Parkinsonia microphylla , yellow paloverde

This review summarizes information that was available in the scientific literature as of 2022 on the biology, ecology, and effects of fire on yellow paloverde in North America. Yellow paloverde is a multi-stemmed shrub or small tree that often grows to 6 m tall. It has thin, photosynthetic bark and small, drought-deciduous leaves. Yellow paloverde is native to the Sonoran Desert, where it occurs most often on bajadas, plains, and hillslopes. Although drought-tolerant, yellow paloverde typically requires winter and summer precipitation. Yellow paloverde is dominant in Sonoran desert scrub and is a nurse plant for several species including saguaro. Yellow paloverde regenerates primarily from seeds. Flower and seed production may be prolific in wet years and diminished or absent after dry winters. Many of its seeds are eaten by insects and granivorous rodents. However, seed-caching rodents also disperse seeds in small clusters, and seed caches that are forgotten or abandoned may germinate. Yellow paloverde has both dormant and nondormant seeds and may form a small, short-term seed bank. Seedlings emerge in pulses after rain and warm temperatures trigger germination; however, seedling establishment and survival are generally low. Although yellow paloverde sometimes sprouts from the root crown after top-kill from fire and/or drought, and has been observed sprouting from roots, yellow paloverde does not typically reproduce vegetatively. Yellow paloverde is easily damaged and often killed or top-killed by fire. Although yellow paloverde may resprout after top-kill or injury from fire, observations suggest that it is more likely to be killed. Postfire mortality rates often exceed 70% within the first few years. Because it is a weak sprouter, postfire recovery of yellow paloverde is largely dependent on establishment from seeds. Given that seed and seedling predation rates are high and seedling establishment and survival rates are low, yellow paloverde postfire seedling establishment is also likely to be low; however, information on its establishment after fire is limited and largely anecdotal. Historically, plant communities dominated by yellow paloverde did not have enough fine fuel to carry fire in most years. Patches of vegetation were separated by large areas of bare ground, and cover of annual and perennial herbs was sparse and discontinuous, except after one or more relatively wet years. Fuel and fire regime characteristics in contemporary Sonoran desert scrub communities have likely shifted outside the range of historical variation, primarily due to the introduction and spread of nonnative invasive grasses. Annual and perennial nonnative grasses have fueled many wildfires in yellow paloverde communities over the last several decades. These fires may lead to a vegetation type conversion on frequently or severely burned sites. Climate models suggest that the Sonoran Desert may become warmer and drier over the next century. Yellow paloverde may be highly vulnerable to regional effects of climate change, particularly in relation to summer moisture availability. Disruptions in the timing of moisture availability could result in a range shift. Climate variability and change may benefit invasive plant species that interfere with yellow paloverde establishment and persistence.