susceptible to browsing which alters woody vegetation demography and inhibits regeneration potential. Our results support previous suggestions of overstocking in Dhofar and highlight the importance of swift measures to reduce livestock browsing pressure in the Anogeissus cloud forests. © 2020 International Association for Vegetation Science Appl Veg Sci. 2020;00:1–14. wileyonlinelibrary.com/journal/avsc | 1 2 BALL ADN TZANOPOULOS | Applied Vegetation Science KEYWORDS camels, cloud forest, constrained correspondence analysis, Dhofar Mountains, livestock browsing, Oman, ordination, overgrazing, pastoralism, rangelands, tree allometry, woody vegetation reproductive adults through sustained browsing pressure (Staver 1 | INTRODUCTION et al., 2009). Third, it can inhibit reproduction via the removal of re- productive components from adult plants (Augustine and Decalesta, One billion people practise pastoralism in rangelands which com- 2003). Browsing can also cause shifts in woody species composi- pose c. 35% of the world's terrestrial surface. Many of the world's tion, often to higher frequencies of unpalatable species (Yamada and rangelands are in a degraded state (Sayre et al., 2013), and live- Takatsuki, 2015). The impact of livestock production in woodland stock production in rangelands is expected to intensify to meet the and forest rangelands is greatest when woody vegetation is cleared food demand and preferences of the growing human population. for pasturage. Wild browsers such as deer, moose and elk have re- Balancing the needs of humans and biodiversity in rangelands will ceived greater research attention than browsing livestock such require sustainable grazing practices that maximise livestock pro- as goats and camels. Moreover, few studies have addressed large duction, vegetation health, and ecosystem functioning and services browsing livestock such as camels, despite 80% of their diet com- (Holechek, 2013). However, despite over a century of scientific at- prising woody plants (Dereje and Uden, 2005). tention, we still lack a comprehensive understanding of the effects Climate is the other major factor that interacts with livestock and of livestock on vegetation. One key reason for this is that the effects other disturbances to affect rangeland vegetation. For example, in can be influenced by a wide range of social and ecological factors African savannahs, a mean annual precipitation of 650 mm is the which often differ within and between rangelands (e.g. livestock threshold above which disturbances are required to maintain gaps in management practices, soil properties and climate). Thus, there is no woody vegetation cover, and below which woody vegetation cover unified set of ecological principles that apply to livestock–vegetation is constrained by precipitation (Sankaran et al., 2005). In arid range- processes (Sayre et al., 2012), making independent studies of dif- lands, woody vegetation is important for controlling soil erosion, im- ferent livestock types, in different rangeland ecosystems, important proving soil nutrient availability (Noumi et al., 2010), and for climate for understanding rangeland dynamics. Here we contribute a rather regulation (Schlesinger et al., 1990). Furthermore, low primary pro- unique study of the effects of camel, cattle and goat browsing on a ductivity and slow vegetation regeneration mean forage resources drought-deciduous cloud forest. can be more vulnerable to overuse than in wetter rangelands. The most commonly reported effects of livestock on vegeta- However, in such ‘non-equilibrium’ rangelands, pastoral practices tion include reductions in vegetation biomass, and changes in com- are often adapted to cope with unpredictable forage distributions munity structure and/or species composition (Tzanopoulos et al., (Moritz et al., 2013), and livestock often respond in a density-de- 2005). Livestock can also impact ecosystem hydrology, the physical pendent manner to available forage resources (Ellis and Swift, 1988). and chemical properties of soils (Briske, 2017), biological soil crusts In the Dhofar Mountains of Oman high numbers of camels, cattle (Belnap and Lange, 2003), and wider biodiversity (Alkemade et al., and goats do not respond in a density-dependent manor to avail- 2013). A common effect of grazing on vegetation species composi- able forage resources, due to twice-daily supplementary feeding tion is woody plant encroachment, which is a threat to the mainte- for 10–12 months of the year. Subsequently, stakeholders, includ- nance of savannah and grassland ecosystems (Briske, 2017). It occurs ing scientists, government officials and pastoralists, are concerned when herbaceous biomass (and subsequently fire frequency) is re- about the impacts of livestock on the natural environment. A sub- duced, giving woody plants a competitive advantage (Tzanopoulos stantial growth in livestock populations since the 1970s is linked to et al., 2007). Three other effects of grazing on vegetation species numerous drivers including population growth, increased wealth, composition are recognised. These are shifts from palatable to un- improved rural infrastructure, poor market access, strong pasto- palatable vegetation, shifts in dominant grass species, and shifts ral values and subsidisation of feedstuffs (Janzen, 1990; El-Mahi, between grass and forb dominance (Vetter, 2005). Under certain 2011). Whilst numerous reports have included objectives to tackle conditions grazing lawns may form, which have reduced vegetation overstocking in Dhofar (HTSL, 1978; GRM International, 1982; WS biomass but increased higher-quality forage (Hempson et al., 2015). Atkins International, 1989; UNEP, 2005), no studies have measured Browsing herbivores affect vegetation differently to grazing her- its impacts on the vegetation. bivores. Whilst grazing often leads to woody plant encroachment, Quantifying the impacts of livestock browsing on woody vege- browsing usually reduces woody cover. Browsing can change woody tation in Dhofar is important because previous research has shown vegetation demography and reduce woody vegetation regeneration that reductions in woody vegetation cover, due to livestock brows- potential through several processes. First, it can reduce seedling ing, could negatively affect the ecosystem hydrology. Fog intercep- and sapling abundance through direct consumption (Khishigjargal tion by the Anogeissus cloud forest has been estimated to contribute et al., 2013). Second, it can suppress the maturation of juveniles into as much water as rainfall to net precipitation which reaches the BALL ADN TZANOPOULOS 3 Applied Vegetation Science | ground (Hildebrandt et al., 2007). Furthermore, woody vegetation forms against