DOI: 10.5061/dryad.5mkkwh731
title: Top-down and bottom-up controls limit woody encroachment into persistent temperate rainforest meadows

description: These data describe soils, woody plant seedlings, and ungulate herbivory
 in and around temperate montane meadows in the Oregon Coast Range, USA.
 Meadows such as these are a global study system for the accelerating
 phenomenon of woody encroachment, but study this phenomenon into meadows
 in western Oregon has been conducted almost entirely in the western and
 High Cascades, with only two extant observational studies of grassy balds
 in the Coast Range. These data describe factors limiting woody
 encroachment into meadows in the Oregon Coast Range, including bottom-up
 control by soil properties, plant-plant interactions, and top-down control
 by large herbivores. I measured chemical and physical properties of soils
 (depth of organic layer; bulk density of top 3 cm of mineral soil; and
 mineral soil profiles: particle size distribution, pH, % total C, % total
 N) to a depth of 50 cm in meadow and forest. I recorded community,
 density, and proportion browsed for shrubs, conifers, and deciduous trees
 ≤2 m tall along transects from meadow into forest. I experimentally
 planted 20 Pseudotsuga menziesii (Douglas-fir) seedlings in each of five
 meadows (n = 100) and factorially manipulated aboveground neighboring
 plant presence and ungulate herbivore access. I found that meadow soils
 were lower in C and C:N; slightly lower in N, and similar in
 plant-available water (derived from particle size distribution) and pH
 relative to forest soils. Shrubs were most dense, but experienced the
 lowest browse pressure, near the meadow edge; while trees were sparse and
 varied by site—although at one site, browse pressure was heavier in meadow
 than forest. Seedling survival and growth varied by site, herbivory
 reduced growth, and total soil N best explained residual variation in
 seedling growth among sites. My findings indicate that ungulate herbivores
 exert top-down control on woody encroachment into temperate montane
 meadows, perhaps in concert with local N-limitation.
description: <b>Study
 area</b> I
 conducted this study in the central-northern Oregon Coast Range, 45.0 to
 46.2 °N and -123.1 to -124.5 °W, bounded by the Pacific Ocean and the
 Columbia, Willamette, and Salmon rivers in northwest Oregon, USA. The OCR
 is distinct from the Pacific coastal flats and the western edge of the
 Willamette Valley contained in the area described above, which are
 typically non-forested alluvial plains. This study focuses on the Coast
 Range ecoregion (EPA Level III Ecoregion 1), specifically the Volcanics
 and Mid-Coastal Sedimentary ecoregions therein (EPA Level IV Ecoregions 1d
 and 1g). Small, graminoid-dominated meadows occur sparsely in the OCR,
 accounting for a fraction of the grasslands which comprise approximately
 5% land cover in the region. I sampled five meadows which share a mesic
 moisture regime but experience a range of abiotic conditions. These
 meadows are visible in aerial photography from the 1950s and are all
 sharply distinct from the adjacent forest, lacking a discernible ecotone
 in which herbs transition through intermediate growth forms to forest
 trees. <b>Field data
 collection</b> To evaluate the physical and
 chemical properties of forest and meadow soils, I sampled two soil
 profiles at each site to a depth of 50 cm, one in the meadow and one in
 the adjacent forest, each 25 m from the meadow edge. I recorded the depth
 of the organic layer; took a 226 cm<sup>3</sup> bulk volume
 sample from the top 3 cm of mineral soil; and sampled 100 g per
 visually-distinct mineral soil horizon, subsampling within a horizon if
 necessary to ensure that no sample represented &gt;15 cm horizon
 depth, resulting in approximately 5 sampled strata per profile. In total I
 recorded 10 organic layer depths, and took 10 bulk samples and 53 profile
 samples in mineral soil. I dried all fixed-volume bulk samples at 60°C
 overnight and recorded their dry mass. I air-dried all horizon samples and
 sieved them to 2 mm. To determine total C and total N content, I ground 6
 mg subsamples and used a Carlo-Erba NA 1500 Series 2 gas analyzer (CE
 Instruments, Milan, Italy) for elemental analysis. To determine pH, I
 mixed 20 g of soil into a slurry with 40 mL of deionized water and
 recorded pH with a probe (VWR Scientific 8005). To determine particle size
 distribution, I used a Buoycous hydrometer method: I deflocculated 50 g of
 soil overnight in 100 mL of 5% sodium hexametaphosphate on a shaker,
 brought the resulting slurry up to 1L with deionized water in a graduated
 cylinder, mixed for 30 seconds to disperse particles, and took hydrometer
 measurements 40 seconds and 7 hours after mixing. To describe the taxonomic
 community of, spatial pattern among, and browse pressure upon woody
 seedlings in and around meadows, I collected data along two transects
 approximately 100 m long at each site from the meadow center into the
 adjacent forest, along random bearings in the spring and summer of 2016.
 At each site I collected data for one transect in spring and another
 transect in summer, capturing synchronic browse pressure but not
 diachronic repeated browse damage. Every 5 m along each transect, I
 recorded all woody plants in the browse zone (≤2 m tall) by species within
 a 1 m<sup>2</sup> quadrat, and whether each individual was
 browsed. I counted clonal shrubs per root collar visible at ground level.
 If any part of an individual plant was browsed I recorded it as browsed;
 if unsure whether a plant had been browsed (e.g., apical meristem was
 absent, but the cause of its absence was unclear), I recorded it as
 unbrowsed. I did not quantify mature (&gt;2 m tall) woody plants, but
 I observed that they occurred almost entirely in forest. My authority for
 plant nomenclature is the Oregon Flora Project (http://oregonflora.org,
 accessed 13 September 2018). To experimentally determine the
 effects of ungulate herbivores, plant-plant interactions, and soil
 conditions on woody encroachment, I planted 20 first-year Douglas-fir
 seedling plugs in each meadow in October 2015 and removed them in October
 2016. These seedings were sourced from the same seed zone as my study
 sites, not inoculated with mycorrhizae prior to planting in the field, and
 spaced 2 m apart in a dispersed plot across the meadow interior. I
 randomly assigned five seedlings per meadow to each of four treatments:
 control, neighboring plant removal, browse exclosure, and both neighboring
 plant removal and browse exclosure. Every three months I removed all
 aboveground live plant material within 1m of each seedling for neighbor
 removals, and maintained a netted Vexar tube (5 cm diameter, 50 cm height)
 around each seedling for browse exclosures. I measured each seedling’s
 height at the beginning and end of the experiment.
description: Missing values from the <em>P. menziesii</em>
 seedling experiment are the result of herbivory, typically by ungulate
 herbivores (occasionally, I would find a seedling 1-10 m from the
 experimental plot, apparently transported by a large animal) but at least
 once by rodents (one seedling disappeared out of an undisturbed Vexar net
 tube overnight, and fresh rodent burrowing was apparent under and around
 its last known whereabouts).