DOI: 10.7291/d1hq28
title: Landscape structure, bird, and vegetation recruitment in restoration plantations

description: Reversing large-scale habitat degradation and deforestation goes beyond
 what can be achieved by site-level ecological restoration and a landscape
 ecology perspective is fundamental. Here we assess the relative importance
 of tree cover and its configuration on forest-dependent birds and
 late-successional tree seedlings in restoration sites in southern Costa
 Rica. The abundance and species richness of birds increased in landscapes
 with more corridors, higher tree cover, and lower levels of fragmentation,
 highlighting the importance of riparian corridors for connectivity, and
 continuous tree cover as suitable habitat. Landscape variables affected
 abundance and species richness of seedlings similarly, but effects were
 weaker, possibly because seedlings face establishment limitation in
 addition to dispersal limitation. Moreover, the scale of landscape effects
 on seedlings was small, likely because proximal individual trees can
 significantly influence recruitment in restoration plots. Results
 underscore the importance of incorporating landscape-level metrics to
 restoration projects, as knowing the extent, and how the landscape may
 affect restoration outcomes can help to infer what kind of species will
 arrive to restoration plots.
description: For the purposes of this study, we used bird and tree seedling
 data collected within three years (2011–2017) of the high-resolution
 aerial imagery from 2014 on which tree cover classifications were
 determined. We used these years to match with the date of landscape tree
 cover image, as we assumed that the landscape in the region did not change
 substantially in that period. Bird composition. Each of
 the 12 plantation plots were surveyed three times annually from 2011 to
 2017 by a single observer, Juan Abel Rosales. Each plot at each site was
 actively searched randomly for 20 min per observation, and all birds
 detected visiting the plot (by sound or sight) were recorded. All surveys
 were conducted from sunrise (~ 05:30) until 09:00. Birds flying over plots
 were excluded from analyses. For detailed information on the field survey
 methodology see Reid et al.2014. From all detections recorded, we
 extracted observations of species categorized as highly forest-dependent
 by BirdLife International. These species have high forest-dependence that
 is characteristic of the interior of undisturbed forest and almost
 invariably breed within the forest. While they may persist in secondary
 forest and forest patches if particular ecological requirements are met,
 they are usually less frequently encountered in such situations. We chose
 to only include forest-dependent birds in this study because generalist
 frugivores are known to be less sensitive to landscape variables, and a
 preliminary analysis including all frugivores weakened explained deviance
 in all models. We used the cumulative number of species recorded over the
 seven survey years to determine species richness observed at each
 plantation plot and the average number of detections per year for each
 species as a proxy for abundance (hereafter ‘abundance’, see Reid et al.
 2014) as our two forest-dependent birds response variables.
 Person to contact with questions about bird data: Francis Joyce,
 fjoyce@ucsc.edu Tree seedling recruitment. We measured
 tree seedling recruitment (hereafter seedlings) at four sampling transects
 located within each plantation (n = 52 transects in total). All tree
 recruits ≥ 0.2 and &lt; 1 m height were censused within four 1 × 2 m
 quadrats along 1 × 8 m recruitment sampling belt transects (Zahawi et al.
 2013). Tree species’ successional stage was determined based on the expert
 opinion of two taxonomists who have each worked in the region for &gt;
 20 years, herbarium specimens at Las Cruces, and literature resources.
 Late-successional species are those mainly found in the interior of
 old-growth forests; they are generally hard wooded, slow growing,
 shadetolerant, and long-lived species. During each annual survey, new
 recruits were permanently tagged, identified to species, and their height
 measured. For this study, we considered the sum of new recruits for each
 species in the period 2011–2017, and the total species richness
 accumulated within that period as seedling response variables.
 Person to contact with questions about tree recruitment data:
 Karen Holl, kholl@ucsc.edu Landscape structure. We used
 a finely detailed tree cover map created by hand digitizing photographs
 taken in 2014 by commercial QuickBird satellites with 0.61-m spatial
 resolution in Google Earth for the canton of Coto Brus (for additional
 details see Mendenhall et al.40). Tree cover included the percentage of
 the landscape covered by old-growth and secondary forest fragments of all
 sizes, single or groups of remnant trees, live-fences,hedgerows, as well
 as non-native timber and fruit tree plantations. Tree cover represents any
 source of fruits and seeds within the landscape and more extensive tree
 cover indicates larger forest patches, which provide habitat to forest
 specialist birds. Total tree cover in the landscape surrounding the
 restoration plots (radius 900 m, ~ 255 ha) ranged from 30 to 79%. We
 classified all tree cover elements in the landscapes according to their
 area (A), perimeter (P), and compactness (SI) where the compactness ratio
 of the polygons was calculated using the shape index formula SI = P/2
 √(A*Pi). A criterion to distinguish live-fences, remnant trees, fragments,
 and corridors was to assign threshold shape index values according to the
 minimal observed values for well detected live-fences (n = 45) and
 corridors (n = 15) within the study region. Categories include: (1)
 patches—A ≥ 0.25 ha, SI &lt; 2 and wider than 40 m; (2) corridors—A
 &gt; 0.25 ha and SI &gt; 2; (3) remnant trees—A &lt; 0.25 ha
 and SI &lt; 1.6; and (4) live-fences – A &lt; 0.25 ha and SI
 &gt; 1.6. For all landscape classification we used Quantum GIS
 v3.10.1245. Then, we obtained the percentage of the
 landscape covered by corridors (riparian and non-riparian) and livefences
 as both are important connectivity elements in the landscape, they are
 widely used by birds and other animals, may promote long-distance
 dispersal, and can also be seed sources for many species. Fragmentation
 was measured as the number of tree patches divided by landscape area
 (n/ha). This classical fragmentation metric is inversely related to mean
 patch size. Thus, for a given land cover area, fragmentation increases the
 edge-to-core ratio at the landscape scale, potentially increasing edge
 effects (i.e., small-scale process). Yet, as it is also positively related
 to landscape connectivity and to the number of (sub)populations (seed
 sources) in the landscape, it can also have stronger effects on seed
 dispersal over larger spatial scales. Remnant tree
 density was calculated as the number of remnant trees divided by landscape
 area (n/ha). Small clusters of trees and isolated trees function as
 stepping stones in the landscape, promoting animal movement, and hence,
 landscape connectivity. The patch aggregation index is a percentage of
 like-adjacencies (nearness of the same land cover) among forest patches,
 where a single compact patch has a maximum aggregation. Aggregation refers
 to the degree of clumping of patches, where more aggregated patches
 facilitate inter-patch movement, promoting dispersal across the
 landscape. The mean inter-patch distance is the Euclidean or straight-line
 (edge-to-edge) distance among all forest patches in the landscape and it
 is a simple measure of patch context and has been used extensively to
 quantify degree of landscape isolation and act as a proxy for structural
 connectivity at the landscape scale. Finally, the
 largest patch index represents the percentage of the landscape comprised
 by the largest patch which can provide important habitat for
 forest-dependent birds and late-successional trees. We determined
 landscape metrics for 17 progressively larger circular areas around each
 plantation plot (radius from plot edge = 20, 40, 60, 80, 100, 150, 200,
 250, 300, 350, 400, 450, 500, 600, 700, 800, and 900 m). All landscape
 metrics (i.e., tree cover, corridor cover, live-fence cover,
 fragmentation, remnant tree density, patch aggregation index, mean
 inter-patch distance, largest patch index) were obtained using the
 FRAGSTATS software56. Person to contact with questions
 about landscape structure data: Miriam San José –
 sanjosemiriam@gmail.com