How to Use Satellites to Find Growing Plants: A Practical and Theoretical Guide

USGS Maximum consecutive dry days, July 2024

Introduction

Knowing where and when plants are green and growing would help botanists and ecologists plan field work and help managers make real-time land management decisions.  There are many potential sources of geospatial data available but it is difficult to know which sources are most useful.

Over the past year I evaluated the accuracy and interpretability of dozens of indicators that could be used to assess current growing conditions.  These websites, maps, and data layers are mainly provided by US Government agencies to help managers respond to natural resource concerns such as rangeland management and drought impacts.

In my opinion, none of the available resources is a perfect fit to find growing plants.  However, understanding how plant growth is related to biophysical constraints can help identify the best available resources.

Plant Growth Theory

Plant growth (Net Primary Productivity, NPP), is proportional to total soil moisture (SM) and Growing Degree Days (GDD) of accumulated Temperature (T) since the start of that plant's growing season.  Soil moisture depends upon accumulated (total and frequency of ) precipitation (P) minus evapotranspiration (ET).  

 NPP = Sum (SM*T)

 SM = Sum (P-ET)

[In the above equations, "equals" is used to mean proportional, or depends upon. ]

The ideal resource for plant growth would be a direct measurement of NPP.  A second option would be measurement of soil moisture and temperature, with a way of combining them to estimate NPP.  A third option would be measurement of precipitation, which could be used to estimate SM. All of these variables can be measured via satellite, but delays make them difficult to use in real time.  Also, there are important details in how they are measured and modelled that make interpretation difficult.  

Details

Plant Growth: satellites can measure NPP via NDVI (Normalized Difference Vegetation Index), but available sources are delayed (DroughtView), low-resolution (GIMMS), weighted toward trees, and contain artefacts early in the growing season.  Existing models of NPP are not well-calibrated (VegDRI), or delayed and not mapped (RAP).

Soil Moisture: satellites can measure SM, but satellite data (SMAP) is not consistently available, may be inaccurate, and only provides a snapshot, not the sum.  Models of SM are not well-calibrated (NASA LIS).

Temperature: sensor networks can measure T and calculate Growing Degree Days (NPN) but aspect and micro variation are often more important than county-level temperatures.  This is helpful early in the growing season.  

Precipitation: radar and rain gauge networks can measure P and are timely and accurate.  Maps of accumulated P are available from NOAA and number of days with/without rain in the last month from USGS.  However, because P is not a direct measure of NPP, this can only be a general guide to plant growth.  

Conclusions

P - Best. Note that both total and frequency matter.

SM - not available.

T - GDD is helpful in Spring phenology, but don't matter later in the season.

NPP - difficult to use.  Good for viewing thinning and forest fires, not very helpful for spotting wildflower growth or distinguishing between grass and tree green-up.  

NOAA precipitation accumulation as percent of normal for July, 2024

Practical How-To

I recommend using a balance-of-evidence approach that combines the two best sources of precipitation information, NOAA for total accumulation, and USGS for frequency.  If both sources show good precipitation during the recent growing season, there is a good chance that plants are growing well in response to abundant and regular moisture. 

NOAA's National Water Prediction Service provides accumulated precipitation over any time period from 2005-present with less than 24 hour delay.  Their web viewer is currently the only way I know to view this data because I don't have the programming skills to use their API.  

Scroll down to Precipitation Estimate, where it is possible to set the time period of interest and map Precipitation in terms of Observed (totals), Normal (average), Departure from Normal (inches more/less than normal), and Percent of Normal.  The map is sometimes glitchy depending on connection speed.  More details about how precipitation is calculated are available in the help guide.  Note that this map is usually up to date for the previous "water day" ending in the early morning (so for AZ, selecting "Today" shows precipitation that occurred yesterday through 7 am today).

USGS's Drought Monitor provides access to several precipitation metrics, with a 48 hour delay. To assess precipitation frequency/regularity, I use Maximum Consecutive Dry Days (Past 30 days) and Days Since Precipitation.  They also offer total accumulated precipitation over the last 7 and 30 days (again, with a 2 day delay).  Their web-viewer is clunky and hard to use, but it is easily available.  Double click on the Dataset of interest in the left pane and resize the resulting window to view the area of interest.  The layers have no opacity, so to view the underlying map they have to be checked on/off in the Layers pane.  

They also make their data available as WMS that can be added to any ArcGIS desktop or online map.  The opacity can be adjusted on the Group layer that is created after the data is mapped.  However, the time-enabled settings can be difficult to use, and I haven't figured out how to show the data time period.  The web viewer is easier to change the time period and to see the data date range.

Note that USGS Drought Monitor also provides VegDRI and QuickDRI, two models that claim to incorporate all of the biophysical variables listed above (and then some!) to model NDVI difference from average.  These models are extremely complex, but they don't seem well-calibrated to Arizona because I have not found them to be very accurate or helpful.  

Joshua Trees Flower Episodically in Arizona

Intro

Joshua trees are large, visually-striking trees in the Mojave desert.  Most of them are in California and Nevada, but there is also a population in the western part of Arizona.  They are frequently photographed and there are more than 17,000 observations (1,000 in AZ) saved on iNaturalist, a website and app used to document biodiversity.  

Arizona Joshua Tree locations observed on iNaturalistiNaturalist.

Joshua trees produce showy clusters of white flowers at the tips of their branches in March, but this year I noticed they were not flowering.  I wondered how often they produce flowers and decided to answer this question using data from iNat.

53 observations in Arizona showed evidence of flowering, always in March and April.  

Methods

iNat observations of Joshua Trees (Yucca brevifolia) in Arizona were marked using the Plant Phenology option in the Annotation Field.  Plant phenology (flower budding, flowering, or fruiting) was determined based on visual inspection of the saved photos in iNat.

The iNat website has a nice phenology visualization tool.  This view is filtered to show only Arizona observations.  However, it cannot show differences in phenology from one year to the next.  

Observations were then filtered on the iNat Explore page by adding &term_id=12&term_value_id=13 to the URL and downloaded for analysis in Excel.

More info about using iNat search URLs.

Results

I graphed the results starting in 2017, because there are fewer iNat observations before 2017.  It appears Joshua Trees flower episodically.  According to this data, Joshua Trees flowered in four out of the last 7 years.  They appear to alternate years from 2017-2020, but then skipped 2021 and flowered in both 2022 and 2023.  

It is interesting to note that the Arizona Joshua Trees didn't flower in 2020, which was one of the wettest springs in the last 10 years. I wonder whether the spring moisture determines flowering, or if perhaps other climate variables, such as moisture in the fall, are more important.  Another possibility could be that the trees are only able to flower every other year, and that the trees were inhibited from flowering in 2020 because of the large number that flowered in 2019.  

According to this data they were able to flower in both 2022 and 2023, but at reduced numbers both years.  Perhaps the plants flowering in 2023 were different from the trees that had already flowered in 2022?  I can't answer that question with this iNat data.  While it appears that the areas of flowering in 2022 and 2023 were the same, not all of the Joshua trees in a given area necessarily flower, even in good years...

Spring Update: NDVI Differences

Last September, I wrote about Finding the Greenest Place in AZ.  This Spring, we have continued to compare and evaluate the different NDVI difference mapping applications and compare them to the actual growth of wildflowers and grasses we see when we go out hiking.  

Methods

I conduct pre-field research to identify predicted greenness/moisture from UA's Droughtview, USGS VegDRI, and NWS Accumulated Precipitation.  I take a screenshot of each product and assign the proposed site a scale from 1 (driest) to 10 (greenest).  We then visit the area and evaluate the plant production, recording example photos of overall landscape greenness, as well as assigning a score.  The data are organized in a OneNote table.  I then compare the numerical scores in an excel table, adding up the differences between each model and the observations.  

Results

So far, the UA model seems to slightly overestimate greenness, the USGS model greatly underestimates greenness, and the NWS precipitation record comes out closest to observation.

For the UA model, I think it might be helpful to have a difference from maximum, instead of the difference from period. The latter overestimates early spring greenness when the denominator NDVI is very small, so any amount of NDVI in the numerator saturates the index.  Using the maximum NDVI for that pixel could help with this phenology issue.  Plus, % of maximum NDVI may be more intuitive than “difference from average”.

The USGS VegDRI index consistently estimates pre-drought to severe drought in areas that have above average precipitation this water year and have an NDVI above average.  This leads me to think that VegDRI 7-Day eVIIRS is either not well calibrated to the desert southwest, or perhaps that it is better used as a predictive index – perhaps these areas are drying out even though they currently appear green?  However, SWCC does not show significant vegetation drying yet in the areas I assessed.  

Examples

Wingfield Mesa:  UA Droughtview shows this area at maximum NDVI (for this time of year)(=10/10), USGS showed it as pre-drought to moderate drought (4/10) , and NWS shows 125-200% of normal year to date precipitation (9/10).  It is quite green, but it is still early in the growing season and the mesquite have not leafed out yet.  We rated it 6 out of 10.  

Dugas Rd:  UA shows above average (8/10), while USGS showed Moderate drought (3.5/10) and NWS showed slightly below average precipitation (75-90%) (3.5/10).  It is quite green right now, but again not quite at maximum greenness production.  We rated it 8 out of 10.   

Rare Plants and High Quality Ecosystems Mapped in Washington State

 The new HDMS mapper from WNHP shows rare plants as well as Ecological Integrity Assessments (EIAs) for a wide range of ecosystems.

For example, here are the rare plant areas East of Renton:

And here are the natural ecosystems with an "A" rating:

Plant-Pollinator Interactions in Yavapai County, AZ

 Introduction

Pollinators visit plants seeking nectar and/or pollen. Pollinators include insects (e.g. butterflies, moths, beetles, bees, wasps, flies), bats, and birds. In any geographic region, native and non-native pollinators visit native and non-native plants.

Pollinators may be specialists and/or generalists who visit plants for different reasons. For example, some pollinators specialize on the pollen of certain plant species such that they visit only certain plants to harvest pollen from them. These pollen-seeking specialists may be nectar-seeking generalists to the extent that they indiscriminately harvest nectar from any plant species.

Pollinator-plant interactions are a subject of ongoing study. In North America alone there are more than 3,600 bee species. Ecologists document pollinator-plant interactions to understand which pollinators visit which plant species and why.

Methods

We use iNaturalist—a citizen science computer application—to document our observations of pollinators and plants in the places we visit. We have five years of non-systematic observation data from Yavapai County, AZ that we use for our analysis. We looked at which plant species are most frequently visited by pollinators across different taxa. This will help us better understand which local plant species are popular amongst pollinators.

We annotated five years of pollinator observation records from Yavapai County, AZ with the scientific name of the plant species each pollinator is visiting. Our database includes a total of 265 distinct counts of pollinator-plant interactions (note this is different from the number of observations).

Here is a link to our current plant-pollinator interactions in iNat.

There are some notable issues that exist with our data:

·        We did not systematically collect the data. We did not employ ecological sampling methods, we did not sample data at regular intervals of time, and we did not take measures to ensure we systematically sought observations of pollinators across distinct plant taxa in unbiased ways. Therefore, our dataset contains bias.

·        We are analyzing our dataset for fun. Since the data contain unintentional bias, we do not intend for the results of our analysis to be reliable for landscape or species management decisions.

·        Our data contain blank fields (unknowns) at the level of insect taxon family, genus, and species. Because we cannot fill in the blanks with reliable data, we conduct our analysis at the level of insect taxon (e.g. insect family, genus, or species).

·        Our database’s plant records contain plant taxa information at the level of genus and species.

See this post for more thoughts on the limitations of this type of analysis.

Total insect taxa associated with plant genera

 

Count of distinct insect taxa associated with the top ten plant genera by month

This graph reflects the top ten plant genera ranked according to the counts of distinct insect taxa associated with them. In our database, we have data for many more plant genera than those shown.

The top ten plant genera include Asclepias, Baccharis, Ceanothus, Cirsium, Dalea, Ericameria, Helianthus, Hymenothrix, Machaeranthera, and Opuntia. 

There may be more associations between distinct insect taxa and plant genera during the summer months of June, July, and August but they are not reflected in this graph because we didn’t observe them due to extreme heat and/or monsoon rains.

This project and data analysis were a collaboration between Conor Flynn and Alexandra Permar.  

Biodiversity on Prescott National Forest

 How many plant species are there in a geographic area?  Previously, I used iNaturalist to calculate total biodiversity for selected areas.  But this method is just a snapshot of the species currently recorded in iNaturalist.  In some areas, people may have already observed most of the biodiversity, while in other areas there may still be much more to discover.

One way to estimate the total unobserved biodiversity of a geographic area is to look at the timeline of species observations.  If more new species are being observed each year, there are likely still many more species to discover, whereas if the number of new species each year is declining, we may be able to fit a decay function that would predict the total number of species that will ever be observed.

iNaturalist offers a couple of ways to find lists of new species.  As an example, I will use the Prescott National Forest in AZ.

The first method: the API function recent_taxa.

According to this method, there have been 57* new plant species observed on the Prescott National Forest in iNat so far this year.  This is filtered for only research grade observations (quality_grade=research).  There are a lot of new observations by experts that just haven’t been confirmed by other experts. *For some reason this returns the species, genus, and family so to get 57 I subtracted repeated taxa (29) from total new taxa this year (86).

https://jumear.github.io/stirfry/iNatAPIv1_identifications_recent_taxa.html?place_id=130970&taxon_id=47126&hrank=species&order=desc&order_by=created_at&per_page=200&quality_grade=research

The URL code is pretty easy to modify for other places (PNF = 130970) and other taxa (plants = 47126).  Here is more background on API query terms: https://api.inaturalist.org/v1/docs/#!/Identifications/get_identifications_recent_taxa

The second method: download data.

 When searching observations for Prescott National Forest and filtering by plants, iNaturalist returns a page with summary statistics.   This can be downloaded and analyzed in Excel.

https://www.inaturalist.org/observations?place_id=130970&iconic_taxa=Plantae 

 After downloading the data:

1. sort the table from oldest to newest by the observation date column

2. select the whole table

3. use “remove duplicates”, and look for duplicates in only the species name column

The resulting list will show you the first observation of each species.  I then summarized the list by year and created this graph showing the year and number of new plant species recorded in iNaturalist for PNF.  

This method also sometimes returns other taxa than species, so the totals don't quite match between the website, the API, and this method.  Also, this graph is not filtered for only Research Grade observations, but it would look basically the same.  The graph appears to increase over time as more people use iNaturalist to record plant species on Prescott National Forest, up to a peak year in 2020.  Since then the number of new species seems to fall off, although it should be noted that 2021 was a drought year and 2022 isn't over yet.  

Where is most biodiverse?

 iNaturalist can be used to compare biodiversity in different locations.  

To do this, it is important to allow for different search effort in different areas: for example, a search of the middle of the Amazon might not return many species, not because there aren't many, but because people haven't observed them.

For the U.S., we will assume that search effort is at least somewhat comparable.  We will also look at total observations and divide them by total species to get some idea of the effort required to document a new species in that area.

We decided to investigate my home town in Washington State, Alexandra's home town in Ohio, one of our favorite places: Maui, and our current home in Arizona.

Port Orchard, WA

A 100 km search radius includes most of Puget Sound, the Olympic mountains, and Seattle.

Dublin, OH

A 100 km search radius includes most of central Ohio creeks, woodlands, agricultural lands, and all of Columbus OH.

Prescott, AZ

A 100 km search radius includes canyons and mountains between Flagstaff and Phoenix.

Maui, HI

A 100 km search radius includes all of Maui as well as ocean channels and nearby islands.

Summary Table

According to this analysis, Washington is most biodiverse, followed by Ohio, then Arizona, and in last place is the island paradise of Maui.  

Island biogeography teaches that islands, although unique for their level of endemic plants and animals, should be deficient in overall biodiversity if there hasn't been enough time for biodiverse taxa to colonize or evolve on the island.  This seems to be the case with Maui, which is especially depauperate in insects, given its tropical location.

Arizona, despite its diverse environments, is significantly lacking in Fungal diversity, which could be due to the arid climate.

The American Midwest, with its perfect seasonal growing climate, is remarkably biodiverse, and would probably surpass Washington if this search had included a more varied part of the Midwest with more mountains and/or rivers and lakes.

Washington tops the list as most biodiverse, probably because of the presence of diverse environments, with everything from alpine mountain tops to ocean kelp forests, and everything in between.  This is despite the lower number of insect species compared to a lower latitude place like Ohio.

A caveat to this entire analysis is revealed by the Total Observations in each area and the resulting Observations per Species.  While I had assumed that search effort would be equivalent across the US, it is evident that many more people are using iNaturalist around major cities like Seattle and Columbus.  Arizona is more sparsely populated and has many less observations, and Maui, despite the huge numbers of tourists, is even less populated.  This means that is only takes 20 or 27 new observations (on average) to observe a new species in Maui and Arizona, respectively, while it takes 47 or 72 new observations in Ohio and Washington, respectively, to observe a new species.  So even though Washington has the most observed biodiversity in iNaturalist, it may be easier to find new, previously-unobserved biodiversity in Maui or Arizona.

Bear's Ears Research on Legacy Human Plant Communities

The research is quite interesting. They have determined that a large suite of plants used by people in the past are more likely to be found in the vicinity of archaeological sites on Bear’s Ears NM. Basically people were planting medicinal and other useful plants, and those plant communities have persisted at these locations in greater numbers to modern times. We see similar things here in Arizona with agaves, yucca, devil’s claw, and a few other plants. In AZ the phenomenon is sometimes referred to as “Legacies on the Landscape.”

https://www.pnas.org/content/118/21/e2025047118

But looking through the Supplemental table for the paper, they basically included every species that grows up there.  Not surprisingly, native peoples utilized most of the naturally-occurring botanical resources on the landscape.   So their results are really more that cultural sites are associated with biodiversity in general, not specific assemblages of “cultural” species.  

Also, the paper implies that the causality goes native people>plant diversity, but it could just as easily go plant diversity>native peoples, since native people would be more likely to settle in places with more plant diversity (e.g. places with water).

I would be more interested in a paired-down list of the plant species that are truly cultivated and remain associated with prehistoric sites.  For AZ, agave, yucca, devil’s claw, and a few other plants.  Definitely Wolfberry (Lycium pallidum).  They list Wild Potato, Solanum jamesii, which is interesting and does occur in AZ above the rim…..they also list Chenopodium sp, which is a common weed so I’m not convinced that is a good marker of anything.

Chenopodium are usually ubiquitous in pollen and macrobotanical samples taken from archaeological contexts. The typical interpretation is that these plants were used way more than we think. Hard to know whether weedy plants were being intentionally planted or if they started growing more in areas where people were eating, processing, and depositing seeds through their waste. There are a few Chenopodium species that were domesticated prehistorically. In the western US these are amaranths, goosefoot in the eastern US, quinoa in South America, etc.

Predicting Plant Phenology

Plants in the Southwestern deserts respond to water availability and temperature:

Map from AHPS Precipitation Analysis from January and February

NM is doing good on water so far this year!

Growing degree day map from PNWPest.org

On average NM is about 6 growind degree days (GDD) behind 2014, but 11 days ahead of 2013 and 6 days ahead of normal.

Thistles in NM

I've compiled a list of common Cirsium species in the lowlands (not mountains) of Southern New Mexico, and mapped their collectioned vouchers from across NM.

Map created using swbiodiversity.org 

Cirsium ochrocentrum – common.  Flower heads are bigger, and petals are longer than C. neomexicanum, often more brilliantly-colored, but plant is smaller.  Flowers usually taller than wide. 

Cirsium neomexicanum  -- Flower head looks more “bushy” because spines are more strongly spreading than on C. ochrocentrum, allowing flower to open more (wider than tall)

Cirsium texanum  - like C. ochrocentrum, but flower heads less than 25mm long, smaller overall.

-Based on Allred's Flora Neomexicana

Antinutrient Resources

In general, plant secondary metabolites can have positive and negative effects (Weston A. Price). The reason I don't try to categorically avoid them, but treat them with caution, is that these effects are multiplicitious and biological: very hard to predict what they will do, good or bad...

However, unless we know about the problems with antinutrients, we won't know why eating raw flour or dough is dangerous, why green potatoes are toxic, or how many raw red kidney beans it takes to kill a man (not very many).

But on the whole, unless you are allergic, most antinutrients will be digested, and some are actually good for you. For example, this article mentions that inositol hexaphosphate is a break-down product of phytic acid. Most phytic acid is broken down by digestion, and there is evidence that it can have beneficial effects as well as deleterious effects.

This article points out that most sweet potato antinutrients are destroyed by baking, as opposed to boiling. This FAO article on all the major food crops and their antinutrients specifies that " Heating to 90°C for several minutes inactivates trypsin inhibitors", which explains why baked sweet potatoes are nontoxic. (But the article also points out that diseased or moldy sweet potatoes may have toxins that are not completely deactivated by cooking ....moldy vegetables should not be consumed. Apparently, toxins in normal potatoes are also not destroyed by normal cooking methods. Furthermore, sweet potatoes do not have lectins, but normal potatoes do. These compounds can have some antidigestive effects, but most should be destroyed by cooking.

Antinutrients are important, but I think methionine and nutrient density / glycemic index considerations are more important overall. A few potatoes or slices of bread shouldn't hurt most people, but if you have the luxury of chooses less toxic plant products, sweet potatoes and especially squash and pumpkins are some of the best sources of nutrients, with the least amount of antinutrients.

Suburban Development Transect: Biodiverse Desert to Trash-filled Parking Lot

2000

2003

2008

2011

A transect walking a few miles from the indisturbed desert through new housing developments into the city looks like time played in fast-motion.  The ecologist's glasses allow us to see the moving picture of life rather than limiting our vision to the usual single frame.  By substituting space-for-time, we can put on time-travel goggles.  What do we see?

Normally we visit a site for a day, maybe once a year for intensive longitudinal studies, maybe never again.  With this transect we could see the changes in species composition from unique, biodiverse desert with its gnarled shrubs to fresh asphalt streets, planted landscaping and lawns, and a monoculture of weeds in the bladed 'empty patches' between houses and in right-of-ways.  The stream channels were all filled in and replaced with impoundments or concrete-lined ditches.

Eventually we ended up in the back lot behind a storage unit complex.  The slight depression there caught water and supported some of the tallest native flowering trees we'd seen.  The lot was also used, apparently, as a dumping ground and was filled with all kinds of trash.

Later that night, back in my home neighborhood, I saw dual-images of what the land looked like before and after development.  I saw the rocky ground thick with idiosyncratic cacti and weird four O'clock flowers.  And I saw wide asphalt streets, joggers, tall pine trees, oleander, and grass lawns.  It is so difficult to see the past, I felt that my dual-vision was a kind of X-ray superpower, a new found ability to see through reality to what might have been.  Reality has a way of erasing the possibility that things could have turned out differently.

A nice walk in the wilderness can sometimes substitute space for space, so that you can see your neighborhood space as the absence of native wildlife instead of the presence of cars, roads, and lawns.  I suppose some people see nature as empty, and even I see it this way sometimes too: some areas are devoid of active communal life.  For example, on this particular transect we saw no rabbits, no ground squirrels, and no other mammals in the wild.  I don't think we saw a lizard until we got to the rock walls of suburbia.  But I was amazed at the botanical emptiness of our developed landscapes: out of the more than 70 native species of wildflowers and Chihuahan desert shrubs, I saw less than 5 after we crossed the first freshly paved asphalt road.

Of course, there are a diverse mix of landscaping plants, many of them native somewhere, if not in the Chihuahan desert.  Interestingly, the mexican palo verde seems to have escaped cultivation and is now growing up into the wild watercourses that snake off the mountains.  Few other weeds seem able to invade intact ecosystems, although Russian thistle is omnipresent wherever the ground has been cleared.

I think, though, that if the transect had continued further into the past/future, through abandoned neighborhoods or restored areas, the native wildflowers and shrubs would reappear.  Especially with the rains this monsoon, they seem quite happy where they are, and old pipelines have a nice covering of desert marigold, creosote, and javalena bush.  I don't really feel that the desert is destroyed by development...maybe in the long-term view it just goes away for awhile, or changes shape for a spell.  Until the wave of bulldozers breaks and subsides, the desert remains as potential...

Herbaceous Vegetation in Southwestern Pine Forests

Herbaceous forage in southwestern pine forests can be few and far between.  Especially in unnaturally-overgrown thickets, there is simply not enough light and too much acidic leaf needle litter to grow robust grasses and forbs.  The high carbon content and resistant nature of conifer bark and needles means that few nutrients are available to growing plants.  

Even when forest thinning restores natural stand densities, the recalcitrant accumulated biomass often seems to limit production.  There is simply too much carbon and it is clogging up microbial turnover of nutrients.  Sure, you'll find plenty of aboveground mushrooms and mycelial hypahe at work in the soil, but I have to wonder if there isn't a more productive alternate-stable state.

What is the limiting resource?  I've theorized that light may still be limiting when forests aren't thinned enough to create light gaps in the canopy.  But it also seems that the overabundance of carbon may be soaking up nitrogen.  In these nutrient-poor systems we typically find 'tolerator' species like sedges, that can eke out a frugal living in acidic conditions.

What about blueberries?  In some parts of the world, conifers and blueberries go together like apples and pie, but in many of the southwestern mountain ranges we have no native Vaccinium.  I'm still not sure why, except that they seem to prefer colder (moister?) climes than New Mexico can provide....

There are two species of Vaccinium in the southwest, with Vaccinium myrtillus much more common.  However, south of Santa Fe even this species only occurs at scattered locations in mixed conifer and subalpine forests.  These high-elevation forests are being rapidly lost to stand-replacing forest fires.  Even with current climate change, it is unlikely that extensive tracts of cooler forests will be able to regrow.

What about legumes?  Fabaceae are often able to supply their own nitrogen requirements and eventually supplement total ecosystem N.  But I'm surprised by how rarely I find good legumes in the forest.  Thermopsis is surprisingly rare, as are Lotus and I almost never find clovers growing in conifer needle duff.  

Robinia neomexicana seems to be one legume shrub that has found its way into a diversity of habitats, growing almost like a weedy in mountainous areas throughout the southwest.  

Seeding mixtures in forests typically use annual grasses, but I wonder if there isn't a Fabaceae that could dramatically enhance production to increase ground-cover, forage, pollinator, and wildlife habitat?  Should standard thin-and-chip treatments be supplemented with seeding efforts?

What about increasing disturbance to disrupt pine duff accumulation?  These thick, undecomposed layers and inhibit germination of many forbs...

Four of my Favorite Characteristic New Mexico Shrubs

Chilopsis linearis, Desert Willow.  In landscaping, this large-flowered shrub will flower for almost half the year.  It is a dependable riparian tree that can survive in washes that are too hot and dry for cottonwood.

Forestiera pubescens.  New Mexico Privet.  Native shrub in the Olive family can form thickets at the base of canyon walls and along upper benches above rivers.  Birds prize the berries almost as much as the non-native Russian Olive.

Lycium pallidum.  Pale Wolfberry.  Lyciums are widespread in the Southwestern deserts, and Lycium pallidum is the most widespread.  Goji berries are Lycium barbarum (nonnative), and Lycium pallidum has been cultivated for its fruit for 1,000s of years.  The trumpet-shaped flowers attract Sphyngid Hawkmoths and Hummingbirds.  

Robinia neomexicana.  New Mexico Robinia, Fabaceae.  Despite its rapacious thorns, this plant made my list for its tenacity and abundance across a range of habitats.  From riparian area in the South to Ponderosa hillsides in the North, Robinia provides abundant pink blossoms and herbaceous cover. 

Are Invasive Species Evil?

Mark Davis argues against seeing invasive species as evil aliens.

In his talk today, "Invasion Biology, the Science and the Ideology" Davis lambasted a prominent paper on Garlic Mustard invasion, Ready or Not, Garlic Mustard Is Moving In: Alliaria petiolata as a Member of Eastern North American Forests. 2008. Vikki L. Rodgers, Kristina A. Stinson, Adrien C. Finzi. Bioscience. He looked up a half dozen of their key citations and showed how the original papers did not support or even directly contradicted, the claims in this prominent paper. Davis argues, persuasively, that ecologists have been too quick to lay blame on invasive plants.

He wrote a paper in 2011, Don't judge species on their origins. 2011 Nature. Mark A. Davis, et al. arguing conservationists should assess organisms on environmental impact rather than on whether they are natives. Are invasive species drivers, or passengers of species loss. They may be beneficiaries rather than agents of change. Eventually, intraspecific competition triumphs over interspecific competition as invasive species run up against resource limitations. Over time, invasive species advantages may erode as other species learn to use them as resources, too. Negative soil feedbacks accumulate over time for non-native plant species. Ecology Letters. Jeffrey M. Diez, Ian Dickie, et al.