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Climate change moves faster than species can migrate. The human landscape is an underused framework for living corridors for biodiversity.



Climate change threatens biodiversity by reorganizing the climatic ranges of organisms. To survive, species must migrate as rising temperatures or changes in precipitation render habitat unsuitable 1. Human landscapes (HL) impede species’ movements, destroying or fragmenting habitat. However, vegetated spaces within HL could be used to increase habitat connectivity. To guard against extinctions, adaptation strategies must provide migration routes for species, accounting for the speed & uncertainty of climate change.

Climate-based conservation management requires both improving habitat & increasing habitat connectivity 2,3. Yet conservation budgets are limited & land managers face tradeoffs between many land-use pressures. A disparate mosaic of conservation plans with uncoordinated goals & varied adoption of adaptation principles is insufficient to provide adequate protection against irreversible biodiversity loss. If these actions could be aligned toward regional biodiversity conservation goals, the outcome would be a powerful & robust network for protecting biodiversity against climate change.

Establishing corridors of habitat-promoting native plant species through HL safeguards biodiversity. A network of carefully planned regional migration corridors would link populations in areas where habitat is shrinking to projected future habitat. Our model connects populations of keystone tree species (biodiversity ‘nodes’) via corridors through under-utilized HL, such as transportation & water supply routes. Nodes may be natural (reserves, forests, wilderness areas) or established (university arboreta, corporate campuses, private estates). 

Habitat decisions are made not only by conservationists, but also by land managers, urban planners, corporations, municipal agencies, homeowners, & anyone who has ever decided to keep, remove, or plant a tree. The Corridors model engages human communities in the protection of natural communities in a world being shaped by climate change.

Category of the action

Mitigation/Adaptation, Changing public attitudes about climate change

What actions do you propose?

Using the California floristic province, a global biodiversity hotspot, as our prototype, we intend to show the world what a thoughtful system of “biodiversity migration corridors” might look like. We focus initially on developing corridors for native Californian oak trees, focusing initially on the threatened Engelmann oak (Q. engelmannii), native to southern California. Oaks are keystone species within the California floristic province, providing habitat for hundreds of endemic animal species. Q. engelmannii is currently threatened by prolonged drought, increasing populations of pests and pathogens, and loss of habitat due to land-use change, and these threats are exacerbated by increasing drought and fire risks projected by climate change models 4. The prototype model makes recommendations for habitat corridors that vary in length from within the current distribution range to projections of suitable habitat locations within the State of California based on four IPCC Representative Concentration Pathways (RCPs) scenarios for 2025 and 2050 5. The prototype project consists of 4 phases: capacity building, corridor planning, implementation, and ongoing education and maintenance.


Phase I of the prototype model focuses on capacity-building and will result in the development of two specific products/outcomes: (1) a map of existing nodes and potential corridors for both species, and (2) the development of a viable propagation stock of Q. engelmannii of sufficient size to facilitate the planting of several corridors.  


We will combine species distribution maps that have been developed for Q. engelmannii (4,5), with the GPS locations of nodes found within the human landscape (e.g., the Shields Oak Grove in the UC Davis Arboretum, the Los Angeles County Arboretum).  Next, we will develop a corridor suitability map, based on spatially-explicit historic and projected temperature and precipitation data, transportation and water supply corridors, topography, geology, soil properties, vegetation, and urban features.  Selection criteria for corridors will be developed to ensure they are practically feasible and scientifically robust.  The resulting maps of potential corridors will provide the basis for implementation, and will be an important communication tool for sharing our work with policymakers, stakeholders, educators, and the general public. 


Collecting and maintaining viable acorns until planting is key to propagating healthy oak trees.  2014 happens to be a “mast” year for oak trees in California, and acorns are likely to be abundant. Several Q. engelmannii collection sites are known throughout the current species range. The Santa Rosa Ecological Preserve contains abundant mature Engelmann oaks, and another population is known in suburban Arcadia. Collection trips are planned throughout November, the typical ripening time for this species.

Once acorns are secured, two strategies may be utilized to grow oaks trees. First, if suitable locations have already been identified, acorns may be direct-seeded into the ground, and various kinds of protective enclosures tailored to minimize local predatory pressures and ensure successful oak establishment. The second strategy is to establish seedlings in nurseries, using a modified version of standard nursery container production. These trees can then be provided to projects in subesquent years, as seedlings and saplings.



Phase 2 will focus on (1) establishing partnerships for multiple corridor plantings, and (2) developing corridor-specific implementation plans. 


We will reach out to state and local officials, land managers, corporate landowners, and large private estate owners whose land has been identified as suitable for the establishment of biodiversity corridors via the corridor suitability map developed in Phase 1.  We will draw upon existing relationships and the extended network of the Corridors team (and our Advisory Committee) with public and private stakeholders in order to maximize our opportunities to pitch site-specific plans for implementation to potential collaborators.

We will also reach out to a variety of potential planting partners, including non-profit organizations, youth education programs, high school educators, university volunteer coordinators, and others, inviting volunteers to contribute their talents in the planning, implementation, and education phases of this project.


Plantings can be designed to be executed wholly by the Corridors team and volunteers on collaborator’s lands, or tailored to fit within existing landscaping activities.  Ideally, corridor plantings will eventually be ‘mainstreamed’ into existing public and private landscaping activities.  Corridors are designed to radiate outward from nodes in continuous north/south and east/west transects. A supply of low-cost or free seedlings and acorns will be available (Phase 1), allowing plans to be tailored to collaborator’s needs.



Phase 3 is concerned with the implementation of corridor plans and has three components: (1) the pre-implementation baseline biodiversity survey, (2) site preparation, (3) the planting process.


We will work with existing academic collaborators to conduct a baseline survey of site biodiversity prior to any planting-related activities on future corridor sites, including full accounting of plant species’ richness and abundance as well as animal and insect surveys.  This is essential for an accurate understanding of the biodiversity implications of the Corridors project.


Preparations for plantings will include activities typical to large landscape installations.  Once potential planting locations have been identified, soil quality must be assessed. If the soils are compacted from previous human activity, this compaction must be mitigated to ensure successful tree establishment. Sub-soiling and other techniques used in orchard preparation can be utilized.

Once assured a quality soil substrate, a tree establishment water supply must be addressed. Direct-seed acorns and seedlings can be established by volunteers delivering water from a water truck. Where the funding and sufficient water supply exist, an irrigation system can also be installed to simplify tree establishment. Whatever water strategy is selected, it should only be needed for 3 to 5 years until the trees are growing on their own, typically after reaching the soil water table.

During the establishment phase, sufficient predator protection must be put in place. If there are gophers or ground squirrels are present, underground metal cages will likely be needed. These can be designed such that they do not cause any long-term negative impacts to the growing tree or surrounding environment. If aboveground herbivory threatens seedlings, variable-height plastic tubular tree shelters have proven an excellent aid to tree establishment in California’s Mediterranean climate.


Plantings of native Californian oaks are best carried out in the fall or early winter in a Mediterranean climate. In general, plantings can be carried out by volunteers or paid landscape personnel. The procedure is as follows: Holes for planting are dug or augured. Any necessary underground protection is put into place. Soil is refilled containing either seedling oak or acorn. Top protection is put into place. Water-holding berms are constructed to facilitate future watering. Any irrigation lines used are installed and tested. The newly planted site is watered thoroughly, to last until the onset of the dry season (provided winter and fall rains are sufficient. The planting is finished with an application of wood chip mulch to help moderate soil temperature and moisture loss.


Phase 4 transitions the prototype model towards the long-term objectives, via 3 endeavors: (1) near-term maintenance of newly-established trees, (2) the post-implementation biodiversity survey, (3) project knowledge-sharing and education.


Water, maintenance of protection devices, pruning as necessary (3-5 years)

Maintenance in the early years is absolutely critical to the successful establishment of seedlings and saplings.  Lack of water and compromised protection devices are the most common causes of juvenile tree mortality. If resources are sufficient, watering should be continued for 3 to 5 years, to ensure that the trees are very well established before having to fend for themselves. By that point, appropriately chosen tree species should be largely self-sustaining unless serious drought is encountered.



Once trees are well established, a post-implementation biodiversity survey will attest to the initial success of the new habitat corridor planting. These surveys are preliminary, as the trees are still rather small. More indicative biodiversity surveys should take place in years 10 to 20, as the trees begin to reach a substantial size. The magnitude of tree benefits is determined by the canopy size—the larger the canopy, the greater the benefits.


A major objective of this project is sharing the lessons we learn and the experience we gain through all phases of the work detailed above.  To this end, we will share our knowledge and experience through online channels, by leading tours of planted corridors, by seeking opportunities to share our story with educators, students, NGOs, universities, and other interested groups, and by sharing protocols and planning materials with those interested in developing corridors for other species and regions.  Our goal is for this to be a project of shared ownership and shared rewards.


After completion of the prototype project, we will begin the cycle again, identifying new species and corridors (with room for overlap between corridors).  We hope to draw in collaborators and Corridor project facilitators globally, in extending the reach of this effort and the protection of natural communities world-wide.

Who will take these actions?

The core team: facilitation and implementation

Corridors- a new non-profit organization with expertise in horticulture, large-scale landscape management, conservation ecology, and GIS for ecological applications


Implementation collaborators

State and local policymakers and governmental agencies

California Department of Transportation

Water supply utilities

Relevant local to international scale NGOs (e.g., working on issues related to urban forestry, open space, conservation)

Land owners, easements, large private estates



Scientific and knowledge-sharing collaborators

Horticultural and arborist associations

Academic researchers and institutions

Native plant societies, NGOs


Volunteer collaborators


High schools, universities

Vocational schools


Outdoor education programs, opportunity providing programs


Educational outreach collaborators

Primary schools through university, education programs, general public


Financial partners


State and federal grantmaking agencies


Propogation collaborators


Volunteer acorn collectors

Backyard seedling growers

Where will these actions be taken?

Initially we will focus on California, within the area of the California Floristic Province.  Adoption by implementation partners worldwide can result in application of the Corridors model globally.

What are other key benefits?

Beyond maintaining biodiversity in light of climate change, other key benefits include: enhancing biodiversity within the urban environment, carbon sequestration, air pollution mitigation, improved human well-being (physical and psychological), human-environment connection, and educational opportunities for learning about natural systems and biodiversity.

What are the proposal’s costs?

The financial costs of the prototype project are minimized by involving a large network of collaborators throughout the process. We propose a suite of planting strategies, from inexpensive but effective direct-seeding to the planting of larger trees.

A rough rule of thumb for a low-cost tree planting in California is that it will cost $100 per tree to plant with basic protection devices, and $100 to maintain until establishment. Suppose a minimally effective corridor system consists of 1 million planted trees. This suggests a corridor system cost of $200 million, implemented through standard commercial practice.

However, the costs of this proposal are intended to be spread among many collaborators, thus the financial impact on any particularly entity is minimized. A key strategy to facilitate implementation is to piggyback on tree planting grants, already being distributed within potential corridor areas.

Additionally, there are many financial levels on which entities can participate. On the inexpensive end, planting locally-collected acorns with simple but effective protective devices, proper technique and appropriate timing, is inexpensive and can be quite successful. Motivated volunteers can further diminish costs. At the other end, a well-funded, perhaps corporate, participant might want to begin with larger plants to increase initial planting impact. Over the long term, plants grown from seed or small nursery stock will catch up with plants which were much larger at planting, often in 10 years or less.

Since successful tree establishment depends on early water availability, irrigation systems can greatly aid establishment and growth rate. Yet irrigation systems are costly to install, and may be unnecessary for simple, low-cost plantings.  Smaller initial planting stock requires less water, so provided the selected species are an excellent match for the local climate, simple watering methods, such distribution by volunteers via water trucks, should be sufficient. 

Time line

Year 1:  Phase 1- Develop habitat suitability maps and propagation stock

Year 2: Phases 1 and 2- Continue to develop propagation stock, secure locations for prototype corridors, build public and private collaborations

Year 3: Phase 3- Plant prototype corridors, work with volunteer groups, develop educational outreach efforts

Year 4: Continue to care for newly-established corridors and share knowledge on project.  Identify next regional/species focus for project, begin again from Phase 1.

Care for newly established trees will continue for approximately 5 years, and culminate in a post-implementation biodiversity survey for each site.  This is a cycle that can go on indefinitely, broadening and enriching the network of corridors.

Related proposals


1.    Loarie SR, Duffy PB, Hamilton H, Asner GP, Field CB, Ackerly DD. 2009. The velocity of climate change. Nature. 462: 1052-1055.

2.    Heller NE and Zavaleta ES. 2009. Biodiversity management in the face of climate change: A review of 22 years of recommendations. Biological conservation. 142: 14-32.

3.    Hodgson JA, Thomas CD, Wintle BA, Moilanen A. 2009.  Climate change, connectivity and conservation decision making: back to basics.  Journal of Applied Ecology. 46: 964-969.

4.    Conlisk E, Lawson D, Syphard AD, Franklin J, Flint L, Flint A, Regan HM. 2012. The roles of dispersal, fecundity, and predation in the population persistence of an oak (Quercus engelmannii) under global change. PLoS ONE. 7(5):e36391.

5.    IPCC, 2013. Climate Change 2013: The Physical Science Basis. Contribution of Working Group 1 to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker TF, Qin D, Plattner GK, Tignor M, Allen SK, Boschung J, Nauels A, Xia Y, Bex V, and Midgley PM (eds.)]. Cambridge University Press, Cambridge, UK. 1535 pp.