Colorado landscapes range from high plains to alpine forests. In both urban and wildland settings, trees are essential for shade, carbon storage, wildlife habitat, and scenic value. One of the most underused strategies to support tree health and resilience in Colorado is establishing and maintaining a diverse native shrub understory. This article explains the ecological and practical benefits of native shrubs under trees, offers species- and site-specific guidance, and provides concrete steps landowners, land managers, and urban foresters can apply today.
Native shrubs interact with trees in multiple beneficial ways. When planned intentionally, shrub layers improve soil, microclimate, and wildlife habitat, and they can reduce management needs while increasing landscape resilience.
Many native shrubs form symbiotic relationships with mycorrhizal fungi and host soil microbes adapted to Colorado soils. These fungal networks increase nutrient uptake for shrubs and nearby trees by extending root reach for phosphorus and micronutrients. Shrubs add organic matter via fine root turnover and leaf litter, improving soil aggregation and water infiltration over time. In rocky, low-organic soils typical of foothills and montane zones, this carbon input from shrubs can be pivotal for young trees.
Shrub canopies and branching patterns intercept snowfall, creating drifts at the base of shrubs and trees. This captured snow melts more slowly and infiltrates near roots rather than running off, which is especially valuable on slopes and in dry years. Some native shrubs also hydraulically lift water at night from deeper soil layers to shallower roots, indirectly benefiting neighboring shallow-rooted tree seedlings. Together, these processes improve soil moisture availability through the growing season.
Shrub understories multiply the structural complexity of a site, supporting a wider array of insects, birds, small mammals, and pollinators. Flowering native shrubs such as serviceberry, chokecherry, and snowberry offer nectar and pollen resources in early spring when trees may not yet be in bloom. Fruit-bearing shrubs provide summer and fall food sources for birds and mammals, increasing seed dispersal and natural regeneration. For many ground-nesting and shrub-nesting bird species, a dense native understory is essential.
Shrub layers moderate wind at the ground and reduce evaporative demand on tree seedlings and roots. In urban heat island contexts, a shrub understory can lower soil and lower-canopy temperatures and reduce irrigation requirements by shading bare soil. For high-elevation plantings, shrubs can reduce frost desiccation for sensitive tree seedlings by creating a more stable, sheltered microenvironment.
Intentional design and management ensure shrubs benefit rather than compete with trees. The following sections describe site-appropriate species choices, planting techniques, spacing and pruning guidelines, and how to integrate shrubs into wildfire resilient landscapes.
Select shrubs that are native to the specific Colorado ecoregion, adapted to local elevation, precipitation, soils, and disturbance regimes. Examples by general zone:
Choose species that match moisture availability. Riparian corridors tolerate dense shrub plantings; xeric slopes require widely spaced, drought-tolerant species. Favor palatable or thornless choices in areas with high deer or elk browse, or plan for protective measures.
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Shrubs can both compete with and protect trees. To maximize benefits and minimize downsides, follow these practical rules:
Different contexts require different approaches. The following recommendations are practical and evidence-based for urban, suburban, rural, and wildland-urban interface settings.
In urban settings, replacing lawn with native shrub understories beneath and around trees reduces irrigation needs and mowing, increases biodiversity, and improves aesthetics. Use layered plantings (groundcovers, low shrubs, and medium shrubs) to create visual interest while ensuring tree trunks remain clear of vegetation for at least the first 2-3 feet to prevent moisture and pest problems. Group shrubs into clumps rather than uniform hedges to mimic natural patterns and improve wildlife value.
On restoration sites and steeper slopes, prioritize shrubs with strong root systems for erosion control (willows, snowberry), and those that fix or conserve nitrogen where soils are depleted (ceanothus can increase soil nitrogen in some contexts). Use native seed mixes and container or bareroot plants spaced to allow natural infill. Incorporate shrubs early in revegetation to encourage mycorrhizal development and to provide nurse-plant effects for tree seedlings.
Track shrub and tree performance annually for the first 3-5 years with these metrics:
Adjust plant species, spacing, or management actions based on monitoring. For example, if shrubs outcompete tree seedlings, increase spacing or reduce watering frequency to favor deeper-rooted trees. If wildlife browse is heavy, install temporary protection and plan for less browse-susceptible species during replanting.
Native shrub understories are not an optional add-on but a powerful, multi-benefit strategy for sustaining Colorado trees across landscapes. They build healthier soils, conserve water, support wildlife, and create more resilient forests and urban green spaces. With thoughtful species selection, placement, and maintenance, landowners and managers can leverage native shrubs to reduce inputs, increase ecological value, and protect trees from the stresses of drought, erosion, and changing climates. Start with a small pilot area, monitor results, and scale up successful configurations to transform tree care in Colorado into a more resilient, native-driven approach.