Mast Year

We have an enormous Valley Oak (Quercus lobata) in our driveway garden. It’s in a very inconvenient place, right on the edge of the driveway, and because of that you’d think its growth would be compromised. Fully half of its root system is compacted by concrete and parked cars. This isn’t good for any tree, and definitely not for Valley Oaks, which usually grow in grasslands and oak woodlands. But this tree was planted many years ago by a squirrel and the previous owners of this house never pulled it out, so it’s grown into the space and is extremely healthy. Valley Oaks can also take some irrigation (they like wet crevices and canyons in the wild) and this one gets that, being surrounded by chosen landscaping. Every year I have my tree guy come out and look at it, and usually it just gets a trim every couple of years. This year, the tree guy was worried about its split trunk (this compromises the strength of the canopy), and so we will be installing cables to decrease the chances of a total split. But anyway, that’s not what I wanted to write about today. No, I wanted to write about the acorns.

We are having a mast year. A mast year is marked by a lot, and I mean a LOT, of acorns. All oaks mast, and in fact many plants mast, which just means they produce a lot of seed in any particular year. Sometimes ithis masting happens every year, sometimes every other year, sometimes two years in a row and then not again for 20 years, there is really no way to tell if it’s going to be a mast year. In the case of this particular Valley Oak, our last mast was three years ago, and frankly, I didn’t expect another one so soon. What makes it an especially interesting natural process is that no one really knows why masting happens.

This is how it looks every single morning - a new carpet every day.

Masting is a great mystery, but an even greater mystery is that all the trees of the species, within a very large geographical area, all mast at the same time. Thinking about that will really twist your noodle. How do they all know to do it at once? And why do they mast in the first place?

Well, there’s lots of theories, and they all make sense. One theory is that mast seeding is for predator satiation. When a population of plants produces seeds in unusual amounts, their predators will never be able to eat them all, leaving some to germinate and produce the next generation of plants. Another theory is about pollen coupling. This is a concern in the timing of flowering in pollinating species - the flowers need to sync with one another in order to cross pollinate. If all individuals in a population flower at the same time, more flowers will be pollinated, leading to increased seed production. But it’s expensive to make a lot of flowers, and plants have to have enough resources to do that. This explains why trees might mast following wet years - more water means more resources, means more flowers, means more seed. But some folks think that trees mast following drought years, as a ‘last gasp’ effort to produce offspring. Resource budgeting is another possible explanation. Plants need energy to produce seed, and they also need energy just for growing. Which do they concentrate on in any given year? In theory, if all plants in a large population are experiencing a similar amount of resources, they will either grow or flower similarly. Or maybe it’s about resource storage, and the trees are ‘saving’ resources for many years until they are ready to produce a great amount of seed. Environmental cues also result in hormonal responses in plants, so masting may have nothing to do with resources or pollination at all. Of course we also can’t leave out the possibility that the trees are ‘talking’ to each other, communicating through underground fungal networks. Other species have been shown to do this, so it’s no great leap to imagine that oaks do this too.

Whatever the reason (and maybe some things will just never be explained, and how lovely is that? that we can still be mystified by nature), what it means for me personally is lots of sweeping and shoveling into the green bin. During our last mast year, I left a lot of the acorns where they lay, and I’m still pulling out oak seedlings. One big Valley Oak is enough, thank you, so I’m collecting as many as I can this year.

Meanwhile, many times every evening, sitting on the couch watching TV, Tom and I jump when a particularly hefty acorn lands on the roof of the chicken coop, producing a loud BANG. I wonder if the chickens are sleeping at all.

The Sound of Chainsaws

The ongoing drought is starting to have quite an effect here in the Bay Area, and is especially evident in the Monterey Pines. Historically, these were planted with abandon all over the area, even though they really only do well near the coast. Driving down the highway, the brown, dead trees simply litter the embankments. The areas where we hike, even the reservoirs (where you’d assume the trees have stretched their roots to the water), are filled with struggling trees, mostly evergreen species.

The redwoods are starting to suffer, too. Again, they’ve been planted widely all over the inland areas, even though they are native to the coast and thrive on drippy, foggy conditions. The interior rarely gets fog.

And now we’re starting to notice the California live oaks, both coast live oaks and interior live oaks, are starting to succumb to the drought. It is getting very depressing.

Wherever we go, we hear the sound of chainsaws. Tree crews are out in force, trying desperately to stay ahead of the problem, but there are too many dead trees and not enough skilled arborists to stay on top of it.

In our own yard, we are watering less and less. I think most of the native and Mediterranean trees will be ok. But we have one Southern Magnolia (NOT planted by us, I hate it) which is starting to look a little peaked. I am thinking that it might be time to have it removed, and to replace it with something like a Desert Willow, which can thrive and look beautiful on far less water. Unfortunately, this means we will lose some shade on the house, but fortunately, it will increase the sun’s influence on our solar panels.

I think I will have to wait until the rains come and the tree companies are less busy. Right now, they have their hands full.

10/7/21 drought report from drought.gov

Ramble On

This time of year puts me in mind of songs about autumn - this morning, for some reason, the old Led Zeppelin tune ‘Ramble On.’ Lyrics like ‘Now it’s time for me to go, the autumn moon lights my way’ just seem to fit the mood of the garden.

the cold nights are taking their toll on the basil

Wandering around the yard, I see such interesting things, signs of change. The gall wasp population exploded this year on our Valley Oak (Quercus lobata), and now that the galls have served their purpose, they are falling from the leaves like rain. When you stand under it, you are in a shower of galls. Our driveway is red with them.

The chickens have mostly stopped laying for the winter - between the annual molt and the shortening days, we are lucky to get an egg every once in awhile.

The garlic is sprouting, the kale and cauliflower and lettuce are growing beautifully, but something has eaten all of the kohlrabi and beets, and my spinach won’t germinate. I’ll just keep seeding and planting on through, until frost.

Fall flowers are still blooming like crazy and the pollinators are frantically bringing in all they can - you can feel the urgency. I noticed the honeybees bringing in bright orange pollen and wondered where it was coming from, and then I saw one collecting pollen from a Tithonia blossom and realized that was the source.

this is a hoverfly, though

my little friend

another hoverfly, this time on the Eryngium

We’ve been eating a good fig crop, and the olives are starting to change color. We won’t harvest them till December or January.

‘Panache’ fig

‘Arbequina’ olive

We have a month or two yet before the flowers succumb to cold weather (our days are still in the 80’s, and we’ve only reached nighttime lows in the 40’s a couple of times; our first average frost date is December 15).

Hollyhocks giving some gorgeous last blooms

Thai basil

Leonotis getting ready to bloom

I spend a good amount of time grooming the brassica leaves, picking off cabbage butterfly worms and eggs. It’s not fun, but it’s satisfying, and the chickens love to eat the worms. They do quite a bit of damage to the leaves of all my cruciferous crops, but the cabbage is looking the worst right now, and I’m hoping it pulls through. The row covers help, but do not entirely deter critters (see earlier note about ravaged kohlrabi and beets). Soon I will begin the daily task of raking leaves and adding them to the chicken run. We are desperate for rain, but none is forthcoming.

White bean, pancetta, and chard pot pie, a sure sign of fall. You can find the recipe at Smitten Kitchen.

A reminder: It pays to be a messy gardener this time of year; many pollinators and other insects overwinter in leaf litter and mulch. So rake up some leaves for your compost (or chickens), but leave a good amount where they fall, to help keep a healthy habitat for those little guys.

What does your garden look? Have you had snow where you live?

Determining the Amount of Carbon Sequestered by your Trees

This past semester, I took an Arboriculture class, and it was great - I learned SO much. As part of the class, we had to pick a tree we felt had some structural or health issues and write a report on it. It was a cumulative project; we had to know how to measure the health of the tree, how to do risk assessments, how to calculate value if the tree was to be replaced, etc., all of which sounds fairly simple but each step sort of builds on the one before. It was fascinating. I chose the valley oak in the photo above, for my project. 

The benefits of trees, particularly in an urban setting, are obvious and numerous: Trees save energy because they provide shade, they intercept stormwater and hold it on the property, they increase property value, and they provide benefits for local wildlife. There are many studies, both recent and ongoing, that show trees can improve the actual physical health of humans. They can intercept allergens and filter air, for instance, helping with breathing and air quality. Mental health and trees is also being studied. It's hard to quantify, but they can improve mental outlook and provide a very real sense of solidity and peace. Trees are also beautiful, a value hard to measure, but one we wouldn't want to live without. 

Another unseen way trees improve our environments is by sequestering CO2, which they use for making food through photosynthesis. Then they take those foods and store them deep in their root systems, in the soil. This kind of storage of carbon, or sequestration, is very important to the health of our planet. I won't go into the 'why' here, but if you're interested, see this article by the USGS, which explains it nicely.

It's rather interesting to take the trees on your property and determine how much carbon they are sequestering every year. There are several ways to do this. The industry standard is a tool called CUFR, which is provided by the US Forest Service.  They have an excel spreadsheet which will do this calculation for you. I had a little trouble with this interface, so I went searching for another way. I found another online calculator which is good if you have a common (not unusual) tree, called National Tree Benefit Calculator. You simply enter your zip code, then choose the kind of tree you have, and enter the diameter of the tree. 

***A word on diameter: This is a trunk measurement you take at breast height, about 4.5 feet up from the soil. It's called 'DBH' or 'diameter at breast height.' You'll see this in all the calculations; it's an important measurement and helps us to know the age of the tree. And remember (I needed a refresher course myself), diameter is the length across one side of the tree trunk; radius would be half that; circumference would be the length all the way around. (Hey you math people, stop giggling.) So for diameter, just take your tape measure or yardstick or ruler out to the tree and estimate about four and a half feet up from the soil, and then just put your ruler up to the trunk and see how wide it is. 

For those of you with multiple tree trunks at breast height, you'll need to do a different calculation (I'm thinking of your Coast Live Oak, Mom and Dad): please see this nifty explanation by the City of Portland. This also explains how to measure if your tree is on a slope.***

The Tree Calculator website is interesting, because it gives more data than just CO2. When you put in your info and it does the calculation, first you will see a pie chart overview; if you go to each tab above that, it will tell you more about each single factor. For instance, when I put in my oak tree, and I then hit the CO2 tab above the pie chart, it reminds me that "most car owners of an average car drive 12k miles generating about 11k pounds of CO2 every year." That's very helpful in context. According to them, my oak is sequestering 660 pounds of carbon per year, but I'm putting a much larger amount into the atmosphere by driving my car. I would need 20 oaks of this size to make up for the emissions from my car. 

So you start to see why trees can be very important even in unseen ways.

in full leaf, in September, a beautiful canopy

For my project, I wanted to actually DO my own calculation, so I found a research paper which explains how. For this calculation you will need to know the DBH and the approximate height of the tree, which can be difficult to estimate. I usually try to look at buildings near by, as one story is usually about 10 feet. I estimated my oak to be about 50 feet tall. 

Click on the box below to get a printable of how to do this calculation. It looks daunting but please don't let that dissuade you - I am the least mathematical person in the world and I was able to do it. It explains the 'why' of every step, but unless you really want to know that, you can just skip down to the bottom of each paragraph to learn how to do the next calculation.

With this process, I determined that my oak sequesters 488 pounds of carbon per year, a bit less than the online calculator said. I think this is because the physical calculation only takes into account the age and size of the tree, whereas the online calculator takes into account the type of species and where it grows, which is important for several reasons. Certain species sequester more carbon - generally trees that grow slower are the ones who store the most. (Side note - slow growing trees are also stronger and live longer.) Plus how the tree is adapted to your climate is important, hence the reason you put in your zip code for the online calculator. If the tree is native to your area, it's naturally going to grow better and store more carbon. For instance, you've already heard the details about my oak tree, which is native here and well-adapted to this climate. However I have a large southern magnolia on the property (Magnolia grandiflora) - it's not quite as large, but it is significantly older than the oak. When I put that tree into the online calculator, I find it's only storing 180 pounds of carbon per year. I would be willing to bet that a similarly sized magnolia in Georgia would be sequestering much more carbon than it is here in California. It's also interesting to see the difference between these two trees when looking at the other factors: the oak is intercepting and storing much more rainwater (very important here in our dry climate), it's doing a better job of cleaning my air, and it raises my property value quite a bit more than the magnolia. I didn't plant either one of these trees, but it sure helps me decide which one I'd rather have going into the future on this property.

This would be a fun exercise to do with kids, leading naturally into a conversation about how the trees on your property are improving it. It's also worthwhile to spend some time observing the tree and how the wild creatures use it (I spent so much time watching the songbirds in my oak that it made me realize what a value it is to them, not just to us). You can discuss how the tree increases habitat for many different creatures, providing food for some, shelter for others. You can discuss how the tree shades the house, decreasing the need for air conditioning. If the tree is native, you can read up on how the native peoples would have used it hundreds of years ago. You could take the leaves and make some art with them.  

But even if you don't have kids, it's worthwhile information to know and absorb. We often pay little mind to the trees on our property, unless there is a problem with them. This helps us appreciate what they are doing, in seen and unseen ways, to improve our immediate and greater environment, every day.