Karen Holl

Karen Holl
University of California, Santa Cruz | UCSC · Department of Environmental Studies

Ph.D.

About

191
Publications
93,989
Reads
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Citations
Introduction
Karen Holl's research focuses on understanding how local and landscape scale processes affect ecosystem recovery and using this information to restore damaged ecosystems. Her current research is focused in rain forests in Latin America and chaparral, grassland and riparian systems in California. She advises numerous public and private agencies on land management and restoration. She teaches courses in restoration ecology, conservation biology, and environmental problem solving.
Additional affiliations
August 2004 - July 2006
Stanford University
Position
  • PostDoc Position
July 1996 - present
University of California, Santa Cruz
Position
  • Professor

Publications

Publications (191)
Article
Full-text available
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 southe...
Article
Full-text available
Understanding tropical biology is important for solving complex problems such as climate change, biodiversity loss, and zoonotic pandemics, but biology curricula view research mostly via a temperate-zone lens. Integrating tropical research into biology education is urgently needed to tackle these issues. Tropical biology is currently largely absent...
Article
Extensive evidence shows that regional (gamma) diversity is often lower across restored landscapes than in reference landscapes, in part due to common restoration practices that favor widespread species through selection of easily-grown species with high survival and propagation practices that reduce genetic diversity. We discuss approaches to coun...
Article
Full-text available
The central motivation to restore ecosystems at a planetary scale has been to reverse degradation and provide multiple environmental benefits, but key global players like governments may be more interested in social outcomes from undertaking restoration, such as job creation. Assessing the job opportunities stemming from ongoing restoration program...
Article
The vast sums of money being spent on planting trees have the potential to transform landscapes and slow global warming but will accomplish little if trees do not survive and grow. We discuss ten key questions to decide which of the numerous tree-growing projects are most likely to succeed.
Article
In a recently published paper, Silva et al. conclude that placing fruit feeders (induced seed dispersal) in restored tropical forests serves to enrich the diversity of animal species and seeds in recovering forests and therefore is a cost-effective tropical forest restoration strategy. We argue that due to poor experimental design and choice of res...
Article
Forest restoration is increasingly heralded as a global strategy to conserve biodiversity and mitigate climate change, yet long-term studies that compare the effects of different restoration strategies on tree recruit demographics are lacking. We measured tree recruit survival and growth annually in three restoration treatments-natural regeneration...
Article
Full-text available
Abstract Large‐seeded, animal‐dispersed (LSAD) trees include some of the most valuable and threatened species in the tropics, but they are chronically underrepresented in regenerating forests. Toucans disperse many LSAD species, so attracting toucans to regenerating forests should help re‐establish more diverse tree communities. We ask: (1) What co...
Article
Full-text available
Remnant trees and forest fragments in agricultural landscapes can be important sources of propagules to facilitate forest recovery. However, many studies simply quantify forest cover in the surrounding landscape as a percentage, with little attention given to species composition, and subsequently fail to detect an effect on recruitment patterns. We...
Article
Insect herbivory is one of the major drivers of seedling mortality in the tropics and influences plant abundances and community composition. Anthropogenic disturbance can alter patterns of insect herbivory with potential consequences on plant communities in restored forests. We planted seedlings of early‐ and later‐stage successional tree species i...
Article
Climate change will increase uncertainty in restoration outcomes due to greater water stress and other abiotic filters that limit plant survival. Drought related plant functional traits can help species withstand filters in a semi‐arid environment. Our objective was to provide guidance for selecting species to improve restoration success in a chang...
Article
Full-text available
In degraded tropical landscapes lack of seed dispersal can strongly limit recovery, and restoration interventions can overcome this barrier by attracting dispersers. However, seed dispersal patterns are typically studied over short time periods, thus the influences of temporal and spatial variability on seed arrival cannot be teased apart. Choice o...
Article
Applied nucleation (i.e., planting vegetation patches) is a restoration strategy that better recreates natural ecosystem heterogeneity and requires fewer resources compared to planting the entire area. Whereas applied nucleation shows promise as a forest restoration strategy, this approach has received little study in grassland restoration, where t...
Article
Full-text available
Reintroduction is an increasingly common practice to conserve and recover threatened and endangered plant species, so understanding how practitioners view their work and identifying persistent resource mismatches are key to the long-term viability of these listed species. We interviewed practitioners involved in reintroduction projects for 14 speci...
Article
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Successful restoration of California terrestrial ecosystems requires knowledge of seed germination rates for a diversity of native species. We quantified greenhouse germination of 25 native perennial forbs, shrubs, and grasses collected coastally near Santa Cruz, CA for restoration at the Younger Lagoon Reserve and nine annual forb species from int...
Article
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To constrain global warming, we must strongly curtail greenhouse gas emissions and capture excess atmospheric carbon dioxide1,2. Regrowing natural forests is a prominent strategy for capturing additional carbon³, but accurate assessments of its potential are limited by uncertainty and variability in carbon accumulation rates2,3. To assess why and w...
Article
A growing number of initiatives at global, regional and national scales propose to plant millions, billions or even trillions of trees as a simple solution to resolve complex environmental problems. However, tree planting is much more complicated than it seems. We summarize the multifaceted decision-making process needed and offer guidelines to inc...
Article
Applied nucleation, mostly based upon planting tree islands, has been proposed as a cost‐effective strategy to meet ambitious global forest and landscape restoration targets. We review results from a 15‐yr study, replicated at 15 sites in southern Costa Rica, that compares applied nucleation to natural regeneration and mixed‐species tree plantation...
Article
Full-text available
Both dispersal and niche‐based factors can impose major barriers on tree establishment. Our understanding of how these factors interact to determine recruitment rates is based primarily on findings from mature tropical forests, despite the fact that a majority of tropical forests are now secondary. Consequently, factors influencing seed limitation...
Article
Full-text available
Plant traits—the morphological, anatomical, physiological, biochemical and phenological characteristics of plants—determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research sp...
Article
Limited funding is a major barrier to implementing ambitious global restoration commitments, so reducing restoration costs is essential to upscale restoration. The lack of rigorous analyses about the major components and drivers of restoration costs limit the development of alternatives to reduce costs and the selection of the most cost-effective m...
Article
To meet their large-scale forest and landscape restoration targets, countries must find ways to accommodate areas for conservation alongside agricultural production. In some pasture-dominated regions of Latin America, intensive silvopastoral systems (SPS) are being promoted to increase cattle productivity on certain lands while facilitating the rem...
Article
1.International forest landscape restoration commitments have promoted the restoration of millions of hectares of degraded and deforested lands globally, but few forest restoration approaches provide both ecologically‐sound and financially‐viable solutions for achieving the spatial scale proposed. One potential revenue source for restoration is sel...
Article
Conservation and restoration of riparian vegetation in agricultural landscapes has had mixed success at protecting in‐stream habitat, potentially due to the mismatch between watershed‐scale impacts and reach‐scale restoration. Prioritizing contiguous placement of small‐scale restoration interventions may effectively create larger‐scale restoration...
Article
Tropical grassland-savanna mosaics are threatened globally, but they are challenging to restore because highly competitive pasture grasses inhibit recovery and are not shaded out by the patchy tree cover. We analyzed the outcomes of restoration projects and experiments established over four years in 55 ha of abandoned pastures dominated by invasive...
Article
We welcome the opportunity to further discuss our analysis and conclusions [1] that Larkin et al.'s [2] (hereafter LEA) comment provides. In this response, we first discuss mischaracterizations and criticisms of our analyses, then highlight how the main conclusions from both LEA's and our analyses are similar, and end with further discussion of wha...
Article
Defining the reference system for restoration projects in regions characterized by complex vegetation mosaics is challenging. Misidentification of anthropogenically‐degraded grasslands or savannas as natural vegetation can lead to inappropriate restoration efforts and legislation. Here we use the Cerrado region of Brazil as an example of the import...
Technical Report
Full-text available
Bangladesh provides a significant global public good by hosting nearly one million Rohingya refugees. Most are living in camps in Cox’s Bazar District, where resources and livelihoods are strained. The refugee situation is likely to be protracted, and medium-term planning is critical. CGD has been working with local and international partners to un...
Article
Full-text available
In tropical areas with high levels of fragmentation due to agricultural use, forest fragments play an important role for biodiversity conservation at the landscape scale. But these fragments are subject to recurrent disturbances, which lead to arrested succession and loss of functional groups. In such cases, active restoration, such as enrichment p...
Article
Restoration frequently aims to improve native species biodiversity at a site, but practitioners have limited resources. In diverse ecosystems, the selective use of certain guilds or species can come at the cost of species that are more challenging to incorporate, resulting in the overall homogenization of the ecosystem and a relative loss of biodiv...
Article
Questions Natural regeneration is increasingly recognized as a potentially cost‐effective strategy to reach ambitious forest landscape restoration targets, but rates of recovery are notoriously variable. We asked how well initial habitat conditions after cessation of agriculture predict forest recovery after nearly a decade. We aimed to provide lan...
Article
We agree with Ramírez-Soto and colleagues that applied nucleation can be an effective approach for tropical forest restoration both in lowland and higher elevation tropical forests. We also contend that it is cheaper than standard plantation-style plantings and is straightforward to train personnel to implement this approach.
Article
Full-text available
Given that few ecosystems on the Earth have been unaffected by humans, restoring them holds great promise for stemming the biodiversity crisis and ensuring ecosystem services are provided to humanity. Nonetheless, few studies have documented the recovery of ecosystems globally or the rates at which ecosystems recover. Even fewer have addressed the...
Article
Full-text available
Multi-year studies comparing changes in litterfall biomass and nutrient inputs in sites under different restoration practices are lacking. We evaluated litterfall dynamics and nutrient inputs at 5 yr and after a decade of recovery in four treatments (natural regeneration—no planting, plantation—entire area planted, tree islands—planting in patches,...
Article
Full-text available
In the past few years, numerous global, national, and regional targets have been set to restore millions of hectares of tropical forest to achieve multiple goals, including carbon sequestration, biodiversity conservation, improvements in the quality and supply of water, and support of human livelihoods. To achieve these ambitious goals, restoration...
Article
Why do some restored ecosystems persist for centuries while others are quickly converted to alternative land uses or land covers? We propose that restored ecosystems have a temporal dimension that is variable, often finite, and likely predictable to some extent based on attributes of stakeholders, environment, and governance. The longevity of a res...
Article
Full-text available
Recent initiatives at regional, national, and global scales have called for unprecedented levels of forest restoration to counteract decades of rapid deforestation ( 1 , 2 ). Thus far, 30 countries have committed to restore 91 million hectares (ha) of deforested landscapes, an area the size of Venezuela, by 2020; at the 2014 United Nations Climate...
Article
Full-text available
Global forest restoration targets have been set, yet policy makers and land managers lack guiding principles on how to invest limited resources to achieve them. We conducted a meta-analysis of 166 studies in naturally regenerating and actively restored forests worldwide to answer: (1) To what extent do floral and faunal abundance and diversity and...
Data
(a) Relationship between the original response ratio (RR) and transformed RR; (b) Normal quantile plot of RR raw data. (BMP)
Data
Details on database compilation and variables. (DOCX)
Data
Relative importance of factors estimated by model averaging. (DOCX)
Data
Degradation level. (a) After all previous land-use types and (b) in actively and passively restored sites after agriculture only. (BMP)
Data
Distribution of number of variables and studies in each category. (DOCX)
Data
Results of model comparisons. (DOCX)
Article
Full-text available
Monitoring protocols are needed to evaluate the millions of hectares of land that are being proposed for forest restoration in the coming decades. Standardized proposals are critical to evaluate efficacy of restoration strategies, identify triggers for corrective actions, compare results across projects, and generally learn from past projects to in...
Article
Developing restoration strategies that accelerate natural successional processes and are resource-efficient is critical to facilitating tropical forest recovery across millions of hectares of deforested lands in the tropics. We compared tree recruitment after a decade in three restoration treatments (natural regeneration, applied nucleation/island...
Article
A substantial share of the remaining tropical forest cover is represented by historically degraded fragments exposed to severe edge effects, where ruderal plants proliferate vigorously and may arrest succession. We tested climber plant cutting as strategy to restore a semideciduous tropical forest remnant that is dominated by ruderal climbers. We c...
Article
Full-text available
Establishing diverse mycorrhizal fungal communities is considered important for forest recovery, yet mycorrhizae may have complex effects on tree growth depending on the composition of fungal species present. In an effort to understand the role of mycorrhizal fungi community in forest restoration in southern Costa Rica, we sampled the arbuscular my...
Article
Full-text available
Soil and litter arthropods represent a large proportion of tropical biodiversity and perform important ecosystem functions, but little is known about the efficacy of different tropical forest restoration strategies in facilitating their recovery in degraded habitats. We sampled arthropods in four 7- to 8-year-old restoration treatments and in nearb...
Data
Table S1. Elevation and site use history. Table S2. Abundance within orders for litter samples (individuals m−2) and pitfall samples (individuals/trap) in each habitat type (N = 4). Table S3. Arthropod functional diversity density per m2 for litter samples and per trap for pitfall samples in four habitat types. Table S4. PERMANOVA analysis resul...
Article
Full-text available
Soil and litter arthropods represent a large proportion of tropical biodiversity and perform important ecosystem functions, but little is known about the efficacy of different tropical forest restoration strategies in facilitating their recovery in degraded habitats. We sampled arthropods in four 7- to 8-year-old restoration treatments and in nearb...
Article
Questions: Vascular epiphytes constitute a large proportion of tropical forest plant biodiversity, but are among the slowest plants to recolonize secondary forests. We asked whether tree planting for ecological restoration accelerates epiphyte community recovery. Does the spatial configuration of tree planting matter? What landscape contexts are mo...
Article
Full-text available
Interspecific interactions are considered to be important structuring forces in early successional vegetation. Whereas competition seems to prevail in less severe environments, facilitation tends to increase in importance in harsh environments. Hence, facilitation is expected to play an important role in degraded tropical areas with high irradiance...
Article
Ecological restoration of modified and degraded landscapes is an important challenge for the 21st century, with potential for major gains in the recovery of biodiversity. However, there is a general lack of agreement between plant- and animal- based approaches to restoration, both in theory and practice. Here, we review these approaches, identify l...
Article
The selection of ecological indicators is an important step toward more effective restoration monitoring. The debate between Reid (2015) and Durigan and Suganuma (2015) regarding the usefulness of species composition for monitoring restoration trajectory is timely and salient, but it lacks a middle way proposal to balance ecological relevance and p...
Article
1. Plant functional traits, in particular specific leaf area (SLA), wood density and seed mass, are often good predictors of individual tree growth rates within communities. Individuals and species with high SLA, low wood density and small seeds tend to have faster growth rates. 2. If community-level relationships between traits and growth have gen...
Article
lanted woodland islets act as sources of seed that may accelerate woodland development in extensive agricultural landscapes. We assessed a 1-ha plot that was planted with 16 100-m2 islets of holm oak Quercus ilex subsp. ballota seedlings near Toledo (Spain) in 1993. In spring 2014 we measured (1) acorn predation and (2) seedling emergence from seed...
Article
Past studies have shown that tropical forest regeneration on degraded farmlands is initially limited by lack of seed dispersal, but few studies have tracked changes in abundance and composition of seed rain past the first few years after land abandonment. We measured seed rain for 12 months in 10 6–9-year-old restoration sites and five mature, refe...
Article
Full-text available
Neotropical fruit bats (family Phyllostomidae) facilitate forest regeneration on degraded lands by dispersing shrub and tree seeds. Accordingly, if fruit bats can be attracted to restoration sites, seed dispersal could be enhanced. We surveyed bat communities at 10 sites in southern Costa Rica to evaluate whether restoration treatments attracted mo...
Article
We agree with Prach and del Moral that passive recovery is often a desirable and effective restoration strategy. Passive and various active restoration approaches need to be weighed on a case-by-case basis and depend on the goals, relative rates of recovery desired, and various social and financial costs implicit in each option. That said, we stres...
Article
Full-text available
Restoration treatments can impact the growth and development of tree seedlings; however, it is often difficult to discern whether responses are driven by changes in microclimate, biotic interactions , or soil properties. To isolate for the latter, we quantified the growth response of four species [Ocotea puberula (Lauraceae); Otoba novogranatensis...