Welcome to the '22 Winter Issue of Urban Tree Talk. We wish you a festive, forestry season! Read on for the latest news, resources, and events.

-Arizona Department of Forestry and Fire Management

Using Data to Better Understand the Value of Access to Urban Trees for All

LoriAnne Barnett Warren, DFFM Urban Forestry Specialist

A recent study by G.H. Donovan et al (2022) explored the relationship between trees planted in urban areas and their association with a reduction in non-accidental and cardiovascular deaths in community members. Through the use of well-documented tree planting projects in Portland, Oregon over 30 years, census tract data, and community health data, the study’s authors were able to identify a relationship between trees and longer human lifespans. Having access to long-term data to tell a more complete story about the value of our urban trees is critical to developing communication strategies for community stakeholders. Armed with data, we can better demonstrate why planting trees should be prioritized, especially in marginalized communities. 

Read an article on the topic or reference the published study for more information.

Western Bark Beetle Initiative (WBBI) Grant Program

Aly McAlexander, DFFM Forest Health Specialist

Arizona Department of Forestry and Fire Management (DFFM) with funding provided by the USDA Forest Service solicit proposals annually to treat a minimum of 10 acres through the Western Bark Beetle Initiative Grant Program. The WBBI Grant Program’s main objectives are to create, restore and maintain healthy stands of trees, reduce bark beetle attacks and tree mortality, and protect high value trees and forests. The primary treatment of WBBI projects is the thinning and removal of green pine trees and related slash treatments. This reduction in stand density can improve tree health and reduce the likelihood of attacks from bark beetles. Grant funding is not for treatment of dried, dead, or other material as they are not suitable for bark beetle brood production.

At this time, DFFM has 4 ongoing WBBI projects around Arizona. One ongoing project is the Loma Sabino Pines HOA project on Mt. Lemmon, AZ. This project was awarded in February 2022, and the HOA went to work immediately. Ten months later, the HOA has completed thinning work on 50 acres of common areas. This is a great example of a successful WBBI project!

Before treatment (Left image): Plot is overcrowded with juvenile trees competing for space and resources.

After treatment (Right image): After thinning the stand, the trees left behind have increased access to water and nutrients, increasing their overall health and vigor. This increases their natural resistance to bark beetle infestation and wildfire. The same tree is marked in both photos for reference purposes only.

Invasive Plant Program: Winter Weed Watch

Willie Sommers, DFFM Invasive Plant Program Coordinator 

In the Sonoran Desert, winter weeds to watch for include several species of annual grasses and forbs. Here are a few common nonnative plant species with invasive characteristics that you can expect to see between December and March. Included are a couple images to help identify these species in their early stages, before they flower and develop seeds. However, we encourage you to utilize additional resources (such as the resources I shared in September) because as many of us know, identification can be difficult without an inflorescence present.

Annual Grasses

Watch out for the brome (Bromus) species – cheatgrass (B. tectorum) and red brome (B. rubens). While these brome species are not on the state noxious weed list, they often outcompete desert wildflowers for resources, and in the case of red brome and cheatgrass, can increase fine fuel loading and contribute to wildfires in arid desert environments. Pictured is red brome; as it matures the seed head turns from green to red to purplish.

Buffelgrass and fountain grass (both nonnative invasive perennials) can also get a start with the winter rains.

Invasive Forbs

One invasive forb that has garnered the most attention lately is stinknet (Oncosiphon piluliferum). Stinknet has quickly become prolific in Maricopa County, and has made its way to Pinal and Pima county as well. Fortunately, one doesn’t need to wait for stinknet to flower to identify it - the plant has a distinct (and some would say unpleasant) smell when the leaves are crushed. With the rains we had in early December, stinknet and other invasive forbs like Sahara mustard (Brassica tournefortii) and Malta star thistle (Centaurea melitensis) are set to initiate growth. Pictured here are stinknet (top), Sahara mustard (middle) and Malta star thistle (bottom) as rosettes, which is an early stage of growth when they are most vulnerable to control and removal. 

The importance of early detection and rapid response can be illustrated with this fact: a single Sahara mustard plant can produce up to 9,000 seeds!  So as you’re out and about this winter, what weeds will you be watching for?

Pictured forbs: Stinknet (top right), Saharan mustard (middle), and Malta star thistle (bottom) in rosette form.