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1. Anthropogenic land‐use change alters the ecological communities in a landscape's remaining natural habitat. These matrix effects are understudied in rare species, which comprise a majority of biodiversity, contribute to ecosystem services, and are particularly vulnerable to population declines.

2. This study used bee species survey data from New Jersey forest fragments, in conjunction with an independent museum data set, to identify rare bee species and developed regularised regularised regression models of matrix effects on their richness and abundance.

3. By using a regularised modelling approach, this study explains 44.43% of variation in rare bee species richness between forest fragments and 27.27% of variation in their abundance (average adjustedR²).

4. The present study's results identified specific subcategories of urban land use in the surrounding 1000 m of forest fragments that explained patterns in rare bee species richness and abundance, providing insights into how to select forest fragments to conserve rare bees. Low priority should be given to fragments in close proximity to high‐ and medium‐density housing, which likely harms rare bees by increasing impervious surface cover. Low priority should also be given to fragments near golf courses and athletic fields; this study speculates that these land uses harm rare bees through mowing and pesticide application. Finally, high priority should be given to fragments composed of a larger proportion of mature forest, which likely provides a greater diversity of native floral resources. Altogether, this study's model results reveal the importance of matrix habitats for the biodiversity of rare species in forest fragments.

The importance of large reserves has been long maintained in the scientific literature, often leading to dismissal of the conservation potential of small reserves. However, over half the global protected‐area inventory is composed of protected areas that are <100 ha, and the median size of added protected area is decreasing. Studies of the conservation value of small reserves and fragments of natural area are relatively uncommon in the literature. We reviewed SCOPUS and WOK for studies on small reserve and fragment contributions to biodiversity conservation and ecosystem services, and fifty‐eight taxon‐specific studies were included in the review. Small reserves harbored substantial portions (upward of 50%) of regional species diversity for many taxa (birds, plants, amphibians, and small mammals) and even some endemic, specialist bird species. Unfortunately, small reserves and fragments almost always harbored more generalist and exotic species than large reserves. Community composition depended on habitat quality, surrounding land use (agricultural vs. urban), and reserve and fragment size, which presents opportunities for management and improvement. Small reserves also provided ecosystem services, such as pollination and biological pest control, and cultural services, such as recreation and improved human health. Limitations associated with small reserves, such as extinction debt and support of area‐sensitive species, necessitate a complement of larger reserves. However, we argue that small reserves can make viable and significant contributions to conservation goals directly as habitat and indirectly by increasing landscape connectivity and quality to the benefit of large reserves. To effectively conserve biodiversity for future generations in landscapes fragmented by human development, small reserves and fragments must be included in conservation planning.