Fire‐ and herbivory‐driven consumer control in a savanna‐like temperate wood‐pasture: An experimental approach

The drivers of open, grass-dominated, wood-pastures and heathlands in the temperate zone Europe have been debated since long (Birks, 2005; Bobek et al., 2017; Bond, Feurdean 2018; Hejcman 2013; Mitchell, Svenning, 2002; Vera, 2000). These types habitats generally referred to as ‘man-made ecosystems’ resulting from anthropogenic fire livestock grazing regimes, dating back early Neolithic culture (e.g. Leuschner & Ellenberg, 2017). This view is challenged by ecologists palaeoecologists, claiming that savanna-like open semi-open ecosystems were present central northwestern already Holocene they survived ‘mid-Holocene bottleneck’ certain portions this landscape such river valleys or on thin sandy soils Pokorný 2015; 2002). Based palaeoecological evidence molluscan fauna, microcharcoal subfossil remains extinct megaherbivore several studies argued that, now partly extinct, large mammalian herbivores (Bakker 2016; Malhi 2000), (Feurdean 2002) a combination both (Svenning, controlled woody recruitment kept European landscapes open. fires then replaced role wild controlling vegetation On global scale, herbivory are two fundamental top-down processes strong structure many terrestrial (Archibald Hempson, Bond Keeley 2011; Kuijper, Jędrzejewska, 2010; Kuijper Veldman 2015). They consumers plant biomass Keeley, 2005), although may differ their occurrence, selectivity way consume plants. For example, while more continuous process comparison with be spatially heterogeneous, occur less frequently time but often uniform space 2016). Moreover, ‘select’ (sensu Archibald 2016) dry nutrient-poor (Schwilk, 2015) fresh nutrient-rich (Owen-Smith Novellie, 1982). Regardless these differences, can strongly control trees next demographic stage affecting seedling sapling survival growth (consumer control: Churski Smit Staver 2009). Studies savannas shown how keep so-called ‘fire-’ ‘browse traps’ preventing them grow into adult (LaMalfa 2019; Sankaran Skowno 1999; 2014) profound effects ecosystem (Higgins 2000; 2014). Due differences affect tree saplings, plants evolved different traits avoid tolerate each process. Spinescence, for enables prevent herbivory, thick bark insulates cambium lethal temperatures caused (Charles-Dominique, Beckett, Charles-Dominique Kruger Some adaptations re-sprouting (Coughenour, 1985; 2011). As result, presence ultimately lead development evolutionary divergent, consumer-controlled communities, characterized species Hoffmann 2012; Ratnam Stevens 2018). (2005) divided fire- herbivory-adapted based whether main disturbance. In fire-controlled systems (‘black world’ sensu communities fire-adapted bark, bud protection accessory buds dominate Staver, herbivore-controlled (‘brown world’), structural defences, thorns, spines cagy architectures, absence fires, resource availability light, water, nutrients), set climate soil conditions, limits (‘green world’: 2005). ‘resource-controlled’ systems, dominated resource-acquisition traits, high vertical rate shade tolerance, when productivity Niinemets Valladares, 2006). addition, elements all three possible states (green, brown black) depending relative importance (consumers) versus bottom-up (resources) mechanisms (Bond, key community has extensively studied tropical Charles-Dominique, North American prairies Briggs Veach However, few looked at where grass coexist, wood-pastures. fact, consumer model 2005) stands contrast classical successional models emphasizing competition facilitation resources driver Connell Slatyer, 1977; Van Andel, 1993). Recent imply impact largely response (Churski Cromsigt, Uytvancket 2008). dendrochronological suggest also an integral part disturbance regimes (pre-)historic (Bond Carcaillet 2009; Niklasson 2010). Today, Europe, only small remnants silvopastoral grasslands) remain Ziobro abandonment rural areas led reduced use general decline herbivorous mammals (Bradshaw 2003; Bradshaw Ceballos, Dirzo 2014; Estes Ripple Similarly, over most elsewhere globally, active prevention its near Bowman southern traditional practices leading increased frequency intensity due accumulated fuel loads (Johnson More recently, however, again returning consequence passive rewilding (Pereira Navarro, example rewilding, across deer increasing numbers expanding ranges (Linnell 2020). free-ranging cattle horses introduced substitutes Aurochs Bos primigenius Tarpan Equus ferus restoration tool (Cromsigt To understand functioning Europe´s ecosystems, we need explore influence dominant species. paper, experimentally tested if consumers, saplings five common (Pinus sylvestris, Picea abies, Quercus robur, Betula pendula Tilia cordata). We hypothesized (a) would induce (in terms growth) (b) responses vary among extensive review literature (Table S1), predicted P. Q. robur B. ‘black higher than indicating systems. contrast, reduce abies T. cordata treatment other species, therefore being ‘brown world’-species adapted test hypotheses, carried out full-factorial experiment manipulating wood-pasture. study plots exposed annual low-intensity surface 3 years evaluated respect rates net height increment. was conducted Ecopark Nordens Ark (ENA, Figure 1) county Västra Götaland western Sweden (58°27′N 11°25′E). ENA total area 400 ha located Åby fjord coast. influenced Atlantic mild winters cool summers (Wastenson 2004). average mean temperature 6–7°C (January −2 −1°C July +16 +17°C) precipitation 800–900 mm, summer (standard period 1961–1990, https://www.smhi.se/klimatdata, 2019-04-25). Evaporation 400–500 mm per year snow covers ground 50–75 days Acid granites, mainly Bohus granite, bedrock (Berglund, 1988). Soils highly variable very deep clay layers valleys, glacial tilt slopes xeric rocky outcrops lying (Blomgren Falk, region area, ice age accumulations clamshells previous shorelines locally enriched base-rich material (Hallberg, 1971). had history human fire. Until century, Calluna vulgaris-dominated maintained frequent burning every 3–10 (Atlestam, 1942; Lindholm, 2019). Burning spring equally used improve quality (Weimarck, 1979). lightning ignite forest sometimes even spring, lower (Granström, There no doubt natural throughout (Högbom, 1934). experimental site mostly grazed cows sheep until 1900s brought commercial forestry (Ernby, 2011 2012, program, 100 conifer plantation converted harvesting planted spruce. fenced corrals, 1.0 m electric fence wires, minor extent sheep, goats (i.e. consisted grazers). During period, grazers adults, juveniles (1–2 years) calves taurus Swedish breeds Rödkulla Fjällnära English breed Hereford. Each year, started May–June ended August–October. aimed creating similar densities management issues some variations pressure which documented during S2). Wild overall surrounding our site, included moose Alces alces, fallow Dama dama, roe Capreolus capreolus (browsers), mouflon Ovis orientalis (grazer) boar Sus scrofa (omnivore) (17, 20, 195, 21 134 animals, respectively, shot whole local hunting unit, Sotenäs, covering 11.360 ha, according statistics type corrals allowed freely enter jumping going under it. camera trap surveys showed rarely comprises far <1% visiting (K. Amsten, unpubl.). Since logging spruce, undergone drastic transformation. From shady conditions little herbaceous spruce monoculture, grassland dominates (mainly Poa, Festuca Deschampsia spp.) after short phase raspberry Rubus idaeus. Several managed regenerate naturally, despite grazing, birches sp., oaks Scots pine Pinus sylvestris Norway (Hedlund, 2015, established 24 plots, four ENA, six (Figure 1). randomly placed avoiding rocks inside plots. plot measured 14 × contained sized subplots 7 each. Before start experiment, surveyed carefully naturally regenerated seedlings removed pulling up roots or, cases, cutting root level. following years, did not remove regeneration. Two 2.0 mesh wire, excluding ungulates entering, one unfenced chosen design gave us combinations: no-fire:no-herbivory (control), fire:no-herbivory (fire), no-fire:herbivory (herbivory) fire:herbivory (fire:herbivory) replicates An initial took place April 2015 before planting. Thereafter, burned enough green-up (usually mid-April). Using drip torch, applied ignition technique subplots. walked drip-line level mimic 7-m subplot, starting wind exit side subplot. If first line spread own low load, drip-lines apart, against wind. After burning, 2,400 (Scots L. (hereafter Pinus), (L.) H. Karst. Picea), oak Quercus), Silver birch Roth. Betula), Small-leaved lime Mill. Tilia)) selected stepwise selection procedure follows. list potential native found followed additional criteria brackets given number available step): extant (27), (25), competitive outside wet (23), co-dominant position national stand (6), market (spring (5). 25 nursery, 5 grid 1.4 spacing, row containing random order within Seedlings 1–2 old differed size; 68.8 (±0.7 SE) cm, 48.6 (±0.8) 41.6 (±0.5) 28.1 cm 20.9 (±0.4) cm. Three planting, recorded increment nearest At time, growing seasons herbivores, 2016 2017. noted status classes (live/dead/gone), dead defined brittle stem, brownish colour leaves needles. broken left above-ground stem signs living sprouts above ground, it study. When there sapling, gone treated analysis. Sapling highest point top stretching Only live height. destroyed accidentally corral maintenance so exclude analysis (Plot 12, 16, 17 18; Therefore, 20 statistical analysis, program R 3.4.3 (R Foundation Statistical Computing). compare heights linear mixed-effects normal distribution using lmerTest package (‘lmer’ function) (Kuznetsova confirmed (F = 1,045.02; df 4; p < 0.001), combinations 1.55; 3; 0.20; S1). effect (fire no-fire; no-herbivory) interaction between treatments (sapling subplot analysed generalized binomial logit link. entered (binary), (binary) (five levels) fixed effects. effects, Plot ID nested Corral. R, lme4 ‘glmer’ function run (Bates multiple pairwise comparisons levels separately, Tukey's post hoc tests ‘emmeans’ emmeans (Lenth (mean distribution. same effects). ‘lmer’ significant difference (no-fire:no-herbivory) except Tilia, S3). Fire combination, individual Pinus, 2; Table S4). Survival (fire:no-herbivory) (no-fire:herbivory) Herbivory Quercus, whereas Adding (herbivory vs. fire:herbivory) further any positive lowest 3). negative increments treatments, means decreased compared planting without herbivory. 0.3 (±5.0), shortest second tallest beginning (Figures S1 Again, increment, clear 2). Picea, S5). Betula, much adding reduction grass-dominated African savannas, important Our contrasting wood-pasture revealed varying (Tables 1 results exert ways functionally comparable herbivore- savanna (cattle), browsers) relatively numbers. variation 2), demonstrating filtering composition. Height either affected explained herbivore, browsers (Staver al. others suggested browsing, increase reducing (Belayneh Tessema, Holdo O’Connor 2014), pattern (Smit do provide support because affected. Importantly, increment) result direct foraging cattle, particularly trampling (Van Uytvanck Hoffmann, surviving significantly general, suppress individuals. Higgins (2000), who stated limit succession establishment saplings. (2009), hand, survivors mortality A explanation lack flame height, never reaching S3), years. Interestingly, While (control fire), highlighted decrease occurrence severity amount firebreaks Hierro Kimuyu Leonard way, complete exclusion efforts, sufficient self-propagating Summarizing, create interactive well competing creates habitat diversity which, turn, affects composition increases Royo seen study, limited intensity, what observed Gambiza (Quercus, Pinus) regime previously associated boreal zones S1; Midgley, Fréjaville Richardson, Spînu likely strategies cope subplots, invested escape 1999). ranking best regime, show fire, investment mechanisms. genus widely acknowledged fire-resistant through capacity (Abrams, 1992; McEwan enabled well, experiments (Petersson Re-sprouting described trait (Keeley It note respond disturbances life Barton Koricheva, Linder 1998). thickness resistance governed individuals require develop (Bär Mayr, 2020; Fernandes 2008; Pausas, Zin timeframe still yet developed protect fires. thus depended resist rapid Quercus. Both, conform suggesting Bär Molinari induced major changes exposure fires: became survivor survival. remained survivors, accompanied Pinus. High conifers conforms zones, showing presence, absence, Lorentzen Kolstad Pastor 1988; Speed 2013). attribute preference deciduous Out intensively browsed S5), strongest tolerance trees. regarded tolerant performance could additionally shade-adapted potentially poorly sites (Brzeziecki Kienast, 1994; Indeed, suggests rather ecosystem. Nevertheless, allow outgrow browse trap, adaptation discussed above, automatically species-specific herbivores). Belsky (1993) Rosenthal Kotanen (1994): ‘tolerance strategy’ ‘avoidance strategy’. strategy entails tolerating maximizing cost (Belsky 1993; Kotanen, 1994), experiment. defence investing ability bottleneck created shows interactively widespread Currently, absent parts processes. histories (tolerance avoidance) towards degrees ways. illustrates impose consequences structure. findings played roles structuring past landscapes. employment K.A., M.N. J.M.L. financed Hasselblad foundation. foundation funded participation M.C., J.P.G.M.C. D.P.J.K. field trips. Stiftelsen Thureus Forskarhem contributed donated Svenska Skogsplantor. authors declare conflict interest. J.P.G.M.C., D.P.J.K., M.C. planned designed research; K.A. performed work; data; drafted revised manuscript; revising manuscript. peer article https://publons.com/publon/10.1111/1365-2745.13783. Data obtain SND (Svensk nationell datatjänst) https://doi.org/10.5878/wd8j-2c36. 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